Examination of Ataxin-3 (atx-3) Aggregation by Structural Mass Spectrometry Techniques: A Rationale for Expedited Aggregation upon Polyglutamine (polyQ) Expansion.
Examination of Ataxin-3 (atx-3) Aggregation by Structural Mass Spectrometry Techniques: A Rationale for Expedited Aggregation upon Polyglutamine (polyQ) Expansion.
复制标题
DOI：
10.1074/mcp.m114.044610
复制
发表时间：
2015-05
期刊：
影响因子：
--
通讯作者：
Ashcroft AE
中科院分区：
文献类型：
--
作者：
Scarff CA;Almeida B;Fraga J;Macedo-Ribeiro S;Radford SE;Ashcroft AE
多聚谷氨酰胺延伸的扩展导致含多聚谷氨酰胺的神经元聚集体的形成和九种疾病中的神经元死亡，目前还没有治疗或治愈的方法。这在很大程度上是由于缺乏对扩展的多聚谷氨酰胺区域导致聚集和疾病的机制的理解。使问题进一步复杂化的是，几种多聚谷氨酰胺疾病相关蛋白，包括共济失调蛋白-3，具有多阶段聚集机制，其中侧翼结构域自组装先于多聚谷氨酰胺聚集，但受多聚谷氨酰胺扩增的影响。多聚谷氨酰胺扩增如何影响侧翼结构域聚集知之甚少。在这里，我们使用质谱和生物物理方法的组合来研究共济失调蛋白-3的这个问题。我们表明，侧接的Josephin结构域在共济失调蛋白-3与扩展的多聚谷氨酰胺道的构象动力学改变相比，其nonexpanded对应物所表现出的，特别是在聚集的Josephin结构域（氨基酸残基73-96）的区域内。因此，在含有扩展的多聚谷氨酰胺束的共济失调蛋白-3中，扩展更频繁地暴露该区域，从而提供了为什么在多聚谷氨酰胺扩展后加速聚集的分子解释。在这里，利用离子迁移谱-质谱的力量，在聚集过程中形成的低聚物物种的特点和低聚物生长的模型提出。结果表明，构象变化发生在二聚体水平，启动自组装。还描述了对共济失调蛋白-3原纤维结构的新见解，揭示了参与原纤维形成的约瑟芬结构域区域，并证明多聚谷氨酰胺聚集是原纤维形成后独特的第二步，而不需要原纤维核心的结构重排。总体而言，这些结果使聚谷氨酰胺扩展对共济失调蛋白-3自组装的每个阶段（从单体到原纤维）的影响得以描述，并提供了聚谷氨酰胺扩展后加速聚集的基本原理。
Expansion of polyglutamine stretches leads to the formation of polyglutamine-containing neuronal aggregates and neuronal death in nine diseases for which there currently are no treatments or cures. This is largely due to a lack in understanding of the mechanisms by which expanded polyglutamine regions contribute to aggregation and disease. To complicate matters further, several of the polyglutamine-disease related proteins, including ataxin-3, have a multistage aggregation mechanism in which flanking domain self-assembly precedes polyglutamine aggregation yet is influenced by polyglutamine expansion. How polyglutamine expansion influences flanking domain aggregation is poorly understood. Here, we use a combination of mass spectrometry and biophysical approaches to investigate this issue for ataxin-3. We show that the conformational dynamics of the flanking Josephin domain in ataxin-3 with an expanded polyglutamine tract are altered in comparison to those exhibited by its nonexpanded counterpart, specifically within the aggregation-prone region of the Josephin domain (amino acid residues 73–96). Expansion thus exposes this region more frequently in ataxin-3 containing an expanded polyglutamine tract, providing a molecular explanation of why aggregation is accelerated upon polyglutamine expansion. Here, harnessing the power of ion mobility spectrometry-mass spectrometry, oligomeric species formed during aggregation are characterized and a model for oligomer growth proposed. The results suggest that a conformational change occurs at the dimer level that initiates self-assembly. New insights into ataxin-3 fibril architecture are also described, revealing the region of the Josephin domain involved in protofibril formation and demonstrating that polyglutamine aggregation proceeds as a distinct second step after protofibril formation without requiring structural rearrangement of the protofibril core. Overall, the results enable the effect of polyglutamine expansion on every stage of ataxin-3 self-assembly, from monomer through to fibril, to be described and a rationale for expedited aggregation upon polyglutamine expansion to be provided.