Amyloid-β (Aβ) peptide and tau protein are two hallmark proteins in Alzheimer's disease (AD), however the parameters which mediate the abnormal aggregation of Aβ and tau have not been fully discovered. Here, we have provided an optimum method to purify tau protein isoform 1N4R by using Ni-NTA agarose chromatography under denaturing condition. The biochemical and biophysical properties of the purified protein was further characterized using in vitro tau filament assembly, tubulin polymerization assay, circular dichroism (CD) spectroscopy and atomic force microscopy. Afterwards, we investigated the effect of tau protein on aggregation of Aβ (25–35) peptide using microscopic imaging and cell viability assay. Incubation of tau at physiologic and supra-physiologic concentrations with Aβ_25–35 for forty days under reducing and non-reducing conditions revealed formation of two types of aggregates with distinct morphologies and dimensions. In non-reducing condition, the co-incubated sample showed granular aggregates, while in reducing condition, they formed annular protofibrils. Results from cell viability assay revealed the increased cell viability for the co-incubated sample. Therefore, the disassembling action shown by tau protein on Aβ_25–35 suggests the possibility that tau may have a protective role in preventing Aβ peptide from acquiring the cytotoxic, aggregated form against oxidative stress damages.

中文翻译：

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在还原和非还原条件下，亚型1N4R tau蛋白与淀粉样β肽片段25-35相互作用。

淀粉样蛋白-β（Aβ）肽和tau蛋白是阿尔茨海默病（AD）的两个标志性蛋白，但是尚未完全找到介导Aβ和tau异常聚集的参数。在这里，我们提供了一种在变性条件下使用Ni-NTA琼脂糖色谱纯化tau蛋白同工型1N4R的最佳方法。纯化的蛋白的生物化学和生物物理特性使用体外tau细丝组装，微管蛋白聚合测定，圆二色性（CD）光谱和原子力显微镜进一步表征。之后，我们使用显微镜成像和细胞活力分析研究了tau蛋白对Aβ（25–35）肽聚集的影响。在用Aβ生理和超生理浓度tau的孵育_25-35在还原和非还原条件下四十天发现形成了两种形态和尺寸各异的聚集体。在非还原条件下，共同孵育的样品显示出颗粒状聚集体，而在还原条件下，它们形成环形原纤维。细胞活力测定的结果表明，共孵育样品的细胞活力增加。因此，通过τ蛋白对Aβ所示的拆卸动作_25-35表明的可能性，tau蛋白可以具有在防止Aβ肽从获取的细胞毒，抗氧化应激损伤聚集形式的保护性作用。