Cytochrome P450s in Papilio multicaudatus and the transition from oligophagy to polyphagy in the Papilionidae

Although substrate-specific CYP6B1 and CYP6B3 enzymes in Papilio polyxenes contribute to specialization on furanocoumarin-containing host plants, CYP6B4 and CYP6B17 enzymes in the polyphagous Papilio glaucus and Papilio canadensis have a broader range of substrates. Papilio multicaudatus, an oligophage with one furanocoumarin-containing host, is putatively ancestral to polyphagous Papilio species. Furanocoumarin-inducible CYP6B33-CYP6B37 and CYP6AB6 were characterized from this species. Heterologous expression of CYP6B33 revealed furanocoumarin metabolism resembling that of CYP6B4-CYP6B17 enzymes from P. glaucus and P. canadensis. Molecular models of CYP6B33 and CYP6B4 indicate that seven conserved aromatic side chains stabilize their hydrophobic catalytic sites and that a Lys484-Ser484 substitution enlarges the CYP6B4 active site pocket to increase the predicted distance between the substrate and reactive oxygen relative to CYP6B1. Loss of specialization in this lineage may have resulted from relatively few mutational changes, allowing acquisition of broader catalytic activities without loss of ancestral furanocoumarin-metabolizing activities.