Assembly and structures of polyglutamine aggregates

包括亨廷顿病在内的九种人类遗传性神经退行性疾病是由 CAG重复序列在不同蛋白质编码区的扩展。这些蛋白质的大小不同， 结构、亚细胞定位，以及已知的功能。因为它们唯一的共同特征是 由CAG重复序列编码的聚谷氨酰胺(PolyGIn)序列，因为除了一个蛋白质外，所有这些蛋白质 疾病风险的重复长度阈值在相同的30-40长度范围内，神经毒性几乎是 当然是由扩展的PolyGIn序列的某些属性触发的。这项建议建立在和 继续上一次拨款的线索，更详细地研究了 扩展的PolyGIn序列，特别关注淀粉样聚集体的形成。在最近 我们的工作表明，PolyGin聚集体的成核涉及到一个非常不利的折叠反应 这项提议的第一个目的是更详细地研究伸长和 聚集反应的成核阶段，以及它们对溶液条件变化的响应。艾弗里 我们最近的工作表明，成核反应，因此聚集的总体侵略性是 受到环境中良性重复长度PolyGIn多肽的极大影响；这的第二个目标 建议研究PolyGIn序列中的局部序列上下文和突变中断是如何，如 在人类基因组中发现富含Gin的序列，影响聚集能力。在最近的其他工作中，我们 研究表明，分子伴侣Hdj2，以前被证明可以保护生物体免受PolyGIn毒性的影响， 在体外抑制PolyGin的聚集过程；新提案的第三个目标是从结构上确定 Hdj2如何识别和中和易于聚集的PolyGin序列。这些研究将继续我们的 长期目标是确定PolyGin序列如何形成有毒聚集体，以及序列和 细胞环境调节其固有的聚集倾向，从而最终决定疾病风险。

Nine human genetic neurodegenerative diseases, including Huntington's Disease, are caused by the expansion of CAG repeat sequences in the coding regions of different proteins. These proteins differ in size, structure, sub-cellular localization, and, where known, function. Since their only common feature is the polyglutamine (polyGIn) sequence encoded by the CAG repeat, and since for all but one of these proteins the repeat length threshold for disease risk is in the same 30-40 length range, neurotoxicity is almost certainly triggered by some property of the expanded polyGIn sequence. This proposal builds on and continues the threads of the previous grant by investigating in more detail the biophysical properties of expanded polyGIn sequences, focusing in particular on the formation of amyloid-like aggregates. In recent work we showed that nucleation of polyGIn aggregation involves a highly unfavorable folding reaction within monomeric polyGIn; the first aim of this proposal is to investigate in greater detail the elongation and nucleation phases of the aggregation reaction, and their responses to changes in solution conditions. Invery recent work we showed that the nucleation reaction, and hence the overall aggressiveness of aggregation, is greatly influenced by benign-repeat length polyGIn peptides in the environment; the second aim of this proposal is to investigate how local sequence context and mutational breaks in the polyGIn sequence, as found in Gin-rich sequences in the human genome, impact aggregation ability. In other recent work we showed that the molecular chaperone Hdj2, previously shown to protect organisms against polyGIn toxicity, inhibits the polyGIn aggregation process in vitro; the third aim of the new proposal is to determine structurally how Hdj2 recognizes and neutralizes aggregation-prone polyGIn sequences. These studies will continue our long-term goal of determining how polyGIn sequences form toxic aggregates, and how both sequence and cellular contexts modulate their intrinsic aggregation propensity, thus ultimately determining disease risk.