Krebs M R H, Bromley E H C, Donald A M
P&C Group, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
J Struct Biol. 2005 Jan;149(1):30-7. doi: 10.1016/j.jsb.2004.08.002.
Amyloid fibrils are a polymeric form of protein, involving a continuous beta-sheet with the strands perpendicular to the long axis of the fibril. Although typically implicated in diseases such as Alzheimer's disease and the transmissible spongiform encephalopathies, non disease-associated protein can also be converted into amyloid fibrils. Traditionally, amyloid fibrils are identified via the use of specific dyes such as Congo red and thioflavin-T, although their specificity is ill understood. Recently, solutions of bovine insulin and bovine beta-lactoglobulin have been found to form spherulites, micron-sized spherical structures containing radially arranged amyloid fibrils. When studied by confocal microscopy using polarised laser light and thioflavin-T, a consistent pattern of emission, rather than a uniform disc, was observed. This suggests the dye binds in a specific, regular fashion to amyloid fibrils. Confocal microscopy studies of thioflavin-T aligned in stretched poly-vinyl alcohol films showed that the dye dipole excitation axis lies parallel to the long molecular axis. Therefore, thioflavin-T binds to amyloid fibrils such that their long axes are parallel. We propose binding occurs in 'channels' that run along the length of the beta-sheet. Steric interactions between dye molecules and side chains indicate why thioflavin-T fluoresces more intensely when bound to amyloid fibrils and can explain why this interaction with amyloid fibrils is specific, but with varying efficiency.
淀粉样纤维是蛋白质的一种聚合形式，由连续的β-折叠片层构成，其链与纤维的长轴垂直。尽管通常与阿尔茨海默病和传染性海绵状脑病等疾病有关，但非疾病相关蛋白也可转化为淀粉样纤维。传统上，淀粉样纤维是通过使用刚果红和硫黄素-T等特定染料来鉴定的，不过其特异性尚不清楚。最近，已发现牛胰岛素和牛β-乳球蛋白溶液会形成球晶，即含有径向排列的淀粉样纤维的微米级球形结构。当使用偏振激光和硫黄素-T通过共聚焦显微镜进行研究时，观察到的是一致的发射模式，而不是均匀的圆盘。这表明该染料以特定、规则的方式与淀粉样纤维结合。对拉伸聚乙烯醇薄膜中排列的硫黄素-T进行的共聚焦显微镜研究表明，染料偶极激发轴与分子长轴平行。因此，硫黄素-T与淀粉样纤维结合，使其长轴平行。我们认为结合发生在沿β-折叠片层长度延伸的“通道”中。染料分子与侧链之间的空间相互作用解释了为什么硫黄素-T与淀粉样纤维结合时荧光更强，以及为什么这种与淀粉样纤维的相互作用具有特异性，但效率各不相同。
