PDF(Pubmed)
Abstract：
The metabolic processes that link Alzheimer\'s disease (AD) to elevated cholesterol levels in the brain are not fully defined. Amyloid beta (Aβ) plaque accumulation is believed to begin decades prior to symptoms and to contribute significantly to the disease. Cholesterol and its metabolites accelerate plaque formation through as-yet-undefined mechanisms. Here, the mechanism of cholesterol (CH) and cholesterol 3-sulfate (CS) induced acceleration of Aβ42 fibril formation is examined in quantitative ligand binding, Aβ42 fibril polymerization, and molecular dynamics studies. Equilibrium and pre-steady-state binding studies reveal that monomeric Aβ42•ligand complexes form and dissociate rapidly relative to oligomerization, that the ligand/peptide stoichiometry is 1-to-1, and that the peptide is likely saturated in vivo. Analysis of Aβ42 polymerization progress curves demonstrates that ligands accelerate polymer synthesis by catalyzing the conversion of peptide monomers into dimers that nucleate the polymerization reaction. Nucleation is accelerated ∼49-fold by CH, and ∼13,000-fold by CS - a minor CH metabolite. Polymerization kinetic models predict that at presumed disease-relevant CS and CH concentrations, approximately half of the polymerization nuclei will contain CS, small oligomers of neurotoxic dimensions (∼12-mers) will contain substantial CS, and fibril-formation lag times will decrease 13-fold relative to unliganded Aβ42. Molecular dynamics models, which quantitatively predict all experimental findings, indicate that the acceleration mechanism is rooted in ligand-induced stabilization of the peptide in non-helical conformations that readily form polymerization nuclei.
摘要：
将阿尔茨海默病（AD）与大脑中胆固醇水平升高联系起来的代谢过程尚未完全确定。淀粉样β(Aβ)斑块的积累被认为是在症状出现前几十年开始的,并且对该疾病有显著贡献。胆固醇及其代谢物通过尚未确定的机制加速斑块形成。这里,在定量配体结合中检查了胆固醇（CH）和胆固醇3-硫酸盐（CS）诱导的Aβ42原纤维形成加速的机制，Aβ42原纤维聚合，和分子动力学研究。平衡和预稳态结合研究表明，单体Aβ42·配体复合物相对于寡聚化迅速形成和解离，配体/肽的化学计量是1比1,并且肽可能在体内饱和。Aβ42聚合进程曲线的分析表明,配体通过催化肽单体转化为使聚合反应成核的二聚体来加速聚合物合成。核化被CH加速了49倍，和~13,000倍的CS-一种次要的CH代谢物。聚合动力学模型预测，在假定的疾病相关CS和CH浓度下，大约一半的聚合核将含有CS，神经毒性尺寸的小寡聚体(〜12-mer)将含有大量CS，相对于无配体的Aβ42，原纤维形成滞后时间将减少13倍。分子动力学模型,定量预测所有实验结果，表明加速机制植根于配体诱导的肽在容易形成聚合核的非螺旋构象中的稳定。
