Linked Oligosaccharides

Removal of the oligosaccharide chain from the glycoprotein usually Involves the use of one of three main methods treatment with NaOH-NaBH4, hydrazinolysis, or proteolysis. " The NaOH-NaBH4 treatment is used to release, somewhat specifically, oligosaccharides 0-linked to serine and threonine. Hydrazinolysis is used to break N-linkages, and proteolysis, to isolate glycopeptides. Each method apparently still has some drawbacks. 

The structures of oligosaccharides linked to these proteins can be complex and many of them contribute to antigenicity, the ability of the cell surface to elicit an immune response. 

The biological function of this dolichol-linked oligosaccharide was revealed in pulse-chase experiments which showed that the intact oligosaccharide was transferred, as such, to protein. Subsequent studies, to be discussed, confirmed that the formation of the oligosaccharide linked to the Asn residues of glycoproteins is probably initiated by transfer of the oligosaccharide from the dolichol diphosphate intermediate to the asparagine residue of a nascent polypeptide (see Refs. 35, 49, 50, and 67 for reviews). 

Fig. 1.—Structures of the Oligosaccharide-linked Lipids (A) Present in Animal Cells and (B) Proposed for Plant Cells.113,115...

As well as chondroitin sulfate, other glycosaminoglycans, such as keratan sulfate, with shorter chains (Mr = 2,500-5,000) are found in cartilage (Fig. 5-22). N-linked oligosaccharides similar to those found in glycoproteins are also present. Note that keratan sulfate in other tissues, e.g., intervertebral disk or cornea, has a longer chain (Mr= 10,000-25,000) and may have a different oligosaccharide link to the core protein. 

HbOC vaccine (Hib oligosaccharides linked to the non-toxic diphtheria toxin variant CRM197), for example HibTITER (produced by Lederle-Praxis Biologicals, Pearl River, NY). 

Keratan sulfate 0-Linked oligosaccharide N-Linked oligosaccharide Link proteins... 

Structure of the common branched inner domain of oligosaccharides linked in N-glycosidic linkages with asparagine. Man = Mannose T, GIcNAc = N-acetylglucosamine , Asn = Asparagine. [Adapted with permission from N. Sharon and H. Lis, Chem. Eng. News, p. 28 (March 30, 1981) 1981 by the American Chemical Society.]... 

Erythropoietin has oligosaccharides linked to three asparagine residues and one serine residue. The structures shown are approximately to scale. See page 315 for the carbohydrate key. [Draw from IBUYpdf.]... 

CDG-type I syndrome [264,266,267] is due to a deficiency in the oligosaccharidyltrans-ferase which transfers en bloc onto the nascent protein the oligosaccharide linked to dolichol diphosphate. Later, van Schaftingen and Jaeken [1995, FEES Lett. 377, 318-320] demonstrated that the syndrome was due in fact to a phosphomannomutase deficiency, an enzyme which provides the mannose-1-phosphate required for the initial steps of protein glycosylation. This leads to four transferrin isoforms non-glycosylated, glycosylated in Asn-413 or in Asn-611 and in both Asn-413 and 611. 

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