G alpha (z) auto-inactivates by hydrolysing GTP to GDP Authored: Jupe, S, 2009-02-27 15:59:25 EC Number: 3.6.5.1 EC Number: 3.6.5.2 EC Number: 3.6.5.3 EC Number: 3.6.5.4 Edited: Jupe, S, 2009-09-09 Reactome Database ID Release 43392133 Reactome, http://www.reactome.org ReactomeREACT_19178 Reviewed: Akkerman, JW, 2009-06-03 When a ligand activates a G protein-coupled receptor, it induces a conformational change in the receptor (a change in shape) that allows the receptor to function as a guanine nucleotide exchange factor (GEF), stimulating the exchange of GDP for GTP on the G alpha subunit. In the traditional view of heterotrimeric protein activation, this exchange triggers the dissociation of the now active G alpha subunit from the beta:gamma dimer, initiating downstream signalling events. The G alpha subunit has intrinsic GTPase activity and will eventually hydrolyze the attached GTP to GDP, allowing reassociation with G beta:gamma. Additional GTPase-activating proteins (GAPs) stimulate the GTPase activity of G alpha, leading to more rapid termination of the transduced signal. In some cases the downstream effector may have GAP activity, helping to deactivate the pathway. This is the case for phospholipase C beta, which possesses GAP activity within its C-terminal region. G-protein alpha (z):GTP G-protein alpha (z):GDP