cDNA cloning, characterization and expression analysis of catalase in swimming crab Portunus trituberculatus: cDNA cloning and expression analysis of catalase gene of Portunus trituberculatus.

Catalase is an important antioxidant protein that protects organisms against various oxidative stresses by eliminating hydrogen peroxide. In the present study, a full-length cDNA sequence of catalase was cloned from the haemocytes of swimming crab Portunus trituberculatus by a reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end method. The catalase cDNA sequence contained 1,851 bp with an open reading frame of 1,551 bp encoding 516 amino acid residues. The conserved catalytic active residues His-71, Asn-144 and Tyr-354 were predicted in the amino acid sequence of P. trituberculatus catalase. The deduced catalase protein had a calculated molecular mass of 58.5 kDa with an estimated isoelectric point of 6.90. Multiple alignment analysis revealed that the deduced amino acid sequence of catalase shared high identity of 68-95 % with those of other species. Quantitative real-time RT-PCR analysis revealed that P. trituberculatus catalase transcript was strongly detected in haemocytes, hepatopancreas, heart, stomach, intestine, gill, ovary and muscle. The expression level of catalase transcripts both in haemocytes and hepatopancreas changed rapidly and dynamically after Vibrio alginolyticus challenging. These facts indicate that catalase was perhaps involved in the acute response against invading bacteria and was an inducible protein involved in the host innate immune response through elimination of H(2)O(2) in crab.