{"gene":"GRIK3","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1997,"finding":"GluR7 (GRIK3) and its splice variant GluR7b are functional kainate receptor subunits with unique pharmacological properties; glutamate exhibits ~10-fold lower potency for GluR7-mediated currents compared to other non-NMDA receptor channels, establishing GluR7 as a low-sensitivity glutamate receptor.","method":"Electrophysiology (whole-cell patch-clamp) in Xenopus oocytes and HEK cells expressing recombinant receptors","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — in vitro electrophysiological reconstitution with pharmacological characterization; foundational paper with 151 citations","pmids":["9390526"],"is_preprint":false},{"year":1999,"finding":"GluK3 (GluR7) coassembles with GluK1 (GluR5) and GluK2 (GluR6) to form heteromeric kainate receptors; coassembly of GluK3 with GluK2 markedly decreases agonist response amplitude, demonstrating a dominant-negative-like modulatory role in heteromeric assemblies.","method":"Electrophysiology with selective agonists (ATPA, I-will) and rectification analysis in Xenopus oocytes; pharmacological dissection of subunit coassembly","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution with pharmacological validation; 113 citations, multiple orthogonal approaches","pmids":["10493729"],"is_preprint":false},{"year":2001,"finding":"The functional differences between GluK3 (GluR7) and GluK2 (GluR6) ion channel properties are localized to the extracellular loop domain L3; specific point mutations in GluK3 restore measurable currents in Xenopus oocytes, and the C-terminal half of L3 determines relative agonist efficacies (glutamate vs. kainate), while the S1 portion of the agonist-binding domain governs the high EC50 for glutamate.","method":"Domain-swap chimeras and point mutagenesis expressed in Xenopus oocytes; electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — structure-function mutagenesis with electrophysiological readout; active-site domain mapping","pmids":["11160421"],"is_preprint":false},{"year":2007,"finding":"GluK3 (GluR7) is an essential subunit of presynaptic kainate autoreceptors at hippocampal mossy fiber synapses; GluK3 knockout mice display markedly reduced short- and long-term synaptic potentiation, and presynaptic KARs are GluK2/GluK3 heteromers localized within synapses with low glutamate sensitivity and likely Ca2+-permeable properties.","method":"GluR7 knockout mice, electrophysiology at mossy fiber synapses, coassembly demonstrated by coexpression in HEK cells, immunolocalization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined synaptic phenotype, reciprocal coassembly validation, localization; 119 citations, multiple orthogonal methods","pmids":["17620617"],"is_preprint":false},{"year":2005,"finding":"Alternative splicing of GluK3 (GluR7) at the C-terminal domain (GluR7a vs. GluR7b) regulates surface expression; GluR7a is highly expressed at the plasma membrane via a stretch of positively charged amino acids, whereas GluR7b is mostly retained in the endoplasmic reticulum. GluR7a promotes surface expression of ER-retained subunit splice variants when assembled into heteromeric KARs.","method":"Live-cell imaging, surface biotinylation, and trafficking assays in cultured hippocampal neurons from wild-type and KAR mutant mice; ER retention analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct localization with functional consequence, multiple cell systems, clean mechanistic dissection","pmids":["15805114"],"is_preprint":false},{"year":2008,"finding":"UBP302, UBP310, and UBP316 effectively block recombinant homomeric GluK3 receptors but are ineffective against homomeric GluK2 or heteromeric GluK2/GluK3 receptors; GYKI 53655 (AMPA receptor antagonist) blocks GluK3-containing receptors at high concentrations and decreases short-term plasticity at mossy fiber synapses.","method":"Fast-application electrophysiology in HEK293 cells expressing recombinant receptors; field recordings at hippocampal mossy fiber synapses","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with pharmacological characterization at recombinant and native receptors","pmids":["18761361"],"is_preprint":false},{"year":2010,"finding":"Crystal structures of GluK3 amino-terminal domain (ATD) reveal it crystallizes as a dimer with a strikingly different dimer assembly at the R1 interface compared to GluK5, while the R2 domain dimer assembly is similar to other non-NMDA iGluRs; extensive intramolecular contacts between R1 and R2 restrict domain movement compared to NMDA receptors, consistent with GluK4/GluK5 requiring obligate coassembly with GluK1-GluK3.","method":"X-ray crystallography of ATD","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional interpretation","pmids":["20951142"],"is_preprint":false},{"year":2011,"finding":"X-ray crystal structure of the GluK3 ligand-binding domain (LBD) in complex with glutamate at 1.6 Å resolution reveals a conserved glutamate binding mode; GluK3 shows slightly lower domain closure around glutamate compared to other kainate receptors, and its LBD is less stabilized through interlobe interactions than GluK1, contributing to faster desensitization kinetics; key residues distinguishing GluK3 binding site are Thr520, Ala691, Asn722, Leu736, and Thr742.","method":"X-ray crystallography of LBD in complex with (S)-glutamate","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with mechanistic interpretation of desensitization","pmids":["21907808"],"is_preprint":false},{"year":2011,"finding":"Endocytosis of GluK3b controls its polarized trafficking; a dileucine motif on the cytoplasmic C-terminal domain of GluK3b drives clathrin- and dynamin2-dependent internalization followed by degradation in heterologous cells, hippocampal neurons, and dentate granule cells; GluK3b is differentially endocytosed in dendrites compared to axons, providing a mechanism for polarized KAR distribution.","method":"Live-cell imaging, surface biotinylation, dominant-negative dynamin2 and clathrin constructs, organotypic slice cultures","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — direct localization with functional consequence, multiple systems and molecular dissection","pmids":["21832194"],"is_preprint":false},{"year":2012,"finding":"Zinc potentiates GluK3 currents at 10–100 μM by reducing desensitization; a specific zinc-binding site is formed at the base of the LBD dimer interface by a GluK3-specific residue Asp759 together with conserved His762 and Asp730 from the partner subunit; zinc stabilizes the labile GluK3 dimer interface to slow desensitization; GluK2/GluK3 tetramers are assembled as pairs of heterodimeric LBDs.","method":"Crystallography of LBD, site-directed mutagenesis, whole-cell electrophysiology (kinetic analysis and desensitization mutants)","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — reconstitution + crystal structure + mutagenesis with functional validation; multiple orthogonal methods in single study","pmids":["23141068"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM structures of GluK3 in desensitized and resting/closed states reveal that antagonist-bound GluK3 traps a resting state with only two LBD domains in dimeric arrangement; N-linked glycans at the interface of GluK3 ATD and LBD mediate inter-domain interactions that modulate receptor gating properties, with mutational analysis identifying putative N-glycan interacting residues.","method":"Single-particle cryo-electron microscopy; site-directed mutagenesis; functional electrophysiology","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with mutagenesis and functional validation","pmids":["31311973"],"is_preprint":false},{"year":2020,"finding":"SEZ6 controls glycosylation and cell surface localization of GluK2/GluK3-containing kainate receptors; loss of SEZ6 reduces surface levels of GluK2/3 in primary neurons and reduces kainate-evoked currents in CA1 neurons; mechanistically, SEZ6 prevents HNK-1 glycan modification of GluK2/3, interacts with GluK2 through its ectodomain, and promotes post-ER transport of GluK2 in the secretory pathway.","method":"Co-immunoprecipitation, surface biotinylation, whole-cell electrophysiology in hippocampal slices, in vitro and in vivo SEZ6 KO models","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, KO with defined electrophysiological phenotype, glycosylation biochemistry; multiple orthogonal methods","pmids":["32567721"],"is_preprint":false},{"year":2020,"finding":"Cryo-EM of full-length GluK3 in apo-state and in complex with agonist kainate or antagonist UBP301 reveals receptor transitions between desensitized and closed states; a 'non-classical' conformation of the neurotransmitter-binding domain is observed in the closed state, distinct from AMPA and other kainate receptors; molecular dynamics simulations show Asp759 influences LBD dimer stability, with lower dimer stability explaining faster desensitization and low agonist sensitivity of GluK3.","method":"Cryo-electron microscopy; molecular dynamics simulations","journal":"International journal of biological macromolecules","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structural analysis with computational validation; consistent with prior biochemical findings","pmids":["32006583"],"is_preprint":false},{"year":2024,"finding":"GluK3 KO mice in pure C57BL/6N background display anxiolytic-like behavior and reduced dopamine D2 receptor (D2R) expression in the striatum, with alteration in D2R-induced anxiety; biochemical studies confirm that GluK3 subunits do not coassemble with GluK4 or GluK5 subunits in mouse cortex.","method":"Genetic KO mice, behavioral assays, co-immunoprecipitation/biochemical fractionation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined behavioral phenotype and biochemical subunit assembly validation; single lab, moderate methods","pmids":["38402313"],"is_preprint":false},{"year":2024,"finding":"Crystal structure of H523A-mutated GluK3 LBD dimer identifies binding sites for BPAM344 (positive allosteric modulator), zinc, sodium, and chloride ions at the dimer interface; molecular dynamics simulations implicate Asp761, Asp790, and Glu797 in zinc ion binding; cryo-EM of full-length GluK3 with glutamate and BPAM344 shows a dimer-of-dimers arrangement.","method":"X-ray crystallography; molecular dynamics simulations; cryo-electron microscopy; fluorescence-based functional assays","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure + cryo-EM + functional assays + MD simulations; multiple orthogonal methods","pmids":["38145505"],"is_preprint":false},{"year":2026,"finding":"Neto1 and Neto2 auxiliary subunits differentially regulate GluK3 gating kinetics: both slow desensitization and relieve polyamine block, but Neto1 accelerates and Neto2 decelerates recovery from desensitization; Neto2 acts synergistically with zinc to produce profound facilitation of peak GluK3 currents; the D759G mutation at the LBD dimer interface zinc-binding site unmasks a secondary inhibitory zinc-binding site; cryo-EM confirms D759G promotes a more compact LBD arrangement.","method":"Whole-cell electrophysiology; site-directed mutagenesis (D759G); cryo-electron microscopy","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 1 — electrophysiology with mutagenesis and cryo-EM structural validation; multiple orthogonal methods in single study","pmids":["41680489"],"is_preprint":false},{"year":1994,"finding":"Human GluK3 (EAA5) expressed in COS-1 cells binds kainate with a dissociation constant of ~2.72 nM, ~20-30 fold higher affinity than rat GluR7; a Ser310Ala variation at position 310 in the extracellular N-terminal region was identified, originally attributed to RNA editing but later reclassified as a genomic polymorphism.","method":"Ligand binding studies with transfected COS-1 cell membranes; cDNA cloning and sequencing","journal":"Receptors & channels","confidence":"Medium","confidence_rationale":"Tier 2 — direct ligand binding assay with recombinant protein; single lab","pmids":["7719709"],"is_preprint":false},{"year":2000,"finding":"The human GluK3 Ser310Ala variant is a genomic single nucleotide polymorphism (T/G at position 928), not RNA editing; whole-cell patch-clamp in HEK-293 cells expressing the two isoforms detected no differences in receptor activation or desensitization, indicating the polymorphism does not affect basic channel function.","method":"Patch-clamp electrophysiology in HEK-293 cells; allele-specific expression analysis in human brain tissue","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 1–2 — direct functional comparison of receptor variants with electrophysiology; single lab but rigorous","pmids":["11124978"],"is_preprint":false}],"current_model":"GluK3 (GRIK3) is a kainate-type ionotropic glutamate receptor subunit with uniquely low agonist sensitivity, whose homomeric and heteromeric (GluK2/GluK3) channels are defined by a labile ligand-binding domain dimer interface (involving Asp759) that drives rapid desensitization; surface trafficking is controlled by C-terminal splice variant-specific motifs and the trafficking factor SEZ6, presynaptic localization at hippocampal mossy fiber synapses requires GluK3 as an essential subunit of GluK2/GluK3 autoreceptors that facilitate synaptic transmission, and receptor function is multilayeredly modulated by zinc (which stabilizes the LBD dimer interface to slow desensitization) and by Neto1/Neto2 auxiliary subunits that differentially tune desensitization kinetics and zinc potentiation."},"narrative":{"teleology":[{"year":1994,"claim":"Initial cloning and ligand-binding characterization of human GluK3 established it as a high-affinity kainate-binding subunit and identified a Ser310Ala variant originally misattributed to RNA editing.","evidence":"Ligand binding assays in transfected COS-1 cells; cDNA sequencing","pmids":["7719709"],"confidence":"Medium","gaps":["Binding affinity measured in isolation; no channel function recorded","Species-specific affinity differences unexplained"]},{"year":1997,"claim":"Functional reconstitution revealed that GluK3 forms channels with ~10-fold lower glutamate potency than other non-NMDA receptors, establishing its defining low-sensitivity pharmacological profile.","evidence":"Whole-cell patch-clamp in Xenopus oocytes and HEK cells expressing recombinant GluK3","pmids":["9390526"],"confidence":"High","gaps":["Structural basis for low potency unknown","Heteromeric assembly properties not yet characterized"]},{"year":1999,"claim":"Demonstration that GluK3 coassembles with GluK1 and GluK2 into heteromeric kainate receptors, with GluK3 exerting a dominant-negative effect on agonist response amplitude, established its modulatory role in heteromeric assemblies.","evidence":"Electrophysiology with selective agonists and rectification analysis in Xenopus oocytes","pmids":["10493729"],"confidence":"High","gaps":["Stoichiometry of heteromeric assemblies not determined","In vivo relevance of dominant-negative effect untested"]},{"year":2001,"claim":"Domain-swap chimeras and point mutations mapped the structural determinants of GluK3's low agonist sensitivity to the S1 portion of the ligand-binding domain and relative agonist efficacies to the L3 extracellular loop, resolving which domains encode its unique pharmacology.","evidence":"Chimeric constructs and point mutagenesis with electrophysiology in Xenopus oocytes","pmids":["11160421"],"confidence":"High","gaps":["No atomic-resolution structure yet available","Desensitization determinants not addressed"]},{"year":2005,"claim":"Discovery that alternative C-terminal splicing dictates GluK3 surface expression—GluK3a reaches the plasma membrane via a polybasic motif while GluK3b is ER-retained—provided the first trafficking mechanism for KAR subunit-specific localization.","evidence":"Live-cell imaging, surface biotinylation in hippocampal neurons and heterologous cells","pmids":["15805114"],"confidence":"High","gaps":["Endocytic fate of surface GluK3b not yet characterized","In vivo relevance at specific synapses not tested"]},{"year":2007,"claim":"GluK3 knockout mice revealed that GluK3 is an essential subunit of presynaptic GluK2/GluK3 autoreceptors at mossy fiber synapses, required for both short- and long-term potentiation, establishing the first defined physiological role for GluK3 in native circuits.","evidence":"GluK3 KO mice; electrophysiology at mossy fiber synapses; coassembly validation in HEK cells; immunolocalization","pmids":["17620617"],"confidence":"High","gaps":["Downstream signaling cascade from presynaptic KAR activation not defined","Calcium permeability of native GluK2/GluK3 heteromers inferred but not directly measured"]},{"year":2011,"claim":"Two advances clarified GluK3 desensitization and polarized trafficking: crystal structures of the GluK3 LBD revealed reduced domain closure and weaker interlobe stabilization explaining fast desensitization, while identification of a dileucine motif in GluK3b driving clathrin/dynamin2-dependent endocytosis explained its axon-enriched distribution.","evidence":"X-ray crystallography of LBD-glutamate complex at 1.6 Å; live-cell imaging, dominant-negative constructs in neurons and organotypic slices","pmids":["21907808","21832194"],"confidence":"High","gaps":["Full-length receptor structure not yet available","Endocytic adaptor linking dileucine motif to clathrin not identified"]},{"year":2012,"claim":"Crystallographic and electrophysiological identification of a zinc-binding site at the GluK3 LBD dimer interface (Asp759/His762/Asp730) revealed how zinc stabilizes the labile dimer to slow desensitization and potentiate currents, and showed GluK2/GluK3 tetramers assemble as pairs of heterodimeric LBDs.","evidence":"LBD crystallography, site-directed mutagenesis, whole-cell kinetic analysis","pmids":["23141068"],"confidence":"High","gaps":["Physiological zinc concentration at mossy fiber synapses not directly correlated with GluK3 modulation in vivo","Whether zinc binding affects presynaptic KAR function at mossy fibers untested"]},{"year":2019,"claim":"Cryo-EM structures of full-length GluK3 in resting and desensitized states revealed that only two of four LBD domains maintain dimeric arrangement in the antagonist-bound state, and identified N-glycan-mediated ATD-LBD interactions that modulate gating.","evidence":"Single-particle cryo-EM; site-directed mutagenesis; electrophysiology","pmids":["31311973"],"confidence":"High","gaps":["Open-state structure not captured","Functional significance of the two-dimer resting arrangement versus four-dimer arrangements in other KARs not fully resolved"]},{"year":2020,"claim":"Two studies advanced understanding of GluK3 conformational dynamics and trafficking: cryo-EM with MD simulations confirmed Asp759 as a key determinant of LBD dimer instability and a 'non-classical' closed-state LBD conformation, while SEZ6 was identified as a trafficking factor that controls GluK2/GluK3 glycosylation and surface delivery.","evidence":"Cryo-EM, MD simulations, Co-IP, surface biotinylation, electrophysiology in SEZ6 KO hippocampal slices","pmids":["32006583","32567721"],"confidence":"High","gaps":["Direct SEZ6-GluK3 interaction not demonstrated (interaction shown with GluK2)","Structural basis for SEZ6-mediated glycosylation control unknown"]},{"year":2024,"claim":"Structural and behavioral studies defined allosteric modulator and ion binding sites at the GluK3 LBD dimer interface and linked GluK3 loss to anxiolytic behavior and reduced striatal D2R expression, expanding GluK3's known roles beyond mossy fiber plasticity.","evidence":"X-ray crystallography and cryo-EM of LBD with BPAM344/zinc/ions; GluK3 KO behavioral assays and Co-IP in mouse cortex","pmids":["38145505","38402313"],"confidence":"High","gaps":["In vivo efficacy of BPAM344 not tested","Mechanism linking GluK3 loss to D2R downregulation not established","Single behavioral study in one genetic background"]},{"year":2026,"claim":"Neto1 and Neto2 auxiliary subunits were shown to differentially modulate GluK3: both slow desensitization, but Neto1 accelerates and Neto2 decelerates recovery; Neto2 synergizes with zinc for profound current facilitation, and D759G mutation unmasked a secondary inhibitory zinc site, revealing multilayered allosteric control.","evidence":"Whole-cell electrophysiology with Neto coexpression; D759G mutagenesis; cryo-EM","pmids":["41680489"],"confidence":"High","gaps":["Native stoichiometry of Neto/GluK3 complexes at mossy fiber synapses unknown","Identity of secondary inhibitory zinc site not structurally resolved"]},{"year":null,"claim":"Key open questions include the structural basis of the GluK3 open/conducting state, the signaling cascade downstream of presynaptic GluK2/GluK3 activation, and the mechanism by which GluK3 loss alters dopamine D2 receptor expression.","evidence":"","pmids":[],"confidence":"High","gaps":["No open-state structure of GluK3","Presynaptic signaling downstream of GluK2/GluK3 autoreceptors undefined","Molecular link between GluK3 and D2R expression unknown","In vivo role of Neto-mediated modulation of GluK3 at synapses untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,8,11]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4,8]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,3,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,13]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,8,11]}],"complexes":["GluK2/GluK3 heteromeric kainate receptor"],"partners":["GRIK2","NETO1","NETO2","SEZ6","GRIK1"],"other_free_text":[]},"mechanistic_narrative":"GRIK3 encodes GluK3, a kainate-type ionotropic glutamate receptor subunit distinguished by uniquely low agonist sensitivity and rapid desensitization, properties determined by its S1 ligand-binding domain and a labile LBD dimer interface centered on residue Asp759 [PMID:9390526, PMID:11160421, PMID:23141068]. GluK3 assembles primarily with GluK2 to form presynaptic heteromeric autoreceptors at hippocampal mossy fiber synapses, where it is essential for both short- and long-term synaptic potentiation; GluK3 knockout mice show impaired mossy fiber plasticity and anxiolytic-like behavior with reduced striatal dopamine D2 receptor expression [PMID:17620617, PMID:38402313]. Surface trafficking is governed by C-terminal splice variant–specific motifs—GluK3a carries a polybasic sequence promoting plasma membrane delivery, while GluK3b contains a dileucine motif driving clathrin/dynamin2-dependent endocytosis and polarized axonal enrichment—and is further regulated by the trafficking factor SEZ6, which controls glycosylation and post-ER transport of GluK2/GluK3 complexes [PMID:15805114, PMID:21832194, PMID:32567721]. Receptor function is multilayeredly modulated by zinc, which stabilizes the LBD dimer interface to slow desensitization, and by Neto1/Neto2 auxiliary subunits that differentially tune desensitization and recovery kinetics, with Neto2 acting synergistically with zinc to profoundly facilitate GluK3 currents [PMID:23141068, PMID:41680489]."},"prefetch_data":{"uniprot":{"accession":"Q13003","full_name":"Glutamate receptor ionotropic, kainate 3","aliases":["Excitatory amino acid receptor 5","EAA5","Glutamate receptor 7","GluR-7","GluR7"],"length_aa":919,"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. 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. The receptor then desensitizes rapidly and enters a transient inactive state, characterized by the presence of bound agonist (PubMed:7719709). In association with GRIK2, involved in presynaptic facilitation of glutamate release at hippocampal mossy fiber synapses (By similarity)","subcellular_location":"Cell membrane; Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q13003/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GRIK3","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GRIK3","total_profiled":1310},"omim":[{"mim_id":"621003","title":"TRANSCRIPTION FACTOR Sp9; SP9","url":"https://www.omim.org/entry/621003"},{"mim_id":"614155","title":"MICRO RNA 1292; MIR1292","url":"https://www.omim.org/entry/614155"},{"mim_id":"600283","title":"GLUTAMATE RECEPTOR, IONOTROPIC, KAINATE 5; GRIK5","url":"https://www.omim.org/entry/600283"},{"mim_id":"600282","title":"GLUTAMATE RECEPTOR, IONOTROPIC, KAINATE 4; GRIK4","url":"https://www.omim.org/entry/600282"},{"mim_id":"138244","title":"GLUTAMATE RECEPTOR, IONOTROPIC, KAINATE 2; GRIK2","url":"https://www.omim.org/entry/138244"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":10.6},{"tissue":"intestine","ntpm":7.4},{"tissue":"pituitary gland","ntpm":8.6}],"url":"https://www.proteinatlas.org/search/GRIK3"},"hgnc":{"alias_symbol":["GluK3","GLUR7"],"prev_symbol":[]},"alphafold":{"accession":"Q13003","domains":[{"cath_id":"3.40.50.2300","chopping":"35-154_316-371","consensus_level":"high","plddt":87.3911,"start":35,"end":371},{"cath_id":"3.40.50.2300","chopping":"157-284_400-417","consensus_level":"high","plddt":89.0335,"start":157,"end":417},{"cath_id":"3.40.190.10","chopping":"432-539","consensus_level":"high","plddt":91.0382,"start":432,"end":539},{"cath_id":"3.40.190.10","chopping":"543-550_667-762","consensus_level":"high","plddt":88.3427,"start":543,"end":762},{"cath_id":"-","chopping":"557-664_820-875","consensus_level":"high","plddt":80.5775,"start":557,"end":875}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13003","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13003-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13003-F1-predicted_aligned_error_v6.png","plddt_mean":82.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GRIK3","jax_strain_url":"https://www.jax.org/strain/search?query=GRIK3"},"sequence":{"accession":"Q13003","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13003.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13003/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13003"}},"corpus_meta":[{"pmid":"9390526","id":"PMC_9390526","title":"Rat GluR7 and a carboxy-terminal splice variant, GluR7b, are functional kainate receptor subunits with a low sensitivity to glutamate.","date":"1997","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/9390526","citation_count":151,"is_preprint":false},{"pmid":"9832144","id":"PMC_9832144","title":"Expression of NMDAR1, GluR1, GluR7, and KA1 glutamate receptor mRNAs is decreased in frontal cortex of \"neuroleptic-free\" schizophrenics: evidence on reversible up-regulation by typical neuroleptics.","date":"1998","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9832144","citation_count":145,"is_preprint":false},{"pmid":"8478682","id":"PMC_8478682","title":"Expression of glutamate receptor genes in the mammalian retina: the localization of GluR1 through GluR7 mRNAs.","date":"1993","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/8478682","citation_count":137,"is_preprint":false},{"pmid":"17620617","id":"PMC_17620617","title":"GluR7 is an essential subunit of presynaptic kainate autoreceptors at hippocampal mossy fiber synapses.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17620617","citation_count":119,"is_preprint":false},{"pmid":"10493729","id":"PMC_10493729","title":"Heteromeric kainate receptors formed by the coassembly of GluR5, GluR6, and GluR7.","date":"1999","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10493729","citation_count":113,"is_preprint":false},{"pmid":"18761361","id":"PMC_18761361","title":"Antagonism of recombinant and native GluK3-containing kainate receptors.","date":"2008","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/18761361","citation_count":68,"is_preprint":false},{"pmid":"11986986","id":"PMC_11986986","title":"Association between the ionotropic glutamate receptor kainate 3 (GRIK3) ser310ala polymorphism and schizophrenia.","date":"2002","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/11986986","citation_count":64,"is_preprint":false},{"pmid":"16958029","id":"PMC_16958029","title":"Association of the human kainate receptor GluR7 gene (GRIK3) with recurrent major depressive disorder.","date":"2007","source":"American journal of medical genetics. 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glutamate exhibits ~10-fold lower potency for GluR7-mediated currents compared to other non-NMDA receptor channels, establishing GluR7 as a low-sensitivity glutamate receptor.\",\n      \"method\": \"Electrophysiology (whole-cell patch-clamp) in Xenopus oocytes and HEK cells expressing recombinant receptors\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro electrophysiological reconstitution with pharmacological characterization; foundational paper with 151 citations\",\n      \"pmids\": [\"9390526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GluK3 (GluR7) coassembles with GluK1 (GluR5) and GluK2 (GluR6) to form heteromeric kainate receptors; coassembly of GluK3 with GluK2 markedly decreases agonist response amplitude, demonstrating a dominant-negative-like modulatory role in heteromeric assemblies.\",\n      \"method\": \"Electrophysiology with selective agonists (ATPA, I-will) and rectification analysis in Xenopus oocytes; pharmacological dissection of subunit coassembly\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution with pharmacological validation; 113 citations, multiple orthogonal approaches\",\n      \"pmids\": [\"10493729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The functional differences between GluK3 (GluR7) and GluK2 (GluR6) ion channel properties are localized to the extracellular loop domain L3; specific point mutations in GluK3 restore measurable currents in Xenopus oocytes, and the C-terminal half of L3 determines relative agonist efficacies (glutamate vs. kainate), while the S1 portion of the agonist-binding domain governs the high EC50 for glutamate.\",\n      \"method\": \"Domain-swap chimeras and point mutagenesis expressed in Xenopus oocytes; electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structure-function mutagenesis with electrophysiological readout; active-site domain mapping\",\n      \"pmids\": [\"11160421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GluK3 (GluR7) is an essential subunit of presynaptic kainate autoreceptors at hippocampal mossy fiber synapses; GluK3 knockout mice display markedly reduced short- and long-term synaptic potentiation, and presynaptic KARs are GluK2/GluK3 heteromers localized within synapses with low glutamate sensitivity and likely Ca2+-permeable properties.\",\n      \"method\": \"GluR7 knockout mice, electrophysiology at mossy fiber synapses, coassembly demonstrated by coexpression in HEK cells, immunolocalization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined synaptic phenotype, reciprocal coassembly validation, localization; 119 citations, multiple orthogonal methods\",\n      \"pmids\": [\"17620617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Alternative splicing of GluK3 (GluR7) at the C-terminal domain (GluR7a vs. GluR7b) regulates surface expression; GluR7a is highly expressed at the plasma membrane via a stretch of positively charged amino acids, whereas GluR7b is mostly retained in the endoplasmic reticulum. GluR7a promotes surface expression of ER-retained subunit splice variants when assembled into heteromeric KARs.\",\n      \"method\": \"Live-cell imaging, surface biotinylation, and trafficking assays in cultured hippocampal neurons from wild-type and KAR mutant mice; ER retention analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, multiple cell systems, clean mechanistic dissection\",\n      \"pmids\": [\"15805114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UBP302, UBP310, and UBP316 effectively block recombinant homomeric GluK3 receptors but are ineffective against homomeric GluK2 or heteromeric GluK2/GluK3 receptors; GYKI 53655 (AMPA receptor antagonist) blocks GluK3-containing receptors at high concentrations and decreases short-term plasticity at mossy fiber synapses.\",\n      \"method\": \"Fast-application electrophysiology in HEK293 cells expressing recombinant receptors; field recordings at hippocampal mossy fiber synapses\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with pharmacological characterization at recombinant and native receptors\",\n      \"pmids\": [\"18761361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structures of GluK3 amino-terminal domain (ATD) reveal it crystallizes as a dimer with a strikingly different dimer assembly at the R1 interface compared to GluK5, while the R2 domain dimer assembly is similar to other non-NMDA iGluRs; extensive intramolecular contacts between R1 and R2 restrict domain movement compared to NMDA receptors, consistent with GluK4/GluK5 requiring obligate coassembly with GluK1-GluK3.\",\n      \"method\": \"X-ray crystallography of ATD\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional interpretation\",\n      \"pmids\": [\"20951142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"X-ray crystal structure of the GluK3 ligand-binding domain (LBD) in complex with glutamate at 1.6 Å resolution reveals a conserved glutamate binding mode; GluK3 shows slightly lower domain closure around glutamate compared to other kainate receptors, and its LBD is less stabilized through interlobe interactions than GluK1, contributing to faster desensitization kinetics; key residues distinguishing GluK3 binding site are Thr520, Ala691, Asn722, Leu736, and Thr742.\",\n      \"method\": \"X-ray crystallography of LBD in complex with (S)-glutamate\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with mechanistic interpretation of desensitization\",\n      \"pmids\": [\"21907808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Endocytosis of GluK3b controls its polarized trafficking; a dileucine motif on the cytoplasmic C-terminal domain of GluK3b drives clathrin- and dynamin2-dependent internalization followed by degradation in heterologous cells, hippocampal neurons, and dentate granule cells; GluK3b is differentially endocytosed in dendrites compared to axons, providing a mechanism for polarized KAR distribution.\",\n      \"method\": \"Live-cell imaging, surface biotinylation, dominant-negative dynamin2 and clathrin constructs, organotypic slice cultures\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, multiple systems and molecular dissection\",\n      \"pmids\": [\"21832194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Zinc potentiates GluK3 currents at 10–100 μM by reducing desensitization; a specific zinc-binding site is formed at the base of the LBD dimer interface by a GluK3-specific residue Asp759 together with conserved His762 and Asp730 from the partner subunit; zinc stabilizes the labile GluK3 dimer interface to slow desensitization; GluK2/GluK3 tetramers are assembled as pairs of heterodimeric LBDs.\",\n      \"method\": \"Crystallography of LBD, site-directed mutagenesis, whole-cell electrophysiology (kinetic analysis and desensitization mutants)\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution + crystal structure + mutagenesis with functional validation; multiple orthogonal methods in single study\",\n      \"pmids\": [\"23141068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structures of GluK3 in desensitized and resting/closed states reveal that antagonist-bound GluK3 traps a resting state with only two LBD domains in dimeric arrangement; N-linked glycans at the interface of GluK3 ATD and LBD mediate inter-domain interactions that modulate receptor gating properties, with mutational analysis identifying putative N-glycan interacting residues.\",\n      \"method\": \"Single-particle cryo-electron microscopy; site-directed mutagenesis; functional electrophysiology\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mutagenesis and functional validation\",\n      \"pmids\": [\"31311973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SEZ6 controls glycosylation and cell surface localization of GluK2/GluK3-containing kainate receptors; loss of SEZ6 reduces surface levels of GluK2/3 in primary neurons and reduces kainate-evoked currents in CA1 neurons; mechanistically, SEZ6 prevents HNK-1 glycan modification of GluK2/3, interacts with GluK2 through its ectodomain, and promotes post-ER transport of GluK2 in the secretory pathway.\",\n      \"method\": \"Co-immunoprecipitation, surface biotinylation, whole-cell electrophysiology in hippocampal slices, in vitro and in vivo SEZ6 KO models\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, KO with defined electrophysiological phenotype, glycosylation biochemistry; multiple orthogonal methods\",\n      \"pmids\": [\"32567721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cryo-EM of full-length GluK3 in apo-state and in complex with agonist kainate or antagonist UBP301 reveals receptor transitions between desensitized and closed states; a 'non-classical' conformation of the neurotransmitter-binding domain is observed in the closed state, distinct from AMPA and other kainate receptors; molecular dynamics simulations show Asp759 influences LBD dimer stability, with lower dimer stability explaining faster desensitization and low agonist sensitivity of GluK3.\",\n      \"method\": \"Cryo-electron microscopy; molecular dynamics simulations\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structural analysis with computational validation; consistent with prior biochemical findings\",\n      \"pmids\": [\"32006583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GluK3 KO mice in pure C57BL/6N background display anxiolytic-like behavior and reduced dopamine D2 receptor (D2R) expression in the striatum, with alteration in D2R-induced anxiety; biochemical studies confirm that GluK3 subunits do not coassemble with GluK4 or GluK5 subunits in mouse cortex.\",\n      \"method\": \"Genetic KO mice, behavioral assays, co-immunoprecipitation/biochemical fractionation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined behavioral phenotype and biochemical subunit assembly validation; single lab, moderate methods\",\n      \"pmids\": [\"38402313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Crystal structure of H523A-mutated GluK3 LBD dimer identifies binding sites for BPAM344 (positive allosteric modulator), zinc, sodium, and chloride ions at the dimer interface; molecular dynamics simulations implicate Asp761, Asp790, and Glu797 in zinc ion binding; cryo-EM of full-length GluK3 with glutamate and BPAM344 shows a dimer-of-dimers arrangement.\",\n      \"method\": \"X-ray crystallography; molecular dynamics simulations; cryo-electron microscopy; fluorescence-based functional assays\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + cryo-EM + functional assays + MD simulations; multiple orthogonal methods\",\n      \"pmids\": [\"38145505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Neto1 and Neto2 auxiliary subunits differentially regulate GluK3 gating kinetics: both slow desensitization and relieve polyamine block, but Neto1 accelerates and Neto2 decelerates recovery from desensitization; Neto2 acts synergistically with zinc to produce profound facilitation of peak GluK3 currents; the D759G mutation at the LBD dimer interface zinc-binding site unmasks a secondary inhibitory zinc-binding site; cryo-EM confirms D759G promotes a more compact LBD arrangement.\",\n      \"method\": \"Whole-cell electrophysiology; site-directed mutagenesis (D759G); cryo-electron microscopy\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — electrophysiology with mutagenesis and cryo-EM structural validation; multiple orthogonal methods in single study\",\n      \"pmids\": [\"41680489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Human GluK3 (EAA5) expressed in COS-1 cells binds kainate with a dissociation constant of ~2.72 nM, ~20-30 fold higher affinity than rat GluR7; a Ser310Ala variation at position 310 in the extracellular N-terminal region was identified, originally attributed to RNA editing but later reclassified as a genomic polymorphism.\",\n      \"method\": \"Ligand binding studies with transfected COS-1 cell membranes; cDNA cloning and sequencing\",\n      \"journal\": \"Receptors & channels\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ligand binding assay with recombinant protein; single lab\",\n      \"pmids\": [\"7719709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The human GluK3 Ser310Ala variant is a genomic single nucleotide polymorphism (T/G at position 928), not RNA editing; whole-cell patch-clamp in HEK-293 cells expressing the two isoforms detected no differences in receptor activation or desensitization, indicating the polymorphism does not affect basic channel function.\",\n      \"method\": \"Patch-clamp electrophysiology in HEK-293 cells; allele-specific expression analysis in human brain tissue\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — direct functional comparison of receptor variants with electrophysiology; single lab but rigorous\",\n      \"pmids\": [\"11124978\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GluK3 (GRIK3) is a kainate-type ionotropic glutamate receptor subunit with uniquely low agonist sensitivity, whose homomeric and heteromeric (GluK2/GluK3) channels are defined by a labile ligand-binding domain dimer interface (involving Asp759) that drives rapid desensitization; surface trafficking is controlled by C-terminal splice variant-specific motifs and the trafficking factor SEZ6, presynaptic localization at hippocampal mossy fiber synapses requires GluK3 as an essential subunit of GluK2/GluK3 autoreceptors that facilitate synaptic transmission, and receptor function is multilayeredly modulated by zinc (which stabilizes the LBD dimer interface to slow desensitization) and by Neto1/Neto2 auxiliary subunits that differentially tune desensitization kinetics and zinc potentiation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GRIK3 encodes GluK3, a kainate-type ionotropic glutamate receptor subunit distinguished by uniquely low agonist sensitivity and rapid desensitization, properties determined by its S1 ligand-binding domain and a labile LBD dimer interface centered on residue Asp759 [PMID:9390526, PMID:11160421, PMID:23141068]. GluK3 assembles primarily with GluK2 to form presynaptic heteromeric autoreceptors at hippocampal mossy fiber synapses, where it is essential for both short- and long-term synaptic potentiation; GluK3 knockout mice show impaired mossy fiber plasticity and anxiolytic-like behavior with reduced striatal dopamine D2 receptor expression [PMID:17620617, PMID:38402313]. Surface trafficking is governed by C-terminal splice variant–specific motifs—GluK3a carries a polybasic sequence promoting plasma membrane delivery, while GluK3b contains a dileucine motif driving clathrin/dynamin2-dependent endocytosis and polarized axonal enrichment—and is further regulated by the trafficking factor SEZ6, which controls glycosylation and post-ER transport of GluK2/GluK3 complexes [PMID:15805114, PMID:21832194, PMID:32567721]. Receptor function is multilayeredly modulated by zinc, which stabilizes the LBD dimer interface to slow desensitization, and by Neto1/Neto2 auxiliary subunits that differentially tune desensitization and recovery kinetics, with Neto2 acting synergistically with zinc to profoundly facilitate GluK3 currents [PMID:23141068, PMID:41680489].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Initial cloning and ligand-binding characterization of human GluK3 established it as a high-affinity kainate-binding subunit and identified a Ser310Ala variant originally misattributed to RNA editing.\",\n      \"evidence\": \"Ligand binding assays in transfected COS-1 cells; cDNA sequencing\",\n      \"pmids\": [\"7719709\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding affinity measured in isolation; no channel function recorded\", \"Species-specific affinity differences unexplained\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Functional reconstitution revealed that GluK3 forms channels with ~10-fold lower glutamate potency than other non-NMDA receptors, establishing its defining low-sensitivity pharmacological profile.\",\n      \"evidence\": \"Whole-cell patch-clamp in Xenopus oocytes and HEK cells expressing recombinant GluK3\",\n      \"pmids\": [\"9390526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for low potency unknown\", \"Heteromeric assembly properties not yet characterized\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstration that GluK3 coassembles with GluK1 and GluK2 into heteromeric kainate receptors, with GluK3 exerting a dominant-negative effect on agonist response amplitude, established its modulatory role in heteromeric assemblies.\",\n      \"evidence\": \"Electrophysiology with selective agonists and rectification analysis in Xenopus oocytes\",\n      \"pmids\": [\"10493729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of heteromeric assemblies not determined\", \"In vivo relevance of dominant-negative effect untested\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Domain-swap chimeras and point mutations mapped the structural determinants of GluK3's low agonist sensitivity to the S1 portion of the ligand-binding domain and relative agonist efficacies to the L3 extracellular loop, resolving which domains encode its unique pharmacology.\",\n      \"evidence\": \"Chimeric constructs and point mutagenesis with electrophysiology in Xenopus oocytes\",\n      \"pmids\": [\"11160421\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution structure yet available\", \"Desensitization determinants not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that alternative C-terminal splicing dictates GluK3 surface expression—GluK3a reaches the plasma membrane via a polybasic motif while GluK3b is ER-retained—provided the first trafficking mechanism for KAR subunit-specific localization.\",\n      \"evidence\": \"Live-cell imaging, surface biotinylation in hippocampal neurons and heterologous cells\",\n      \"pmids\": [\"15805114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic fate of surface GluK3b not yet characterized\", \"In vivo relevance at specific synapses not tested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"GluK3 knockout mice revealed that GluK3 is an essential subunit of presynaptic GluK2/GluK3 autoreceptors at mossy fiber synapses, required for both short- and long-term potentiation, establishing the first defined physiological role for GluK3 in native circuits.\",\n      \"evidence\": \"GluK3 KO mice; electrophysiology at mossy fiber synapses; coassembly validation in HEK cells; immunolocalization\",\n      \"pmids\": [\"17620617\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling cascade from presynaptic KAR activation not defined\", \"Calcium permeability of native GluK2/GluK3 heteromers inferred but not directly measured\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Two advances clarified GluK3 desensitization and polarized trafficking: crystal structures of the GluK3 LBD revealed reduced domain closure and weaker interlobe stabilization explaining fast desensitization, while identification of a dileucine motif in GluK3b driving clathrin/dynamin2-dependent endocytosis explained its axon-enriched distribution.\",\n      \"evidence\": \"X-ray crystallography of LBD-glutamate complex at 1.6 Å; live-cell imaging, dominant-negative constructs in neurons and organotypic slices\",\n      \"pmids\": [\"21907808\", \"21832194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length receptor structure not yet available\", \"Endocytic adaptor linking dileucine motif to clathrin not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Crystallographic and electrophysiological identification of a zinc-binding site at the GluK3 LBD dimer interface (Asp759/His762/Asp730) revealed how zinc stabilizes the labile dimer to slow desensitization and potentiate currents, and showed GluK2/GluK3 tetramers assemble as pairs of heterodimeric LBDs.\",\n      \"evidence\": \"LBD crystallography, site-directed mutagenesis, whole-cell kinetic analysis\",\n      \"pmids\": [\"23141068\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological zinc concentration at mossy fiber synapses not directly correlated with GluK3 modulation in vivo\", \"Whether zinc binding affects presynaptic KAR function at mossy fibers untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Cryo-EM structures of full-length GluK3 in resting and desensitized states revealed that only two of four LBD domains maintain dimeric arrangement in the antagonist-bound state, and identified N-glycan-mediated ATD-LBD interactions that modulate gating.\",\n      \"evidence\": \"Single-particle cryo-EM; site-directed mutagenesis; electrophysiology\",\n      \"pmids\": [\"31311973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Open-state structure not captured\", \"Functional significance of the two-dimer resting arrangement versus four-dimer arrangements in other KARs not fully resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two studies advanced understanding of GluK3 conformational dynamics and trafficking: cryo-EM with MD simulations confirmed Asp759 as a key determinant of LBD dimer instability and a 'non-classical' closed-state LBD conformation, while SEZ6 was identified as a trafficking factor that controls GluK2/GluK3 glycosylation and surface delivery.\",\n      \"evidence\": \"Cryo-EM, MD simulations, Co-IP, surface biotinylation, electrophysiology in SEZ6 KO hippocampal slices\",\n      \"pmids\": [\"32006583\", \"32567721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SEZ6-GluK3 interaction not demonstrated (interaction shown with GluK2)\", \"Structural basis for SEZ6-mediated glycosylation control unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Structural and behavioral studies defined allosteric modulator and ion binding sites at the GluK3 LBD dimer interface and linked GluK3 loss to anxiolytic behavior and reduced striatal D2R expression, expanding GluK3's known roles beyond mossy fiber plasticity.\",\n      \"evidence\": \"X-ray crystallography and cryo-EM of LBD with BPAM344/zinc/ions; GluK3 KO behavioral assays and Co-IP in mouse cortex\",\n      \"pmids\": [\"38145505\", \"38402313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo efficacy of BPAM344 not tested\", \"Mechanism linking GluK3 loss to D2R downregulation not established\", \"Single behavioral study in one genetic background\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Neto1 and Neto2 auxiliary subunits were shown to differentially modulate GluK3: both slow desensitization, but Neto1 accelerates and Neto2 decelerates recovery; Neto2 synergizes with zinc for profound current facilitation, and D759G mutation unmasked a secondary inhibitory zinc site, revealing multilayered allosteric control.\",\n      \"evidence\": \"Whole-cell electrophysiology with Neto coexpression; D759G mutagenesis; cryo-EM\",\n      \"pmids\": [\"41680489\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native stoichiometry of Neto/GluK3 complexes at mossy fiber synapses unknown\", \"Identity of secondary inhibitory zinc site not structurally resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the structural basis of the GluK3 open/conducting state, the signaling cascade downstream of presynaptic GluK2/GluK3 activation, and the mechanism by which GluK3 loss alters dopamine D2 receptor expression.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No open-state structure of GluK3\", \"Presynaptic signaling downstream of GluK2/GluK3 autoreceptors undefined\", \"Molecular link between GluK3 and D2R expression unknown\", \"In vivo role of Neto-mediated modulation of GluK3 at synapses untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 8, 11]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 8, 11]}\n    ],\n    \"complexes\": [\n      \"GluK2/GluK3 heteromeric kainate receptor\"\n    ],\n    \"partners\": [\n      \"GRIK2\",\n      \"NETO1\",\n      \"NETO2\",\n      \"SEZ6\",\n      \"GRIK1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}