Glycoproteins - Hughes, R. 1985

Structure
Sequence Determination

Only in rare cases is a single specific carbohydrate chain attached to the polypeptide backbone of a glycoprotein. Typically, multiple amino acid residues are glycosylated, and each of these glycosylated residues can be linked to several highly similar glycans. Proteolysis can be used to cleave these glycans attached to the binding Amino Acids or small Peptides. The resulting glycopeptides are then separated and analyzed for their monosaccharide composition. Often, the complete carbohydrate sequence can be established [7] by combining various chemical, enzymatic, and physical Methods (Table 2.2).

Class="center">Table 2.2. Steps in determining the sugar sequence of glycans

1.

Proteolysis: prolase, Trypsin, Chymotrypsin, collagenase, etc.

2.

Glycopeptide Separation: Gel filtration, Ion-exchange Chromatography, Electrophoresis, and paper chromatography

3.

Composition: Gas-Liquid Chromatography (Monosaccharides), ion-exchange chromatography (amino acids)

4.

Determination of sugar sequence:

a) chemical: methylation, periodic acid oxidation

b) enzymatic: exo- and Endoglycosidases

c) physical: mass spectrometry, nuclear magnetic Resonance

Fig. 2.3. Structure of N-acetylneuraminic acid and other sialic acids.

Name

Substitution site

Substituting group

Typical source

N-acetylneuraminic acid

C-5

CH3CONH—

Common

N-glycolylneuraminic acid

C-5

HOCH3CONH—

Pig Tissues (>90%)

O-acetyl derivatives

C-9

C-7

СН3СО—

СР3СО—

Bovine submandibular gland (rare)

C-4

СН3СО—

Horse tissues

The identification of sialic acids incorporated into Glycoproteins presents a particular analytical challenge, as the core ring structure of neuraminic acid exists in numerous variants that differ in the positions of their substituent groups. The most frequently occurring derivative is N-acetylneuraminic acid (Fig. 2.3); in addition, about 20 other sialic acid derivatives are known. For instance, N-glycolylneuraminic acid is commonly found in glycoproteins or Glycolipids, and several O-acyl derivatives of this and N-acetylneuraminic acid are also known. The hydroxyl group at C-2 takes part in The formation of the glycosidic bond.



Last update: 06/08/2026

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