Department of Materials Science and Engineering, University of California, Los Angeles, California, 90095.
Department of Neurology, David Geffen School of Medicine at UCLA, 635 Charles E. Young Drive South, Room 445, Los Angeles, California, 90095.
Protein Sci. 2018 Aug;27(8):1427-1438. doi: 10.1002/pro.3434. Epub 2018 Jul 10.
Amyloid β-protein (Aβ) self-association is one process linked to the development of Alzheimer's disease (AD). Aβ peptides, including its most abundant forms, Aβ40 and Aβ42, are associated with the two predominant neuropathologic findings in AD, vascular and parenchymal amyloidosis, respectively. Efforts to develop therapies for AD often have focused on understanding and controlling the assembly of these two peptides. An obligate step in these efforts is the monitoring of assembly state. We show here that surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) readily distinguishes Aβ40 and Aβ42. We show further, through comparison of assembly dependent changes in secondary structure and morphology, that the SERS/PCA approach unambiguously differentiates closely related assembly stages not readily differentiable by circular dichroism spectroscopy, electron microscopy, or other techniques. The high discriminating power of SERS/PCA is based on the rich structural information present in its spectra, which comprises not only on interatomic resonances between covalently associated atoms and hydrogen bond interactions important in controlling secondary structure, but effects of protein orientation relative to the substrate surface. Coupled with the label-free, single molecule sensitivity of SERS, the approach should prove useful for determining structure activity relationships, suggesting target sites for drug development, and for testing the effects of such drugs on the assembly process. The approach also could be of value in other systems in which assembly dependent changes in protein structure correlate with the formation of toxic peptide assemblies.
淀粉样 β 蛋白（Aβ）的自缔合是与阿尔茨海默病（AD）发展相关的过程之一。Aβ 肽，包括其最丰富的形式 Aβ40 和 Aβ42，分别与 AD 中两种主要的神经病理学发现——血管淀粉样变性和实质淀粉样变性相关。开发 AD 治疗方法的努力通常集中在理解和控制这两种肽的组装上。这些努力中的一个必要步骤是监测组装状态。我们在这里展示，表面增强拉曼光谱（SERS）与主成分分析（PCA）相结合，可以轻松区分 Aβ40 和 Aβ42。我们进一步通过比较二级结构和形态依赖的组装变化表明，SERS/PCA 方法可以明确区分难以通过圆二色光谱、电子显微镜或其他技术区分的密切相关的组装阶段。SERS/PCA 的高区分能力基于其光谱中存在的丰富结构信息，这些信息不仅包括共价结合原子之间的原子间共振和对二级结构控制很重要的氢键相互作用，还包括蛋白质相对于基底表面的取向的影响。与 SERS 的无标记、单分子灵敏度相结合，该方法应该有助于确定结构-活性关系，为药物开发提供靶标，并测试这些药物对组装过程的影响。该方法在其他蛋白质结构与毒性肽组装形成相关的组装依赖性变化的系统中也可能具有价值。
