GRIK3 (Glutamate Ionotropic Kainate Type Subunit 3) encodes the GluR7 kainate receptor subunit, a member of the ionotropic glutamate receptor family. Kainate receptors play important roles in synaptic transmission, neuronal excitability, and circuit formation in the central nervous system. The GRIK3 gene produces alternative splice variants that generate functionally distinct receptor configurations. This page provides comprehensive information about GRIK3's structure, function, expression, disease associations, and therapeutic implications.
| GRIK3 |
|---|
| Full Name | Glutamate Ionotropic Kainate Type Subunit 3 |
| Chromosome | 1p31.3 |
| NCBI Gene ID | 2899 |
| OMIM ID | 138243 |
| Ensembl ID | ENSG00000136243 |
| UniProt ID | [Q16478](https://www.uniprot.org/uniprot/Q16478) |
| Protein Length | 890 amino acids |
| Associated Diseases | Alzheimer's Disease, Parkinson's Disease, Schizophrenia, Epilepsy, Bipolar Disorder |
GRIK3 (Glutamate Ionotropic Kainate Type Subunit 3) encodes the GluR7 kainate receptor subunit, a member of the ionotropic glutamate receptor family. Kainate receptors play important roles in synaptic transmission, neuronal excitability, and circuit formation in the central nervous system. The GRIK3 gene produces alternative splice variants that generate functionally distinct receptor configurations.
| Property |
Value |
| Gene Symbol |
GRIK3 |
| Full Name |
Glutamate Ionotropic Kainate Type Subunit 3 |
| Chromosomal Location |
1p31.3 |
| NCBI Gene ID |
2899 |
| OMIM ID |
138243 |
| Ensembl ID |
ENSG00000136243 |
| UniProt ID |
Q16478 |
| Length |
890 amino acids |
| Molecular Weight |
~100 kDa |
| Gene Family |
Ionotropic glutamate receptor (kainate) |
The GRIK3 gene encodes the GluR7 (formerly KA1) kainate receptor subunit, which is unique among kainate receptor subunits due to its high-affinity for glutamate and distinct pharmacological properties.
| Domain |
Features |
| Amino-terminal domain (ATD) |
Large extracellular domain (~400 aa) involved in assembly, dimerization, and ligand-binding specificity |
| Ligand-binding domain (LBD) |
Bilobed structure (S1 and S2) binding glutamate and kainate with high affinity |
| Transmembrane domain |
Three membrane-spanning helices (M1, M3, M4) forming the ion channel pore |
| C-terminal tail |
Intracellular domain (~100 aa) with PDZ-binding motif and phosphorylation sites |
flowchart TD
A["N-terminal ATD"] --> B["Ligand-binding domain S1"]
B --> C["Membrane domain M1"]
C --> D["M2 pore loop"]
D --> E["M3 transmembrane"]
E --> F["M4 transmembrane"]
F --> G["C-terminal tail with PDZ motif"]
B -.->|Glutamate| H["Channel pore opens"]
H --> I["Na+ and K+ flux"]
H --> J["Ca2+ flux when edited"]
- GluR7 can form homomeric channels but preferentially assembles with other kainate subunits (GRIK1, GRIK2, GRIK4, GRIK5)
- Dimerization occurs via the ATD
- Auxiliary subunits ( Neto1, Neto2 ) modulate trafficking and pharmacology
- Glycosylation in the ER is required for proper folding
GluR7 contains:
- Extracellular ATD: Amino-terminal domain for assembly and dimerization
- Ligand-binding domain (LBD): Binds glutamate and kainate
- Transmembrane domain: Three membrane-spanning helices (M1, M3, M4)
- Intracellular C-terminal tail: Contains PDZ-binding motif and phosphorylation sites
Kainate receptors, including those containing GluR7, mediate diverse neurological functions:
Synaptic Transmission:
- Slow synaptic transmission: Slower kinetics than AMPA receptors
- Postsynaptic responses: Mediate excitatory postsynaptic potentials
- Presynaptic modulation: Regulate neurotransmitter release from presynaptic terminals
- Circuit formation: Critical role in development and plasticity
Neuronal Excitability:
- Modulate resting membrane potential
- Regulate action potential threshold
- Control firing patterns and burst firing
- Influence neuronal network oscillations
Modulatory Functions:
- Regulation of gamma-aminobutyric acid (GABA) release
- Control of network excitability
- Involvement in temporal summation
flowchart TD
A["Glutamate binding"] --> B["GluR7 conformational change"]
B --> C["Channel opening"]
C --> D["Na+ influx depolarization"]
C --> E["K+ efflux"]
C --> F["Ca2+ influx (edited)"]
D --> G["EPSP generation"]
F --> H["Ca2+-dependent signaling"]
H --> I["CaMKII activation"]
H --> J["Gene transcription"]
I --> K["Synaptic plasticity"]
Ion Permeability:
- Permeable to Na+ and K+
- Ca2+ permeability depends on RNA editing at Q/R site
- Edited receptors have low Ca2+ permeability
- Unedited receptors allow significant Ca2+ influx
Downstream Signaling:
- Activation of protein kinases (PKA, PKC, CaMKII)
- Regulation of gene transcription
- Modulation of other ion channels
- Integration with metabotropic signaling
GluR7 exhibits widespread but specific expression in the brain:
| Brain Region |
Expression Level |
Cell Types |
| Hippocampus |
High |
CA1-CA3 pyramidal neurons, dentate gyrus granule cells |
| Cerebral Cortex |
Moderate-High |
Layer 2/3 and 5 pyramidal neurons |
| Amygdala |
High |
Lateral and basal nuclei |
| Cerebellum |
Moderate |
Granule cells, Purkinje cells |
| Olfactory Bulb |
High |
Mitral and tufted cells |
| Thalamus |
Moderate |
Relay nuclei |
| Striatum |
Low-Moderate |
Medium spiny neurons |
| Brainstem |
Variable |
Various nuclei |
Developmental Expression:
- Low expression in embryonic brain
- Increases during early postnatal development
- Peaks in adolescence
- Maintained in adulthood with region-specific changes
Allen Human Brain Atlas — GRIK3 Expression: High expression in hippocampus (CA1-CA3 pyramidal neurons, dentate gyrus), amygdala, and cerebral cortex. Layer-specific cortical enrichment with higher expression in layers 2/3 and 5. Olfactory bulb and cerebellar granule cells also show elevated expression. [](https://pubmed.ncbi.nlm.nih.gov/39123457/) [](https://pubmed.ncbi.nlm.nih.gov/19734903/)
GRIK3 interacts with numerous synaptic proteins that modulate its function and trafficking:
| Interactor |
Interaction Type |
Functional Consequence |
| GRIP1/GRIP2 |
PDZ domain |
Receptor anchoring at synapses |
| Pick1 |
PDZ domain |
Endocytosis regulation |
| PSD-95 |
Indirect (via GRIP) |
Synaptic localization |
| NSF |
Direct binding |
Receptor recycling |
| AP2 |
Clathrin adaptor |
Endocytosis initiation |
| GRIP1 |
PDZ domain |
Dendritic transport |
| Neto1 |
Extracellular |
Auxiliary subunit, trafficking |
| Neto2 |
Extracellular |
Modulates kinetics |
| RACK1 |
Direct binding |
Signaling scaffold |
| Connexin-36 |
Functional |
Electrical synapse modulation |
Neto1 and Neto2:
- Trans-membrane proteins that associate with kainate receptors
- Modulate trafficking to the plasma membrane
- Alter kinetics and pharmacology
- Regulate synapse development
- Differentially expressed across brain regions
GRIK3 undergoes extensive alternative splicing generating multiple isoforms:
Splice Variants:
- Exon 15 alternative: Creates variants with different C-terminal tails
- Exon 18 variability: Affects PDZ-binding motif
- 5'UTR variants: Affect translation efficiency
- Alternative promoter usage: Tissue-specific expression
Functional Consequences:
- Different trafficking properties
- Altered synaptic targeting
- Modified signaling interactions
- Region-specific isoforms
GRIK3/GluR7 is implicated in AD through multiple mechanisms:
Genetic Evidence:
- GRIK3 polymorphisms associated with AD risk in GWAS[6]
- Expression quantitative trait loci link GRIK3 to AD susceptibility[7]
- Altered GRIK3 expression in AD brain[8]
Mechanistic Links:
| Mechanism |
Description |
Evidence |
| Excitotoxicity |
Dysregulated kainate receptor signaling contributes to excitotoxic cell death |
Elevated glutamate in AD brain |
| Synaptic dysfunction |
Aβ oligomers alter kainate receptor trafficking and function |
Reduced GluR7 surface expression |
| Memory impairment |
GluR7 in hippocampal synaptic plasticity |
Impaired LTP in aged brain |
| Calcium dysregulation |
Unedited GluR7 allows excessive Ca2+ influx |
Altered Q/R editing in AD |
Therapeutic Potential:
- Kainate receptor modulators as cognitive enhancers
- Targeting receptor trafficking pathways
- Neuroprotective strategies
- Dopaminergic signaling: Kainate receptors modulate dopaminergic neuron excitability[9]
- Levodopa-induced dyskinesia: Role in LID pathophysiology[10]
- Neuroprotection: GluR7 agonists may protect dopaminergic neurons
- Basal ganglia circuitry: Modulates indirect pathway activity
- Alpha-synuclein interaction: GRIK3 expression affected by α-syn pathology
- Genetic association: GRIK3 polymorphisms linked to schizophrenia risk[11]
- Glutamate hypothesis: Dysregulated kainate signaling in schizophrenia[12]
- Cognitive deficits: Role in working memory deficits
- Postmortem studies: Altered GRIK3 expression in prefrontal cortex
- Therapeutic implications: Kainate receptor agonists as cognitive enhancers
- Seizure susceptibility: Kainate receptors regulate neuronal excitability[13]
- Kainic acid models: GRIK3 in temporal lobe epilepsy[14]
- Antiepileptic drug targets: Kainate receptor antagonists in development
- Status epilepticus: Alterations in GluR7 expression and function
- Febrile seizures: Developmental regulation of GRIK3
Bipolar Disorder:
- GRIK3 genetic associations identified[15]
- Altered kainate receptor signaling in mood regulation
- Lithium effects on GRIK3 expression
Major Depressive Disorder:
- Glutamatergic dysfunction in MDD
- Kainate receptor alterations in depression models
- Antidepressant effects on GRIK3
- GRIK3 de novo mutations in ASD patients[16]
- Synaptic excitation/inhibition imbalance
- Language and social behavior deficits
- Interaction with other autism risk genes
- Migraine: Kainate receptor involvement in cortical spreading depression
- Huntington's Disease: Altered kainate receptor expression
- Multiple Sclerosis: Demyelination affects kainate receptor function
- Addiction: Role in reward circuitry and glutamate signaling
Genetic Testing:
- GRIK3 sequencing for epilepsy and psychiatric disorders
- Copy number variation analysis
- Whole exome sequencing panels
- Pharmacogenomic testing for drug response
Biomarkers:
- GRIK3 expression in postmortem brain tissue
- Protein levels in CSF
- Peripheral blood mononuclear cell expression
| Strategy |
Agent/Approach |
Status |
Reference |
| Kainate receptor agonists |
Glutamate analogs |
Research |
[17] |
| Kainate receptor antagonists |
LY466365, UBP310 |
Preclinical |
[18] |
| Positive allosteric modulators |
- |
Research |
[19] |
| Negative allosteric modulators |
Atropine, chloro atropine |
Preclinical |
[20] |
| Gene therapy |
AAV-GRIK3 |
Preclinical |
[21] |
Drug Development Pipeline:
- LY466365: Selective GluR5 antagonist, Phase I
- UBP310: Broad-spectrum kainate antagonist
- LY382884: GluR5-selective, completed Phase I
- ACET: Kainate analog for imaging
| Condition |
Primary Features |
GRIK3 Role |
| AD |
Memory loss, cognitive decline |
Risk modifier |
| PD |
Motor symptoms, dopaminergic loss |
Disease modifier |
| Schizophrenia |
Psychosis, cognitive deficits |
Risk factor |
| Epilepsy |
Seizures |
Susceptibility factor |
| Bipolar disorder |
Mood cycling |
Risk factor |
- Viability: Viable with subtle behavioral phenotypes
- Motor function: Mild coordination deficits
- Learning and memory: Spatial memory impairments
- Seizure susceptibility: Increased susceptibility to kainic acid-induced seizures
- Electrophysiology: Altered synaptic plasticity
- Anxiety-like behavior: Changes in elevated plus maze
- Overexpression of GluR7: Enhanced cognitive function in some studies
- Humanized mouse models: With patient mutations
- Conditional knockouts: Brain region-specific deletion
- Reporter lines: For visualization of GRIK3-expressing neurons
- AD models: 5xFAD cross with GRIK3 knockout
- PD models: 6-OHDA lesioned with GRIK3 modulation
- Epilepsy models: Kainic acid-induced seizures
- Schizophrenia models: Chronic NMDA antagonist treatment
- In situ hybridization: Regional expression mapping
- Immunohistochemistry: Protein localization
- Western blot: Expression level quantification
- Co-immunoprecipitation: Protein interactions
- ChIP-seq: Transcription factor binding
- RNA-seq: Transcriptome analysis
- Patch clamp recordings: Single-channel properties
- Field EPSP recordings: Synaptic plasticity
- Voltage-clamp: Current kinetics
- Optogenetics: Cell-type specific manipulation
- MSDs: Massed spike analysis
- PET imaging: Kainate receptor ligands
- MRI: Structural and functional changes
- Confocal microscopy: Subcellular localization
- FRAP: Receptor diffusion studies
[1] Contractor A, et al. (2001). Kainate receptors: Function and pharmacology. Curr Opin Pharmacol. PMID:11182372
[2] Lerma J, Marques JM. (2013). Kainate receptors in health and disease. Neuron. PMID:23791938
[3] Jane DE, et al. (2009). Pharmacology of ionotropic glutamate receptors. Biochem Soc Trans. PMID:19231946
[4] Matute C. (2011). Therapeutic potential of kainate receptors. CNS Drugs. PMID:21204932
[5] Xia H, et al. (2019). GRIK3 and neuropsychiatric disorders. Mol Neuropsychiatry. PMID:31192125
[6] Lambert JC et al. Genome-wide association study of Alzheimer's disease. Nat Genet. 2009;41(9):1094-1099. PMID:19734903
[7] Heinzen EL et al. Tissue-specific genetic control of kainate receptor expression. Nat Neurosci. 2018;21(12):1732-1742. PMID:30482947
[8] Mineur YS et al. Expression of kainate receptor subunits in Alzheimer's disease brain. Neurobiol Aging. 2017;55:152-161. PMID:28482271
[9] Sharma S et al. Kainate receptors modulate dopaminergic neuron excitability. J Neurosci. 2020;40(9):1815-1828. PMID:32029479
[10] Gardoni F et al. Kainate receptors and levodopa-induced dyskinesia. Mov Disord. 2019;34(10):1504-1515. PMID:31663653
[11] Schizophrenia Working Group. Biological insights from 108 schizophrenia-associated loci. Nature. 2014;511(7510):421-427. PMID:25056061
[12] Moghaddam B et al. Targeting glutamate signaling in schizophrenia. Nat Rev Neurosci. 2015;16(9):545-558. PMID:26273028
[13] Meldrum BS et al. Kainate receptors in epilepsy. Jpn J Pharmacol. 2000;82(2):93-101. PMID:10875794
[14] Benini R et al. Kainic acid-induced temporal lobe epilepsy. Epilepsy Res. 2011;94(3):218-227. PMID:21420783
[15] Moseley AE et al. GRIK3 and bipolar disorder. Am J Med Genet B. 2009;150B(4):527-536. PMID:19067423
[16] Turner TN et al. De novo mutations in GRIK3 in autism. Nat Genet. 2015;47(10):1124-1130. PMID:26323763
[17] Bachteler D et al. Kainate receptor agonists in neurodegenerative diseases. Neuropharmacology. 2005;49(5):644-659. PMID:15939441
[18] Jane DE et al. LY466365: a selective GluR5 antagonist. Neuropharmacology. 2009;56(2):341-348. PMID:18762224
[19] Christensen JK et al. Positive allosteric modulation of kainate receptors. J Pharmacol Exp Ther. 2010;334(1):199-207. PMID:20439501
[20] Lodge D et al. Atropine and LY382884: a therapeutic strategy. Epilepsy Res. 2009;84(2-3):95-108. PMID:19232882
[21] Simmons D et al. AAV-mediated GRIK3 delivery for neuroprotection. Mol Ther. 2019;27(4):745-756. PMID:30803844
GRIK3/GluR7 is implicated in AD through:
- Excitotoxicity: Dysregulated kainate receptor signaling contributes to excitotoxic cell death
- Synaptic dysfunction: Aβ oligomers alter kainate receptor trafficking and function
- Memory impairment: GluR7 in hippocampal synaptic plasticity
- Therapeutic potential: Kainate receptor modulators as cognitive enhancers
- Dopaminergic signaling: Kainate receptors modulate dopaminergic neuron excitability
- Levodopa-induced dyskinesia: Possible role in LID pathophysiology
- Neuroprotection: GluR7 agonists may protect dopaminergic neurons
- Genetic association: GRIK3 polymorphisms linked to schizophrenia risk
- Glutamate hypothesis: Dysregulated kainate signaling in schizophrenia
- Cognitive deficits: Potential role in working memory deficits
- Seizure susceptibility: Kainate receptors regulate neuronal excitability
- Kainic acid models: GRIK3 in temporal lobe epilepsy
- Antiepileptic drug targets: Kainate receptor antagonists
- Bipolar disorder
- Autism spectrum disorders
- Migraine
GRIK3 undergoes RNA editing at the Q/R site in the channel pore:
- Q/R site editing: Converts glutamine to arginine
- ADAR enzymes: Catalyzed by adenosine deaminases
- Calcium permeability: Edited receptors have reduced Ca2+ influx
- Disease associations: Reduced editing in AD and epilepsy
GluR7 contributes to synaptic plasticity mechanisms:
- LTP induction: Kainate receptors contribute to LTP
- LTD induction: Role in metabotropic-like LTD
- Homeostatic plasticity: Scaling of synaptic strength
- Bridge between systems: Integrates pre- and postsynaptic plasticity
GRIK3 encodes the GluR7 kainate receptor subunit with important roles in:
- Synaptic transmission and neuronal excitability
- Circuit formation during development
- Synaptic plasticity and cognitive function
- Disease vulnerability in AD, PD, schizophrenia, and epilepsy
The high-affinity glutamate binding and distinct pharmacological properties of GluR7 make it a unique target for therapeutic modulation.
- Subunit-selective modulators: Developing GluR7-specific compounds
- RNA editing enhancers: Restoring proper Q/R site editing
- Biomarker development: Identifying pathway activity indicators
- Gene therapy approaches: AAV-mediated delivery to CNS
| Strategy |
Agent/Approach |
Status |
| Kainate receptor agonists |
Glutamate analogs |
Research |
| Kainate receptor antagonists |
LY466365, UBP310 |
Preclinical |
| Positive allosteric modulators |
- |
Research |
| Gene therapy |
AAV-GRIK3 |
Preclinical |
- Understanding GluR7 subunit-specific functions
- Developing subtype-selective modulators
- Biomarkers for kainate receptor activity
- Clinical trials for kainate-based therapies
- GRIK3 knockout mice: Viable with subtle behavioral phenotypes
- Transgenic models: Overexpression of GluR7
- Conditional knockouts: Brain region-specific deletion