Molecular cloning, characterization and expression analysis of cathepsin C gene involved in the antibacterial response in Chinese mitten crab, Eriocheir sinensis

Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, function in immune response in vertebrates; however, their function within the innate immune system of invertebrates remains largely unknown. Therefore, we investigated the immune functionality of cathepsin C (catC) in Chinese mitten crab (Eriocheir sinensis), a commercially important and disease vulnerable aquaculture species. The full-length catC cDNA (1481 bp) was cloned via PCR based upon an initial expressed sequence tag (EST) isolated from a hepatopancreatic cDNA library. The catC cDNA contained a 1284 bp open reading frame (ORF) that encoded a putative 427 amino acid (aa) protein. Comparisons with other reported invertebrate and vertebrate cathepsins sequences revealed high percent identity. CatC mRNA expression in E. sinensis was responsive in hemocytes to a Vibrio anguillarum challenge, with peak exposure observed 6 h post-injection. Collectively, data demonstrate the successful isolation of catC from the Chinese mitten crab, and its involvement in the innate immune system of an invertebrate.