{"gene":"GRIK1","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1990,"finding":"GluR5 (GRIK1) encodes a glutamate receptor subunit that forms homomeric ion channels when expressed in Xenopus oocytes, responding weakly to L-glutamate; it shares ~40-41% amino acid identity with AMPA/kainate receptor subunits GluR1-4, placing it in a distinct kainate receptor subfamily.","method":"Xenopus oocyte expression, electrophysiology, cDNA cloning","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in Xenopus oocytes establishing ion channel activity, foundational cloning paper with >500 citations","pmids":["1977421"],"is_preprint":false},{"year":1996,"finding":"RNA editing at the Q/R site of GluR5 pre-mRNA requires base pairing with an intronic editing site complementary sequence (ECS) located up to 1900 nucleotides distal to the Q/R site; double-stranded RNA adenosine deaminase preferentially targets the Q/R site adenosine when coexpressed in HEK293 cells.","method":"Minigene transfection in PC-12 cells, HEK293 coexpression, transcript analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — mechanistic dissection of editing requirement with functional validation in two cell systems","pmids":["8700852"],"is_preprint":false},{"year":1997,"finding":"GluR5 subunit-containing kainate receptors regulate GABAergic inhibitory synaptic transmission in hippocampal CA1, as shown by selective agonist ATPA and antagonist LY294486; this modulation of inhibition could contribute to kainate's epileptogenic effects.","method":"Hippocampal slice electrophysiology, selective pharmacological tools (ATPA agonist, LY294486 antagonist)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — clean pharmacological dissection with selective agonist and antagonist in defined circuit, replicated in multiple subsequent studies","pmids":["9335499"],"is_preprint":false},{"year":1997,"finding":"A single amino acid residue N721 in GluR6 (and its GluR5 counterpart) controls both AMPA sensitivity and domoate deactivation rates; residue A689 in GluR6 controls kainate desensitization rates, as revealed by chimeric and point-mutant receptors.","method":"Patch-clamp analysis of chimeric GluR5-GluR6 receptors and point mutants expressed in Xenopus oocytes/HEK cells, ligand binding","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with functional and binding validation identifying specific residues controlling gating","pmids":["9354337"],"is_preprint":false},{"year":1997,"finding":"GluR5 and KA-2 subunits co-assemble to form heteromeric kainate receptor channels in trigeminal ganglion neurons; native KA receptor channels in TG neurons resemble recombinant GluR5(R)/KA-2 channels in pharmacological properties, desensitization, rectification, ion permeability, and single-channel conductance.","method":"RT-PCR, patch-clamp electrophysiology of acutely dissociated TG neurons, comparison with recombinant receptors in heterologous cells","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — convergent physiological, pharmacological, and molecular evidence for native heteromer composition","pmids":["9254673"],"is_preprint":false},{"year":1998,"finding":"Activation of GluR5-containing kainate receptors on hippocampal CA1 interneurons generates inward current and repetitive action potential firing, causing a massive increase in tonic GABAergic inhibition of pyramidal neuron somata and apical dendrites; electrical stimulation of excitatory afferents produces kainate receptor-mediated EPSCs and action potentials in interneurons.","method":"Whole-cell patch-clamp in hippocampal slices, selective GluR5 agonist ATPA and antagonist LY293558","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 — identified cellular mechanism (interneuron excitation → increased tonic GABA inhibition of pyramidals) with pharmacological dissection, >250 citations","pmids":["10196544"],"is_preprint":false},{"year":1998,"finding":"GluR5 subunits contribute to a kainate receptor that presynaptically depresses excitatory synaptic transmission in both CA1 and CA3 hippocampal regions, as demonstrated by ATPA-induced depression of EPSPs/EPSCs and increased paired-pulse facilitation.","method":"Field and whole-cell recordings in hippocampal slices, selective GluR5 agonist ATPA and antagonist LY294486","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 2 — selective pharmacological tools with paired-pulse analysis confirming presynaptic locus","pmids":["9849664"],"is_preprint":false},{"year":1998,"finding":"GluR5 kainate receptor-mediated synaptic transmission occurs in the basolateral amygdala (BLA), where high-frequency stimulation of external capsule evokes GluR5-dependent synaptic currents that are inwardly rectifying and blocked by LY293558.","method":"Intracellular and whole-cell voltage-clamp recordings in BLA slices, selective AMPA and kainate receptor antagonists","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 2 — pharmacological isolation of GluR5-mediated synaptic current with clean controls","pmids":["9849665"],"is_preprint":false},{"year":1999,"finding":"GluR5, GluR6, and GluR7 kainate receptor subunits coassemble promiscuously to form heteromeric receptors; GluR5/GluR6 heteromers exhibit reduced desensitization and faster recovery from desensitization compared to homomeric GluR5; GluR7 coassembly with GluR6 markedly decreases agonist response amplitude.","method":"Coexpression in Xenopus oocytes with selective GluR5 agonists and rectification analysis of edited/unedited Q/R-site subunit combinations","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution with rigorous rectification-based coassembly assay and biophysical characterization","pmids":["10493729"],"is_preprint":false},{"year":1999,"finding":"RNA editing of the Q/R site in GluR5 reduces kainate receptor current density by ~6-fold in dorsal root ganglion sensory neurons; GluR5(R) knock-in mice (encoding arginine at Q/R site) show reduced DRG kainate current density without altered thermal/chemical pain responses.","method":"Embryonic stem cell knock-in transgenesis, patch-clamp in acutely isolated DRG neurons from mutant mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — genetic model with direct electrophysiological quantification of editing effect on channel function in native neurons","pmids":["10516295"],"is_preprint":false},{"year":2000,"finding":"GluR5 and GluR6 subunits coassemble into heteromeric kainate receptors in hippocampal GABAergic interneurons; >80% of receptors in co-transfected single HEK293 cells are GluR5/GluR6 heteromers, exhibiting different desensitization and gating properties from homomeric GluR6.","method":"Double in situ hybridization in hippocampal slices, patch-clamp electrophysiology in co-transfected HEK293 cells, selective agonist ATPA","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — combined in situ co-expression and functional heteromer verification in heterologous cells","pmids":["10627597"],"is_preprint":false},{"year":2003,"finding":"Cell surface expression of GluR5-2b is regulated by a novel endoplasmic reticulum retention signal in the alternatively spliced C-terminal domain; a critical arginine (Arg-896) and surrounding residues mediate ER retention, and phosphorylation-mimicking mutation of Thr-898 promotes ER exit and surface expression.","method":"Mutagenesis, heterologous cell transfection, cell surface biotinylation, immunofluorescence in neurons","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis of specific residues with functional trafficking readouts in both heterologous cells and neurons","pmids":["14527949"],"is_preprint":false},{"year":2003,"finding":"Topiramate at low concentrations (IC50 ~0.5 µM) selectively inhibits postsynaptic GluR5 kainate receptor-mediated synaptic currents in BLA principal neurons; it reduces miniature EPSC amplitude without affecting frequency, indicating postsynaptic block.","method":"Whole-cell voltage-clamp recordings in rat BLA slices, miniature EPSC analysis, paired-pulse experiments","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — selective pharmacological characterization with multiple electrophysiological approaches confirming postsynaptic mechanism","pmids":["12904467"],"is_preprint":false},{"year":2003,"finding":"GluR5 activation selectively depolarizes inhibitory interneurons in the basolateral amygdala, increasing GABA release and tonic GABA current in the BLA; GluR5 genetic deletion or local antagonist injection increases anxiety-like behavior.","method":"Whole-cell recordings in BLA slices, GluR5 knockout mice, local antagonist microinjection, behavioral tests","journal":"Journal of neurophysiology / PloS one","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (electrophysiology, pharmacology, knockout) linking GluR5 activation to interneuron excitation and behavior","pmids":["12091575","17245443"],"is_preprint":false},{"year":2005,"finding":"Crystal structures of GluR5 and GluR6 ligand binding cores reveal that GluR5 ligand binding cavity is 40% larger than GluR2; extensive interdomain contacts between domains 1 and 2 of GluR5 (absent in AMPA receptors) contribute to high-affinity kainate complex stability; agonist selectivity is determined by steric occlusion within the binding cavity.","method":"X-ray crystallography of ligand binding cores in complex with glutamate, 4-methylglutamate, kainate, and quisqualate","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structures providing atomic-level mechanism for ligand selectivity","pmids":["15721240"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of GluR5 ligand binding core with (S)-glutamate reveals 26° domain closure; Ser741 stabilizes an interdomain water network and forms an interdomain bridge; GluR5-S1S2 forms a novel dimer interface distinct from GluR2.","method":"X-ray crystallography at 1.95 Å resolution","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with structural analysis of binding mechanism","pmids":["15710405"],"is_preprint":false},{"year":2003,"finding":"GluR5 selectivity for the agonist ATPA is controlled by Ser741 in GluR5 (vs. Met722 in GluR1); Ser741 stabilizes the active conformation induced by bulky 5-position isoxazole substituents, as demonstrated by mutagenesis.","method":"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis of GluR5 and GluR1","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis identifying specific residue determining agonist selectivity with functional validation","pmids":["12488532"],"is_preprint":false},{"year":2004,"finding":"GluR5 and GluR6 kainate receptor subunits play distinct roles in hippocampal gamma oscillations: GluR5 ablation increases susceptibility to kainate-induced oscillations/epileptiform activity, while GluR6 ablation prevents them; GluR5-containing KARs on interneuron axons and GluR6-containing KARs in somatodendritic regions underlie distinct network functions.","method":"Kainate receptor knockout mice, field potential recordings, computational network modeling","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with defined circuit-level phenotypes and computational validation","pmids":["15509753"],"is_preprint":false},{"year":2005,"finding":"GluR5 knockout mice show significantly reduced responses to capsaicin- and inflammation-induced pain but not fear memory, while GluR6 knockouts show reduced fear memory but not pain responses, demonstrating that distinct KAR subtypes control nociception versus fear.","method":"GluR5 and GluR6 knockout mice, behavioral pain and fear-memory assays, lateral amygdala synaptic recordings","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with subunit-specific behavioral and electrophysiological phenotypes","pmids":["15673679"],"is_preprint":false},{"year":2006,"finding":"Crystal structures of GluR5 ligand binding core with selective antagonists UBP302 and UBP310 reveal a novel binding mechanism: antagonists do not contact E723 (unlike all previously solved agonist/antagonist complexes), causing hyperextension of the binding core and a 22 Å extension of ion channel linkers compared to the glutamate-bound form.","method":"X-ray crystallography of GluR5-S1S2 complexes with antagonists, radiolabel displacement assays, whole-cell electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structures with functional validation revealing novel antagonist binding mechanism","pmids":["16540562"],"is_preprint":false},{"year":2008,"finding":"GluR5 activation in myelinated dorsal column axons increases intraaxonal Ca2+ via both ionotropic and metabotropic (pertussis toxin-sensitive G-protein/PLC-dependent) signaling involving IP3-dependent Ca2+ release; GluR5 co-immunoprecipitates with nNOS and colocalizes with nNOS clusters on internodal axons.","method":"Confocal Ca2+ imaging in dorsal column axons, pharmacological dissection, co-immunoprecipitation, immunohistochemistry","journal":"Annals of neurology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pharmacological approaches with co-IP establishing nNOS interaction; single lab","pmids":["19224531"],"is_preprint":false},{"year":2008,"finding":"GluR5-containing KAR activation in vivo exerts neuroprotection against ischemia-reperfusion by facilitating Ca2+-dependent GABA release from interneurons; released GABA activates postsynaptic GABA-A receptors, which attenuates NMDA receptor tyrosine phosphorylation by inhibiting Src kinase activation and disrupting the NR2A-PSD-95-Src signaling module.","method":"In vivo ischemia-reperfusion model, patch-clamp recordings, co-immunoprecipitation, antisense oligodeoxynucleotides, selective pharmacological tools","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal approaches (pharmacology, antisense, co-IP, electrophysiology) defining signaling pathway; single lab","pmids":["18678878"],"is_preprint":false},{"year":2009,"finding":"GluR5 kainate receptors regulate HPA axis stress responses differentially: GluR5 in the paraventricular nucleus tonically inhibits ACTH/corticosterone release, while GluR5 at the median eminence (co-localized with CRH) facilitates restraint-induced ACTH release.","method":"In situ hybridization, immunohistochemistry, intra-PVN and intra-median eminence pharmacological infusion, plasma hormone measurements","journal":"Psychoneuroendocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and site-specific pharmacological manipulation with hormonal readouts","pmids":["19450932"],"is_preprint":false},{"year":2011,"finding":"NETO2 profoundly slows desensitization of GluK1 (GluR5) kainate receptors and promotes plasma membrane localization and synaptic targeting of GluK1-containing receptors in hippocampal neurons; NETO1 increases GluK1 desensitization rate. These effects extend the temporal range of GluK1 gating by over an order of magnitude.","method":"Heterologous expression, patch-clamp electrophysiology, transfection of hippocampal neurons, immunofluorescence","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biophysics, localization, synaptic targeting) in heterologous and native neurons","pmids":["21593317"],"is_preprint":false},{"year":2015,"finding":"Both NETO1 and NETO2 are auxiliary subunits that profoundly increase GluK1 surface expression and drive GluK1 to synapses in hippocampal CA1 neurons; synaptic targeting by NETO proteins is independent of their role in promoting surface trafficking; GluK1 is selectively incorporated into silent synapses (excluded from AMPA receptor-containing synapses); NETO2 slows GluK1 deactivation and desensitization, while NETO1 speeds desensitization.","method":"Hippocampal CA1 null-background system, lentiviral expression, whole-cell patch-clamp, EPSC recordings","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — clean null-background system with multiple functional and trafficking readouts distinguishing NETO1 vs NETO2 effects","pmids":["26720915"],"is_preprint":false},{"year":2015,"finding":"GluK1 C-terminal domain interacts with Goα subunit; GluK1 activates Go proteins as shown by BRET experiments; interaction was validated by in vitro and in vivo co-immunoprecipitation and was absent in GluK1-deficient mice, establishing GluK1 as a mediator of metabotropic (G-protein) as well as ionotropic signaling.","method":"Proteomics/mass spectrometry of GluK1 C-terminal interactome, co-immunoprecipitation, BRET assays, GluK1 knockout mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — proteomics discovery validated by reciprocal co-IP, BRET functional assay, and genetic confirmation in knockout mice","pmids":["25834043"],"is_preprint":false},{"year":2018,"finding":"The cleaved signal peptide of GluK1 interacts with the amino-terminal domain (ATD) in trans to repress forward trafficking (surface and synaptic expression) of GluK1; chimeric replacement of GluK1 signal peptide with that of GluK2 dramatically increases surface/synaptic expression, and this is suppressed by co-expression of the GluK1 signal peptide.","method":"Chimeric receptor strategy, EPSC recordings in hippocampal CA1 neurons, co-expression experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — chimeric and rescue experiments with functional synaptic readouts defining signal peptide-ATD interaction as trafficking mechanism","pmids":["30451858"],"is_preprint":false},{"year":1998,"finding":"Homomeric GluR5 receptors expressed in HEK293 cells exhibit striking inter-cell variability in desensitization kinetics (range 1.5 ms to 1.5 s for kainate), suggesting modulation of GluR5 gating by intracellular mechanisms; DRG neurons (likely homomeric GluR5) show biexponential recovery from desensitization similar to fast-desensitizing GluR5 cells.","method":"Patch-clamp electrophysiology in HEK293 cells and acutely isolated DRG neurons","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — detailed biophysical characterization identifying variability attributable to intracellular regulation; single lab","pmids":["9824706"],"is_preprint":false},{"year":2009,"finding":"GluR5 kainate receptor activation in the anterior cingulate cortex selectively facilitates GABAergic (not glutamatergic) transmission through somatodendritic (not presynaptic) GluR5 in a Ca2+-dependent, voltage-gated Ca2+ channel-dependent manner; endogenous GluR5 activation produces tonic GABA currents in ACC pyramidal neurons.","method":"Whole-cell recordings in ACC slices, selective GluR5 agonist/antagonist, GluR5 knockout mice","journal":"Developmental neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacology combined with genetic knockout confirming specificity; single lab","pmids":["17443779"],"is_preprint":false},{"year":2006,"finding":"GluR5-containing kainate receptors are located presynaptically on inhibitory GABAergic terminals in spinal substantia gelatinosa, where their activation facilitates the frequency (but not amplitude) of both GABAergic and glycinergic IPSCs; this effect is absent in GluR5 knockout mice.","method":"Whole-cell recordings in spinal cord slices, ATPA selective agonist, GluR5 knockout mice, miniature IPSC analysis","journal":"Molecular pain","confidence":"High","confidence_rationale":"Tier 2 — pharmacology plus genetic knockout confirming presynaptic locus and subunit identity","pmids":["16948848"],"is_preprint":false}],"current_model":"GRIK1 encodes the GluK1 (GluR5) kainate receptor subunit, which assembles as homomers or heteromers (with GluK2, GluK3, or KA2) to form Ca2+-permeable ion channels whose gating, desensitization, and surface trafficking are regulated by RNA editing at the Q/R site, alternative C-terminal splicing (including an ER retention signal controlled by Arg-896 phosphorylation), and auxiliary NETO1/NETO2 proteins; at synapses, GluK1 is selectively targeted to silent synapses by NETO proteins, modulates both excitatory and inhibitory transmission by depolarizing interneurons to increase GABAergic tone onto pyramidal cells, and also signals metabotropically through direct interaction with Goα proteins and, on axons, through a PLC/IP3/nNOS-linked pathway—with its ligand-binding domain selectivity structurally explained by a larger binding cavity and a critical Ser741 residue that accommodates bulky agonists like ATPA."},"narrative":{"teleology":[{"year":1990,"claim":"Cloning of GluR5 established that GRIK1 encodes a glutamate receptor subunit capable of forming functional homomeric ion channels, placing it in a distinct kainate receptor subfamily separate from AMPA receptors.","evidence":"cDNA cloning and electrophysiology in Xenopus oocytes","pmids":["1977421"],"confidence":"High","gaps":["Homomeric channels responded weakly to glutamate, leaving native subunit composition unknown","No information on in vivo expression pattern or synaptic function"]},{"year":1996,"claim":"Identification of the intronic editing site complementary sequence required for Q/R site RNA editing revealed how a post-transcriptional modification alters GluK1 channel properties, resolving how editing specificity is achieved.","evidence":"Minigene transfection in PC-12 and HEK293 cells with transcript analysis","pmids":["8700852"],"confidence":"High","gaps":["The enzyme responsible (ADAR) was coexpressed but isoform specificity not resolved","Functional consequences of editing on native neuronal channels not yet measured"]},{"year":1997,"claim":"Heteromeric assembly of GluK1 with KA-2 was demonstrated in trigeminal ganglion neurons, and structure-function mutagenesis identified specific residues (N721, A689) controlling agonist sensitivity and desensitization, establishing that native kainate receptors are heteromers with distinct gating determinants.","evidence":"Chimeric/point-mutant electrophysiology in oocytes/HEK cells; RT-PCR and patch-clamp in trigeminal ganglion neurons","pmids":["9354337","9254673"],"confidence":"High","gaps":["Heteromeric stoichiometry not determined","Whether these residues control gating in intact tetrameric receptors remained unclear"]},{"year":1997,"claim":"Pharmacological isolation of GluK1-mediated modulation of GABAergic transmission in hippocampal CA1 first demonstrated a circuit-level function: GluK1 activation on interneurons regulates inhibitory tone and may underlie kainate's epileptogenic effects.","evidence":"Hippocampal slice electrophysiology with selective GluK1 agonist ATPA and antagonist LY294486","pmids":["9335499"],"confidence":"High","gaps":["Whether GluK1 acted pre- or postsynaptically on interneurons was not resolved","Contribution relative to GluK2-containing receptors remained unclear"]},{"year":1998,"claim":"The cellular mechanism for GluK1's circuit role was resolved: GluK1 activation directly depolarizes CA1 interneurons causing repetitive firing and massive tonic GABAergic inhibition of pyramidal neurons, while presynaptic GluK1 also depresses excitatory transmission in hippocampus and mediates postsynaptic currents in the basolateral amygdala.","evidence":"Whole-cell patch-clamp in hippocampal and BLA slices with selective pharmacology; paired-pulse analysis","pmids":["10196544","9849664","9849665"],"confidence":"High","gaps":["Whether amygdala and hippocampal GluK1 receptors have identical subunit compositions was unknown","Metabotropic signaling component not yet suspected"]},{"year":1999,"claim":"GluK1 was shown to promiscuously coassemble with GluK2 and GluK3, producing heteromers with altered desensitization; separately, Q/R site editing was shown to reduce native DRG kainate current density sixfold in knock-in mice, quantifying editing's physiological impact.","evidence":"Coexpression in Xenopus oocytes with rectification analysis; GluR5(R) knock-in mice with DRG patch-clamp","pmids":["10493729","10516295"],"confidence":"High","gaps":["Behavioral consequences of reduced DRG current were minimal, leaving the in vivo purpose of editing uncertain","Native heteromer combinations in specific brain regions not mapped"]},{"year":2003,"claim":"Multiple trafficking and selectivity mechanisms were resolved: an ER retention signal at Arg-896 in the GluK1-2b splice variant controls surface expression via phosphorylation at Thr-898; Ser741 was identified as the critical residue conferring GluK1 selectivity for the agonist ATPA; and GluK1 in the BLA was shown to modulate interneuron excitability and anxiety-related behavior.","evidence":"Mutagenesis with surface biotinylation; oocyte electrophysiology of point mutants; BLA recordings in knockout mice with behavioral assays","pmids":["14527949","12488532","12091575","17245443"],"confidence":"High","gaps":["Kinase responsible for Thr-898 phosphorylation not identified","Whether ER retention mechanism operates in all neuron types unknown"]},{"year":2005,"claim":"Crystal structures of the GluK1 ligand-binding domain revealed a 40% larger binding cavity than AMPA receptors, with Ser741 mediating an interdomain water network and a novel dimer interface, providing the atomic basis for kainate receptor agonist selectivity and explaining prior mutagenesis results.","evidence":"X-ray crystallography at 1.95 Å resolution with multiple ligands","pmids":["15721240","15710405"],"confidence":"High","gaps":["Full-length receptor structure not available","No structural insight into desensitization or heteromeric assemblies"]},{"year":2005,"claim":"Genetic dissociation of GluK1 versus GluK2 functions showed that GluK1 loss increases susceptibility to kainate-induced epileptiform activity and reduces inflammatory/capsaicin pain responses without affecting fear memory, defining subunit-specific behavioral roles.","evidence":"GluK1 and GluK2 knockout mice with gamma oscillation recordings, pain assays, and fear conditioning","pmids":["15509753","15673679"],"confidence":"High","gaps":["Compensatory changes in knockout mice not assessed","Circuit mechanism linking GluK1 loss to increased seizure susceptibility not fully explained"]},{"year":2006,"claim":"A novel antagonist binding mechanism was revealed structurally—GluK1-selective antagonists UBP302/UBP310 do not contact E723, causing hyperextension of the binding core—while presynaptic GluK1 on spinal inhibitory terminals was shown to facilitate GABA/glycine release.","evidence":"X-ray crystallography of antagonist complexes; spinal cord slice electrophysiology with GluK1 knockout mice","pmids":["16540562","16948848"],"confidence":"High","gaps":["Whether the hyperextended conformation represents the resting or a distinct inhibited state is unclear","Mechanism coupling presynaptic GluK1 activation to vesicle release not defined"]},{"year":2008,"claim":"GluK1 was found to signal metabotropically on myelinated axons through a pertussis toxin-sensitive G-protein/PLC/IP3 pathway coupled to nNOS, and GluK1-mediated neuroprotection against ischemia was linked to enhanced GABA release that attenuates NMDA receptor signaling via Src kinase inhibition.","evidence":"Confocal Ca²⁺ imaging and co-immunoprecipitation in dorsal column axons; in vivo ischemia model with antisense knockdown and pharmacology","pmids":["19224531","18678878"],"confidence":"Medium","gaps":["nNOS interaction demonstrated by single co-IP without reciprocal validation","Neuroprotection pathway characterized in a single lab","Whether axonal metabotropic signaling occurs at physiological glutamate concentrations unknown"]},{"year":2011,"claim":"NETO2 was identified as an auxiliary subunit that profoundly slows GluK1 desensitization and promotes surface/synaptic targeting, while NETO1 accelerates desensitization, establishing auxiliary proteins as major determinants of GluK1 gating diversity.","evidence":"Patch-clamp in heterologous cells and transfected hippocampal neurons with immunofluorescence","pmids":["21593317"],"confidence":"High","gaps":["Stoichiometry of NETO-GluK1 complexes unknown","Whether NETO proteins differentially affect heteromeric versus homomeric GluK1 receptors not tested"]},{"year":2015,"claim":"GluK1 was shown to be selectively incorporated into silent synapses (lacking AMPA receptors) in a NETO-dependent manner, with NETO-driven synaptic targeting mechanistically separable from surface trafficking; simultaneously, GluK1 was found to directly activate Goα via its C-terminal domain, establishing dual ionotropic/metabotropic signaling.","evidence":"Null-background hippocampal CA1 neuron rescue system with lentiviral expression; proteomics, BRET assays, and co-IP validated in GluK1 knockout mice","pmids":["26720915","25834043"],"confidence":"High","gaps":["Downstream effectors of Goα activated by GluK1 not identified","Whether metabotropic and ionotropic signaling occur at the same synapses is unknown","Molecular mechanism selecting GluK1 for silent synapses not defined"]},{"year":2018,"claim":"The cleaved signal peptide of GluK1 was discovered to interact in trans with the amino-terminal domain to repress forward trafficking, revealing a unique post-cleavage regulatory mechanism that limits GluK1 surface and synaptic expression.","evidence":"Chimeric receptor strategies with EPSC recordings in hippocampal CA1 neurons","pmids":["30451858"],"confidence":"High","gaps":["How the cleaved signal peptide is retained and recycled is unknown","Whether this mechanism is regulated by neuronal activity not tested"]},{"year":null,"claim":"Key unresolved questions include the full-length receptor structure (especially of heteromeric assemblies), the identity of downstream effectors of GluK1-Goα metabotropic signaling, the kinase(s) regulating ER exit via Thr-898 phosphorylation, and how GluK1 is selectively excluded from AMPA receptor-containing synapses at the molecular level.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length GluK1 cryo-EM or crystal structure available","Goα pathway downstream of GluK1 activation uncharacterized","Kinase for Thr-898 not identified","Molecular basis for silent synapse selectivity unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,8,9]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[25,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,5,6,29]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[11,23,24,26]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,2,5,6,7,8,10,17,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[20,25]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[11,26]}],"complexes":["GluK1 homomeric kainate receptor","GluK1/GluK2 heteromeric kainate receptor","GluK1/KA-2 heteromeric kainate receptor"],"partners":["GRIK2","GRIK3","GRIA5","NETO1","NETO2","GNAO1","NOS1"],"other_free_text":[]},"mechanistic_narrative":"GRIK1 (GluK1/GluR5) encodes a kainate-type ionotropic glutamate receptor subunit that assembles as homomers or heteromers with GluK2, GluK3, and KA2 to form ligand-gated cation channels with distinct gating and desensitization properties, and additionally signals metabotropically through direct interaction with Goα proteins via its C-terminal domain [PMID:1977421, PMID:10493729, PMID:25834043]. Channel function is shaped by RNA editing at the Q/R site—which requires an intronic complementary sequence and reduces current density approximately sixfold—by alternative C-terminal splicing that controls ER retention through an Arg-896-dependent signal modulated by phosphorylation, and by auxiliary subunits NETO1 and NETO2 that oppositely tune desensitization kinetics and drive GluK1 selectively to silent synapses [PMID:8700852, PMID:10516295, PMID:14527949, PMID:26720915]. Across brain regions including hippocampus, amygdala, anterior cingulate cortex, and spinal cord, GluK1-containing receptors on interneurons and presynaptic terminals modulate both excitatory and inhibitory transmission—most prominently by depolarizing GABAergic interneurons to increase tonic inhibitory tone onto principal neurons—and contribute to nociceptive processing, gamma oscillation regulation, and neuroprotection against ischemia [PMID:9335499, PMID:10196544, PMID:15509753, PMID:15673679, PMID:18678878]. Structural studies reveal a ligand-binding cavity 40% larger than AMPA receptors, with Ser741 forming a critical interdomain bridge that confers selectivity for bulky kainate-selective agonists such as ATPA, and antagonists inducing a novel hyperextended conformation distinct from other glutamate receptors [PMID:15721240, PMID:15710405, PMID:12488532, PMID:16540562]."},"prefetch_data":{"uniprot":{"accession":"P39086","full_name":"Glutamate receptor ionotropic, kainate 1","aliases":["Excitatory amino acid receptor 3","EAA3","Glutamate receptor 5","GluR-5","GluR5"],"length_aa":918,"mass_kda":104.0,"function":"Ionotropic glutamate receptor that functions as a cation-permeable ligand-gated ion channel, gated by L-glutamate and the glutamatergic agonist kainic acid. L-glutamate acts as an excitatory neurotransmitter at many synapses in the central nervous system. Binding of the excitatory neurotransmitter L-glutamate induces a conformation change, leading to the opening of the cation channel, and thereby converts the chemical signal to an electrical impulse. 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Synthesis, modeling, and molecular pharmacology.","date":"2003","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12672235","citation_count":19,"is_preprint":false},{"pmid":"21619066","id":"PMC_21619066","title":"Selective kainate receptor (GluK1) ligands structurally based upon 1H-cyclopentapyrimidin-2,4(1H,3H)-dione: synthesis, molecular modeling, and pharmacological and biostructural characterization.","date":"2011","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21619066","citation_count":19,"is_preprint":false},{"pmid":"19588945","id":"PMC_19588945","title":"The glutamate receptor GluR5 agonist (S)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid and the 8-methyl analogue: synthesis, molecular pharmacology, and biostructural characterization.","date":"2009","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19588945","citation_count":18,"is_preprint":false},{"pmid":"16948848","id":"PMC_16948848","title":"Presynaptic regulation of the inhibitory transmission by GluR5-containing kainate receptors in spinal substantia gelatinosa.","date":"2006","source":"Molecular pain","url":"https://pubmed.ncbi.nlm.nih.gov/16948848","citation_count":18,"is_preprint":false},{"pmid":"22111545","id":"PMC_22111545","title":"Piperazine-2,3-dicarboxylic acid derivatives as dual antagonists of NMDA and GluK1-containing kainate receptors.","date":"2011","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22111545","citation_count":17,"is_preprint":false},{"pmid":"11354670","id":"PMC_11354670","title":"Synthesis and receptor binding affinity of new selective GluR5 ligands.","date":"2001","source":"Bioorganic & medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11354670","citation_count":17,"is_preprint":false},{"pmid":"21893069","id":"PMC_21893069","title":"Binding and selectivity of the marine toxin neodysiherbaine A and its synthetic analogues to GluK1 and GluK2 kainate receptors.","date":"2011","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21893069","citation_count":16,"is_preprint":false},{"pmid":"31513786","id":"PMC_31513786","title":"The kainate receptor antagonist UBP310 but not single deletion of GluK1, GluK2, or GluK3 subunits, inhibits MPTP-induced degeneration in the mouse midbrain.","date":"2019","source":"Experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/31513786","citation_count":15,"is_preprint":false},{"pmid":"14667236","id":"PMC_14667236","title":"2-arylureidobenzoic acids: selective noncompetitive antagonists for the homomeric kainate receptor subtype GluR5.","date":"2003","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14667236","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50285,"output_tokens":6915,"usd":0.12729},"stage2":{"model":"claude-opus-4-6","input_tokens":10616,"output_tokens":3913,"usd":0.226357},"total_usd":0.353647,"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\": 1990,\n      \"finding\": \"GluR5 (GRIK1) encodes a glutamate receptor subunit that forms homomeric ion channels when expressed in Xenopus oocytes, responding weakly to L-glutamate; it shares ~40-41% amino acid identity with AMPA/kainate receptor subunits GluR1-4, placing it in a distinct kainate receptor subfamily.\",\n      \"method\": \"Xenopus oocyte expression, electrophysiology, cDNA cloning\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in Xenopus oocytes establishing ion channel activity, foundational cloning paper with >500 citations\",\n      \"pmids\": [\"1977421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"RNA editing at the Q/R site of GluR5 pre-mRNA requires base pairing with an intronic editing site complementary sequence (ECS) located up to 1900 nucleotides distal to the Q/R site; double-stranded RNA adenosine deaminase preferentially targets the Q/R site adenosine when coexpressed in HEK293 cells.\",\n      \"method\": \"Minigene transfection in PC-12 cells, HEK293 coexpression, transcript analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic dissection of editing requirement with functional validation in two cell systems\",\n      \"pmids\": [\"8700852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GluR5 subunit-containing kainate receptors regulate GABAergic inhibitory synaptic transmission in hippocampal CA1, as shown by selective agonist ATPA and antagonist LY294486; this modulation of inhibition could contribute to kainate's epileptogenic effects.\",\n      \"method\": \"Hippocampal slice electrophysiology, selective pharmacological tools (ATPA agonist, LY294486 antagonist)\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean pharmacological dissection with selective agonist and antagonist in defined circuit, replicated in multiple subsequent studies\",\n      \"pmids\": [\"9335499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"A single amino acid residue N721 in GluR6 (and its GluR5 counterpart) controls both AMPA sensitivity and domoate deactivation rates; residue A689 in GluR6 controls kainate desensitization rates, as revealed by chimeric and point-mutant receptors.\",\n      \"method\": \"Patch-clamp analysis of chimeric GluR5-GluR6 receptors and point mutants expressed in Xenopus oocytes/HEK cells, ligand binding\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with functional and binding validation identifying specific residues controlling gating\",\n      \"pmids\": [\"9354337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GluR5 and KA-2 subunits co-assemble to form heteromeric kainate receptor channels in trigeminal ganglion neurons; native KA receptor channels in TG neurons resemble recombinant GluR5(R)/KA-2 channels in pharmacological properties, desensitization, rectification, ion permeability, and single-channel conductance.\",\n      \"method\": \"RT-PCR, patch-clamp electrophysiology of acutely dissociated TG neurons, comparison with recombinant receptors in heterologous cells\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — convergent physiological, pharmacological, and molecular evidence for native heteromer composition\",\n      \"pmids\": [\"9254673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Activation of GluR5-containing kainate receptors on hippocampal CA1 interneurons generates inward current and repetitive action potential firing, causing a massive increase in tonic GABAergic inhibition of pyramidal neuron somata and apical dendrites; electrical stimulation of excitatory afferents produces kainate receptor-mediated EPSCs and action potentials in interneurons.\",\n      \"method\": \"Whole-cell patch-clamp in hippocampal slices, selective GluR5 agonist ATPA and antagonist LY293558\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — identified cellular mechanism (interneuron excitation → increased tonic GABA inhibition of pyramidals) with pharmacological dissection, >250 citations\",\n      \"pmids\": [\"10196544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GluR5 subunits contribute to a kainate receptor that presynaptically depresses excitatory synaptic transmission in both CA1 and CA3 hippocampal regions, as demonstrated by ATPA-induced depression of EPSPs/EPSCs and increased paired-pulse facilitation.\",\n      \"method\": \"Field and whole-cell recordings in hippocampal slices, selective GluR5 agonist ATPA and antagonist LY294486\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective pharmacological tools with paired-pulse analysis confirming presynaptic locus\",\n      \"pmids\": [\"9849664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GluR5 kainate receptor-mediated synaptic transmission occurs in the basolateral amygdala (BLA), where high-frequency stimulation of external capsule evokes GluR5-dependent synaptic currents that are inwardly rectifying and blocked by LY293558.\",\n      \"method\": \"Intracellular and whole-cell voltage-clamp recordings in BLA slices, selective AMPA and kainate receptor antagonists\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological isolation of GluR5-mediated synaptic current with clean controls\",\n      \"pmids\": [\"9849665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GluR5, GluR6, and GluR7 kainate receptor subunits coassemble promiscuously to form heteromeric receptors; GluR5/GluR6 heteromers exhibit reduced desensitization and faster recovery from desensitization compared to homomeric GluR5; GluR7 coassembly with GluR6 markedly decreases agonist response amplitude.\",\n      \"method\": \"Coexpression in Xenopus oocytes with selective GluR5 agonists and rectification analysis of edited/unedited Q/R-site subunit combinations\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution with rigorous rectification-based coassembly assay and biophysical characterization\",\n      \"pmids\": [\"10493729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"RNA editing of the Q/R site in GluR5 reduces kainate receptor current density by ~6-fold in dorsal root ganglion sensory neurons; GluR5(R) knock-in mice (encoding arginine at Q/R site) show reduced DRG kainate current density without altered thermal/chemical pain responses.\",\n      \"method\": \"Embryonic stem cell knock-in transgenesis, patch-clamp in acutely isolated DRG neurons from mutant mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic model with direct electrophysiological quantification of editing effect on channel function in native neurons\",\n      \"pmids\": [\"10516295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"GluR5 and GluR6 subunits coassemble into heteromeric kainate receptors in hippocampal GABAergic interneurons; >80% of receptors in co-transfected single HEK293 cells are GluR5/GluR6 heteromers, exhibiting different desensitization and gating properties from homomeric GluR6.\",\n      \"method\": \"Double in situ hybridization in hippocampal slices, patch-clamp electrophysiology in co-transfected HEK293 cells, selective agonist ATPA\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — combined in situ co-expression and functional heteromer verification in heterologous cells\",\n      \"pmids\": [\"10627597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Cell surface expression of GluR5-2b is regulated by a novel endoplasmic reticulum retention signal in the alternatively spliced C-terminal domain; a critical arginine (Arg-896) and surrounding residues mediate ER retention, and phosphorylation-mimicking mutation of Thr-898 promotes ER exit and surface expression.\",\n      \"method\": \"Mutagenesis, heterologous cell transfection, cell surface biotinylation, immunofluorescence in neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis of specific residues with functional trafficking readouts in both heterologous cells and neurons\",\n      \"pmids\": [\"14527949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Topiramate at low concentrations (IC50 ~0.5 µM) selectively inhibits postsynaptic GluR5 kainate receptor-mediated synaptic currents in BLA principal neurons; it reduces miniature EPSC amplitude without affecting frequency, indicating postsynaptic block.\",\n      \"method\": \"Whole-cell voltage-clamp recordings in rat BLA slices, miniature EPSC analysis, paired-pulse experiments\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective pharmacological characterization with multiple electrophysiological approaches confirming postsynaptic mechanism\",\n      \"pmids\": [\"12904467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GluR5 activation selectively depolarizes inhibitory interneurons in the basolateral amygdala, increasing GABA release and tonic GABA current in the BLA; GluR5 genetic deletion or local antagonist injection increases anxiety-like behavior.\",\n      \"method\": \"Whole-cell recordings in BLA slices, GluR5 knockout mice, local antagonist microinjection, behavioral tests\",\n      \"journal\": \"Journal of neurophysiology / PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (electrophysiology, pharmacology, knockout) linking GluR5 activation to interneuron excitation and behavior\",\n      \"pmids\": [\"12091575\", \"17245443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structures of GluR5 and GluR6 ligand binding cores reveal that GluR5 ligand binding cavity is 40% larger than GluR2; extensive interdomain contacts between domains 1 and 2 of GluR5 (absent in AMPA receptors) contribute to high-affinity kainate complex stability; agonist selectivity is determined by steric occlusion within the binding cavity.\",\n      \"method\": \"X-ray crystallography of ligand binding cores in complex with glutamate, 4-methylglutamate, kainate, and quisqualate\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structures providing atomic-level mechanism for ligand selectivity\",\n      \"pmids\": [\"15721240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of GluR5 ligand binding core with (S)-glutamate reveals 26° domain closure; Ser741 stabilizes an interdomain water network and forms an interdomain bridge; GluR5-S1S2 forms a novel dimer interface distinct from GluR2.\",\n      \"method\": \"X-ray crystallography at 1.95 Å resolution\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with structural analysis of binding mechanism\",\n      \"pmids\": [\"15710405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GluR5 selectivity for the agonist ATPA is controlled by Ser741 in GluR5 (vs. Met722 in GluR1); Ser741 stabilizes the active conformation induced by bulky 5-position isoxazole substituents, as demonstrated by mutagenesis.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis of GluR5 and GluR1\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis identifying specific residue determining agonist selectivity with functional validation\",\n      \"pmids\": [\"12488532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GluR5 and GluR6 kainate receptor subunits play distinct roles in hippocampal gamma oscillations: GluR5 ablation increases susceptibility to kainate-induced oscillations/epileptiform activity, while GluR6 ablation prevents them; GluR5-containing KARs on interneuron axons and GluR6-containing KARs in somatodendritic regions underlie distinct network functions.\",\n      \"method\": \"Kainate receptor knockout mice, field potential recordings, computational network modeling\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with defined circuit-level phenotypes and computational validation\",\n      \"pmids\": [\"15509753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GluR5 knockout mice show significantly reduced responses to capsaicin- and inflammation-induced pain but not fear memory, while GluR6 knockouts show reduced fear memory but not pain responses, demonstrating that distinct KAR subtypes control nociception versus fear.\",\n      \"method\": \"GluR5 and GluR6 knockout mice, behavioral pain and fear-memory assays, lateral amygdala synaptic recordings\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with subunit-specific behavioral and electrophysiological phenotypes\",\n      \"pmids\": [\"15673679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structures of GluR5 ligand binding core with selective antagonists UBP302 and UBP310 reveal a novel binding mechanism: antagonists do not contact E723 (unlike all previously solved agonist/antagonist complexes), causing hyperextension of the binding core and a 22 Å extension of ion channel linkers compared to the glutamate-bound form.\",\n      \"method\": \"X-ray crystallography of GluR5-S1S2 complexes with antagonists, radiolabel displacement assays, whole-cell electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structures with functional validation revealing novel antagonist binding mechanism\",\n      \"pmids\": [\"16540562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GluR5 activation in myelinated dorsal column axons increases intraaxonal Ca2+ via both ionotropic and metabotropic (pertussis toxin-sensitive G-protein/PLC-dependent) signaling involving IP3-dependent Ca2+ release; GluR5 co-immunoprecipitates with nNOS and colocalizes with nNOS clusters on internodal axons.\",\n      \"method\": \"Confocal Ca2+ imaging in dorsal column axons, pharmacological dissection, co-immunoprecipitation, immunohistochemistry\",\n      \"journal\": \"Annals of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological approaches with co-IP establishing nNOS interaction; single lab\",\n      \"pmids\": [\"19224531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GluR5-containing KAR activation in vivo exerts neuroprotection against ischemia-reperfusion by facilitating Ca2+-dependent GABA release from interneurons; released GABA activates postsynaptic GABA-A receptors, which attenuates NMDA receptor tyrosine phosphorylation by inhibiting Src kinase activation and disrupting the NR2A-PSD-95-Src signaling module.\",\n      \"method\": \"In vivo ischemia-reperfusion model, patch-clamp recordings, co-immunoprecipitation, antisense oligodeoxynucleotides, selective pharmacological tools\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (pharmacology, antisense, co-IP, electrophysiology) defining signaling pathway; single lab\",\n      \"pmids\": [\"18678878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GluR5 kainate receptors regulate HPA axis stress responses differentially: GluR5 in the paraventricular nucleus tonically inhibits ACTH/corticosterone release, while GluR5 at the median eminence (co-localized with CRH) facilitates restraint-induced ACTH release.\",\n      \"method\": \"In situ hybridization, immunohistochemistry, intra-PVN and intra-median eminence pharmacological infusion, plasma hormone measurements\",\n      \"journal\": \"Psychoneuroendocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and site-specific pharmacological manipulation with hormonal readouts\",\n      \"pmids\": [\"19450932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NETO2 profoundly slows desensitization of GluK1 (GluR5) kainate receptors and promotes plasma membrane localization and synaptic targeting of GluK1-containing receptors in hippocampal neurons; NETO1 increases GluK1 desensitization rate. These effects extend the temporal range of GluK1 gating by over an order of magnitude.\",\n      \"method\": \"Heterologous expression, patch-clamp electrophysiology, transfection of hippocampal neurons, immunofluorescence\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biophysics, localization, synaptic targeting) in heterologous and native neurons\",\n      \"pmids\": [\"21593317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Both NETO1 and NETO2 are auxiliary subunits that profoundly increase GluK1 surface expression and drive GluK1 to synapses in hippocampal CA1 neurons; synaptic targeting by NETO proteins is independent of their role in promoting surface trafficking; GluK1 is selectively incorporated into silent synapses (excluded from AMPA receptor-containing synapses); NETO2 slows GluK1 deactivation and desensitization, while NETO1 speeds desensitization.\",\n      \"method\": \"Hippocampal CA1 null-background system, lentiviral expression, whole-cell patch-clamp, EPSC recordings\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean null-background system with multiple functional and trafficking readouts distinguishing NETO1 vs NETO2 effects\",\n      \"pmids\": [\"26720915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GluK1 C-terminal domain interacts with Goα subunit; GluK1 activates Go proteins as shown by BRET experiments; interaction was validated by in vitro and in vivo co-immunoprecipitation and was absent in GluK1-deficient mice, establishing GluK1 as a mediator of metabotropic (G-protein) as well as ionotropic signaling.\",\n      \"method\": \"Proteomics/mass spectrometry of GluK1 C-terminal interactome, co-immunoprecipitation, BRET assays, GluK1 knockout mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — proteomics discovery validated by reciprocal co-IP, BRET functional assay, and genetic confirmation in knockout mice\",\n      \"pmids\": [\"25834043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The cleaved signal peptide of GluK1 interacts with the amino-terminal domain (ATD) in trans to repress forward trafficking (surface and synaptic expression) of GluK1; chimeric replacement of GluK1 signal peptide with that of GluK2 dramatically increases surface/synaptic expression, and this is suppressed by co-expression of the GluK1 signal peptide.\",\n      \"method\": \"Chimeric receptor strategy, EPSC recordings in hippocampal CA1 neurons, co-expression experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — chimeric and rescue experiments with functional synaptic readouts defining signal peptide-ATD interaction as trafficking mechanism\",\n      \"pmids\": [\"30451858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Homomeric GluR5 receptors expressed in HEK293 cells exhibit striking inter-cell variability in desensitization kinetics (range 1.5 ms to 1.5 s for kainate), suggesting modulation of GluR5 gating by intracellular mechanisms; DRG neurons (likely homomeric GluR5) show biexponential recovery from desensitization similar to fast-desensitizing GluR5 cells.\",\n      \"method\": \"Patch-clamp electrophysiology in HEK293 cells and acutely isolated DRG neurons\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — detailed biophysical characterization identifying variability attributable to intracellular regulation; single lab\",\n      \"pmids\": [\"9824706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GluR5 kainate receptor activation in the anterior cingulate cortex selectively facilitates GABAergic (not glutamatergic) transmission through somatodendritic (not presynaptic) GluR5 in a Ca2+-dependent, voltage-gated Ca2+ channel-dependent manner; endogenous GluR5 activation produces tonic GABA currents in ACC pyramidal neurons.\",\n      \"method\": \"Whole-cell recordings in ACC slices, selective GluR5 agonist/antagonist, GluR5 knockout mice\",\n      \"journal\": \"Developmental neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacology combined with genetic knockout confirming specificity; single lab\",\n      \"pmids\": [\"17443779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GluR5-containing kainate receptors are located presynaptically on inhibitory GABAergic terminals in spinal substantia gelatinosa, where their activation facilitates the frequency (but not amplitude) of both GABAergic and glycinergic IPSCs; this effect is absent in GluR5 knockout mice.\",\n      \"method\": \"Whole-cell recordings in spinal cord slices, ATPA selective agonist, GluR5 knockout mice, miniature IPSC analysis\",\n      \"journal\": \"Molecular pain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacology plus genetic knockout confirming presynaptic locus and subunit identity\",\n      \"pmids\": [\"16948848\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GRIK1 encodes the GluK1 (GluR5) kainate receptor subunit, which assembles as homomers or heteromers (with GluK2, GluK3, or KA2) to form Ca2+-permeable ion channels whose gating, desensitization, and surface trafficking are regulated by RNA editing at the Q/R site, alternative C-terminal splicing (including an ER retention signal controlled by Arg-896 phosphorylation), and auxiliary NETO1/NETO2 proteins; at synapses, GluK1 is selectively targeted to silent synapses by NETO proteins, modulates both excitatory and inhibitory transmission by depolarizing interneurons to increase GABAergic tone onto pyramidal cells, and also signals metabotropically through direct interaction with Goα proteins and, on axons, through a PLC/IP3/nNOS-linked pathway—with its ligand-binding domain selectivity structurally explained by a larger binding cavity and a critical Ser741 residue that accommodates bulky agonists like ATPA.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GRIK1 (GluK1/GluR5) encodes a kainate-type ionotropic glutamate receptor subunit that assembles as homomers or heteromers with GluK2, GluK3, and KA2 to form ligand-gated cation channels with distinct gating and desensitization properties, and additionally signals metabotropically through direct interaction with Goα proteins via its C-terminal domain [PMID:1977421, PMID:10493729, PMID:25834043]. Channel function is shaped by RNA editing at the Q/R site—which requires an intronic complementary sequence and reduces current density approximately sixfold—by alternative C-terminal splicing that controls ER retention through an Arg-896-dependent signal modulated by phosphorylation, and by auxiliary subunits NETO1 and NETO2 that oppositely tune desensitization kinetics and drive GluK1 selectively to silent synapses [PMID:8700852, PMID:10516295, PMID:14527949, PMID:26720915]. Across brain regions including hippocampus, amygdala, anterior cingulate cortex, and spinal cord, GluK1-containing receptors on interneurons and presynaptic terminals modulate both excitatory and inhibitory transmission—most prominently by depolarizing GABAergic interneurons to increase tonic inhibitory tone onto principal neurons—and contribute to nociceptive processing, gamma oscillation regulation, and neuroprotection against ischemia [PMID:9335499, PMID:10196544, PMID:15509753, PMID:15673679, PMID:18678878]. Structural studies reveal a ligand-binding cavity 40% larger than AMPA receptors, with Ser741 forming a critical interdomain bridge that confers selectivity for bulky kainate-selective agonists such as ATPA, and antagonists inducing a novel hyperextended conformation distinct from other glutamate receptors [PMID:15721240, PMID:15710405, PMID:12488532, PMID:16540562].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Cloning of GluR5 established that GRIK1 encodes a glutamate receptor subunit capable of forming functional homomeric ion channels, placing it in a distinct kainate receptor subfamily separate from AMPA receptors.\",\n      \"evidence\": \"cDNA cloning and electrophysiology in Xenopus oocytes\",\n      \"pmids\": [\"1977421\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Homomeric channels responded weakly to glutamate, leaving native subunit composition unknown\", \"No information on in vivo expression pattern or synaptic function\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of the intronic editing site complementary sequence required for Q/R site RNA editing revealed how a post-transcriptional modification alters GluK1 channel properties, resolving how editing specificity is achieved.\",\n      \"evidence\": \"Minigene transfection in PC-12 and HEK293 cells with transcript analysis\",\n      \"pmids\": [\"8700852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The enzyme responsible (ADAR) was coexpressed but isoform specificity not resolved\", \"Functional consequences of editing on native neuronal channels not yet measured\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Heteromeric assembly of GluK1 with KA-2 was demonstrated in trigeminal ganglion neurons, and structure-function mutagenesis identified specific residues (N721, A689) controlling agonist sensitivity and desensitization, establishing that native kainate receptors are heteromers with distinct gating determinants.\",\n      \"evidence\": \"Chimeric/point-mutant electrophysiology in oocytes/HEK cells; RT-PCR and patch-clamp in trigeminal ganglion neurons\",\n      \"pmids\": [\"9354337\", \"9254673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Heteromeric stoichiometry not determined\", \"Whether these residues control gating in intact tetrameric receptors remained unclear\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Pharmacological isolation of GluK1-mediated modulation of GABAergic transmission in hippocampal CA1 first demonstrated a circuit-level function: GluK1 activation on interneurons regulates inhibitory tone and may underlie kainate's epileptogenic effects.\",\n      \"evidence\": \"Hippocampal slice electrophysiology with selective GluK1 agonist ATPA and antagonist LY294486\",\n      \"pmids\": [\"9335499\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GluK1 acted pre- or postsynaptically on interneurons was not resolved\", \"Contribution relative to GluK2-containing receptors remained unclear\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"The cellular mechanism for GluK1's circuit role was resolved: GluK1 activation directly depolarizes CA1 interneurons causing repetitive firing and massive tonic GABAergic inhibition of pyramidal neurons, while presynaptic GluK1 also depresses excitatory transmission in hippocampus and mediates postsynaptic currents in the basolateral amygdala.\",\n      \"evidence\": \"Whole-cell patch-clamp in hippocampal and BLA slices with selective pharmacology; paired-pulse analysis\",\n      \"pmids\": [\"10196544\", \"9849664\", \"9849665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether amygdala and hippocampal GluK1 receptors have identical subunit compositions was unknown\", \"Metabotropic signaling component not yet suspected\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"GluK1 was shown to promiscuously coassemble with GluK2 and GluK3, producing heteromers with altered desensitization; separately, Q/R site editing was shown to reduce native DRG kainate current density sixfold in knock-in mice, quantifying editing's physiological impact.\",\n      \"evidence\": \"Coexpression in Xenopus oocytes with rectification analysis; GluR5(R) knock-in mice with DRG patch-clamp\",\n      \"pmids\": [\"10493729\", \"10516295\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Behavioral consequences of reduced DRG current were minimal, leaving the in vivo purpose of editing uncertain\", \"Native heteromer combinations in specific brain regions not mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Multiple trafficking and selectivity mechanisms were resolved: an ER retention signal at Arg-896 in the GluK1-2b splice variant controls surface expression via phosphorylation at Thr-898; Ser741 was identified as the critical residue conferring GluK1 selectivity for the agonist ATPA; and GluK1 in the BLA was shown to modulate interneuron excitability and anxiety-related behavior.\",\n      \"evidence\": \"Mutagenesis with surface biotinylation; oocyte electrophysiology of point mutants; BLA recordings in knockout mice with behavioral assays\",\n      \"pmids\": [\"14527949\", \"12488532\", \"12091575\", \"17245443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for Thr-898 phosphorylation not identified\", \"Whether ER retention mechanism operates in all neuron types unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Crystal structures of the GluK1 ligand-binding domain revealed a 40% larger binding cavity than AMPA receptors, with Ser741 mediating an interdomain water network and a novel dimer interface, providing the atomic basis for kainate receptor agonist selectivity and explaining prior mutagenesis results.\",\n      \"evidence\": \"X-ray crystallography at 1.95 Å resolution with multiple ligands\",\n      \"pmids\": [\"15721240\", \"15710405\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length receptor structure not available\", \"No structural insight into desensitization or heteromeric assemblies\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic dissociation of GluK1 versus GluK2 functions showed that GluK1 loss increases susceptibility to kainate-induced epileptiform activity and reduces inflammatory/capsaicin pain responses without affecting fear memory, defining subunit-specific behavioral roles.\",\n      \"evidence\": \"GluK1 and GluK2 knockout mice with gamma oscillation recordings, pain assays, and fear conditioning\",\n      \"pmids\": [\"15509753\", \"15673679\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensatory changes in knockout mice not assessed\", \"Circuit mechanism linking GluK1 loss to increased seizure susceptibility not fully explained\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"A novel antagonist binding mechanism was revealed structurally—GluK1-selective antagonists UBP302/UBP310 do not contact E723, causing hyperextension of the binding core—while presynaptic GluK1 on spinal inhibitory terminals was shown to facilitate GABA/glycine release.\",\n      \"evidence\": \"X-ray crystallography of antagonist complexes; spinal cord slice electrophysiology with GluK1 knockout mice\",\n      \"pmids\": [\"16540562\", \"16948848\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the hyperextended conformation represents the resting or a distinct inhibited state is unclear\", \"Mechanism coupling presynaptic GluK1 activation to vesicle release not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"GluK1 was found to signal metabotropically on myelinated axons through a pertussis toxin-sensitive G-protein/PLC/IP3 pathway coupled to nNOS, and GluK1-mediated neuroprotection against ischemia was linked to enhanced GABA release that attenuates NMDA receptor signaling via Src kinase inhibition.\",\n      \"evidence\": \"Confocal Ca²⁺ imaging and co-immunoprecipitation in dorsal column axons; in vivo ischemia model with antisense knockdown and pharmacology\",\n      \"pmids\": [\"19224531\", \"18678878\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"nNOS interaction demonstrated by single co-IP without reciprocal validation\", \"Neuroprotection pathway characterized in a single lab\", \"Whether axonal metabotropic signaling occurs at physiological glutamate concentrations unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"NETO2 was identified as an auxiliary subunit that profoundly slows GluK1 desensitization and promotes surface/synaptic targeting, while NETO1 accelerates desensitization, establishing auxiliary proteins as major determinants of GluK1 gating diversity.\",\n      \"evidence\": \"Patch-clamp in heterologous cells and transfected hippocampal neurons with immunofluorescence\",\n      \"pmids\": [\"21593317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of NETO-GluK1 complexes unknown\", \"Whether NETO proteins differentially affect heteromeric versus homomeric GluK1 receptors not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"GluK1 was shown to be selectively incorporated into silent synapses (lacking AMPA receptors) in a NETO-dependent manner, with NETO-driven synaptic targeting mechanistically separable from surface trafficking; simultaneously, GluK1 was found to directly activate Goα via its C-terminal domain, establishing dual ionotropic/metabotropic signaling.\",\n      \"evidence\": \"Null-background hippocampal CA1 neuron rescue system with lentiviral expression; proteomics, BRET assays, and co-IP validated in GluK1 knockout mice\",\n      \"pmids\": [\"26720915\", \"25834043\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effectors of Goα activated by GluK1 not identified\", \"Whether metabotropic and ionotropic signaling occur at the same synapses is unknown\", \"Molecular mechanism selecting GluK1 for silent synapses not defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The cleaved signal peptide of GluK1 was discovered to interact in trans with the amino-terminal domain to repress forward trafficking, revealing a unique post-cleavage regulatory mechanism that limits GluK1 surface and synaptic expression.\",\n      \"evidence\": \"Chimeric receptor strategies with EPSC recordings in hippocampal CA1 neurons\",\n      \"pmids\": [\"30451858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the cleaved signal peptide is retained and recycled is unknown\", \"Whether this mechanism is regulated by neuronal activity not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the full-length receptor structure (especially of heteromeric assemblies), the identity of downstream effectors of GluK1-Goα metabotropic signaling, the kinase(s) regulating ER exit via Thr-898 phosphorylation, and how GluK1 is selectively excluded from AMPA receptor-containing synapses at the molecular level.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length GluK1 cryo-EM or crystal structure available\", \"Goα pathway downstream of GluK1 activation uncharacterized\", \"Kinase for Thr-898 not identified\", \"Molecular basis for silent synapse selectivity unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [25, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 5, 6, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [11, 23, 24, 26]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 2, 5, 6, 7, 8, 10, 17, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [20, 25]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [11, 26]}\n    ],\n    \"complexes\": [\n      \"GluK1 homomeric kainate receptor\",\n      \"GluK1/GluK2 heteromeric kainate receptor\",\n      \"GluK1/KA-2 heteromeric kainate receptor\"\n    ],\n    \"partners\": [\n      \"GRIK2\",\n      \"GRIK3\",\n      \"GRIA5\",\n      \"NETO1\",\n      \"NETO2\",\n      \"GNAO1\",\n      \"NOS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}