Characterization, expression profiling and functional characterization of cathepsin Z (CTSZ) in turbot (Scophthalmus maximus L.).

Cathepsin Z (CTSZ) is a lysosomal cysteine protease of the papain superfamily. It participates in the host immune defense via phagocytosis, signal transduction, cell-cell communication, proliferation, and migration of immune cells such as monocytes, macrophages, and dendritic cells. In this study, we reported the identification of SmCTSZ, a CTSZ homolog from turbot (Scophthalmus maximus L.). SmCTSZ was 317 residues in length and contains a Pept-C1 domain. In multiple species comparison, SmCTSZ shared 65-93% overall sequence identities with the CTSZ counterparts from human, rat, and several fish species. In the phylogenetic analysis, SmCTSZ showed the closest relationship to Cynoglossus semilaevis. The syntenic analysis revealed the similar neighboring genes of CTSZ across all the selected species, which suggested the synteny encompassing CTSZ region during vertebrate evolution. Subsequently, SmCTSZ was constitutively expressed in various tissues, with the lowest and highest levels in brain and intestine respectively. In addition, SmCTSZ was significantly up-regulated in intestine following both Gram-negative bacteria Vibrio anguillarum, and Gram-positive bacteria Streptococcus iniae immersion challenge. Finally, the rSmCTSZ showed strong binding ability to all the examined microbial ligands, and the agglutination effect to different bacteria. Taken together, these results indicated SmCTSZ could play important roles in mucosal immune response in the event of bacterial infection in teleost. However, the knowledge of CTSZ are still limited in teleost species, further studies should be carried out to better characterize its detailed roles in teleost mucosal immunity.