<div class="infobox">
<table>
<tr><td><strong>Gene</strong></td><td>GRM5</td></tr>
<tr><td><strong>UniProt</strong></td><td>[P41594](https://www.uniprot.org/uniprot/P41594)</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>132 kDa</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Plasma membrane, [Dendritic spines](/mechanisms/dendritic-spines)</td></tr>
<tr><td><strong>PDB Structures</strong></td><td>[6N51](https://www.rcsb.org/structure/6N51), [4OO9](https://www.rcsb.org/structure/4OO9)</td></tr>
<tr><td><strong>Aliases</strong></td><td>GRM5, mGlu5, MGLUR5</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/schizophrenia" style="color:#ef9a9a">Schizophrenia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">6 edges</a></td>
</tr>
</table>
</div>
Overview
...<div class="infobox">
<table>
<tr><td><strong>Gene</strong></td><td>GRM5</td></tr>
<tr><td><strong>UniProt</strong></td><td>[P41594](https://www.uniprot.org/uniprot/P41594)</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>132 kDa</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Plasma membrane, [Dendritic spines](/mechanisms/dendritic-spines)</td></tr>
<tr><td><strong>PDB Structures</strong></td><td>[6N51](https://www.rcsb.org/structure/6N51), [4OO9](https://www.rcsb.org/structure/4OO9)</td></tr>
<tr><td><strong>Aliases</strong></td><td>GRM5, mGlu5, MGLUR5</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/schizophrenia" style="color:#ef9a9a">Schizophrenia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">6 edges</a></td>
</tr>
</table>
</div>
Overview
Mermaid diagram (expand to render)
mGluR5 (metabotropic glutamate receptor 5) is a G-protein-coupled receptor (GPCR) that mediates slow, modulatory glutamate signaling in the central nervous system. As a member of the Group I metabotropic glutamate receptors, mGluR5 couples to Gq proteins to activate phospholipase C and intracellular calcium signaling. mGluR5 plays critical roles in synaptic plasticity, learning, and memory, and has emerged as a promising therapeutic target in Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions.[@niswender2010]
Structure and Domains
mGluR5 is a Class C GPCR with a distinctive architecture:[@koehl2019]
Domain organization:
- Venus flytrap domain (VFT): Large extracellular N-terminal domain that binds glutamate
- Cysteine-rich domain (CRD): Connects VFT to transmembrane domain
- Seven transmembrane domain (7TM): Classic GPCR domain for G-protein coupling
- Intracellular C-terminal tail: Contains phosphorylation sites and protein interaction motifs
Functional dimer:
- mGluR5 functions as an obligate homodimer (or heterodimer with mGluR1)
- Dimerization occurs through the VFT domain
- Two glutamate binding sites per dimer
- Cooperative activation mechanism
Allosteric binding sites:
- Orthosteric site: Glutamate binding in VFT domain
- Allosteric sites: Multiple modulatory sites in 7TM domain (MPEP site, etc.)
Normal Function
mGluR5 mediates modulatory glutamate signaling:[@lscher2010]
Signal transduction pathway:
Glutamate → mGluR5 → Gq → PLCβ → IP3 + DAG →
IP3R → Ca²⁺ release from ER → PKC activation
Synaptic functions:
- [Long-term potentiation](/mechanisms/long-term-potentiation) (LTP): Perisynaptic mGluR5 facilitates LTP induction
- Long-term depression (LTD): mGluR5-dependent LTD at certain synapses
- Synaptic protein synthesis: Links to local translation machinery
- Metaplasticity: Modulates thresholds for plasticity induction
Neuronal excitability:
- Modulates [NMDA receptor](/entities/nmda-receptor) function
- Regulates voltage-gated calcium channels
- Influences neuronal intrinsic excitability
Brain distribution:
- High expression in striatum, [hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex)
- Particularly enriched in medium spiny [neurons](/entities/neurons) of striatum
- Located perisynaptically (near, but not within, synapses)
Role in Neurodegeneration
Alzheimer's Disease
mGluR5 has complex roles in AD pathophysiology:[@um2013]
Pathogenic mechanisms:
- mGluR5 can act as a co-receptor for [Aβ](/proteins/amyloid-beta) oligomers
- Aβ-mGluR5 interaction triggers pathological signaling
- Promotes synaptic dysfunction and spine loss
- May contribute to [tau](/proteins/tau) hyperphosphorylation via [GSK-3β](/entities/gsk3-beta) activation
Protective mechanisms:
- Normal mGluR5 function supports synaptic plasticity
- mGluR5-mediated protein synthesis supports memory
- Loss of mGluR5 function may contribute to cognitive decline
Therapeutic targeting:
- Negative allosteric modulators (NAMs) show promise in animal models
- MPEP and analogues reduce Aβ toxicity
- Balance between therapeutic inhibition and preserving normal function[@hamilton2016]
Parkinson's Disease
mGluR5 is a validated target in PD:[@morin2013]
Motor symptoms:
- mGluR5 antagonism reduces motor symptoms in PD models
- Indirect pathway striatal neurons express high mGluR5
- Reduces excessive glutamatergic transmission
- Works synergistically with L-DOPA
L-DOPA-induced dyskinesias:
- mGluR5 NAMs reduce dyskinesia severity
- Dipraglurant showed efficacy in clinical trials
- May allow lower L-DOPA doses
Neuroprotection:
- mGluR5 inhibition may protect dopaminergic neurons
- Reduces excitotoxic glutamate signaling
- Anti-inflammatory effects via microglial mGluR5
Huntington's Disease
mGluR5 in HD:[@ribeiro2014]
- Altered mGluR5 expression and signaling in HD striatum
- Mutant [huntingtin](/proteins/huntingtin) affects mGluR5 membrane expression
- mGluR5 NAMs show benefit in HD animal models
- Reduce striatal neuron degeneration
Fragile X Syndrome and Autism
While not neurodegenerative, these conditions inform mGluR5 biology:
- mGluR5 theory of fragile X: excessive mGluR5 signaling
- mGluR5 NAMs in clinical trials for fragile X
- Relevance to cognitive aspects of neurodegeneration
Therapeutic Targeting
Drug Development
mGluR5 modulators in development:[@gregory2021]
| Compound | Type | Status | Indication |
|----------|------|--------|------------|
| MPEP | NAM (research) | Preclinical | Research tool |
| Fenobam | NAM | Phase II | Anxiety, Fragile X |
| Dipraglurant | NAM | Phase II | PD dyskinesia |
| Basimglurant | NAM | Phase II | Depression, Fragile X |
| CTIEP | NAM | Discontinued | Fragile X |
| CDPPB | PAM (research) | Preclinical | Cognitive enhancement |
Clinical Trial Results
Parkinson's Disease:
- Dipraglurant reduced L-DOPA-induced dyskinesia in Phase II
- Well-tolerated, good safety profile
- Moving to Phase III development
Fragile X (informative for cognition):
- Mixed results with mGluR5 NAMs
- May have been underdosed
- Ongoing research continues
Mechanism-Based Considerations
NAMs vs Antagonists:
- NAMs reduce but don't completely block receptor
- Preserve basal signaling while reducing overactivation
- Allosteric site provides selectivity
PAMs (Positive Allosteric Modulators):
- Enhance receptor function
- Potential for cognitive enhancement in AD
- Risk of overactivation and excitotoxicity
Protein Interactions
| Interacting Partner | Function | Relevance |
|---------------------|----------|-----------|
| Gq/11 | G-protein coupling | Primary signaling |
| Homer proteins | Scaffold, coupling | Links to mGluR1, NMDAR |
| NMDA receptors | Co-modulation | Synaptic plasticity |
| PLCβ | Effector enzyme | IP3/DAG production |
| Aβ oligomers | Pathological ligand | AD toxicity |
| PKC | Phosphorylation | Desensitization |
Key Publications
[Conn PJ, et al., Metabotropic glutamate receptors in the basal ganglia (2005)](https://doi.org/10.1016/j.tips.2004.12.003) — Trends in Pharmacological Sciences. Comprehensive review of mGluR5 in basal ganglia.
[Um et al., Metabotropic glutamate receptor 5 is a coreceptor for Alzheimer Aβ oligomer (2013)](https://doi.org/10.1016/j.neuron.2012.11.004) — Neuron. Establishes mGluR5 as Aβ co-receptor.
[Morin et al., mGluR5 in Parkinson's disease (2013)](https://doi.org/10.1016/j.neuropharm.2013.04.018) — Neuropharmacology. Reviews mGluR5 as PD therapeutic target.
[Trenque et al., mGluR5 NAM dipraglurant in Parkinson's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/33607834/) — Clinical trial results.
[Ribeiro et al., mGluR5 in neurodegeneration (2017)](https://doi.org/10.1007/s13311-017-0566-7) — Neurotherapeutics. Comprehensive review.See Also
- [NMDA Receptor](/proteins/nmda-receptor)
- [AMPA Receptor](/proteins/ampa-receptor)
- [Glutamate Signaling](/mechanisms/glutamate-signaling)
- [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
References
[Niswender CM, Conn PJ, Metabotropic glutamate receptors: physiology, pharmacology, and disease (2010)](https://doi.org/10.1146/annurev.pharmtox.011008.145533)
[Koehl A, et al, Structural insights into the activation of metabotropic glutamate receptors (2019)](https://doi.org/10.1038/s41586-019-0949-0)
[Lüscher C, Huber KM, Group 1 mGluR-dependent synaptic long-term depression: mechanisms and implications for circuitry and disease (2010)](https://doi.org/10.1016/j.neuron.2010.01.016)
[Um JW, et al, Metabotropic glutamate receptor 5 is a coreceptor for Alzheimer Aβ oligomer linked to synaptic dysfunction (2013)](https://doi.org/10.1016/j.neuron.2013.08.008)
[Hamilton A, et al, Pharmacological inhibition of mGluR5 restores cognitive function in a mouse model of Down syndrome (2016)](https://doi.org/10.1016/j.neuropharm.2016.07.006)
[Morin N, et al, mGlu5 receptor antagonist for L-DOPA-induced dyskinesia (2013)](https://doi.org/10.1016/j.neuropharm.2013.04.018)
[Ribeiro FM, et al, Metabotropic glutamate receptor 5 signalling promotes autophagy and is required for neuronal health (2014)](https://doi.org/10.1096/fj.14-254540)
[Gregory KJ, et al, Allosteric modulation of metabotropic glutamate receptors: structural insights and therapeutic potential (2021)](https://doi.org/10.1016/j.neuropharm.2021.108278)Pathway Diagram
The following diagram shows the key molecular relationships involving mGluR5 (Metabotropic Glutamate Receptor 5) discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)