RESUMO
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 (CpGSTσ1 and 2) cDNA sequences were cloned from freshwater bivalve Cristaria plicata. The full length cDNA of CpGSTσ1 and 2 was 826â¯bp and 1609â¯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 CpGSTσ1 and 2 in hepatopancreas and hemocytes showed a significantly increased trend after bacterial challenge. The recombinant CpGSTσ1 was successfully expressed as a soluble form in Escherichia coli DE3. The specific activity of recombinase toward CDNB was 46.965⯱â¯0.082⯵mol/min/mg, and its optimum temperature and pH was 37⯰C and 9.0, respectively. The recombinant of CpGSTσ1 could bear 6â¯M urea and 8% SDS, when the concentration of urea was 8â¯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.