EPR Characterization of the Heme Domain of a Self-Sufficient Cytochrome P450 (CYP116B5)

CYP116B5 is a self-sufficient cytochrome P450 (CYP450) with interesting catalytic properties for synthetic
purposes. When isolated, its heme domain can act as a peroxygenase on different substrates of biotechnological
interest. Here, by means of continuous wave and advanced EPR techniques, the coordination environment of iron
in the isolated CYP116B5 heme domain (CYP116b5hd) is characterized. The ligand-free protein shows the
characteristic EPR spectrum of a low-spin (S = 1/2) FeIII-heme with [gz = 2.440 ± 0.005, gy = 2.25 ± 0.01, gx =
1.92 ± 0.01]. These g-values reflect an electronic ground state very similar to classical P450 monooxygenases
rather than P450 peroxygenases. Binding of imidazole results in g-values very close to the ones reported for
CYP152 peroxygenases. The detection of hyperfine interactions through HYperfine Sub-level CORrElation
(HYSCORE) Spectroscopy experiments, shows that this is due to a nitrogen-mediated axial coordination. This
work adds a piece of experimental evidence to the research, aimed at elucidating the features that distinguish the
classical P450 enzymes from peroxygenases. It shows that the electronic environment of heme iron of CYP116B5
in the resting state is similar to the classical P450 monooxygenases. Therefore, it is not the critical factor that
confers to CYP116B5hd its peroxygenase-like activity, suggesting a crucial role of the protein matrix.