Glycans and Monosaccharides

The glycan chains of glycoconjugates are composed of monosaccharides. Because the number of oligosaccharide structures associated with a specific glycoconjugate may be highly variable, glycoproteins and glycolipids usually exist as complex mixtures of glycosylated variants (glycoforms). This heterogeneity significantly complicates the structural analysis of glycoconjugates. For example, proteins having the same sequence but different glycosylation patterns show different bands or spots on SDS-PAGE gels and additional efforts are thus necessary to identify the protein expression patterns.

Mannose, N-acetylglucosamine (GlcNAc), galactose, fucose, and sialic acid are the most common monosaccharides in the glycans of vertebrate glycoproteins. Figure 1 shows the structures and the symbols generally used in this field. These monosaccharides connect with one another to form the glycan chains.

ch2oh

hOsOh h/oh

h^oh ho/oh

H H

ch2oh OH H O\H H\OH H /OH H NHAc

W-Acetyl-glucosamine (GlcNAc)

Mannose (Man)

Fucose (Fuc)

Galactose (Gal)

Sialic Acid (NANA)

W-Acetyl-galactosamine (GalNAc)

Figure 1 The most common monosaccharides in the glycans of glycoproteins with corresponding structures and symbols. Most species other than humans may have N-glycolyl as well as N-acetyl substitution on sialic acid. For sialic acid, R=CHOHCHOHCH2OH.

Figure 1 The most common monosaccharides in the glycans of glycoproteins with corresponding structures and symbols. Most species other than humans may have N-glycolyl as well as N-acetyl substitution on sialic acid. For sialic acid, R=CHOHCHOHCH2OH.

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