Flavin‐N5OOH Functions as both a Powerful Nucleophile and a Base in the Superfamily of Flavoenzymes

Abstract

Flavoenzymes can mediate a large variety of oxidation reactions via the activation of oxygen. However, the O2 activation chemistry by flavin enzymes is not yet fully exploited. Normally, the O2 activation occurs at the C4a site of the flavin cofactor, yielding the flavin C4a‐(hydro)hydroperoxyl species in monooxygenases or oxidases. Using extensive MD simulations, QM/MM calculations and QM calculations, our studies reveal the formation of the common nucleophilic species, flavin‐N5OOH, in two distinct flavoenzymes (RutA and EncM). Our studies show that flavin‐N5OOH acts as a powerful nucleophile that promotes C–N cleavage of uracil in RutA, and a powerful base in the deprotonation of substrates in EncM. We reason that flavin‐N5OOH can be a common reactive species in the superfamily of flavoenzymes, which accomplishes the generally selective general base catalysis, and the C–X (X= N, S, Cl, O) cleavage reactions that are otherwise challenging by solvated hydroxide ion base. These results expand our understanding of the chemistry and catalysis of flavoenzymes.