Center for Fundamental and Applied Molecular Evolution, NSF/NASA Center for Chemical Evolution, Departments of Chemistry and Biology, Atlanta, Georgia 30322, USA.
Langmuir. 2012 Apr 17;28(15):6386-95. doi: 10.1021/la300143j. Epub 2012 Apr 5.
Recent evidence suggests that simple peptides can access diverse amphiphilic phases, and that these structures underlie the robust and widely distributed assemblies implicated in nearly 40 protein misfolding diseases. Here we exploit a minimal nucleating core of the Aβ peptide of Alzheimer's disease to map its morphologically accessible phases that include stable intermolecular molten particles, fibers, twisted and helical ribbons, and nanotubes. Analyses with both fluorescence lifetime imaging microscopy (FLIM) and transmission electron microscopy provide evidence for liquid-liquid phase separations, similar to the coexisting dilute and dense protein-rich liquid phases so critical for the liquid-solid transition in protein crystallization. We show that the observed particles are critical for transitions to the more ordered cross-β peptide phases, which are prevalent in all amyloid assemblies, and identify specific conditions that arrest assembly at the phase boundaries. We have identified a size dependence of the particles in order to transition to the para-crystalline phase and a width of the cross-β assemblies that defines the transition between twisted fibers and helically coiled ribbons. These experimental results reveal an interconnected network of increasing molecularly ordered cross-β transitions, greatly extending the initial computational models for cross-β assemblies.
最近的证据表明，简单肽可以进入多种两亲相，而这些结构是构成近 40 种蛋白质错误折叠疾病中广泛存在的稳健组装体的基础。在这里，我们利用阿尔茨海默病 Aβ肽的最小成核核心来绘制其形态上可及的相，包括稳定的分子间熔融颗粒、纤维、扭曲和螺旋带以及纳米管。使用荧光寿命成像显微镜 (FLIM) 和透射电子显微镜的分析为液-液相分离提供了证据，类似于对蛋白质结晶中液-固转变至关重要的共存稀相和富含蛋白质的浓相。我们表明，观察到的颗粒对于向更有序的交叉-β肽相转变至关重要，这种相在所有淀粉样组装体中都很普遍，并确定了在相边界处阻止组装的具体条件。我们已经确定了颗粒的尺寸依赖性，以转变为准晶相，以及交叉-β组装体的宽度，这决定了扭曲纤维和螺旋卷曲带之间的转变。这些实验结果揭示了分子有序交叉-β转变的相互关联网络，极大地扩展了交叉-β组装体的初始计算模型。
