Conformation and Dynamics of Complex Polysaccarides

点击翻译按钮获取中文摘要

The oligosaccharides and polysaccharides of the cell surface have complex structures encoding information which controls cellular interactions. The information is decoded by binding to proteins such as lectins which is often complex and multivalent and may also involve cooperative interactions between protein and carbohydrate binding sites. The solution conformation and the dynamics of the oligosaccharide ligands, which can have a significant influence on the free energy of binding, is poorly understood and will be studied in this project by physical methods including computational molecular modeling and NMR spectroscopy. The model proposed for flexibility in complex oligosaccharides and polysaccharides will be useful for interpretation of protein-carbohydrate binding equilibria and will serve as a basis for interpretation of the dynamic properties of high molecular weight polysaccharides. The glycosidic linkages joining the comparatively rigid pyranoside chairs in complex, branched oligosaccharides have highly varied stereochemistry with some linkages being relatively rigid and others highly flexible. In this research, examples of relatively rigid oligosaccharides will be selected from the Lewis and blood group oligosaccharides while oligosaccharides and polysaccharides isolated from the cell walls of the viridans streptococci, S. mitis and S. oralis will be models for more flexible oligosaccharides. In addition to traditional nuclear Overhauser methods, NMR experiments involving heteronuclear scalar coupling across the glycosidic linkages will be studied both in natural abundance samples and in samples prepared with biosynthetic incorporation of stable isotopes. The recently introduced method of residual dipolar coupling of oligosaccharides partially oriented in dilute liquid crystal solutions is capable of giving abundant and very precise experimental information on the conformation of rigid oligosaccharide epitopes and new methods for treating flexible oligosaccharides will be used which will lead to greatly improved models for conformation and dynamics of the hinges which join more rigid domains. The experimental results will be interpreted with computer molecular modeling calculations including molecular dynamics simulations and Monte Carlo methods.This project will support training in structural biochemistry for graduate and undergraduate students who will learn modern nuclear magnetic resonance experiments and computer molecular modeling methods along with aspects of the analytical and physical biochemistry of complex carbohydrates. The PI's department has an especially strong tradition in training of under represented minority students, both at the graduate and undergraduate level.