GTP analogue hydrolysis by the Gs protein: Implication for the role of catalytic glutamine in the GTPase reaction

Hydrolysis of GTP, bound to members of the G-protein superfamily, terminates their downstream signaling activity. A conserved glutamine serves a critical role in this pivotal guanosine triphosphatase (GTPase) reaction. However, the role of the catalytic glutamine in GTP hydrolysis is still not well understood. We have employed substrate-assisted catalysis to probe the catalytic mechanism of G_sα using GTP analogues. These GTP analogues, each having different functional groups, were designed to support or refute particular putative GTPase mechanisms. We have found that a hydrogen donor group, in close proximity to the γ-phosphate of GTP, is necessary and sufficient to substitute for the function of the catalytic glutamine in the GTPase reaction.