纳米颗粒调控淀粉样肽聚集的物理机制研究

Protein/peptide misfolding and aggregation are associated with many amyloidosis such as Alzheimer disease. The inhibition of amyloid formation has been considered as the primary therapeutic strategy for the amyloidosis diseases. In recent years, nanoparticles have been received considerable attention due to their potential applications in the field of nanomedicine. Experimental studies have shown that nanoparticles inhibit/promote amyloid formation by increasing/decreasing the nucleation process. However, the details of molecular interactions between amyloid peptide and nanoparticle are still not well understood. In this proposal, we investigate the detailed interactions of different nanoparticles (including carbon nanoparticles and covalently functionalized carbon-nanoparticles) with Alzheimer's amyloid beta peptide as well as its different fragments by performing molecular dynamics and replica-exchange molecular dynamics simulations in explicit solvent comined with experimental methods. We will examine the impact of hydrophobicity, hydrophilicity, size, shape, and concentration of nanoparticles on the dynamics and thermodynamics of amyloid peptide oligomerization. The structure, aggregation path, and the free energy surface of amyloid ologomers will be identified. The aim of this project is to reveal the molecular mechanism of nanoparticle-mediated amyloid peptide aggregation. The results and the findings would provide new clues for the development of drug candidates against amyloidosis.

淀粉样肽的错误折叠和聚集（或纤维化）与阿兹海默症等多种淀粉样变性病密切相关，人们一直在寻找能有效抑制淀粉样肽聚集的抑制剂。由于纳米颗粒较短肽抑制剂能更容易地通过血脑屏障进入人体，纳米颗粒调控淀粉样肽聚集的研究越来越受到人们的关注。然而，由于二者相互作用的复杂性，纳米颗粒抑制或促进淀粉样肽纤维化的微观机理尚不清楚。本项目拟采用分子动力学、副本交换分子动力学模拟、和实验方法，以碳纳米颗粒（包括碳纳米管和富勒烯）和表面修饰不同基团的碳纳米颗粒与阿兹海默症beta淀粉样肽及其不同氨基酸片段的相互作用为主要研究内容，通过分析纳米颗粒的大小、形状、浓度、亲疏水性、带电性等对淀粉样肽聚集的影响，揭示淀粉样肽的构象动力学、聚集体结构、聚集路径、聚集自由能面及与纳米颗粒作用的关键氨基酸，找出影响聚集的主要因素，阐明纳米颗粒调控淀粉样肽聚集的物理机制。此研究将为开发治疗淀粉样变性病相关药物提供新的思路。

本项目主要采用常规分子动力学和增强采样副本交换分子动力学模拟，并辅以原子力显微成像等实验手段，主要研究了碳纳米颗粒（碳管、富勒烯C60和C180，和石墨烯）的大小、形状、浓度和表面修饰不同基团（羟基、羧基和二甲氧基甲烷）的碳纳米颗粒对阿兹海默氏beta-淀粉样肽（Ab1-42）以及不同氨基酸片段（包括疏水的Ab16-22和Ab33-42、以及亲水的GNNQQNY）聚集体结构和聚集自由能面的影响及其背后的物理机制。另外，还探索了人胰岛淀粉样多肽（hIAPP）的聚集机制以及羟基化富勒烯和富勒烯的羟基化程度对其聚集体结构和纤维化的影响。主要结果为：1）当C60与Ab16-22的摩尔比大于1:8时，C60能明显抑制双层beta-片结构的形成和Ab16-22的纤维化。在相同纳米颗粒浓度下，碳纳米管、C180和C60对Ab16-22 beta-片层的形成均具有显著的抑制作用，碳管的抑制效果最强，C180的次之，C60的最弱，表明六元环比五元环对抑制beta-片的形成更加重要。2）羟基化的碳管与Ab16-22间存在强的疏水和静电相互作用，这种作用严重减弱了对双层beta-片层的形成起关键作用的F19-F19间的芳香环堆积作用和F19-L17间的疏水相互作用，从而抑制Ab16-22的纤维化。我们的AFM实验进一步验证了模拟结果。3）二甲氧基甲烷富勒烯（DMF）通过结合到Aβ1-42二聚体关键疏水核心区域LVFFA、包含F4和Y10的芳香族氨基酸区域、和C-端疏水氨基酸区域AIIGLMV，来抑制A的聚集和纤维化。DMF主要通过三种机制（芳香环堆积、疏水作用和曲率匹配）分别结合到Ab1-42原纤维的三个位点：LVFFA疏水核心区、NKGAI转角区、和C-端的IIGLMVGGVVI beta-片层区域。其中结合到转角区会破坏对Ab纤维化起关键作用的D23-K28盐桥，从而破坏原纤维结构。4）大尺寸的氧化石墨烯与Ab33-42之间的有效接触面积更大、形成的氢键更多、相互作用更强，对Aβ33-42聚集的抑制效果更好，此发现从原子水平解释了文献中报道的实验现象。5）碳纳米颗粒主要通过疏水和芳香环堆积作用来抑制疏水氨基酸多肽的聚集，通过与亲水氨基酸的脂肪族集团的疏水作用来抑制亲水氨基酸多肽的聚集。研究结果对淀粉样变性病相关药物的设计和开发提供了理论依据和新的思路。