Functional Characterization of Cytochromes P450 2B from Woodrats

Abstract

Much of the structure‐function information on cytochromes P450 (P450) 2B is from a limited number of pharmacologically relevant species. Recent data suggest that desert woodrats (Neotoma lepida) have multiple P450 2B enzymes with greater than 85% identity to P450 2B1. Populations of N. lepida consuming creosote (Larrea tridentata) or juniper (Juniperus osteosperma) have differential expression of P450s 2B. Following previous protocols, we modified, expressed, and purified one P450 2B from one woodrat fed a creosote diet and one fed a juniper diet. (−)‐a‐pinene, β‐myrcene, and d‐limonene, which are common in juniper and previously reported to be inhibitors of P450 2B1, show very high affinity (<50 nM) for both woodrat enzymes. The woodrat enzymes show similar activity to P450 2B1 with 7‐ethoxy‐4‐ trifluoromethyl‐coumarin (7‐EFC), but significant differences in activity and product profile are seen in ticlopidine metabolism. Residue 262 shows a lysine – arginine difference between the two enzymes. This residue has demonstrated functional differences in the human P450 2B6, and the known human genetic polymorphism K262R produces significant changes in ligand interactions. Differences in P450 2B structure in woodrats may confer functional differences in the metabolism of dietary toxins. (Supported by ES003619 and T32‐DK07233).