Molecular cloning and characterization of omega class glutathione S-transferase (GST-O) from the polychaete Neanthes succinea: Biochemical comparison with theta class glutathione S-transferase (GST-T)

We cloned and sequenced a full-length cDNA of an omega class glutathione S-transferase (GST-O) from the polychaete Neanthes succinea (ns-GST-O). The full-length cDNA of ns-GST-O was 1562 bp in length, containing an open reading frame (OR) of 732 bp that encoded a 244 amino acid protein. The deduced amino acid sequence of ns-GST-O showed a low similarity with the theta class N. suucinea GST (ns-GST-T). As GSTs play a significant role in antioxidant defense, we checked the expression pattern of ns-GST-O in N. succinea after exposure to copper (CuCl2 12 to 72 μg/L), which is an oxidative stress-inducing agent. After exposure to CuCl2, ns-GST-O gene was dramatically up-regulated and when compared with ns-GST-T the expression pattern was more pronounced at all the concentrations of copper. Even the basal transcription levels of ns-GST-O were higher than those of ns-GST-T. To further characterize the catalytic properties of ns-GST-O, we constructed a recombinant ns-GST-O plasmid with a 6× His-Tag at the N-terminal of the full-length ns-GST-O cDNA. Recombinant ns-GST-O protein was highly expressed in transformed Escherichia coli. The effect of pH, temperature and chemical inhibitors on the enzyme activity of ns-GST-O was also studied and compared with the reported effect of these factors on recombinant ns-GST-T protein. These results suggest that, like other types of GSTs, ns-GST-O protein plays a conserved antioxidant role in the polychaete N. succinea.