Dipartimento di Fisica e Chimica, Università di Palermo , 90136 Palermo, Italy.
J Phys Chem B. 2014 Mar 20;118(11):2913-23. doi: 10.1021/jp412277y. Epub 2014 Mar 7.
Proteins and polypeptides are characterized by low-frequency vibrations in the terahertz regime responsible for the so-called "boson peak". The shape and position of this peak are related to the mechanical properties of peptide chains. Amyloid fibrils are ordered macromolecular assemblies, spontaneously formed in nature, characterized by unique biological and nanomechanical properties. In this work, we investigate the effects of the amyloid state and its polymorphism on the boson peak. We used inelastic neutron scattering to probe low-frequency vibrations of the glucagon polypeptide in the native state and in two different amyloid morphologies in both dry and hydrated sample states. The data show that amyloid fibril formation and hydration state affect the softness of the polypeptide not only by changing the distribution of vibrational modes but also, and most significantly, the dissipative mechanisms of collective low-frequency vibrations provided by water-protein and protein-protein interactions. We show how the morphology of the fibril is able to tune these effects. Atomic fluctuations were also measured by elastic neutron scattering. The data confirm that any effect of protein aggregation on fluctuation amplitudes is essentially due to changes in surface exposure to hydration water. The results demonstrate the importance of protein-protein and protein-water interactions in the dynamics and mechanics of amyloid fibrils.
蛋白质和多肽的特征是太赫兹区域的低频振动，这些振动负责所谓的“玻色峰”。该峰的形状和位置与肽链的机械性能有关。淀粉样纤维是在自然界中自发形成的有序大分子组装体，具有独特的生物和纳米力学性质。在这项工作中，我们研究了淀粉样状态及其多态性对玻色峰的影响。我们使用非弹性中子散射来探测在天然状态和两种不同的淀粉样形态下、在干燥和水合样品状态下的胰高血糖素多肽的低频振动。数据表明，淀粉样纤维的形成和水合状态不仅通过改变振动模式的分布，而且最重要的是通过改变水-蛋白质和蛋白质-蛋白质相互作用提供的集体低频振动的耗散机制，影响多肽的柔软性。我们展示了纤维形态如何能够调节这些效应。弹性中子散射还测量了原子波动。数据证实，蛋白质聚集对波动幅度的任何影响本质上都归因于对水合水的表面暴露的变化。结果表明了蛋白质-蛋白质和蛋白质-水相互作用在淀粉样纤维的动力学和力学中的重要性。
