Wang Hongsu, Lee Yoon Kyung, Xue Christine, Guo Zhefeng
Department of Neurology, Brain Research Institute, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
R Soc Open Sci. 2018 Jul 4;5(7):180166. doi: 10.1098/rsos.180166. eCollection 2018 Jul.
Deposition of amyloid fibrils is a pathological hallmark of Alzheimer's disease. Aβ42 is the major protein whose aggregation leads to the formation of these fibrils. Understanding the detailed structure of Aβ42 fibrils is of particular importance for delineating the mechanism of Aβ42 aggregation and developing specific amyloid-targeting drugs. Here, we use site-directed spin labelling and electron paramagnetic resonance spectroscopy to study the site-specific structural order at each and every residue position in Aβ42 fibrils. Strong interactions between spin labels indicate highly ordered protein backbone at the labelling site, while weak interactions suggest disordered local structure. Our results show that Aβ42 consists of five β-strands (residues 2-7, 10-13, 17-20, 31-36, 39-41), three turns (residues 7-8, 14-16, 37-38) and one ordered loop (residues 21-30). Spin labels introduced at β-strand sites show strong spin-spin interactions, while spin labels at turn or loop sites show weak interactions. However, residues 24, 25 and 28 also show strong interactions between spin labels, suggesting that the loop 21-30 is partly ordered. In the context of recent structural work using solid-state NMR and cryoEM, the site-specific structural order revealed in this study provides a different perspective on backbone and side chain dynamics of Aβ42 fibrils.
淀粉样纤维的沉积是阿尔茨海默病的一个病理标志。Aβ42是主要的蛋白质，其聚集导致这些纤维的形成。了解Aβ42纤维的详细结构对于阐明Aβ42聚集机制和开发针对淀粉样蛋白的特异性药物尤为重要。在此，我们使用定点自旋标记和电子顺磁共振波谱来研究Aβ42纤维中每个残基位置的位点特异性结构顺序。自旋标记之间的强相互作用表明标记位点处蛋白质主链高度有序，而弱相互作用则表明局部结构无序。我们的结果表明，Aβ42由五条β链（残基2 - 7、10 - 13、17 - 20、3l - 36、39 - 41）、三个转角（残基7 - 8、14 - 16、37 - 38）和一个有序环（残基21 - 30）组成。在β链位点引入的自旋标记显示出强的自旋 - 自旋相互作用，而在转角或环位点的自旋标记显示出弱相互作用。然而，残基24、25和28之间的自旋标记也显示出强相互作用，这表明环21 - 30部分有序。在最近使用固态核磁共振和冷冻电镜的结构研究背景下，本研究中揭示的位点特异性结构顺序为Aβ42纤维的主链和侧链动力学提供了不同的视角。
