Detoxification of insecticides, allechemicals and heavy metals by glutathione S-transferase SlGSTE1 in the gut of Spodoptera litura

Insect glutathione S-transferases (GSTs) play important roles in detoxifying toxic compounds and eliminating oxidative stress caused by these compounds. In this study, detoxification activity of the epsilon GST SlGSTE1 in Spodoptera litura was analyzed for several insecticides and heavy metals. SlGSTE1 was significantly up-regulated by chlorpyrifos and xanthotoxin in the midgut of S. litura. The recombinant SlGSTE1 had V-max (reaction rate of the enzyme saturated with the substrate) and K-m (michaelis constant and equals to the substrate concentration at half of the maximum reaction rate of the enzyme) values of 27.95 +/- 0.88 mol/min/mg and 0.87 +/- 0.028mmol/L for glutathione, respectively, and V-max and K-m values of 22.96 +/- 0.78 mol/min/mg and 0.83 +/- 0.106 mmol/L for 1-chloro-2,4-dinitrobenzene, respectively. In vitro enzyme indirect activity assay showed that the recombinant SlGSTE1 possessed high binding activities to the insecticides chlorpyrifos, deltamethrin, malathion, phoxim and dichloro-diphenyl-trichloroethane (DDT). SlGSTE1 showed higher binding activity to toxic heavy metals cadmium, chromium and lead than copper and zinc that are required for insect normal growth. Western blot analysis showed that SlGSTE1 was induced in the gut of larvae fed with chlorpyrifos or cadmium. SlGSTE1 also showed high peroxidase activity. All the results together indicate that SlGSTE1 may play an important role in the gut of S. litura to protect the insect from the toxic effects of these compounds and heavy metals.