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Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
carbohydrate-carbohydrate interaction

Until recently there practically has not been any data on existence of biologically significant carbohydrate-carbohydrate interaction. Only after the works of S. Hakomoriís group on interaction of glycolipid oligosaccharide fragments it has become clear that this recognition type is one of the fundamental ones in cell biology.
Polysaccharides have rather favorable structures for participation in carbohydrate-carbohydrate recognition. As carbohydrate epitopes are situated tightly and repeatedly forming a surface principally similar to that of the carbohydrate pattern of membrane glycolipids, it could be expected that such epitope position is realised on polysaccharide envelop of bacteria and yeast. Our attention was attracted to zymosan, polysaccharide complex from yeast Saccharomices cerevisiae. About 90% of zymosan weight is presented by polysaccharides, β(1-3) glucan containing some amount of 1-6 branching (65%) and highly branched mannan (25%), whereas only 10% is protein. In our attempt to inhibit zymosan macrophage interaction mediated by macrophage lectins, by the glycoconjugate Man-PAA, we have observed the increase of interaction instead of inhibition. The effect could be explained either by binding of zymosan due to protein component or by interaction of Man-PAA with zymosan by the carbohydrate-carbohydrate fashion. We have proved the latter possibility: 1) neither protease nor alkali treatment of zymosan decrease its binding with glycoconjugates; 2) periodate treatment abolishes the binding; 3) individual β-glucan binds glycoconjugates similarly to zymosan. The binding is reversible, Ca2+-dependent, it can be inhibited by methyl mannoside and mannose-rich N-chains of glycoproteins. Glycoproteins with mannose termination, their glycopeptides and oligosaccharides, neoglycoconjugates of mannose-rich chains, all these compounds bound zymosan or inhibited its binding to Man-PAA.
As glycoprotein mannose-rich chains are typical peripheral components of animal cell membranes, whereas glucans are those of bacteria and yeast cell wall, the obtained results could initiate the search of glycoprotein/polysaccharide mediated cell adhesion in vivo.

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