Fundamental Molecular-Level Studies of Polyglutamine Folding and Early-Stage Aggregation

CBET-0755730聚谷氨酰胺是一种由谷氨酰胺单体组成的聚合物，与许多神经退行性疾病有关，包括亨廷顿病。在非HD个体中，亨廷顿蛋白通常表现出19个残基长的多聚谷氨酰胺（PolyQ）序列。亨廷顿蛋白质显示出长于36个残基的序列的个体发展为亨廷顿病。在水溶液中，PolyQ分子与水形成多个氢键，并采用无规卷曲构象。然而，在某些情况下，长PolyQ链可以与自身氢键结合并形成亚稳态折叠结构，据信该亚稳态折叠结构充当另外的PolyQ分子的后续聚集或聚合的核，从而导致其特征令人联想到淀粉样蛋白原纤维的聚集体的形成。也有人提出，一旦形成，折叠的核促进额外链的折叠，导致聚集体的快速伸长。折叠亚稳态的确切性质及其形成机制仍然未知。然而，文献研究一致认为，阐明折叠PolyQ核的结构对于理解PolyQ聚集和亨廷顿病的发病至关重要。该项目旨在确定该核心的结构，更重要的是，它出现的路径。该项目还建议研究折叠的核是否以及如何介导或诱导额外链的折叠，以及链聚集的早期阶段。一个精心构思的分子建模方法，提出了详细的原子模型的聚谷氨酰胺和先进的模拟技术将用于实现这些目标。PI预计，PolyQ折叠和早期聚集的相对完整的分子水平机制解释将从我们的研究中出现。初步结果已经揭示了PolyQ折叠途径的令人兴奋和前所未有的见解。智力优势：PolyQ折叠和聚集的理论和计算研究一直很少见。这种性质的研究提供了独特的可能性，为折叠PolyQ分子的结构、其聚集体和各自的折叠过程提供了重要的见解。该项目概述的研究将以前所未有的分子细节水平研究构成PolyQ折叠和聚集过渡态系综的轨迹或蛋白质构象系综。通过这项工作获得的知识不仅将提供对亨廷顿病发病的见解，而且还可能提供关于淀粉样纤维形成过程的重要线索。与我们提出的研究相关的计算挑战是惊人的。一系列有前途的新的分子建模方法将被开发，以满足这些挑战。这些方法将推动分子建模和科学计算的发展，并将在从生物分子到复杂流体的各种系统中找到广泛的应用。更广泛的影响：亨廷顿氏病目前每10，000人中就有1人受到折磨。高毒性PolyQ寡聚体被认为是导致疾病发作的原因。了解PolyQ折叠和寡聚体形成的分子起源将提供重要的见解，可能有助于开发治疗策略。除了发现PolyQ折叠机制对社会产生的固有影响外，这里提出的研究提供了一个特别相关的论坛，可以向社会传播基础分子水平研究的好处。研究所建议利用这一机会，针对代表性不足的少数民族背景的高中生，举办一个关于蛋白质聚集和神经变性疾病的讲习班。

CBET-0755730De PabloPolyglutamine, a polymer consisting of glutamine monomers, has been implicated in a number of neurodegenerative diseases, including Huntington's Disease. In non-HD individuals, the Huntingtin protein typically exhibits a 19-residue long polyglutamine (PolyQ) sequence. Individuals whose Huntingtin protein exhibits a sequence longer than 36 residues develop Huntington's Disease. In aqueous solution, PolyQ molecules form multiple hydrogen bonds with water and adopt a random coil conformation. Under certain circumstances, however, a long PolyQ chain can hydrogen bond with itself and form a metastable folded structure that is believed to act as a nucleus for subsequent aggregation or polymerization of additional PolyQ molecules, thereby leading to the formation of aggregates whose characteristics are reminiscent of amyloid fibrils. It has also been suggested that, once formed, the folded nucleus facilitates the folding of additional chains, leading to a rapid elongation of the aggregates. The precise nature of that folded metastable state and the mechanism behind its formation remain unknown. Literature studies, however, concur in that elucidating the structure of the folded PolyQ nucleus is essential for understanding PolyQ aggregation and the onset of Huntington's Disease. The project seeks to determine the structure of that nucleus and, more importantly, the path through which it appears. The project also proposes to investigate if and how a folded nucleus might mediate or induce the folding of additional chains, and the early stages of chain aggregation. A carefully conceived molecular modeling approach is proposed, in which detailed atomistic models of polyglutamine and advanced simulation techniques will be used towards such ends. The PIs anticipate that a relatively complete, molecular-level mechanistic explanation of PolyQ folding and early-stage aggregation will emerge from our studies. Preliminary results already reveal exciting and unprecedented insights into the pathways through which PolyQ folds.Intellectual Merit: Theoretical and computational studies of PolyQ folding and aggregation have been scarce. Studies of that nature offer the distinct possibility of providing important insights into the structure of folded PolyQ molecules, their aggregates, and the respective folding processes. The research outlined in this project will examine at an unprecedented level of molecular detail the ensemble of trajectories or protein conformations that constitute the transition state ensemble for the folding and aggregation of PolyQ. The knowledge gained through this effort will not only provide insights into the onset of Huntington's Disease, but it might also provide important clues about the process of amyloid fibril formation in general. The computational challenges associated with our proposed research are staggering. A promising array of novel molecular modeling methods will be developed to meet those challenges. Such methods will advance the state of the art in molecular modeling and scientific computing, and will find wide ranging applications in a wide variety of systems, ranging from biomolecules to complex fluids.Broader Impacts: Huntington's disease currently afflicts 1 in 10,000 individuals. Highly toxic PolyQ oligomers are believed to be responsible for the onset of the disease. Understanding the molecular origins of PolyQ folding and oligomer formation will provide important insights that may help in the development of therapeutic strategies. Beyond the inherent impact to society that would arise from discovering the mechanism of PolyQ folding, the research proposed here offers a particularly relevant forum in which to disseminate the benefits of fundamental molecular-level research to society. The PIs propose to capitalize on that opportunity by developing a workshop on protein aggregation and neurodegenerative disorders aimed at high school students from under-represented minority backgrounds.1