The microtubule-associated protein tau aggregates into distinct neurofibrillary tangles in brains afflicted with multiple neurodegenerative diseases such as Alzheimer’s disease and corticobasal degeneration (CBD). The mechanism of tau misfolding and aggregation is poorly understood. Determining the structure, dynamics, and water accessibility of tau filaments may provide insight into the pathway of tau misfolding. Here, we investigate the hydration and dynamics of the β-sheet core of heparin-fibrillized 0N4R tau using solid-state nuclear magnetic resonance spectroscopy. This β-sheet core consists of the second and third microtubule-binding repeats, R2 and R3, respectively, which form a hairpin. Water-edited two-dimensional (2D) ¹³C–¹³C and ¹⁵N–¹³C correlation spectra show that most residues in R2 and R3 domains have low water accessibility, indicating that this hairpin is surrounded by other proteinaceous segments. However, a small number of residues, especially S285 and S316, are well hydrated compared to other Ser and Thr residues, suggesting that there is a small water channel in the middle of the hairpin. To probe whether water accessibility correlates with protein dynamics, we measured the backbone N–H dipolar couplings of the β-sheet core. Interestingly, residues in the fourth microtubule-binding repeat, R4, show rigid-limit N–H dipolar couplings, even though this domain exhibits weaker intensities in the 2D ¹⁵N–¹³C correlation spectra. These results suggest that the R4 domain participates in cross-β hydrogen bonding in some of the subunits but exhibits dynamic disorder in other subunits. Taken together, these hydration and dynamics data indicate that the R2–R3 hairpin of 0N4R tau is shielded from water by other proteinaceous segments on the exterior but contains a small water pore in the interior. This structural topology has various similarities with the CBD tau fibril structure but also shows specific differences. The disorder of the R4 domain and the presence of a small water channel in the heparin-fibrillized 4R tau have implications for the structure of tau fibrils in diseased brains.

中文翻译：

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通过固态核磁共振研究全长 Tau 淀粉样蛋白原纤维的水合作用和动力学。

微管相关蛋白 tau 在患有多种神经退行性疾病（如阿尔茨海默病和皮质基底节变性 (CBD)）的大脑中聚集成不同的神经原纤维缠结。tau 错误折叠和聚集的机制知之甚少。确定 tau 细丝的结构、动力学和水可及性可以深入了解 tau 错误折叠的途径。在这里，我们使用固态核磁共振波谱研究了肝素原纤维化 0N4R tau 的 β 折叠核心的水合作用和动力学。该 β-折叠核心由第二个和第三个微管结合重复序列 R2 和 R3 组成，分别形成发夹。水编辑二维 (2D) ¹³ C– ¹³ C 和¹⁵ N– ¹³C 相关谱显示 R2 和 R3 域中的大多数残基具有低水可及性，表明该发夹被其他蛋白质片段包围。然而，与其他 Ser 和 Thr 残基相比，少数残基，尤其是 S285 和 S316，水合良好，表明发夹中间有一个小的水通道。为了探究水的可及性是否与蛋白质动力学相关，我们测量了 β-折叠核心的骨架 N-H 偶极耦合。有趣的是，第四个微管结合重复序列 R4 中的残基显示出刚性极限 N–H 偶极耦合，尽管该域在 2D ¹⁵ N– ^{13 中}表现出较弱的强度C 相关光谱。这些结果表明 R4 结构域参与了一些亚基中的交叉 β 氢键，但在其他亚基中表现出动态无序。综上所述，这些水合作用和动力学数据表明 0N4R tau 的 R2-R3 发夹被外部的其他蛋白质片段挡住水，但在内部包含一个小水孔。这种结构拓扑与 CBD tau 原纤维结构有各种相似之处，但也显示出特定的差异。R4 结构域的紊乱和肝素原纤维化 4R tau 中小水通道的存在对患病大脑中 tau 原纤维的结构有影响。