Characterization and cloning of the cathepsin L proteinases of schistosoma japonicum

Adult Schistosoma japonicum parasites synthesize and secrete both cathepsin L and cathepsin B cysteine proteinases. The specific activities of cathepsin L were many-fold higher than that of cathepsin B. The cDNAs encoding two distinct cathepsin L proteinases, here termed cathepsin L1 and L2, were isolated. The deduced amino acid sequences of the mature cathepsin L1 and L2 were ∼ 41% identical, and moreover, S. japonicum cathepsin L2 showed more similarity with human cathepsin L than with schistosome cathepsin L1. Schistosome cathepsin L proteinases may be involved in the digestion of hemoglobin obtained from host erythrocytes. However, since we detected their presence in schistosome eggs, the release of these enzymes by eggs trapped in the liver and other organs may be associated with the granulomatous responses which characterize the pathology of human schistosomiasis.