Macromolecules tend to respond to applied forces in many different ways. Chemistry at high shear forces can be intriguing, with relatively soft bonds becoming very stiff in specific force-loading geometries. Largely used in bionanotechnology, an important case is the streptavidin (SA)/biotin interaction. Although SA’s four subunits have the same affinity, we find that the forces required to break the SA/biotin bond depend strongly on the attachment geometry. With AFM-based single-molecule force spectroscopy (SMFS), we measured unbinding forces of biotin from different SA subunits to range from 100 to more than 400 pN. Using a wide-sampling approach, we carried out hundreds of all-atom steered molecular dynamics (SMD) simulations for the entire system, including molecular linkers. Our strategy revealed the molecular mechanism that causes a fourfold difference in mechanical stability: Certain force-loading geometries induce conformational changes in SA’s binding pocket lowering the energy barrier, which biotin has to overcome to escape the pocket.

大分子倾向于以多种不同的方式响应所施加的力。高剪切力下的化学反应可能很有趣，相对较软的键在特定的力加载几何形状中变得非常坚硬。广泛用于生物纳米技术，一个重要的例子是链霉亲和素（SA）/生物素相互作用。尽管SA的四个亚基具有相同的亲和力，但我们发现打破SA/生物素键所需的力在很大程度上取决于附着几何形状。利用基于 AFM 的单分子力谱 (SMFS)，我们测量了不同 SA 亚基的生物素解离力，范围为 100 至 400 pN 以上。使用广泛采样方法，我们对整个系统（包括分子连接器）进行了数百次全原子引导分子动力学（SMD）模拟。我们的策略揭示了导致机械稳定性四倍差异的分子机制：某些力加载几何形状会引起SA结合口袋的构象变化，从而降低生物素必须克服的能量障碍才能逃离口袋。