G Protein Related

The heterotrimeric G protein is composed of Gα, Gβ and Gγ subunits, and Gα subunit contains guanosine 5′-diphosphate (GDP) in its inactive resting state. Agonist-activated GPCRs stimulate the release of GDP from Gα subunit, and the GPCR and the empty (e.g. nucleotidefree) G protein form a complex with a high-affinity. Soon after, guanosine 5′-triphosphate (GTP) is recruited to the empty Gα nucleotide-binding pocket, which subsequently induces the dissociation of the heterotrimer into Gα and Gβγ subunits; the separated subunits interact with various effector molecules such as adenylyl cyclase, phospholipase and G protein-coupled receptor kinase for further downstream signal cascades. The activated G proteins go back to the resting state by hydrolyzing a phosphate group from GTP, converting it to GDP.