| The interaction between proteins and carbohydrates is an important first step for many biological processes. For example, viral and bacterial infections, antibody-antigen interactions, fertilization and other cell-cell interactions all rely on protein-carbohydrate interactions as a first step in recognition. It is known, however, that the affinity between a lectin and a single sugar is quite weak. The increase in binding affinity in most biological systems is a result of what is often generically referred to as multivalent binding.;A number of carbohydrate-containing synthetic organic molecules have been synthesized to study multivalent protein carbohydrate interactions. Examples include small molecules that typically contain fewer than 10 sugars, medium sized molecules that contain between 10 and 100 sugars, and large polymeric systems that can contain thousands of sugars.;While most carbohydrate-containing systems have provided valuable insight into the mechanism of multivalent interactions, no class of carbohydrate containing system existed prior to this work in which the number of sugars and the size of the ligand could be varied independently. Such a system should provide specific information on the optimal geometric arrangement of ligands toward various receptors.;We have homogeneously and heterogeneously functionalized polyamidoamine (PAMAM) dendrimers up to generation six with mannose using a thiourea linkage by the reaction of an isothiocyanate on the carbohydrate with the terminal amines on the dendrimer. The result is water-soluble carbohydrate-containing dendritic molecules. Methods to characterize these dendritic macromolecules by nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry were developed.;The effectiveness of the dendrimers as ligands for the lectin Concanavalin A has been demonstrated by means of a hemagglutination assay, a precipitation assay and a turbidity assay. Results indicate that the size of the dendrimer has a great effect, with the larger dendrimers being most active with Concanavalin A. In addition, the degree of functionalization has a profound effect, with the optimum degree of functionalization for binding being below full functionalization. Results also suggest mannose-functionalized PAMAM dendrimers effectively recruit and cluster lectins. |
