Assessing the Relative Affinities of Bacterial Lectins for Sugars

In this method, a bacterial lectin is allowed to bind to its target polysaccharide in the form of a matrix suspension that can be recovered by centrifugation or filtration. After an initial test to show that the lectin is fully bound to the matrix, a measured amount of competing free sugar is added to the matrix resuspended in buffer. After mixing, the suspension is centrifuged, and the protein content of the supernatant fraction is measured before being returned to the matrix with the addition of another aliquot of sugar. The cycle of mixing, centrifugation, and quantification of protein (lectin) in the supernatant fraction is continued until the released protein reaches plateau levels. The procedure is repeated with a variety of different sugars to compare their efficiencies at binding and displacing the lectin from its polysaccharide ligand. This procedure is illustrated here using a PA14-type bacterial lectin that has affinity for fucosylated glycans and will, as a result, bind to dextran-based resins like Superdex 200 (S200). A second example features the release of Escherichia coli maltose-binding protein from amylose resin by mono- and disaccharides. The purpose of this assay is to determine the relative binding affinity of different sugars for a bacterial lectin.