Downstream processing - Pharmaceutical Biotechnology: Concepts and Aapplications - page 153

Table 6.4 Some lectins commonly used in immobilized format for the purifi cation of glycoproteins. The
sugar specifi city is listed, as are the free sugars used to elute the bound glycoprotein

Lectin Source Sugar specifi city Eluting sugar

Con A Jack bean seeds α- D -Mannose, α- D -glucose α- D -Methyl mannose

WG A Wheat germ N -Acetyl-β- D -glucosamine N -Acetyl-β- D -glucosamine

PSA Peas α- D -Mannose α- D -Methyl mannose

LEL Tomato N -Acetyl-β- D -glucosamine N -Acetyl-β- D -glucosamine

STL Potato tubers N -Acetyl-β- D -glucosamine N -Acetyl-β- D -glucosamine

PHA Red kidney bean N -Acetyl- D -galactosamine N -Acetyl- D -galactosamine

ELB Elderberry bark Sialic acid or N -acetyl- D -galactosamine Lactose

GNL Snowdrop bulbs α-1 → 3 Mannose α-Methyl mannose

AAA Freshwater eel α- L -Fucose

L -Fucose

phytohaemagglutinins. All lectins have the ability to bind certain monosaccharides (such as α - D -

mannose, - D -glucose, D - N -acetyl galactosamine), and the sugar specifi city for many is known

( Table 6.4). Among the best-known and most widely used lectins are concanavalin A (Con A),
soybean lectin (SBL) and wheat germ agglutinin (WGA).
Glycoproteins generally bind to lectin affi nity columns at pH values close to neutrality. Desorp-
tion may be achieved in some cases by alteration of the pH of the eluting buffer. The most common
method of desorption, however, involves inclusion of free sugar molecules for which the lectin
exhibits a high affi nity in this elution buffer, i.e. the inclusion of a competing ligand.
Although lectin affi nity chromatography may be utilized to purify a variety of glycoproteins, it
has not been widely employed for a number of reasons:

α

Immobilized antibody

Antigen which was originally
employed to stimulate
antibody production

Additional ligands in solution
not recognized by the antibody

Bead support

Figure 6.15 Principle of immunoaffi nity chromatography. Only antigen that is specifi cally recognized by the
immobilized antibody will be retained on the column