Identification and characterization of two distinct sigma-class glutathione-S-transferase from freshwater bivalve Cristaria plicata

Glutathione-S-transferases (GSTs) are multifunctional phase II detoxification enzymes that catalyze the attachment of electrophilic substrates to glutathione, and play an important role in protecting organisms against the toxicity of reactive oxygen species. In this study, two distinct sigma-class GST (CpGST sigma 1 and 2) cDNA sequences were cloned from freshwater bivalve Cristaria plicata. The full length cDNA of CpGST sigma 1 and 2 was 826 bp and 1609 bp, which encoded 213 and 248 amino acid residues, respectively. Their transcripts were expressed in all detected tissues and the highest expression level was in hepatopancreas from C. plicata The expression level of CpGST sigma 1 and 2 in hepatopancreas and hemocytes showed a significantly increased trend after bacterial challenge. The recombinant CpGST sigma l was successfully expressed as a soluble form in Escherichia coil DE3. The specific activity of recombinase toward CDNB was 46.965 +/- 0.082 mu mol/min/mg, and its optimum temperature and pH was 37 degrees C and 9.0, respectively. The recombinant of CpGST sigma 1 could bear 6 M urea and 8% SDS, when the concentration of urea was 8 M and its activity was only below 20%. The results might provide a better perspective on the mechanisms of resistance to bacterial infection in molluscs.