Dolichol phosphate glucose

Figure 2 Examples of glycosyl donors. Nucleotide donors are represented by UDP-galactose (UDP-Gal), GDP-fucose (GDP-Fuc), GMP-N-acetyIneuraminic acid (CMP-sialic acid, CMP-Neu5Ac), GDP-galactose (GDP-Gal), dTDP-rhamnose (dTDP-Rha), and dTDP-daunosamine lipid phosphate donors are represented by Lipid II and dolichol-phosphate-glucose (Dol-P-GIc) sugar phosphate donors are represented by glucose-1-phosphate. The saccharides are transferred from these donors by GTs to form oligo/polysaccharides and glycoconjugate products.

UDP-D-xylose, GDP-D-mannose, GDP-L-Fucose, or CMP-D-A-acetylneuraminic acid. Mammalian GTs also use dolichol-diphosphate-GlcNAc2Man9GlC3, dolichol-phosphate-mannose and dolichol-phosphate-glucose (Fig. 2). 

Figure 47-7. Pathway of biosynthesis of dolichol-P-P-oligosaccharide. The specific linkages formed are indicated in Figure 47-8. Note that the first five internal mannose residues are donated by GDP-mannose, whereas the more external mannose residues and the glucose residues are donated by dolichol-P-mannose and dolichol-P-glucose. (UDP, uridine diphosphate Dol, dolichol P, phosphate UMP, uridine monophosphate GDP, guanosine diphosphate M, mannose G, glucose.)...

If the synthesis starts from glucose molecules, then the initial step is the transfer of glucose residues from UDP-glucose onto an intermediary acceptor-dolichol phosphate (membrane-bound polyprenol phosphate). Dolichol phosphate assists in the synthesis of an... 

In the first Section, the dolichol pathway of protein glycosylation is introduced, and the reader is made familiar with the various reactions in the formation of the lipid and carbohydrate moieties of lipid-linked saccharides. Three different classes of compound are known so far (a) isoprenoid alcohol esters of monosaccharide monophosphates, such as D-mannosyl and D-glucosyl (dolichol phosphate), (b) such isoprenoid alcohol esters of saccharide diphosphates as dolichol diphosphate linked to 2-acetamido-2-deoxy-D-glucose and to oligosaccharides, and (c) retinol (D-mannosyl phosphate). The dolichol-linked sugars occur in all eukaryotes. 

Scheme 2. —Proposed Scheme for the Reactions Involved in the Synthesis of Cellulose in the Green Alga Prototheca zopfii (After Hopp and Coworkers141). [Abbreviations used are Dol = dolichol, Glc = D-glucose, Dol-P = dolichol phosphate, -P-P = diphosphate, and P, = inorganic phosphate.]...

UDP-glucose transfers glucose to dolichol phosphate to form dolichol phospho-glucose in synthesis of N-linked glycoproteins. 

Dolichol phosphate is a carrier of sugars to oligosaccharide chain synthesis assembly. Such activated sugars include dolichol-P-mannose and dolichol-P-glucose. 

The lipid-soluble intermediate that accumulates is dolichol pyrophosphate, whose terminal phosphate comes from glucose 1-phosphate. (See Figure 11.23 in Section 11.3.3 in the text.) Bacitracin is an antibiotic that forms a 1 1 complex with dolichol pyrophosphate, preventing its hydrolysis to dolichol phosphate and inorganic phosphate. Thus, in the presence of bacitracin, the label will remain in dolichol pyrophosphate. In the absence of bacitracin, the terminal phosphate will be released as inorganic phosphate. 

Initial experiments with dolichol phosphate and UDP-glucose. 

Fig. 20.1. Abbreviated scheme of the synthesis of a diantennary N-glycan. Fucose modification has been omitted. 20.1, Phosphomannomutase 2 (PMM2) 20.2, phosphoman-nose isomerase (PMI) 20.3, glucosyltransferase I (GT I) 20.4, mannosyltransferase VI (MT VI) 20.5, dolichol phosphate-mannose synthase-1 (DPM synthase-1) 20.5, N-acet-ylglucosaminyltransferase II (GnT II) 20.7, glucosidase I (G I) GDP, guanosine diphosphate Marly mannose GlcNACy N-acetylglucosamine Do/, dolichol P, phosphate G/c, glucose Gal galactose SiUy sialic acid. Dotted arrow indicates multiple steps...

Although it could be established that saturation of the a-isoprene unit of polyprenol phosphate is important for these compounds to act as effective acceptors of glycosyl moieties in eukaryotic cells, little chain-length specificity was observed in such studies.39-41 This observation found support in the result that the same set of prenylogs occurs in total-yeast dolichol and in dolichol diphosphate-linked 2-acetamido-2-deoxy-D-glucose synthesized in vitro with yeast-cell homogenates.42 As already noted by Chojnacki and coworkers,40 dur-... 

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