A molecular dynamics study of Amyloid Beta peptide structure near lipid bilayers

描述（由申请人提供）：神经退行性疾病是全世界疾病和死亡的主要原因。这些病症中的许多代表一类蛋白质聚集疾病，其中小的错误折叠蛋白质聚集并导致细胞功能恶化。为了确定这些疾病的适当治疗和潜在治愈方法，必须了解蛋白质错误折叠和聚集的机制。这项工作的长期研究目标是确定老化神经元中促进聚集障碍，特别是阿尔茨海默病常见的毒性结构形成的因素。在阿尔茨海默氏病中，淀粉样蛋白β（A β）肽是可能的聚集物质。在实验中，A β在低肽浓度下不聚集，但将脂质作为囊泡或双层添加到低浓度的A β肽中导致聚集。为了更好地理解脂质影响A β聚集的机制，本提案的目的是确定脂质双层是否通过直接促进肽中纤维样形态的转化来刺激聚集。我们假设A β肽转化为纤维特有的β折叠结构是（1）与阴离子脂质双层表面的静电相互作用直接影响的，（2）与刚性、富含胆固醇的脂筏表面的相互作用促进的。我们还假设高胆固醇含量的双层通过阻止A β插入双层促进原纤维形成，这将A β从可用于聚集的可溶性肽池中隔离。在具体目标1中，将使用分子动力学（MD）模拟来确定脂质头基的电荷是否影响A β结构和膜表面附近的结合自由能。在具体目标2中，MD模拟将通过自由能和二级结构计算来确定双层刚性是否影响A β与胆固醇含量不同的二元脂质/胆固醇混合物表面之间的相互作用。在具体目标3中，将从MD模拟计算A β插入双层的自由能和在不同胆固醇含量的双层内缔合的两种肽的自由能，这将提供对A β潜在孔形成的洞察。这项工作的结果将提供单个肽水平的细节，以确定膜在A β聚集途径中的作用。使用这些结果，再加上对A β聚集的实验工作，A β聚集及其在阿尔茨海默病神经元毒性中的功能的更清晰描述可用于开发治疗方法，以阻止进展或可能预防和治愈最致命的神经退行性疾病之一，阿尔茨海默病。

DESCRIPTION (provided by applicant): Neurodegenerative disorders are a major cause of sickness and death throughout the world. Many of these disorders represent a class of protein aggregation diseases wherein small misfolded proteins aggregate and lead to deteriorating cellular function. To determine appropriate treatments and potential cures for these disorders, it is imperative to understand the mechanism by which proteins misfold and aggregate. The long- term research goal of this work is to identify factors in aged neurons that promote formation of toxic structures common to aggregation disorders, in particular Alzheimer's disease. In Alzheimer's disease, the Amyloid Beta (A Beta) peptide is the probable aggregate species. In experiments, A Beta does not aggregate at low peptide concentrations, but the addition of lipids as vesicles or bilayers to a low concentration of A Beta peptides leads to aggregation. To better understand the mechanism by which lipids influence A Beta aggregation, the objective of this proposal is to determine if lipid bilayers stimulate aggregation by directly promoting a conversion to a fibril-like morphology in peptides. We hypothesize that conversion of A Beta peptides to Beta-sheet structure characteristic of fibrils is (1) directly influenced by electrostatic interactions with the surface of anionic lipid bilayers and (2) promoted by interactions with the surface of rigid, cholesterol-rich lipid rafts. We also hypothesize that bilayers of high cholesterol content promote fibril formation by preventing A Beta insertion into the bilayer, which sequesters A Beta from the pool of soluble peptides available for aggregation. In specific aim 1, molecular dynamics (MD) simulations will be used to determine if the charge of lipid headgroups influence A Beta structure and binding free energies near the membrane surface. In specific aim 2, MD simulations will ascertain, by free energy and secondary structure calculations, if bilayer rigidity affects interactions between A Beta and the surface of binary lipid/cholesterol mixtures of varying cholesterol content. In specific aim 3, both the free energy of insertion of A Beta into bilayers and the free energy of two peptides associating within bilayers of varying cholesterol content will be calculated from MD simulations, which will provide insight into potential pore formation by A Beta. The results of this work will provide details on a single peptide level to determine the role of membranes in the A Beta aggregation pathway. Using these results, coupled with experimental work on A Beta aggregation, a clearer description of A Beta aggregation and its function in neuron toxicity in Alzheimer's disease can be used to develop treatments to either halt the progression or possibly prevent and cure one of the most lethal neurodegenerative disorders, Alzheimer's disease.