Adult Schistosoma mansoni express cathepsin L proteinase activity

This report presents the deduced amino acid sequence of a novel cathepsin L proteinase from Schistosoma mansoni, and describes cathepsin L-like activity in extracts of adult schistosomes. Using consensus primers specific for cysteine proteinases, gene fragments were amplified from adult S. mansoni cDNA by PCR and cloned. One of these fragments showed marked identity to Sm31, the cathepsin B cysteine proteinase of adult S. mansoni, whereas another differed from Sm31 and was employed as a probe to isolate two cDNAs from an adult S. mansoni gene library. Together these cDNAs encoded a novel preprocathepsin L of 319 amino acids; this zymogen is predicted to be processed in vivo into a mature, active cathepsin L proteinase of 215 amino acids. Closest homologies were with cathepsins L from rat, mouse, and chicken (46-47% identity). Southern hybridization analysis suggested that only one or a few copies of the gene was present per genome, demonstrated that its locus was distinct from that of Sm31, and that a homologous sequence was present in Schistosoma japonicum. Because these results indicated that schistosomes expressed a cathepsin L proteinase, extracts of adult S. mansoni were examined for acidic, cysteine proteinase activity. Based on rats of cleavage of peptidyl substrates employed to discriminate between classes of cysteine proteinases, namely cathepsin L (Z-phe-arg-AMC), cathepsin B (Z-arg-arg-AMC) and cathepsin H (Bz-arg-AMC), the extracts were found to contain vigorous cathepsin L-like activity. In contrast, complete inhibition of this activity was observed when the cathepsin L inhibitor Z-phe-ala-CHN₂ was included, which together demonstrated that the conspicuous, acidic cysteine proteinase activity in extracts of adult S. mansoni was cathepsin L-like. The cathepsin L may be crucial for schistosome metabolism of host hemoglobin.