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 cDNA of Paphia textile (PtCAT) was cloned using RTPCR and rapid amplification of cDNA ends (RACE). PtCAT 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 kD and an estimated isoelectric point of 8.2. Sequence alignment indicated that PtCAT contained a highly conserved catalytic signature motif ((61)FNRERIPERVVHAKGAG(77)), a proximal heme-ligand signature sequence ((RLFSYSDP359)-R-352), and three catalytic amino acid residues (H-72, N-145, and Y-356). PtCAT also contains two putative N-glycosylation sites ((NKT36)-N-34 and (NFT439)-N-437) and a peroxisome-targeting signal ((511)AQL(513)). Furthermore, PtCAT shares 53%-88% identity and 29%-89% similarity with other catalase amino acid sequences. PtCAT mRNA 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 PtCAT mRNA: 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 PtCAT is a typical member of the catalase family and might be involved in the responses to harmful environmental factors.