Molecular characterization of mu class glutathione- S-transferase from disk abalone ( Haliotis discus discus), a potential biomarker of endocrine-disrupting chemicals

Abstract

The present study has reported the cloning, expression, and characterization of a mu class glutathione S-transferase (GST) gene, HdGSTM1, identified from disk abalone ( Haliotis dicus discus) cDNA library. HdGSTM1 encodes a polypeptide of 215 amino acids with a calculated molecular mass of 25 kDa. The recombinant HdGSTM1 exhibited a relatively low activity of 0.172 ± 0.01 μmol/min/mg protein toward 1-chloro-2, 4-dinitrobenzenel (CDNB), and 0.114 ± 0.03 μmol/min/mg protein toward ethacrynic acid (ECA). Kinetic analysis with respect to glutathione and CDNB gave a K m value of 0.734 ± 0.053 mM and 2.721 ± 0.236 mM, respectively. HdGSTM1 had an optimum temperature of 35 °C and an optimum pH of 8.0. It also showed stability in a wide range of temperatures and pH. Modeling structure analysis revealed that the low catalytic activity of HdGSTM1 was caused by the improper residues in key active sites. The transcripts of HdGSTM1 were detected in all five examined organs, with the highest levels in gills and gonads. After 48 h waterborne exposure of three model endocrine-disrupting chemicals (PAH, PCB, and TBT), the expression of HdGSTM1 was significantly induced in both gill and digestive tract tissues through semi-quantitative RT-PCR examination, suggesting good biomarker potentials.