Molecular characterization of cu/Zn SOD gene in Asian clam Corbicula fluminea and mRNA expression and enzymatic activity modulation induced by metals.

The copper/zinc superoxide dismutase (Cu/Zn SOD) could effectively eliminate reactive oxygen species (ROS). In this study, the cDNA sequence of Cu/Zn SOD from Corbicula fluminea (designated as CfCu/Zn SOD) was cloned by the rapid amplification of cDNA ends (RACE) approaches. The full-length cDNA of CfCu/Zn SOD was of 1288 bp, including a 465 bp ORF encoding a protein of 154 amino acids. Two SOD family signatures were identified in CfCu/Zn SOD amino acids sequence. Multiple sequence alignments indicated that CfCu/Zn SOD amino acid sequences exhibited high similarities to those of other species. The tissue distribution of the CfCu/Zn SOD of C. fluminea was detected by fluorescent real-time quantitative PCR. The mRNA expression levels in digestive gland and gill were significantly higher than those of other four tissues. In response to metal ions (Cd, Cu, and Pb) challenge, the expression and enzymatic activities of CfCu/Zn SOD in the gills were measured after exposure for 0, 6, 12, 24, 48, and 72 h. The results showed that the mRNA expression and enzymatic activities of CfCu/Zn SOD could be induced by three metal ions. After Cd and Cu exposure, the mRNA expression levels increased gradually and reach the peak at 24 h, afterwards it slowed down. The change trends of enzymatic activities were similar to the mRNA expression. After Pb exposure, the expression and activities CfCu/Zn SOD were raised up gradually and reach the highest value at 72 h. All these results indicated that the mRNA expression and enzymatic activity of CfCu/Zn SOD are sensitive to Cd, Cu and Pb ions and can be used as molecular biomarkers of metal pollution in water.