Tyrosine Templating in the Self-Assembly and Crystallization of Silk Fibroin
Tyrosine Templating in the Self-Assembly and Crystallization of Silk Fibroin
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DOI：
10.1021/acs.biomac.6b01086
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发表时间：
2016-11-01
影响因子：
6.2
通讯作者：
Kaplan, David L.
中科院分区：
文献类型：
--
作者：
Partlow, Benjamin P.;Bagheri, Mehran;Kaplan, David L.
天然丝纤维具有与最好的合成纤维相媲美的强度和韧性。尽管进行了大量的研究，但仍需要进一步的了解来了解蚕能够纺出如此坚韧的纤维的机制。在这里，我们提出酪氨酸侧链的pi-pi和pi-OH基团相互作用提供模板效应，使得晶体形成结构域对齐，从而促进纺丝原液的自组装。固有荧光测量，结合圆二色性，表明在再生丝溶液的自组装过程中，酪氨酸残基被定位在一个更疏水的局部环境中，这表明优先组装。原位傅里叶变换红外光谱表明，交联的酪氨酸残基导致扩展的β-折叠结构的发展。另外，交联密度的控制直接影响干燥时的结晶度。为了更深入地了解酪氨酸的作用，对丝素模拟肽进行了分子动力学模拟。结果表明，酪氨酸残基倾向于在溶液中瞬时共定位，由于π-π相互作用和与相邻残基和与肽骨架的氢键。这些更稳定的酪氨酸相互作用导致侧链波动减少和协调的链内关联的发生率增加，而引入二酪氨酸键直接促进β-折叠结构的形成。总之，实验和建模数据支持酪氨酸-酪氨酸相互作用作为再生丝蛋白链自组装的关键早期特征的关键作用，因此在该过程中最终实现的稳健和不寻常的机械性能中是重要的。
Native silk fibers exhibit strength and toughness that rival those of the best synthetic fibers. Despite significant research, further insight is still needed to understand the mechanisms by which silkworms are capable of spinning such tough fibers. Here we propose that pi-pi and pi-OH group interactions of tyrosine side chains provide templating effects, such that the crystal-forming domains are in registration, thereby fostering the self-assembly of the spinning dope. Intrinsic fluorescence measurements, in conjunction with circular dichroism, showed that during self-assembly of regenerated silk solutions, the tyrosine residues were localized in a more hydrophobic local environment, suggesting preferential assembly. In situ Fourier transform infrared spectroscopy indicated that cross-linking of the tyrosine residues resulted in the development of extended beta-sheet structure. Additionally, control of cross-link density directly influenced the degree of crystallinity upon drying. Molecular dynamics simulations were performed on silk mimetic peptides in order to more thoroughly understand the role of tyrosines. The results indicated that tyrosine residues tended to transiently colocate in solution due to pi-pi interactions and hydrogen bonds with adjacent residues and with the peptide backbone. These more stable tyrosine interactions resulted in reduced lateral chain fluctuations and increased incidence of coordinated intrachain association, while introduction of a dityrosine bond directly promoted the formation of beta-sheet structures. In total, the experimental and modeling data support a critical role for tyrosine-tyrosine interactions as a key early feature in the self-assembly of regenerated silk protein chains and therefore are important in the robust and unusual mechanical properties ultimately achieved in the process.