Chi Eva Y, Ege Canay, Winans Amy, Majewski Jaroslaw, Wu Guohui, Kjaer Kristian, Lee Ka Yee C
Department of Chemistry, Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, IL 60307, USA.
Proteins. 2008 Jul;72(1):1-24. doi: 10.1002/prot.21887.
The lipid membrane has been shown to mediate the fibrillogenesis and toxicity of Alzheimer's disease (AD) amyloid-beta (Abeta) peptide. Electrostatic interactions between Abeta40 and the phospholipid headgroup have been found to control the association and insertion of monomeric Abeta into lipid monolayers, where Abeta exhibited enhanced interactions with charged lipids compared with zwitterionic lipids. To elucidate the molecular-scale structural details of Abeta-membrane association, we have used complementary X-ray and neutron scattering techniques (grazing-incidence X-ray diffraction, X-ray reflectivity, and neutron reflectivity) in this study to investigate in situ the association of Abeta with lipid monolayers composed of either the anionic lipid 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DPPG), the zwitterionic lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), or the cationic lipid 1,2-dipalmitoyl 3-trimethylammonium propane (DPTAP) at the air-buffer interface. We found that the anionic lipid DPPG uniquely induced crystalline ordering of Abeta at the membrane surface that closely mimicked the beta-sheet structure in fibrils, revealing an intriguing templated ordering effect of DPPG on Abeta. Furthermore, incubating Abeta with lipid vesicles containing the anionic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) induced the formation of amyloid fibrils, confirming that the templated ordering of Abeta at the membrane surface seeded fibril formation. This study provides a detailed molecular-scale characterization of the early structural fluctuation and assembly events that may trigger the misfolding and aggregation of Abeta in vivo. Our results implicate that the adsorption of Abeta to anionic lipids, which could become exposed to the outer membrane leaflet by cell injury, may serve as an in vivo mechanism of templated-aggregation and drive the pathogenesis of AD.
脂质膜已被证明可介导阿尔茨海默病（AD）淀粉样β（Aβ）肽的纤维形成和毒性。已发现Aβ40与磷脂头部基团之间的静电相互作用可控制单体Aβ与脂质单层的缔合和插入，与两性离子脂质相比，Aβ在脂质单层中与带电脂质表现出更强的相互作用。为了阐明Aβ与膜缔合的分子尺度结构细节，在本研究中我们使用了互补的X射线和中子散射技术（掠入射X射线衍射、X射线反射率和中子反射率）来原位研究Aβ与由阴离子脂质1,2-二棕榈酰-sn-甘油-3-[磷酸-rac-（1-甘油）]（DPPG）、两性离子脂质1,2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）或阳离子脂质1,2-二棕榈酰-3-三甲基铵丙烷（DPTAP）组成的脂质单层在空气-缓冲液界面的缔合情况。我们发现阴离子脂质DPPG在膜表面独特地诱导了Aβ的晶体有序排列，这种排列与原纤维中的β-折叠结构非常相似，揭示了DPPG对Aβ具有有趣的模板化有序排列作用。此外，将Aβ与含有阴离子脂质1-棕榈酰-2-油酰-sn-甘油-3-[磷酸-rac-（1-甘油）]（POPG）的脂质囊泡一起孵育可诱导淀粉样原纤维的形成，证实了膜表面Aβ的模板化有序排列引发了原纤维形成。本研究提供了可能触发体内Aβ错误折叠和聚集的早期结构波动和组装事件的详细分子尺度表征。我们的结果表明，Aβ吸附到阴离子脂质上（细胞损伤可能使其暴露于外膜小叶）可能作为体内模板化聚集的机制，并推动AD的发病机制。
