Department of Chemistry, Tongji University, Shanghai 200092, China.
Biochemistry. 2013 Mar 19;52(11):1893-902. doi: 10.1021/bi400240c. Epub 2013 Mar 6.
Inhibition of anomalous aggregation of tau protein would be an attractive therapeutic target for Alzheimer's disease (AD). In this study, tannic acid (TA), a polymeric plant polyphenol, and its monomer, gallic acid (GA), were introduced as the references to afford a molecular framework that integrates tau binding properties and inhibitory effects. Using a thioflavin S fluorescence assay and electron microscopy, we demonstrated that TA could competently inhibit the in vitro aggregation of tau peptide R3, corresponding to the third repeat unit of the microtubule-binding domain, with an IC50 of 3.5 μM, while GA's inhibition was comparatively piddling (with an IC50 of 92 μM). In the isothermal titration calorimetry experiment, we found that TA could strongly bind to R3 with a large amount of heat released. Circular dichroism spectra showed TA dose-dependently suppressed the conformational transition of R3 from a random coil structure to a β-sheet structure during the aggregation process. Finally, a structural model was built using molecular docking simulation to elucidate the possible binding sites for TA on the tau peptide surface. Our results suggest that TA recognizably interacts with tau peptide by forming a hairpin binding motif, a key framework required for inhibiting tau polymerization, in addition to hydrogen bonding, hydrophilic-hydrophobic interactions, and static electrical interactions, as reported previously. The inhibitory effect of TA on human full-length tau protein (tau441) was also verified by electron microscopy. This finding hints at the possibility of TA as a leading compound of anti-AD drugs and offers a new stratagem for the rational molecular design of a tau aggregation inhibitor.
抑制 tau 蛋白的异常聚集将成为治疗阿尔茨海默病（AD）的一个有吸引力的治疗靶点。在这项研究中，单宁酸（TA），一种聚合植物多酚，及其单体没食子酸（GA），被引入作为参考，提供了一个整合 tau 结合特性和抑制作用的分子框架。通过硫黄素 S 荧光测定法和电子显微镜，我们证明 TA 能够有效地抑制微管结合域第三重复单元的 tau 肽 R3 的体外聚集，IC50 为 3.5 μM，而 GA 的抑制作用相对微不足道（IC50 为 92 μM）。在等温滴定量热实验中，我们发现 TA 可以与 R3 强烈结合，并释放大量热量。圆二色性光谱表明 TA 剂量依赖性地抑制了 R3 在聚集过程中从无规卷曲结构向 β-折叠结构的构象转变。最后，使用分子对接模拟构建了一个结构模型，以阐明 TA 在 tau 肽表面上的可能结合位点。我们的结果表明，TA 通过形成发夹结合基序与 tau 肽明显相互作用，这是抑制 tau 聚合所必需的关键框架，除了氢键、亲水-疏水相互作用和静电相互作用，如先前报道的那样。TA 对人全长 tau 蛋白（tau441）的抑制作用也通过电子显微镜得到了验证。这一发现暗示了 TA 作为抗 AD 药物先导化合物的可能性，并为 tau 聚集抑制剂的合理分子设计提供了一种新策略。
