Isolation of glucose-containing high-mannose glycoprotein core oligosaccharides.

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Abstract
The total cell wall mannoprotein was isolated from a mutant of Saccharomyces cerevisiae that fails to remove the glucose units of the dolichol-linked precursor after transfer of the oligosaccharide to ASN units in the protein. The oligosaccharides released from this mannoprotein by endoglucosaminidase H digestion show 1H NMR signals assignable to 3 .alpha.-linked glucose units at .delta. 5.52, 5.27 and 5.17, and a comparison with the chemical shifts of reference compounds shows that these signals are consistent with the structure .alpha.Glc .fwdarw. 2 .alpha.Glc .fwdarw. 3 .alpha.Glc .fwdarw. 3 .alpha.Man .fwdarw. 2. This provides a direct confirmation for the structure previously assigned to the lipid-linked precursor. Analysis of the larger oligosaccharides confirms that the presence of the glucose units does not prevent elongation of the .alpha.1 .fwdarw. 6-linked polymannose backbone or addition of .alpha.1 .fwdarw. 3-linked mannose to the core.