{"gene":"SLC6A5","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1995,"finding":"GLYT2 (SLC6A5) is expressed predominantly in neurons of the spinal cord, brainstem, and cerebellum, with immunoreactivity localized to axonal processes with varicosities but not cell bodies, correlating with the distribution of glycine receptors and suggesting a role in terminating glycine neurotransmission at inhibitory synapses.","method":"Western blot, immunocytochemistry with polyclonal antibodies against recombinant N-terminus and loop fusion proteins in mouse brain","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 — direct localization by immunocytochemistry with specific antibodies, replicated across labs (PMID 7861131 and 7582108)","pmids":["7861131","7582108"],"is_preprint":false},{"year":1997,"finding":"GLYT2 is the active concentrator of glycine in glycinergic neurons: GLYT2 expression in cultured spinal neurons and GLYT2-transfected COS cells directly correlates with intracellular glycine accumulation, establishing that GLYT2-mediated uptake is responsible for the high glycine content of glycinergic neurons and that GLYT2 can be used as a reliable marker for glycinergic neurons.","method":"Double-immunofluorescence co-localization, glycine uptake assays in cultured spinal neurons and GLYT2-transfected COS cells","journal":"Brain research. Molecular brain research","confidence":"High","confidence_rationale":"Tier 2 — functional uptake assay with both native neurons and transfected cells, strong evidence","pmids":["9387864"],"is_preprint":false},{"year":1998,"finding":"Human GlyT2 encodes a 797 amino acid Na+/Cl−-dependent glycine transporter with an apparent Km of 108 μM for glycine, insensitive to sarcosine, and the gene maps to chromosome 11p15.1-15.2.","method":"Expression cloning, stable expression in CHO cells, glycine uptake assays, radiation hybrid mapping","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in CHO cells with kinetic characterization","pmids":["9845349"],"is_preprint":false},{"year":1998,"finding":"Two alternative 5' isoforms of rat GLYT2 (GLYT2a and GLYT2b) are generated by alternative exon usage; GLYT2a actively accumulates glycine in transfected COS cells whereas GLYT2b only exchanges (releases) glycine, indicating functionally distinct transport modes.","method":"RACE analysis, genomic DNA analysis, transport assays in transfected COS cells","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 2 — functional comparison of two isoforms in transfected cells, single lab","pmids":["9509996"],"is_preprint":false},{"year":2000,"finding":"Tyrosine 289 in transmembrane domain III of GLYT2a is critical for ion coupling and glycine transport: mutations Y289W, Y289F, and Y289S abolish or dramatically reduce transport activity, alter Na+ affinity and cooperativity, reduce Na+ selectivity, and decrease Cl− dependence, indicating that TM III forms part of the ion and substrate permeation pathway.","method":"Site-directed mutagenesis, electrophysiology (steady-state currents), glycine uptake assays in HEK-293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis with functional assays (electrophysiology + transport) in multiple mutants","pmids":["10788509"],"is_preprint":false},{"year":2000,"finding":"N-glycosylation at four sites (Asn-345, Asn-355, Asn-360, Asn-366) in the large extracellular loop of GLYT2 is required for transport activity, proper intracellular trafficking to the plasma membrane in COS cells, and apical sorting in polarized MDCK cells; enzymatic deglycosylation reduces transport activity by 35-40%; apical localization occurs via a glycolipid raft-independent pathway.","method":"Site-directed mutagenesis of glycosylation sites, enzymatic deglycosylation, transport assays, biotinylation assays, transfection in COS and MDCK cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with multiple functional and trafficking assays","pmids":["11036075"],"is_preprint":false},{"year":2000,"finding":"Syntaxin 1A physically interacts with both GLYT1 and GLYT2 in COS cells and rat brain tissue (co-immunoprecipitation), and co-transfection of syntaxin 1A inhibits glycine transport by ~40%; this inhibition is reversed by Munc18; syntaxin 1A interaction partially removes the transporters from the plasma membrane as shown by biotinylation.","method":"Co-immunoprecipitation in COS cells and rat brain, glycine transport assays, cell-surface biotinylation","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP in native and heterologous systems, functional consequence demonstrated","pmids":["10722844"],"is_preprint":false},{"year":2000,"finding":"Ethanol selectively and acutely inhibits GLYT2a but not GLYT1b in a non-competitive (allosteric) manner, with a cut-off at alcohols with four carbons suggesting a specific binding site; chronic ethanol treatment decreases GLYT2a activity and surface expression while slightly increasing GLYT1b function.","method":"Glycine uptake assays in stably transfected HEK-293 cells, n-alkanol inhibition series","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic pharmacological characterization in stable cell lines, single lab","pmids":["10683205"],"is_preprint":false},{"year":2001,"finding":"Syntaxin 1 mediates GLYT2 trafficking to the plasma membrane via a SNARE-dependent mechanism: under conditions stimulating vesicular glycine release (exocytosis) in synaptosomes, GLYT2 traffics first to the plasma membrane and then is internalized; inactivation of syntaxin 1 with BoNT/C prevents GLYT2 from reaching the plasma membrane but does not block internalization. Immunogold labeling shows GLYT2 is present in small synaptic-like vesicles.","method":"Synaptosome stimulation, BoNT/C neurotoxin treatment, surface expression assays, immunogold electron microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — mechanistic dissection with neurotoxin and imaging in brain-derived preparation","pmids":["11278707"],"is_preprint":false},{"year":2004,"finding":"Calpain (Ca2+-dependent protease) cleaves the extended N-terminal cytoplasmic region of GlyT2 at two sites (after Met-156 and Gly-164) in spinal cord synaptosomes and cultured neurons; the resulting ~70 kDa N-terminally truncated GlyT2 retains full transport activity upon expression in HEK293 cells, suggesting calpain-mediated proteolysis may regulate GlyT2 trafficking or function.","method":"Calpain activation in synaptosomes and cultured neurons, protein sequence analysis of cleavage sites, expression of truncated GlyT2 in HEK293 cells with transport assay","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — cleavage site mapping combined with functional assay, single lab","pmids":["14675166"],"is_preprint":false},{"year":2006,"finding":"Missense, nonsense, and frameshift mutations in SLC6A5 (encoding GlyT2) cause hereditary hyperekplexia; these mutations result in defective subcellular GlyT2 localization, decreased glycine uptake, or both; selected mutations affect predicted glycine and Na+ binding sites, establishing SLC6A5 as a presynaptic disease gene.","method":"Human genetics (sequencing), heterologous expression with glycine uptake assays, subcellular localization studies","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — human disease mutations functionally validated in multiple assays, large patient cohort","pmids":["16751771"],"is_preprint":false},{"year":2006,"finding":"Truncating mutations in the human GlyT2 gene (SLC6A5) cause complete loss of glycine transport function, confirming SLC6A5 as a disease gene in human hyperekplexia.","method":"DNA sequencing of patients, heterologous expression and glycine uptake assays","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — functional validation of human disease mutations","pmids":["16884688"],"is_preprint":false},{"year":2007,"finding":"GlyT2 (but not GlyT1) maintains the high cytosolic glycine concentration required for efficient vesicular loading by VIAAT: in a neuroendocrine cell reconstitution system, GlyT2 more effectively than GlyT1 supports glycinergic quantal release because GlyT2 cannot operate in reverse mode, thereby maintaining cytosolic glycine for vesicle refilling.","method":"Reconstitution in neuroendocrine cells co-expressing VIAAT and plasmalemmal transporters; double-sniffer patch-clamp technique measuring quantal glycine/GABA release","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — reconstitution system with novel electrophysiological readout; mechanistic distinction between GlyT1 and GlyT2","pmids":["17554001"],"is_preprint":false},{"year":2007,"finding":"The C-terminal PDZ-ligand motif of GlyT2 is required for efficient synaptic localization in neurons: inactivation of this motif does not impair transport function in HEK293T cells but reduces co-localization with synaptic markers by up to 50% in hippocampal neurons, indicating the PDZ motif is important for trafficking to and/or stabilization at synaptic sites.","method":"Site-directed mutagenesis, transfection of hippocampal neurons, immunofluorescence co-localization with synaptic markers","journal":"Molecular and cellular neurosciences","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function approach in neurons with specific synaptic co-localization readout, single lab","pmids":["17851090"],"is_preprint":false},{"year":2007,"finding":"GLYT2 is expressed in a subset of GFAP-positive astrocyte-derived gliosomes in mouse spinal cord and contributes to glycine-evoked GABA release from GABAergic synaptosomes, demonstrating that GLYT2 localization is not exclusively neuronal and that it functionally contributes to GABAergic signaling via glycine transport.","method":"Purified synaptosome and gliosome preparations, pharmacological blockade with selective GLYT1/GLYT2 inhibitors, confocal microscopy co-labeling with GAT1, GFAP, MAP2","journal":"Neurochemistry international","confidence":"Medium","confidence_rationale":"Tier 2 — functional pharmacological dissection with morphological confirmation, single lab","pmids":["17597258"],"is_preprint":false},{"year":2008,"finding":"GlyT2-mediated glycine uptake is directly coupled to the refilling of recycling synaptic vesicles: GlyT2 inhibition in cultured spinal neurons causes a switch from glycinergic to GABAergic inhibitory phenotype through cytosolic glycine depletion, fully reversible by glycine resupply; high-frequency stimulation reveals two kinetically distinct phases of vesicle release with different requirements for GlyT2-mediated glycine refilling.","method":"Whole-cell and synaptic electrophysiology in GlyT2-eGFP transgenic mouse spinal cord neurons; glycine transport current recording; pharmacological GlyT2 inhibition","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — electrophysiological reconstitution of vesicle refilling in transgenic neurons with multiple controls","pmids":["18815261"],"is_preprint":false},{"year":2008,"finding":"GLYT2 is associated with membrane rafts (Triton X-100-insoluble fractions) in brainstem terminals and neurons; cholesterol and sphingomyelin depletion with methyl-β-cyclodextrin disrupts raft association and impairs transport activity, indicating that the lipid raft environment is required for optimal GLYT2 function.","method":"Detergent-resistant membrane fractionation, methyl-β-cyclodextrin treatment, confocal microscopy, electron microscopy on purified raft fractions, transport assays in synaptosomes and neurons","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods linking raft association to functional activity","pmids":["18266927"],"is_preprint":false},{"year":2008,"finding":"Protein kinase C (PKC) activation by PMA inhibits GLYT2 transport by increasing internalization rate and accumulating GLYT2 in intracellular compartments; PMA also redistributes GLYT2 from raft to non-raft membrane domains; a regulatory lysine mutant K422E is resistant to PMA-induced trafficking modulation; Rac1 signaling also participates in PMA action on GLYT2.","method":"PMA treatment, monensin trafficking assay, surface biotinylation, raft fractionation, mutagenesis (K422E), siRNA knockdown in HEK cells, brainstem neurons and synaptosomes","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis combined with pharmacological and trafficking assays in multiple systems","pmids":["18341477"],"is_preprint":false},{"year":2009,"finding":"GLYT2 resides intracellularly in Rab11-positive recycling endosomes and synaptophysin-containing vesicles in rat brainstem; coexpression of dominant-negative Rab11 impairs GLYT2 trafficking and glycine transport, establishing that GlyT2 recycles through Rab11-positive endosomal compartments.","method":"Biochemical fractionation, immunofluorescence and immunogold electron microscopy, dominant-negative Rab11 co-expression with transport assay","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — direct subcellular localization linked to functional consequence via dominant-negative approach","pmids":["19374720"],"is_preprint":false},{"year":2011,"finding":"GlyT2 endocytosis is mediated primarily by the clathrin pathway; PKC activation promotes redistribution of GLYT2 from raft to non-raft membrane domains and increases ubiquitinated GLYT2 endocytosis; GLYT2 is constitutively internalized from cell-surface lipid rafts while remaining raft-associated in recycling structures.","method":"Pharmacological inhibitors of clathrin pathway, dominant-negative mutants, siRNA knockdown, raft fractionation, internalization assays in HEK cells and neurons","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — multiple pharmacological and genetic tools confirming clathrin-mediated endocytosis with raft redistribution","pmids":["21910806"],"is_preprint":false},{"year":2012,"finding":"Twenty SLC6A5 sequence variants were identified in hyperekplexia patients, all defective in glycine transport; pathogenic mechanisms include protein truncation (R439X most common), splice site mutations, missense mutations affecting Cl− binding, extracellular loop 4 conformational changes, and cation-π interactions; mutation A275T causes voltage-sensitive decrease in glycine transport through lower Na+ affinity.","method":"DNA sequencing of 93 hyperekplexia patients, glycine uptake assays for 16 novel mutations, electrophysiology (A275T)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — large patient cohort, functional validation of multiple mutations with electrophysiology","pmids":["22700964"],"is_preprint":false},{"year":2012,"finding":"The dominant hyperekplexia mutation Y705C in TM11 of GlyT2 introduces a cysteine that interacts with the Cys-311–Cys-320 pair in external loop 2, impairing transporter maturation through the secretory pathway, reducing surface expression, and inhibiting transport; Y705C also shows altered H+ and Zn2+ sensitivity of glycine transport.","method":"Molecular modeling, electrophysiology, [3H]glycine transport assays, cell surface expression assays, cysteine labeling, secretory pathway analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — structure-function with mutagenesis, multiple orthogonal methods including electrophysiology","pmids":["22753417"],"is_preprint":false},{"year":2012,"finding":"A MusD retrotransposon insertion in mouse Slc6a5 abolishes GlyT2 protein expression (null allele), causing handling-induced spasms from day 5 and death by two weeks; loss of GlyT2 accelerates NMJ synapse elimination and the embryonic-to-adult AChR subunit switch, consistent with increased motor neuron activity; heterozygous mice show repetitive grooming and hyperactivity.","method":"Spontaneous mouse mutant characterization, Western blot, neuromuscular junction analysis, behavioral phenotyping","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — null mouse model with defined cellular and behavioral phenotypes","pmids":["22272310"],"is_preprint":false},{"year":2012,"finding":"Asp471 in the external vestibule of GLYT2 controls cation access and Na+ coupling: substitution of Asp471 reduces Na+ affinity and cooperativity, increases sodium leakage and uncoupled ion movements through GLYT2, and alters Na+/Li+-induced conformational changes; this residue is distinct from the homologous Asp295 in GLYT1, explaining the different lithium sensitivity of the two transporters.","method":"Homology modeling, molecular dynamics simulation, site-directed mutagenesis, electrophysiology, [3H]glycine transport assays, cation accessibility assays","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — computational plus experimental mutagenesis with electrophysiology and transport assays","pmids":["22132725"],"is_preprint":false},{"year":2013,"finding":"Na+/K+-ATPase (NKA) is a direct interacting partner of GlyT2 in the CNS: identified by mass spectrometry interactomics, confirmed by reciprocal co-immunoprecipitation and immunocytochemistry; NKA preferentially interacts with the raft-associated active pool of GlyT2; ouabain-mediated NKA inhibition modulates GlyT2 endocytosis and total expression in neurons, in zebrafish embryos, and in adult rats, indicating an evolutionarily conserved regulatory mechanism.","method":"High-throughput mass spectrometry, reciprocal co-immunoprecipitation, immunocytochemistry, ouabain treatment in neurons, in vivo zebrafish and rat models","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — MS discovery confirmed by reciprocal Co-IP, functional validation in vitro and in vivo across species","pmids":["23986260"],"is_preprint":false},{"year":2013,"finding":"Ubiquitination of a C-terminal four-lysine cluster (K751, K773, K787, K791) in GlyT2 is required for constitutive endocytosis, sorting into the slow recycling pathway, and transporter turnover; increased ubiquitination by PKC activation accelerates GlyT2 degradation, while decreased ubiquitination increases stability; UCHL1, as major regulator of neuronal ubiquitin homeostasis, indirectly modulates GlyT2 turnover.","method":"Mutagenesis of lysine cluster, ubiquitination assays, endocytosis assays, turnover/half-life measurements, PKC activation, siRNA UCHL1 knockdown","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — systematic mutagenesis of ubiquitination sites linked to functional trafficking outcomes","pmids":["23484054"],"is_preprint":false},{"year":2013,"finding":"Calnexin (CNX) assists GlyT2 biogenesis in the ER: CNX binds transiently to an under-glycosylated GlyT2 precursor via both glycan-dependent and polypeptide-based (lectin-independent) interactions; CNX knockdown reduces GlyT2 accumulation and transport activity while CNX overexpression enhances them; CNX can stabilize non-glycosylated GlyT2 conformational states and rescue transport but not surface expression of fully non-glycosylated mutants; GlyT2 is degraded in lysosomes.","method":"siRNA-mediated CNX knockdown, CNX overexpression, pharmacological inhibition of glycosylation, transport assays, surface expression assays, lysosomal inhibitor treatments","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches dissecting ER chaperone-transporter interaction","pmids":["23650557"],"is_preprint":false},{"year":2013,"finding":"GlyT2 activation by glycine uptake can stimulate GABA release from cerebellar nerve terminals via two mechanisms: (1) reversal of GAT1 GABA transporter driven by Na+ influx through GlyT2 and subsequent mitochondrial Na+/Ca2+ exchange; (2) Ca2+-dependent anion channels permeable to GABA; ~20% of evoked GABA release is Ca2+-dependent via NCX reversal.","method":"[3H]GABA release assays from purified cerebellar nerve endings, pharmacological dissection with selective GlyT2, GAT1 and NCX inhibitors, Ca2+ manipulation","journal":"Journal of neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection in purified nerve endings, single lab, multiple mechanisms proposed","pmids":["24273061"],"is_preprint":false},{"year":2014,"finding":"GlyT2 forms a functional complex with plasma membrane Ca2+-ATPase (PMCA) isoforms 2 and 3 and Na+/Ca2+ exchanger 1 (NCX1) in lipid raft subdomains of the presynaptic terminal; endogenous PMCA and NCX activities are required for GlyT2 activity; this complex is proposed to help control local Na+ increases generated by GlyT2 cotransport.","method":"Co-immunoprecipitation, lipid raft fractionation, pharmacological inhibition of PMCA and NCX, GlyT2 transport assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP and functional pharmacology, single lab","pmids":["25315779"],"is_preprint":false},{"year":2014,"finding":"Glycogen synthase kinase 3β (GSK3β) differentially modulates GlyT1 and GlyT2: GSK3β co-expression inhibits GlyT1 and stimulates GlyT2 activity/surface expression in COS-7 cells and Xenopus oocytes; GSK3β increases 32Pi incorporation into GlyT1 and decreases it in GlyT2; pharmacological inhibition of endogenous GSK3β in brainstem/spinal cord neurons produces opposite modulation of the two transporters.","method":"Co-expression in COS-7 cells and Xenopus oocytes, transport assays, phosphorylation (32Pi) assays, GSK3β inhibitors (LiCl, TDZD-8) in neuronal cultures","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple expression systems and phosphorylation readout, single lab","pmids":["25301276"],"is_preprint":false},{"year":2015,"finding":"BDNF acting on truncated TrkB-T1 receptors promotes internalization of GlyT2 (and GlyT1) in astrocytes via a Rho-GTPase-dependent, dynamin/clathrin-dependent endocytosis mechanism; BDNF decreases GlyT2 Vmax without changing Km, consistent with transporter internalization rather than kinetic inhibition.","method":"Primary astrocyte cultures, [3H]glycine uptake assays, dynasore treatment, siRNA TrkB-T knockdown, Rho-GTPase inhibitor (toxin B), immunofluorescence of GlyT endosomes","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic dissection with pharmacology, siRNA, and imaging in primary cells","pmids":["26200505"],"is_preprint":false},{"year":2017,"finding":"P2X purinergic receptor stimulation upregulates GlyT2 surface expression and transport activity by reducing transporter ubiquitination; this effect requires co-stimulation of homomeric P2X3 and P2X2 receptors, or heteromeric P2X2/3 receptors; P2X3 receptor activation modulates glycinergic neurotransmission through GlyT2 regulation.","method":"Pharmacological P2X receptor agonists/antagonists, siRNA knockdown of P2X subtypes, dorsal root ganglion enrichment, transport assays, surface expression, ubiquitination assays, glycinergic current recording","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic dissection of receptor subtypes with functional transport readout, single lab","pmids":["28734869"],"is_preprint":false},{"year":2019,"finding":"E3 ubiquitin ligases LNX1 and LNX2 ubiquitinate a C-terminal lysine cluster (K751, K773, K787, K791) in GlyT2 via their RING-finger domains, regulating GlyT2 expression and transport activity; genetic deletion of endogenous LNX2 in spinal cord neurons increases GlyT2 expression; LNX2 is required for PKC-mediated control of GlyT2 transport.","method":"Unbiased E3 ligase screening, co-immunoprecipitation, ubiquitination assays, RING-domain mutagenesis, LNX2 knockout neurons, PKC activation experiments","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — systematic screening confirmed by co-IP and genetic knockout, functional consequence demonstrated","pmids":["31628376"],"is_preprint":false},{"year":2021,"finding":"Molecular dynamics simulations of GlyT2 in a complex neuronal membrane reveal a distinct lipid fingerprint: GlyT2 shows specific enrichment and depletion of lipid species (including cholesterol contacts) compared to other SLC6 transporters (dDAT, hDAT, hSERT), with the lipid environment influencing local membrane biophysical properties near the transporter.","method":"Molecular dynamics simulation in complex neuronal membrane, lipid fingerprint analysis","journal":"BBA advances","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only, no experimental validation","pmids":["37082011"],"is_preprint":false}],"current_model":"GlyT2 (SLC6A5) is a presynaptic Na+/Cl−-dependent glycine transporter that cotransports 3 Na+/Cl−/glycine with a stoichiometry enabling concentrative glycine uptake into glycinergic terminals; its transport activity depends on N-glycosylation, membrane raft association, and interaction with syntaxin 1A (for membrane delivery), Na+/K+-ATPase, PMCA, and NCX1; surface expression is dynamically regulated by clathrin-mediated endocytosis controlled by PKC-dependent ubiquitination of a C-terminal lysine cluster by E3 ligases LNX1/2, with intracellular recycling through Rab11-positive endosomes; loss-of-function mutations in SLC6A5 impair vesicular glycine refilling, causing hereditary hyperekplexia (startle disease) in humans, cattle, and dogs."},"narrative":{"teleology":[{"year":1995,"claim":"Establishing where GlyT2 acts: immunolocalization to axonal varicosities in spinal cord, brainstem, and cerebellum—matching glycine receptor distribution—positioned GlyT2 as the presynaptic glycine reuptake system at inhibitory synapses.","evidence":"Immunocytochemistry with antibodies against recombinant GlyT2 domains in mouse brain","pmids":["7861131","7582108"],"confidence":"High","gaps":["Subcellular resolution to synaptic boutons not achieved","Glial expression possibility not addressed"]},{"year":1997,"claim":"Demonstrating GlyT2 is the glycine concentrator: functional uptake assays showed GlyT2 expression directly correlates with intracellular glycine accumulation, establishing its role in loading glycinergic terminals with substrate.","evidence":"Double-immunofluorescence and glycine uptake in spinal neurons and GlyT2-transfected COS cells","pmids":["9387864"],"confidence":"High","gaps":["Coupling to vesicular filling not yet demonstrated","Stoichiometry of Na⁺/Cl⁻/glycine cotransport not established"]},{"year":1998,"claim":"Molecular characterization of human GlyT2 revealed a 797-residue transporter with Km ~108 µM for glycine, sarcosine-insensitive, mapping to 11p15.1-15.2, and alternative splicing yielding functionally distinct isoforms (uptake vs. exchange modes).","evidence":"Expression cloning in CHO cells with kinetic analysis; RACE analysis and transport assays of splice variants in COS cells","pmids":["9845349","9509996"],"confidence":"High","gaps":["Physiological relevance of the exchange-mode isoform (GLYT2b) unclear","3 Na⁺ stoichiometry not yet formally demonstrated"]},{"year":2000,"claim":"Structure–function dissection identified key determinants of transport: Tyr-289 in TM III is essential for ion coupling and substrate permeation, four N-glycosylation sites (N345/N355/N360/N366) are required for surface delivery and activity, and syntaxin 1A interaction regulates membrane expression.","evidence":"Site-directed mutagenesis with electrophysiology and uptake assays in HEK-293 and COS cells; co-immunoprecipitation of syntaxin 1A in COS cells and rat brain with functional consequence","pmids":["10788509","11036075","10722844"],"confidence":"High","gaps":["High-resolution structural basis for ion/glycine coordination not available","Whether syntaxin 1A interaction is direct or scaffolded unclear"]},{"year":2001,"claim":"Resolving how GlyT2 reaches the surface: syntaxin 1A mediates SNARE-dependent exocytic delivery of GlyT2 from intracellular vesicles to the plasma membrane, as BoNT/C blockade prevents surface insertion without affecting internalization, and immunogold EM placed GlyT2 on small synaptic-like vesicles.","evidence":"Synaptosome stimulation, BoNT/C neurotoxin treatment, immunogold electron microscopy in brain-derived preparations","pmids":["11278707"],"confidence":"High","gaps":["Identity of the vesicle population (recycling vs. biosynthetic) carrying GlyT2 not resolved","Whether SNARE-dependent insertion is activity-regulated in vivo unknown"]},{"year":2006,"claim":"SLC6A5 was established as a human disease gene: multiple loss-of-function mutations cause hereditary hyperekplexia by impairing glycine uptake and/or subcellular localization, linking presynaptic glycine recycling failure to startle disease.","evidence":"Sequencing of hyperekplexia patient cohorts with heterologous functional validation of missense, nonsense, and frameshift mutations","pmids":["16751771","16884688"],"confidence":"High","gaps":["Genotype–phenotype severity correlations incomplete","Whether partial loss-of-function alleles cause milder phenotypes not established"]},{"year":2007,"claim":"The physiological rationale for GlyT2 was clarified: GlyT2's inability to operate in reverse (unlike GlyT1) enables it to maintain cytosolic glycine at concentrations sufficient for vesicular loading by VIAAT, directly coupling plasma membrane uptake to quantal glycinergic release.","evidence":"Reconstitution in neuroendocrine cells co-expressing VIAAT and plasmalemmal transporters with double-sniffer patch clamp","pmids":["17554001"],"confidence":"High","gaps":["Structural basis for the irreversibility of GlyT2 transport not known","Whether VIAAT and GlyT2 physically interact not tested"]},{"year":2008,"claim":"GlyT2-mediated glycine refilling was shown to be rate-limiting for sustained glycinergic transmission: pharmacological GlyT2 blockade in spinal neurons caused a switch from glycinergic to GABAergic phenotype, revealing two kinetically distinct vesicle pools with different refilling requirements; membrane raft association was demonstrated as essential for transport activity.","evidence":"Electrophysiology in GlyT2-eGFP transgenic neurons with GlyT2 inhibitors; detergent-resistant membrane fractionation and cholesterol depletion in synaptosomes","pmids":["18815261","18266927"],"confidence":"High","gaps":["Molecular mechanism of raft-dependent transport enhancement unknown","Whether glycine-to-GABA switch occurs in vivo not shown"]},{"year":2008,"claim":"PKC was identified as a central regulator of GlyT2 surface levels: PKC activation promotes GlyT2 internalization and redistribution from raft to non-raft domains, with K422 identified as a regulatory determinant; this introduced ubiquitination-dependent trafficking control.","evidence":"PMA treatment with surface biotinylation, raft fractionation, and K422E mutagenesis in HEK cells and brainstem neurons","pmids":["18341477"],"confidence":"High","gaps":["Whether K422 is directly ubiquitinated or indirectly involved not resolved","In vivo PKC activating signal identity unknown"]},{"year":2009,"claim":"GlyT2 recycling was mapped to Rab11-positive endosomes: dominant-negative Rab11 impaired both GlyT2 trafficking and glycine transport, establishing the slow recycling pathway as the intracellular itinerary for internalized transporter.","evidence":"Biochemical fractionation, immunogold EM, dominant-negative Rab11 co-expression with transport assay in rat brainstem","pmids":["19374720"],"confidence":"High","gaps":["Sorting signals directing GlyT2 into Rab11 compartments not identified","Whether Rab4-dependent fast recycling also contributes not tested"]},{"year":2011,"claim":"The endocytic route was defined: GlyT2 internalization is primarily clathrin-mediated, with constitutive endocytosis occurring from raft domains and PKC-stimulated endocytosis following redistribution to non-raft membrane.","evidence":"Clathrin pathway inhibitors, dominant-negative mutants, siRNA knockdown with internalization assays in HEK cells and neurons","pmids":["21910806"],"confidence":"High","gaps":["Adaptor proteins linking GlyT2 to clathrin not identified","Relative contribution of ubiquitin-dependent vs. -independent endocytosis not quantified"]},{"year":2012,"claim":"Expanded genotype–function mapping revealed diverse pathogenic mechanisms in hyperekplexia: 20 SLC6A5 variants disrupted Cl⁻ binding, Na⁺ affinity, cation-π interactions, or extracellular loop conformation; the dominant Y705C mutation in TM11 impaired secretory pathway maturation via aberrant disulfide interactions.","evidence":"Large patient cohort sequencing with functional validation of 16 mutations; electrophysiology, cysteine labeling, and secretory pathway analysis for Y705C","pmids":["22700964","22753417"],"confidence":"High","gaps":["No high-resolution structure to map all mutation sites","Therapeutic rescue strategies for trafficking-defective mutants not explored"]},{"year":2013,"claim":"The GlyT2 interactome was expanded: Na⁺/K⁺-ATPase was identified as a direct partner that preferentially associates with raft-resident active GlyT2 and regulates its endocytosis across species; C-terminal ubiquitination at K751/K773/K787/K791 was shown to drive constitutive endocytosis and degradation; calnexin was identified as an ER chaperone for GlyT2 biogenesis via both glycan-dependent and lectin-independent modes.","evidence":"Mass spectrometry interactomics with reciprocal co-IP, ouabain treatment in neurons/zebrafish/rats; systematic lysine mutagenesis with ubiquitination and turnover assays; CNX knockdown/overexpression with transport and surface expression assays","pmids":["23986260","23484054","23650557"],"confidence":"High","gaps":["Direct binding interface between NKA and GlyT2 not mapped","Whether calnexin interaction is specific to GlyT2 among SLC6 family unknown"]},{"year":2014,"claim":"A raft-resident functional complex of GlyT2 with PMCA2/3 and NCX1 was identified, suggesting coordinated local Na⁺/Ca²⁺ handling at glycinergic terminals; GSK3β was shown to differentially stimulate GlyT2 activity while inhibiting GlyT1.","evidence":"Co-immunoprecipitation and pharmacological inhibition of PMCA/NCX with transport assays; co-expression in COS-7 and oocytes with phosphorylation and transport readouts","pmids":["25315779","25301276"],"confidence":"Medium","gaps":["Whether PMCA/NCX/GlyT2 complex exists in vivo at synapses not confirmed by super-resolution imaging","GSK3β phosphorylation site(s) on GlyT2 not mapped","Functional significance of GSK3β regulation in vivo unknown"]},{"year":2019,"claim":"The E3 ubiquitin ligases responsible for GlyT2 ubiquitination were identified: LNX1 and LNX2 ubiquitinate the same C-terminal lysine cluster via their RING domains; genetic deletion of LNX2 in spinal neurons increased GlyT2 expression, and LNX2 is required for PKC-mediated transport regulation.","evidence":"Unbiased E3 ligase screening, co-IP, RING-domain mutagenesis, LNX2 knockout neurons with PKC activation","pmids":["31628376"],"confidence":"High","gaps":["Whether LNX1 and LNX2 are redundant or specialized in vivo not determined","Upstream signals activating LNX2 beyond PKC not identified"]},{"year":null,"claim":"Key unresolved questions include the high-resolution structure of GlyT2 in multiple conformational states, the structural basis for its inability to operate in reverse, whether GlyT2 and VIAAT are physically coupled for vesicular glycine refilling, and therapeutic strategies to rescue trafficking-defective hyperekplexia mutants.","evidence":"","pmids":[],"confidence":"High","gaps":["No experimental GlyT2 structure available","Physical coupling between GlyT2 and VIAAT not tested","Pharmacological chaperone rescue of misfolded mutants not explored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,2,4,12,15]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5,8,16,17,19]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[8,18]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[18,19]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,1,12,15]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,2,4,12,15]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[5,8,18,19,25]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[8,19,25]}],"complexes":[],"partners":["STX1A","ATP1A1","ATP2B2","ATP2B3","SLC8A1","LNX1","LNX2","CANX"],"other_free_text":[]},"mechanistic_narrative":"SLC6A5 (GlyT2) is a presynaptic Na⁺/Cl⁻-dependent glycine transporter that concentrates glycine into glycinergic nerve terminals to sustain vesicular glycine loading and inhibitory neurotransmission in the spinal cord, brainstem, and cerebellum [PMID:7861131, PMID:9387864, PMID:17554001, PMID:18815261]. Transport depends on residues in transmembrane domains that coordinate Na⁺ and glycine binding (e.g., Tyr-289, Asp-471), N-glycosylation for ER-to-surface trafficking assisted by calnexin, and association with cholesterol-rich membrane rafts [PMID:10788509, PMID:22132725, PMID:11036075, PMID:23650557, PMID:18266927]. Surface expression is dynamically regulated by syntaxin 1A–mediated exocytic delivery, clathrin-dependent endocytosis driven by PKC-stimulated ubiquitination of a C-terminal lysine cluster (K751/K773/K787/K791) by E3 ligases LNX1/LNX2, and recycling through Rab11-positive endosomes, with Na⁺/K⁺-ATPase, PMCA, and NCX1 forming a functional raft-resident complex that sustains local ion homeostasis required for transport [PMID:11278707, PMID:21910806, PMID:23484054, PMID:31628376, PMID:19374720, PMID:23986260, PMID:25315779]. Loss-of-function mutations in SLC6A5 cause hereditary hyperekplexia (startle disease) in humans by impairing glycine uptake and presynaptic glycine recycling [PMID:16751771, PMID:22700964]."},"prefetch_data":{"uniprot":{"accession":"Q9Y345","full_name":"Sodium- and chloride-dependent glycine transporter 2","aliases":["Solute carrier family 6 member 5"],"length_aa":797,"mass_kda":87.4,"function":"Sodium- and chloride-dependent glycine transporter (PubMed:10381548, PubMed:10606742, PubMed:16751771, PubMed:31370103, PubMed:9845349). Terminates the action of glycine by its high affinity sodium-dependent reuptake into presynaptic terminals (PubMed:9845349). May be responsible for the termination of neurotransmission at strychnine-sensitive glycinergic synapses (PubMed:9845349) Lacks sodium- and chloride-dependent glycine transporter activity Lacks sodium- and chloride-dependent glycine transporter activity","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y345/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC6A5","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"NET1","ensg_id":"ENSG00000173848","cell_line_id":"CID000580","localizations":[{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"KPNB1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000580","total_profiled":1310},"omim":[{"mim_id":"614618","title":"HYPEREKPLEXIA 3; HKPX3","url":"https://www.omim.org/entry/614618"},{"mim_id":"604159","title":"SOLUTE CARRIER FAMILY 6 (NEUROTRANSMITTER TRANSPORTER, GLYCINE), MEMBER 5; SLC6A5","url":"https://www.omim.org/entry/604159"},{"mim_id":"163970","title":"SOLUTE CARRIER FAMILY 6 (NEUROTRANSMITTER TRANSPORTER, NORADRENALINE), MEMBER 2; SLC6A2","url":"https://www.omim.org/entry/163970"},{"mim_id":"149400","title":"HYPEREKPLEXIA 1; HKPX1","url":"https://www.omim.org/entry/149400"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Not detected","tissue_distribution":"Not detected","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SLC6A5"},"hgnc":{"alias_symbol":["GLYT2","GlyT-2"],"prev_symbol":["NET1"]},"alphafold":{"accession":"Q9Y345","domains":[{"cath_id":"1.20.1740,1.20.1730","chopping":"215-307_375-766","consensus_level":"medium","plddt":92.1866,"start":215,"end":766}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y345","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y345-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y345-F1-predicted_aligned_error_v6.png","plddt_mean":73.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC6A5","jax_strain_url":"https://www.jax.org/strain/search?query=SLC6A5"},"sequence":{"accession":"Q9Y345","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y345.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y345/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y345"}},"corpus_meta":[{"pmid":"10219245","id":"PMC_10219245","title":"Net1, a Sir2-associated nucleolar protein required for rDNA silencing and nucleolar integrity.","date":"1999","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/10219245","citation_count":335,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"7582108","id":"PMC_7582108","title":"Regional distribution and developmental variation of the glycine transporters GLYT1 and GLYT2 in the rat CNS.","date":"1995","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/7582108","citation_count":243,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"16751771","id":"PMC_16751771","title":"Mutations in the gene encoding GlyT2 (SLC6A5) define a presynaptic component of human startle disease.","date":"2006","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16751771","citation_count":179,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15717291","id":"PMC_15717291","title":"Support for association between ADHD and two candidate genes: NET1 and DRD1.","date":"2005","source":"American journal of medical genetics. 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Molecular brain research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct functional reconstitution in transfected cells plus endogenous neuron correlations\",\n      \"pmids\": [\"9387864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"N-glycosylation of GlyT2 at four sites (Asn-345, Asn-355, Asn-360, Asn-366) in the large extracellular loop is required for transport activity and proper trafficking to the plasma membrane; enzymatic deglycosylation reduces transport by 35–40%, and mutations of all four sites produce an inactive protein retained intracellularly.\",\n      \"method\": \"Site-directed mutagenesis, enzymatic deglycosylation, transport assay, biotinylation, transfection in COS and MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + in vitro transport assay + surface biotinylation with multiple mutant combinations\",\n      \"pmids\": [\"11036075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"GLYT2 physically interacts with the SNARE protein syntaxin 1A; co-transfection of syntaxin 1A inhibits glycine transport by ~40%, an effect reversed by Munc18, and immunoprecipitation confirms the interaction in both COS cells and rat brain tissue, with syntaxin 1A causing partial removal of GLYT2 from the plasma membrane.\",\n      \"method\": \"Co-immunoprecipitation, transport assay, surface biotinylation, co-transfection\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP in both heterologous cells and native brain tissue, functional consequence confirmed\",\n      \"pmids\": [\"10722844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Syntaxin 1 (via SNARE-mediated mechanism) controls GlyT2 trafficking to the plasma membrane during exocytosis: stimulation of vesicular glycine release causes rapid GlyT2 translocation to then internalization from the plasma membrane; inactivation of syntaxin 1 with BoNT/C prevents GlyT2 from reaching the membrane but not leaving it. GlyT2 is also found in small synaptic-like vesicles.\",\n      \"method\": \"Synaptosome calcium stimulation, BoNT/C inactivation, surface expression assays, immunogold labeling on purified synaptosomal fractions\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in native brain preparation with toxin-based functional dissection\",\n      \"pmids\": [\"11278707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Tyrosine 289 in transmembrane domain III of GlyT2 is crucial for ion coupling, glycine affinity, and sodium selectivity; mutations Y289W, Y289F, and Y289S abolish or severely impair glycine uptake and alter Na+ cooperativity and Cl- dependence.\",\n      \"method\": \"Site-directed mutagenesis, electrophysiology (steady-state currents), glycine uptake assays in transfected HEK-293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + electrophysiology + uptake assays with multiple substitutions\",\n      \"pmids\": [\"10788509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GlyT2-mediated uptake is directly coupled to the accumulation of glycine into recycling synaptic vesicles; GlyT2 inhibition causes a switch from glycinergic to GABAergic inhibitory phenotype by reducing cytosolic glycine available for vesicle filling, an effect fully reversed by glycine resupply.\",\n      \"method\": \"Electrophysiology (transporter current recording), glycine/GABA phenotype switching in GlyT2-EGFP transgenic mouse spinal cord cultures, pharmacological inhibition\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — functional reconstitution in primary neurons from transgenic mice with electrophysiology and pharmacological rescue\",\n      \"pmids\": [\"18815261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GlyT2 cooperates with VIAAT to determine the vesicular glycinergic phenotype; GlyT2 is more effective than GlyT1 because it cannot operate in reverse mode, maintaining the high cytosolic glycine concentration required for efficient vesicular loading by VIAAT.\",\n      \"method\": \"Reconstitution in neuroendocrine cells, double-sniffer patch-clamp quantal release measurement, co-expression of VIAAT and GlyT2/GlyT1\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with novel quantitative electrophysiology assay, mechanistic comparison of transporters\",\n      \"pmids\": [\"17554001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human GlyT2 (SLC6A5) encodes a 797 amino acid protein that transports glycine in a Na+/Cl--dependent manner when stably expressed in CHO cells, with an apparent Km of 108 μM; transport is insensitive to sarcosine. The gene maps to chromosome 11p15.1-15.2.\",\n      \"method\": \"cDNA cloning, stable expression in CHO cells, glycine uptake assays, radiation hybrid mapping\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct functional expression and kinetic characterization in mammalian cells\",\n      \"pmids\": [\"9845349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Twenty SLC6A5 sequence variants in 17 hyperekplexia patients result in defective glycine transport through diverse mechanisms including protein truncation, splice site mutations, and missense mutations affecting Cl- binding, extracellular loop 4 conformational changes, and cation-π interactions. Mutation A275T causes voltage-sensitive decrease in glycine transport due to lower Na+ affinity.\",\n      \"method\": \"DNA sequencing, glycine uptake assays, electrophysiology of specific mutations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — systematic functional analysis of 16 mutations with electrophysiology and uptake assays\",\n      \"pmids\": [\"22700964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mutations in SLC6A5 causing truncation of GlyT2 result in complete loss of transport function, confirming GlyT2 as a disease gene in hyperekplexia.\",\n      \"method\": \"Genetic sequencing, glycine transport assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab, genetic plus functional assay\",\n      \"pmids\": [\"16884688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GlyT2 is associated with cholesterol- and sphingomyelin-enriched membrane raft domains in brainstem synaptosomes and neurons; depletion of raft components by methyl-β-cyclodextrin impairs both raft association and transport activity, indicating that membrane raft localization is required for optimal GlyT2 function.\",\n      \"method\": \"Detergent-resistant membrane fractionation, confocal microscopy, electron microscopy immunogold, pharmacological cholesterol/sphingomyelin depletion, transport assays\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in native brain tissue with functional consequence\",\n      \"pmids\": [\"18266927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Protein kinase C (PKC) activation by PMA inhibits GlyT2 transport by increasing internalization rate via clathrin-mediated endocytosis, redistributing GlyT2 from raft to non-raft membrane domains; these effects involve both PKC-dependent and PKC-independent pathways including Rac1 signaling. A regulatory site mutant (K422E) is resistant to PMA-induced modulation.\",\n      \"method\": \"PMA treatment, pharmacological PKC inhibition, site-directed mutagenesis (K422E), glycine uptake assay, membrane fractionation, primary neuron and synaptosome experiments\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis + pharmacology + native brain preparations, multiple orthogonal methods\",\n      \"pmids\": [\"18341477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GlyT2 constitutive and PKC-regulated endocytosis occurs primarily via the clathrin-mediated pathway; PKC negatively modulates GlyT2 by redistributing it from raft to non-raft domains and increasing ubiquitinated GlyT2 endocytosis. GlyT2 is constitutively internalized from lipid rafts and remains raft-associated in recycling structures.\",\n      \"method\": \"Dominant-negative mutants, siRNA, pharmacological inhibitors, membrane fractionation, biotinylation assays in heterologous cells and neurons\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches including genetic and pharmacological in both cell lines and neurons\",\n      \"pmids\": [\"21910806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Intracellular GlyT2 in rat brainstem resides in Rab11-positive recycling endosomes and synaptophysin-positive vesicles; co-expression of a Rab11 dominant-negative mutant impairs GlyT2 trafficking and glycine transport, demonstrating that Rab11-dependent recycling endosomes are the main intracellular compartment for GlyT2.\",\n      \"method\": \"Electron microscopy immunogold, confocal microscopy, subcellular fractionation, dominant-negative Rab11 co-expression, transport assays\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple techniques in native tissue plus functional consequence of dominant-negative intervention\",\n      \"pmids\": [\"19374720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GlyT2 physically interacts with Na+/K+-ATPase (NKA) in CNS; this interaction mainly occurs in the raft-associated active pool of GlyT2. Ouabain-mediated modulation of NKA regulates GlyT2 endocytosis and total expression in neurons in vitro, and this mechanism is conserved in vivo in zebrafish embryos and adult rats.\",\n      \"method\": \"Mass spectrometry, reciprocal co-immunoprecipitation, immunocytochemistry, ouabain treatment in neurons, in vivo zebrafish and rat experiments\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS identification + reciprocal co-IP + in vivo validation across two species\",\n      \"pmids\": [\"23986260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ubiquitination of a C-terminal four-lysine cluster (GlyT2 C-terminus) is required for constitutive GlyT2 endocytosis, sorting into the slow recycling pathway, and turnover; PKC activation accelerates degradation by increasing ubiquitination, while decreased ubiquitination extends GlyT2 half-life. UCHL1 indirectly modulates GlyT2 turnover by controlling neuronal ubiquitin availability.\",\n      \"method\": \"Ubiquitination assays, C-terminal lysine mutagenesis, turnover/pulse-chase analysis, PKC activation, siRNA of UCHL1, primary neuron experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis of ubiquitin sites + pharmacological + neuronal validation\",\n      \"pmids\": [\"23484054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The C-terminal PDZ-ligand motif of GlyT2 interacts with syntenin-1 and is required for efficient synaptic localization in neurons; inactivation of the motif reduces GlyT2 co-localization with synaptic markers by up to 50% in hippocampal neurons, though it does not affect transport function in HEK293T cells.\",\n      \"method\": \"PDZ-ligand motif mutagenesis, transfection in HEK293T cells and hippocampal neurons, co-localization with synaptic markers\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function mutagenesis with clear localization phenotype in neurons\",\n      \"pmids\": [\"17851090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A dominant hyperekplexia mutation Y705C in transmembrane domain 11 of GlyT2 introduces a cysteine that interacts with the Cys-311-Cys-320 pair in external loop 2, impairing transporter maturation through the secretory pathway, reducing surface expression, and inhibiting transport function. Y705C also shows altered H+ and Zn2+ dependence of glycine transport.\",\n      \"method\": \"Molecular modeling, electrophysiology, [3H]glycine transport assay, cell surface expression analysis, cysteine labeling assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biochemical and functional methods including mutagenesis and electrophysiology\",\n      \"pmids\": [\"22753417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GlyT2 forms a presynaptic complex with plasma membrane Ca2+-ATPase (PMCA) isoforms 2 and 3, and Na+/Ca2+-exchanger 1 (NCX1) in lipid raft subdomains; endogenous PMCA and NCX activities are necessary for GlyT2 activity, and this modulation depends on lipid raft integrity. The complex is proposed to help control local Na+ increases from GlyT2 cotransport.\",\n      \"method\": \"Co-immunoprecipitation, lipid raft fractionation, pharmacological inhibition of PMCA and NCX, glycine uptake assays in synaptosomes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP + functional inhibition assays in native presynaptic preparations\",\n      \"pmids\": [\"25315779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"E3 ubiquitin ligases LNX1 and LNX2 ubiquitinate a C-terminal lysine cluster (K751, K773, K787, K791) in GlyT2 via their N-terminal RING-finger domains, regulating GlyT2 expression levels and transport activity. Genetic deletion of endogenous LNX2 in spinal cord neurons increases GlyT2 expression, and LNX2 is required for PKC-mediated control of GlyT2 transport.\",\n      \"method\": \"Unbiased protein interaction screening, ubiquitination assays, RING-domain mutagenesis, LNX2 genetic knockout in spinal cord neurons, transport assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — identified by screening, validated with mutagenesis + genetic KO + functional assays in neurons\",\n      \"pmids\": [\"31628376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Calnexin (CNX) facilitates GlyT2 biogenesis in the ER by transiently binding to an underglycosylated transporter precursor via both glycan-dependent and glycan-independent (polypeptide-based) interactions; CNX knockdown attenuates GlyT2 surface expression and transport activity, while CNX overexpression enhances them.\",\n      \"method\": \"siRNA knockdown of CNX, CNX overexpression, pharmacological glycosylation inhibition, co-immunoprecipitation, transport assays, N-glycan mutant analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function + pharmacology + mutagenesis with functional readout\",\n      \"pmids\": [\"23650557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"An aspartate residue (Asp471) in the external vestibule of GlyT2 controls cation access and transport coupling; D471 mutation reduces Na+ affinity and cooperativity, increases sodium leakage and uncoupled ion movements, and is involved in Na+- and Li+-induced conformational changes, explaining the distinct responses of GlyT2 and GlyT1 to lithium.\",\n      \"method\": \"Molecular dynamics simulation, in silico mutagenesis, site-directed mutagenesis, electrophysiology, [3H]glycine transport assay, cysteine accessibility assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — computational + mutagenesis + electrophysiology + transport assays with mechanistic interpretation\",\n      \"pmids\": [\"22132725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Activation of calpain (Ca2+-dependent protease) in spinal cord synaptosomes and neurons cleaves GlyT2 at its N-terminal region, with major cleavage sites after Met156 and Gly164; the resulting N-terminally truncated ~70 kDa GlyT2 retains full transport activity when expressed in HEK293 cells.\",\n      \"method\": \"Calpain activation in synaptosomes, protein sequence analysis of cleavage products, expression of truncated GlyT2 in HEK293 cells, transport assays\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical identification of cleavage sites + functional assay of truncated transporter\",\n      \"pmids\": [\"14675166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"BDNF, acting through truncated TrkB-T1 receptor, decreases GlyT2-mediated glycine transport in astrocytes by promoting transporter internalization via dynamin/clathrin-dependent endocytosis in a Rho-GTPase-dependent manner; knockdown of TrkB-T1 abolishes the BDNF effect.\",\n      \"method\": \"siRNA knockdown of TrkB-T1, pharmacological inhibition (dynasore, toxin B, kinase inhibitors), [3H]glycine uptake assay, immunofluorescence of GlyT in endosomes, primary astrocyte cultures\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockdown + pharmacological dissection + multiple orthogonal readouts\",\n      \"pmids\": [\"26200505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GSK3β differentially modulates glycine transporters: co-expression of GSK3β with GlyT2 stimulates transport activity and increases GlyT2 surface expression, while it inhibits GlyT1. GSK3β decreases 32Pi incorporation into GlyT2 (in contrast to GlyT1), and pharmacological inhibition of GSK3β in neurons has opposite effects on GlyT1 and GlyT2 activity.\",\n      \"method\": \"Co-expression in COS-7 cells and Xenopus oocytes, catalytically inactive GSK3β mutant, GSK3β inhibitors, 32Pi incorporation assays, brainstem and spinal cord neuron cultures\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple heterologous systems + pharmacological validation in neurons, but kinase-substrate relationship not directly mapped on GlyT2\",\n      \"pmids\": [\"25301276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"P2X purinergic receptor stimulation (via homomeric P2X3 and P2X2 receptors or heteromeric P2X2/3 receptors) up-regulates GlyT2 transport activity by increasing total and plasma membrane expression and reducing transporter ubiquitination; this modulation of GlyT2 impacts glycinergic neurotransmission.\",\n      \"method\": \"Pharmacological P2X agonists, siRNA knockdown of receptor subtypes, GlyT2 transport assay, surface biotinylation, ubiquitination assay, glycine release measurement, electrophysiology, primary neuron cultures\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological + genetic (siRNA) dissection with multiple functional readouts in primary neurons\",\n      \"pmids\": [\"28734869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A homozygous 4.2 kb microdeletion in SLC6A5 (encompassing exons 2 and 3) in Irish wolfhound dogs causes loss of GlyT2 protein expression and startle disease, confirming that loss-of-function of GlyT2 causes the disorder by a recessive mechanism.\",\n      \"method\": \"Genetic sequencing, Southern blotting, MLPA, deletion breakpoint analysis, protein expression analysis\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic confirmation with multiple molecular validation methods but no functional transport assay\",\n      \"pmids\": [\"21420493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GlyT2 exists as two isoforms (GLYT2a and GLYT2b) generated by alternative use of exons 1a or 1b; GLYT2a actively accumulates glycine into transfected COS cells, whereas GLYT2b only exchanges (releases) glycine, despite similar regional distribution and kinetics.\",\n      \"method\": \"RACE analysis, genomic DNA characterization, transfection into COS cells, glycine uptake assay\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular characterization + functional assay in heterologous cells\",\n      \"pmids\": [\"9509996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A retrotransposon insertion in mouse Slc6a5 causing absence of GlyT2 protein results in handling-induced spasms, accelerated neuromuscular junction synapse elimination, premature switch from embryonic to adult acetylcholine receptor subunits, and elevated AChR transcription, consistent with increased motor neuron activity when glycinergic inhibition is lost.\",\n      \"method\": \"Spontaneous mouse mutant characterization, protein expression analysis, NMJ immunostaining, AChR subunit switch analysis, behavioral testing\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — null allele with defined cellular phenotypes but mechanistic pathway not fully dissected\",\n      \"pmids\": [\"22272310\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC6A5 encodes GlyT2, a presynaptic Na+/Cl−-dependent neuronal glycine transporter that removes glycine from the inhibitory synaptic cleft and recycles it into the presynaptic terminal to refill VIAAT-containing synaptic vesicles; its transport activity depends on N-glycosylation, membrane raft association, interaction with syntaxin 1A (controlling exocytic trafficking), and a C-terminal PDZ-ligand motif (controlling synaptic localization), and is dynamically regulated by PKC-driven clathrin-mediated endocytosis, ubiquitination of a C-terminal lysine cluster by E3 ligases LNX1/2, interaction with Na+/K+-ATPase and PMCA/NCX complexes, and signaling through P2X receptors and BDNF/TrkB-T1, with loss-of-function mutations in SLC6A5 being the second major cause of hereditary hyperekplexia in humans.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI need to carefully classify each paper before extracting discoveries.\n\n**Classification:**\n\nThe target gene is **SLC6A5** (encoding **GlyT2**, the neuronal glycine transporter 2).\n\nPapers about SLC6A5/GlyT2: Papers [2], [3], [5], [6], [8], [10], [12], [14], [17], [18], [19], [22], [25], [28], [30], [35], [37], [40], [42], [43], [44], [47], [50], [51], [55], [56], [57], [58], [59], [60], [61], [63], [65], [66], [69], [74], [77], [78], [80], [82], [84], [86], [87], [89], [91], [92], [99] from the main corpus, and from additional curated papers, none are directly about GlyT2 mechanistically (they're about NET/SLC6A2 or general).\n\nPapers about NET1 (RhoA GEF, neuroepithelial cell transforming gene 1) — ALIAS COLLISION: [1], [4], [7], [9], [11], [13], [15], [16], [20], [21], [23], [24], [26], [27], [29], [31], [32], [33], [34], [36], [38], [39], [41], [45], [46], [53], [54], [62], [67], [68], [70], [71], [73], [79], [81], [83], [85], [88], [90], [94], [95], [96], [97], [98], [100] — EXCLUDE (alias collision: NET1 GEF ≠ SLC6A5)\n\nPapers about NET/SLC6A2 (norepinephrine transporter) — ALIAS COLLISION: Additional papers [2], [5], [9], [10], [11], [16], [20], [22], [23], [26], [27], [28], [30] — EXCLUDE\n\nPapers about circ RNAs/lncRNAs involving NET1 — EXCLUDE (alt-locus product or alias collision): [48], [68]\n\nPaper [46] — about Netrin-1 (NET1 ligand) and NEO1 — EXCLUDE (alias collision, different gene entirely)\n\nNow extracting from KEPT papers about SLC6A5/GlyT2:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"GLYT2 (SLC6A5) is expressed predominantly in neurons of the spinal cord, brainstem, and cerebellum, with immunoreactivity localized to axonal processes with varicosities but not cell bodies, correlating with the distribution of glycine receptors and suggesting a role in terminating glycine neurotransmission at inhibitory synapses.\",\n      \"method\": \"Western blot, immunocytochemistry with polyclonal antibodies against recombinant N-terminus and loop fusion proteins in mouse brain\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by immunocytochemistry with specific antibodies, replicated across labs (PMID 7861131 and 7582108)\",\n      \"pmids\": [\"7861131\", \"7582108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GLYT2 is the active concentrator of glycine in glycinergic neurons: GLYT2 expression in cultured spinal neurons and GLYT2-transfected COS cells directly correlates with intracellular glycine accumulation, establishing that GLYT2-mediated uptake is responsible for the high glycine content of glycinergic neurons and that GLYT2 can be used as a reliable marker for glycinergic neurons.\",\n      \"method\": \"Double-immunofluorescence co-localization, glycine uptake assays in cultured spinal neurons and GLYT2-transfected COS cells\",\n      \"journal\": \"Brain research. Molecular brain research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional uptake assay with both native neurons and transfected cells, strong evidence\",\n      \"pmids\": [\"9387864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human GlyT2 encodes a 797 amino acid Na+/Cl−-dependent glycine transporter with an apparent Km of 108 μM for glycine, insensitive to sarcosine, and the gene maps to chromosome 11p15.1-15.2.\",\n      \"method\": \"Expression cloning, stable expression in CHO cells, glycine uptake assays, radiation hybrid mapping\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in CHO cells with kinetic characterization\",\n      \"pmids\": [\"9845349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Two alternative 5' isoforms of rat GLYT2 (GLYT2a and GLYT2b) are generated by alternative exon usage; GLYT2a actively accumulates glycine in transfected COS cells whereas GLYT2b only exchanges (releases) glycine, indicating functionally distinct transport modes.\",\n      \"method\": \"RACE analysis, genomic DNA analysis, transport assays in transfected COS cells\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional comparison of two isoforms in transfected cells, single lab\",\n      \"pmids\": [\"9509996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Tyrosine 289 in transmembrane domain III of GLYT2a is critical for ion coupling and glycine transport: mutations Y289W, Y289F, and Y289S abolish or dramatically reduce transport activity, alter Na+ affinity and cooperativity, reduce Na+ selectivity, and decrease Cl− dependence, indicating that TM III forms part of the ion and substrate permeation pathway.\",\n      \"method\": \"Site-directed mutagenesis, electrophysiology (steady-state currents), glycine uptake assays in HEK-293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis with functional assays (electrophysiology + transport) in multiple mutants\",\n      \"pmids\": [\"10788509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"N-glycosylation at four sites (Asn-345, Asn-355, Asn-360, Asn-366) in the large extracellular loop of GLYT2 is required for transport activity, proper intracellular trafficking to the plasma membrane in COS cells, and apical sorting in polarized MDCK cells; enzymatic deglycosylation reduces transport activity by 35-40%; apical localization occurs via a glycolipid raft-independent pathway.\",\n      \"method\": \"Site-directed mutagenesis of glycosylation sites, enzymatic deglycosylation, transport assays, biotinylation assays, transfection in COS and MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with multiple functional and trafficking assays\",\n      \"pmids\": [\"11036075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Syntaxin 1A physically interacts with both GLYT1 and GLYT2 in COS cells and rat brain tissue (co-immunoprecipitation), and co-transfection of syntaxin 1A inhibits glycine transport by ~40%; this inhibition is reversed by Munc18; syntaxin 1A interaction partially removes the transporters from the plasma membrane as shown by biotinylation.\",\n      \"method\": \"Co-immunoprecipitation in COS cells and rat brain, glycine transport assays, cell-surface biotinylation\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP in native and heterologous systems, functional consequence demonstrated\",\n      \"pmids\": [\"10722844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Ethanol selectively and acutely inhibits GLYT2a but not GLYT1b in a non-competitive (allosteric) manner, with a cut-off at alcohols with four carbons suggesting a specific binding site; chronic ethanol treatment decreases GLYT2a activity and surface expression while slightly increasing GLYT1b function.\",\n      \"method\": \"Glycine uptake assays in stably transfected HEK-293 cells, n-alkanol inhibition series\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic pharmacological characterization in stable cell lines, single lab\",\n      \"pmids\": [\"10683205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Syntaxin 1 mediates GLYT2 trafficking to the plasma membrane via a SNARE-dependent mechanism: under conditions stimulating vesicular glycine release (exocytosis) in synaptosomes, GLYT2 traffics first to the plasma membrane and then is internalized; inactivation of syntaxin 1 with BoNT/C prevents GLYT2 from reaching the plasma membrane but does not block internalization. Immunogold labeling shows GLYT2 is present in small synaptic-like vesicles.\",\n      \"method\": \"Synaptosome stimulation, BoNT/C neurotoxin treatment, surface expression assays, immunogold electron microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with neurotoxin and imaging in brain-derived preparation\",\n      \"pmids\": [\"11278707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Calpain (Ca2+-dependent protease) cleaves the extended N-terminal cytoplasmic region of GlyT2 at two sites (after Met-156 and Gly-164) in spinal cord synaptosomes and cultured neurons; the resulting ~70 kDa N-terminally truncated GlyT2 retains full transport activity upon expression in HEK293 cells, suggesting calpain-mediated proteolysis may regulate GlyT2 trafficking or function.\",\n      \"method\": \"Calpain activation in synaptosomes and cultured neurons, protein sequence analysis of cleavage sites, expression of truncated GlyT2 in HEK293 cells with transport assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cleavage site mapping combined with functional assay, single lab\",\n      \"pmids\": [\"14675166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Missense, nonsense, and frameshift mutations in SLC6A5 (encoding GlyT2) cause hereditary hyperekplexia; these mutations result in defective subcellular GlyT2 localization, decreased glycine uptake, or both; selected mutations affect predicted glycine and Na+ binding sites, establishing SLC6A5 as a presynaptic disease gene.\",\n      \"method\": \"Human genetics (sequencing), heterologous expression with glycine uptake assays, subcellular localization studies\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human disease mutations functionally validated in multiple assays, large patient cohort\",\n      \"pmids\": [\"16751771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Truncating mutations in the human GlyT2 gene (SLC6A5) cause complete loss of glycine transport function, confirming SLC6A5 as a disease gene in human hyperekplexia.\",\n      \"method\": \"DNA sequencing of patients, heterologous expression and glycine uptake assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional validation of human disease mutations\",\n      \"pmids\": [\"16884688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GlyT2 (but not GlyT1) maintains the high cytosolic glycine concentration required for efficient vesicular loading by VIAAT: in a neuroendocrine cell reconstitution system, GlyT2 more effectively than GlyT1 supports glycinergic quantal release because GlyT2 cannot operate in reverse mode, thereby maintaining cytosolic glycine for vesicle refilling.\",\n      \"method\": \"Reconstitution in neuroendocrine cells co-expressing VIAAT and plasmalemmal transporters; double-sniffer patch-clamp technique measuring quantal glycine/GABA release\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution system with novel electrophysiological readout; mechanistic distinction between GlyT1 and GlyT2\",\n      \"pmids\": [\"17554001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The C-terminal PDZ-ligand motif of GlyT2 is required for efficient synaptic localization in neurons: inactivation of this motif does not impair transport function in HEK293T cells but reduces co-localization with synaptic markers by up to 50% in hippocampal neurons, indicating the PDZ motif is important for trafficking to and/or stabilization at synaptic sites.\",\n      \"method\": \"Site-directed mutagenesis, transfection of hippocampal neurons, immunofluorescence co-localization with synaptic markers\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function approach in neurons with specific synaptic co-localization readout, single lab\",\n      \"pmids\": [\"17851090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GLYT2 is expressed in a subset of GFAP-positive astrocyte-derived gliosomes in mouse spinal cord and contributes to glycine-evoked GABA release from GABAergic synaptosomes, demonstrating that GLYT2 localization is not exclusively neuronal and that it functionally contributes to GABAergic signaling via glycine transport.\",\n      \"method\": \"Purified synaptosome and gliosome preparations, pharmacological blockade with selective GLYT1/GLYT2 inhibitors, confocal microscopy co-labeling with GAT1, GFAP, MAP2\",\n      \"journal\": \"Neurochemistry international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional pharmacological dissection with morphological confirmation, single lab\",\n      \"pmids\": [\"17597258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GlyT2-mediated glycine uptake is directly coupled to the refilling of recycling synaptic vesicles: GlyT2 inhibition in cultured spinal neurons causes a switch from glycinergic to GABAergic inhibitory phenotype through cytosolic glycine depletion, fully reversible by glycine resupply; high-frequency stimulation reveals two kinetically distinct phases of vesicle release with different requirements for GlyT2-mediated glycine refilling.\",\n      \"method\": \"Whole-cell and synaptic electrophysiology in GlyT2-eGFP transgenic mouse spinal cord neurons; glycine transport current recording; pharmacological GlyT2 inhibition\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — electrophysiological reconstitution of vesicle refilling in transgenic neurons with multiple controls\",\n      \"pmids\": [\"18815261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GLYT2 is associated with membrane rafts (Triton X-100-insoluble fractions) in brainstem terminals and neurons; cholesterol and sphingomyelin depletion with methyl-β-cyclodextrin disrupts raft association and impairs transport activity, indicating that the lipid raft environment is required for optimal GLYT2 function.\",\n      \"method\": \"Detergent-resistant membrane fractionation, methyl-β-cyclodextrin treatment, confocal microscopy, electron microscopy on purified raft fractions, transport assays in synaptosomes and neurons\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking raft association to functional activity\",\n      \"pmids\": [\"18266927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Protein kinase C (PKC) activation by PMA inhibits GLYT2 transport by increasing internalization rate and accumulating GLYT2 in intracellular compartments; PMA also redistributes GLYT2 from raft to non-raft membrane domains; a regulatory lysine mutant K422E is resistant to PMA-induced trafficking modulation; Rac1 signaling also participates in PMA action on GLYT2.\",\n      \"method\": \"PMA treatment, monensin trafficking assay, surface biotinylation, raft fractionation, mutagenesis (K422E), siRNA knockdown in HEK cells, brainstem neurons and synaptosomes\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis combined with pharmacological and trafficking assays in multiple systems\",\n      \"pmids\": [\"18341477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GLYT2 resides intracellularly in Rab11-positive recycling endosomes and synaptophysin-containing vesicles in rat brainstem; coexpression of dominant-negative Rab11 impairs GLYT2 trafficking and glycine transport, establishing that GlyT2 recycles through Rab11-positive endosomal compartments.\",\n      \"method\": \"Biochemical fractionation, immunofluorescence and immunogold electron microscopy, dominant-negative Rab11 co-expression with transport assay\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization linked to functional consequence via dominant-negative approach\",\n      \"pmids\": [\"19374720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GlyT2 endocytosis is mediated primarily by the clathrin pathway; PKC activation promotes redistribution of GLYT2 from raft to non-raft membrane domains and increases ubiquitinated GLYT2 endocytosis; GLYT2 is constitutively internalized from cell-surface lipid rafts while remaining raft-associated in recycling structures.\",\n      \"method\": \"Pharmacological inhibitors of clathrin pathway, dominant-negative mutants, siRNA knockdown, raft fractionation, internalization assays in HEK cells and neurons\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological and genetic tools confirming clathrin-mediated endocytosis with raft redistribution\",\n      \"pmids\": [\"21910806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Twenty SLC6A5 sequence variants were identified in hyperekplexia patients, all defective in glycine transport; pathogenic mechanisms include protein truncation (R439X most common), splice site mutations, missense mutations affecting Cl− binding, extracellular loop 4 conformational changes, and cation-π interactions; mutation A275T causes voltage-sensitive decrease in glycine transport through lower Na+ affinity.\",\n      \"method\": \"DNA sequencing of 93 hyperekplexia patients, glycine uptake assays for 16 novel mutations, electrophysiology (A275T)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — large patient cohort, functional validation of multiple mutations with electrophysiology\",\n      \"pmids\": [\"22700964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The dominant hyperekplexia mutation Y705C in TM11 of GlyT2 introduces a cysteine that interacts with the Cys-311–Cys-320 pair in external loop 2, impairing transporter maturation through the secretory pathway, reducing surface expression, and inhibiting transport; Y705C also shows altered H+ and Zn2+ sensitivity of glycine transport.\",\n      \"method\": \"Molecular modeling, electrophysiology, [3H]glycine transport assays, cell surface expression assays, cysteine labeling, secretory pathway analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structure-function with mutagenesis, multiple orthogonal methods including electrophysiology\",\n      \"pmids\": [\"22753417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A MusD retrotransposon insertion in mouse Slc6a5 abolishes GlyT2 protein expression (null allele), causing handling-induced spasms from day 5 and death by two weeks; loss of GlyT2 accelerates NMJ synapse elimination and the embryonic-to-adult AChR subunit switch, consistent with increased motor neuron activity; heterozygous mice show repetitive grooming and hyperactivity.\",\n      \"method\": \"Spontaneous mouse mutant characterization, Western blot, neuromuscular junction analysis, behavioral phenotyping\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null mouse model with defined cellular and behavioral phenotypes\",\n      \"pmids\": [\"22272310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Asp471 in the external vestibule of GLYT2 controls cation access and Na+ coupling: substitution of Asp471 reduces Na+ affinity and cooperativity, increases sodium leakage and uncoupled ion movements through GLYT2, and alters Na+/Li+-induced conformational changes; this residue is distinct from the homologous Asp295 in GLYT1, explaining the different lithium sensitivity of the two transporters.\",\n      \"method\": \"Homology modeling, molecular dynamics simulation, site-directed mutagenesis, electrophysiology, [3H]glycine transport assays, cation accessibility assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — computational plus experimental mutagenesis with electrophysiology and transport assays\",\n      \"pmids\": [\"22132725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Na+/K+-ATPase (NKA) is a direct interacting partner of GlyT2 in the CNS: identified by mass spectrometry interactomics, confirmed by reciprocal co-immunoprecipitation and immunocytochemistry; NKA preferentially interacts with the raft-associated active pool of GlyT2; ouabain-mediated NKA inhibition modulates GlyT2 endocytosis and total expression in neurons, in zebrafish embryos, and in adult rats, indicating an evolutionarily conserved regulatory mechanism.\",\n      \"method\": \"High-throughput mass spectrometry, reciprocal co-immunoprecipitation, immunocytochemistry, ouabain treatment in neurons, in vivo zebrafish and rat models\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS discovery confirmed by reciprocal Co-IP, functional validation in vitro and in vivo across species\",\n      \"pmids\": [\"23986260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ubiquitination of a C-terminal four-lysine cluster (K751, K773, K787, K791) in GlyT2 is required for constitutive endocytosis, sorting into the slow recycling pathway, and transporter turnover; increased ubiquitination by PKC activation accelerates GlyT2 degradation, while decreased ubiquitination increases stability; UCHL1, as major regulator of neuronal ubiquitin homeostasis, indirectly modulates GlyT2 turnover.\",\n      \"method\": \"Mutagenesis of lysine cluster, ubiquitination assays, endocytosis assays, turnover/half-life measurements, PKC activation, siRNA UCHL1 knockdown\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis of ubiquitination sites linked to functional trafficking outcomes\",\n      \"pmids\": [\"23484054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Calnexin (CNX) assists GlyT2 biogenesis in the ER: CNX binds transiently to an under-glycosylated GlyT2 precursor via both glycan-dependent and polypeptide-based (lectin-independent) interactions; CNX knockdown reduces GlyT2 accumulation and transport activity while CNX overexpression enhances them; CNX can stabilize non-glycosylated GlyT2 conformational states and rescue transport but not surface expression of fully non-glycosylated mutants; GlyT2 is degraded in lysosomes.\",\n      \"method\": \"siRNA-mediated CNX knockdown, CNX overexpression, pharmacological inhibition of glycosylation, transport assays, surface expression assays, lysosomal inhibitor treatments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches dissecting ER chaperone-transporter interaction\",\n      \"pmids\": [\"23650557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GlyT2 activation by glycine uptake can stimulate GABA release from cerebellar nerve terminals via two mechanisms: (1) reversal of GAT1 GABA transporter driven by Na+ influx through GlyT2 and subsequent mitochondrial Na+/Ca2+ exchange; (2) Ca2+-dependent anion channels permeable to GABA; ~20% of evoked GABA release is Ca2+-dependent via NCX reversal.\",\n      \"method\": \"[3H]GABA release assays from purified cerebellar nerve endings, pharmacological dissection with selective GlyT2, GAT1 and NCX inhibitors, Ca2+ manipulation\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection in purified nerve endings, single lab, multiple mechanisms proposed\",\n      \"pmids\": [\"24273061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GlyT2 forms a functional complex with plasma membrane Ca2+-ATPase (PMCA) isoforms 2 and 3 and Na+/Ca2+ exchanger 1 (NCX1) in lipid raft subdomains of the presynaptic terminal; endogenous PMCA and NCX activities are required for GlyT2 activity; this complex is proposed to help control local Na+ increases generated by GlyT2 cotransport.\",\n      \"method\": \"Co-immunoprecipitation, lipid raft fractionation, pharmacological inhibition of PMCA and NCX, GlyT2 transport assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP and functional pharmacology, single lab\",\n      \"pmids\": [\"25315779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Glycogen synthase kinase 3β (GSK3β) differentially modulates GlyT1 and GlyT2: GSK3β co-expression inhibits GlyT1 and stimulates GlyT2 activity/surface expression in COS-7 cells and Xenopus oocytes; GSK3β increases 32Pi incorporation into GlyT1 and decreases it in GlyT2; pharmacological inhibition of endogenous GSK3β in brainstem/spinal cord neurons produces opposite modulation of the two transporters.\",\n      \"method\": \"Co-expression in COS-7 cells and Xenopus oocytes, transport assays, phosphorylation (32Pi) assays, GSK3β inhibitors (LiCl, TDZD-8) in neuronal cultures\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple expression systems and phosphorylation readout, single lab\",\n      \"pmids\": [\"25301276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"BDNF acting on truncated TrkB-T1 receptors promotes internalization of GlyT2 (and GlyT1) in astrocytes via a Rho-GTPase-dependent, dynamin/clathrin-dependent endocytosis mechanism; BDNF decreases GlyT2 Vmax without changing Km, consistent with transporter internalization rather than kinetic inhibition.\",\n      \"method\": \"Primary astrocyte cultures, [3H]glycine uptake assays, dynasore treatment, siRNA TrkB-T knockdown, Rho-GTPase inhibitor (toxin B), immunofluorescence of GlyT endosomes\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with pharmacology, siRNA, and imaging in primary cells\",\n      \"pmids\": [\"26200505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"P2X purinergic receptor stimulation upregulates GlyT2 surface expression and transport activity by reducing transporter ubiquitination; this effect requires co-stimulation of homomeric P2X3 and P2X2 receptors, or heteromeric P2X2/3 receptors; P2X3 receptor activation modulates glycinergic neurotransmission through GlyT2 regulation.\",\n      \"method\": \"Pharmacological P2X receptor agonists/antagonists, siRNA knockdown of P2X subtypes, dorsal root ganglion enrichment, transport assays, surface expression, ubiquitination assays, glycinergic current recording\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic dissection of receptor subtypes with functional transport readout, single lab\",\n      \"pmids\": [\"28734869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"E3 ubiquitin ligases LNX1 and LNX2 ubiquitinate a C-terminal lysine cluster (K751, K773, K787, K791) in GlyT2 via their RING-finger domains, regulating GlyT2 expression and transport activity; genetic deletion of endogenous LNX2 in spinal cord neurons increases GlyT2 expression; LNX2 is required for PKC-mediated control of GlyT2 transport.\",\n      \"method\": \"Unbiased E3 ligase screening, co-immunoprecipitation, ubiquitination assays, RING-domain mutagenesis, LNX2 knockout neurons, PKC activation experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic screening confirmed by co-IP and genetic knockout, functional consequence demonstrated\",\n      \"pmids\": [\"31628376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Molecular dynamics simulations of GlyT2 in a complex neuronal membrane reveal a distinct lipid fingerprint: GlyT2 shows specific enrichment and depletion of lipid species (including cholesterol contacts) compared to other SLC6 transporters (dDAT, hDAT, hSERT), with the lipid environment influencing local membrane biophysical properties near the transporter.\",\n      \"method\": \"Molecular dynamics simulation in complex neuronal membrane, lipid fingerprint analysis\",\n      \"journal\": \"BBA advances\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no experimental validation\",\n      \"pmids\": [\"37082011\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GlyT2 (SLC6A5) is a presynaptic Na+/Cl−-dependent glycine transporter that cotransports 3 Na+/Cl−/glycine with a stoichiometry enabling concentrative glycine uptake into glycinergic terminals; its transport activity depends on N-glycosylation, membrane raft association, and interaction with syntaxin 1A (for membrane delivery), Na+/K+-ATPase, PMCA, and NCX1; surface expression is dynamically regulated by clathrin-mediated endocytosis controlled by PKC-dependent ubiquitination of a C-terminal lysine cluster by E3 ligases LNX1/2, with intracellular recycling through Rab11-positive endosomes; loss-of-function mutations in SLC6A5 impair vesicular glycine refilling, causing hereditary hyperekplexia (startle disease) in humans, cattle, and dogs.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SLC6A5 encodes GlyT2, a presynaptic Na+/Cl⁻-dependent glycine transporter that terminates inhibitory glycinergic neurotransmission by recapturing glycine from the synaptic cleft and maintaining the high cytosolic glycine concentration required for vesicular refilling via VIAAT [PMID:7582108, PMID:17554001, PMID:18815261]. GlyT2 transport activity depends on N-glycosylation for ER-to-surface trafficking (facilitated by calnexin), association with cholesterol-rich membrane raft domains where it forms functional complexes with Na+/K+-ATPase and PMCA/NCX calcium transporters, and syntaxin 1A–mediated SNARE-dependent exocytic delivery to the presynaptic membrane [PMID:11036075, PMID:10722844, PMID:18266927, PMID:25315779, PMID:23650557]. Surface expression is dynamically regulated by PKC-driven clathrin-mediated endocytosis, ubiquitination of a C-terminal lysine cluster by E3 ligases LNX1/LNX2, Rab11-dependent recycling, and modulatory inputs from P2X purinergic receptors and BDNF/TrkB-T1 signaling [PMID:18341477, PMID:31628376, PMID:19374720, PMID:28734869, PMID:26200505]. Loss-of-function mutations in SLC6A5 cause hereditary hyperekplexia (startle disease) in humans through diverse mechanisms including disrupted glycine/Na+ binding, impaired protein maturation, and defective membrane trafficking [PMID:16751771, PMID:22700964].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing where GlyT2 operates: immunolocalization resolved that GlyT2 is a neuronal transporter concentrated at presynaptic terminals in spinal cord, brainstem, and cerebellum, defining its role in terminating glycinergic inhibitory transmission rather than being glial like GlyT1.\",\n      \"evidence\": \"Immunocytochemistry, in situ hybridization, and Western blot in rat CNS tissue\",\n      \"pmids\": [\"7582108\", \"7861131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subcellular trafficking itinerary not yet defined\", \"No functional transport data in native neurons at this stage\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Cloning and functional characterization of human GlyT2 established the molecular identity of SLC6A5 and its basic transport kinetics (Km ~108 µM, Na+/Cl⁻-dependent, sarcosine-insensitive), while identification of splice variants (GLYT2a vs GLYT2b) revealed that alternative N-terminal exons can switch the transporter between uptake and exchange modes.\",\n      \"evidence\": \"cDNA cloning, stable expression in CHO cells, glycine uptake assays, RACE analysis of isoforms in COS cells\",\n      \"pmids\": [\"9845349\", \"9509996\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of exchange-mode isoform GLYT2b unknown\", \"Stoichiometry of Na+/Cl⁻/glycine coupling not precisely determined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mechanistic dissection of GlyT2 revealed that N-glycosylation at four extracellular loop sites is required for surface trafficking and transport activity, that syntaxin 1A directly binds GlyT2 to regulate its plasma membrane delivery, and that Tyr289 in TM3 is critical for ion coupling and glycine binding — together establishing the structural and trafficking requirements for transporter function.\",\n      \"evidence\": \"Site-directed mutagenesis, enzymatic deglycosylation, co-immunoprecipitation in brain and COS cells, electrophysiology in HEK-293 cells\",\n      \"pmids\": [\"11036075\", \"10722844\", \"10788509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full ion:substrate stoichiometry not determined\", \"Three-dimensional structure not available\", \"Syntaxin 1A binding site on GlyT2 not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The question of how GlyT2 reaches the synapse was answered: syntaxin 1A/SNARE machinery controls Ca²⁺-stimulated exocytic insertion of GlyT2 from intracellular vesicles to the plasma membrane, while GlyT2 internalization proceeds independently of syntaxin 1A, establishing bidirectional trafficking as a regulatory mechanism.\",\n      \"evidence\": \"BoNT/C inactivation of syntaxin 1A, calcium stimulation of synaptosomes, immunogold labeling of synaptic vesicle fractions\",\n      \"pmids\": [\"11278707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic pathway for GlyT2 retrieval not yet defined\", \"Whether GlyT2 is active on intracellular vesicles unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery that calpain cleaves GlyT2 at its N-terminal domain (after Met156/Gly164) without abolishing transport activity revealed that the large cytoplasmic N-terminus is dispensable for transport function, suggesting it serves regulatory rather than catalytic roles.\",\n      \"evidence\": \"Calpain activation in synaptosomes, sequencing of cleavage products, transport assays of truncated GlyT2 in HEK293 cells\",\n      \"pmids\": [\"14675166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological conditions triggering calpain cleavage of GlyT2 in vivo not established\", \"Functional consequences of N-terminal loss on trafficking or regulation not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The causal link between SLC6A5 and human disease was established: diverse loss-of-function mutations (missense, nonsense, frameshift) cause hereditary hyperekplexia by disrupting glycine uptake, surface localization, or both, making GlyT2 the second major hyperekplexia gene after GLRA1.\",\n      \"evidence\": \"Patient sequencing across multiple families, functional glycine uptake assays, subcellular localization in transfected cells\",\n      \"pmids\": [\"16751771\", \"16884688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genotype-phenotype correlations not fully mapped\", \"Incomplete penetrance and modifier genes not explored\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"The critical question of why neurons need GlyT2 specifically was answered: GlyT2 cooperates with VIAAT to establish the glycinergic vesicular phenotype because, unlike GlyT1, GlyT2 cannot operate in reverse mode, maintaining high cytosolic glycine for efficient vesicular loading — and a C-terminal PDZ-ligand motif directs GlyT2 to synaptic sites via interaction with syntenin-1.\",\n      \"evidence\": \"Reconstitution in neuroendocrine cells with double-sniffer patch-clamp quantal release; PDZ-ligand mutagenesis with synaptic marker co-localization in hippocampal neurons\",\n      \"pmids\": [\"17554001\", \"17851090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full set of PDZ-domain partners at synapses not identified\", \"Whether PDZ-ligand mutations affect glycinergic transmission in vivo not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Multiple regulatory layers converged: GlyT2 inhibition causes a glycinergic-to-GABAergic phenotype switch confirming its essential role in vesicular glycine supply; membrane raft association is required for optimal transport; and PKC activation drives GlyT2 from raft to non-raft domains, promoting clathrin-mediated endocytosis — establishing the first post-translational regulatory circuit for GlyT2 surface expression.\",\n      \"evidence\": \"Electrophysiology in GlyT2-EGFP transgenic mouse neurons, cholesterol depletion with MβCD, PMA/PKC inhibitors, membrane fractionation, mutagenesis of K422E in synaptosomes and neurons\",\n      \"pmids\": [\"18815261\", \"18266927\", \"18341477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PKC phosphorylation site(s) on GlyT2 not identified\", \"How raft exit triggers endocytosis mechanistically unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The intracellular itinerary of GlyT2 was mapped: internalized GlyT2 resides in Rab11-positive recycling endosomes, and dominant-negative Rab11 impairs GlyT2 recycling and transport, establishing Rab11-dependent slow recycling as the main pathway maintaining surface GlyT2 pools.\",\n      \"evidence\": \"Immunogold EM, confocal microscopy, subcellular fractionation, dominant-negative Rab11 co-expression with transport assays in neurons\",\n      \"pmids\": [\"19374720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals directing GlyT2 to Rab11 endosomes not identified\", \"Role of Rab4 fast recycling not excluded\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"BDNF signaling through truncated TrkB-T1 was shown to reduce GlyT2 transport by promoting dynamin/clathrin-dependent endocytosis via Rho-GTPases, establishing a neurotrophin-based modulatory input onto glycinergic transmission; separately, a canine SLC6A5 deletion confirmed GlyT2 loss-of-function causes startle disease across species.\",\n      \"evidence\": \"siRNA knockdown of TrkB-T1, pharmacological endocytosis inhibitors in primary astrocytes; genetic deletion mapping in Irish wolfhound dogs\",\n      \"pmids\": [\"26200505\", \"21420493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"TrkB-T1-mediated GlyT2 regulation not confirmed in neurons (shown in astrocytes)\", \"Downstream Rho-GTPase effectors on GlyT2 endocytosis not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Structural determinants of GlyT2 ion coupling were refined: Asp471 in the external vestibule controls cation access and explains differential Li+ sensitivity versus GlyT1; the dominant Y705C hyperekplexia mutation disrupts transporter maturation via aberrant disulfide bonding; and systematic analysis of 20 patient mutations revealed diverse mechanisms of transport failure including impaired Cl⁻ binding and cation-π interactions.\",\n      \"evidence\": \"Molecular dynamics, site-directed mutagenesis, electrophysiology, cysteine accessibility assays, systematic functional analysis of 16 mutations\",\n      \"pmids\": [\"22132725\", \"22753417\", \"22700964\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution crystal or cryo-EM structure of GlyT2\", \"Structural basis of 3Na+:1Cl⁻:1glycine stoichiometry not confirmed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The molecular machinery controlling GlyT2 turnover and biogenesis was defined: ubiquitination of a C-terminal four-lysine cluster governs constitutive endocytosis, sorting into slow recycling, and degradation; calnexin facilitates GlyT2 folding in the ER via both glycan-dependent and glycan-independent interactions; and Na+/K+-ATPase physically associates with GlyT2 in raft domains to regulate its endocytosis, validated in vivo in zebrafish and rat.\",\n      \"evidence\": \"Lysine mutagenesis, pulse-chase turnover assays, UCHL1 siRNA, calnexin knockdown/overexpression, mass spectrometry identification of NKA, reciprocal co-IP, ouabain treatment in neurons and in vivo\",\n      \"pmids\": [\"23484054\", \"23650557\", \"23986260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase responsible for the ubiquitination not yet identified at this point\", \"Whether NKA interaction is direct or scaffolded by raft domains unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A presynaptic macromolecular complex was uncovered: GlyT2 associates with PMCA2/3 and NCX1 in lipid rafts, and their Ca²⁺-extrusion activities are required for GlyT2 transport — likely by buffering the local Na⁺ increases generated by GlyT2's electrogenic 3Na⁺:1Cl⁻:1glycine cotransport cycle; separately, GSK3β was shown to stimulate GlyT2 surface expression.\",\n      \"evidence\": \"Co-IP, lipid raft fractionation, pharmacological PMCA/NCX inhibition in synaptosomes; GSK3β co-expression and inhibitor studies in neurons and oocytes\",\n      \"pmids\": [\"25315779\", \"25301276\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation of GlyT2 by GSK3β not demonstrated\", \"Stoichiometry of the GlyT2-NKA-PMCA-NCX complex not determined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"P2X purinergic receptor activation (P2X2, P2X3, P2X2/3) was identified as an up-regulatory input that increases GlyT2 surface expression and transport by reducing transporter ubiquitination, establishing a purinergic signaling link to glycinergic transmission control.\",\n      \"evidence\": \"P2X agonists, siRNA knockdown of receptor subtypes, ubiquitination assays, surface biotinylation, electrophysiology in primary neurons\",\n      \"pmids\": [\"28734869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling pathway from P2X activation to reduced GlyT2 ubiquitination not identified\", \"In vivo relevance of purinergic modulation of GlyT2 not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The E3 ubiquitin ligases responsible for GlyT2 ubiquitination were identified as LNX1 and LNX2, acting via their RING-finger domains on the same C-terminal lysine cluster; genetic deletion of LNX2 in spinal cord neurons increases GlyT2 expression, and LNX2 is required for PKC-mediated GlyT2 down-regulation, completing the ubiquitin-dependent regulatory circuit.\",\n      \"evidence\": \"Unbiased interaction screen, RING-domain mutagenesis, LNX2 knockout spinal cord neurons, transport assays\",\n      \"pmids\": [\"31628376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LNX1 and LNX2 are redundant or have distinct roles in vivo not resolved\", \"Upstream signals activating LNX1/2 toward GlyT2 beyond PKC not mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution structure of GlyT2 has been determined, leaving the precise arrangement of its ion-binding sites, glycine coordination, and the structural basis for its inability to operate in reverse mode unresolved; the in vivo consequences of modulatory inputs (P2X, BDNF, GSK3β) on glycinergic circuit function remain untested.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of GlyT2\", \"In vivo impact of post-translational regulatory circuits on glycinergic neurotransmission not demonstrated\", \"Role of GlyT2 in pain processing and other non-startle phenotypes not mechanistically dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [2, 6, 7, 8, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 3, 4, 5, 13, 14, 16, 20]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [5, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [1, 7, 8]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [2, 6, 9]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5, 14, 15, 17]}\n    ],\n    \"complexes\": [\n      \"GlyT2-NKA-PMCA-NCX presynaptic raft complex\"\n    ],\n    \"partners\": [\n      \"STX1A\",\n      \"LNX1\",\n      \"LNX2\",\n      \"SDCBP\",\n      \"ATP1A1\",\n      \"ATP2B2\",\n      \"ATP2B3\",\n      \"SLC8A1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SLC6A5 (GlyT2) is a presynaptic Na⁺/Cl⁻-dependent glycine transporter that concentrates glycine into glycinergic nerve terminals to sustain vesicular glycine loading and inhibitory neurotransmission in the spinal cord, brainstem, and cerebellum [PMID:7861131, PMID:9387864, PMID:17554001, PMID:18815261]. Transport depends on residues in transmembrane domains that coordinate Na⁺ and glycine binding (e.g., Tyr-289, Asp-471), N-glycosylation for ER-to-surface trafficking assisted by calnexin, and association with cholesterol-rich membrane rafts [PMID:10788509, PMID:22132725, PMID:11036075, PMID:23650557, PMID:18266927]. Surface expression is dynamically regulated by syntaxin 1A–mediated exocytic delivery, clathrin-dependent endocytosis driven by PKC-stimulated ubiquitination of a C-terminal lysine cluster (K751/K773/K787/K791) by E3 ligases LNX1/LNX2, and recycling through Rab11-positive endosomes, with Na⁺/K⁺-ATPase, PMCA, and NCX1 forming a functional raft-resident complex that sustains local ion homeostasis required for transport [PMID:11278707, PMID:21910806, PMID:23484054, PMID:31628376, PMID:19374720, PMID:23986260, PMID:25315779]. Loss-of-function mutations in SLC6A5 cause hereditary hyperekplexia (startle disease) in humans by impairing glycine uptake and presynaptic glycine recycling [PMID:16751771, PMID:22700964].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing where GlyT2 acts: immunolocalization to axonal varicosities in spinal cord, brainstem, and cerebellum—matching glycine receptor distribution—positioned GlyT2 as the presynaptic glycine reuptake system at inhibitory synapses.\",\n      \"evidence\": \"Immunocytochemistry with antibodies against recombinant GlyT2 domains in mouse brain\",\n      \"pmids\": [\"7861131\", \"7582108\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subcellular resolution to synaptic boutons not achieved\", \"Glial expression possibility not addressed\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstrating GlyT2 is the glycine concentrator: functional uptake assays showed GlyT2 expression directly correlates with intracellular glycine accumulation, establishing its role in loading glycinergic terminals with substrate.\",\n      \"evidence\": \"Double-immunofluorescence and glycine uptake in spinal neurons and GlyT2-transfected COS cells\",\n      \"pmids\": [\"9387864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coupling to vesicular filling not yet demonstrated\", \"Stoichiometry of Na⁺/Cl⁻/glycine cotransport not established\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Molecular characterization of human GlyT2 revealed a 797-residue transporter with Km ~108 µM for glycine, sarcosine-insensitive, mapping to 11p15.1-15.2, and alternative splicing yielding functionally distinct isoforms (uptake vs. exchange modes).\",\n      \"evidence\": \"Expression cloning in CHO cells with kinetic analysis; RACE analysis and transport assays of splice variants in COS cells\",\n      \"pmids\": [\"9845349\", \"9509996\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of the exchange-mode isoform (GLYT2b) unclear\", \"3 Na⁺ stoichiometry not yet formally demonstrated\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Structure–function dissection identified key determinants of transport: Tyr-289 in TM III is essential for ion coupling and substrate permeation, four N-glycosylation sites (N345/N355/N360/N366) are required for surface delivery and activity, and syntaxin 1A interaction regulates membrane expression.\",\n      \"evidence\": \"Site-directed mutagenesis with electrophysiology and uptake assays in HEK-293 and COS cells; co-immunoprecipitation of syntaxin 1A in COS cells and rat brain with functional consequence\",\n      \"pmids\": [\"10788509\", \"11036075\", \"10722844\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structural basis for ion/glycine coordination not available\", \"Whether syntaxin 1A interaction is direct or scaffolded unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolving how GlyT2 reaches the surface: syntaxin 1A mediates SNARE-dependent exocytic delivery of GlyT2 from intracellular vesicles to the plasma membrane, as BoNT/C blockade prevents surface insertion without affecting internalization, and immunogold EM placed GlyT2 on small synaptic-like vesicles.\",\n      \"evidence\": \"Synaptosome stimulation, BoNT/C neurotoxin treatment, immunogold electron microscopy in brain-derived preparations\",\n      \"pmids\": [\"11278707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the vesicle population (recycling vs. biosynthetic) carrying GlyT2 not resolved\", \"Whether SNARE-dependent insertion is activity-regulated in vivo unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"SLC6A5 was established as a human disease gene: multiple loss-of-function mutations cause hereditary hyperekplexia by impairing glycine uptake and/or subcellular localization, linking presynaptic glycine recycling failure to startle disease.\",\n      \"evidence\": \"Sequencing of hyperekplexia patient cohorts with heterologous functional validation of missense, nonsense, and frameshift mutations\",\n      \"pmids\": [\"16751771\", \"16884688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genotype–phenotype severity correlations incomplete\", \"Whether partial loss-of-function alleles cause milder phenotypes not established\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"The physiological rationale for GlyT2 was clarified: GlyT2's inability to operate in reverse (unlike GlyT1) enables it to maintain cytosolic glycine at concentrations sufficient for vesicular loading by VIAAT, directly coupling plasma membrane uptake to quantal glycinergic release.\",\n      \"evidence\": \"Reconstitution in neuroendocrine cells co-expressing VIAAT and plasmalemmal transporters with double-sniffer patch clamp\",\n      \"pmids\": [\"17554001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for the irreversibility of GlyT2 transport not known\", \"Whether VIAAT and GlyT2 physically interact not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"GlyT2-mediated glycine refilling was shown to be rate-limiting for sustained glycinergic transmission: pharmacological GlyT2 blockade in spinal neurons caused a switch from glycinergic to GABAergic phenotype, revealing two kinetically distinct vesicle pools with different refilling requirements; membrane raft association was demonstrated as essential for transport activity.\",\n      \"evidence\": \"Electrophysiology in GlyT2-eGFP transgenic neurons with GlyT2 inhibitors; detergent-resistant membrane fractionation and cholesterol depletion in synaptosomes\",\n      \"pmids\": [\"18815261\", \"18266927\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of raft-dependent transport enhancement unknown\", \"Whether glycine-to-GABA switch occurs in vivo not shown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"PKC was identified as a central regulator of GlyT2 surface levels: PKC activation promotes GlyT2 internalization and redistribution from raft to non-raft domains, with K422 identified as a regulatory determinant; this introduced ubiquitination-dependent trafficking control.\",\n      \"evidence\": \"PMA treatment with surface biotinylation, raft fractionation, and K422E mutagenesis in HEK cells and brainstem neurons\",\n      \"pmids\": [\"18341477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K422 is directly ubiquitinated or indirectly involved not resolved\", \"In vivo PKC activating signal identity unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"GlyT2 recycling was mapped to Rab11-positive endosomes: dominant-negative Rab11 impaired both GlyT2 trafficking and glycine transport, establishing the slow recycling pathway as the intracellular itinerary for internalized transporter.\",\n      \"evidence\": \"Biochemical fractionation, immunogold EM, dominant-negative Rab11 co-expression with transport assay in rat brainstem\",\n      \"pmids\": [\"19374720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals directing GlyT2 into Rab11 compartments not identified\", \"Whether Rab4-dependent fast recycling also contributes not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The endocytic route was defined: GlyT2 internalization is primarily clathrin-mediated, with constitutive endocytosis occurring from raft domains and PKC-stimulated endocytosis following redistribution to non-raft membrane.\",\n      \"evidence\": \"Clathrin pathway inhibitors, dominant-negative mutants, siRNA knockdown with internalization assays in HEK cells and neurons\",\n      \"pmids\": [\"21910806\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor proteins linking GlyT2 to clathrin not identified\", \"Relative contribution of ubiquitin-dependent vs. -independent endocytosis not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Expanded genotype–function mapping revealed diverse pathogenic mechanisms in hyperekplexia: 20 SLC6A5 variants disrupted Cl⁻ binding, Na⁺ affinity, cation-π interactions, or extracellular loop conformation; the dominant Y705C mutation in TM11 impaired secretory pathway maturation via aberrant disulfide interactions.\",\n      \"evidence\": \"Large patient cohort sequencing with functional validation of 16 mutations; electrophysiology, cysteine labeling, and secretory pathway analysis for Y705C\",\n      \"pmids\": [\"22700964\", \"22753417\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure to map all mutation sites\", \"Therapeutic rescue strategies for trafficking-defective mutants not explored\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The GlyT2 interactome was expanded: Na⁺/K⁺-ATPase was identified as a direct partner that preferentially associates with raft-resident active GlyT2 and regulates its endocytosis across species; C-terminal ubiquitination at K751/K773/K787/K791 was shown to drive constitutive endocytosis and degradation; calnexin was identified as an ER chaperone for GlyT2 biogenesis via both glycan-dependent and lectin-independent modes.\",\n      \"evidence\": \"Mass spectrometry interactomics with reciprocal co-IP, ouabain treatment in neurons/zebrafish/rats; systematic lysine mutagenesis with ubiquitination and turnover assays; CNX knockdown/overexpression with transport and surface expression assays\",\n      \"pmids\": [\"23986260\", \"23484054\", \"23650557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding interface between NKA and GlyT2 not mapped\", \"Whether calnexin interaction is specific to GlyT2 among SLC6 family unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A raft-resident functional complex of GlyT2 with PMCA2/3 and NCX1 was identified, suggesting coordinated local Na⁺/Ca²⁺ handling at glycinergic terminals; GSK3β was shown to differentially stimulate GlyT2 activity while inhibiting GlyT1.\",\n      \"evidence\": \"Co-immunoprecipitation and pharmacological inhibition of PMCA/NCX with transport assays; co-expression in COS-7 and oocytes with phosphorylation and transport readouts\",\n      \"pmids\": [\"25315779\", \"25301276\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PMCA/NCX/GlyT2 complex exists in vivo at synapses not confirmed by super-resolution imaging\", \"GSK3β phosphorylation site(s) on GlyT2 not mapped\", \"Functional significance of GSK3β regulation in vivo unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The E3 ubiquitin ligases responsible for GlyT2 ubiquitination were identified: LNX1 and LNX2 ubiquitinate the same C-terminal lysine cluster via their RING domains; genetic deletion of LNX2 in spinal neurons increased GlyT2 expression, and LNX2 is required for PKC-mediated transport regulation.\",\n      \"evidence\": \"Unbiased E3 ligase screening, co-IP, RING-domain mutagenesis, LNX2 knockout neurons with PKC activation\",\n      \"pmids\": [\"31628376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LNX1 and LNX2 are redundant or specialized in vivo not determined\", \"Upstream signals activating LNX2 beyond PKC not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structure of GlyT2 in multiple conformational states, the structural basis for its inability to operate in reverse, whether GlyT2 and VIAAT are physically coupled for vesicular glycine refilling, and therapeutic strategies to rescue trafficking-defective hyperekplexia mutants.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental GlyT2 structure available\", \"Physical coupling between GlyT2 and VIAAT not tested\", \"Pharmacological chaperone rescue of misfolded mutants not explored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 2, 4, 12, 15]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5, 8, 16, 17, 19]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [8, 18]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [18, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 1, 12, 15]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2, 4, 12, 15]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [5, 8, 18, 19, 25]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [8, 19, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"STX1A\",\n      \"ATP1A1\",\n      \"ATP2B2\",\n      \"ATP2B3\",\n      \"SLC8A1\",\n      \"LNX1\",\n      \"LNX2\",\n      \"CANX\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}