Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0FE, U.K.
Biomacromolecules. 2023 Apr 10;24(4):1709-1716. doi: 10.1021/acs.biomac.2c01479. Epub 2023 Mar 16.
Silk proteins obtained from the silkworm have been extensively studied due to their remarkable mechanical properties. One of the major structural components of this complex material is silk fibroin, which can be isolated and processed further in vitro to form artificial functional materials. Due to the excellent biocompatibility and rich self-assembly behavior, there has been sustained interest in such materials formed through the assembly of regenerated silk fibroin feedstocks. The molecular mechanisms by which the soluble regenerated fibroin molecules self-assemble into protein nanofibrils remain, however, largely unknown. Here, we use the framework of chemical kinetics to connect macroscopic measurements of regenerated silk fibroin self-assembly to the underlying microscopic mechanisms. Our results reveal that the aggregation of regenerated silk fibroin is dominated by a nonclassical secondary nucleation processes, where the formation of new fibrils is catalyzed by the existing aggregates in an autocatalytic manner. Such secondary nucleation pathways were originally discovered in the context of polymerization of disease-associated proteins, but the present results demonstrate that this pathway can also occur in functional assembly. Furthermore, our results show that shear flow induces the formation of nuclei, which subsequently accelerate the process of aggregation through an autocatalytic amplification driven by the secondary nucleation pathway. Taken together, these results allow us to identify the parameters governing the kinetics of regenerated silk fibroin self-assembly and expand our current understanding of the spinning of bioinspired protein-based fibers, which have a wide range of applications in materials science.
蚕丝蛋白因其出色的机械性能而得到了广泛的研究。这种复杂材料的主要结构成分之一是丝素蛋白，它可以被分离出来，并在体外进一步加工，形成人工功能性材料。由于其出色的生物相容性和丰富的自组装行为，人们对通过再生丝素蛋白原料组装形成的此类材料一直保持着浓厚的兴趣。然而，可溶性再生丝素蛋白分子自组装成蛋白质纳米纤维的分子机制在很大程度上仍然未知。在这里，我们使用化学动力学的框架将再生丝素蛋白自组装的宏观测量与潜在的微观机制联系起来。我们的结果表明，再生丝素蛋白的聚集主要由非经典的二次成核过程主导，其中新纤维的形成以自催化的方式被现有聚集体催化。这种二次成核途径最初是在与疾病相关的蛋白质聚合的背景下发现的，但目前的结果表明，这种途径也可能发生在功能性组装中。此外，我们的结果表明，剪切流诱导核的形成，随后通过二次成核途径驱动的自催化放大加速聚集过程。总之，这些结果使我们能够确定控制再生丝素蛋白自组装动力学的参数，并扩展我们对仿生蛋白质纤维纺丝的现有理解，这些纤维在材料科学中有广泛的应用。
