Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706-1396.
Proc Natl Acad Sci U S A. 2014 Apr 22;111(16):5796-801. doi: 10.1073/pnas.1401587111. Epub 2014 Feb 18.
Polyglutamine (polyQ) sequences are found in a variety of proteins, and mutational expansion of the polyQ tract is associated with many neurodegenerative diseases. We study the amyloid fibril structure and aggregation kinetics of K2Q24K2W, a model polyQ sequence. Two structures have been proposed for amyloid fibrils formed by polyQ peptides. By forming fibrils composed of both (12)C and (13)C monomers, made possible by protein expression in Escherichia coli, we can restrict vibrational delocalization to measure 2D IR spectra of individual monomers within the fibrils. The spectra are consistent with a β-turn structure in which each monomer forms an antiparallel hairpin and donates two strands to a single β-sheet. Calculated spectra from atomistic molecular-dynamics simulations of the two proposed structures confirm the assignment. No spectroscopically distinct intermediates are observed in rapid-scan 2D IR kinetics measurements, suggesting that aggregation is highly cooperative. Although 2D IR spectroscopy has advantages over linear techniques, the isotope-mixing strategy will also be useful with standard Fourier transform IR spectroscopy.
多聚谷氨酰胺（polyQ）序列存在于多种蛋白质中，polyQ 序列的突变扩展与许多神经退行性疾病有关。我们研究了 K2Q24K2W 的淀粉样纤维结构和聚集动力学，这是一个模型 polyQ 序列。由 polyQ 肽形成的淀粉样纤维有两种结构假设。通过在大肠杆菌中表达蛋白质，形成由（12）C 和（13）C 单体组成的纤维，可以限制振动离域，从而测量纤维内单个单体的 2D IR 光谱。该光谱与β-转角结构一致，其中每个单体形成一个反平行发夹，并向单个β-片贡献两条链。两种假设结构的原子分子动力学模拟计算光谱证实了该结构。在快速扫描 2D IR 动力学测量中没有观察到光谱上明显不同的中间体，这表明聚集具有高度协同性。尽管 2D IR 光谱比线性技术具有优势，但同位素混合策略也将与标准傅里叶变换 IR 光谱一样有用。
