Characterization and expression analysis of phospholipid hydroperoxide glutathione peroxidase cDNA from Chironomus riparius on exposure to cadmium

Phospholipid-hydroperoxide glutathione peroxidase (PHGPx) is an antioxidant enzyme in the glutathione peroxidases (GPx) family that reduces hydroperoxides of phospholipids and maintains the integrity of biomembranes. Here, we report the identification and characterization of a full length cDNA of PHGPx from the ecotoxicologically important aquatic midge Chironomus riparius (CrPHGPx1) from the Expressed Sequence Tags (ESTs) database generated through pyrosequencing. The 837 base pair (bp) cDNA contained an open reading frame of 597bp, and a 75bp 5' and a 159bp 3'untranslated region. The theoretical molecular mass of the deduced amino acid (aa) sequence (197 aa) was 22.40kDa with an estimated pI of 8.77. The Cys-codon was present at residue 74 and also the active site residues Gln⁹¹ and Trp¹⁶⁴. The active-site motifs and GPx family signature motifs LAFPCNQF^101-108 and WNFTK^163-168 were also found. Phylogenetic analysis showed that CrPHGPx1 is grouped with PHGPx1 from other species and is more closely related to insects belonging to the dipteran order. The mRNA of CrPHGPx1 was detected in larvae, pupae and adults. The expression of CrPHGPx1 is induced by cadmium exposure indicating that the mRNA expression of CrPHGPx1 is differently regulated in response to oxidative stress caused by environmental stressors.