Amino acid and carbohydrate composition of a lysosomal cysteine proteinase from Trypanosoma cruzi. Absence of phosphorylated mannose residues.

The size of a lysosomal cysteine proteinase from epimastigotes of Trypanosoma cruzi decreased from 60 to 54 kDa upon treatment with endo beta-N-acetylglucosaminidase H. A lower-molecular weight component (30-35 kDa), which usually accompanies the 60-kDa protein also increased its electrophoretic mobility, and seems to consist of a mixture of degradation products of the enzyme, since both the larger and the smaller components had the same N-terminal sequence as the 60-kDa protein. The amino acid composition of the protein moiety and the composition of the oligosaccharide chains have been determined. The oligosaccharide chains are of the high-mannose type, and contain 6, 7, 8 or 9 mannose residues, as shown both by in vivo labeling with [U-14C]glucose, and by labeling the endo-beta-N-acetylglucosaminidase H-sensitive oligosaccharides of the purified enzyme with tritiated sodium borohydride. The oligosaccharide chains did not contain phosphate residues. Further studies with [U-14C]-labeled total glycoproteins of T. cruzi and enzyme assays, suggest that T. cruzi and other trypanosomatids do not target their lysosomal enzymes to the organelle through the mannose-6-phosphate marker pathway.