The high mannose oligosaccharides of Dictyostelium discoideum glycoproteins contain a novel intersecting N-acetylglucosamine residue

Previous studies have shown that the majority of the asparagine-linked high mannose oligosaccharide units present on the lysosomal enzymes of the slime mold Dictyostelium discoideum contain mannose 6-sulfate and mannose 6-phosphate residues, the latter being diesterified to methyl groups. Using a variety of techniques, including NMR spectroscopy and fast atom bombardment mass spectrometry, we have found that many of these oligosaccharides also contain an N-acetylglucosamine residue linked β1-4 to the mannose residue linked α1-6 to the β-linked core mannose. (MeOP→6)Manα1-2Manα1-6; GlcNAcβ1-4-Manα1-6; Manα1-2Manα1-3; Manβ1-4GlcNAc; (MeOP→6)Manα1-2Manα1-3. As far as we are aware, this is the first description of an intersecting N-acetylglucosamine residue in this position on a high mannose oligosaccharide.