Processing of neutral N-linked oligosaccharides during early Dictyostelium discoideum development

We have used metabolic radiolabeling with oligosaccharide precursors, coupled with subcellular fractionation, to examine the distribution of several classes of asparagine-linked oligosaccharides during early development. In Dictyostelium, we have observed endoglycosidase H (endo H)-sensitive structures with sizes corresponding to 10 (Hex10) and 11 (Hex11) hexose residues on the chitobiose core. Only Hex11 was detected as the major structure on fucosylated endo H-resistant species. All Hex11 species co-fractionated with plasma membrane and secreted glycoproteins, whereas Hex10 appeared to be confined to intracellular membrane and soluble glycoproteins. Sulfated species correlated with lysosomal and secreted fractions, and glucose residues were markedly depressed in Hex11 of secreted glycoproteins. Outer branch structural studies have revealed several components of the endo H-sensitive species. Using alpha-mannosidase and beta-hexosaminidase as diagnostic tools, species elucidated thus far are: a structure with 10 mannoses, a structure with nine mannoses and an intersecting N-acetylglucosamine, structures with three glucoses and seven or eight mannoses and several larger species with multiple blocks to digestion