Molecular mechanism of acetylcholinesterase insensitivity to insecticide and its utilization.

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Molecular mechanism of acetylcholinesterase (AChE) insensitivity to organophosphates and carbamates was studied, and the insensitivity was elucidated to be caused by amino acid substitutions in the active cite of the enzyme. In cyclorrhapha dipterans, only one gene of AChE exists in their genome, and several amino acids were replaced in the insensitive AChE. In the orthologous AChE of other insects, however, no amino acid substitution has been found in relation to the insensitivity. After the discovery of the second AChE (Ace paralogous AChE, AP-AChE) gene in an aphid and a mosquito species in 2002, we cloned AP-AChE cDNA from several species of resistant insects and mites ; Myzus persicae, Aphis gossypii, Nephotettix cincticeps, Tetranychus urticae and Tetranychus kanzawai, and found species specific amino acid substitutions causing the insensitivity at the important position in the active site of the enzyme. When 6 recombinant AChEs having respective amino acid substitutions were expressed in baculovirus-insect cultured cell system, AChEs produced showed specific characteristics in the reduction of sensitivity to insecticides.Purification of AChE and gene expression of two AChE were also studied in the mosquitoes.