State Key Laboratory of Molecular Engineering of Polymers, Laboratory of Advanced Materials and Department of Macromolecular Science , Fudan University , Shanghai 200433 , People's Republic of China.
Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Shanghai Key Laboratory of Magnetic Resonance, Department of Physics , East China Normal University , Shanghai 200062 , People's Republic of China.
Biomacromolecules. 2018 Jun 11;19(6):1999-2006. doi: 10.1021/acs.biomac.7b01691. Epub 2018 Feb 23.
Like most major ampullate silks of spider, the length of Antheraea pernyi silkworm silk can shrink to a certain degree when the fiber is in contact with water. However, what happens in terms of molecule chain level and how it correlates to the mechanical properties of the silk during its contraction is not yet fully understood. Here, we investigate the water-induced mechanical property changes as well as the structure transition of two kinds of A. pernyi silk fiber, which are forcibly reeled from two different individuals (silkworm a and silkworm b; the silk fiber from either one represents the lower and upper limit of the distribution of mechanical properties, respectively). The tensile test results present that most of the mechanical parameters except the post-yield modulus and breaking strain for both silk fibers have the same variation trend before and after their water contraction. Synchrotron FTIR and Raman spectra show that the native filament from silkworm a contains more α-helix structures than that in silkworm b filament, and these α-helices are partially converted to β-sheet structures after the contraction of the fibers, while the order of both β-sheet and α-helix slightly increase. On the other side, the content and orientation of both secondary structural components in silkworm b fiber keep unchanged, no matter if it is native or contracted. C CP/MAS NMR results further indicate that the α-helix/random coil to β-sheet conformational transition that occurred in the silk of silkworm a corresponds the Ala residues. Based upon these results, the detailed structure transition models of both as-reeled A. pernyi silk fibers during water contraction are proposed finally to interpret their properties transformation.
与大多数大型壶腹状丝的蜘蛛一样，当纤维与水接触时，柞蚕丝的长度可以在一定程度上收缩。然而，在分子链水平上发生了什么，以及它如何与丝的机械性能相关，目前还不完全清楚。在这里，我们研究了两种柞蚕丝纤维的水诱导机械性能变化以及结构转变，这两种纤维是从两个不同个体（蚕 a 和蚕 b；其中一种的丝纤维分别代表机械性能分布的下限和上限）强制纺出的。拉伸试验结果表明，两种丝纤维的大多数力学参数（屈服后模量和断裂应变除外）在水收缩前后都有相同的变化趋势。同步辐射 FTIR 和 Raman 光谱表明，蚕 a 的天然原丝比蚕 b 的原丝含有更多的α-螺旋结构，这些α-螺旋在纤维收缩后部分转化为β-折叠结构，而β-折叠和α-螺旋的有序度都略有增加。另一方面，无论是否为天然或收缩状态，蚕 b 纤维中的这两种二级结构成分的含量和取向都保持不变。CCP/MAS NMR 结果进一步表明，在蚕 a 的丝中发生的α-螺旋/无规卷曲到β-折叠构象转变对应于 Ala 残基。基于这些结果，最后提出了两种柞蚕丝纤维在水收缩过程中的详细结构转变模型，以解释它们的性能转变。
