Koppaka Vishwanath, Paul Cynthia, Murray Ian V J, Axelsen Paul H
Department of Pharmacology, Johnson Foundation for Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA.
J Biol Chem. 2003 Sep 19;278(38):36277-84. doi: 10.1074/jbc.M301334200. Epub 2003 Jun 23.
Oxidative lipid membrane damage is known to promote the misfolding of Abeta42 into pathological beta structure. In fully developed senile plaques of Alzheimer's disease, however, it is the shorter and more soluble amyloid beta protein, Abeta40, that predominates. To investigate the role of oxidative membrane damage in the misfolding of Abeta40, we have examined its interaction with supported lipid monolayer membranes using internal reflection infrared spectroscopy. Oxidatively damaged lipids modestly increased Abeta40 accumulation, with adsorption kinetics and a conformation that are distinct from that of Abeta42. In stark contrast, pretreatment of oxidatively damaged monolayer membranes with Abeta42 vigorously promoted Abeta40 accumulation and misfolding. Pretreatment of saturated or undamaged membranes with Abeta42 had no such effect. Parallel studies of lipid bilayer vesicles using a dye binding assay to detect fibril formation and electron microscopy to examine morphology demonstrated that Abeta42 pretreatment of oxidatively damaged membranes promoted the formation of mature Abeta40 amyloid fibrils. We conclude that oxidative membrane damage and Abeta42 act synergistically at an early stage to promote fibril formation by Abeta40. This synergy could be detected within minutes using internal reflection spectroscopy, whereas a dye-binding assay required several days and much higher protein concentrations to demonstrate this synergy.
已知氧化脂质膜损伤会促使β淀粉样蛋白42（Aβ42）错误折叠成病理性β结构。然而，在阿尔茨海默病完全形成的老年斑中，占主导地位的却是较短且更易溶的淀粉样β蛋白Aβ40。为了研究氧化膜损伤在Aβ40错误折叠中的作用，我们使用内反射红外光谱法检测了其与支持脂质单分子层膜的相互作用。氧化损伤的脂质适度增加了Aβ40的积累，其吸附动力学和构象与Aβ42不同。与之形成鲜明对比的是，用Aβ42对氧化损伤的单分子层膜进行预处理，会强烈促进Aβ40的积累和错误折叠。用Aβ42对饱和或未受损的膜进行预处理则没有这种效果。使用染料结合测定法检测纤维形成以及用电子显微镜检查形态对脂质双层囊泡进行的平行研究表明，用Aβ42对氧化损伤的膜进行预处理会促进成熟Aβ40淀粉样纤维的形成。我们得出结论，氧化膜损伤和Aβ42在早期协同作用，促进Aβ40形成纤维。使用内反射光谱法可在数分钟内检测到这种协同作用，而染料结合测定法则需要数天时间且蛋白质浓度要高得多才能证明这种协同作用。
