Crystallographic insights into a cobalt (III) sepulchrate based alternative cofactor system of P450 BM3 monooxygenase.

P450 BM3 is a multi-domain heme-containing soluble bacterial monooxygenase. P450 BM3 and variants are known to oxidize structurally diverse substrates. Crystal structures of individual domains of P450 BM3 are available. However, the spatial organization of the full-length protein is unknown. In this study, crystal structures of the P450 BM3 M7 heme domain variant with and without cobalt (III) sepulchrate are reported. Cobalt (III) sepulchrate acts as an electron shuttle in an alternative cofactor system employing zinc dust as the electron source. The crystal structure shows a binding site for the mediator cobalt (III) sepulchrate at the entrance of the substrate access channel. The mediator occupies an unusual position which is far from the active site and distinct from the binding of the natural redox partner (FAD/NADPH binding domain).