Asparaginyl endopeptidase activity in adultSchistosoma mansoni

Abstract

Sequence comparisons have recently shown that the Schistosoma mansoni protein Sm32 is similar to asparaginyl endoproteinases, a novel family of cysteine proteinases, of which the legumains from legumes are the best characterized. By synthesizing and employing fluorogenic peptide substrates for the specific detection of asparaginyl endopeptidases, we have identified this type of activity in extracts of adult S. mansoni. The S. mansoni activity is similar to that of the legumains in its substrate specificity and sensitivity to thiol inhibitors, but differs in its pH and temperature optima for activity. In contrast, unlike the legumains, the schistosome asparaginyl endopeptidase activity is not activated by the reducing agent dithiothreitol. As suggested for legumains, Sm32 may function in the post-translational modification processes that regulate the activity of other molecules.

Cloning, Isolation, and Characterization of Mammalian Legumain, an Asparaginyl Endopeptidase

“…The purified pig enzyme is active only in the presence of thiol compounds, but the enzyme in crude extracts of mammalian tissues did not require a thiol activator, and the same has been reported for Schistosoma (5).…”

“…In this respect it resembles such lysosomal cysteine endopeptidases of family C1 as cathepsins B and L. Legumains of the plants Phaseolus vulgaris and C. ensiformis are also unstable at pH 7.5 (28,29), and pH optima are in the region of 5.5 (29,30). Legumain of Schistosoma differs in this respect, with its pH optimum of 6.8, as has been shown directly by Dalton et al (5).…”

“…In V. aconitifolia, too, we found this substrate to be quite specific (3), but Schistosoma contains at least one other major enzyme active in the assay (5).…”

“…The amino acid sequence of legumain from Ricinus communis (castor bean) showed it to be homologous with an enzyme from the fluke Schistosoma mansoni (4). At that time, the fluke enzyme was of unknown specificity, but it has now been shown also to be an asparaginyl endopeptidase (5), active on the test substrate that had been introduced by Kembhavi et al The appearance of sequences homologous to legumain among the human expressed sequence tags (ESTs) 1 in the data bases alerted us to the presence of the enzyme in vertebrates, and accordingly, we made assays for asparaginyl endopeptidase activity in mammalian tissues. It was soon evident that legumain is present in human and other mammalian cells.…”

Blastocystis Legumain Is Localized on the Cell Surface, and Specific Inhibition of Its Activity Implicates a Pro-survival Role for the Enzyme

“…Legumains from parasite origins, in contrast, have pH optimum near neutral pH, e.g. T. vaginalis legumain at pH 7.0 (24) and the helminths Hemonchus contortus and Schistosoma mansoni legumains at pH 7.0 (25) and 6.8 (26), respectively. Blastocystis legumain is active over the wide range of pH 4 -8 with the optimum pH at 7.5, similar to what has been reported in T. vaginalis (23).…”