Arya Shruti, Ganguly Pritam, Arsiccio Andrea, Claud Sarah L, Trapp Benjamin, Schonfeld Grace E, Liu Xikun, Lazar Cantrell Kristi, Shea Joan-Emma, Bowers Michael T
Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States.
Department of Chemistry, Westmont College, Santa Barbara, California 93108, United States.
J Phys Chem B. 2020 Oct 8;124(40):8772-8783. doi: 10.1021/acs.jpcb.0c05768. Epub 2020 Sep 9.
Aberrant protein folding leading to the formation of characteristic cross-β-sheet-rich amyloid structures is well known for its association with a variety of debilitating human diseases. Often, depending upon amino acid composition, only a small segment of a large protein participates in amyloid formation and is in fact capable of self-assembling into amyloid, independent of the rest of the protein. Therefore, such peptide fragments serve as useful model systems for understanding the process of amyloid formation. An important factor that has often been overlooked while using peptides to mimic full-length protein is the charge on the termini of these peptides. Here, we show the influence of terminal charges on the aggregation of an amyloidogenic peptide from microtubule-associated protein Tau, implicated in Alzheimer's disease and tauopathies. We found that modification of terminal charges by capping the peptide at one or both of the termini drastically modulates the fibrillation of the hexapeptide sequence paired helical filament 6 (PHF6) from repeat 3 of Tau, both with and without heparin. Without heparin, the PHF6 peptide capped at both termini and PHF6 capped only at the N-terminus self-assembled to form amyloid fibrils. With heparin, all capping variants of PHF6, except for PHF6 with both termini free, formed typical amyloid fibrils. However, the rate and extent of aggregation both with and without heparin as well as the morphology of aggregates were found to be highly dependent on the terminal charges. Our molecular dynamics simulations on PHF6 capping variants corroborated our experiments and provided critical insights into the mechanism of PHF6 self-assembly. Overall, our results emphasize the importance of terminal modifications in fibrillation of small peptide fragments and provide significant insights into the aggregation of a small Tau fragment, which is considered essential for Tau filament assembly.
异常的蛋白质折叠导致富含特征性交叉β-折叠的淀粉样结构形成，这与多种使人衰弱的人类疾病相关，这是众所周知的。通常，取决于氨基酸组成，大蛋白质中只有一小部分参与淀粉样形成，并且实际上能够独立于蛋白质的其余部分自组装成淀粉样。因此，此类肽片段可作为理解淀粉样形成过程的有用模型系统。在使用肽模拟全长蛋白质时，一个经常被忽视的重要因素是这些肽末端的电荷。在这里，我们展示了末端电荷对来自微管相关蛋白Tau的淀粉样生成肽聚集的影响，该蛋白与阿尔茨海默病和tau蛋白病有关。我们发现，通过在一个或两个末端封闭肽来修饰末端电荷，会显著调节来自Tau重复3的六肽序列配对螺旋丝6（PHF6）的纤维化，无论有无肝素。没有肝素时，两端封闭的PHF6肽和仅在N端封闭的PHF6自组装形成淀粉样纤维。有肝素时，除了两端都游离的PHF6外，PHF6的所有封闭变体都形成了典型的淀粉样纤维。然而，发现无论有无肝素，聚集的速率和程度以及聚集体的形态都高度依赖于末端电荷。我们对PHF6封闭变体的分子动力学模拟证实了我们的实验，并为PHF6自组装机制提供了关键见解。总体而言，我们的结果强调了末端修饰在小肽片段纤维化中的重要性，并为小Tau片段的聚集提供了重要见解，小Tau片段被认为是Tau丝组装所必需的。
