G protein-coupled receptors (GPCRs) are a class of cell surface receptors that play a vital role in transmitting signals from the extracellular environment to the inside of cells. They are an integral part of the cellular communication system and are found in abundance on the surface of most cells in the human body.
These receptors consist of a single peptide chain that threads through the plasma membrane seven times, creating seven transmembrane helices. This structural pattern gives GPCRs their characteristic appearance. The primary function of GPCRs is to recognize and bind to specific signaling molecules, such as hormones, neurotransmitters, or even light-sensitive molecules. Once the ligand binds to the receptor, a conformational change occurs, activating the GPCR.
Upon activation, GPCRs are capable of interacting with a class of proteins known as G proteins. G proteins are guanine nucleotide-binding proteins that act as intermediaries between GPCRs and intracellular signaling pathways. When a GPCR is activated, it triggers the exchange of guanosine diphosphate (GDP) bound to the G protein for guanosine triphosphate (GTP), resulting in the dissociation of the G protein into its subunits.
These liberated subunits influence the activity of various effector proteins, leading to the initiation of diverse intracellular signaling cascades. Ultimately, these signaling cascades regulate a wide range of cellular processes, including neurotransmission, hormone production, muscle contraction, and cell growth.
Due to their crucial role in cellular signaling, GPCRs have become an important target for drug development. Approximately one-third of all currently marketed medications target GPCRs, making them one of the most significant classes of therapeutic targets in pharmacology.
