Donets Sergii, Guskova Olga, Sommer Jens-Uwe
Institute Theory of Polymers, Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, 01069 Dresden, Germany.
Dresden Center for Computational Materials Science (DCMS), Technische Universität Dresden, 01062 Dresden, Germany.
J Phys Chem B. 2021 Apr 1;125(12):3238-3250. doi: 10.1021/acs.jpcb.1c00647. Epub 2021 Mar 22.
In this paper, we elucidate a generic mechanism behind strain-induced phase transition in aqueous solutions of silk-inspired biomimetics by atomistic molecular dynamics simulations. We show the results of modeling of homopeptides polyglycine Gly and polyalanine Ala and a heteropeptide (Gly-Ala-Gly-Ala-Gly-Ser), i.e., the simplest and yet relevant sequences that could mimic the behavior of natural silk under stress conditions. First, we analyze hydrophobicities of the sequences by calculating the Gibbs free energy of hydration and inspecting the interchain hydrogen bonding and hydration by water. Second, the force-extension profiles are scanned and compared with the results for poly(ethylene oxide), the synthetic polymer for which the aquamelt behavior has been proved recently. Additionally, the conformational transitions of oligopeptides from coiled to extended states are characterized by a generalized order parameter and by the dependence of the solvent-accessible surface area of the chains on applied stretching. Fibrillation itself is surveyed using both the two-dimensional interchain pair correlation function and the SAXS/WAXS patterns for the aggregates formed under stress. These are compared with experimental data found in the literature on fibril structure of silk composite materials doped with oligoalanine peptides. Our results show that tensile stress introduced into aqueous oligopeptide solutions facilitates interchain interactions. The oligopeptides display both a greater resistance to extension as compared to poly(ethylene oxide) and a reduced ability for hydrogen bonding of the stretched chains between oligomers and with water. Fiber formation is proved for all simulated objects, but the most structured one is made of a heteropeptide (Gly-Ala-Gly-Ala-Gly-Ser): For this sequence, we obtain the highest degree of the secondary structure motifs in the fiber. We conclude that this is the most promising candidate among considered sequences to find the aquamelt behavior in further experimental studies.
在本文中，我们通过原子分子动力学模拟阐明了丝素启发的仿生水溶液中应变诱导相变背后的一般机制。我们展示了同聚肽聚甘氨酸Gly和聚丙氨酸Ala以及杂聚肽（Gly-Ala-Gly-Ala-Gly-Ser）的模拟结果，即能够在应力条件下模拟天然丝行为的最简单但相关的序列。首先，我们通过计算水合吉布斯自由能来分析序列的疏水性，并检查链间氢键和水的水合作用。其次，扫描力-伸长曲线，并与聚环氧乙烷的结果进行比较，聚环氧乙烷是一种最近已被证明具有水溶体行为的合成聚合物。此外，寡肽从卷曲态到伸展态的构象转变通过广义序参量以及链的溶剂可及表面积对施加拉伸的依赖性来表征。使用二维链间对相关函数和应力下形成的聚集体的小角X射线散射/广角X射线散射图案来研究纤维化本身。将这些结果与文献中关于掺杂寡丙氨酸肽的丝复合材料原纤维结构的实验数据进行比较。我们的结果表明，引入到寡肽水溶液中的拉伸应力促进了链间相互作用。与聚环氧乙烷相比，寡肽对伸长表现出更大的抵抗力，并且拉伸链在寡聚物之间以及与水形成氢键的能力降低。所有模拟对象都证明了纤维的形成，但结构最有序的是由杂聚肽（Gly-Ala-Gly-Ala-Gly-Ser）制成的：对于该序列，我们在纤维中获得了最高程度的二级结构基序。我们得出结论，在进一步的实验研究中，这是所考虑序列中寻找水溶体行为最有希望的候选者。
