Structural insights from a P450 Carrier Protein complex reveal how specificity is achieved in the P450BioI ACP complex

Cytochrome P450_BioI (CYP107H1) from the biotin operon of Bacillus subtilis forms a seven-carbon diacid through a multistep oxidative cleavage of a fatty acid linked to acyl carrier protein (ACP). Crystal structures of P450_BioI in complex with three different length fatty acyl-ACP (Escherichia coli) ligands show that P450_BioI binds the fatty acid such as to force the carbon chain into a U-shape above the active site heme. This positions the C7 and C8 carbons for oxidation, with a large additional cavity extending beyond the heme to accommodate the methyl termini of fatty acids beyond the site of cleavage. The structures explain the experimentally observed lack of stereo- and regiospecificity in the hydroxylation and cleavage of free fatty acids. The P450_BioI-ACP complexes represent the only structurally characterized P450-carrier protein complexes to date, which has allowed the generation of a model of the interaction of the vancomycin biosynthetic P450 OxyB with its proposed carrier protein bound substrate.