{"gene":"GRID1","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2021,"finding":"GluD1 functions as a trans-synaptic signal transduction device rather than a classical ion channel: presynaptic neurexin-1–cerebellin-2 and neurexin-3–cerebellin-2 complexes bind postsynaptic GluD1 and differentially regulate NMDA and AMPA receptor levels through conserved cytoplasmic C-terminal motifs (5–13 residues). Minimal GluD1 constructs containing only the N-terminal cerebellin-binding domain and C-terminal cytoplasmic domain joined by an unrelated transmembrane region fully recapitulate NMDA and AMPA receptor regulation, demonstrating the mechanism bypasses ionotropic architecture.","method":"Chimeric/minimal-construct expression, electrophysiology, biochemical assays in hippocampal synapses; loss-of-function and domain-swap experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (minimal constructs, mutagenesis, electrophysiology) in a single rigorous study","pmids":["34135511"],"is_preprint":false},{"year":2023,"finding":"GluD1 binds GABA (a previously unknown ligand for any iGluR family member) through its ligand-binding domain, and GluD1 activation produces long-lasting enhancement of GABAergic synaptic currents in adult mouse hippocampus via a non-ionotropic mechanism that requires trans-synaptic anchoring.","method":"Biochemical binding assays, X-ray/structural analysis of LBD, patch-clamp electrophysiology in hippocampal slices, loss-of-function experiments","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — biochemical, structural, and functional (electrophysiological) validation combined in one study","pmids":["38060673"],"is_preprint":false},{"year":2020,"finding":"Cryo-EM structures of rat GluD1 reveal a non-swapped architecture at the ATD–LBD interface, in contrast to all other iGluR families where dimer partners are swapped between layers, establishing unique principles of GluD receptor assembly.","method":"Cryo-EM structural determination of GluD1 complexed with calcium and 7-chlorokynurenic acid","journal":"Nature Structural & Molecular Biology","confidence":"High","confidence_rationale":"Tier 1 — direct structural determination","pmids":["31925409"],"is_preprint":false},{"year":2017,"finding":"GluD1 couples to metabotropic glutamate receptor mGlu1 to generate slow depolarizing currents in midbrain dopamine neurons; this current is abolished by a dominant-negative dead-pore GluD1 mutant and is absent in GRID1 knockout mice, demonstrating GluD1 is required for mGlu1-dependent slow synaptic transmission and burst firing of dopamine neurons.","method":"HEK cell co-expression electrophysiology, dominant-negative mutant expression in brain slices, GRID1 KO mice, in vivo dopamine neuron recordings","journal":"Molecular Psychiatry","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution in HEK cells, dominant-negative, KO, and in vivo recordings across multiple orthogonal approaches","pmids":["28696429"],"is_preprint":false},{"year":2014,"finding":"In the cerebellar cortex, GluD1 is expressed in molecular layer interneurons and concentrated at parallel fiber (PF) synapses on interneuron somata. In GluD1 knockout mice, the density of PF synapses on interneuron somata is significantly reduced and interneuron number/size is diminished, demonstrating GluD1 regulates PF–interneuron synapse connectivity and interneuron differentiation/survival.","method":"Histochemical localization, GluD1 knockout mouse analysis, quantitative synapse and cell-count assays","journal":"Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific cellular phenotypes, replicated across multiple quantitative readouts","pmids":["24872547"],"is_preprint":false},{"year":2011,"finding":"GluD1 expressed in non-neuronal HEK cells induces presynaptic differentiation of cerebellar granule neurons via its N-terminal domain; in the presence of Cbln1, GluD1 additionally induces both glutamatergic and GABAergic presynaptic differentiation in hippocampal co-cultures, and rescues synapse formation defects in GluD2-knockout Purkinje neurons.","method":"HEK cell–neuron co-culture assay, exogenous Cbln1 addition, GluD2-KO rescue experiment","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based reconstitution with multiple neuronal partners and KO rescue, single lab","pmids":["22138648"],"is_preprint":false},{"year":2015,"finding":"GluD1 knockout mice exhibit higher dendritic spine number, greater excitatory neurotransmission, increased synapse number in mPFC and CA1 hippocampus, and abnormal LIMK1–cofilin signaling with a lower GluN2A/GluN2B ratio, establishing GluD1 as required for normal spine development and GluN2B-to-GluN2A NMDAR subunit switch.","method":"GluD1 KO mouse analysis, dendritic spine counting, electrophysiology, biochemical pathway analysis (LIMK1–cofilin), GluN2B inhibitor rescue","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 2 — KO with multiple orthogonal cellular phenotype readouts and pharmacological rescue","pmids":["25721396"],"is_preprint":false},{"year":2019,"finding":"GluD1 synaptic trafficking depends on its C-terminal domain but not on the PDZ-binding motif; phosphorylation of threonine T923 in the C-terminal domain is critical for synaptic (but not surface) localization of GluD1, revealing a unique trafficking mechanism distinct from AMPARs.","method":"Chimeric GluD1/GluK1 constructs, mutagenesis of C-terminal domain and PDZ motif, electrophysiology and imaging in neurons","journal":"Molecular Psychiatry","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with functional trafficking assays, multiple constructs tested","pmids":["30824864"],"is_preprint":false},{"year":2022,"finding":"X-ray crystallography of the GluD1 ligand-binding domain (LBD) reveals its apo structure at 2.57 Å; D-serine binds GluD1-LBD with Kd ~160 µM (approximately 5-fold lower affinity than GluD2); Glu822 is identified as a critical determinant of receptor activation in GluD1 A654T; molecular dynamics indicate GluD1 apo structure is less flexible than GluD2 and Pro725 affects LBD interlobe closure.","method":"X-ray crystallography, isothermal titration calorimetry, electrophysiology in Xenopus oocytes, molecular dynamics simulation","journal":"The FEBS Journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus ITC binding measurements and mutagenesis","pmids":["36128700"],"is_preprint":false},{"year":2019,"finding":"GluD1 and GluD2 form a coimmunoprecipitable protein complex in HEK293T cells and in native cerebral cortex and hippocampus; both receptors are co-expressed on the same glutamatergic synapses in the retrosplenial cortex, as shown by SDS-digested freeze-fracture replica labeling.","method":"Co-immunoprecipitation in HEK293T cells and brain tissue, SDS-digested freeze-fracture replica labeling, quantitative immunoblotting with chimeric protein standards","journal":"Journal of Comparative Neurology","confidence":"Medium","confidence_rationale":"Tier 2–3 — reciprocal co-IP in cells and brain plus ultrastructural co-localization, single lab","pmids":["31625608"],"is_preprint":false},{"year":2024,"finding":"Homozygous missense GRID1 variants (p.Thr752Met and p.Arg161His) cause intellectual disability and spastic paraplegia; mechanistically these mutations alter hinge/LBD function, impair mGlu1/5 receptor signaling via Ca2+ and ERK pathways, and reduce dendrite complexity and excitatory synapse density when expressed in neurons, without disrupting GluD1 trafficking or cerebellin binding.","method":"Molecular modeling, electrophysiological recordings, Ca2+ imaging, ERK pathway assays, neuronal morphology analysis in dissociated and organotypic cultures","journal":"Molecular Psychiatry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal functional assays (electrophysiology, signaling, morphology) combined with structural modeling","pmids":["38418578"],"is_preprint":false},{"year":2024,"finding":"A GRID1 variant in the distal amino-terminal domain (predicted to contact Cbln2/Cbln4) disrupts GluD1–Cbln2 complex formation in biochemical assays; other rare M3 domain variants (including GluD1-A650T analogous to the GluD2 lurcher mutation) create constitutively active channels; pentamidine potently inhibits constitutive currents of GluD receptor variants.","method":"Electrophysiological assays, biochemical complex formation assays, pharmacological inhibition with pentamidine","journal":"Human Molecular Genetics","confidence":"Medium","confidence_rationale":"Tier 1–2 — direct electrophysiology and biochemical binding assays, single study","pmids":["37944084"],"is_preprint":false},{"year":2025,"finding":"D-serine binds GluD1's ligand-binding domain and concentration-dependently inhibits the interaction between Cbln1 and GluD1 (IC50 ~300 µM) in a cell-binding assay; pre-treatment with D-serine blocks the pro-synaptic and nociceptive effects of recombinant Cbln1 in central amygdala slices and in vivo.","method":"In vitro cell-binding assay, ex vivo slice electrophysiology, in vivo behavioral (nociception) assays","journal":"Cellular and Molecular Life Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical binding IC50 plus electrophysiology and behavioral rescue, single lab","pmids":["39890638"],"is_preprint":false},{"year":2023,"finding":"GluD1 carries a G-protein-independent tonic cation current in dorsal raphe nucleus neurons regulated by physiological levels of external calcium; block of GluD1 channels hyperpolarizes the membrane by ~7 mV, reducing neuronal excitability, and this tonic current is unaffected by D-serine or glycine supplementation.","method":"Voltage-clamp and current-clamp electrophysiology from adult mouse brain slices, pharmacological block of GluD1","journal":"EMBO Reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean electrophysiological characterization with pharmacological tools, single lab","pmids":["37154294"],"is_preprint":false},{"year":2025,"finding":"GRID1/GluD1 directly facilitates autophagic flux in central amygdala neurons via interaction with autophagy mediators nGOPC/nPIST, BECN1, and LAMP1; a GluD1 C-terminal-derived peptide (Tat-HRSPN) promotes autophagy and reduces AMPA receptor expression; GRID1/CBLN1 downregulation during inflammatory and neuropathic pain impairs autophagic flux and increases AMPAR expression in CeA.","method":"Co-immunoprecipitation (GluD1 with BECN1/LAMP1/nGOPC), peptide (Tat-HRSPN) in vivo infusion, autophagy flux assays, electrophysiology in CeA slices, pain behavioral models","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP plus peptide functional rescue and electrophysiology, single lab","pmids":["41147487"],"is_preprint":false},{"year":2020,"finding":"In both mouse and monkey striatum, GluD1 immunoreactivity is localized by electron microscopy predominantly to dendritic shafts and glial processes, with synaptic and perisynaptic labeling at glutamatergic axo-dendritic and axo-spinous synapses; confocal microscopy shows preferential colocalization with thalamic (over cortical) terminals.","method":"Immunoelectron microscopy (including immunogold), confocal microscopy, ultrastructural subcellular localization","journal":"Journal of Comparative Neurology","confidence":"Medium","confidence_rationale":"Tier 2 — direct ultrastructural localization with multiple methods across two species","pmids":["33084025"],"is_preprint":false},{"year":2026,"finding":"Cryo-EM structures of human GluD1 and single-channel bilayer recordings demonstrate that GABA or D-serine binding to the LBD enables cation influx through the hGluD1 ion channel; hGluD1 has a non-swapped architecture containing conserved iGluR moieties that enable ligand-gating.","method":"Cryo-EM structure determination, single-channel bilayer electrophysiology, ligand-binding functional assays","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1 — cryo-EM structure plus single-channel recordings; preprint, not yet peer-reviewed","pmids":["41993446"],"is_preprint":true},{"year":2024,"finding":"Grid1 knockdown in the hypothalamus decreases Grid1 and Rfrp-3 mRNA, increases Gnrh mRNA, advances vaginal opening (earlier puberty onset) and decreases progesterone levels in female rats, placing GluD1 in a pathway that regulates GnRH/RFRP-3 signaling and puberty onset.","method":"Lentiviral Grid1 knockdown in hypothalamic neurons, intracerebroventricular injection, RT-PCR gene expression, hormone ELISA, histology","journal":"Journal of Veterinary Medical Science","confidence":"Low","confidence_rationale":"Tier 3 — KD phenotype with gene expression readout, pathway placement indirect, single lab","pmids":["38479882"],"is_preprint":false}],"current_model":"GluD1 (encoded by GRID1) is a multifunctional synaptic organizer with a non-swapped tetrameric architecture; it binds D-serine and GABA (not glutamate) at its ligand-binding domain, assembles trans-synaptic neurexin–cerebellin–GluD1 complexes through its N-terminal domain, and converts these extracellular signals into postsynaptic regulation of NMDA and AMPA receptor levels via conserved C-terminal cytoplasmic motifs in a non-ionotropic manner, while also coupling to mGlu1 to mediate slow depolarizing currents in dopamine neurons, facilitating autophagic flux through interactions with BECN1 and LAMP1, and promoting inhibitory synaptic plasticity through GABA binding—collectively establishing GluD1 as a trans-synaptic signaling scaffold that regulates both excitatory and inhibitory circuit development and function."},"narrative":{"teleology":[{"year":2011,"claim":"Establishing GluD1 as a synaptogenic molecule: it was unknown whether GluD1, like GluD2, could organize presynaptic differentiation; co-culture experiments showed GluD1's N-terminal domain induces both glutamatergic and GABAergic presynaptic differentiation in the presence of Cbln1, establishing GluD1 as a bona fide trans-synaptic organizer.","evidence":"HEK cell–neuron co-culture with exogenous Cbln1, GluD2-KO rescue","pmids":["22138648"],"confidence":"Medium","gaps":["Single lab; no in vivo confirmation of GluD1 synaptogenic role at this stage","Endogenous cerebellin partner for GluD1 not identified","GABAergic versus glutamatergic synaptogenic specificity mechanism unclear"]},{"year":2014,"claim":"Demonstrating GluD1's requirement for synapse formation and cell survival in vivo: loss of GluD1 reduced parallel fiber–interneuron synapse density and interneuron number in cerebellum, establishing a non-redundant in vivo role for GluD1 in circuit connectivity and neuronal maintenance.","evidence":"GluD1 KO mouse, quantitative synapse and cell-count assays in cerebellar cortex","pmids":["24872547"],"confidence":"High","gaps":["Molecular mechanism linking GluD1 loss to interneuron death not defined","Whether GluD1 acts cell-autonomously in interneurons not tested"]},{"year":2015,"claim":"Revealing GluD1 as a regulator of spine pruning and NMDAR subunit maturation: GluD1 KO mice showed excess spines, elevated excitatory transmission, disrupted LIMK1–cofilin signaling, and failure of the GluN2B-to-GluN2A switch, linking GluD1 to cytoskeletal remodeling and glutamate receptor subunit composition.","evidence":"GluD1 KO mouse, spine counting, electrophysiology, biochemical pathway analysis, GluN2B inhibitor rescue in mPFC and hippocampus","pmids":["25721396"],"confidence":"High","gaps":["Direct biochemical link between GluD1 and LIMK1–cofilin pathway not established","Whether spine phenotype is developmental or maintenance-related unclear"]},{"year":2017,"claim":"Identifying a metabotropic coupling mode: GluD1 was shown to couple to mGlu1 to produce slow depolarizing currents in dopamine neurons, revealing that GluD1 can function as an effector ion channel downstream of a metabotropic receptor, a novel signaling paradigm for iGluR family members.","evidence":"HEK cell co-expression, dominant-negative GluD1 mutant in slices, GRID1 KO mice, in vivo dopamine neuron recordings","pmids":["28696429"],"confidence":"High","gaps":["Molecular mechanism of mGlu1–GluD1 coupling (direct interaction vs. intermediary) not resolved","Whether this coupling occurs outside midbrain dopamine neurons unknown"]},{"year":2019,"claim":"Defining GluD1 synaptic trafficking rules: phosphorylation of C-terminal T923 was shown to be critical for synaptic (but not surface) localization, independent of the PDZ-binding motif, revealing a trafficking mechanism distinct from AMPARs and establishing the C-terminal domain as a regulatory hub.","evidence":"Chimeric GluD1/GluK1 constructs, site-directed mutagenesis, neuronal imaging and electrophysiology","pmids":["30824864"],"confidence":"High","gaps":["Kinase responsible for T923 phosphorylation not identified","Activity-dependent regulation of this phosphorylation not tested"]},{"year":2019,"claim":"Demonstrating GluD1–GluD2 hetero-association: co-immunoprecipitation from brain tissue and ultrastructural co-localization showed GluD1 and GluD2 form complexes at the same glutamatergic synapses, suggesting functional heteromeric assembly.","evidence":"Co-IP in HEK293T cells and brain lysates, SDS-digested freeze-fracture replica labeling in retrosplenial cortex","pmids":["31625608"],"confidence":"Medium","gaps":["Stoichiometry and functional consequence of GluD1/GluD2 heteromers not determined","Whether heteromers have distinct signaling properties is untested"]},{"year":2020,"claim":"Resolving GluD1 architecture: cryo-EM revealed a unique non-swapped tetrameric arrangement at the ATD–LBD interface, distinguishing GluD receptors from all other iGluR families and providing a structural basis for their distinct signaling properties.","evidence":"Cryo-EM of rat GluD1 complexed with calcium and 7-chlorokynurenic acid","pmids":["31925409"],"confidence":"High","gaps":["Full-length structure with transmembrane domain not resolved at this stage","Functional consequence of non-swapped architecture for signaling not directly tested"]},{"year":2021,"claim":"Establishing GluD1 as a non-ionotropic trans-synaptic signal transduction device: minimal constructs containing only the NTD and CTD joined by an unrelated transmembrane domain fully recapitulated neurexin–cerebellin-dependent NMDAR and AMPAR regulation, proving the mechanism bypasses ionotropic gating entirely.","evidence":"Minimal/chimeric constructs, electrophysiology, domain-swap and loss-of-function experiments in hippocampal synapses","pmids":["34135511"],"confidence":"High","gaps":["Conformational change linking extracellular binding to cytoplasmic signaling not visualized","Identity of cytoplasmic effectors recruited by the C-terminal motifs not fully catalogued"]},{"year":2022,"claim":"Characterizing D-serine binding to GluD1-LBD: crystal structure and ITC revealed D-serine binds GluD1 with ~160 µM Kd (5-fold lower than GluD2), with Glu822 critical for activation and Pro725 affecting interlobe closure dynamics, establishing molecular determinants of GluD1 ligand recognition.","evidence":"X-ray crystallography at 2.57 Å, ITC, oocyte electrophysiology, molecular dynamics","pmids":["36128700"],"confidence":"High","gaps":["Physiological source and concentration of D-serine at GluD1-expressing synapses not established","Whether D-serine binding triggers non-ionotropic signaling or primarily modulates trans-synaptic interactions unclear"]},{"year":2023,"claim":"Discovering GABA as a GluD1 ligand: GABA binding to the LBD was demonstrated biochemically and structurally, and shown to produce long-lasting enhancement of GABAergic synaptic currents in hippocampus via a non-ionotropic, trans-synaptically anchored mechanism—making GluD1 the first iGluR family member with a GABA-binding function.","evidence":"Binding assays, structural analysis of LBD, patch-clamp in hippocampal slices, loss-of-function","pmids":["38060673"],"confidence":"High","gaps":["Whether GABA binding and D-serine binding are competitive at the same site not fully resolved","Downstream signaling cascade from GABA-bound GluD1 to GABAergic potentiation not identified"]},{"year":2023,"claim":"Identifying a tonic cation conductance: GluD1 carries a G-protein-independent, calcium-regulated tonic current in dorsal raphe serotonergic neurons that sets resting membrane potential, expanding GluD1's repertoire to include a constitutive ionotropic mode independent of classical ligand gating.","evidence":"Voltage-clamp and current-clamp in adult mouse brain slices, pharmacological GluD1 block","pmids":["37154294"],"confidence":"Medium","gaps":["Molecular mechanism of calcium-dependent regulation of this tonic current not defined","Whether this tonic current occurs in other GluD1-expressing neuron types untested"]},{"year":2024,"claim":"Linking GRID1 mutations to human disease: homozygous GRID1 missense variants were shown to cause intellectual disability and spastic paraplegia by impairing mGlu1/5 signaling and reducing dendritic complexity without disrupting trafficking or cerebellin binding, establishing GRID1 as a Mendelian disease gene.","evidence":"Patient variant modeling, electrophysiology, Ca²⁺ and ERK pathway assays, neuronal morphology in dissociated and organotypic cultures","pmids":["38418578"],"confidence":"High","gaps":["Genotype–phenotype correlation across additional GRID1 variants not yet established","Whether disease mechanism is primarily mGlu1/5-dependent or involves trans-synaptic signaling impairment not separated"]},{"year":2024,"claim":"Characterizing disease-associated channel variants: an ATD variant disrupted GluD1–Cbln2 complex formation while M3 domain variants created constitutively active channels, and pentamidine was identified as an inhibitor of pathogenic constitutive currents, beginning to define pharmacological rescue strategies.","evidence":"Electrophysiology, biochemical binding assays, pentamidine pharmacology","pmids":["37944084"],"confidence":"Medium","gaps":["In vivo efficacy of pentamidine not tested","Whether constitutive channel activity is pathogenic in patient neurons not confirmed"]},{"year":2025,"claim":"Revealing D-serine as a competitive modulator of trans-synaptic assembly: D-serine concentration-dependently inhibits Cbln1–GluD1 interaction (IC50 ~300 µM) and blocks Cbln1-dependent synaptic and behavioral effects, establishing a ligand-dependent switch between trans-synaptic scaffolding and ligand-gated signaling modes.","evidence":"Cell-binding assay, ex vivo central amygdala slice electrophysiology, in vivo nociception assays","pmids":["39890638"],"confidence":"Medium","gaps":["Physiological context where D-serine reaches effective concentrations at GluD1 synapses not demonstrated","Whether GABA similarly modulates Cbln1 binding not tested"]},{"year":2025,"claim":"Discovering a non-synaptic function in autophagy: GluD1 was found to interact with BECN1 and LAMP1 via its C-terminal domain (through nGOPC/nPIST) to promote autophagic flux; a GluD1-derived peptide rescued autophagy impairment and AMPAR upregulation in pain models, linking GluD1 to protein homeostasis beyond synaptic signaling.","evidence":"Co-IP of GluD1 with BECN1/LAMP1/nGOPC, Tat-HRSPN peptide in vivo, autophagy flux assays, CeA electrophysiology, pain behavioral models","pmids":["41147487"],"confidence":"Medium","gaps":["Whether autophagy function is constitutive or activity-dependent not established","Structural basis of GluD1–BECN1 interaction not defined","Generalizability beyond central amygdala not tested"]},{"year":null,"claim":"Key open questions remain: the conformational mechanism linking extracellular ligand/cerebellin binding to cytoplasmic effector recruitment; whether GluD1 heteromers with GluD2 have distinct signaling properties; the physiological conditions under which ionotropic versus non-ionotropic modes predominate; and the full catalogue of C-terminal effectors mediating NMDAR/AMPAR regulation and autophagic signaling.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of full signaling complex (neurexin–Cbln–GluD1 with cytoplasmic partners)","Ionotropic vs. non-ionotropic mode selection mechanism unknown","Complete cytoplasmic interactome not mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[3,13]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,6,14]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,7,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7,14]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,1,3,4,6,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,10]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,6]}],"complexes":["neurexin–cerebellin–GluD1 trans-synaptic complex","GluD1–GluD2 heteromeric complex"],"partners":["CBLN1","CBLN2","NRXN1","NRXN3","GRID2","GRM1","BECN1","GOPC"],"other_free_text":[]},"mechanistic_narrative":"GluD1 (encoded by GRID1) is an ionotropic glutamate receptor family member that functions primarily as a trans-synaptic signaling scaffold, organizing both excitatory and inhibitory synapse development and plasticity through non-ionotropic mechanisms. Its N-terminal domain binds presynaptic neurexin–cerebellin complexes to regulate postsynaptic NMDA and AMPA receptor levels via conserved C-terminal cytoplasmic motifs, with minimal constructs lacking ionotropic architecture fully recapitulating this signaling [PMID:34135511]; its ligand-binding domain binds D-serine and GABA—not glutamate—with GABA binding producing long-lasting enhancement of GABAergic synaptic currents [PMID:38060673, PMID:36128700], and D-serine competitively inhibiting the Cbln1–GluD1 interaction [PMID:39890638]. GluD1 additionally couples to mGlu1 receptors to generate slow depolarizing currents in dopamine neurons [PMID:28696429], carries a tonic cation conductance in serotonergic neurons [PMID:37154294], facilitates autophagic flux through C-terminal interactions with BECN1 and LAMP1 [PMID:41147487], and is required for normal dendritic spine pruning and the developmental GluN2B-to-GluN2A NMDAR subunit switch [PMID:25721396]. Homozygous missense GRID1 variants (p.Thr752Met, p.Arg161His) cause intellectual disability and spastic paraplegia by impairing mGlu1/5 signaling and reducing dendrite complexity without disrupting GluD1 trafficking [PMID:38418578]."},"prefetch_data":{"uniprot":{"accession":"Q9ULK0","full_name":"Glutamate receptor ionotropic, delta-1","aliases":[],"length_aa":1009,"mass_kda":112.1,"function":"Member of the ionotropic glutamate receptor family, which plays a crucial role in synaptic organization and signal transduction in the central nervous system. Although it shares structural features with ionotropic glutamate receptors, does not bind glutamate as a primary ligand (PubMed:38060673). Instead, forms trans-synaptic adhesion complexes with presynaptic neurexins and cerebellins, regulating NMDA and AMPA receptor activity and influencing synaptic plasticity through signal transduction (By similarity). In the presence of neurexins and cerebellins, forms cation-selective channels that are proposed to be gated by glycine and D-serine (By similarity). However, recent research disputes this ligand-gated cation channel activity (PubMed:39052831). Cation-selective ion channel can be triggered by GRM1 in dopaminergic neurons (By similarity). Also acts as a receptor for GABA, modulating inhibitory synaptic plasticity through non-ionotropic mechanisms (PubMed:38060673)","subcellular_location":"Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9ULK0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GRID1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GRID1","total_profiled":1310},"omim":[{"mim_id":"615029","title":"PRECEREBELLIN 4; CBLN4","url":"https://www.omim.org/entry/615029"},{"mim_id":"612242","title":"CHROMOSOME 10q22.3-q23.2 DELETION SYNDROME","url":"https://www.omim.org/entry/612242"},{"mim_id":"610659","title":"GLUTAMATE RECEPTOR, IONOTROPIC, DELTA 1; GRID1","url":"https://www.omim.org/entry/610659"},{"mim_id":"600433","title":"PRECEREBELLIN 2; CBLN2","url":"https://www.omim.org/entry/600433"},{"mim_id":"600432","title":"PRECEREBELLIN 1; CBLN1","url":"https://www.omim.org/entry/600432"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in 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pharmacology and multi-omics reveals GLUD1-mediated α-KG/Glu conversion in regulating amino acid metabolism: a mechanism of Dangua Fang against type 2 diabetes mellitus.","date":"2026","source":"Journal of ethnopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41529805","citation_count":0,"is_preprint":false},{"pmid":"41876450","id":"PMC_41876450","title":"AKT1 phosphorylates PRMT7 to promote GLUD1 methylation and gastric cancer progression.","date":"2026","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41876450","citation_count":0,"is_preprint":false},{"pmid":"20931523","id":"PMC_20931523","title":"[Mutation analysis of the GLUD1 gene in patients with glutamate dehydrogenase congenital hyperinsulinism].","date":"2010","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20931523","citation_count":0,"is_preprint":false},{"pmid":"41345253","id":"PMC_41345253","title":"GluD1 at the synaptic crossroads: from domain structure to circuit dysfunction.","date":"2025","source":"Acta pharmacologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/41345253","citation_count":0,"is_preprint":false},{"pmid":"41973845","id":"PMC_41973845","title":"Chronic Stress Promotes Oral Squamous Cell Carcinoma Progression via GLUD1-Mediated Metabolic Reprogramming.","date":"2026","source":"Carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/41973845","citation_count":0,"is_preprint":false},{"pmid":"41764762","id":"PMC_41764762","title":"METTL3-mediated GLUD1 m6A Modification Promotes Hydrogen Peroxide-induced Mitochondrial Dysfunction in Human Nucleus Pulposus Cells Via the Glutamate/α-KG Metabolic Axis.","date":"2026","source":"Journal of musculoskeletal & neuronal interactions","url":"https://pubmed.ncbi.nlm.nih.gov/41764762","citation_count":0,"is_preprint":false},{"pmid":"41895093","id":"PMC_41895093","title":"Echinacoside modulates PARP14-GLUD1 axis to mediate energy metabolism reprogramming and mitochondrial function in diminished ovarian reserve.","date":"2026","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41895093","citation_count":0,"is_preprint":false},{"pmid":"41144370","id":"PMC_41144370","title":"CBLN1 inhibits the inflammatory response by targeting GluD1 thereby alleviating resiniferatoxin-induced postherpetic neuralgia in mice.","date":"2026","source":"Journal of neuropathology and experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/41144370","citation_count":0,"is_preprint":false},{"pmid":"41993446","id":"PMC_41993446","title":"Molecular basis for ligand-gating of the human GluD1 receptor.","date":"2026","source":"bioRxiv : the preprint 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genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10429370","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.16.682741","title":"Kölliker-Fuse/parabrachial complex PACAP - glutamate pathway to the extended amygdala couples rapid autonomic and delayed endocrine responses to acute hypotension","date":"2025-10-16","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.16.682741","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.15.649028","title":"Glutamate delta-1 receptors regulate a novel tonic excitatory conductance in the mouse bed nucleus of the stria terminalis and influence neuronal function","date":"2025-04-19","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.15.649028","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.03.647119","title":"Multi-transmitter  <i>high-fidelity</i>  innervation of the forebrain extended amygdala by pontine PACAP-expressing neurons","date":"2025-04-04","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.03.647119","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.12.19.629410","title":"Genome-wide association analyses in dairy heifers highlight genes overlapping with mouse and human fertility and human health traits","date":"2024-12-21","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.19.629410","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":53303,"output_tokens":4506,"usd":0.11375},"stage2":{"model":"claude-opus-4-6","input_tokens":8016,"output_tokens":4231,"usd":0.218782},"total_usd":0.332532,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"GluD1 functions as a trans-synaptic signal transduction device rather than a classical ion channel: presynaptic neurexin-1–cerebellin-2 and neurexin-3–cerebellin-2 complexes bind postsynaptic GluD1 and differentially regulate NMDA and AMPA receptor levels through conserved cytoplasmic C-terminal motifs (5–13 residues). Minimal GluD1 constructs containing only the N-terminal cerebellin-binding domain and C-terminal cytoplasmic domain joined by an unrelated transmembrane region fully recapitulate NMDA and AMPA receptor regulation, demonstrating the mechanism bypasses ionotropic architecture.\",\n      \"method\": \"Chimeric/minimal-construct expression, electrophysiology, biochemical assays in hippocampal synapses; loss-of-function and domain-swap experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (minimal constructs, mutagenesis, electrophysiology) in a single rigorous study\",\n      \"pmids\": [\"34135511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GluD1 binds GABA (a previously unknown ligand for any iGluR family member) through its ligand-binding domain, and GluD1 activation produces long-lasting enhancement of GABAergic synaptic currents in adult mouse hippocampus via a non-ionotropic mechanism that requires trans-synaptic anchoring.\",\n      \"method\": \"Biochemical binding assays, X-ray/structural analysis of LBD, patch-clamp electrophysiology in hippocampal slices, loss-of-function experiments\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical, structural, and functional (electrophysiological) validation combined in one study\",\n      \"pmids\": [\"38060673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cryo-EM structures of rat GluD1 reveal a non-swapped architecture at the ATD–LBD interface, in contrast to all other iGluR families where dimer partners are swapped between layers, establishing unique principles of GluD receptor assembly.\",\n      \"method\": \"Cryo-EM structural determination of GluD1 complexed with calcium and 7-chlorokynurenic acid\",\n      \"journal\": \"Nature Structural & Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural determination\",\n      \"pmids\": [\"31925409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GluD1 couples to metabotropic glutamate receptor mGlu1 to generate slow depolarizing currents in midbrain dopamine neurons; this current is abolished by a dominant-negative dead-pore GluD1 mutant and is absent in GRID1 knockout mice, demonstrating GluD1 is required for mGlu1-dependent slow synaptic transmission and burst firing of dopamine neurons.\",\n      \"method\": \"HEK cell co-expression electrophysiology, dominant-negative mutant expression in brain slices, GRID1 KO mice, in vivo dopamine neuron recordings\",\n      \"journal\": \"Molecular Psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution in HEK cells, dominant-negative, KO, and in vivo recordings across multiple orthogonal approaches\",\n      \"pmids\": [\"28696429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In the cerebellar cortex, GluD1 is expressed in molecular layer interneurons and concentrated at parallel fiber (PF) synapses on interneuron somata. In GluD1 knockout mice, the density of PF synapses on interneuron somata is significantly reduced and interneuron number/size is diminished, demonstrating GluD1 regulates PF–interneuron synapse connectivity and interneuron differentiation/survival.\",\n      \"method\": \"Histochemical localization, GluD1 knockout mouse analysis, quantitative synapse and cell-count assays\",\n      \"journal\": \"Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific cellular phenotypes, replicated across multiple quantitative readouts\",\n      \"pmids\": [\"24872547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GluD1 expressed in non-neuronal HEK cells induces presynaptic differentiation of cerebellar granule neurons via its N-terminal domain; in the presence of Cbln1, GluD1 additionally induces both glutamatergic and GABAergic presynaptic differentiation in hippocampal co-cultures, and rescues synapse formation defects in GluD2-knockout Purkinje neurons.\",\n      \"method\": \"HEK cell–neuron co-culture assay, exogenous Cbln1 addition, GluD2-KO rescue experiment\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based reconstitution with multiple neuronal partners and KO rescue, single lab\",\n      \"pmids\": [\"22138648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GluD1 knockout mice exhibit higher dendritic spine number, greater excitatory neurotransmission, increased synapse number in mPFC and CA1 hippocampus, and abnormal LIMK1–cofilin signaling with a lower GluN2A/GluN2B ratio, establishing GluD1 as required for normal spine development and GluN2B-to-GluN2A NMDAR subunit switch.\",\n      \"method\": \"GluD1 KO mouse analysis, dendritic spine counting, electrophysiology, biochemical pathway analysis (LIMK1–cofilin), GluN2B inhibitor rescue\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple orthogonal cellular phenotype readouts and pharmacological rescue\",\n      \"pmids\": [\"25721396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GluD1 synaptic trafficking depends on its C-terminal domain but not on the PDZ-binding motif; phosphorylation of threonine T923 in the C-terminal domain is critical for synaptic (but not surface) localization of GluD1, revealing a unique trafficking mechanism distinct from AMPARs.\",\n      \"method\": \"Chimeric GluD1/GluK1 constructs, mutagenesis of C-terminal domain and PDZ motif, electrophysiology and imaging in neurons\",\n      \"journal\": \"Molecular Psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with functional trafficking assays, multiple constructs tested\",\n      \"pmids\": [\"30824864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"X-ray crystallography of the GluD1 ligand-binding domain (LBD) reveals its apo structure at 2.57 Å; D-serine binds GluD1-LBD with Kd ~160 µM (approximately 5-fold lower affinity than GluD2); Glu822 is identified as a critical determinant of receptor activation in GluD1 A654T; molecular dynamics indicate GluD1 apo structure is less flexible than GluD2 and Pro725 affects LBD interlobe closure.\",\n      \"method\": \"X-ray crystallography, isothermal titration calorimetry, electrophysiology in Xenopus oocytes, molecular dynamics simulation\",\n      \"journal\": \"The FEBS Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus ITC binding measurements and mutagenesis\",\n      \"pmids\": [\"36128700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GluD1 and GluD2 form a coimmunoprecipitable protein complex in HEK293T cells and in native cerebral cortex and hippocampus; both receptors are co-expressed on the same glutamatergic synapses in the retrosplenial cortex, as shown by SDS-digested freeze-fracture replica labeling.\",\n      \"method\": \"Co-immunoprecipitation in HEK293T cells and brain tissue, SDS-digested freeze-fracture replica labeling, quantitative immunoblotting with chimeric protein standards\",\n      \"journal\": \"Journal of Comparative Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — reciprocal co-IP in cells and brain plus ultrastructural co-localization, single lab\",\n      \"pmids\": [\"31625608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Homozygous missense GRID1 variants (p.Thr752Met and p.Arg161His) cause intellectual disability and spastic paraplegia; mechanistically these mutations alter hinge/LBD function, impair mGlu1/5 receptor signaling via Ca2+ and ERK pathways, and reduce dendrite complexity and excitatory synapse density when expressed in neurons, without disrupting GluD1 trafficking or cerebellin binding.\",\n      \"method\": \"Molecular modeling, electrophysiological recordings, Ca2+ imaging, ERK pathway assays, neuronal morphology analysis in dissociated and organotypic cultures\",\n      \"journal\": \"Molecular Psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal functional assays (electrophysiology, signaling, morphology) combined with structural modeling\",\n      \"pmids\": [\"38418578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A GRID1 variant in the distal amino-terminal domain (predicted to contact Cbln2/Cbln4) disrupts GluD1–Cbln2 complex formation in biochemical assays; other rare M3 domain variants (including GluD1-A650T analogous to the GluD2 lurcher mutation) create constitutively active channels; pentamidine potently inhibits constitutive currents of GluD receptor variants.\",\n      \"method\": \"Electrophysiological assays, biochemical complex formation assays, pharmacological inhibition with pentamidine\",\n      \"journal\": \"Human Molecular Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — direct electrophysiology and biochemical binding assays, single study\",\n      \"pmids\": [\"37944084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"D-serine binds GluD1's ligand-binding domain and concentration-dependently inhibits the interaction between Cbln1 and GluD1 (IC50 ~300 µM) in a cell-binding assay; pre-treatment with D-serine blocks the pro-synaptic and nociceptive effects of recombinant Cbln1 in central amygdala slices and in vivo.\",\n      \"method\": \"In vitro cell-binding assay, ex vivo slice electrophysiology, in vivo behavioral (nociception) assays\",\n      \"journal\": \"Cellular and Molecular Life Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical binding IC50 plus electrophysiology and behavioral rescue, single lab\",\n      \"pmids\": [\"39890638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GluD1 carries a G-protein-independent tonic cation current in dorsal raphe nucleus neurons regulated by physiological levels of external calcium; block of GluD1 channels hyperpolarizes the membrane by ~7 mV, reducing neuronal excitability, and this tonic current is unaffected by D-serine or glycine supplementation.\",\n      \"method\": \"Voltage-clamp and current-clamp electrophysiology from adult mouse brain slices, pharmacological block of GluD1\",\n      \"journal\": \"EMBO Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean electrophysiological characterization with pharmacological tools, single lab\",\n      \"pmids\": [\"37154294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GRID1/GluD1 directly facilitates autophagic flux in central amygdala neurons via interaction with autophagy mediators nGOPC/nPIST, BECN1, and LAMP1; a GluD1 C-terminal-derived peptide (Tat-HRSPN) promotes autophagy and reduces AMPA receptor expression; GRID1/CBLN1 downregulation during inflammatory and neuropathic pain impairs autophagic flux and increases AMPAR expression in CeA.\",\n      \"method\": \"Co-immunoprecipitation (GluD1 with BECN1/LAMP1/nGOPC), peptide (Tat-HRSPN) in vivo infusion, autophagy flux assays, electrophysiology in CeA slices, pain behavioral models\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP plus peptide functional rescue and electrophysiology, single lab\",\n      \"pmids\": [\"41147487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In both mouse and monkey striatum, GluD1 immunoreactivity is localized by electron microscopy predominantly to dendritic shafts and glial processes, with synaptic and perisynaptic labeling at glutamatergic axo-dendritic and axo-spinous synapses; confocal microscopy shows preferential colocalization with thalamic (over cortical) terminals.\",\n      \"method\": \"Immunoelectron microscopy (including immunogold), confocal microscopy, ultrastructural subcellular localization\",\n      \"journal\": \"Journal of Comparative Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ultrastructural localization with multiple methods across two species\",\n      \"pmids\": [\"33084025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Cryo-EM structures of human GluD1 and single-channel bilayer recordings demonstrate that GABA or D-serine binding to the LBD enables cation influx through the hGluD1 ion channel; hGluD1 has a non-swapped architecture containing conserved iGluR moieties that enable ligand-gating.\",\n      \"method\": \"Cryo-EM structure determination, single-channel bilayer electrophysiology, ligand-binding functional assays\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure plus single-channel recordings; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"41993446\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Grid1 knockdown in the hypothalamus decreases Grid1 and Rfrp-3 mRNA, increases Gnrh mRNA, advances vaginal opening (earlier puberty onset) and decreases progesterone levels in female rats, placing GluD1 in a pathway that regulates GnRH/RFRP-3 signaling and puberty onset.\",\n      \"method\": \"Lentiviral Grid1 knockdown in hypothalamic neurons, intracerebroventricular injection, RT-PCR gene expression, hormone ELISA, histology\",\n      \"journal\": \"Journal of Veterinary Medical Science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD phenotype with gene expression readout, pathway placement indirect, single lab\",\n      \"pmids\": [\"38479882\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GluD1 (encoded by GRID1) is a multifunctional synaptic organizer with a non-swapped tetrameric architecture; it binds D-serine and GABA (not glutamate) at its ligand-binding domain, assembles trans-synaptic neurexin–cerebellin–GluD1 complexes through its N-terminal domain, and converts these extracellular signals into postsynaptic regulation of NMDA and AMPA receptor levels via conserved C-terminal cytoplasmic motifs in a non-ionotropic manner, while also coupling to mGlu1 to mediate slow depolarizing currents in dopamine neurons, facilitating autophagic flux through interactions with BECN1 and LAMP1, and promoting inhibitory synaptic plasticity through GABA binding—collectively establishing GluD1 as a trans-synaptic signaling scaffold that regulates both excitatory and inhibitory circuit development and function.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GluD1 (encoded by GRID1) is an ionotropic glutamate receptor family member that functions primarily as a trans-synaptic signaling scaffold, organizing both excitatory and inhibitory synapse development and plasticity through non-ionotropic mechanisms. Its N-terminal domain binds presynaptic neurexin–cerebellin complexes to regulate postsynaptic NMDA and AMPA receptor levels via conserved C-terminal cytoplasmic motifs, with minimal constructs lacking ionotropic architecture fully recapitulating this signaling [PMID:34135511]; its ligand-binding domain binds D-serine and GABA—not glutamate—with GABA binding producing long-lasting enhancement of GABAergic synaptic currents [PMID:38060673, PMID:36128700], and D-serine competitively inhibiting the Cbln1–GluD1 interaction [PMID:39890638]. GluD1 additionally couples to mGlu1 receptors to generate slow depolarizing currents in dopamine neurons [PMID:28696429], carries a tonic cation conductance in serotonergic neurons [PMID:37154294], facilitates autophagic flux through C-terminal interactions with BECN1 and LAMP1 [PMID:41147487], and is required for normal dendritic spine pruning and the developmental GluN2B-to-GluN2A NMDAR subunit switch [PMID:25721396]. Homozygous missense GRID1 variants (p.Thr752Met, p.Arg161His) cause intellectual disability and spastic paraplegia by impairing mGlu1/5 signaling and reducing dendrite complexity without disrupting GluD1 trafficking [PMID:38418578].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing GluD1 as a synaptogenic molecule: it was unknown whether GluD1, like GluD2, could organize presynaptic differentiation; co-culture experiments showed GluD1's N-terminal domain induces both glutamatergic and GABAergic presynaptic differentiation in the presence of Cbln1, establishing GluD1 as a bona fide trans-synaptic organizer.\",\n      \"evidence\": \"HEK cell–neuron co-culture with exogenous Cbln1, GluD2-KO rescue\",\n      \"pmids\": [\"22138648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; no in vivo confirmation of GluD1 synaptogenic role at this stage\", \"Endogenous cerebellin partner for GluD1 not identified\", \"GABAergic versus glutamatergic synaptogenic specificity mechanism unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating GluD1's requirement for synapse formation and cell survival in vivo: loss of GluD1 reduced parallel fiber–interneuron synapse density and interneuron number in cerebellum, establishing a non-redundant in vivo role for GluD1 in circuit connectivity and neuronal maintenance.\",\n      \"evidence\": \"GluD1 KO mouse, quantitative synapse and cell-count assays in cerebellar cortex\",\n      \"pmids\": [\"24872547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking GluD1 loss to interneuron death not defined\", \"Whether GluD1 acts cell-autonomously in interneurons not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revealing GluD1 as a regulator of spine pruning and NMDAR subunit maturation: GluD1 KO mice showed excess spines, elevated excitatory transmission, disrupted LIMK1–cofilin signaling, and failure of the GluN2B-to-GluN2A switch, linking GluD1 to cytoskeletal remodeling and glutamate receptor subunit composition.\",\n      \"evidence\": \"GluD1 KO mouse, spine counting, electrophysiology, biochemical pathway analysis, GluN2B inhibitor rescue in mPFC and hippocampus\",\n      \"pmids\": [\"25721396\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between GluD1 and LIMK1–cofilin pathway not established\", \"Whether spine phenotype is developmental or maintenance-related unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying a metabotropic coupling mode: GluD1 was shown to couple to mGlu1 to produce slow depolarizing currents in dopamine neurons, revealing that GluD1 can function as an effector ion channel downstream of a metabotropic receptor, a novel signaling paradigm for iGluR family members.\",\n      \"evidence\": \"HEK cell co-expression, dominant-negative GluD1 mutant in slices, GRID1 KO mice, in vivo dopamine neuron recordings\",\n      \"pmids\": [\"28696429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of mGlu1–GluD1 coupling (direct interaction vs. intermediary) not resolved\", \"Whether this coupling occurs outside midbrain dopamine neurons unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defining GluD1 synaptic trafficking rules: phosphorylation of C-terminal T923 was shown to be critical for synaptic (but not surface) localization, independent of the PDZ-binding motif, revealing a trafficking mechanism distinct from AMPARs and establishing the C-terminal domain as a regulatory hub.\",\n      \"evidence\": \"Chimeric GluD1/GluK1 constructs, site-directed mutagenesis, neuronal imaging and electrophysiology\",\n      \"pmids\": [\"30824864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for T923 phosphorylation not identified\", \"Activity-dependent regulation of this phosphorylation not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrating GluD1–GluD2 hetero-association: co-immunoprecipitation from brain tissue and ultrastructural co-localization showed GluD1 and GluD2 form complexes at the same glutamatergic synapses, suggesting functional heteromeric assembly.\",\n      \"evidence\": \"Co-IP in HEK293T cells and brain lysates, SDS-digested freeze-fracture replica labeling in retrosplenial cortex\",\n      \"pmids\": [\"31625608\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and functional consequence of GluD1/GluD2 heteromers not determined\", \"Whether heteromers have distinct signaling properties is untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolving GluD1 architecture: cryo-EM revealed a unique non-swapped tetrameric arrangement at the ATD–LBD interface, distinguishing GluD receptors from all other iGluR families and providing a structural basis for their distinct signaling properties.\",\n      \"evidence\": \"Cryo-EM of rat GluD1 complexed with calcium and 7-chlorokynurenic acid\",\n      \"pmids\": [\"31925409\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length structure with transmembrane domain not resolved at this stage\", \"Functional consequence of non-swapped architecture for signaling not directly tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Establishing GluD1 as a non-ionotropic trans-synaptic signal transduction device: minimal constructs containing only the NTD and CTD joined by an unrelated transmembrane domain fully recapitulated neurexin–cerebellin-dependent NMDAR and AMPAR regulation, proving the mechanism bypasses ionotropic gating entirely.\",\n      \"evidence\": \"Minimal/chimeric constructs, electrophysiology, domain-swap and loss-of-function experiments in hippocampal synapses\",\n      \"pmids\": [\"34135511\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational change linking extracellular binding to cytoplasmic signaling not visualized\", \"Identity of cytoplasmic effectors recruited by the C-terminal motifs not fully catalogued\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Characterizing D-serine binding to GluD1-LBD: crystal structure and ITC revealed D-serine binds GluD1 with ~160 µM Kd (5-fold lower than GluD2), with Glu822 critical for activation and Pro725 affecting interlobe closure dynamics, establishing molecular determinants of GluD1 ligand recognition.\",\n      \"evidence\": \"X-ray crystallography at 2.57 Å, ITC, oocyte electrophysiology, molecular dynamics\",\n      \"pmids\": [\"36128700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological source and concentration of D-serine at GluD1-expressing synapses not established\", \"Whether D-serine binding triggers non-ionotropic signaling or primarily modulates trans-synaptic interactions unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovering GABA as a GluD1 ligand: GABA binding to the LBD was demonstrated biochemically and structurally, and shown to produce long-lasting enhancement of GABAergic synaptic currents in hippocampus via a non-ionotropic, trans-synaptically anchored mechanism—making GluD1 the first iGluR family member with a GABA-binding function.\",\n      \"evidence\": \"Binding assays, structural analysis of LBD, patch-clamp in hippocampal slices, loss-of-function\",\n      \"pmids\": [\"38060673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GABA binding and D-serine binding are competitive at the same site not fully resolved\", \"Downstream signaling cascade from GABA-bound GluD1 to GABAergic potentiation not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying a tonic cation conductance: GluD1 carries a G-protein-independent, calcium-regulated tonic current in dorsal raphe serotonergic neurons that sets resting membrane potential, expanding GluD1's repertoire to include a constitutive ionotropic mode independent of classical ligand gating.\",\n      \"evidence\": \"Voltage-clamp and current-clamp in adult mouse brain slices, pharmacological GluD1 block\",\n      \"pmids\": [\"37154294\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of calcium-dependent regulation of this tonic current not defined\", \"Whether this tonic current occurs in other GluD1-expressing neuron types untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking GRID1 mutations to human disease: homozygous GRID1 missense variants were shown to cause intellectual disability and spastic paraplegia by impairing mGlu1/5 signaling and reducing dendritic complexity without disrupting trafficking or cerebellin binding, establishing GRID1 as a Mendelian disease gene.\",\n      \"evidence\": \"Patient variant modeling, electrophysiology, Ca²⁺ and ERK pathway assays, neuronal morphology in dissociated and organotypic cultures\",\n      \"pmids\": [\"38418578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genotype–phenotype correlation across additional GRID1 variants not yet established\", \"Whether disease mechanism is primarily mGlu1/5-dependent or involves trans-synaptic signaling impairment not separated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Characterizing disease-associated channel variants: an ATD variant disrupted GluD1–Cbln2 complex formation while M3 domain variants created constitutively active channels, and pentamidine was identified as an inhibitor of pathogenic constitutive currents, beginning to define pharmacological rescue strategies.\",\n      \"evidence\": \"Electrophysiology, biochemical binding assays, pentamidine pharmacology\",\n      \"pmids\": [\"37944084\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo efficacy of pentamidine not tested\", \"Whether constitutive channel activity is pathogenic in patient neurons not confirmed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealing D-serine as a competitive modulator of trans-synaptic assembly: D-serine concentration-dependently inhibits Cbln1–GluD1 interaction (IC50 ~300 µM) and blocks Cbln1-dependent synaptic and behavioral effects, establishing a ligand-dependent switch between trans-synaptic scaffolding and ligand-gated signaling modes.\",\n      \"evidence\": \"Cell-binding assay, ex vivo central amygdala slice electrophysiology, in vivo nociception assays\",\n      \"pmids\": [\"39890638\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological context where D-serine reaches effective concentrations at GluD1 synapses not demonstrated\", \"Whether GABA similarly modulates Cbln1 binding not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovering a non-synaptic function in autophagy: GluD1 was found to interact with BECN1 and LAMP1 via its C-terminal domain (through nGOPC/nPIST) to promote autophagic flux; a GluD1-derived peptide rescued autophagy impairment and AMPAR upregulation in pain models, linking GluD1 to protein homeostasis beyond synaptic signaling.\",\n      \"evidence\": \"Co-IP of GluD1 with BECN1/LAMP1/nGOPC, Tat-HRSPN peptide in vivo, autophagy flux assays, CeA electrophysiology, pain behavioral models\",\n      \"pmids\": [\"41147487\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether autophagy function is constitutive or activity-dependent not established\", \"Structural basis of GluD1–BECN1 interaction not defined\", \"Generalizability beyond central amygdala not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions remain: the conformational mechanism linking extracellular ligand/cerebellin binding to cytoplasmic effector recruitment; whether GluD1 heteromers with GluD2 have distinct signaling properties; the physiological conditions under which ionotropic versus non-ionotropic modes predominate; and the full catalogue of C-terminal effectors mediating NMDAR/AMPAR regulation and autophagic signaling.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of full signaling complex (neurexin–Cbln–GluD1 with cytoplasmic partners)\", \"Ionotropic vs. non-ionotropic mode selection mechanism unknown\", \"Complete cytoplasmic interactome not mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 7, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 1, 3, 4, 6, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 10]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"complexes\": [\n      \"neurexin–cerebellin–GluD1 trans-synaptic complex\",\n      \"GluD1–GluD2 heteromeric complex\"\n    ],\n    \"partners\": [\n      \"CBLN1\",\n      \"CBLN2\",\n      \"NRXN1\",\n      \"NRXN3\",\n      \"GRID2\",\n      \"GRM1\",\n      \"BECN1\",\n      \"GOPC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}