The natively unfolded character of Tau and its aggregation to Alzheimer-like paired helical filaments
The natively unfolded character of Tau and its aggregation to Alzheimer-like paired helical filaments
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DOI：
10.1021/bi800783d
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发表时间：
2008-10-07
期刊：
影响因子：
2.9
通讯作者：
Mandelkow, Eckhard
中科院分区：
文献类型：
--
作者：
Jeganathan, Sadasivam;von Bergen, Martin;Mandelkow, Eckhard
微管相关蛋白Tau异常聚集成成对的螺旋丝(PHF)是阿尔茨海默病(AD)的特征之一。Tau在溶液中表现为一种天然的未折叠或本质上无序的蛋白质，而它的聚集是基于从随机卷曲到结构的部分结构转变。我们的目的是更详细地了解Tau的展开性质，研究Tau在不同条件下的聚集以及Tau在细丝中的分子相互作用。我们发现，与其他未折叠的蛋白质相比，即使在净电荷最小的情况下，可溶的Tau仍然保持天然的未折叠状态。Tau的无规卷曲特征的CD特征在电荷(PH)、离子强度、溶剂极性和变性的广泛变化中没有明显的变化。因此，无论是在微管结合的重复结构域结构中，还是在全长的Tau中，都没有迹象表明疏水性驱动的折叠。这认为，缺乏疏水残基，而不是净电荷，是可溶性Tau展开的原因。在成核多阴离子辅因子(肝素)存在下，Tau重复结构域(构成PHF的核心)的聚集在一系列缓冲液和pH值类似于5到10的范围内是有效的，但超过该范围就会分解，可能是因为带电相互作用的模式消失了。同样，升高的离子强度会减弱聚集，温度依赖关系是钟形的，最佳温度在50℃左右。报道染料和ANS记录了聚集过程，但以不同的动力学检测不同的状态(交叉贝塔结构与疏水口袋)。预制的PHF令人惊讶地不稳定，在相当低的浓度下(类似于1.0M GdnHCl)可以被变性剂破坏，远低于变性球状蛋白所需的浓度。CD和EM监测到的Tau纤维在极端pH值下的部分解聚表明了盐桥在纤维形成中的重要作用。相比之下，Tau长丝具有显著的耐高温和高离子强度。总体而言，PHF的稳定性似乎主要取决于直接盐桥以及疏水相互作用的贡献，这与最近从固体核磁共振(Andronesi，O.C.，von Bergen，M.，Biernat，J.，Seidel，K.，Griesinger，C.，Mandelkow，E.和Baldus，M.)获得的PHF核心结构模型一致(2008)使用固态核磁共振光谱表征了tau蛋白核心域中类似阿尔茨海默氏症的成对螺旋细丝。
The abnormal aggregation of the microtubule-associated protein Tau into paired helical filaments (PHFs) is one of the hallmarks of Alzheimer disease (AD). Tau in solution behaves as a natively unfolded or intrinsically disordered protein while its aggregation is based on the partial structural transition from random coil to-structure. Our aim is to understand in more detail the unfolded nature of Tau, to investigate the aggregation of Tau under different conditions and the molecular interactions of Tau in filaments. We show that soluble Tau remains natively unfolded even when its net charge is minimized, in contrast to other unfolded proteins. The CD signature of the random-coil character of Tau shows no major change over wide variations in charge (pH), ionic strength, solvent polarity, and denaturation. Thus there is no indication of a hydrophobicity-driven collapse, neither in the microtubule-binding repeat domain constructs nor in full-length Tau. This argues that the lack of hydrophobic residues but not the net charge accounts for unfolded nature of soluble Tau. The aggregation of the Tau repeat domain (that forms the core of PHFs) in the presence of nucleating polyanionic cofactors (heparin) is efficient in a range of buffers and pH values between similar to 5 and 10 but breaks down beyond that range, presumably because the pattern of charged interactions disappears. Similarly, elevated ionic strength attenuates aggregation, and the temperature dependence is bell-shaped with an optimum around 50 degrees C. Reporter dyes ThS and ANS record the aggregation process but sense different states (cross-beta-structure vs hydrophobic pockets) with different kinetics. Preformed PHFs are surprisingly labile and can be disrupted by denaturants at rather low concentration (similar to 1.0 M GdnHCl), much less than required to denature globular proteins. Partial disaggregation of Tau filaments at extreme pH values monitored by CD and EM indicate the importance of salt bridges in filament formation. In contrast, Tau filaments are remarkably resistant to high temperature and high ionic strength. Overall, the stability of PHFs appears to depend mainly on directed salt bridges with contributions from hydrophobic interactions as well, consistent with a recent structural model of the PHF core derived from solid state NMR (Andronesi, O. C., von Bergen, M., Biernat, J., Seidel, K., Griesinger, C., Mandelkow, E., and Baldus, M. (2008) Characterization of Alzheimer's-like paired helical filaments from the core domain of tau protein using solid-state NMR spectroscopy.