Molecular characterization of a manganese superoxide dismutase and copper/zinc superoxide dismutase from the mussel Mytilus galloprovincialis

The full-length cDNA sequences coding respectively for a manganese superoxide dismutase (Mg–MnSOD) and copper/zinc superoxide dismutase (Mg–CuZnSOD) were cloned from Mytilus galloprovincialis. Mg–MnSOD and Mg–CuZnSOD cDNAs encoded a polypeptide of 228 and 211 amino acids, respectively. Sequence analysis indicated Mg–MnSOD was a mitochondrial MnSOD and Mg–CuZnSOD was an intracellular CuZnSOD. Multiple alignment analysis showed that both Mg–MnSOD and Mg–CuZnSOD sequences had the common features conserved in MnSODs and CuZnSODs, respectively. Phylogenetic analysis revealed that Mg–MnSOD clustered together with MnSODs from other mollusks, whereas Mg–CuZnSOD clustered with other mollusk intracellular CuZnSODs with a wider phylogenetic distance. By quantitative real-time RT-PCR (qPCR) analysis, both Mg–MnSOD and Mg–CuZnSOD transcripts were detected in all tissues examined with the highest expression level in hepatopancreas. Following bacterial challenge, the expression level of Mg–MnSOD and Mg–CuZnSOD increased first and subsequently decreased to the original level in hemocytes. In hepatopancreas, Mg–CuZnSOD mRNA was up-regulated significantly at 72 h and 96 h post challenge, while the level of Mg–MnSOD transcript had no significant change. Therefore, Mg–MnSOD and Mg–CuZnSOD expressions were inducible and they were probably involved in the immune response against bacterial challenge. These results suggest that these SODs may play important roles in the immune defense system of M. galloprovincialis and perhaps contribute to the protective effects against oxidative stress in this mussel.