Identification and biochemical characterization of carboxylesterase 001G associated with insecticide detoxification in Helicoverpa armigera

Carboxylesterases (CarEs) are a major class of detoxification enzymes involved in insecticide resistance in various insect species. In this study, a novel CarE 001G was isolated from the cotton bollworm Helicoverpa armigera , one of the most destructive agricultural insect pests . The open reading frame of 001G has 2244 nucleotides and putatively encodes 747 amino acid residues. The deduced CarE possessed the highly conserved catalytic triads(Ser-Glu-His) and pentapeptide motifs (Gly-X-Ser-X-Gly), suggesting 001G is biologically active. The truncated 001G was successfully expressed in Escherichia coli , and the recombinant proteins were purified and tested. The enzyme kinetic assay showed the purified proteins could catalyze two model substrates, α-naphthyl acetate and β-naphthyl acetate, with a kcat of 8.8 and 2.3 s −1 , a K m of 9.6 and 16.2 μM, respectively. The inhibition study with pyrethroid , organophosphate and neonicotinoid insecticides showed different inhibition profile against the purified CarE. The HPLC assay demonstrated that the purified proteins were able to metabolize β -cypermethrin, λ-cyhalothrin and fenvalerate insecticides, exhibiting respective specific activities of 1.7, 1.4 and 0.5 nM/min/mg protein. However, the purified proteins were not able to metabolize the chlorpyrifos , parathion-methyl, paraoxon-ethyl and imidacloprid . The modeling and docking analyses consistently demonstrated that the pyrethroid molecule fits snugly into the catalytic pocket of the CarE 001G. Collectively, our results suggest that 001G may play a role in pyrethroids detoxification in H. armigera .