Facilitation of Signal Onset and Termination by Adenylyl Cyclase

The α subunit (G sα ) of the stimulatory heterotrimeric guanosine triphosphate binding protein (G protein) G s activates all isoforms of mammalian adenylyl cyclase. Adenylyl cyclase (Type V) and its subdomains, which interact with G sα , promoted inactivation of the G protein by increasing its guanosine triphosphatase (GTPase) activity. Adenylyl cyclase and its subdomains also augmented the receptor-mediated activation of heterotrimeric G s and thereby facilitated the rapid onset of signaling. These findings demonstrate that adenylyl cyclase functions as a GTPase activating protein (GAP) for the monomeric G sα and enhances the GTP/GDP exchange factor (GEF) activity of receptors.