Lectins specific carbohydrate ligands

In the purification of lectins, special adsorbents have been employed. The adsorbents have been prepared by attaching specific, carbohydrate ligands to activated supports.41-106,157 An affinity adsorbent prepared from chitobiose and (2-aminoethyl)-Bio-Gel was used to purify the 2-acetamido-2-deoxy-D-glucose-binding lectin from wheat germ. The data for the purification of this lectin are shown in Fig. 6. 

The ability of water to act as both donor and acceptor of hydrogen bonds makes it an excellent mediator in protein-carbohydrate complexes. Results of numerous X-ray crystallographic studies of protein-carbohydrate complexes attest to the pervasiveness of water-mediated hydrogen bonds in protein-carbohydrate interactions. Lectin-bound water molecules are proposed to act as an extension of the protein surface itself [1]. This idea is supported by the fact that water molecules occupy conserved sites in the structures of related lectins [24]. In addition, water molecules can mediate similar hydrogen bonding interactions in the complexes of different proteins with a specific carbohydrate ligand or in complexes of the same lectin with different saccharide ligands [1]. 

Table 1 gives the lectins most commonly used to analyze structural changes of glycoconjugates present at cell surface with their usual abbreviations and their specific carbohydrate ligands. 

S. Sakai, Y. Shigemasa, and T. Sasaki, A self-adjusting carbohydrate ligand for GalNac specific lectins, Tetrahedron Lett., 38 (1997) 8145-8148. 

Affinity adsorbents having carbohydrate ligands have been used for the isolation and purification of many types of macromolecular substances. To illustrate, several types of antibodies, enzymes, lectins, and myeloma proteins have been obtained in highly purified form. All of the substances that have been purified by this procedure exhibit specificity for a particular carbohydrate moiety. It is the purpose of this article to assemble information on the methods for preparing affinity adsorbents having carbohydrate ligands, and to illustrate the use of these adsorbents for the purification of representative, macromolecular substances. 

The presence of specific targeting ligands monoclonal antibodies with specificity for M cells, or lectins which bind to specific carbohydrate residues found on M-cells, can increase the uptake of microparticulate delivery systems. 

Suitable pairs of protein and ligand combination for affinity chromatography are antigen-antibody, hormone-receptor, glycoprotein-lectin or enzyme-substrate/cofactor/ effector (Table 3.6). The affinity of lectins for specific carbohydrate moieties (Lis and Sharon, 1973 Barondes, 1981) has made them particularly useful for the purification of distinct groups of glycans and glycoproteins (Table 3.7). 

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