Molecular characterization, expression and antimicrobial activities of a c-type lysozyme from the mud crab, Scylla paramamosain.

Lysozyme is an important immune protein involved in the first line of defense for crustaceans. In the present study, a c-type lysozyme gene (SpLyzC) was cloned and characterized from the mud crab, Scylla paramamosain. The full-length cDNA was 849 bp with an open reading frame of 669 bp, and encoded a polypeptide of 223 amino acids with a calculated molecular mass of 23.7 kDa and an isoelectric point of 8.90. SpLyzC shared conserved active sites with c-type lysozymes from other species, detected in all tested tissues and had higher expression levels in hepatopancreas and gill tissues. The expression of SpLyzC was up-regulated in hepatopancreas and gill after infection with Vibrio parahaemolyticus and Staphylococcus aureus. The density of bacteria in the hemolymph and the mortality of crabs increased following infection with V. parahaemolyticus after SpLyzC expression was silenced by injecting double-strand RNA of SpLyzC. The recombinant protein of the S. paramamosain c-type lysozyme (rSpLyzC) exhibited antibacterial activities against Micrococcus lysodeikticus, S. aureus, Vibrio harveyi and V. parahaemolyticus. These results indicate that SpLyzC could help eliminate bacteria in S. paramamosain and may play an important role in resistance to bacterial infection.