Force-induced Conformational Transitions in Single Polysaccharide Molecules by AFM

AFMPyranose环上的分子对生物系统(如葡萄糖)具有非常重要的作用，可以诱导单个多糖分子的构象转变。许多具有重要生物学意义的多糖是由吡喃糖环组成的，它们在各种各样的细胞结构中受到张应力，如植物的细胞壁或动物组织中的细胞外基质(ECM)。机械应力被认为调节这些复杂弹性系统的组装和生理特性。这些多糖通过其组成成分的机械重排来响应这种压力，但其潜在的机制还不是很清楚。最简单的观点认为，多糖是熵弹簧，而吡喃糖环结构通常被描绘为无弹性并锁定在稳定构象中。单分子原子力显微镜技术的发展使得批判性地检查这些观点成为可能。原子力显微镜仪器可以机械地拉伸单分子，并具有卓越的长度和力分辨率。原子力显微镜对多糖的拉伸表明，它们的行为不是简单的熵弹簧，而是表现出屈服现象。这些弹性偏差的起源被准确地定位为吡喃环，它被发现在拉伸时经历了构象转变，如椅子-船或椅子反转。这些强制转变以逐步的方式改变了糖苷氧原子的分离，因此影响了多糖链的轮廓长度及其弹性。轴向糖苷键被发现通过充当原子杠杆来驱动这些转变。这一提议的长期目标是在原子水平上理解多糖类中力诱导构象转变的机制。在第二个授权期内，单分子原子力显微镜技术将与计算化学工具相结合，详细研究吡喃糖环中力诱导的构象转变。通过从不同的方向和不同的连接点拉环，可以探索环的力学性质和它的力学构象转变。这些研究将确定每种类型的单体对混合链的复杂弹性的贡献，并将对解释许多天然多糖的分子弹性有价值。这一建议的实验和理论结果将被整合在一起，以开发一种基于AFM的方法，从溶液中单个多糖分子的独特的力伸展光谱中识别它们。这种方法将是碳水化合物研究分析工具武器库的重要补充。

Force-induced conformational transitions in single polysaccharide molecules by AFMPyranose ring-based molecules are of extraordinary importance to biological systems (e.g.glucose). Many biologically important polysaccharides are composed of pyranose rings and theyare placed under tensile stress in a wide variety of cellular structures such as the cell wall ofplants or the extracellular matrix (ECM) in animal tissues. Mechanical stress is thought toregulate assembly and physiological properties of these complex elastic systems. Thepolysaccharides respond to that stress by mechanical rearrangements of their components butthe underlying mechanism is not well understood. The simplest view assumes thatpolysaccharides are entropic springs and the pyranose ring structure is typically portrayed asinelastic and locked into a stable conformation. The development of single molecule AFMtechniques allowed for critically examining these views. AFM instruments can stretchmechanically single molecules and have superb length and force resolution. Stretching ofpolysaccharides by AFM revealed that they do not behave as simple entropic springs but thatthey display yielding phenomena. The origin of these elastic deviations was pinpointed to thepyranose ring that was found to undergo, upon stretching, conformational transitions such aschair-boat or chair inversion. These forced transitions change, in a step-wise fashion, theseparation of the glycosidic oxygen atoms, and therefore affect the contour length of thepolysaccharide chain and its elasticity. Axial glycosidic bonds were found to drive thosetransitions by acting as atomic levers. The long-term objective of this proposal is to understand,at the atomic level, the mechanism of these force-induced conformational transitions inpolysaccharides. During the second grant period single molecule AFM techniques will becombined with the tools of computational chemistry to examine in detail force-inducedconformational transitions in the pyranose ring. The mechanical properties of the ring and itsmechanical conformational transitions will be probed by pulling on the ring from variousdirections and by different attachment points. These studies will determine the contribution of each type of the monomer to thecomplex elasticity of a mixed chain and will be valuable in interpreting the molecular elasticity ofmany native polysaccharides. The experimental and theoretical findings of this proposal will beintegrated to develop an AFM-based methodology for identifying individual polysaccharidemolecules in solution from their unique force-extension spectra. Such a methodology will be animportant addition to the arsenal of analytical tools for carbohydrate research.