Beyond the thiolate: Discovering natural variation in cytochrome P450 proximal ligation.

In a recent issue of Nature Chemical Biology, Nguy et al.1 report the discovery of an array of cytochrome P450 enzymes that challenge the long-standing view that P450 hemes must be coordinated by a cysteine thiolate. Many of these "noncanonical" P450s instead use serine or selenocysteine ligands. The characterization of two selected variants revealed distinct structural and spectroscopic features.