Identification and characterization of mutations in housefly (Musca domestica) acetylcholinesterase involved in insecticide resistance

Acetylcholinesterase (AChE) insensitive to organophosphate and carbamate in secticides has been identified as a major resistance mechanism in numerous arthropod species. However, the associated genetic changes have been report ed in the AChE genes from only three insect species: their role in conferri ng insecticide insensitivity has been confirmed. using functional expressio n. only for those in Drosophila melanogaster. The housefly. Musca domestica , was one of the first insects shown to have this mechanism, here we report the occurrence of five mutations (Val-180 --> Leu, Gly-262 --> Ala, Gly-26 2 --> Val, Phe-327 --> Tyr and Gly-365 --> Ala) in the AChE gene of this sp ecies that, either singly or in combination, confer different spectra of in secticide resistance. The baculovirus expression of wild-type and mutated h ousefly AChE proteins has confirmed that the mutations each confer relative ly modest levels of insecticide insensitivity except the novel Gly-262 --> Val mutation, which results in much stronger resistance (up to 100-fold) to certain compounds. In all cases the effects of mutation combinations are a dditive. The mutations introduce amino acid substitutions that are larger t han the corresponding wild-type residues and are located within the active site of the enzyme, close to the catalytic triad. The likely influence of t hese substitutions on the accessibility of the different types of inhibitor and the orientation of key catalytic residues are discussed in the light o f the three-dimensional structures of the AChE protein from Torpedo califor nica and D. melanogaster.