Polyvalent protein-saccharide interactions are intriguing targets for investigation and application, as they mediate recognition processes involved in virus infection, tumor metastasis, and immunogenic and inflammatory responses. It is known that the identity of the saccharide, the nature of the template on which it is displayed, and the number of saccharides on the template are important variables in binding. However, further understanding of these important recognition processes has been limited because the natural glycoproteins involved in binding are very difficult to synthesize and characterize, and essentially all of the polymeric materials used to study these processes are heterogeneous in both molecular weight and composition. The production of glycopolymer scaffolds in which molecular weight, composition, and saccharide placement are precisely controlled would therefore offer enormous advantages for designing materials capable of interacting with specific protein or cellular targets. In this proposal, we will use protein engineering methods to produce well-controlled artificial repetitive proteins capable of precise presentation of saccharides. The level of control afforded by protein engineering will permit the synthesis of alanine/glycine-rich random coil proteins and alanine-rich or-helical proteins with precisely placed reactive groups; these groups will subsequently be modified with saccharides. The identity of the saccharide, the spacing between saccharides, the number of saccharides on the scaffold, and the flexibility of the protein scaffold will be varied systematically. These macromolecules will be characterized by a variety of methods (e.g., NMR, circular dichroism, MALDI-TOF mass spectrometry, light scattering) and tested for their ability to bind to both protein and cellular receptors of known structure; results will be used to improve glycoprotein design. Ultimately, our goals are not only to understand these binding events, but also to produce well controlled polymeric architectures that can direct cellular responses.
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