The complex kinetics of disease-related amyloid aggregation of proteins such as α-Synuclein (α-Syn) in Parkinson’s disease and Aβ42 in Alzheimer’s disease include primary nucleation, amyloid fibril elongation and secondary nucleation. The latter can be a key accelerator of the aggregation process. It has been demonstrated that the chaperone domain BRICHOS can interfere with the secondary nucleation process of Aβ42. Here, we explore the mechanism of secondary nucleation inhibition of the BRICHOS domain of the lung surfactant protein (proSP-C) against α-Syn aggregation and amyloid formation. We determine the 3D NMR structure of an inactive trimer of proSP-C BRICHOS and its active monomer using a designed mutant. Furthermore, the interaction between the proSP-C BRICHOS chaperone and a substrate peptide has been studied. NMR-based interaction studies of proSP-C BRICHOS with α-Syn fibrils show that proSP-C BRICHOS binds to the C-terminal flexible fuzzy coat of the fibrils, which is the secondary nucleation site on the fibrils. Super-resolution fluorescence microscopy demonstrates that proSP-C BRICHOS runs along the fibrillar axis diffusion-dependently sweeping off monomeric α-Syn from the fibrils. The observed mechanism explains how a weakly binding chaperone can inhibit the α-Syn secondary nucleation pathway via avidity where a single proSP-C BRICHOS molecule is sufficient against up to ~7-40 α-Syn molecules embedded within the fibrils.

帕金森病中的 α-突触核蛋白 （α-Syn） 和阿尔茨海默病中的 Aβ42 等蛋白质与疾病相关的淀粉样蛋白聚集的复杂动力学包括初级成核、淀粉样蛋白原纤维伸长和次级成核。后者可以是聚合过程的关键加速器。已经证明伴侣结构域 BRICHOS 可以干扰 Aβ42 的次级成核过程。在这里，我们探讨了肺表面活性蛋白 （proSP-C） 的 BRICHOS 结构域对 α-Syn 聚集和淀粉样蛋白形成的二级成核抑制机制。我们使用设计的突变体确定 proSP-C BRICHOS 的无活性三聚体及其活性单体的 3D NMR 结构。此外，还研究了 proSP-C BRICHOS 伴侣与底物肽之间的相互作用。proSP-C BRICHOS 与 α-Syn 原纤维的基于 NMR 的相互作用研究表明，proSP-C BRICHOS 与原纤维的 C 末端柔性模糊涂层结合，这是原纤维上的次级成核位点。超分辨率荧光显微镜表明，proSP-C BRICHOS 沿原纤维轴扩散依赖性地运行，从原纤维中清除单体 α-Syn。观察到的机制解释了弱结合伴侣如何通过亲和力抑制 α-Syn 次级成核途径，其中单个 proSP-C BRICHOS 分子足以对抗嵌入原纤维内的多达 ~7-40 个 α-Syn 分子。