Thesis

Sugar inhibition of yeast binding to lectin beads

Lectins, which are carbohydrate binding proteins, are used in the purification of glycan-containing molecules and in histochemical studies that have identified important cellular properties. Differences in cells with various carbohydrates on their surfaces influence malignancy and pathogenicity. Pathogenic organisms often bind to human cell surfaces via lectin-glycan interaction. Pharmaceutical companies are developing medications based upon their ability to inhibit carbohydrate mediated binding reactions. In this study, I used microbeads derivatized with concanavalin A (Con A), a mannose-binding lectin, as a model in order to examine the binding properties of mannose-rich yeast, a model for pathogenic organisms. Ten sugars- including monosaccharides and oligosaccharides, at four concentrations each, were examined for their ability to inhibit cell-lectin binding in this model system. If a reagent causes disaggregation of yeast from lectin derivatized beads, that reagent might for example, block pathogen binding to cells. T- tests were performed to determine if any disaggregation of yeast from the Con A beads in the experimental samples was significantly different from the controls. About 500 total trials were performed at each of the four concentrations of the ten sugars studied and controls, by counting the number of yeast that remain bound to the beads over a 60 minute time course. It is generally accepted that reagents that are most active are those that are effective at the lowest concentrations, suggesting that they bind most strongly to surface receptors. Here we found that Methyl-a-D-mannopyranoside, D(+)mannose and D(+)melezitose were most effective in disaggregating yeast from Concanavalin A at the lowest concentration tested (0.005M) at 60 minutes. A similar but slightly different ranking was observed at the 20 minute time. Most important is that the method used in this study is highly quantitative and can easily identify reagents that may be useful in anti-infection, anti-biofilm and anti-cancer venues

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