Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain.
Institute of Chemistry, Slovak Academy of Sciences, Bratislava, Slovakia.
Biophys J. 2012 Aug 8;103(3):453-463. doi: 10.1016/j.bpj.2012.06.043.
To explore the initial stages of amyloid β peptide (Aβ42) deposition on membranes, we have studied the interaction of Aβ42 in the monomeric form with lipid monolayers and with bilayers in either the liquid-disordered or the liquid-ordered (L(o)) state, containing negatively charged phospholipids. Molecular dynamics (MD) simulations of the system have been performed, as well as experimental measurements. For bilayers in the L(o) state, in the absence of the negatively charged lipids, interaction is weak and it cannot be detected by isothermal calorimetry. However, in the presence of phosphatidic acid, or of cardiolipin, interaction is detected by different methods and in all cases interaction is strongest with lower (2.5-5 mol%) than higher (10-20 mol%) proportions of negatively charged phospholipids. Liquid-disordered bilayers consistently allowed a higher Aβ42 binding than L(o) ones. Thioflavin T assays and infrared spectroscopy confirmed a higher proportion of β-sheet formation under conditions when higher peptide binding was measured. The experimental results were supported by MD simulations. We used 100 ns MD to examine interactions between Aβ42 and three different 512 lipid bilayers consisting of palmitoylsphingomyelin, dimyristoyl phosphatidic acid, and cholesterol in three different proportions. MD pictures are different for the low- and high-charge bilayers, in the former case the peptide is bound through many contact points to the bilayer, whereas for the bilayer containing 20 mol% anionic phospholipid only a small fragment of the peptide appears to be bound. The MD results indicate that the binding and fibril formation on the membrane surface depends on the composition of the bilayer, and is the result of a subtle balance of many inter- and intramolecular interactions between the Aβ42 and membrane.
为了探索淀粉样β肽 (Aβ42) 在膜上最初沉积的阶段，我们研究了单体形式的 Aβ42 与单层膜以及处于无序态或有序态 (L(o)) 的双层膜的相互作用，其中包含带负电荷的磷脂。对该体系进行了分子动力学 (MD) 模拟和实验测量。对于处于 L(o) 态的双层膜，在不存在带负电荷的磷脂时，相互作用较弱，无法通过等温量热法检测到。然而，当存在磷脂酸或心磷脂时，通过不同的方法可以检测到相互作用，在所有情况下，与较低 (2.5-5 mol%) 而非较高 (10-20 mol%) 的带负电荷的磷脂比例相比，相互作用更强。无序态双层膜始终允许 Aβ42 结合的比例高于有序态双层膜。硫黄素 T 测定和红外光谱证实，在测量到较高肽结合的情况下，β-折叠结构的形成比例更高。实验结果得到了 MD 模拟的支持。我们使用 100 ns MD 来研究 Aβ42 与三种不同的 512 脂质双层之间的相互作用，这三种双层由棕榈酰鞘氨醇、二肉豆蔻酰磷脂酸和胆固醇以三种不同的比例组成。对于低电荷和高电荷双层，MD 图像是不同的，在前一种情况下，肽通过许多接触点与双层结合，而对于含有 20 mol% 阴离子磷脂的双层，只有一小部分肽似乎被结合。MD 结果表明，在膜表面上的结合和纤维形成取决于双层的组成，并且是 Aβ42 与膜之间许多分子间和分子内相互作用的微妙平衡的结果。
