Molecular cloning, characterization and expression analysis of a catalase gene in Paphia textile

Catalase is an important antioxidant protein that can protect organisms against various forms of oxidative damage by eliminating hydrogen peroxide. In this study, the catalase c DNA of Paphia textile（Pt CAT） was cloned using RTPCR and rapid amplification of c DNA ends（RACE）. Pt CAT is 1 921 bp long and consists of a 5′-UTR of 50 bp, a 3′-UTR of 349 bp, and an ORF of 1 542 bp that encodes 513 amino acids with a molecular weight of 58.4 k D and an estimated isoelectric point of 8.2. Sequence alignment indicated that Pt CAT contained a highly conserved catalytic signature motif(61FNRERIPERVVHAKGAG77), a proximal heme-ligand signature sequence(352RLFSYSDP359), and three catalytic amino acid residues(H72, N145, and Y356). Pt CAT also contains two putative N-glycosylation sites(34NKT36 and 437NFT439) and a peroxisome-targeting signal(511AQL513). Furthermore, Pt CAT shares 53%–88% identity and 29%–89% similarity with other catalase amino acid sequences. Pt CAT m RNA was present in all tested organs, including the heart, digestive gland, adductor muscle, gonad, gill, and mantle, but its expression was highest in the digestive gland. High-temperature-induced stress produced two expression patterns of Pt CAT m RNA: first, an initial up-regulation followed by a down-regulation in the heart, digestive gland, and gonad and, second, consistent down-regulation in all other organs. These results demonstrate that Pt CAT is a typical member of the catalase family and might be involved in the responses to harmful environmental factors.