title: Do mosquitoes acquire organophosphate resistance by functional changes in carboxylesterases?
abstract: Carboxylesterase-based metabolic resistance to organophosphates (OPs) in insects has been shown to originate either from mutations in esterase-encoding sequences or from amplification of esterase genes. This study aimed to test the hypothesis that mosquitoes can acquire OP resistance by functional changes in carboxylesterases. Mutations were introduced into the esterase B1 of mosquito Culex pipiens by site-directed mutagenesis at positions 110 and 224. Three single mutants (G110D, W224L, and W224S) and two double mutants (G110D/W224L and G110D/W224S) were expressed and purified. All five mutants lost native carboxylesterase activity. Mutation W224L converted esterase B1 to an OP hydrolase and increased its malathion carboxylesterase activity. No obvious OP hydrolysis was observed by G110D or W224S. Our data strongly support our hypothesis and suggest that mutation W224L might occur in natural populations of mosquitoes. Sequence comparison shows that the site 224 is especially highly conserved among various insect carboxylesterases. This leads to another hypothesis: that the position 224 plays a key role in insect carboxylesterases' switching from their native physiological functions to other functional niches under selection pressure exerted by insecticides.
authors.affiliation: State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Cui
authors.forename: Hong
authors.initials: H
authors.lastname: Qu
authors.forename: Jian
authors.initials: J
authors.lastname: Cong
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Liu
authors.forename: Chuan-Ling
authors.initials: CL
authors.lastname: Qiao
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003465:Culex / Q000502:physiology*; D007305:Insecticide Resistance; D008969:Molecular Sequence Data; D009943:Organophosphorus Compounds / Q000633:toxicity*; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D009943:Organophosphorus Compounds; D002265:Carboxylic Ester Hydrolases