Structures and interactions of N-acetylated oligosaccharides
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Oligosaccharides are of central importance in the development and maintenance of biological systems. They are found free in solution and as constituents of proteins (glycoproteins) and lipids (glycolipids) on the cell surface; they have been implicated in the mechanisms of action of diverse cellular processes including inflammation, cell-cell recognition and adhesion, protein turnover, and bacterial infection. Oligosaccharides, or molecular mimics thereof, are also becoming more frequent targets in drug design for the treatment of human illness and disease. As cellular functions of oligosaccharides are intimately related to their three-dimensional shapes or conformations, generating 3D structures of these molecules and their complexes with receptors is an essential step in deciphering their function. This dissertation aims to develop NMR-based probes of conformation and protein interaction for N-acetylated oligosaccharides. Efforts focus largely on utilization of information that can be retrieved from 13C enriched acetyl groups. Novel means of introducing 13C-enriched sites, post isolation in natural carbohydrate products, are introduced and the ability to acquire sufficient information to characterize the conformation of the carbohydrate targets is illustrated. Structural information is obtained from chemical shift anisotropy offsets of 13C carbonyl resonances and 13C-13C dipolar couplings between the labeled methyl and carbonyl carbons of the acetyl groups. Three applications are presented: a structure determination of a chitin dimer in free solution, a structure determination of a chondroitin sulfate (CS) pentamer in free solution, and a preliminary study of CS hexamers bound to a chemokine (CCL5) important to T-cell migration.