QM/MM and MD Studies of the First Proton Transfer for O2 Activation in the Catalytic Cycle of Cytochrome P450cin

P450 cin(CYP176 A1) isolated from Citrobacter braakii is a biodegradation enzyme that catalyzes the enantiospecific conversion of 1,8-cineole to(1 R)-6β-hydroxycineole. In many P450 family members the mechanism of proton delivery for O2activation is proposed to require a conserved acid-alcohol dyad in the active area, while P450 cin has no such residue with alcohol but asparagine instead. In the present work, the mechanism of the first proton transfer of O2activation in P450 cin has been investigated by molecular dynamics(MD) and hybrid quantum mechanics/molecular mechanics(QM/MM) techniques. The MD simulation suggests there are two hydrogen bonding networks around the active site, one involving Asp241 and the other involving Glu356. According to our MD and QM/MM calculations, this Asp241 channel is proposed to be the energy accessible. MD results show that the hydrogen bonds around the substrate may contribute to regio-and stereo-oxidation of the substrate.