Department of Biochemistry and Structural Biology, Lund University, 221 00 Lund, Sweden;
Department of Biochemistry and Structural Biology, Lund University, 221 00 Lund, Sweden.
Proc Natl Acad Sci U S A. 2020 May 26;117(21):11265-11273. doi: 10.1073/pnas.1918481117. Epub 2020 May 21.
The nucleation of Alzheimer-associated Aβ peptide monomers can be catalyzed by preexisting Aβ fibrils. This leads to autocatalytic amplification of aggregate mass and underlies self-replication and generation of toxic oligomers associated with several neurodegenerative diseases. However, the nature of the interactions between the monomeric species and the fibrils during this key process, and indeed the ultrastructural localization of the interaction sites have remained elusive. Here we used NMR and optical spectroscopy to identify conditions that enable the capture of transient species during the aggregation and secondary nucleation of the Aβ42 peptide. Cryo-electron microscopy (cryo-EM) images show that new aggregates protrude from the entire length of the progenitor fibril. These protrusions are morphologically distinct from the well-ordered fibrils dominating at the end of the aggregation process. The data provide direct evidence that self-replication through secondary nucleation occurs along the sides of fibrils, which become heavily decorated under the current solution conditions (14 µM Aβ42, 20 mM sodium phosphate, 200 µM EDTA, pH 6.8).
阿尔茨海默病相关 Aβ 肽单体的成核可以被预先存在的 Aβ 纤维催化。这导致了聚集质量的自动催化放大，是与几种神经退行性疾病相关的自我复制和有毒寡聚体产生的基础。然而，在这个关键过程中，单体物种与纤维之间的相互作用的性质，以及相互作用位点的超微结构定位，仍然难以捉摸。在这里，我们使用 NMR 和光学光谱来确定在 Aβ42 肽聚集和二次成核过程中捕获瞬时物种的条件。低温电子显微镜 (cryo-EM) 图像显示，新的聚集体从原纤维的全长突出。这些突起在形态上与在聚合过程结束时占主导地位的有序纤维明显不同。这些数据提供了直接的证据，表明通过二次成核的自我复制发生在纤维的侧面，在当前的溶液条件下（14µM Aβ42、20mM 磷酸钠、200µM EDTA、pH6.8），纤维的侧面会被严重修饰。
