In Crystallo Reactions with an Engineered Cytochrome P450 Peroxygenase

The cytochrome P450 monooxygenases are a class of heme-thiolate enzymes that are able to insert oxygen into unactivated C-H bonds. These enzymes can be converted into peroxygenases via protein engineering which enables this activity to occur using hydrogen peroxide (H2O2) with-out the requirement for additional nicotinamide co-factors or partner proteins. This offers significant advantages in terms of applications and mechanistic studies. Here, we investigate whether soaking crystals of an engineered P450 peroxygenase with H2O2 enables the enzymatic reactions to occur within the crystal. A designed bacterial P450 peroxy-genase, CYP199A4 (T252E variant), which has enhanced activity for the O-demethylation of 4-methoxybenzoic acid using H2O2 was used. Crystals of T252E-CYP199A4 in complex with 4-methoxybenzoic acid were soaked with different concentrations of H2O2 for varying times to initiate an in crystallo O-demethylation reaction. Crystal structures of T252E-CYP199A4 showed a distinct loss of electron density that was consistent with the O-demethylated metabolite, 4-hydroxybenzoic acid when compared to the crystal structures of the same enzyme with the 4-hydroxybenzoic acid product and the 4-methoxybenzoic acid substrate bound. The visualisation of enzymatic catalysis in action is challenging in structural biology and the ability to start and monitor the reactions of P450 enzymes, or their progress, in crystallo by simply soaking crystals with H2O2 will enable new information on intermediates, such as product bound structures, and the mechanisms of these oxygenase reactions to be obtained.