Division of Molecular Medicine, Clinical Proteomics Unit, St. John's Research Institute, St. John's National Academy of Health Sciences, 100 Feet Road, Koramangala, Bangalore 560034, India.
Division of Epidemiology & Biostatistics, St. John's Research Institute, St. John's National Academy of Health Sciences, 100 Feet Road, Koramangala, Bangalore 560034, India.
Biochim Biophys Acta Gen Subj. 2019 Jun;1863(6):993-1005. doi: 10.1016/j.bbagen.2019.03.006. Epub 2019 Mar 8.
Aggregation of tau into paired helical filament (PHF) is a hallmark of Alzheimer's disease (AD), and Cys-mediated disulfide bond formation plays a vital role in tau fibrillation. While intermolecular disulfide bond between Cys residues in microtubule-binding repeat (MTBR) region facilitates tau aggregation, intramolecular disulfide bond attenuates the same, though the molecular basis for such phenomenon remains obscure. Thus intramolecular disulfide-bonded tau monomer might be an excellent model to understand the unique features of aggregation-resistant tau conformer.
We synthesized the Cys cross-linked tau40 monomer by oxidation and characterized the altered conformational dynamics in the molecule by Hydrogen-deuterium exchange, limited proteolysis and fluorescence quenching.
Deuterium exchange study showed that rigidity was imparted in the core PHF region of oxidized tau40 in MTBR segment, consisting of the fundamental PHF6 motif. Conformational rigidity was prominent in C-terminal tail region also. Limited proteolysis supported reduced accessibility of MTBR region in the molecule.
PHF formation of oxidized tau40 might be attenuated either by induction of intramolecular H-bonding between the regions of high β-structure propensity in second and third MTBR (R, R), thus preventing intermolecular interaction between them, or by imparted rigidity in R-R, preventing the formation of extended β-structure preceding fibrillation. Data indicated plausible effect of conformational adaptation on the nucleation process of oxidized tau40 assembly.
Our findings unravel the essential molecular features of aggregation-resistant tau conformer. Therapeutics stabilizing such conformers in vivo might be of high benefit in arresting tau assembly during AD and other tauopathies.
tau 聚集成配对螺旋丝（PHF）是阿尔茨海默病（AD）的一个标志，半胱氨酸介导的二硫键形成在 tau 纤维形成中起着至关重要的作用。虽然微管结合重复（MTBR）区域中半胱氨酸残基之间的分子间二硫键有助于 tau 聚集，但分子内二硫键会减弱这种作用，尽管这种现象的分子基础仍不清楚。因此，分子内二硫键结合的 tau 单体可能是理解聚集抗性 tau 构象独特特征的极好模型。
我们通过氧化合成了 Cys 交联的 tau40 单体，并通过氢氘交换、有限蛋白酶解和荧光猝灭来研究分子中改变的构象动力学。
氘交换研究表明，氧化 tau40 的核心 PHF 区域在 MTBR 片段中具有刚性，该片段由基本 PHF6 基序组成。在 C 端尾部区域也存在明显的构象刚性。有限蛋白酶解支持分子中 MTBR 区域的可及性降低。
氧化 tau40 的 PHF 形成可能会减弱，要么是因为第二和第三 MTBR（R，R）中高β-结构倾向区域之间诱导了分子内氢键，从而阻止了它们之间的分子间相互作用，要么是因为 R-R 中赋予了刚性，阻止了纤维形成前扩展β-结构的形成。数据表明构象适应对氧化 tau40 组装成核过程的可能影响。
我们的发现揭示了聚集抗性 tau 构象的基本分子特征。在体内稳定这种构象的治疗方法可能在阻止 AD 和其他 tau 病期间 tau 组装方面具有很高的益处。
