Complex oligosaccharide chains

Figure 52-6. Diagrammatic representation of the structures of the H, A,and B blood group substances. R represents a long complex oligosaccharide chain, joined either to ceramide where the substances are glycosphingolipids, or to the polypeptide backbone of a protein via a serine or threonine residue where the substances are glycoproteins. Note that the blood group substances are biantenna ry ie, they have two arms, formed at a branch point (not indicated) between the GIcNAc—R, and only one arm of the branch is shown. Thus, the H, A,and B substances each contain two of their respective short oligosaccharide chains shown above. The AB substance contains one type A chain and one type B chain.

Synthesis of Complex Oligosaccharide Chains of Glycoproteins. Paulsen, H. Chem. Soc. Rev., 1984, 73, 15. 

Fibrinogen (factor I, 340 kDa see Figures 51-1 and 51-4 and Tables 51-1 and 51-2) is a soluble plasma glycoprotein that consists of three nonidentical pairs of polypeptide chains (Aa,Bpy)2 covalently linked by disulfide bonds. The B(3 and y chains contain asparagine-linked complex oligosaccharides. All three... 

In order to investigate, and deduce, the complex carbohydrate structures of glycoproteins, it must be possible to release, and isolate, the oligosaccharide chain(s) from the glycoprotein. Following this, the structure is usually deduced by a combination of enzymic, chemical, and instrumental methods.34-36... 

C5-derived peptide in serum. This molecule lacks anaphylatoxin activity (i.e. it cannot cause smooth muscle contraction), and its ability to cause che-motaxis in neutrophils is about 10-20 times lower than that of C5a. However, human serum also contains a heat-stable, anionic protein termed co-chemotaxin (relative molecular mass = 60 kDa), which acts in a concentration-dependent manner to permit C5a des Arg to act as a chemoattractant for neutrophils. Thus, C5a des Arg plus cochemotaxin working together probably account for most of the neutrophil chemoattractant activity in vivo following complement activation. The mechanism of action of cochemotaxin is unknown, but it may form a physical complex by attaching to a sialic acid residue on the oligosaccharide chain of C5a des Arg. Deglycosylation of C5a des Arg increases its chemoattractant activity more than 10-fold, and its dependency upon cochemotaxin is decreased. 

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