Characterisation of cathepsin B-like cysteine protease of Lepeophtheirus salmonis

Lepeophtheirus salmonis, otherwise known as the salmon louse, is an ectoparasite that feeds on Salmo salar (Atlantic salmon), causing large losses to the aquaculture industry. The parasite feeds on the skin and mucus tissues of its host causing extensive damage and bleeding. A cDNA clone encoding a cathepsin B cysteine protease was isolated from adult female L. salmonis (LsCtB). The nucleotide sequence encoded a preproenzyme and a mature-enzyme. The mature portion shares 69% identity to human cathepsin B and contains all of the conserved regions of cathepsin B including the occluding loop, the double histidine sequence and active site residues. Additionally, cathepsin B activity in L. salmonis was identified and characterised using fluorogenic peptide substrates. The pH optimum for hydrolytic activity was 3.5, and temperature optimum 45 °C.