A G-protein-coupled receptor (GPCR) is a member of the largest superfamily of cell-surface receptors in the human genome. All GPCRs share a common architecture of seven α-helical transmembrane domains connected by three extracellular and three intracellular loops, with an extracellular N-terminus and an intracellular C-terminus.
Ligand binding stabilises an active receptor conformation that catalyses GDP-to-GTP exchange on the α-subunit of an associated heterotrimeric G protein (Gs, Gi/o, Gq/11, G12/13), which dissociates from Gβγ and engages downstream effectors such as adenylyl cyclase, phospholipase C or ion channels. GPCRs are further regulated by phosphorylation and β-arrestin recruitment, leading to desensitisation and biased signalling.
Most receptor-targeted research peptides in this catalogue — GLP-1R, GIPR, GCGR, GHSR, MC1R–MC5R — are class B or class A GPCRs.