Department of Pathology , Yale School of Medicine , New Haven , Connecticut 06520 , United States.
Department of Molecular Biophysics & Biochemistry , Yale University , New Haven , Connecticut 06520 , United States.
J Am Chem Soc. 2019 Sep 11;141(36):14168-14179. doi: 10.1021/jacs.9b04995. Epub 2019 Sep 3.
Mitochondrially derived peptides (MDPs) such as humanin (HN) have shown a remarkable ability to modulate neurological amyloids and apoptosis-associated proteins in cells and animal models. Recently, we found that humanin-like peptides also inhibit amyloid formation outside of neural environments in islet amyloid polypeptide (IAPP) fibrils and plaques, which are hallmarks of Type II diabetes. However, the biochemical basis for regulating amyloids through endogenous MDPs remains elusive. One hypothesis is that MDPs stabilize intermediate amyloid oligomers and discourage the formation of insoluble fibrils. To test this hypothesis, we carried out simulations and experiments to extract the dominant interactions between the S14G-HN mutant (HNG) and a diverse set of IAPP structures. Replica-exchange molecular dynamics suggests that MDPs cap the growth of amyloid oligomers. Simulations also indicate that HNG-IAPP heterodimers are 10 times more stable than IAPP homodimers, which explains the substoichiometric ability of HNG to inhibit amyloid growth. Despite this strong attraction, HNG does not denature IAPP. Instead, HNG binds IAPP near the disordered NFGAIL motif, wedging itself between amyloidogenic fragments. Shielding of NFGAIL-flanking fragments reduces the formation of parallel IAPP β-sheets and subsequent nucleation of mature amyloid fibrils. From ThT spectroscopy and electron microscopy, we found that HNG does not deconstruct mature IAPP fibrils and oligomers, consistent with the simulations and our proposed hypothesis. Taken together, this work provides new mechanistic insight into how endogenous MDPs regulate pathological amyloid growth at the molecular level and in highly substoichiometric quantities, which can be exploited through peptidomimetics in diabetes or Alzheimer's disease.
线粒体衍生肽（MDPs），如神经保护因子（HN），在细胞和动物模型中显示出对神经淀粉样蛋白和凋亡相关蛋白的显著调节能力。最近，我们发现 HN 样肽还可以抑制胰岛淀粉样多肽（IAPP）纤维和斑块中神经外环境的淀粉样形成，这是 II 型糖尿病的标志。然而，通过内源性 MDPs 调节淀粉样蛋白的生化基础仍然难以捉摸。一种假设是 MDPs 稳定中间淀粉样寡聚物并阻止不溶性纤维的形成。为了验证这一假设，我们进行了模拟和实验，以提取 S14G-HN 突变体（HNG）与各种 IAPP 结构之间的主要相互作用。复制交换分子动力学表明，MDPs 阻止了淀粉样寡聚物的生长。模拟还表明，HNG-IAPP 杂二聚体比 IAPP 同二聚体稳定 10 倍，这解释了 HNG 以亚化学计量抑制淀粉样蛋白生长的能力。尽管有这种强烈的吸引力，但 HNG 不会使 IAPP 变性。相反，HNG 在无规 NFGAIL 基序附近结合 IAPP，将自身楔入淀粉样蛋白片段之间。NFGAIL 侧翼片段的屏蔽减少了平行 IAPP β-片层的形成，并随后形成成熟的淀粉样纤维核。通过 ThT 光谱和电子显微镜，我们发现 HNG 不会解构成熟的 IAPP 纤维和寡聚物，这与模拟和我们提出的假设一致。总之，这项工作为内源性 MDPs 如何在分子水平上以高度亚化学计量的方式调节病理性淀粉样蛋白的生长提供了新的机制见解，可以通过糖尿病或阿尔茨海默病的肽模拟物加以利用。
