Functional Characterization of an α-Esterase Gene Associated with Malathion Detoxification in Bradysia odoriphaga

Abstract

Carboxylesterases (CarEs) are a multigene superfamily of metabolic enzymes involved in metabolic detoxification of xenobiotics. In this study, an α-esterase gene (BoαE1) was identified from Bradysia odoriphaga. Phylogenetic analysis classified BoαE1 into the α-esterase clade. Developmental expression analysis indicated that BoαE1 was significantly expressed in the second to fourth larval stages. Tissue-specific expression analysis indicated that BoαE1 was highly expressed in the larval midgut. After exposure to LC30 of malathion, the CarE activity of B. odoriphaga was induced and the transcriptional level of BoαE1 was significantly up-regulated. Silencing of BoαE1 significantly increased the susceptibility of B. odoriphaga larvae to malathion. Inhibition assays in vitro indicated that malathion significantly inhibited BoαE1 activity. GC-MS assay showed that BoαE1 possesses hydrolase activity toward malathion and participates in the detoxification of malathion. These results strongly suggest that BoαE1 plays a crucial role in detoxification of malathion in B. odoriphaga.

Characterization of the insecticide detoxification carboxylesterase Boest1 from Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae)

“…69 Several studies have reported that a P. xylostella CarE could metabolize bifenthrin, cyfluthrin, cypermethrin, and ⊗-cyhalothrin with different efficiencies. 70 Additionally, CarE Bo⊍E1 of B. odoriphaga could metabolize 27% of a 90 mg L -1 dose of malathion in 2 h. 45 Our results demonstrated that BoEST1 could hydrolyze bifenthrin and malathion with specific activities of 12.80 and 12.41 nmol L −1 min -1 mg -1 protein, respectively. Furthermore, BoEST1 showed no hydrolytic activity against imidacloprid, further verifying that the CarE is unable to hydrolyze non-carboxylic ester insecticides.…”

“…BoEST1 shows relatively lower catalytic efficiency and affinity toward ⊍-NA than the previously reported B. odoriphaga Bo⊍E1 with a reported k cat of 1.12 s −1 and K m of 106.6 mmol L −1 . 45 The catalytic efficiency ratio (k cat /K m ) of BoEST1 was 2.035 L mmol −1 s −1 . Thus, recombinant BoEST1 exhibits CarE activity, indicating it may have the capacity to metabolize insecticides as well as carboxyl esters.…”

“…It has been reported that CarE genes are up-regulated with aging in some insect species. 45,58 Stage-dependent expression patterns of Boest1 were determined in all developmental stages by RT-qPCR, with the results showing that BoEST1 was expressed in all developmental stages of B. odoriphaga. It was found to be highly transcribed across all the feeding stages, which may relate to the detoxification of xenobiotics in food.…”

“…Previous research has shown that the CarEs are involved in the detoxification of certain groups of insecticides, including the organophosphates and pyrethroids. 45,68,69 It has been reported that the Helicoverpa armigera CarE 001G showed relatively higher hydrolytic activity towards ⊎-cypermethrin and ⊗-cyhalothrin with activities of 1.7 and 1.4 nmol L −1 min -1 mg -1 protein, respectively. In contrast, no hydrolysis of imidacloprid was observed.…”

“…44 To date, only one CarE gene, Bo⊍E1, has been cloned; this gene plays a crucial role in the detoxification of malathion. 45 The metabolic capacity and binding modes of CarEs with insecticides in B. odoriphaga are still yet to be clarified.…”