Abstract
The glutathione transferase (GST) superfamily plays key roles in the detoxification of various xenobiotics. Here, we report the isolation and characterization of a silkworm protein belonging to a previously reported theta-class GST family. The enzyme (bmGSTT) catalyzes the reaction of glutathione with 1-chloro-2,4-dinitrobenzene, 1,2-epoxy-3-(4-nitrophenoxy)-propane, and 4-nitrophenethyl bromide. Mutagenesis of highly conserved residues in the catalytic site revealed that Glu66 and Ser67 are important for enzymatic function. These results provide insights into the catalysis of glutathione conjugation in silkworm by bmGSTT and into the metabolism of exogenous chemical agents.
Highlights
Glutathione (GSH) conjugation is essential for the detoxification of xenobiotics [1,2]
Amino acid residues involved in catalytic function Based on the GSH-binding site (G-site) of hGSTT1-1 and hGSTT2-2, we identified His40, Val54, Glu66, Ser67, and Arg107, as the candidate G-site of bmGSTT (Figs. 1 and 3)
This is a critical gap in our knowledge, because understanding the metabolic profile of thetaclass GSTs may provide novel insecticide-targeting strategies
Summary
Glutathione (GSH) conjugation is essential for the detoxification of xenobiotics [1,2]. GSH transferases (GSTs, EC 2.5.1.18) are responsible for catalysis of this conjugation and are distributed ubiquitously among aerobic organisms [5]. Six GST classes (delta, epsilon, omega, sigma, theta, and zeta) have been identified in dipteran insects, such as Anopheles gambiae [9] and Drosophila melanogaster [10,11]. We have previously characterized several GSTs in the silkworm, Bombyx mori, a lepidopteran model insect [13,14,15,16,17,18,19], and a sigma-class GST in the fall webworm, Hyphantria cunea, one of the most serious lepidopteran pests of broad-leaved trees [16]. There have been no reports to date on the characterization of theta-class GSTs from silkworms
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