Elucidating the GTP Hydrolysis Mechanism in FeoB: A Hydrophobic Amino-Acid Substituted GTPase

Employing hybrid quantum mechanics/molecular dynamics (QM/MM) molecular dynamics simulations and experimental mutational studies, we investigate the GTP hydrolysis mechanism in a hydrophobic amino-acid substituted (HAS)-GTPase, FeoB. We identify glutamates, Glu66 and Glu67, that are acting as bases and find that proton transfer occurs from the attacking water to either of the glutamates through a water chain. However, GTP hydrolysis is not abolished, despite mutating these glutamates; instead, an alternative substrate-assisted hydrolysis becomes active with the same rate. Thus, mutational studies would misinterpret the role of glutamates. We trace the origin of the alternative mechanism to a structural feature conserved across all HAS-GTPases, distinct from the Ras-like GTPases.