Molecular Cloning, Characterization, and Expression of a Catalase Gene in the Japanese Scallop Mizuhopecten yessoensis Induced in the Presence of Cadmium

Cadmium (Cd) is known to influence the oxidative status of marine organisms and can induce the formation of reactive oxygen species (ROS). Catalase (CAT) is one of the important enzymes involved in scavenging high levels of ROS. In present study, we cloned CAT cDNA and investigated the response of this enzyme at the transcriptional level in the Japanese scallop Mizuhopecten yessoensis exposed to Cd. The full-length CAT cDNA (MyCAT) of 1,870 nucleotides including a 57 bp 5'-UTR, a coding sequence of 1,500 bp and a 313 bp 3'-UTR were identified from the scallop. The deduced amino acid sequence of MyCAT corresponds to 499 amino acids with predicted molecular weight of 56.48 kDa and contains highly conserved motifs of the proximal heme-binding site RLFSYSTH, proximal active signature FNRERIPERVVHAKGGG and three catalytic amino acid residues His(72), Asn(145), and Tyr(355). Its significant homology to CATs from multiple alignments revealed that MyCAT had a high identity with CATs from other mollusks. CAT mRNA expression analysis revealed that expression level was highest in the digestive gland (p < 0.01) but weak in muscle. Following exposure to 200 and 400 mu g/ l of Cd, a high amount of Cd was found to have accumulated in the digestive gland and CAT mRNA expression had significantly increased in this organ among 7-day exposed scallops (p < 0.001). The result demonstrated that antioxidant enzymes such as CAT play important roles in counteracting Cd stress in M. yessoensis.