Sequence and expression analysis of cathepsin S gene in the miiuy croaker Miichthys miiuy

Cathepsin S (CTSS) is a lysosomal cysteine endopeptides of the papain family. In the present study, CTSS gene was isolated from miiuy croaker (Miichthys miiuy) by expressed sequence tag analysis. The complete miiuy croaker CTSS cDNA comprised 1,454 nucleotides, including 56 bp at the 5'-UTR and 394 bp at the 3'-UTR. The open reading frame is 1,017 bp, and it encodes 338 amino acid residues with a calculated molecular weight of 37.1 kDa. BLAST analysis revealed that miiuy croaker cathepsin S shared high similarity with other known cathepsin S, and it showed significant homology with that of Japanese flounder, the degree of conservation of the miiuy croaker CTSS nucleotide sequence in comparison with other teleost species ranged from 63.0 to 81.7%. The N-linked glycosylation sites and catalytic sites are conserved in miiuy croaker CTSS. The CTSS transcript was expressed in all tissues examined; high levels of transcripts of CTSS were detected liver, muscle, and fin. These results provide important information for further exploring the roles of cathepsin S in antigen processing.