ROLE OF CHAIN LENGTH AND SEQUENCE CONTEXTS ON POLYGLUTAMINE OLIGOMERIZATION

描述（申请人提供）：亨廷顿病是一种破坏性神经退行性疾病，由亨廷顿（htt）基因外显子1中CAG密码子扩增引起。其他八种蛋白质中类似的CAG重复扩增与八种不同的神经退行性疾病相关。在所有九种疾病中，CAG重复扩增编码蛋白质产物中的多聚谷氨酰胺扩增，并且疾病的发作和严重程度与多聚谷氨酰胺长度呈负相关，尽管这种相关性的定量性质对于九种疾病中的每一种是不同的。多聚谷氨酰胺扩增最终在不溶性神经元包涵体中，并且越来越多的证据表明，聚集机制和可溶性寡聚物种类与九种疾病中的每一种中的选择性神经变性直接相关。多聚谷氨酰胺扩增使其宿主蛋白不稳定并增加蛋白水解的可能性。蛋白水解片段由多聚谷氨酰胺束和侧翼的N-和C-末端片段组成。侧接多聚谷氨酰胺延伸的N-和C-末端区段对于每种疾病相关蛋白是独特的。随着链长的增加，均聚谷氨酰胺聚集的驱动力变得更强，天然存在的N-和C-末端侧翼序列调节这种驱动力。我们的目标是了解如何侧翼序列的多聚谷氨酰胺在疾病相关的蛋白质的扩展调制的内在的，长度依赖的构象偏好和聚集机制的多聚谷氨酰胺。我们的方法是基于新的原子模拟和体外实验的面板相结合。我们最近的研究结果是一致的假设，自然发生的侧翼序列可以作为“看门人”，以抑制固有的聚集倾向的聚集区域。因此，目前的建议是由以下假设指导：疾病相关蛋白质中天然存在的侧翼序列可以作为看门人，以减少聚谷氨酰胺束的内在聚集趋势。这种效应可以通过导致多聚谷氨酰胺长度增加的扩增突变来克服。此外，守门机制可能随侧翼序列而变化，从而导致守门效率的差异。我们将使用新的原子模拟和体外实验的组合来表征1）不同天然存在的末端侧翼序列内的构象变化以及这些变化与分子内界面内聚集倾向的聚谷氨酰胺区域的隔离/暴露程度之间的耦合，作为聚谷氨酰胺长度的函数，以及2）如果天然存在的侧翼序列是真正的看门人，并定量这些序列调节聚集的程度作为多聚谷氨酰胺长度的函数。精确理解侧翼序列和多聚谷氨酰胺扩增之间的耦合机制将使我们能够确定抑制聚集介导的毒性和神经变性途径的靶点。

DESCRIPTION (provided by applicant): Huntington's disease is a devastating neurodegenerative disease caused by CAG codon expansion in exon 1 of the huntingtin (htt) gene. Similar CAG repeat expansions in eight other proteins are associated with eight different neurodegenerative diseases. In all nine diseases, the CAG repeat expansions encode polyglutamine expansions in the protein products, and the onset and severity of disease are inversely correlated with the polyglutamine length although the quantitative nature of this correlation is different for each of the nine disorders. Polyglutamine expansions end up in insoluble neuronal inclusions and there is growing evidence that the mechanisms of aggregation and the soluble oligomeric species are directly linked to selective neurodegeneration in each of the nine diseases. Polyglutamine expansions destabilize their host proteins and increase the likelihood of proteolysis. Fragments of proteolysis consist of polyglutamine tracts and flanking N- and C-terminal segments. The N- and C-terminal segments that flank the polyglutamine stretch are unique to each disease-related protein. Driving forces for aggregation of homopolymeric polyglutamine becomes stronger with increasing chain length and naturally occurring N- and C-terminal flanking sequences modulate this driving force. Our goal is to understand how sequences that flank polyglutamine expansions in disease-related proteins modulate the intrinsic, length-dependent conformational preferences and aggregation mechanisms of polyglutamine. Our approaches are based on a combination of novel atomistic simulations and a panel of in vitro experiments. Our recent results are consistent with the hypothesis that naturally occurring flanking sequences can act as "gatekeepers" to suppress intrinsic aggregation propensities of aggregation-prone regions. Therefore, the current proposal is guided by the following hypothesis: Naturally occurring flanking sequences in disease-related proteins can act as gatekeepers to decrease the intrinsic aggregation tendencies of polyglutamine tracts. This effect can be overcome by expansion mutations that lead to increased polyglutamine lengths. Additionally, gatekeeping mechanisms likely vary with flanking sequence, giving rise to differences in gatekeeping efficiencies. We will use a combination of novel atomistic simulations and in vitro experiments to characterize 1) conformational changes within different naturally occurring terminal flanking sequences and the coupling between these changes and the degree of sequestration / exposure of aggregation-prone polyglutamine regions within intramolecular interfaces as a function of polyglutamine length and 2) if naturally occurring flanking sequences are bona fide gatekeepers and to quantify the degree to which these sequences modulate aggregation as a function of polyglutamine length. Precise understanding of the mechanisms of coupling between flanking sequences and polyglutamine expansions will allow us to identify targets for inhibition of routes to aggregation-mediated toxicity and neurodegeneration.