Mechanism of the intrinsic arginine finger in heterotrimeric G proteins.

ABSTRACT: Heterotrimeric G proteins are crucial molecular switches that maintain a large number of physiological processes in cells. The signal is encoded into surface alterations of the G? subunit that carries GTP in its active state and GDP in its inactive state. The ability of the G? subunit to hydrolyze GTP is essential for signal termination. Regulator of G protein signaling (RGS) proteins accelerates this process. A key player in this catalyzed reaction is an arginine residue, Arg178 in G?i1, which is already an intrinsic part of the catalytic center in G? in contrast to small GTPases, at which the corresponding GTPase-activating protein (GAP) provides the arginine "finger." We applied time-resolved FTIR spectroscopy in combination with isotopic labeling and site-directed mutagenesis to reveal the molecular mechanism, especially of the role of Arg178 in the intrinsic G?i1 mechanism and the RGS4-catalyzed mechanism. Complementary biomolecular simulations (molecular mechanics with molecular dynamics and coupled quantum mechanics/molecular mechanics) were performed. Our findings show that Arg178 is bound to ?-GTP for the intrinsic G?i1 mechanism and pushed toward a bidentate ?-?-GTP coordination for the G?i1·RGS4 mechanism. This movement induces a charge shift toward ?-GTP, increases the planarity of ?-GTP, and thereby catalyzes the hydrolysis.

SUBMITTER: Mann D 

PROVIDER: S-EPMC5167181 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature