Department of Biophysics and Radiation Biology, Faculty of Medicine, Semmelweis University, Budapest, Hungary.
PLoS One. 2012;7(9):e44992. doi: 10.1371/journal.pone.0044992. Epub 2012 Sep 12.
Defects in protein folding may lead to severe degenerative diseases characterized by the appearance of amyloid fibril deposits. Cytotoxicity in amyloidoses has been linked to poration of the cell membrane that may involve interactions with amyloid intermediates of annular shape. Although annular oligomers have been detected in many amyloidogenic systems, their universality, function and molecular mechanisms of appearance are debated.
METHODOLOGY/PRINCIPAL FINDINGS: We investigated with high-resolution in situ atomic force microscopy the assembly and disassembly of transthyretin (TTR) amyloid protofibrils formed of the native protein by pH shift. Annular oligomers were the first morphologically distinct intermediates observed in the TTR aggregation pathway. Morphological analysis suggests that they can assemble into a double-stack of octameric rings with a 16 ± 2 nm diameter, and displaying the tendency to form linear structures. According to light scattering data coupled to AFM imaging, annular oligomers appeared to undergo a collapse type of structural transition into spheroid oligomers containing 8-16 monomers. Disassembly of TTR amyloid protofibrils also resulted in the rapid appearance of annular oligomers but with a morphology quite distinct from that observed in the assembly pathway.
CONCLUSIONS/SIGNIFICANCE: Our observations indicate that annular oligomers are key dynamic intermediates not only in the assembly but also in the disassembly of TTR protofibrils. The balance between annular and more compact forms of aggregation could be relevant for cytotoxicity in amyloidogenic disorders.
蛋白质折叠缺陷可能导致严重的退行性疾病，其特征是出现淀粉样纤维沉积物。淀粉样变中的细胞毒性与细胞膜穿孔有关，这可能涉及与环形形状的淀粉样中间产物的相互作用。尽管在许多淀粉样蛋白系统中都检测到了环形寡聚物，但它们的普遍性、功能和出现的分子机制仍存在争议。
方法/主要发现：我们通过高分辨率原位原子力显微镜研究了由 pH 变化形成的天然蛋白质转甲状腺素蛋白 (TTR) 淀粉样原纤维的组装和拆卸。环形寡聚物是在 TTR 聚集途径中观察到的第一个形态独特的中间产物。形态分析表明，它们可以组装成双堆叠的八聚体环，直径为 16±2nm，并显示出形成线性结构的趋势。根据与原子力显微镜成像相结合的光散射数据，环形寡聚物似乎经历了一种坍塌型结构转变，形成含有 8-16 个单体的球状寡聚物。TTR 淀粉样原纤维的拆卸也导致了环形寡聚物的快速出现，但与组装途径中观察到的形态明显不同。
结论/意义：我们的观察表明，环形寡聚物不仅是 TTR 原纤维组装的关键动态中间产物，也是其拆卸的关键中间产物。环形和更紧凑的聚集形式之间的平衡可能与淀粉样蛋白紊乱中的细胞毒性有关。
