Intermediate species are hypothesized to play an important role in the toxicity of amyloid formation, a process associated with many diseases. This process can be monitored with conventional and two-dimensional infrared spectroscopy, vibrational circular dichroism, and optical and electron microscopy. Here, we present how combining these techniques provides insight into the aggregation of the hexapeptide VEALYL (Val-Glu-Ala-Leu-Tyr-Leu), the B-chain residue 12-17 segment of insulin that forms amyloid fibrils (intermolecularly hydrogen-bonded β-sheets) when the pH is lowered below 4. Under such circumstances, the aggregation commences after approximately an hour and continues to develop over a period of weeks. Singular value decompositions of one-dimensional and two-dimensional infrared spectroscopy spectra indicate that intermediate species are formed during the aggregation process. Multivariate curve resolution analyses of the one and two-dimensional infrared spectroscopy data show that the intermediates are more fibrillar and deprotonated than the monomers, whereas they are less ordered than the final fibrillar structure that is slowly formed from the intermediates. A comparison between the vibrational circular dichroism spectra and the scanning transmission electron microscopy and optical microscope images shows that the formation of mature fibrils of VEALYL correlates with the appearance of spherulites that are on the order of several micrometers, which give rise to a "giant" vibrational circular dichroism effect.

中文翻译：

---

使用先进的振动光谱和显微镜解开 VEALYL 淀粉样蛋白的形成

中间物种被假设在淀粉样蛋白形成的毒性中起重要作用，淀粉样蛋白形成过程与许多疾病相关。这个过程可以用传统和二维红外光谱、振动圆二色性、光学和电子显微镜来监测。在这里，我们介绍如何结合这些技术提供对六肽 VEALYL（Val-Glu-Ala-Leu-Tyr-Leu）的聚集的洞察，这是胰岛素的 B 链残基 12-17 段，形成淀粉样纤维（分子间氢-当 pH 值低于 4 时，结合的 β-折叠）。在这种情况下，聚集在大约一个小时后开始，并在数周内继续发展。一维和二维红外光谱的奇异值分解表明在聚集过程中形成了中间物种。一维和二维红外光谱数据的多元曲线分辨率分析表明，中间体比单体更纤维化和去质子化，而它们比由中间体缓慢形成的最终纤维状结构更不有序。振动圆二色光谱与扫描透射电子显微镜和光学显微镜图像之间的比较表明，VEALYL 成熟原纤维的形成与几微米数量级的球晶的出现有关，从而产生了一个“巨大的”振动圆二色性效应。