Protein Protocols Protein Protocols

Lectin Blotting to Detect Glycoproteins 781
Fig. 2. Glycoprotein blot pattern of 2-D PAGE separation of plasma proteins (120 µg) probed
with RCA (specific for galactose) and revealed using chemiluminescence (5 s film exposure).
1, Complement 3 α-chain; 2, transferrin; 3, IgM µ-chain; 4, hemopexin; 5, IgA α-chain; 6,
α 1-β-glycoprotein; 7, fibrinogen β-chain; 8, IgG γ-chain; 9, fibrinogen γ-chain; 10, haptoglobin
β-chain; 11, haptoglobin cleaved β-chain; 12, Ig light chain.
(Table 1). They all have in common the inner core structure presented in Fig. 5. The
presence of this common core structure reflects the fact that all these asparagine-linked
oligosaccharides originate from the same precursor.
O-glycans are found frequently in mucins, but rarely in plasma glycoproteins. Table 2
illustrates the three different groups of O-glycosyl protein glycans.
1.2. Lectins as a Tool for Glycoprotein Detection
Lectins are a class of carbohydrate binding proteins, commonly detected by their
ability to precipitate glycoconjugates or to agglutinate cells. (Some lectins react selectively
with erythrocytes of different blood types.) Lectins are present in plants, animals,
and microorganisms (14).
Each lectin binds specifically and noncovalently to a certain sugar sequence in oligosaccharides
and glycoconjugates. Lectins are traditionally classified into specificity