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.