Molecular characterization and functional divergence of glutathione s-transferase from Locusta migratoria

Glutathione S-transferases are multifunctional detoxification enzymes, which involved in insecticide resistance. Based on the transcriptome database, twenty-eight cytosolic GSTs and four microsomal GSTs were identified from Locusta migratoria. Phylogenetic analyses showed that the cytosolic GSTs were assigned into sigma, epsilon, delta, theta, omega and zeta classes; While microsomal GSTs were classified into insect and MGST3 subclass, respectively; LmGSTm4 was the first member of MGST3 subclass found in insect. The tissue-expression patterns of GSTs can be divided into wide-, partial- and specific-expression types. The stage-expression profiles of GSTs can be classified into low and high expression groups, according to egg expression level. The substrate specificity, kinetic constant and GPX activity of the cytosolic GSTs showed obviously difference in protein level. Finally, likelihood ratio tests provided strong evidence for positive selection in sigma, delta and epsilon classes. Bayes Empirical Bayes analysis showed that four amino acid sites in delta class, three in epsilon, and four in sigma were identified as positive selection sites, which were located in protein surface, and either situated at functional α-helix or nearby essential sites.