Definition
A large family of seven-transmembrane receptors that signal through G proteins; the target of most peptide hormones.
G protein-coupled receptors are membrane proteins that cross the cell membrane seven times. When a ligand binds, the receptor changes shape and activates an intracellular heterotrimeric G protein. Gs raises cAMP, Gi lowers it, and Gq activates phospholipase C and calcium release, while β-arrestins mediate desensitisation and additional signalling. Humans have more than 800 GPCRs, and they are the targets of roughly a third of approved medicines. Class B GPCRs, including the GLP-1, GIP, glucagon and GHRH receptors, have a large extracellular domain that binds peptide hormones. The ghrelin, melanocortin and somatostatin receptors belong to class A. The 2012 Nobel Prize in Chemistry recognised GPCR research.