Carbohydrates attached to asparagine, serine or threonine residues in proteins influence the physical, chemical and biological properties of the polypeptide backbone. This research proposal focuses on the chemical synthesis of various glycopeptide structures and the characterization of the conformational changes observed in the peptides when sugar side- chains are incorporated. We have successfully synthesized and analyzed medium-sized (6-20 amino acids) glycopeptides carrying mono, di-, tri, tetra, and heptasaccharide units of the natural glycoprotein antennae. We propose to extend the solid-phase glycopeptide synthetic studies to incorporate more expensive, branched carbohydrate systems to investigate the interference of saccharides with the processing of the peptides as a function of the spatial configuration. Since post-translational modifications in the recognition sites of otherwise non-modified T cell epitopes sometimes destroy the T cell activity, we plan to downregulate unwanted immune responses by incorporating N-acetyl-glucosamine, N-acetyl-galactosamine, and maltoheptaose moieties into T cell epitopes. We also plan to study whether mono- or oligosaccharides are recognized when they are attached to B cell epitopic peptides. Based on our and our collaborators' results, we will attempt to prepare glycopeptides with antibacterial activity and we will study the increase of the serum half-life after glycosylation of synthetic peptides. We have also documented that glycosylation of synthetic peptides results in the formation, stabilization or alteration of reverse-turns. We will collect further evidences for this phenomenon, and we will also investigate whether structures other than reverse-turns can also be stabilized by glycosylation. The resulting secondary structural changes will be qualitatively and quantitatively studied by circular dichroism, Fourier-transformed infrared, and nuclear magnetic resonance spectroscopies and by computer and cyclohexyl-peptides to subtract the spectroscopical and non-specific conformational contribution of the incorporated sugar moieties.
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