SeGSTo, a novel glutathione S-transferase from the beet armyworm (Spodoptera exigua), involved in detoxification and oxidative stress.

Members of the glutathione S-transferase superfamily can protect organisms against oxidative stress. In this study, we characterized an omega glutathione S-transferase from Spodoptera exigua (SeGSTo). The SeGSTo gene contains an open reading frame (ORF) of 744 nucleotides encoding a 248-amino acid polypeptide. The predicted molecular mass and isoelectric point of SeGSTo are 29007 Da and 7.74, respectively. Multiple amino acid sequence alignment analysis shows that the SeGSTo sequence is closely related to the class 4 GSTo of Bombyx mori BmGSTo4 (77 % protein sequence similarity). Homologous modeling and molecular docking reveal that Cys35 may play an essential role in the catalytic process. Additionally, the phylogenetic tree indicates that SeGSTo belongs to the omega group of the GST superfamily. During S. exigua development, SeGSTo is expressed in the midgut of the fifth instar larval stage, but not in the epidermis or fat body. Identification of recombinant SeGSTo via SDS-PAGE and Western blot shows that its molecular mass is 30 kDa. The recombinant SeGSTo was able to protect super-coiled DNA from damage in a metal-catalyzed oxidation (MCO) system and catalyze the 1-chloro-2,4-dinitrobenzene (CDNB), but not 1,2-dichloro-4-nitrobenzene (DCNB), 4-nitrophenethyl bromide (4-NPB), or 4-nitrobenzyl chloride (4-NBC). The optimal reaction pH and temperature were 8 and 50 °C, respectively, in the catalysis of CDNB by recombinant SeGSTo. The mRNA expression of SeGSTo was up-regulated by various oxidative stresses, such as CdCl2, CuSO4, and isoprocarb, and the catalytic activity of recombinant SeGSTo was noticeably inhibited by heavy metals (Cu(2+) and Cd(2+)) and various pesticides. Taken together, these results indicate that SeGSTo plays an important role in the antioxidation and detoxification of pesticides.