Meta-Biol

• Pathways

G Protein Coupled Receptors (GPCR) sense extracellular signals and activate different Guanine nucleotide binding proteins (G proteins). Upon activation, GPCRs can replace the GDP with GTP in the alpha subunit of G proteins. GTP binding modifies the conformation of G alpha proteins and activates them. The Regulator of G protein Signalling (RGS) are GTPase Accelerating Proteins (GAPs) that can directly inhibit the G alpha subunit activity. There are at least 25 different types of RGS proteins known. Several of these RGS proteins (1, 2, 3, 4, 5, 8, 13, 16, 17, 18, 19, 21) can bind and stabilize the transition state of Guanine nucleotide binding protein G(q) subunit alpha class (GNAQ/GNA11/GNA14/GNA15). Following this, the RGS domain of the proteins exert GAP activity on G alpha (q) and allosterically modulate residues within G-alpha subunit to accelerate the intrinsic GTPase activity that hydrolyses GTP to GDP. This inactivates G alpha (q) and terminates downstream signalling (Neubig & Siderovski 2002, Kach et al. 2012). The primary function of G alpha (q) is activation of phospholipase C beta thereby triggering phosphoinositide hydrolysis, calcium mobilization and protein kinase C activation.