Lambda-cyhalothrin stress response and functional analysis of AiGSTe3 from the black cutworm Agrotis ipsilon

This study aims to elucidate the lambda-cyhalothrin stress response and biological function of the glutathione-S-transferase (GST) gene AiGSTe3 from the black cutworm Agrotis ipsilon. The cDNA sequence of AiGSTe3 was retrieved from the transcriptome database of A. ipsilon by the homology search method. The sequence characteristics and expression level of AiGSTe3 were analyzed, together with the enzymatic properties and lambda-cyhalothrin detoxification and antioxidant activities of the protein encoded by AiGSTe3. The results showed that AiGSTe3 contained an open reading frame of 654 bp and encoded a protein consisting of 217 amino-acid residues. Phylogenetic analysis revealed that the protein encoded by AiGSTe3 belonged to the epsilon class. The highest expression level of AiGSTe3 was detected in the larval midgut and at the pupal stage. The expression level of AiGSTe3 was significantly upregulated at 12 h after treatment with the median lethal concentration (LC₅₀) of lambda-cyhalothrin. The AiGSTE3 recombinant protein was successfully expressed in Escherichia coli. AiGSTE3 was capable of catalyzing the conjugation of reduced glutathione (GSH) to 1-chloro-2, 4-dinitrobenzene (CDNB) with a maximum velocity (v_max) of 4.33 μmol/(min•mg) and a Michaelis constant (K_m) of 0.33 mmol/L. The results of the high performance liquid chromatography analysis indicated that AiGSTE3 was able to metabolize lambda-cyhalothrin in vitro. In addition, E. coli cells overexpressing AiGSTE3 displayed significant tolerance to oxidative injury. Taken together, AiGSTe3 can respond to the stress induced by lambda-cyhalothrin. AiGSTE3, encoded by AiGSTe3, can not only metabolize lambda-cyhalothrin directly, but also enhance the tolerance of A. ipsilon to lambda-cyhalothrin by alleviating the oxidative damage induced by insecticide exposure.