Integrative Science Center of Germplasm Creation in Western China (CHONGQING) Science City, Biological Science Research Center, Southwest University, Chongqing 400715, China; National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
Integrative Science Center of Germplasm Creation in Western China (CHONGQING) Science City, Biological Science Research Center, Southwest University, Chongqing 400715, China.
Sci Bull (Beijing). 2024 Mar 30;69(6):792-802. doi: 10.1016/j.scib.2023.12.050. Epub 2023 Dec 29.
Silk is one of the toughest fibrous materials known despite spun at ambient temperature and pressure with water as a solvent. It is a great challenge to reproduce high-performance artificial fibers comparable to natural silk by bionic for the incomplete understanding of silkworm spinning in vivo. Here, we found that amphipol and digitonin stabilized the structure of natural silk fibroin (NSF) by a large-scale screening in vitro, and then studied the close-to-native ultrastructure and hierarchical assembly of NSF in the silk gland lumen. Our study showed that NSF formed reversible flexible nanofibrils mainly composed of random coils with a sedimentation coefficient of 5.8 S and a diameter of about 4 nm, rather than a micellar or rod-like structure assembled by the aggregation of globular NSF molecules. Metal ions were required for NSF nanofibril formation. The successive pH decrease from posterior silk gland (PSG) to anterior silk gland (ASG) resulted in a gradual increase in NSF hydrophobicity, thus inducing the sol-gelation transition of NSF nanofibrils. NSF nanofibrils were randomly dispersed from PSG to ASG-1, and self-assembled into anisotropic herringbone patterns at ASG-2 near the spinneret ready for silkworm spinning. Our findings reveal the controlled self-assembly mechanism of the multi-scale hierarchical architecture of NSF from nanofibrils to herringbone patterns programmed by metal ions and pH gradient, which provides novel insights into the spinning mechanism of silk-secreting animals and bioinspired design of high-performance fibers.
丝素在环境温度和压力下、以水为溶剂纺丝，却具有所有纤维中最高的强度，这一特性令人惊叹。由于对蚕体内纺丝过程的不完全了解，仿生学方法很难复制出与天然丝性能相当的高性能人工纤维。在这里，我们通过大规模的体外筛选发现两亲聚合物和胆甾醇硫酸盐能够稳定天然丝素蛋白（NSF）的结构，然后研究了 NSF 在丝腺管腔内接近天然的超微结构和分级组装。我们的研究表明，NSF 主要形成由无规线团组成的可逆柔性纳米纤维，其沉降系数为 5.8 S，直径约为 4nm，而不是由球状 NSF 分子聚集组装而成的胶束或棒状结构。NSF 纳米纤维的形成需要金属离子。从后部丝腺（PSG）到前部丝腺（ASG）的 pH 值连续下降导致 NSF 疏水性逐渐增加，从而诱导 NSF 纳米纤维的溶胶-凝胶转变。NSF 纳米纤维从 PSG 随机分散到 ASG-1，并在靠近喷丝头的 ASG-2 处自组装成各向异性的人字形图案，为蚕的纺丝做好准备。我们的研究结果揭示了 NSF 从纳米纤维到人字形图案的多尺度分级结构的受控自组装机制，该机制由金属离子和 pH 梯度编程，为研究动物吐丝的纺丝机制和高性能纤维的仿生设计提供了新的思路。
