Channel catfish, Ictalurus punctatus, cysteine proteinases: cloning, characterisation and expression of cathepsin H and L.

The antigen recognition by the host immune system is a complex biochemical process that requires a battery of enzymes. Cathepsins are one of the enzyme superfamilies involved in antigen degradation. We observed the up-regulation of catfish cathepsin H and L transcripts during the early stage of Edwardsiella ictaluri infection in preliminary studies, and speculated that cathepsin H and L may play roles in infection. We identified, sequenced and characterized the complete channel catfish cathepsin H and L cDNAs, which comprised 1415 and 1639 nucleotides, respectively. The open reading frames of cathepsin H appeared to encode a protein of 326-amino acid residues, which that of cathepsin L encoded a protein of 336 amino acids. The degree of conservation of the channel catfish cathepsin H and L amino acid sequences in comparison to other species ranged from 61% to 77%, and 67% to 85%, respectively. The catalytic triad and substrate binding sites are conserved in cathepsin H and L amino acid sequences. The cathepsin L transcript was expressed in all tissues examined, while the cathepsin H was expressed in restricted tissues. These results provide important information for further exploring the roles of channel catfish cathepsins in antigen processing.