Carbohydrate binding site

Firon, N., Ofek, I., and Sharon, N. (1984). Carbohydrate-binding sites of the mannose-specific fimbrial lectins of enterobacteria. Infect. Immun. 43,1088-1090. 

Carbohydrate Systems Carbohydrate binding sites, 46, 362 glu-cosidases, 46, 368 glycidol phosphates and 1,2-anhydrohexitol 6-phosphates, 46, 381 /3-galactosidase, 46, 398 lysozyme, 46, 403. 

Figure 13.2 The crystal structures of (a) concanavalin A and (b) the carbohydrate recognition domain of galectin-3. Residues in the carbohydrate binding sites are black.

Due to the vast amount of recent research on lectins, it is quite apparent that proteins which bind to specific cell-surface glycoproteins are involved in modulation of a variety of mitotic and metabolic events within the cell. It is hoped that structural studies of these proteins and their receptors will prove to be informative in determining the mechanisms of these and other such events. In this presentation, I would like to discuss the structural features of Con A, such as the /3-sheets, subunit structure, the manganese, calcium and carbohydrate binding sites and close, by mentioning some recent advances in crystallography which are relevant to the studies of proteins and how these should effect such future research. 

Figure 2A. Another orientation of the monomer, which includes some of the side chain atoms in the Mn2, Ca2 , and carbohydrate binding sites. /3-sheet I is to the left (including His 127), (3-sheet II is through the center (almost perpendicular to the plane of the paper), and (3-sheet III is to the lotoer-left.

Figure 5. The metal ions Mn3 and Ca2 and their ligands, near the carbohydrate binding site (CHO). (Figures 5-8 have same orientation as Figure 1.)...

The single polypeptide-chain protomers (however, see later) are compactly folded, forming dome-shaped structures approximately 4.2 nm high x 4.0 nm wide x 3.9 nm thick. Each subunit contains one Mn2+, one Ca2+, and one carbohydrate binding-site,172,278-280 believed, until recently, to be situated in a prominent cavity in the molecular model.280 Two such subunits are joined with their flattened bases proximal, to form roughly ellipsoidal domes. The dimers pair across one another, to form tetramers as depicted in Fig. 2. 

Inasmuch as extensive maleylation of free amino groups did not abolish the hemagglutinating and polysaccharide-precipitating activity of the lentil lectin, it is probable that amino groups are not involved in the carbohydrate-binding site of the lectin.4473 Treatment of the lentil lectin with 1-acetylimidazole resulted in the modification of 3-5 tyrosyl and 7-17 amino groups.4473 The modified proteins had lost their hemagglutinating activity, but retained their capacity to interact with polysaccharides and to bind to erythrocytes.4473... 

The carbohydrate-binding sites of WGA are probably situated at the surface of the protein molecule. The pH dependences of association constants for lectin-chitotriose binding indicate that an ionizable group, pK = 3.9, is probably involved in complex-formation.494,504 This observation is especially noteworthy, inasmuch as protein carboxyl... 

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