Molecular characterization of a Se-containing glutathione peroxidases gene and its expressions to heavy metals compared with non-Se-containing glutathione peroxidases in Venerupis philippinarum

Heavy metal pollution is an increasing environmental problem around the coastline. As a kind of sedentary mollusk, Venerupis philippinarum is an important sentinel to survey the environmental quality of coastal flat. Glutathione peroxidases are important anti-oxidant enzymes to alleviate oxidative stress caused by heavy metals. In the present study, a new cDNA sequence encoding a Se-containing glutathione peroxidase (VpSeGPx2) was isolated from V. philippinarum. The full-length cDNA of VpSeGPx2 was 963 bp with a conserved selenocysteine insertion sequence (SECIS) in its 3′-UTR, encoding a polypeptide of 242 amino acids with a signal peptide of 19-amino acids. Phylogenetic analysis revealed that VpSeGPx2 was clustered with Se-GPx proteins from marine mollusks. VpSeGPx2 was found to be significantly down-regulated by 10 μg/L of copper and up-regulated by 40 μg/L of copper. However, cadmium exposure seemed to have no significant effect on the expression of VpSeGPx2 transcripts. As for a previously cloned non-Se-containing VpGPx, both concentrations of copper exposure (10 and 40 μg/L) significantly increased its mRNA expression, and a higher concentration (40 μg/L) of cadmium significantly inhibited the expression of VpGPx transcript. These results suggested that VpSeGPx2 and VpGPx were both involved in the detoxification of copper pollution but seemed to play a different role in cadmium pollution.