Mapping determinants of the substrate selectivities of P450 enzymes by site-directed mutagenesis

Point-mutation studies in cytochrome P450s by site-directed mutagenesis have identified key residues that can confer the catalytic properties of one cytochrome P450 onto another. Most of these key residues cluster at sites that map to amino acids forming the substrate-binding site of P450cam, a distantly related enzyme. These sites are found on topological elements of P450cam, which by their surface location and lack of extensive secondary structure are likely to permit genetic variation without extensive disruption of the overall topology of the enzyme. If these topological features of P450cam are conserved in the mammalian enzymes, they are likely to accommodate the structural diversity seen for mammalian P450s in a manner that conserves a basic structure for P450 enzymes but that leads to the catalytic diversity seen for the mammalian enzymes.