How Chorismatases Regulate Distinct Reaction Channels in a Single Conserved Active Pocket: Mechanistic Analysis with QM/MM (ONIOM) Investigations

Abstract

The FkbO and Hyg5 subfamilies of chorismatases share the same active-site architectures, but perform distinct reactionm echanisms, that is, FkbOe mploys ah ydrolysis reaction whereasH yg5 proceeds through an intramolecular mechanism. Despite extensive researche fforts, the detailed mechanism of the product selectivity in chorismatasesn eed to be further unmasked. In this study,t he effects of the A/G residueg roup (A244 FkbO /G240 Hyg5 )a nd the V/Q residue group (V209 FkbO /Q201 Hyg5 )o nt he catalytic mechanisms are investigated by employing molecular dynamics simulations and hybrid quantumm echanical/molecularm echanical (QM/MM) calculations of the two wild-type models (FkbO/CHO and Hyg5/CHO;C HO = chorismate)a nd four mutants models (A244G-FkbO/CHO and G240A-Hyg5/CHO;V 209Q-FkbO/CHO and Q201V-Hyg5/CHO). Our results showed that the A/G residue group mentionedb yp revious worksw ould cause changes in the binding stateso fthe substratea nd the orientation of the catalytic glutamate, but only these changes affectt he product selectivity in chorismatases limitedly.I nterestingly,t he distalV /Q residue group, which determines the internal water self-regulating ability at the active site, has significant impact on the selectivity of the catalytic mechanisms. The V/Q residueg roup is suggested to be an important factor to control the catalytic activities in chorismatases. Ther esultsa re consistent with biochemical and structurale xperiments,p roviding novel insight into the mechanism of product selectivity in chorismatases.[a] Dr.