Catalase is one of the key
antioxidant enzymes and it appears to be involved in protection against immune
infection and oxidative stress. Here, two
catalase cDNAs (ChCat-1 and ChCat-2) were isolated from hemocytes of Crassostrea hongkongensis using SSH and RACE. The full-length cDNAs of ChCat-1 and ChCat-2 are 1913 and 2466 bp in length, encoding
proteins of 515 and 511
amino acids, respectively. Multiple alignments of amino acid sequences revealed that both ChCat-1 and ChCat-2 possess several characteristic features of the
catalase family of
enzymes, including one proximal active site signature, one
heme-
ligand signature, and three catalytic
amino acid residues (His(72), Asn(145) and Tyr(355)). Phylogenetic analysis indicates that these two catalases may share a common ancestral gene and result from a gene duplication event following the divergence of bivalves and gastropods. Constitutive expression of ChCat-1 and ChCat-2 was observed in all tissues studied, with highest levels of expression in gill and muscle, respectively. The expression of both genes was inducible by
bacterial infection, and reached the maximum at 8 h (9.0-fold) and 12 h (2.3-fold) post-
infection, respectively. Furthermore, both the purified ChCat-1 and ChCat-2
protein displayed a strong
catalase activity, and S2 cells carrying ChCat-1 or ChCat-2 showed a higher degree of resistance to H(2)O(2) than that of control cells. In a word, this is the first report of the presence of two
catalase genes in a single marine bivalve, and our results highlight the involvement of both ChCat-1 and ChCat-2 in host protection against pathogen
infection and oxidative stress in C. hongkongensis.