Oligosaccharide chains glycoprotein

Glycoproteins are proteins to which one or more oligosaccharide chains are covalently linked. 

Metastasis Abnormalities in the oligosaccharide chains of membrane glycoproteins and glycolipids are thought to be of importance... 

Many studies have been conducted in an attempt to define the precise roles oligosaccharide chains play in the functions of glycoproteins. Table 47-2 summarizes results from such studies. Some of the functions listed... 

Numerous lectins have been purified and are commercially available three plant lectins that have been widely used experimentally are listed in Table 47-7. Among many uses, lectins have been employed to purify specific glycoproteins, as tools for probing the glycoprotein profiles of cell surfaces, and as reagents for generating mutant cells deficient in certain enzymes involved in the biosynthesis of oligosaccharide chains. 

Based on the nature of the linkage between their polypeptide chains and their oligosaccharide chains, glycoproteins can be divided into three major classes (Figure 47-1) (1) those containing an O-glycosidic linkage (ie,... 

The structures of many oligosaccharide chains can be elucidated by gas-liquid chromatography, mass spectrometry, and high-resolution NMR spectrometry. Glycosidases hydrolyze specific linkages in oligosaccharides and are used to explore both the structures and functions of glycoproteins. 

Many of the proteins are glycoproteins (eg, the glyco-phorins) containing 0- or N-linked (or both) oligosaccharide chains iocated on the externai surface of the membrane. 

Glycophorins A, B, and C are also transmembrane glycoproteins but of the single-pass type, extending across the membrane only once. A is the major gly-cophorin, is made up of 131 amino acids, and is heavily glycosylated (about 60% of its mass). Its amino terminal end, which contains 16 oligosaccharide chains (15 of which are O-glycans), extrudes out from the surface of... 

The ABO Substances Are Glycosphingolipids Glycoproteins Sharing Common 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.

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... 

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.34-36 The NaOH-NaBH4 treatment is used to release, somewhat specifically, oligosaccharides O-linked to serine and threonine. Hydrazinolysis is used to break N-linkages, and proteolysis, to isolate glycopeptides. Each method apparently still has some drawbacks. 

It is clear from the two spectra that resonances corresponding to inner carbohydrate residues, such as peaks 5, 6, and 13, display a much larger line-width than resonances corresponding to outer residues, such as peaks 2-4. This reflects the relative mobility of such residues, and aids in distinguishing between terminal residues and inner residues of the intact oligosaccharide chains of intact glycoproteins. 

---