The cytochrome P450 gene family CYP157 does not contain EXXR in the K-helix reducing the absolute conserved P450 residues to a single cysteine

In this work, we have spectroscopically characterised CYP157C1 from Streptomyces coelicolor A3(2) which has the motif E297QSLW301 rather than the invariant EXXR motif in the P450 K-helix. Site-directed mutagenesis of native E297QSLW301 in CYP157C1 to E297ESLR301 or E297QSRW301 both containing standard EXXR motifs produced cytochrome P420 proteins thought to be inactive forms of P450 even though wild type CYP157C1 has the spectral properties of a normal P450. These results indicate that the EXXR motif is not required in all CYP tertiary architectures and only a single cysteine residue, which coordinates as the fifth thiolate ligand to the P450 haem iron, is invariant in all CYPs structures.