Genome-wide identification, expression signature and immune functional analysis of two cathepsin S (CTSS) genes in turbot (Scophthalmus maximus L.).

Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, play multiple roles at physiological and pathological states. Cathepsin S is a lysosomal cysteine endopeptidase of the papain family, and exerts critical roles in the regulation of MHC class II immune responses. In the present study, we captured two Cathepsin S genes in turbot (Sm CTSS1 and Sm CTSS2.1), characterized their expression patterns following V. anguillarum and S. iniae infections, and explored their binding ability and agglutination capability. Firstly, the Sm CTSS1 contained a 990 bp ORF encoding 329 amino acids, while Sm CTSS2.1 contained a 1,014 bp ORF encoding 337 amino acids. The phylogenetic analysis revealed that both genes showed the closest relationship to their counterparts of Japanese flounder (Paralichthys olivaceus). In addition, both genes were ubiquitously expressed in all examined healthy tissues, with the highest expression level observed in spleen and intestine, respectively, while the lowest expression level both observed in liver. Both Sm CTSS1 and Sm CTSS2.1 were significantly differentially expressed, and exhibited general down-regulations at most time points in skin and intestine after two bacterial infections. Finally, both r Sm CTSS1 and r Sm CTSS2.1 showed significant binding ability to three examined microbial ligands (LPS, PGN and LTA), and strong agglutination effect to different bacteria (E. tarda , S. agalactiae , S. aureus and V. anguillarum). Collectively, this study provided valuable data for understanding the roles of CTSS in the host defense against bacterial infections in turbot, and indicated the potential vital roles of CTSS in innate immune responses of teleost species. • Two cathepsin S genes were characterized from turbot (Sm CTSS). • The Sm CTSS genes were both ubiquitously expressed in turbot tissues. • The Sm CTSS genes were generally down-regulated following V. anguillarum and S. iniae infections. • The Sm CTSS genes showed strong binding ability to LPS, PGN and LTA. • The Sm CTSS genes exhibited strong agglutination capability with E. tarda, S. agalactiae, S. aureus and V. anguillarum. [ABSTRACT FROM AUTHOR]