Cloning, characterization and tissue distribution of a pi-class glutathione S-transferase from clam (Venerupis philippinarum): Response to benzo[α]pyrene exposure

Glutathione S-transferases (GSTs) are phase II enzymes involved in major detoxification reactions of xenobiotics in many organisms. In this study, a full-length cDNA of GST-pi was cloned from the gill of Venerupis philippinarum by rapid amplification of cDNA ends (RACE) method for the first time. The full-length cDNA of V. philippinarum GST-pi (denoted as VpGSTp) was 1142 bp, with a 5′ untranslated region (UTR) of 87 bp, a 3′ UTR of 438 bp, and an open reading frame (ORF) of 618 bp encoding a protein of 205 amino acid residues with an estimated molecular mass of 23.9 kDa and an predicted isoelectric point (pI) of 7.9. The comparison of the deduced amino acid sequences with GSTs from other species showed that the enzyme belongs to the pi-class, and the amino acids defining the binding sites of glutathione (G-site) and for xenobiotic substrates (H-site) were highly conserved. Tissue distribution analysis of the VpGSTp mRNA revealed that the GST-pi expression level was observed higher in gill, adductor muscle, mantle and foot while lower in digestive gland. Using quantitative real-time PCR, the dose- and time-related effects of benzo[α]pyrene (B[α]P) on VpGSTp mRNA expression were investigated in gills and digestive gland. The results showed that a time-dependant increase in the expression of VpGSTp was induced by B[α]P and appeared a good linear relationship with B[α]P concentrations. All these results suggested that GST-pi in bivalve had an antioxidant role and VpGSTp expression may be a useful biomarker candidate for monitoring environmental contaminants such as PAHs.