Mechanism of Cytochrome P450 17A1-Catalyzed Hydroxylase and Lyase Reactions

Cytochrome P450 17A1 (CYP17A1) catalyzes C17 hydroxylation of pregnenolone and progesterone and the subsequent C17–C20 bond cleavage (lyase reaction) to form androgen precursors. Compound I (Cpd I) and peroxo anion (POA) are the heme-reactive species underlying the two reactions. We have characterized the reaction path for both the hydroxylase and lyase reactions using density functional theory (DFT) calculations and the enzyme–substrate interactions by molecular dynamics (MD) simulations. Activation barriers for positions subject to hydroxylase reaction have values close to each other and span from 54 to 60 kJ·mol–1 with a small preference for 17α hydroxylation, in agreement with experimental observations. For the lyase reaction, two different types of mechanisms, concerted and stepwise, with identical activation energies (87 kJ·mol–1) were identified. Embedding the DFT-optimized transition states (TSs) for the two reactions into the active site of CYP17A1 showed that the TS for the C17 hydroxylation nee...