A vast and varied family of cell surface receptors known as G-protein coupled receptors (GPCRs) is essential to signal transduction across cell membranes. Numerous physiological processes, such as immunological response, neurotransmission, sensory perception, and hormone signaling, are regulated by these receptors. Integral membrane proteins with seven transmembrane domains joined by intra- and extracellular loops make up GPCRs structurally. Whereas the C-terminus is usually found inside cells, the N-terminus is usually found outside of them. When ligands, including ions, hormones, or neurotransmitters, attach to the extracellular domain of a receptor, their conformational changes cause the receptor to become active. The recruitment and activation of G proteins, which are heterotrimeric complexes made up of α, β, and γ subunits, are brought about by the activation of GPCRs. GDP and the G protein are connected when the protein is inactive. GTP is switched for GDP during receptor activation, which leads to the Gα subunit's separation from the Gβγ dimer. Subsequently, the Gα and Gβγ elements have the ability to regulate several intracellular effectors, including ion channels and enzymes. G proteins are classified into four primary classes: Gs, Gi/o, Gq/11, and G12/13. Gs causes adenylyl cyclase to become more active, which raises cyclic AMP (cAMP) levels and activates protein kinase A (PKA). Inositol trisphosphate (IP3) and diacylglycerol (DAG), which further modify intracellular signaling pathways, are produced when Gq/11 activates phospholipase C. G12/13 controls cell migration and cytoskeletal dynamics. Internalization and desensitization are important processes that control GPCR signaling. In this process, β-arrestins are essential because they attach to phosphorylated GPCRs, which causes the receptor to become less sensitive and internalize. This, in turn, affects the length and strength of the cellular response. GPCRs are desirable targets for drugs because of their critical function in cellular communication. Given that a sizable portion of medications target GPCRs, this receptor family is among the most researched and significant in drug development. Research is still being done to better understand the complexities of GPCR signaling, as this could lead to therapeutic approaches for a range of disorders.
