Affinage

GRIK4

Glutamate receptor ionotropic, kainate 4 · UniProt Q16099

Length
956 aa
Mass
107.2 kDa
Annotated
2026-04-28
47 papers in source corpus 11 papers cited in narrative 11 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

GRIK4 encodes the GluK4 (KA1) high-affinity kainate receptor subunit, which functions as a critical modulator of excitatory synaptic transmission, synaptic plasticity, and excitatory/inhibitory balance in forebrain circuits. The GluK4 ligand-binding domain adopts a hybrid architecture with AMPA-receptor-like binding-site residues and kainate-receptor-like domain closure, accounting for its high kainate affinity (PMID:27524200). In the adult brain, GluK4 expression is concentrated in hippocampal CA3 and dentate gyrus, where it regulates mossy fiber long-term potentiation (PMID:22203159), mediates kainate-induced excitotoxic neurodegeneration downstream of extracellular matrix laminin proteolysis via JNK signaling (PMID:19114596, PMID:23357115), and—when overexpressed—shifts excitatory/inhibitory balance in hippocampal and amygdala circuits to produce social impairment, anxiety, and depressive phenotypes that are reversible upon normalization of expression (PMID:26446216, PMID:29949767).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1994 High

    Establishing GRIK4 as a distinct genomic locus on human 11q22.3 resolved confusion with the related GRIK5 (KA2) gene and enabled targeted genetic studies.

    Evidence FISH and somatic cell hybrid mapping in human, mouse, and rat

    PMID:7527545

    Open questions at the time
    • No functional data at this stage
    • Genomic organization and regulatory elements uncharacterized
  2. 2000 Medium

    Defining the spatio-temporal expression profile revealed that GluK4, broadly expressed during development, becomes restricted to hippocampal CA3 and dentate gyrus in the adult, and localizes to postsynaptic dendrites rather than presynaptic mossy fiber terminals.

    Evidence YAC-Cre reporter transgenic mice for promoter activity; anti-peptide antibody immunohistochemistry and electron microscopy for protein localization

    PMID:10973593 PMID:11000488

    Open questions at the time
    • Functional significance of dendritic versus presynaptic localization not tested
    • Glial expression detected but physiological role unexplored
    • Protein localization based on single antibody without genetic validation
  3. 2008 High

    Placing GluK4 downstream of extracellular matrix laminin proteolysis in an excitotoxic cascade revealed a previously unknown non-synaptic signaling axis through which ECM remodeling drives neuronal death via kainate receptor upregulation.

    Evidence Conditional laminin gamma1 KO, tPA KO mice, plasmin-digested laminin infusion, and anti-KA1 antibody blockade in vivo and in vitro

    PMID:19114596

    Open questions at the time
    • Exact mechanism by which laminin fragments upregulate GluK4 protein not defined
    • Downstream intracellular death pathway not fully mapped at this point
  4. 2011 High

    Loss-of-function analysis via Grik4 knockout demonstrated that GluK4 is required for normal mossy fiber LTP and modulates anxiety- and depression-related behaviors, establishing direct causal links between this subunit and hippocampal synaptic plasticity and affective behavior.

    Evidence Grik4 KO mice with electrophysiological LTP recordings and multiple behavioral paradigms

    PMID:22203159

    Open questions at the time
    • Whether LTP impairment is cell-autonomous or circuit-level not resolved
    • Compensatory changes in other kainate receptor subunits not assessed
  5. 2013 High

    Extended KO phenotyping revealed GluK4's role in spatial memory, sensorimotor gating, and excitotoxic neurodegeneration, and identified the JNK pathway as a downstream effector of GluK4-mediated excitotoxicity.

    Evidence Grik4 KO mice, Morris water maze, pre-pulse inhibition, intrahippocampal kainate and hypoxia-ischemia models, Western blotting for JNK cascade

    PMID:23357115

    Open questions at the time
    • JNK pathway link based on biochemical correlation, not direct epistasis or rescue
    • Relative contribution of GluK4 versus other kainate subunits to excitotoxicity unclear
  6. 2015 High

    Gain-of-function analysis showed that forebrain GluK4 overexpression enhances hippocampal trisynaptic circuit transmission and produces ASD-like social and affective behavioral abnormalities, demonstrating that GluK4 dosage is a critical determinant of circuit function and behavior.

    Evidence Forebrain-specific Grik4-overexpressing transgenic mice with behavioral testing and electrophysiology

    PMID:26446216

    Open questions at the time
    • Whether phenotypes reflect pre- or postsynaptic GluK4 action not distinguished
    • Molecular mechanism linking increased GluK4 to enhanced transmission not resolved
  7. 2016 High

    The crystal structure of the GluK4 ligand-binding domain provided the first atomic-resolution view explaining its high kainate affinity through a hybrid structural mechanism combining AMPA-like binding residues with kainate-receptor-like domain closure.

    Evidence X-ray crystallography at 2.05 Å, thermofluor assay, radiolabel binding

    PMID:27524200

    Open questions at the time
    • Full-length receptor structure unavailable
    • How LBD conformation couples to channel gating in GluK4-containing heteromers not determined
  8. 2018 High

    Demonstrating that GluK4 overexpression persistently shifts excitatory/inhibitory balance in amygdala output circuits—and that this is reversible upon normalization—established GluK4 dosage as a tunable regulator of forebrain E/I balance with therapeutic implications.

    Evidence Grik4-overexpressing transgenic mice with electrophysiology, circuit analysis, and genetic normalization of expression

    PMID:29949767

    Open questions at the time
    • Molecular basis of reversibility not defined
    • Whether amygdala phenotype is direct or secondary to hippocampal changes not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the full-length heteromeric receptor structure, the mechanism of GluK4 upregulation by laminin fragments, the direct substrates connecting GluK4 activation to JNK signaling, and whether postsynaptic versus presynaptic GluK4 pools differentially contribute to plasticity and behavior.
  • No full-length GluK4-containing heteromeric receptor structure
  • Mechanism of GluK4 upregulation by ECM laminin fragments undefined
  • Direct link between GluK4 activation and JNK pathway not established by epistasis

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 2
Localization
GO:0005829 cytosol 1 GO:0005886 plasma membrane 1
Pathway
R-HSA-112316 Neuronal System 3 R-HSA-162582 Signal Transduction 2 R-HSA-5357801 Programmed Cell Death 2
Partners
GRIK5LAMC1

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2016 Crystal structure of the GluK4 (GRIK4) ligand-binding domain (LBD) with kainate at 2.05 Å resolution revealed that binding-site residues in GluK4 are most similar to the AMPA receptor subfamily, while the domain closure and D1-D2 interlobe contacts induced by kainate resemble those of the low-affinity kainate receptor GluK1, providing a structural explanation for GluK4's high kainate binding affinity. X-ray crystallography, thermofluor assay, radiolabel binding affinity measurements Structure High 27524200
2011 Genetic ablation of GluK4 (Grik4 knockout mice) produced anxiolytic and antidepressant-like behavior and impaired mossy fiber long-term potentiation, demonstrating GluK4's role in modulating presynaptic mossy fiber excitability and hippocampal synaptic plasticity. Grik4 knockout mouse model, behavioral tests (elevated zero-maze, marble-burying, forced swim test, sucrose preference), electrophysiological LTP recordings at mossy fiber synapses Behavioural brain research High 22203159
2013 GluK4 knockout mice showed impairments in spatial memory acquisition and recall, marked hyperactivity, impaired pre-pulse inhibition, and robust neuroprotection against kainate-induced excitotoxicity in hippocampal CA3. Biochemical analysis suggested GluK4 acts through the JNK pathway to regulate excitotoxic molecular cascades. Grik4 knockout mouse model, Morris water maze, pre-pulse inhibition testing, intrahippocampal kainate injection, hypoxia-ischemia model, Western blotting for JNK pathway components Neuroscience High 23357115
2008 Proteolytic fragments of laminin (generated by plasmin via tPA) up-regulate the KA1 (GluK4) kainate receptor subunit in the hippocampus following kainate injection, and blocking KA1 function with a specific anti-KA1 antibody protected against kainate-induced neuronal death both in vitro and in vivo, placing KA1 downstream of ECM proteolysis in a novel excitotoxic neurodegeneration pathway. Conditional laminin gamma1 knockout mice, tPA knockout mice, intrahippocampal infusion of plasmin-digested laminin-1, anti-KA1 antibody blockade in vitro and in vivo, Western blotting The Journal of cell biology High 19114596
2015 Forebrain overexpression of Grik4 (GluK4) in mice produced social impairment, enhanced anxiety, and depressive states, accompanied by altered synaptic transmission with more efficient information transfer through the hippocampal trisynaptic circuit, demonstrating that increased GluK4 dosage alters excitatory synaptic function and reproduces autism spectrum disorder-like behavioral features. Grik4-overexpressing transgenic mice (forebrain-specific), behavioral tests, electrophysiological recordings of hippocampal trisynaptic circuit The Journal of neuroscience High 26446216
2018 Mild gain of Grik4 dosage in forebrain enhances synaptic transmission, causing a persistent imbalance in inhibitory and excitatory activity and disturbing amygdala output circuits; these changes in glutamatergic activity were reversible when Grik4 levels were normalized. Grik4-overexpressing transgenic mice, electrophysiological recordings, circuit-level analysis of amygdala outputs, genetic normalization of Grik4 expression Cell reports High 29949767
2008 A deletion variant within the 3' UTR of GRIK4 associated with protection against bipolar disorder was found to increase transcript abundance, likely by altering RNA secondary structure, suggesting the protective genetic effect is mediated through increased kainate receptor expression. Case-control genetic association studies (discovery and replication), mRNA expression quantification, RNA secondary structure prediction Proceedings of the National Academy of Sciences of the United States of America Medium 18824690
2000 KA1 (GluK4) immunoreactivity in the CNS was localized to dendritic structures in CA3 postsynaptic to commissural-associational fibers (not mossy fiber terminals), CA1 pyramidal cell apical dendrites, layer V cortical pyramidal neurons, Purkinje cells and their dendrites, Bergmann glia, oligodendrocytes, and astrocytes, indicating a broader CNS distribution than previously thought. Novel anti-peptide antibody immunohistochemistry, electron microscopy, in vitro cell culture immunostaining Brain research. Molecular brain research Medium 11000488
2000 During early brain development KA1 gene promoter activity is widespread across all major brain areas, but in the adult brain expression becomes restricted to hippocampal CA3 pyramidal and dentate gyrus granule cells, establishing the developmental spatio-temporal expression profile of GRIK4. Yeast artificial chromosome (YAC) transgenic mice expressing Cre from KA1 promoter; Cre immunohistochemistry; X-gal staining of double-transgenic KA1-Cre/lacZ indicator mice Brain research Medium 10973593
1994 GRIK4 was chromosomally mapped to human chromosome 11q22.3, mouse chromosome 9, and rat chromosome 8, establishing it as a distinct locus from GRIK5 (KA2) which maps to separate chromosomes in all species. Southern analysis of somatic cell hybrid panels, fluorescence in situ hybridization (FISH), interspecific backcross mapping Proceedings of the National Academy of Sciences of the United States of America High 7527545
2010 KA1 (GluK4) subunit mRNA and protein are expressed in the substantia gelatinosa of the trigeminal subnucleus caudalis and expression decreases with postnatal development, suggesting age-dependent KA1 expression as a potential mechanism of age-dependent pain perception. RT-PCR, Western blot, immunohistochemistry in juvenile, prepubescent, and adult mice Journal of veterinary science Low 21113098

Source papers

Stage 0 corpus · 47 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 Association of GRIK4 with outcome of antidepressant treatment in the STAR*D cohort. The American journal of psychiatry 156 17671280
1998 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. Journal of neurochemistry 145 9832144
2006 Cytogenetic and genetic evidence supports a role for the kainate-type glutamate receptor gene, GRIK4, in schizophrenia and bipolar disorder. Molecular psychiatry 91 16819533
2007 Are some genetic risk factors common to schizophrenia, bipolar disorder and depression? Evidence from DISC1, GRIK4 and NRG1. Neurotoxicity research 54 17449450
2008 A common variant in the 3'UTR of the GRIK4 glutamate receptor gene affects transcript abundance and protects against bipolar disorder. Proceedings of the National Academy of Sciences of the United States of America 53 18824690
2011 Genetic ablation of the GluK4 kainate receptor subunit causes anxiolytic and antidepressant-like behavior in mice. Behavioural brain research 47 22203159
2002 Sphingomonas sp. strain KA1, carrying a carbazole dioxygenase gene homologue, degrades chlorinated dibenzo-p-dioxins in soil. FEMS microbiology letters 45 12052549
1996 The effect of chronic haloperidol treatment on glutamate receptor subunit (GluR1, GluR2, KA1, KA2, NR1) mRNAs and glutamate binding protein mRNA in rat forebrain. Neuroscience letters 45 8843098
2015 Increased Dosage of High-Affinity Kainate Receptor Gene grik4 Alters Synaptic Transmission and Reproduces Autism Spectrum Disorders Features. The Journal of neuroscience : the official journal of the Society for Neuroscience 44 26446216
2005 Association study of polymorphisms in the GluR7, KA1 and KA2 kainate receptor genes (GRIK3, GRIK4, GRIK5) with schizophrenia. Psychiatry research 40 16325263
2013 The GluK4 kainate receptor subunit regulates memory, mood, and excitotoxic neurodegeneration. Neuroscience 38 23357115
2013 1p34.3 deletion involving GRIK3: Further clinical implication of GRIK family glutamate receptors in the pathogenesis of developmental delay. American journal of medical genetics. Part A 31 24449200
2018 Increased Grik4 Gene Dosage Causes Imbalanced Circuit Output and Human Disease-Related Behaviors. Cell reports 29 29949767
2017 AMPA, NMDA and kainate glutamate receptor subunits are expressed in human peripheral blood mononuclear cells (PBMCs) where the expression of GluK4 is altered by pregnancy and GluN2D by depression in pregnant women. Journal of neuroimmunology 24 28284346
2016 Molecular determinants of KA1 domain-mediated autoinhibition and phospholipid activation of MARK1 kinase. The Biochemical journal 24 27879374
2014 GRIK4 polymorphism and its association with antidepressant response in depressed patients: a meta-analysis. Pharmacogenomics 24 25303296
2000 KA1-like kainate receptor subunit immunoreactivity in neurons and glia using a novel anti-peptide antibody. Brain research. Molecular brain research 23 11000488
2012 AKAP13, CACNA1, GRIK4 and GRIA1 genetic variations may be associated with haloperidol efficacy during acute treatment. European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology 21 22980146
2015 The role of GRIK4 gene in treatment-resistant depression. Genetics research 20 26139080
2018 Structural Basis for MARK1 Kinase Autoinhibition by Its KA1 Domain. Structure (London, England : 1993) 19 30099988
2008 Proteolytic fragments of laminin promote excitotoxic neurodegeneration by up-regulation of the KA1 subunit of the kainate receptor. The Journal of cell biology 19 19114596
1994 The genes encoding the glutamate receptor subunits KA1 and KA2 (GRIK4 and GRIK5) are located on separate chromosomes in human, mouse, and rat. Proceedings of the National Academy of Sciences of the United States of America 19 7527545
2012 Failure to replicate influence of GRIK4 and GNB3 polymorphisms on treatment outcome in major depression. Neuropsychobiology 18 22222462
2000 Developmental profile of kainate receptor subunit KA1 revealed by Cre expression in YAC transgenic mice. Brain research 17 10973593
2016 Influence of GRIK4 genetic variants on the electroconvulsive therapy response. Neuroscience letters 13 27222927
1996 Contrasting effects of electroconvulsive shock on mRNAs encoding the high affinity kainate receptor subunits (KA1 and KA2) and cyclophilin in the rat. Brain research 12 8963683
2015 KA1-targeted regulatory domain mutations activate Chk1 in the absence of DNA damage. Scientific reports 11 26039276
2016 The Structure of a High-Affinity Kainate Receptor: GluK4 Ligand-Binding Domain Crystallized with Kainate. Structure (London, England : 1993) 10 27524200
2018 Chk1 KA1 domain auto-phosphorylation stimulates biological activity and is linked to rapid proteasomal degradation. Scientific reports 9 30510197
2015 Optimization of crude oil degradation by Dietzia cinnamea KA1, capable of biosurfactant production. Journal of basic microbiology 9 26615815
2008 No genetic association between polymorphisms in the kainate-type glutamate receptor gene, GRIK4, and schizophrenia in the Chinese population. Progress in neuro-psychopharmacology & biological psychiatry 8 18289755
2024 GRIK phosphorylates and activates KIN10 which also promotes its degradation. Frontiers in plant science 7 38590740
2012 Synaptic Pattern of KA1 and KA2 upon the Direction-Selective Ganglion Cells in Developing and Adult Mouse Retina. Acta histochemica et cytochemica 7 22489103
2019 GRIK4 and GRM7 gene may be potential indicator of venlafaxine treatment reponses in Chinese of Han ethnicity. Medicine 6 31083176
2018 A kainate receptor GluK4 deletion, protective against bipolar disorder, is associated with enhanced cognitive performance across diagnoses in the TwinsUK cohort. The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry 6 29243543
2008 Crystallization and preliminary X-ray diffraction studies of a novel ferredoxin involved in the dioxygenation of carbazole by Novosphingobium sp. KA1. Acta crystallographica. Section F, Structural biology and crystallization communications 5 18607094
2020 Impact of GRIK4 gene polymorphisms on cognitive dysfunction in patients with major depression. Revue neurologique 4 32245654
2017 Common variants in GRIK4 and major depressive disorder: An association study in the Chinese Han population. Neuroscience letters 4 28583584
2010 Crystallization and preliminary X-ray diffraction studies of a ferredoxin reductase component of carbazole 1,9a-dioxygenase from Novosphingobium sp. KA1. Acta crystallographica. Section F, Structural biology and crystallization communications 4 20516607
2018 KA1 Domains: Unity in Mechanistic Diversity. Structure (London, England : 1993) 3 30089246
2010 Crystallization and preliminary X-ray diffraction studies of a terminal oxygenase of carbazole 1,9a-dioxygenase from Novosphingobium sp. KA1. Acta crystallographica. Section F, Structural biology and crystallization communications 3 21045300
2024 SARS-CoV-2-derived protein Orf9b enhances MARK2 activity via interaction with the autoinhibitory KA1 domain. FEBS letters 1 38969617
2025 Mitosis Localization Signal (MLS) extends KA1 and regulates MELK kinase localization to plasma membrane and activity in Xenopus embryo. Developmental biology 0 40816457
2015 [Role of KA1 receptor in excitotoxic neurodegeneration in mouse hippocampus triggered by kainic acid- or tunicamycin-induced endoplasmic reticulum stress]. Nan fang yi ke da xue xue bao = Journal of Southern Medical University 0 25736111
2010 Expression of KA1 kainate receptor subunit in the substantia gelatinosa of the trigeminal subnucleus caudalis in mice. Journal of veterinary science 0 21113098
1998 Linkage mapping of the interleukin 1beta converting enzyme (Il1bc) and the glutamate receptor subunit KA1 (Grik4) genes to rat chromosome 8. Folia biologica 0 10730851
1993 Epithelial cell membrane specific, novel monoclonal antibody KA-1. Journal of dermatological science 0 8395199