Lectins, sugar-specific binding

Lectins have a high degree of specificity for the sugars they bind, and hence the proposal that more than one type of oligosaccharide signal is involved in elicitation necessarily dictates that more than one receptor is present at the cell surface. Since the different signals ultimately result in the same response, it is presumed that the signal transduction pathways... 

Lectins, sugar-binding proteins, have become powerful molecular probes to investigate the structure, topography and dynamics of cell-surface saccharide determinants (1). The utility of these proteins in the study of the surface properties of a variety of cell types has stimulated renewed interest in the determination of the molecular basis of their saccharide specificity. Furthermore lectins provide relatively simple models for the investigation of noncovalent interactions between saccharides and proteins. 

Inbar and coworkers689 determined that [3H]-acetylated lectin did not bind to the surface of normal cell-lines (hamster and rat embryo, and mouse 3T3 cells) or to the transformed counterparts of these cells. Trypsinization did not alter these results. The authors concluded688 that L-fucosyl residues were not exposed on the cell surface. In view of the specificity studies of Kabat and coworkers,200,686 this interpretation may be incorrect L-fucosyl residues may be rendered sterically inaccessible by glycosylation of neighboring sugar residues. 

The structure of the mannose 6-phosphate recep-tor/lectin has also been resolved crystallographically, revealing details of its interaction with mannose 6-phosphate that explain the specificity of the binding and the necessity for a divalent cation in the lectin-sugar interaction (Fig. 7-35c). Arg of the receptor is hydrogen-bonded to the C-2 hydroxyl of mannose and coordinated with Mn L His ° is hydrogen-bonded to... 

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