Protein-bound oligosaccharides, structural

The transfer of the oligosaccharide to protein is followed in vivo by the excision of the D-glucosyl residues the nine D-mannosyl residues present in the transferred oligosaccharide probably remain in the inner core of the D-mannan. However, the possibility that some D-mannosyl residues could be almost simultaneously removed and added cannot be precluded.117,167 Finally, terminal, < -d-(1 - 3)-linked D-mannosyl groups are added to the trimmed, protein-bound oligosaccharide.118 The outer chain of the d-mannan is formed after the inner-core oligosaccharide has been transferred to protein and processed, apparently by direct transfer of D-mannosyl groups from GDP-D-mannose.168 The similarity of the structures of the outer chain... 

Parodi, A. J., Lederkremer, G. Z., and Mendelzon, D. H. (1983). Protein glycosylation in Trypanosoma cruzi. The mechanism of glycosylation and structure of protein-bound oligosaccharides./. Biol. Chem. 258, 5589-5595. 

Speake and White (1978a, b) identified a glycolipid in the mammary explants to which they assigned the tentative structure Dol.PP.Glc-NAc2Man gGlc2, but they could not show any simple precursor-product relationship between the lipid and protein-bound oligosaccharides. It appears that the reason for this was that the mammary tissue contained appreciable inaccessible pools of labelled sugar nucleotides, which could not... 

Many secretory and membrane proteins are modified in the lumen of the ER. Protein glycosylation, the addition of covalently bound oligosaccharide chains, is a common reaction in the ER lumen and the Golgi complex. Most proteins in the ER lumen destined for secretion from the cell or for transport to other intracellular sites are glycoproteins. The carbohydrate content of glycoproteins can vary from 0.5 to 80% or more of the glycoprotein mass. Glycoprotein structures were described in Chapter 9, and their biosynthesis are covered in Chapter 20. 

When CIDNP-reactive amino acids are accessible on the surface of a glycoprotein, a possible impact of the covalently bound oligosaccharide chain on the protein part can be scrutinized [14, 15, 61] by this method. Therefore, CIDNP-experiments are also suitable to improve structural models of glycoproteins. On the basis of a X-ray structure of a glycoprotein, very often only the coordinates for the protein part are available since the flexibility of the oligosaccharide chain hampers a complete crys-... 

Figure 41-7. The fluid mosaic model of membrane structure. The membrane consists of a bimolecu-lar lipid layer with proteins inserted in it or bound to either surface. Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, while others are embedded in either the outer or inner leaflet of the lipid bilayer. Loosely bound to the outer or inner surface of the membrane are the peripheral proteins. Many of the proteins and lipids have externally exposed oligosaccharide chains. (Reproduced, with permission, from Junqueira LC, Carneiro J Basic Histology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

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