Class C GPCR

Class C G Protein-Coupled Receptors (GPCRs) represent a large family of G protein-coupled receptors that are characterized by their unique structure and mechanism of signal transduction. These receptors play crucial roles in various physiological processes, including neurotransmission, metabolic regulation, and immune response. This article provides an overview of Class C GPCRs, focusing on their structure, signaling mechanisms, and physiological functions.

Structure

Class C GPCRs are distinguished from other GPCR classes by their distinct structural features. They possess a large extracellular domain (ECD) responsible for ligand binding, which is linked to the seven-transmembrane (7TM) domain characteristic of all GPCRs. The ECD often contains a Venus flytrap-like module (VFTM) that captures ligands, leading to receptor activation. Additionally, many Class C GPCRs form dimers or higher-order oligomers, which is essential for their function.

Signaling Mechanisms

The signaling mechanism of Class C GPCRs involves the binding of a ligand to the ECD, causing a conformational change that is transmitted to the 7TM domain. This leads to the activation of heterotrimeric G proteins, which then modulate various intracellular signaling pathways. Class C GPCRs can signal through multiple G proteins, including G_i/o, G_s, and G_q/11, allowing them to exert diverse physiological effects. Moreover, some members of this class can also signal through G protein-independent mechanisms, such as the activation of beta-arrestin pathways.

Physiological Functions

Class C GPCRs are involved in a wide range of physiological functions. For example:

- Metabotropic Glutamate Receptors (mGluRs): These receptors modulate glutamate neurotransmission in the central nervous system, playing key roles in synaptic plasticity, learning, and memory. - GABA_B Receptors: GABA_B receptors mediate the inhibitory effects of GABA, the primary inhibitory neurotransmitter in the brain, contributing to the regulation of neuronal excitability. - Calcium-Sensing Receptors (CaSRs): These receptors detect changes in extracellular calcium levels, important for maintaining calcium homeostasis in the body. - Taste Receptors: Certain Class C GPCRs are involved in taste perception, particularly the detection of umami and sweet tastes.

Clinical Significance

Due to their involvement in critical physiological processes, Class C GPCRs are targets for therapeutic intervention in various diseases. For instance, mGluR modulators are being explored for the treatment of neurological disorders such as schizophrenia and anxiety. Similarly, agonists and antagonists of the CaSR are used to manage disorders of calcium metabolism, such as primary hyperparathyroidism.

Conclusion

Class C G Protein-Coupled Receptors are a vital component of the GPCR superfamily, with unique structural features and signaling mechanisms that enable them to regulate a broad spectrum of physiological functions. Their importance in health and disease makes them a significant focus of biomedical research, with ongoing efforts to develop drugs targeting these receptors for various therapeutic applications.