Theoretical investigation on proton transfer mechanism of extradiol dioxygenase

Abstract

A QM/MM method ONIOM (B3LYP: Amber) was employed to discuss the catalytic mechanism of non-heme iron extradiol dioxygenases (HPCD). Previous research suggested that protonation of alkylperoxo intermediate was achieved by transferring the proton from monoanionic catechol substrate to superoxide anion via the histidine residue near the active site. Herein, our results demonstrated that the proton was transferred from the monoanionic catechol substrate to the superoxide anion directly. The catalytic mechanism could be performed via two parallel pathways, named pathway A and B. Both of them consisted of a proton-transfer process and distal oxygen attack procedure but occurred in a different sequence. Our key mechanistic discovery for catalytic reactions revealed a two-state reactivity (TSR) scenario, in which quintet state crossed over the septet state. Pathway A was more kinetically and thermodynamically favorable.