Ion and ligand interactions of hyaluronic acid

透明质酸是一种具有多种功能的生物分子。它是软骨不可或缺的组成部分，在促进关节健康功能方面发挥着生物力学作用。此外，由于它可以大量获得，并且可以进行化学修饰，因此在生物医学和生物材料应用方面得到了广泛的研究。这些生物和技术作用依赖于透明质酸的物理特征：它是一种长而线性的聚合物，高度带电，可溶于水，它与盐离子和生物分子结合伙伴有各种相互作用，这些相互作用改变了它的结构和行为。然而，与其他生物聚合物(如DNA或细胞骨架成分)相比，透明质酸的基本物理行为还没有得到广泛的研究，本项目的主要目标是对透明质酸的物理行为进行精确测量，以及它被离子和其他分子修饰。研究人员将使用现代生物物理方法进行此类实验，并使用先进的理论方法进行解释。实验将集中在两个领域：首先，研究人员将量化盐对透明质酸行为的静电影响，特别是寻求了解与生理相关的混合盐条件对分子形状的影响。其次，研究人员将调查这一假设，即当透明质酸与特定的生物分子伙伴结合时，可以在透明质酸中诱导显著的形状变化。总体而言，该项目的科学工作将导致对盐和生物分子结合在影响透明质酸行为中的作用的直接、定量的估计；反过来，这将导致更好地理解分子的各种生物学作用，并将使透明质酸在生物材料环境中的合理工程成为可能。与这些科学影响相辅相成的还有一系列其他好处，尤其是通过与一所德国大学的交流项目扩大研究生培训的重大努力，该项目的重点是向生物工程师和生物物理学家教授现代计算方法。与国家实验室合作以及通过本科生培训增强科技人力资源还将带来其他好处。 技术摘要透明质酸是一种长的、线性的、带负电荷的多糖，具有中等构象灵活性。它发挥着广泛的生物学作用，特别是在定义细胞外空间的力学和粘弹性属性方面。羟基磷灰石的性质也使人们对其作为合成生物材料的用途进行了广泛的调查，例如形成可注射或细胞/组织生长基质。HA的聚合物性质是这些生物和生物技术作用的基础，但还没有得到充分的研究。这项建议的首要目标是通过对离子和配体诱导的HA构象行为进行高分辨率物理测量，并辅之以先进的理论解释方法，来填补这一知识空白。研究人员将应用一种独特的单分子力学仪器对HA的溶液介导的构象和力学性质进行精确测量。具体目标包括：1)利用机器学习方法来提高仪器在筛选生物分子弹性方面的能力；2)验证和探索最近的一项发现，即混合离子条件下的HA构象是由一个离子外壳主导的，它屏蔽了主体盐浓度的影响；以及3)研究特定的生物配体对HA构象的影响，重点是那些可能导致链中螺旋/螺旋转变的配体，以及那些引起全球链膨胀的配体。实验结果将参考溶液静电学和聚合物瓶刷行为的分析理论以及粗粒度分子动力学模拟来解释。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL ABSTRACTHyaluronic acid is a biological molecule with a range of functions. It is an integral component of cartilage, where it plays a biomechanical role in promoting healthy joint function. Further, since it can be obtained in large quantities, and can be chemically modified, it has become widely studied for biomedical and biomaterial applications. These biological and technological roles rely on hyaluronic acid’s physical features: it is a long, linear polymer that is highly charged and water soluble, and it has a variety of interactions, both with salt ions and with biomolecular binding partners, that modify its structure and behavior. However, compared to other biopolymers (such as DNA or cytoskeletal components), the basic physical behavior of hyaluronic acid has not been extensively studied.The main goal of the present project is to perform precision measurements of the physical behavior of hyaluronic acid, and its modification by ions and other molecules. The researchers will carry out such experiments using modern biophysical approaches, and interpret them using advanced theoretical methods. Experiments will be focused on two areas: first, researchers will quantify electrostatic effects of salt on hyaluronic acid behavior, and particularly pursue understanding of physiologically-relevant mixed-salt conditions on molecular shape. Second, researchers will investigate the hypothesis that dramatic shape-changes can be induced in hyaluronic acid upon binding to specific biomolecular partners. Overall, the scientific work in this project will result in direct, quantitative estimates of the role of salt and biomolecular-binding in affecting hyaluronic acid behavior; in turn, this will lead to better understanding of the molecule’s various biological roles, and will permit rational engineering of hyaluronic acid in biomaterials environments. These scientific impacts are complemented by a range of other benefits, notably including a major effort to broaden graduate-student training through an exchange program with a German university, focused on teaching modern computational methods to bioengineers and biophysicists. Other benefits will accrue from collaboration with a national lab, and enhancing STEM human resources through undergraduate student training. TECHNICAL ABSTRACTHyaluronic acid, HA, is a long, linear, negatively-charged polysaccharide with moderate conformational flexibility. It plays broad biological roles, particularly in defining the mechanical and viscoelastic properties of extracellular spaces. HA’s properties have also led to broad investigation of its use as a synthetic biomaterial, e.g. forming injectables or cell/tissue growth substrates. The polymeric properties of HA underlie these biological and biotechnological roles, but are understudied. The overarching goal of this proposal is to fill that gap in knowledge by performing high-resolution physical measurements, supported by advanced theoretical interpretation methods, of ion- and ligand-induced HA conformational behaviors. The researchers will apply a unique single-molecule mechanics instrument to carry out precision measurements of HA’s solution-mediated conformational and mechanical properties. Specific goals include 1) exploiting machine-learning methods to improve instrument capabilities in screening biomolecular elasticity; 2) validating and exploring a recent finding that HA conformation in mixed-ionic conditions is dominated by an ‘ion jacket’ that screens the effect of bulk salt concentration; and 3) studying the effects of specific biological ligands on HA conformation, with a focus on ligands posited to induce a helix/coil transition in the chain, and those that cause global chain swelling. Experimental results will be interpreted with reference to analytical theories of solution electrostatics and polymer bottle-brush behavior, as well as coarse-grained molecular dynamics simulations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.