Structural polymorphism in the misfolding and aggregation of expanded polyglutamine proteins

描述(申请人提供)：许多毁灭性的神经退行性疾病是由于蛋白质错误折叠导致斑块或包涵体包含错误折叠的蛋白质造成的。尽管蛋白质错误折叠的核心作用得到了公认，但我们普遍缺乏对致病分子事件的了解，部分原因是阿尔茨海默病(AD)等疾病的复杂病因学。亨廷顿氏病(HD)和至少其他八种神经退行性疾病被追溯到一种显著的明确突变，该突变发生在不同的基因上：先前存在的CAG密码子重复序列的扩展。在HD中，这会导致Huntingtin蛋白内的聚谷氨酰胺(PolyQ)区扩张，超过~35Gln的“门槛”会导致毁灭性的神经退行性疾病，发病年龄取决于扩张的程度。仅HD一项就使20多万美国人面临疾病风险，目前还没有有效的根治性或预防性治疗。我们对错误折叠途径的认识的显著提高对于设计能够改善错误折叠、疾病发病和毒性的治疗方法至关重要。为了满足这一需求，我们将部署最先进的魔角旋转(MAS)核磁共振光谱学。这种方法以前已经使我们能够用特定的位置和原子分辨率来表征各种蛋白质聚集体，最近包括了一系列与聚谷氨酰胺相关的聚集体。我们过去和未来在这方面的成功得益于深入的核磁共振专业知识、精致的核磁共振硬件和高效的合作，这使得我们能够对HD的错误折叠过程和致病毒性进行关键的洞察。根据我们现有的核磁共振数据和机理研究，我们假设分子内坍塌成为可能的共同β-发夹构象具有关键作用。重要的是，这种构象变化促进了错误折叠的多聚Q自组装成低聚物和纤维状聚集体，这些聚集体可能包含折叠初始结构的特征结构基序。因此，通过研究错折态，我们探索了 膨化聚谷氨酰胺错误折叠的分子基础。使用MAS ss核磁共振，我们将表征并利用我们假设的不寻常的光谱特征来反映错误折叠的多Q结构域的独特内部多态。将这些方法应用于不同的疾病相关蛋白，我们验证了我们的假设，即在多谷氨酰胺疾病家族中，共同的结构机制正在发挥作用。我们将研究以前的工作表明错误折叠结构(从而错误折叠机制)中存在质量差异的疾病，并在HD中检查据报道具有不同毒性的多态聚集体。这项工作将提供这一疾病家族亟需的系统和详细的特征，这不仅有利于他们的治疗，而且还将影响我们对应用于具有更复杂病因的淀粉样蛋白相关疾病的结构和毒性的理解，从AD到各种系统性淀粉样变性。

DESCRIPTION (provided by applicant): Many devastating neurodegenerative diseases result from protein misfolding that leads to plaques or inclusions containing the misfolded protein. Despite a recognized central role of protein misfolding, we generally lack insight into the causative molecular events, in part due to the complex etiology of diseases like Alzheimer's Disease (AD). Huntington's Disease (HD) and at least eight other neurodegenerative disorders have been traced to a remarkable well-defined mutation occurring across different genes: the expansion of a pre-existing CAG codon repeat. In HD, this leads to expansion of a polyglutamine (polyQ) tract within the huntingtin protein, with expansion beyond a "threshold" of ~35 Gln leading to a devastating neurodegenerative disease, with the age of onset dependent on the degree of expansion. HD alone places more than 200,000 Americans at risk of disease, with currently no effective curative or preventative treatments. A dramatic improvement in our knowledge of the misfolding pathway is essential to enable the design of treatments that can ameliorate misfolding, disease onset and toxicity. To address this need, we will deploy state-of-the-art magic-angle-spinning (MAS) NMR spectroscopy. This approach has previously allowed us to characterize various protein aggregates with site-specific and atomic resolution, most recently including an array of polyglutamine-related aggregates. Our past and future success in this endeavor is enabled by an in-depth NMR expertise, exquisite NMR hardware, and highly effective collaborations, which have allowed for key insights into the misfolding process and disease-causing toxicity in HD. Informed by our existing NMR data and mechanistic studies, we hypothesize that there is a critical role for intramolecular collapse into a likely common β-hairpin conformation. Crucially, this conformational change facilitates self-assembly of the misfolded polyQ into oligomeric and fibrillar aggregates that likely contain a signature structural motif characteristic of the collapsed initial structure. Thus, by studying the misfolded states, we probe the molecular underpinnings of the misfolding by expanded polyglutamine. Using MAS ssNMR we will both characterize and leverage an unusual spectroscopic signature that we hypothesize to reflect a unique internal polymorphism that is characteristic of misfolded polyQ domains. Applying these methods to different disease-related proteins, we test our hypothesis that a common structural mechanism is at work across the polyglutamine disease family. We will examine diseases where previous work suggests qualitative differences in the misfolded structure (and thus misfolding mechanism), and in HD will examine polymorphic aggregates that reportedly have differing toxicities. This work will provide the much needed systematic and detailed characterization of this family of disorders that will not only benefit their treatment, bt will also impact our understanding of structure and toxicity as applied to amyloid-related diseases with more complex etiologies, ranging from AD to various systemic amyloidoses.