Characterization of the mechanism of protein glycosylation and the structure of glycoconjugates in tissue culture trypomastigotes and intracellular amastigotes of Trypanosoma cruzi

Abstract

Trypomastigote cells of Trypanosoma cruzi incubated with [U-14C]glucose accumulated dolichol-P-P-linked Man2GlcNAc2 and Man9GlcNAc2. Evidence is presented indicating that both oligosaccharides were transferred to asparagine residues in proteins. On the other hand, intracellular amastigotes behaved as epimastigotes, i.e., only Man9GlcNAc2 accumulated and was transferred to proteins under similar incubation conditions. Intracellular amastigotes differed, therefore, from amastigotes obtained from an axenic culture, which behaved as trypomastigotes. A similar processing of protein-linked Man9GlcNAc2 and Man8GlcNAc2 occurred in epimastigotes and trypomastigotes but the structure of the main Man7GlcNAc2 isomer produced by demannosylation of the above mentioned oligosaccharides differed from that of the Man7GlcNAc2 transferred in trypomastigotes and amastigotes from axenic cultures. The infective trypomastigote stage of the parasite showed, therefore, an alteration in the mechanism of protein N-glycosylation when compared to the other stages, namely epimastigote (insect vector stage) and amastigote (mammalian intracellular stage). Complex-type, asparagine-bound oligosaccharides were found to be synthesized in both epimastigotes and trypomastigotes but the amounts of those compounds were extremely low when compared to those of high mannose-type oligosaccharides.