Department of Physics , University of South Florida , Tampa , Florida 33620 , United States.
Institut für Physikalische Biologie , Heinrich-Heine-Universität , 40204 Düsseldorf , Germany.
J Phys Chem B. 2019 Jul 11;123(27):5678-5689. doi: 10.1021/acs.jpcb.9b02338. Epub 2019 Jun 27.
Assembly and deposition of insoluble amyloid fibrils with a distinctive cross-β-sheet structure is the molecular hallmark of amyloidogenic diseases affecting the central nervous system as well as non-neuropathic amyloidosis. Amyloidogenic proteins form aggregates via kinetic pathways dictated by initial solution conditions. Often, early stage, cytotoxic, small globular amyloid oligomers (gOs) and curvilinear fibrils (CFs) precede the formation of late-stage rigid fibrils (RFs). Growing experimental evidence suggests that soluble gOs are off-pathway aggregates that do not directly convert into the final stage RFs. Yet, the kinetics of RFs aggregation under conditions that either promote or suppress the growth of gOs remain incompletely understood. Here we present a self-assembly model for amyloid fibril formation in the presence and absence of early stage off-pathway aggregates, driven by our experimental results on hen egg white lysozyme (HewL) and beta amyloid (Aβ) aggregation. The model reproduces a range of experimental observations including the sharp boundary in the protein concentration above which the self-assembly of gOs occurs. This is possible when both primary and secondary RFs nucleation rates are allowed to have a nonlinear dependence on initial protein concentration, hinting toward more complex prenucleation and RFs assembly scenarios. Moreover, analysis of RFs lag period in the presence and absence of gOs indicates that these off-pathway aggregates have an inhibitory effect on RFs nucleation. Finally, we incorporate the effect of an Aβ binding protein on the aggregation process in the model that allows us to identify the most suitable solution conditions for suppressing gOs and RFs formation.
不溶性淀粉样纤维的组装和沉积具有独特的交叉-β-片层结构，是影响中枢神经系统的淀粉样变性疾病以及非神经淀粉样变性的分子标志。淀粉样蛋白通过受初始溶液条件支配的动力学途径形成聚集体。通常，在形成晚期刚性纤维（RFs）之前，早期、细胞毒性的、小的球状淀粉样寡聚物（gOs）和曲线纤维（CFs）先出现。越来越多的实验证据表明，可溶性 gOs 是偏离途径的聚集体，不会直接转化为最终阶段的 RFs。然而，在促进或抑制 gOs 生长的条件下 RFs 聚集的动力学仍不完全清楚。在这里，我们提出了一个在存在和不存在早期偏离途径聚集体的情况下淀粉样纤维形成的自组装模型，该模型由我们对鸡卵清溶菌酶（HewL）和β淀粉样蛋白（Aβ）聚集的实验结果驱动。该模型再现了一系列实验观察结果，包括 gOs 自组装发生时蛋白质浓度的急剧边界。当初级和次级 RFs 成核速率都允许对初始蛋白质浓度具有非线性依赖性时，就可以实现这一点，这表明预成核和 RFs 组装的情况更加复杂。此外，分析存在和不存在 gOs 时 RFs 的滞后期表明，这些偏离途径的聚集体对 RFs 成核具有抑制作用。最后，我们在模型中纳入了 Aβ 结合蛋白对聚集过程的影响，这使我们能够确定抑制 gOs 和 RFs 形成的最合适溶液条件。
