Fluorescence readouts for an amyloid fibril sensor critically depend on its molecular interaction and local environment offered by the available structural motifs. Here we employ polarized points accumulation for imaging in nanoscale topography with intramolecular charge transfer probes transiently bound to amyloid fibrils to investigate the organization of fibril nanostructures and probe binding configurations. Besides the in-plane (θ ≈ 90°) mode for binding on the fibril surface parallel to the long fibril axis, we also observed a sizable population of over 60% out-of-plane (θ < 60°) dipoles for rotor probes experiencing a varying degree of orientational mobility. Highly confined dipoles exhibiting an out-of-plane configuration probably reflect tightly bound dipoles in the inner channel grooves, while the weakly bound ones on amyloid enjoy rotational flexibility. Our observation of an out-of-plane binding mode emphasizes the pivotal role played by the electron donor amino group toward fluorescence detection and hence the emergence of anchored probes alongside conventional groove binders.

中文翻译：

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单分子定向成像揭示了淀粉样原纤维上两种不同的结合构型

淀粉样蛋白原纤维传感器的荧光读数主要取决于可用结构基序提供的分子相互作用和局部环境。在这里，我们采用极化点累积在纳米级地形中成像，分子内电荷转移探针瞬时结合到淀粉样蛋白原纤维，以研究原纤维纳米结构的组织和探针结合配置。除了在平行于长原纤维轴的原纤维表面上结合的面内 (θ ≈ 90°) 模式外，我们还观察到转子探针有超过 60% 的面外 (θ < 60°) 偶极子经历不同程度的定向流动性。表现出平面外配置的高度限制的偶极子可能反映了内部通道凹槽中紧密结合的偶极子，而淀粉样蛋白上的弱结合蛋白则具有旋转灵活性。我们对平面外结合模式的观察强调了电子供体氨基对荧光检测所起的关键作用，因此锚定探针与传统凹槽结合剂一起出现。