Keten Sinan, Buehler Markus J
Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 1-235A&B, Cambridge, Massachusetts 02139, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Dec;78(6 Pt 1):061913. doi: 10.1103/PhysRevE.78.061913. Epub 2008 Dec 16.
Elasticity and strength of individual beta-sheet protein domains govern key biological functions and the mechanical properties of biopolymers including spider silk, amyloids, and muscle fibers. The worm-like-chain (WLC) model is commonly used to describe the entropic elasticity of polypeptides and other biomolecules. However, force spectroscopy experiments have shown pronounced deviations from the ideal WLC behavior, leading to controversial views about the appropriate elastic description of proteins at nanoscale. Here we report a simple model that explains the physical mechanism that leads to the breakdown of the WLC idealization in experiments by using only two generic parameters of the protein domain, the H-bond energy and the protein backbone's persistence length. We show that a rupture initiation condition characterized by the free energy release rate of H-bonds characterizes the limit of WLC entropic elasticity of beta-sheet protein domains and the onset of rupture. Our findings reveal that strength and elasticity are coupled and cannot be treated separately. The predictions of the model are compared with atomic force microscopy experiments of protein rupture.
单个β折叠蛋白质结构域的弹性和强度决定了关键的生物学功能以及包括蜘蛛丝、淀粉样蛋白和肌肉纤维在内的生物聚合物的机械性能。蠕虫状链（WLC）模型通常用于描述多肽和其他生物分子的熵弹性。然而，力谱实验表明，其与理想的WLC行为存在明显偏差，这导致了关于蛋白质在纳米尺度上合适的弹性描述的争议性观点。在此，我们报告了一个简单的模型，该模型仅使用蛋白质结构域的两个通用参数——氢键能量和蛋白质主链的持久长度，来解释在实验中导致WLC理想化失效的物理机制。我们表明，以氢键自由能释放速率为特征的破裂起始条件表征了β折叠蛋白质结构域WLC熵弹性的极限和破裂的开始。我们的研究结果表明，强度和弹性是相互关联的，不能分开处理。该模型的预测结果与蛋白质破裂的原子力显微镜实验进行了比较。
