Purified M1 muscarinic cholinergic receptor and Gq/11 were coreconstituted in lipid vesicles. Addition of purified phospholipase C-β1 (PLC-β1) further stimulated the receptor-promoted steady-state GTPase activity of Gq/11 up to 20-fold. Stimulation depended upon receptor-mediated GTP-GDP exchange. Addition of PLC-β1 caused a rapid burst of hydrolysis of Gq/11-bound GTP that was at least 50-fold faster than in its absence. Thus, PLC-β1 stimulates hydrolysis of Gq/11-bound GTP and acts as a GTPase-activating protein (GAP) for its physiologic regulator, Gq/11. GTPase-stimulating activity was specific both for PLC-β1 and Gq/11. Such GAP activity by an effector coupled to a trimeric G protein can reconcile slow GTP hydrolysis by pure G proteins in vitro with fast physiologic deactivation of G protein-mediated signaling.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)