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 E ²⁹⁷ QSLW ³⁰¹ rather than the invariant EXXR motif in the P450 K-helix. Site-directed mutagenesis of native E ²⁹⁷ QSLW ³⁰¹ in CYP157C1 to E ²⁹⁷ ESLR ³⁰¹ or E ²⁹⁷ QSRW ³⁰¹ 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.