Conformation and Dynamics of Complex Polysaccarides

细胞表面的寡糖和多糖具有复杂的结构，编码控制细胞相互作用的信息。这些信息通过与凝集素等蛋白质的结合来解码，凝集素通常是复杂和多价的，也可能涉及蛋白质和碳水化合物结合位点之间的合作相互作用。低聚糖配体的溶液构象和动力学对结合自由能有重大影响，但目前对其了解甚少，本项目将通过计算分子模型和核磁共振波谱等物理方法进行研究。该模型将有助于解释蛋白质-碳水化合物的结合平衡，并为解释高分子量多糖的动态特性奠定基础。在复杂的支链寡糖中，连接相对刚性的吡喃苷基团的糖苷键具有高度不同的立体化学性质，有些键相对刚性，有些键具有高度柔性。在本研究中，将从Lewis低聚糖和血型低聚糖中选择相对刚性的低聚糖，而从翠绿链球菌、S. mitis和S. oral细胞壁中分离的低聚糖和多糖将作为柔性低聚糖的模型。除了传统的核Overhauser方法外，将在天然丰度样品和生物合成稳定同位素制备的样品中研究涉及糖苷键上异核标量耦合的核磁共振实验。最近提出的寡糖在稀液晶溶液中部分取向的残余偶极偶联方法能够提供关于刚性寡糖表位构象的丰富和非常精确的实验信息，并且将使用处理柔性寡糖的新方法，这将大大改进连接更多刚性结构域的铰链的构象和动力学模型。实验结果将用包括分子动力学模拟和蒙特卡罗方法在内的计算机分子模拟计算来解释。本项目将为研究生和本科生提供结构生物化学方面的培训，他们将学习现代核磁共振实验和计算机分子建模方法，以及复杂碳水化合物的分析和物理生物化学方面的知识。PI的部门在培养少数民族学生方面有着特别强大的传统，无论是在研究生阶段还是在本科阶段。

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.