Abstract：
Spider dragline (major ampullate) silk is one of the toughest known fibers in nature and exhibits an excellent combination of high tensile strength and elasticity. Increasing evidence has indicated that preassembly plays a crucial role in facilitating the proper assembly of silk fibers by bridging the mesoscale gap between spidroin molecules and the final strong fibers. However, it remains challenging to control the preassembly of spidroins and investigate its influence on fiber structural and mechanical properties. In this study, we explored to bridge this gap by modulating the polyalanine (polyA) motifs in repetitive region of spidroins to tune their preassemblies in aqueous dope solutions. Three biomimetic silk proteins with varying numbers of alanine residues in polyA motif and comparable molecular weights were designed and biosynthesized, termed as N16C-5A, N15C-8A, and N13C-12A, respectively. It was found that all three proteins could form nanofibril assemblies in the concentrated aqueous dopes, but the size and structural stability of the fibrils were distinct from each other. The silk protein N15C-8A with 8 alanine residues in polyA motif allowed for the formation of stable nanofibril assemblies with a length of approximately 200 nm, which were not prone to disassemble or aggregate as that of N16C-5A and N13C-12A. More interestingly, the stable fibril assembly of N15C-8A enabled spinning of simultaneously strong (623.3 MPa) and tough (107.1 MJ m-3) synthetic fibers with fine molecular orientation and close interface packing of fibril bundles. This work highlights that modulation of polyA motifs is a feasible way to tune the morphology and stability of the spidroin preassemblies in dope solutions, thus controlling the structural and mechanical properties of the resulting fibers.
摘要：
蜘蛛拉丝(主要壶腹)丝是自然界中最坚韧的已知纤维之一,并且表现出高拉伸强度和弹性的优异组合。越来越多的证据表明，预组装在促进丝纤维的适当组装中起着至关重要的作用，通过桥接蛛丝蛋白分子和最终的强纤维之间的中尺度间隙。然而,它仍然是具有挑战性的控制的预组装和研究其对纤维结构和力学性能的影响。在这项研究中,我们探索通过调节spidroins重复区域中的聚丙氨酸（polyA）基序来调节其在水性掺杂溶液中的预组装来弥合这一差距。设计并生物合成了三种仿生丝蛋白，这些蛋白在polyA基序中具有不同数量的丙氨酸残基和相当的分子量，被称为N16C-5A，N15C-8A,和N13C-12A,分别。发现所有三种蛋白质都可以在浓缩的水性涂料中形成纳米原纤维组装体，但是原纤维的大小和结构稳定性彼此不同。在polyA基序中具有8个丙氨酸残基的丝蛋白N15C-8A允许形成长度约为200nm的稳定的纳米原纤维组装体，不像N16C-5A和N13C-12A那样容易分解或聚集。更有趣的是，N15C-8A的稳定原纤维组装使同时具有细分子取向和原纤维束紧密界面堆积的坚固（623.3MPa）和坚韧（107.1MJm-3）合成纤维的纺丝成为可能。这项工作突出表明，polyA基序的调制是一种可行的方法，可以在涂料溶液中调节spidroin预组装体的形态和稳定性，从而控制所得纤维的结构和机械性能。
