Diversification of furanocoumarin-metabolizing cytochrome P450 monooxygenases in two papilionids: Specificity and substrate encounter rate

Abstract

Diversification of cytochrome P450 monooxygenases (P450s) is thought to result from antagonistic interactions between plants and their herbivorous enemies. However, little direct evidence demonstrates the relationship between selection by plant toxins and adaptive changes in herbivore P450s. Here we show that the furanocoumarin-metabolic activity of CYP6B proteins in two species of swallowtail caterpillars is associated with the probability of encountering host plant furanocoumarins. Catalytic activity was compared in two closely related CYP6B4 and CYP6B17 groups in the polyphagous congeners Papilio glaucus and Papilio canadensis. Generally, P450s from P. glaucus, which feeds occasionally on furanocoumarin-containing host plants, display higher activities against furanocoumarins than those from P. canadensis, which normally does not encounter furanocoumarins. These P450s in turn catalyze a larger range of furanocoumarins at lower efficiency than CYP6B1, a P450 from Papilio polyxenes, which feeds exclusively on furanocoumarin-containing host plants. Reconstruction of the ancestral CYP6B sequences using maximum likelihood predictions and comparisons of the sequence and geometry of their active sites to those of contemporary CYP6B proteins indicate that host plant diversity is directly related to P450 activity and inversely related to substrate specificity. These predictions suggest that, along the lineage leading to Papilio P450s, the ancestral, highly versatile CYP6B protein presumed to exist in a polyphagous species evolved through time into a more efficient and specialized CYP6B1-like protein in Papilio species with continual exposure to furanocoumarins. Further diversification of Papilio CYP6Bs has likely involved interspersed events of positive selection in oligophagous species and relaxation of functional constraints in polyphagous species.insects ͉ metabolism ͉ molecular modeling

Resistance of developing honeybee larvae during chronic exposure to dietary nicotine

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The genetic basis of a plant–insect coevolutionary key innovation

“…NSP, expressed solely in the larval midgut, promotes the formation of nitrile breakdown products instead of toxic isothiocyanates upon myrosinasecatalyzed glucosinolate hydrolysis (20). The GSS and NSP detoxification mechanisms are distinctly different from each other, as well as the other identified host plant detoxification mechanisms of the Lepidoptera: the cytochrome P450 monooxygenase gene superfamily in Papilio butterflies used against furanocoumarins (25) and the flavin-dependent monooxygenase system of the arctiid moth Tyria jacobaeae used against pyrrolizidine alkaloids (26).…”

Insecticidal effects of Moroccan plant extracts on development, energy reserves and enzymatic activities of Plodia interpunctella

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