Multivalent interactions involving antibody binding to multivalent antigens have been studied extensively. Antibodies themselves can be multivalent, existing as the bivalent immunoglobulin D, E, and G types, the tetravalent IgE, or the immuno-glubulin M type, displaying 10 associated binding sites. Models for multivalent antibody binding were developed by Crothers and Metzger in the 1970s [32-34]. These early studies emphasized that for multidentate ligands to simultaneously occupy multiple binding sites, they must present recognition epitopes that are both properly spaced and sufficiently flexible. As expected, these variables are also important in multivalent carbohydrate binding. Still, an understanding of how much increase in activity is to be gained by such presentation and how the structures of multivalent ligands should be optimized for maximal potencies remains a mystery. The following sections describe some of the molecular features and general mechanisms that lead to enhanced activities.
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