Structural model and functional characterization of the Bemisia tabaci CYP6CM1vQ, a cytochrome P450 associated with high levels of imidacloprid resistance.

The neonicotinoid imidacloprid is one of the most important insecticides worldwide. It is used extensively against the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae), an insect pest of eminent importance globally, which was also the first pest to develop high levels of resistance against imidacloprid and other neonicotinoids in the field. Recent reports indicated that in both the B and Q biotypes of B. tabaci, the resistant phenotype is associated with over-expression of the cytochrome P450 gene CYP6CM1. In this study, molecular docking and dynamic simulations were used to analyze interactions of imidacloprid with the biotype Q variant of the CYP6CM1 enzyme (CYP6CM1vQ). The binding mode with the lowest energy in the enzyme active site, the key amino acids involved (i.e. Phe-130 and Phe-226), and the putative hydroxylation site (lowest distance to carbon 5 of the imidazolidine ring system of imidacloprid) were predicted. Heterologous expression of the CYP6CM1vQ confirmed the accuracy of our predictions and demonstrated that the enzyme catalyses the hydroxylation of imidacloprid to its less toxic 5-hydroxy form (K(cat) = 3.2 pmol/min/pmol P450, K(m) = 36 microM). The data identify CYP6CM1vQ as a principle target for inhibitor design, aimed at inactivating insecticide-metabolizing P450s in natural insect pest populations.