A mutation that prevents GTP-dependent activation of the α chain of G_s

Membrane-bound G proteins carry information from receptors on the outside of cells to effector proteins inside cells. The α subunits of these heterotrimeric proteins bind and hydrolyse GTP and control the specificity of interactions with receptor and effector elements^1,2. Signalling by G proteins involves a cycle in which the inactive αβγ-GDP complex dissociates to produce α*-GTP, which is capable of activating the effector enzyme or ion channel; the α*-GTP complex hydrolyses bound GTP and reassociates with βγ to form the inactive complex. We have characterized a mutation that interrupts this GTP-driven cycle in α_s, the α-chain of G_s, the G protein that stimulates adenylyl cyclase. The mutation converts a glycine to an alanine residue in the presumed GDP-binding domain of α_s. The location and biochemical consequences of this mutation suggest a common mechanism by which binding of GTP or ATP may induce changes in the conformation of a number of nucleoside triphosphate binding proteins.