Figure 1: The GTPase active site in EF-Tu and possible hydrolysis mechanisms.
From: Energetics of activation of GTP hydrolysis on the ribosome
(a) The crystallographic structure with EF-Tu and the non-hydrolyzable GTP analogue GDPCP bound to the ribosome8 is shown with the geometry around the catalytic water molecule (red sphere) indicated. The Mg2+ ion bound between the β- and γ-phosphate groups is shown as a green sphere. (b) Three possible hydrolysis mechanisms corresponding to His84 acting as a general base, a stepwise substrate-assisted mechanism and a dissociative path involving expulsion of metaphosphate, both of the latter with His84 protonated. The different nature of the transition states in the associative and dissociative cases with His84 protonated are indicated by the structures within parentheses.
