GO:0031805 type 8 metabotropic glutamate receptor binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031805 (type 8 metabotropic glutamate receptor binding) is a molecular function defined as binding to a type 8 metabotropic glutamate receptor (mGlu8).
• mGlu8 is a group III metabotropic glutamate receptor that couples to Gi/Go proteins and inhibits N-type Ca2+ channels, as shown in rat sympathetic neurons.
• The term is distinct from ligand binding to other mGlu subtypes; it specifically captures interactions with the mGlu8 receptor protein.
• mGlu8 is expressed in brain regions such as the suprachiasmatic nucleus, where it modulates glutamate responses.
• Research on mGlu8 binding is relevant to neurological and psychiatric conditions, including alcohol dependence, as suggested by altered mGlu2/3 binding in alcoholics.
• Experimental approaches to study this function include radioligand binding assays, electrophysiology, and CRISPR-based gene editing to create knockout or knock-in models.
Description
GO:0031805, type 8 metabotropic glutamate receptor binding, is a molecular function term in the Gene Ontology that describes the selective interaction with the metabotropic glutamate receptor 8 (mGlu8). Metabotropic glutamate receptors are G protein-coupled receptors that modulate synaptic transmission and neuronal excitability. mGlu8 belongs to group III mGlu receptors, which are generally presynaptic and inhibitory. The binding of ligands or proteins to mGlu8 can trigger downstream signaling cascades, such as inhibition of N-type calcium channels, as demonstrated in rat sympathetic neurons. Understanding this binding event is crucial for elucidating how mGlu8 regulates neurotransmitter release and neuronal circuits. The term is also relevant for pharmacological studies, as selective ligands for mGlu8 can serve as research tools or therapeutic candidates. For example, radioligand binding assays have been used to characterize mGlu receptor pharmacology, including type 1 receptors [1,5], and similar approaches can be applied to mGlu8. Moreover, mGlu8 modulation has been implicated in circadian rhythms through its action in the suprachiasmatic nucleus. Thus, GO:0031805 provides a precise annotation for experimental observations of mGlu8 interactions.
type 8 metabotropic glutamate receptor binding At A Glance
| GO ID | GO:0031805 |
|---|---|
| GO term | type 8 metabotropic glutamate receptor binding |
| Ontology | molecular_function |
| Synonym | type 8 metabotropic glutamate receptor ligand |
| Major function | Binding to the metabotropic glutamate receptor 8 (mGlu8), a group III GPCR that inhibits cAMP and N-type Ca2+ channels. |
| Related receptor | mGlu8 (GRM8 gene) |
| Signaling pathway | Gi/Go-mediated inhibition of adenylyl cyclase and calcium channels |
| Tissue expression | Brain, including suprachiasmatic nucleus |
| Research tools | Radioligands, selective agonists/antagonists, knockout mice |
What Is GO:0031805?
Type 8 metabotropic glutamate receptor binding is the molecular function of selectively interacting with the metabotropic glutamate receptor 8 (mGlu8) protein. This binding event can involve endogenous ligands such as glutamate, synthetic agonists or antagonists, or other proteins that associate with mGlu8. It is a specific term that excludes binding to other metabotropic glutamate receptor subtypes, such as mGlu1 or mGlu2/3 [1,2]. The function is typically measured in vitro using radioligand binding assays or in vivo via electrophysiological recordings that assess downstream effects of mGlu8 activation [3,4].
Why Is type 8 metabotropic glutamate receptor binding Important in Cell Biology?
GO:0031805 is important because mGlu8 is a key modulator of synaptic transmission and neuronal excitability, and its dysfunction has been linked to neurological and psychiatric disorders. For instance, altered metabotropic glutamate receptor binding has been observed in alcohol dependence, and mGlu8 may play a role in circadian rhythm regulation. Studying this binding function helps researchers develop selective pharmacological tools and understand the mechanistic basis of mGlu8-related pathologies.
• mGlu8 is a presynaptic inhibitory receptor that regulates neurotransmitter release.
• Binding to mGlu8 can inhibit N-type calcium channels, affecting neuronal firing.
• mGlu8 is expressed in the suprachiasmatic nucleus, where it modulates glutamate responses and circadian rhythms.
• Alterations in metabotropic glutamate receptor binding are associated with alcohol dependence.
• Selective ligands for mGlu8 are valuable for pharmacological research and drug discovery.
• CRISPR-based editing of GRM8 can create models to study mGlu8 function in vivo.
• Understanding mGlu8 binding may inform therapies for anxiety, epilepsy, and neurodegenerative diseases.
• The term provides a standardized annotation for high-throughput screening of mGlu8 interactions.
Molecular Mechanism of type 8 metabotropic glutamate receptor binding
Ligand recognition and binding site
In simple terms: This is how a molecule docks onto the mGlu8 receptor.
mGlu8 belongs to the group III metabotropic glutamate receptors, which have a large extracellular Venus flytrap domain that binds glutamate or synthetic ligands. Binding of agonists to this domain induces conformational changes that activate the receptor. Although direct structural studies on mGlu8 are limited, insights from other mGlu receptors, such as mGlu1, show that ligand binding involves key residues in the Venus flytrap domain and can exhibit negative cooperativity in dimeric receptors. For mGlu8, selective ligands like (S)-3,4-DCPG have been used to characterize its pharmacology, but specific binding residues are inferred from homology models.
G protein coupling and downstream signaling
In simple terms: Once a molecule binds, the receptor activates G proteins to send signals inside the cell.
Activated mGlu8 couples to Gi/Go proteins, inhibiting adenylyl cyclase and reducing cAMP levels. This signaling cascade leads to the inhibition of N-type calcium channels, as demonstrated in rat sympathetic neurons where mGlu8 activation decreased calcium currents. This mechanism is crucial for presynaptic inhibition of neurotransmitter release.
Modulation of neuronal excitability
In simple terms: This binding event can make neurons less likely to fire.
By inhibiting calcium channels and activating potassium channels, mGlu8 binding reduces neuronal excitability. In the suprachiasmatic nucleus, mGlu8 modulates glutamate responses, affecting circadian clock resetting. This modulation is essential for normal brain function and is a target for neurological disorders.
Pharmacological regulation and allosteric modulation
In simple terms: Drugs can enhance or block the binding to mGlu8.
Allosteric modulators can bind to sites distinct from the orthosteric ligand-binding pocket, altering receptor activity. For mGlu1, negative cooperativity of glutamate binding has been observed in dimeric receptors, suggesting similar complexities may exist for mGlu8. Selective antagonists like YM-298198 for mGlu1 highlight the potential for developing mGlu8-specific modulators. These compounds are valuable for dissecting mGlu8 function in vivo.
Key Genes Involved in GO:0031805 type 8 metabotropic glutamate receptor binding
The following genes and proteins are directly or indirectly involved in type 8 metabotropic glutamate receptor binding and its signaling pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| GRM8 | Encodes mGlu8 receptor, the primary binding target | Knockout and knock-in models to study mGlu8 function |
| GRM1 | Encodes mGlu1 receptor, a related group I mGlu receptor | Comparative studies of mGlu receptor pharmacology [1,5,6] |
| GRM2 | Encodes mGlu2 receptor, a group II mGlu receptor | Implicated in alcohol dependence |
| GRM3 | Encodes mGlu3 receptor, a group II mGlu receptor | Target for psychiatric disorders |
| GNAI1 | Encodes Gi alpha subunit | Mediates mGlu8 signaling to inhibit cAMP |
| GNAO1 | Encodes Go alpha subunit | Couples mGlu8 to calcium channel inhibition |
| CACNA1B | Encodes N-type calcium channel | Effector of mGlu8-mediated inhibition |
| SLC1A1 | Glutamate transporter | Regulates extracellular glutamate available for mGlu8 binding |
| SLC1A2 | Glutamate transporter | Regulates glutamate levels in synapses |
| GRIP1 | Glutamate receptor interacting protein | May scaffold mGlu8 and modulate binding |
| HOMER1 | Scaffolding protein | Interacts with group I mGlu receptors, not mGlu8, but relevant for comparison |
| ARRB1 | Beta-arrestin 1 | Regulates GPCR desensitization, potentially mGlu8 |
| ARRB2 | Beta-arrestin 2 | Regulates GPCR internalization |
| PRKCA | Protein kinase C alpha | Downstream signaling molecule for mGlu receptors |
| CAMK2A | Calcium/calmodulin-dependent protein kinase II | Modulates synaptic plasticity downstream of mGlu8 |
| DLG4 | PSD-95 scaffolding protein | Organizes postsynaptic density, may interact with mGlu8 indirectly |
| GRK2 | G protein-coupled receptor kinase 2 | Phosphorylates activated GPCRs, including mGlu8 |
How Is type 8 metabotropic glutamate receptor binding Regulated?
The binding function of mGlu8 is regulated by several mechanisms. Receptor desensitization and internalization are controlled by G protein-coupled receptor kinases (GRKs) and beta-arrestins. Allosteric modulators can enhance or inhibit ligand binding and signaling. Additionally, the availability of glutamate, regulated by transporters like SLC1A1 and SLC1A2, affects mGlu8 activation. Dimerization of mGlu receptors can lead to negative cooperativity, as seen in mGlu1, which may also apply to mGlu8. Furthermore, phosphorylation by kinases such as PKC and CaMKII can modulate receptor function.
type 8 metabotropic glutamate receptor binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| GRM8 | Alcohol dependence, circadian rhythm disorders | Grm8 knockout mouse, CRISPR knock-in of human variants |
| GRM2 | Alcohol dependence | Grm2 knockout rat, overexpression models |
| GRM3 | Schizophrenia, addiction | Grm3 knockout mouse, point mutation models |
| GRM1 | Alzheimer's disease, neuropathic pain | Grm1 knockout mouse, PET imaging |
| CACNA1B | Pain, epilepsy | Cacna1b knockout mouse, electrophysiology |
Alcohol dependence
Alterations in metabotropic glutamate receptor binding have been observed in alcohol-dependent individuals. A study using whole-hemisphere autoradiography found increased mGlu2/3 receptor binding in the perigenual anterior cingulate cortex of Cloninger type 2 alcoholics. Although this study focused on mGlu2/3, it highlights the involvement of metabotropic glutamate receptors in addiction. mGlu8, as a group III receptor, may also contribute to alcohol-related behaviors, but direct evidence is limited.
Circadian rhythm disorders
mGlu8 is expressed in the suprachiasmatic nucleus, the master circadian clock. Modulation of glutamate responses by mGlu8 in this region affects circadian rhythm regulation. Dysregulation of mGlu8 binding could therefore impact sleep-wake cycles and circadian disorders, though specific human studies are needed.
Neurodegenerative diseases
Metabotropic glutamate receptors are implicated in neurodegenerative conditions. For example, type 1 metabotropic glutamate receptor availability was studied in Alzheimer's disease patients using PET, showing no significant change. While mGlu8 has not been directly linked to Alzheimer's, its role in modulating excitotoxicity suggests potential relevance. Further research is required to establish any association.
From type 8 metabotropic glutamate receptor binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does mGlu8 binding regulate neurotransmitter release? | Grm8 knockout mouse with electrophysiology |
| What are the structural determinants of mGlu8 ligand binding? | Point mutations in GRM8 Venus flytrap domain, expressed in HEK293 cells |
| How does mGlu8 modulate circadian rhythms? | Knock-in mouse with tagged mGlu8, suprachiasmatic nucleus recordings |
| Can mGlu8 overexpression alter anxiety-like behavior? | Transgenic mouse overexpressing GRM8 in forebrain |
| What proteins interact with mGlu8? | Knock-in mouse with epitope-tagged mGlu8, co-immunoprecipitation |
| Does mGlu8 activation affect alcohol consumption? | Grm8 knockout mouse in drinking-in-the-dark paradigm |
How to Study the type 8 metabotropic glutamate receptor binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radioligand binding | Receptor affinity and density | Pharmacological characterization of mGlu8 ligands |
| Electrophysiology | Ion channel activity and neuronal excitability | Measuring mGlu8-mediated inhibition of Ca2+ channels |
| Autoradiography | Receptor distribution in brain sections | Comparing mGlu receptor binding in disease models |
| CRISPR knockout | Loss of receptor function | Creating Grm8-/- mice for behavioral studies |
| CRISPR knock-in | Tagged or mutant receptor expression | Studying mGlu8 localization and interactions |
| RNA-seq | Gene expression changes | Transcriptomic profiling after mGlu8 activation |
| Proteomics | Protein-protein interactions | Identifying mGlu8 binding partners |
Radioligand binding assays
Radioligand binding assays are used to measure the affinity and density of mGlu8 receptors in tissue homogenates or recombinant cells. For example, [35S]-GTPgammaS binding has been used to characterize mGlu1 receptor-stimulated G protein activation. Similar assays with selective mGlu8 radioligands can quantify binding in brain regions. This method is high-throughput and suitable for pharmacological profiling.
Electrophysiology
Electrophysiological recordings, such as patch-clamp, can measure the functional consequences of mGlu8 binding, such as inhibition of N-type calcium channels or modulation of glutamate responses in the suprachiasmatic nucleus. This method provides real-time readout of receptor activity in neurons.
Autoradiography
Whole-hemisphere autoradiography allows visualization and quantification of receptor binding in brain sections. This technique has been used to study mGlu2/3 binding in alcoholics and can be adapted for mGlu8 with specific radioligands. It provides anatomical resolution of receptor distribution.
CRISPR/Cas9 genome editing
CRISPR/Cas9 can generate knockout, knock-in, or point mutations in the GRM8 gene to study mGlu8 function. For example, knockout mice lacking mGlu8 can be used to assess the role of this receptor in behavior and physiology. Knock-in of tagged mGlu8 allows for pull-down and proteomic analysis of interacting proteins.
How CRISPR Can Be Used to Study GO:0031805 type 8 metabotropic glutamate receptor binding
Knockout
CRISPR/Cas9-mediated knockout of GRM8 creates cell lines or animal models lacking mGlu8. These models are essential for studying the loss of mGlu8 binding and its downstream effects. For example, Grm8 knockout mice can be used in behavioral assays to assess anxiety, addiction, and circadian rhythms. Knockout cell lines can confirm the specificity of radioligands and antibodies.
Point Mutation
Point mutations in GRM8 can be introduced to study the structural determinants of ligand binding. For instance, mutating residues in the Venus flytrap domain can reveal their role in agonist or antagonist binding. Such models help validate homology models and identify key interaction sites. Point mutations can also mimic human polymorphisms associated with disease.
Knock-in
Knock-in of tagged mGlu8 (e.g., HA or GFP) allows for visualization and immunoprecipitation of the receptor. This approach enables the study of mGlu8 trafficking, localization, and interacting proteins in native tissues. Knock-in of human disease-associated variants can model their functional consequences in vivo.
Overexpression
Overexpression of GRM8 in cell lines or transgenic animals increases mGlu8 levels, facilitating biochemical assays and behavioral studies. Overexpression models can be used to screen for ligands or to study the effects of excessive mGlu8 signaling. However, careful controls are needed to avoid artifacts from supraphysiological expression.
How EDITGENE Supports type 8 metabotropic glutamate receptor binding Research
Researchers studying type 8 metabotropic glutamate receptor binding-related genes often need to determine whether a candidate gene is causally involved in receptor function, signaling, or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to create precise genetic models, enabling rigorous investigation of mGlu8 biology.
Contact EDITGENE today to design your custom CRISPR model for type 8 metabotropic glutamate receptor binding research.
Frequently Asked Questions About type 8 metabotropic glutamate receptor binding
What is type 8 metabotropic glutamate receptor binding?
It is a molecular function (GO:0031805) describing the selective interaction with the metabotropic glutamate receptor 8 (mGlu8), a group III GPCR that inhibits neuronal activity.
What genes are involved in type 8 metabotropic glutamate receptor binding?
The primary gene is GRM8, which encodes the mGlu8 receptor. Other genes such as GNAI1, GNAO1, and CACNA1B are involved in downstream signaling.
How is type 8 metabotropic glutamate receptor binding studied?
Common methods include radioligand binding assays, electrophysiology, autoradiography, and CRISPR-based genetic models [1,3,4].
What diseases are associated with mGlu8 binding?
mGlu8 has been implicated in alcohol dependence, circadian rhythm disorders, and potentially neurodegenerative diseases, though direct evidence is limited.
What is the role of mGlu8 in the brain?
mGlu8 is a presynaptic inhibitory receptor that modulates neurotransmitter release and neuronal excitability, including in the suprachiasmatic nucleus [3,4].
Can CRISPR be used to study mGlu8 binding?
Yes, CRISPR/Cas9 can create knockout, knock-in, and point mutation models in GRM8 to study its function and binding properties.
What are the synonyms for GO:0031805?
The synonym is type 8 metabotropic glutamate receptor ligand.
Which ontology does GO:0031805 belong to?
It belongs to the molecular_function ontology.
What is the difference between mGlu8 and other mGlu receptors?
mGlu8 is a group III receptor that couples to Gi/Go, while group I (mGlu1/5) couple to Gq and group II (mGlu2/3) couple to Gi/Go but differ in pharmacology and distribution [1,2,3].
How can I create a knockout of GRM8?
EDITGENE offers custom CRISPR knockout services for GRM8 in various cell types and animal models.
Conclusion
GO:0031805, type 8 metabotropic glutamate receptor binding, represents a specific molecular interaction critical for neuronal signaling and potential therapeutic targeting. Understanding this function through pharmacological and genetic approaches, including CRISPR-based models, can illuminate its role in health and disease. EDITGENE provides the tools and expertise to accelerate such research.
References
- 1. Akam EC et al.. 1997. Pharmacological characterization of type 1alpha metabotropic glutamate receptor-stimulated [35S]-GTPgammaS binding.. Br J Pharmacol 121(6):1203-9 PMID: 9249258
- 2. Laukkanen V et al.. 2015. Increased metabotropic glutamate 2/3 receptor binding in the perigenual anterior cingulate cortex of Cloninger type 2 alcoholics: a whole-hemisphere autoradiography study.. Alcohol Alcohol 50(1):62-7 PMID: 25425009
- 3. Guo J et al.. 2005. Coupling of metabotropic glutamate receptor 8 to N-type Ca2+ channels in rat sympathetic neurons.. Mol Pharmacol 67(6):1840-51 PMID: 15755905
- 4. Haak LL. 1999. Metabotropic glutamate receptor modulation of glutamate responses in the suprachiasmatic nucleus.. J Neurophysiol 81(3):1308-17 PMID: 10085357
- 5. Kohara A et al.. 2005. Radioligand binding properties and pharmacological characterization of 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198), a high-affinity, selective, and noncompetitive antagonist of metabotropic glutamate receptor type 1.. J Pharmacol Exp Ther 315(1):163-9 PMID: 15976016
- 6. Suzuki Y et al.. 2004. Negative cooperativity of glutamate binding in the dimeric metabotropic glutamate receptor subtype 1.. J Biol Chem 279(34):35526-34 PMID: 15199056
- 8. Ishibashi K et al.. 2019. Unchanged type 1 metabotropic glutamate receptor availability in patients with Alzheimer's disease: A study using (11)C-ITMM positron emission tomography.. Neuroimage Clin 22:101783 PMID: 30909027
