Structure Of Beta Amyloid Fibrils

阿尔茨海默病与淀粉样β蛋白(Ab)的异常沉积有关，这种蛋白以纤维形式出现在大脑神经纤维中。为了表征这些纤维在不同pH条件下的聚集方式，我们对合成的全长抗体多肽以及各种截短序列的抗体多肽进行了透射电子显微镜(TEM)和扫描电子显微镜(STEM)观察。负染制剂的透射电子显微镜图像提供了有关原纤维宽度和形态的信息，而未染色制剂的STEM分析提供了每长度质量(MPL)的定量测定，从而确定了原纤维中的β-片数。综上所述，这些结果揭示了从阿尔茨海默氏症相关抗体多肽生长出来的纤维的结构是如何依赖于生长条件的，包括蛋白质浓度和pH。MPL测量揭示了基本发光单元或“原丝”的存在，它由定义明确的交叉贝塔片数组成。NIDDK的科学家正在利用EM水平上纤维形态的变化与核磁共振光谱获得的关于肽骨架构象的原子水平信息相关联。最近的STEM测量表明，由双β片组成的纤维与含有三β片的纤维在不同的生长条件下形成。

Alzheimer's disease is associated with the abnormal deposits of amyloid beta protein (Ab) that occurs as fibrils within the cerebral neuropil. To characterize the way in which these fibrils assemble under different pH conditions, we have performed transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) on synthetic full-length Ab peptides as well as various Ab peptides with truncated sequences. TEM images of negatively stained preparations provide information about the fibril width and morphology, and STEM analysis of unstained preparations provides a quantitative determination of the mass-per-length (MPL) and thus the numbers of beta-sheets within fibrils. Taken together the results reveal how the structure of fibrils grown from Alzheimer-related Ab peptides depend on the growth conditions, including protein concentration and pH. MPL measurements reveal the existence of fundamental fibrillizing units, or "protofilaments," consisting of well-defined numbers of cross-beta sheets. Variations in fibril morphology at the EM level are being used by scientists in NIDDK to correlate with atomic-level information about the peptide backbone conformation obtained from NMR spectroscopy. Recent STEM measurements have shown that fibrils composed of double beta sheets form under different growth conditions than fibrils containing triple beta sheets.