淀粉样蛋白病理性聚集及αB-crystallin内源性蛋白对其调控机制的分子模拟研究

The pathological self-assembly of normally soluble intrinsic amyloid proteins into ordered insoluble amyloid fibers is associated with more than 35 human diseases, including Alzheimer’s, Parkinson’s, and type II diabetes (T2D). Despite the differences in primary, secondary and tertiary structures of precursor proteins, experimental studies using x-ray crystallography, solid-state NMR or cryo-EM have demonstrated that the final amyloid fibrils share a common cross-β core structure with β-strands aligned perpendicular to the fibril axis and multiple β-sheets facing each other. More and more experimental evidences suggest that soluble low molecular weight oligomer intermediates are more cytotoxic than mature fibrils. However, these oligomers are not generally stable, transient, heterogenous and dynamic, which makes experimental challenging to characterize their structure. Characterization of these oligomeric intermediates pinpointing the toxic oligomer species are thus crucial for both understanding the pathogenesis and designing therapeutic approaches for the treatment of amyloid diseases. Thus, in this project we plan to apply computational molecular dynamic simulation to study the oligomerization and fibrillization of multiple amyloidogenic core segments. Together with the oligomerization and nucleation investigation of full-length hIAPP/Aβ from monomer to hexamer multiple systems simulation uncover their aggregation mechanism. Numerous experimental studies have demonstrated that amyloid formation pathways can be manipulated by small molecules, nanoparticles and chaperone proteins. Comparing with the small molecules and nanoparticles the inherent biocompatibility of chaperone proteins, found in many regions of human body, displayed good promising in amyloid disease treatment. Lots of experiments studies revealed that the small heat-shock chaperon protein αB-crystallin could inhibit amyloid protein aggregation by directly binding the monomer or proto-fibrils of amyloid peptides (e. g. Aβ, α-synuclein，tau), but the detail mechanism was still elusive. In this project, we plan to use computational simulation to detect the inhibition mechanism of αB-crystallin against amyloid peptides aggregation and to provide theoretical insights for the future amyloid disease drug development. Overall, we plan to uncover the mechanism of amyloid protein (e. g. Aβ, hIAPP) oligomerization/fibrillization and the inhibitory mechanism of amyloid peptides aggregation by the αB-crystallin，which will be helpful in the design of therapeutic agents to amyloid degenerative diseases.

天然无序淀粉样蛋白病理性聚集引起的退行性疾病多达35种。这些淀粉样多肽高度柔性、天然无序，聚集过程中间产物存在时间极短，构象间相互转变极其频繁复杂多样，使得实验上对寡聚物的结构解析非常困难。淀粉样多肽从单体到淀粉样沉淀的寡聚化、纤维化的微观聚集机理目前尚不清楚,也导致对淀粉样多肽聚集相关疾病的药物设计进展缓慢。为了在原子层面揭示淀粉蛋白病理性聚集的微观机理，我们计划通过计算机模拟方法来研究淀粉样多肽片段和全长的寡聚化、纤维化的聚集动力学，揭示其病理性聚集机理。目前已有实验数据显示αB-crystallin内源蛋白可以有效抑制天然无序淀粉样蛋白的病理性聚集和细胞毒性，但是其抑制机理目前尚不清楚。因此，我们计划通过分子动力学模拟研究淀粉样蛋白与αB-crystallin内源蛋白作用机理，在原子层面揭示该蛋白对淀粉样蛋白聚集的调控机理，为未来淀粉样蛋白病理性聚集的抗体设计提供理论数据支持。

蛋白质多肽由游离单体聚集成形态特异且结构高度纤维结构是阿兹海默症等淀粉样退行性病的主要临床表现。大量实验研究发现相比于成熟的淀粉样纤维沉积物，淀粉样多肽聚集产生的中间态寡聚物的细胞毒性更强。因此，揭示淀粉样多肽病理性纤维化聚集分子机制，特别是中间态毒性寡聚物结构，对阐明淀粉样退行性病致病机理以及针对此类疾病的临床诊断药物的开发设计至关重要。人体内源性多肽生物兼容性好、无细胞毒性等优点，内源性多肽对淀粉样病理性聚集的调控也引起科学家的广泛关注，深度揭示人体内源性多肽对淀粉样蛋白调控的分子机理也是针对淀粉样退行性疾病多肽临床药物开发的关键所在。在本项目执行期间，项目负责人团队基于理论模拟结合实验论证探究了不同细胞毒性蛋白质多肽寡聚化和纤维化分子机制以及寡聚物构象特征，提出β-sheet 桶构象模型是Aβ等淀粉多肽潜在毒性寡聚体结构，该理论预测模型也随之在Aβ聚集过程中被其他课题组通过冷冻电镜构象表征证实。此外，我们基于分子动力学模拟探究了αB-crystallin内源性蛋白与淀粉样Aβ多肽单体及寡聚体的动力学结合过程以及其复合寡聚物构象特征，发现αB-crystallin会特异性结合到Aβ单体以及寡聚体的β-sheet生长面，从而阻止其进一步聚集和向纤维结构转变，该作用机理也会抑制纤维种子的生长。本项目所提出的淀粉样多肽寡聚物构象模型和阐明的αB-crystallin对Aβ抑制分子机理对揭示淀粉样退行性疾病的致病机理以及此类疾病的多肽临床药物开发具有重要的理论指导意义。