Molecular cloning and expression analysis of a selenium-independent glutathione peroxidase identified from Manila clam Venerupis philippinarum

Glutathione peroxidase (GPx) is a key enzyme of cellular detoxification systems that defend cells against reactive oxygen species. It can be divided into selenium-dependent GPx (Se-GPx) and selenium-independent GPx (non-Se-GPx) subfamilies. In this study, the full-length cDNA of a non-Se-GPx was identified from Venerupis philippinarum (denoted as VpGPx) using EST analysis and RACE approaches. The full-length cDNA of VpGPx encoded a polypeptide of 226 amino acids with the predicted molecular mass of 25.41 similar to kDa. Phylogenetic analysis indicated that VpGPx had higher evolutional conservation to invertebrate than vertebrate counterparts and should be a new member of the GPx protein family. Spatial expression analysis found that VpGPx transcript was most abundantly expressed in hepatopancreas, gills and haemocytes, and weakly expressed in the tissues of mantle. After Vibrio anguillarum challenge, the expression of VpGPx transcript in overall haemocyte population was down-regulated in the first 6 similar to h, and increased to the peak at 48 similar to h. As time progressed, the expression level dropped to 0.5-fold of the control level at 96 similar to h. All these results indicated that VpGPx was perhaps involved in the immune response against microbe infection and might be contributed to the clearance of bacterial pathogens.Glutathione peroxidase (GPx) is a key enzyme of cellular detoxification systems that defend cells against reactive oxygen species. It can be divided into selenium-dependent GPx (Se-GPx) and selenium-independent GPx (non-Se-GPx) subfamilies. In this study, the full-length cDNA of a non-Se-GPx was identified from Venerupis philippinarum (denoted as VpGPx) using EST analysis and RACE approaches. The full-length cDNA of VpGPx encoded a polypeptide of 226 amino acids with the predicted molecular mass of 25.41 similar to kDa. Phylogenetic analysis indicated that VpGPx had higher evolutional conservation to invertebrate than vertebrate counterparts and should be a new member of the GPx protein family. Spatial expression analysis found that VpGPx transcript was most abundantly expressed in hepatopancreas, gills and haemocytes, and weakly expressed in the tissues of mantle. After Vibrio anguillarum challenge, the expression of VpGPx transcript in overall haemocyte population was down-regulated in the first 6 similar to h, and increased to the peak at 48 similar to h. As time progressed, the expression level dropped to 0.5-fold of the control level at 96 similar to h. All these results indicated that VpGPx was perhaps involved in the immune response against microbe infection and might be contributed to the clearance of bacterial pathogens