Cloning and sequence analysis of the major cysteine protease expressed in the trematode parasite Fasciola sp.

A cDNA encoding the Fasciola cysteine protease precursor has been cloned and sequenced. The deduced precursor contains 325 amino acid residues (M(r) 36,768) consisting of a signal sequence (pre-region, 15 residues), pro-region (90 residues), and mature protease (220 residues, M(r) 24,371). Cys27, His164, and Asn184 form the catalytic triad in the active site of the mature enzyme, and their adjacent regions are highly conserved. The parasite enzyme showed 50, 44, and 27% amino acid sequence homologies, compared with mammalian lysosomal cathepsins L, H, and B, respectively. N-linked glycosylation sites which are thought to be targeting signals for cathepsins into lysosomes is absent in any region of the Fasciola protease precursor.