Pathologic polyglutamine aggregation begins with a self-poisoning polymer crystal.
Pathologic polyglutamine aggregation begins with a self-poisoning polymer crystal.
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DOI：
10.7554/elife.86939
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发表时间：
2023-11-03
期刊：
影响因子：
7.7
通讯作者：
Halfmann R
中科院分区：
文献类型：
--
作者：
Kandola T;Venkatesan S;Zhang J;Lerbakken BT;Von Schulze A;Blanck JF;Wu J;Unruh JR;Berry P;Lange JJ;Box AC;Cook M;Sagui C;Halfmann R
淀粉样蛋白研究的长期目标是表征决定速率成核事件的结构基础。然而，成核的短暂性使得现有的生物化学、结构生物学和计算方法无法实现这一目标。在这里，我们解决了聚谷氨酰胺（polyQ）的限制，聚谷氨酰胺是一种多肽序列，当其长度超过特征阈值时，会导致亨廷顿氏舞蹈症和其他淀粉样蛋白相关的神经退行性疾病。为了确定polyQ淀粉样蛋白核的基本特征，我们使用直接细胞内自联报告基因来量化淀粉样蛋白出现的频率，作为浓度、构象模板和合理的polyQ序列排列的函数。我们发现病理性扩张的polyQ的成核涉及每隔一个位置的三个谷氨酰胺（Q）残基的片段。我们使用分子模拟证明了这种模式编码具有叉指式 Q 侧链的四链空间拉链。一旦形成，拉链就会通过在正交面上接合原始多肽来毒害其自身的生长，这是具有分子内核的聚合物晶体的时尚特征。我们进一步表明，通过在成核之前对 PolyQ 进行基因寡聚，可以利用自中毒来阻止淀粉样蛋白的形成。通过揭示细胞内polyQ聚集限速事件的物理性质，我们的研究结果阐明了polyQ疾病的分子病因学。通常在晚年发生的疾病，例如阿尔茨海默病，通常是由特定蛋白质聚集成淀粉样蛋白结构引起的。一旦这个过程开始，淀粉样蛋白将继续形成，导致更严重的无法治愈的症状。因此，治疗这些疾病的最佳方法是首先阻止淀粉样蛋白的产生。淀粉样蛋白最初是由蛋白质聚集在一起形成称为细胞核的不稳定结构而形成的。原子核的不稳定性意味着它不能被直接观察到，这使得研究这个成核过程变得困难。为了克服这个问题，Kandola、Venkatesan 等人。研究了已知形成淀粉样蛋白的最简单的蛋白质——聚谷氨酰胺，它由一系列被称为氨基酸的重复结构单元组成。聚谷氨酰胺仅形成一种淀粉样蛋白，与九种神经退行性疾病相关，包括亨廷顿病。然而，只有当其氨基酸链超过一定长度时，它才会这样做，这表明成核开始可能需要特定的结构。坎多拉，文卡特桑等人。制作了聚谷氨酰胺蛋白的替代版本，每个版本都含有略有不同的氨基酸序列，这将改变蛋白质折叠的方式。然后他们测试了这些不同变体在酵母细胞中形成淀粉样蛋白的能力。这表明，为了连接在一起形成核，聚谷氨酰胺需要能够折叠成由四根互锁链组成的拉链形状。形成这种形状所需的蛋白质的长度也与产生与神经退行性疾病相关的淀粉样蛋白的长度相同。坎多拉，文卡特桑等人。还发现聚谷氨酰胺倾向于与已经形成的细胞核结合，从而阻碍其生长。这种“自我中毒”的影响可能被用来作为一种先发制人地阻止淀粉样蛋白最初产生的方法。这些发现揭示了一种阻止淀粉样蛋白形成的潜在治疗策略，最终可能使患有或有患与多聚谷氨酰胺相关的神经退行性疾病风险的人受益。此外，这种方法为理解其他蛋白质如何经历淀粉样蛋白成核提供了蓝图，包括那些导致阿尔茨海默氏症、帕金森氏症和其他疾病的蛋白质。
A long-standing goal of amyloid research has been to characterize the structural basis of the rate-determining nucleating event. However, the ephemeral nature of nucleation has made this goal unachievable with existing biochemistry, structural biology, and computational approaches. Here, we addressed that limitation for polyglutamine (polyQ), a polypeptide sequence that causes Huntington’s and other amyloid-associated neurodegenerative diseases when its length exceeds a characteristic threshold. To identify essential features of the polyQ amyloid nucleus, we used a direct intracellular reporter of self-association to quantify frequencies of amyloid appearance as a function of concentration, conformational templates, and rational polyQ sequence permutations. We found that nucleation of pathologically expanded polyQ involves segments of three glutamine (Q) residues at every other position. We demonstrate using molecular simulations that this pattern encodes a four-stranded steric zipper with interdigitated Q side chains. Once formed, the zipper poisoned its own growth by engaging naive polypeptides on orthogonal faces, in a fashion characteristic of polymer crystals with intramolecular nuclei. We further show that self-poisoning can be exploited to block amyloid formation, by genetically oligomerizing polyQ prior to nucleation. By uncovering the physical nature of the rate-limiting event for polyQ aggregation in cells, our findings elucidate the molecular etiology of polyQ diseases. Diseases that typically occur later in life, such as Alzheimer’s, are often caused by specific proteins clumping together into structures known as amyloids. Once the process starts, amyloids will continue to form, leading to worse symptoms that cannot be cured. The best way to treat these diseases is therefore to stop amyloids from arising in the first place. Amyloids initially develop by proteins coming together to create an unstable structure referred to as the nucleus. The instability of the nucleus means it cannot be observed directly, making it hard to study this nucleation process. To overcome this, Kandola, Venkatesan et al. investigated the simplest protein known to form an amyloid – polyglutamine, which is made up of a chain of repeating building blocks known as amino acids. Polyglutamine forms only one type of amyloid which is associated with nine neurodegenerative diseases, including Huntington’s disease. However, it only does this when its chain of amino acids exceeds a certain length, suggesting that a specific structure may be required for nucleation to begin. Kandola, Venkatesan et al. made alternative versions of the polyglutamine protein which each contained slightly different sequences of amino acids that will alter the way the protein folds. They then tested how well these different variants could form amyloids in yeast cells. This revealed that in order to join together into a nucleus, polyglutamine needs to be able to fold into a zipper shape made up of four interlocking strands. The length of the protein required to form this shape is also the same length that causes the amyloid associated with neurodegenerative diseases. Kandola, Venkatesan et al. also found that polyglutamine tends to bind to nuclei that have already formed in a way that hinders their growth. This ‘self-poisoning’ affect could potentially be exploited as a way to pre-emptively stop amyloids from initially arising. These findings have uncovered a potential therapeutic strategy for blocking amyloid formation that could eventually benefit people with or at risk of developing neurodegenerative diseases linked to polyglutamine. Additionally, this approach provides a blueprint for understanding how other proteins undergo amyloid nucleation, including those responsible for Alzheimer’s, Parkinson’s, and other diseases.
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