Pathway of protein glycosylation in the trypanosomatid Crithidia fasciculata.

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Abstract
Cells of the insect parasite C. fasciculata incubated with [14C]glucose possessed only 1 lipid-bound oligosaccharide with solubility in chloroform/methanol/water mixtures and net charge similar to the charges of dolichol pyrophosphate derivatives. The saccharide moiety could be released from lipid by mild acid hydrolysis. Several enzymatic and chemical treatments of the oligosaccharide indicated that the latter had the structure Man.alpha. .fwdarw. Man.alpha. .fwdarw. Man.alpha. .fwdarw. [Man.alpha. .fwdarw. Man.alpha. .fwdarw. Man(.alpha.1 .fwdarw. 6)]Man .fwdarw. GlcNAc(.beta.1 .fwdarw. 4)GlcNAc. Two labeled oligosaccharides were liberated from proteins by a sequential treatment with a protease and endo-.beta.-N-acetylglucosaminidase H. One of the protein-bound oligosaccharides had the same structure as the lipid-linked compound, whereas in the 2nd oligosaccharide some mannose residues had been replaced by galactose units; however, both compounds migrated as did a Man-GlcNAc standard. These were the largest oligosaccharides obtained even after short labeling periods. Evidently, glycosylation of proteins in C. fasciculata does not involve glycosylated lipid-bound oligosaccharides as intermediates.