Oligosaccharide precursors, lipid-linked

Other mutants of Chinese-hamster ovary-cells having decreased amounts of lipid-linked oligosaccharides are known, although they are less well characterized. G-Protein of vesicular stomatitis virus grown in one of these mutants appeared to contain fewer, but full-sized rather than truncated, oligosaccharide side-chains. There may be insufficient amounts of oligosaccharide precursor available for transfer to nascent glycoproteins.172... 

Lipid-Linked Oligosaccharides Are Precursors for Bacterial Cell Wall Synthesis... 

Many other oligosaccharides and polysaccharides are synthesized by similar routes in which sugars are activated for subsequent reactions by attachment to nucleotides. In the glycosylation of proteins, for example (see Fig. 27-34), the precursors of the carbohydrate moieties include sugar nucleotides and lipid-linked oligosaccharides. 

This lipid-linked oligosaccharide is present in fungi, seed plants, and animals, and serves as precursor for yeast mannans116-1,8 or L-asparagine-linked glycans.13-16... 

Fig. 45.—Pathway of the Biosynthesis of Lipid-linked Oligosaccharide Precursor of the N-Acetyl-lactosaminic Type of Glycans, and of the Intermediary Glycopeptide. (See general reviews 126-136, 226, and 227.)...

The discovery that dolichol phosphates and pyrophosphates (diphosphates) are carriers for oligosaccharides in eukaryotic cells initiated the modem era of glycoprotein biochemistry. These lipid-linked oligosaccharides are precursors for the carbohydrate side chains of the asparagine-linked glycoproteins. Because of this common precursor, all of the side chains of these glycoproteins share the same carbohydrate core, shown within the dashed box in Figure 16-la. 

Fig. 2. Structures of glycans found in Dictyostelium discoideum. Structures of known carbohydrate components in Dictyostelium discoideum. The structures have been determined by physical/chemical methods or by the analysis of radiolabeled materials. (A) Lipid-linked oligosaccharide precursor of N-linked oligosaccharides [14] (B) truncated lipid-linked oligosaccharide precursor found in mutant strains HL24I and HL243[I4] (C) oligosaccharide with GlcNAc residues at the intersecting position and locations of the methylphosphate esters [16].

Ballou, L., Copal, P., Krummel, B., Tammi, M., and Ballou, C. E. (1986). A mutation that prevents glucosylation of the lipid-linked oligosaccharide precursor leads to underglycosylation of secreted yeast invertase. Proc. Natl. Acad. Sci. USA 83, 3081-... 

Synthesis of a lipid-linked core precursor. N-Unked oligosaccharides are initially synthesized as Upid-linked precursors. The lipid component is dolichol (Dol), a long chain polyisoprenol of n = 14-24 isoprene units, which is linked to the oligosaccharide precursor via pyrophosphate bridge. 

Now that the composition of one of the most complex enzymes in nature as well as some of the interactions between subunits have been defined, further work needs to concentrate on a number of issues. These include the specific functions of the various subunits of the complex in the glycosylation process, the regulation of the enzyme and the coupling of OST to lipid-linked oligosaccharide precursor formation, to protein translocation and to protein folding. One may also predict defects in this enzyme that may lead to abnormal glycosylation as it occurs in the so-called carbohydrate deficient glycoprotein syndrome, a severe human disorder with a multisystemic clinical picture [157-160]. 

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