Abstract

• Bivalves can accumulate high concentrations of paralytic shellfish toxins (PSTs) produced by toxic algae that may induce oxidative stress. Catalase (CAT) is one of the important antioxidant enzymes involved in scavenging the high level of ROS and plays a significant role in the protection of aerobic organisms against oxidative stress by degrading hydrogen peroxide. In the present study, a total of two CATs were identified in the Chlamys farreri genome. Sequence characterization revealed CfCAT protein sequences contained proximal heme-ligand signature sequence (354RLFSYSDTH362), two N-glycosylation sites (440NFS442 and 482NFT484 domains), the proximal catalase active site signature (64FNRERIPERVVHAKGGGA81), the peroxisome targeting signal in the C-terminus 495QKL497 and 12 amino acids (H89, N171, F154, S122, R112, N142, Y325, K169, I311, W277, Q331, and Y260), which were identified as the putative residues involved in NADPH binding. Eight amino acids: R320, H364, R365, N369, F409, R432, Y404, and R457 were identified as the heme-binding site residues. Three conserved catalytic amino acids (H166, N148, and Y137) and catalase signature sequences were essential for the structure and function of CfCATs. The homology of deduced amino acid sequences revealed that CfCATs had high identity with catalases from other mollusks. RNA-Seq data analysis revealed there were no regulation patterns of scallop CATs were significantly induced in the kidney after exposed to Alexandrium minutum (AM-1). Gene expression analysis in the scallop revealed all CATs being predominantly expressed in the mantle, gill, muscle, and hepatopancreas after feeding the scallop with PST producing dinoflagellates. All these results indicate that CAT involves an important role in counteracting oxidative stress in C. farreri by PST accumulation. The tissue-, species-, and toxin dependent expression pattern of scallop CATs might be involved in their functional diversity in response to toxin exposure.