Protein glycosylation in Trypanosoma cruzi. II. Partial characterization of protein-bound oligosaccharides labeled "in vivo".

The protein-bound oligosaccharides were isolated from Trypanosoma cruzi cells incubated with [U-14C]glucose by means of as proteolytic digestion of delipidated proteinaceous pellets, followed by separation of oligosaccharides from glycopeptides through incubation with endo-N-acetylglucosaminidase H. The saccharides obtained after very short incubation periods were tentatively identified as Glc1Man9GlcNAc, Glc1Man8GlcNAc and Glc1Man7GlcNAc and the label was almost exclusively present in the glucose residues. On longer incubations, however, two more labeled oligosaccharides could be isolated, Man9GlcNAc (which appeared first) and Man9GlcNAc. The relative proportion of the three glucose-containing saccharides did not change with the length of the incubation of cells with [U-14C]glucose nor after chasing the label with the unlabeled monosaccharide. Moreover, the more internal mannose residues were labeled before in Man9GlcNAc than in Glc1Man9GlcNAc.l All this evidence indicated that Glc1Man9GlcNAc was not an intermediate in the formation of the other saccharides. On the basis of these results and of those reported in the preceding paper, the following pathway is proposed for the first stages of protein glycosylation: (formula, see text).