Department of Civil and Environmental Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Max Planck Institute of Colloids and Interfaces , Science Park Golm, 14424 Potsdam, Germany.
ACS Nano. 2017 Oct 24;11(10):9750-9758. doi: 10.1021/acsnano.7b01532. Epub 2017 Sep 19.
Spider dragline silk is a protein material that has evolved over millions of years to achieve finely tuned mechanical properties. A less known feature of some dragline silk fibers is that they shrink along the main axis by up to 50% when exposed to high humidity, a phenomenon called supercontraction. This contrasts the typical behavior of many other materials that swell when exposed to humidity. Molecular level details and mechanisms of the supercontraction effect are heavily debated. Here we report a molecular dynamics analysis of supercontraction in Nephila clavipes silk combined with in situ mechanical testing and Raman spectroscopy linking the reorganization of the nanostructure to the polar and charged amino acids in the sequence. We further show in our in silico approach that point mutations of these groups not only suppress the supercontraction effect, but even reverse it, while maintaining the exceptional mechanical properties of the silk material. This work has imminent impact on the design of biomimetic equivalents and recombinant silks for which supercontraction may or may not be a desirable feature. The approach applied is appropriate to explore the effect of point mutations on the overall physical properties of protein based materials.
蜘蛛牵引丝是一种蛋白质材料，经过数百万年的进化，具有精细调节的机械性能。一些牵引丝纤维的一个不太为人知的特征是，当暴露在高湿度环境中时，它们会沿着主轴收缩多达 50%，这种现象被称为超收缩。这与许多其他材料在暴露于湿度时膨胀的典型行为形成鲜明对比。超收缩效应的分子水平细节和机制存在很大争议。在这里，我们报告了对 Nephila clavipes 丝的超收缩的分子动力学分析，结合原位力学测试和拉曼光谱，将纳米结构的重组与序列中的极性和带电氨基酸联系起来。我们还在我们的计算方法中表明，这些基团的点突变不仅抑制了超收缩效应，甚至可以逆转它，同时保持丝材料的卓越机械性能。这项工作对仿生等效物和重组丝的设计具有直接影响，因为超收缩可能是也可能不是理想的特征。所应用的方法适用于探索点突变对基于蛋白质的材料整体物理性能的影响。
