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.