DIRECT MEASUREMENT OF FORCES BETWEEN MEMBRANES OR MACROMOLECULES

使用我们课题组开发的渗透应激法来测量 膜之间或大分子之间的直接作用力已经扩散 在过去的一年里迅速转移到欧洲和北方的几个实验室 美国。最近这种做法在实践中扩散的一个结果是 为了提出这样一种观点，即当分子或膜接近接触时， 方法的重要工作包括去除有组织的水溶剂 从相对的表面。这些“水合力量”越来越多地 被认为作用于各种物质，如脂质双层，蛋白质， DNA双螺旋和硬多糖。不断增长的产品目录 有关交互的信息继续创建新的逻辑 思考分子识别和折叠。 在今年，我们主要关注蛋白质之间的作用力， 特别检查天然和重组胶原纤维，网址为 不同的温度、pH、离子条件以及在 几个小的溶质。已经证明，盐不能完全 深入胶原蛋白三股螺旋之间的空隙。渗透性 被排除的盐从外部施加的压力是一个重要的 胶原蛋白纤维组件的组成部分。 力的测量已经证明了温度有利的装配 是由水介导的氢键驱动的， 与极性残基相反，而不是通过疏水效应 用来解释蛋白质组装的。人们现在可以想到一种 排斥力和吸引力水合力之间的竞争，取决于 蛋白质表面相互匹配的程度。 DNA分子之间的水合力对小溶质的依赖， 在溶液中观察到的，已经被研究过了。一次不同寻常的重演- 进入液体-凝胶-液体相变序列，观察到在 双十二烷基磷酸盐双分子层之间作用力的测量 解释过了。 渗透应力技术已经扩展到测量 球形粒子，以便创建方便的模型 “分子拥挤”现象在人类社会中的重要地位 胞内环境。

Use of the Osmotic Stress method, developed by our group to measure directly forces between membranes or between macromolecules, has spread rapidly this past year to several laboratories in Europe and North America. One result of this recent proliferation in practice has been to advance the idea that as molecules or membranes approach contact, the important work of approach involves removal of organized water solvent from the apposing surfaces. These "hydration forces" are increasingly recognized to act in materials as diverse as lipid bilayers, proteins, DNA double helices, and stiff polysaccharides. The growing catalog of information about interactions continues to create a new logic for thinking about molecular recognition and folding. During the current year, we have concentrated on forces between proteins, specifically examining native and reconstituted collagen fibers at various temperatures, pH, ionic conditions, and in the presence of several small solutes. It has been shown that salt does not fully penetrate into the space between collagen triple helices. Osmotic pressure applied from outside by the excluded salt is an important component of collagen fiber assembly. Force measurements have demonstrated that temperature-favored assembly of the fibers is driven by water-mediated hydrogen bonding between the apposing polar residues rather than by the hydrophobic effect usually invoked to explain assembly of proteins. One can now think of a competition between repulsive and attractive hydration forces, depending on how well protein surfaces match each other. A dependence of hydration forces between DNA molecules on small solutes, observed present in the solution, has been studied. An unusual re- entrant liquid-gel-liquid phase transition sequence, observed during measurement of forces between didodecylphosphate bilayers, has been explained. The osmotic stress technique has been extended to measure forces between spherical particles in order to create convenient models for the "molecular crowding" phenomenon important in the regime of the intracellular milieu.