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Affinity Chromatography - Department of Molecular and Cellular ...

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Glycoproteins or polysaccharides<br />

Con A Sepharose 4B, Lentil Lectin Sepharose 4B, Agarose Wheat Germ Lectin<br />

Glycoproteins <strong>and</strong> polysaccharides react reversibly, via specific sugar residues, with a group<br />

<strong>of</strong> proteins known as lectins.<br />

As lig<strong>and</strong>s for purification media, lectins are used to isolate <strong>and</strong> separate glycoproteins,<br />

glycolipids, polysaccharides, subcellular particles <strong>and</strong> cells, <strong>and</strong> to purify detergentsolubilized<br />

cell membrane components. Substances bound to the lectin are resolved by<br />

using a gradient <strong>of</strong> ionic strength or <strong>of</strong> a competitive binding substance.<br />

Media screening<br />

To select the optimum lectin for purification, it may be necessary to screen different media.<br />

The lig<strong>and</strong>s, Concanavalin A (Con A), Lentil Lectin <strong>and</strong> Wheat Germ Lectin provide a<br />

spectrum <strong>of</strong> parameters for the separation <strong>of</strong> glycoproteins. Table 5 gives their specificity.<br />

Table 5. Specificity <strong>of</strong> lectins.<br />

Lectin<br />

Mannose/glucose binding lectins<br />

Con A, Canavalia ensiformis<br />

Lentil Lectin, Lens culinaris<br />

N-acetylglucosamine binding lectins<br />

Wheat Germ Lectin, Triticum vulgare<br />

Specificity<br />

Branched mannoses, carbohydrates with terminal<br />

mannose or glucose (aMan > aGlc > GlcNAc).<br />

Branched mannoses with fucose linked a(1,6) to<br />

N-acetyl-glucosamine, (aMan > aGlc > GlcNAc).<br />

Chitobiose core <strong>of</strong> N-linked oligosaccharides,<br />

[GlcNAc(b1,4GlcNAc) 1–2 > bGlcNac].<br />

Con A for binding <strong>of</strong> branched mannoses, carbohydrates with terminal mannose<br />

or glucose (aMan > aGlc > GlcNAc)<br />

Concanavalin A (Con A) is a tetrameric metalloprotein isolated from Canavalia ensiformis<br />

(jack bean). Con A binds molecules containing a-D-mannopyranosyl, a-D-glucopyranosyl<br />

<strong>and</strong> sterically related residues. The binding sugar requires the presence <strong>of</strong> C-3, C-4 <strong>and</strong> C-5<br />

hydroxyl groups for reaction with Con A. Con A can be used for applications such as:<br />

• Separation <strong>and</strong> purification <strong>of</strong> glycoproteins, polysaccharides <strong>and</strong> glycolipids.<br />

• Detection <strong>of</strong> changes in composition <strong>of</strong> carbohydrate-containing substances,<br />

e.g. during development.<br />

• Isolation <strong>of</strong> cell surface glycoproteins from detergent-solubilized membranes.<br />

• Separation <strong>of</strong> membrane vesicles into "inside out" <strong>and</strong> "right side out" fractions.<br />

79

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