Qiang Wei, Yau Wai-Ming, Schulte Jürgen
Department of Chemistry, Binghamton University, State University of New York, Binghamton, NY 13902-6000, USA; Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
Biochim Biophys Acta. 2015 Jan;1848(1 Pt B):266-76. doi: 10.1016/j.bbamem.2014.04.011. Epub 2014 Apr 22.
Fibrillation of β amyloid (Aβ) peptides and the accumulation of amyloid plaques are considered as an important clinical hallmark to identify Alzheimer's disease (AD). The physiological connection between Aβ plaques and the disruption of neuronal cells has not been clearly understood. One hypothesis to explain the Aβ neurotoxicity is that the fibrillation process induces disruption to the cellular membrane. We studied the Aβ fibrillation process in two biologically relevant conditions with the peptide either pre-incorporated into or externally added to the synthetic phospholipid bilayers. These two sample preparation conditions mimic the physiological membrane proximities of Aβ peptides before and after the enzymatic cleavage of amyloid precursor protein (APP). Using thioflavin T (ThT) fluorescence and transmission electron microscopy (TEM), we were able to monitor the kinetics and morphological evolution of fibril formation, which was highly sensitive to the two sample preparation protocols. While the external addition protocol generates long and mature fibrils through normal fibrillation process, the pre-incubation protocol was found to stabilize the immature protofibrils. Fluorescence spectroscopy studies with doubly-labeled phospholipids indicated that there may be a lipid uptake process associated with the fibril formation. Solid state nuclear magnetic resonance (NMR) spectroscopy provided evidence for high resolution structural variations in fibrils formed with different protocols, and in particular the stabilization of long-range contact between N- and C-terminal β strands. In addition, disruption of phospholipid bilayers was supported by measurements with ³¹P chemical shifts and relaxation time constants.
β淀粉样蛋白（Aβ）肽的纤维化和淀粉样斑块的积累被认为是识别阿尔茨海默病（AD）的重要临床标志。Aβ斑块与神经元细胞破坏之间的生理联系尚未完全清楚。一种解释Aβ神经毒性的假说是，纤维化过程会导致细胞膜破坏。我们在两种生物学相关条件下研究了Aβ纤维化过程，一种是将肽预先掺入合成磷脂双层中，另一种是将肽外部添加到合成磷脂双层中。这两种样品制备条件模拟了淀粉样前体蛋白（APP）酶切前后Aβ肽的生理膜邻近情况。使用硫黄素T（ThT）荧光和透射电子显微镜（TEM），我们能够监测纤维形成的动力学和形态演变，这对两种样品制备方案高度敏感。虽然外部添加方案通过正常纤维化过程产生长而成熟的纤维，但预孵育方案被发现可稳定未成熟的原纤维。用双标记磷脂进行的荧光光谱研究表明，纤维形成过程中可能存在脂质摄取过程。固态核磁共振（NMR）光谱为不同方案形成的纤维中的高分辨率结构变化提供了证据，特别是N端和C端β链之间长程接触的稳定化。此外，通过³¹P化学位移和弛豫时间常数的测量支持了磷脂双层的破坏。
