J Phys Chem B. 2019 Feb 28;123(8):1749-1763. doi: 10.1021/acs.jpcb.8b10783. Epub 2019 Feb 19.
Fibrillization of polyglutamine (polyQ) tracts in proteins is implicated in at least 10 neurodegenerative diseases. This generates great interest in the structure and the aggregation mechanism(s) of polyQ peptides. The fibrillization of polyQ is thought to result from the peptide's insolubility in aqueous solutions; longer polyQ tracts show decreased aqueous solution solubility, which is thought to lead to faster fibrillization kinetics. However, few studies have characterized the structure(s) of polyQ peptides with low solubility. In the work here, we use UV resonance Raman spectroscopy to examine the secondary structures, backbone hydrogen bonding, and side chain hydrogen bonding for a variety of solution-state, solid, and fibril forms of DQK (Q20). Q20 is insoluble in water and has a β-strand-like conformation with extensive inter- and intrapeptide hydrogen bonding in both dry and aqueous environments. We find that Q20 has weaker backbone-backbone and backbone-side chain hydrogen bonding and is less ordered compared to that of polyQ fibrils. Interestingly, we find that the insoluble Q20 will form fibrils when incubated in water at room temperature for ∼5 h. Also, Q20 can be prepared using a well-known disaggregation procedure to produce a water-soluble PPII-like conformation with negligible inter- and intrapeptide hydrogen bonding and a resistance to aggregation.
多聚谷氨酰胺（polyQ）序列在蛋白质中的纤维化与至少 10 种神经退行性疾病有关。这使得人们对 polyQ 肽的结构和聚集机制产生了极大的兴趣。polyQ 的纤维化被认为是由于肽在水溶液中的不溶性；更长的 polyQ 序列表现出降低的水溶液溶解度，这被认为导致更快的纤维化动力学。然而，很少有研究描述低溶解度的 polyQ 肽的结构。在本工作中，我们使用紫外共振拉曼光谱来研究 DQK（Q20）的各种溶液态、固态和原纤维态的二级结构、主链氢键和侧链氢键。Q20 在水中不溶，并且在干燥和水相环境中具有β-折叠样构象，具有广泛的肽内和肽间氢键。我们发现，与 polyQ 原纤维相比，Q20 的主链-主链和主链-侧链氢键较弱，有序性较低。有趣的是，我们发现不溶性的 Q20 在室温下在水中孵育约 5 小时后会形成原纤维。此外，Q20 可以使用一种众所周知的解聚集程序来制备具有可忽略的肽间和肽内氢键以及抗聚集性的水溶性 PPII 样构象。
