Department of Chemistry, East Carolina University, Greenville, NC, 27858, USA.
Center of Interdisciplinary Magnetic Resonance (CIMAR), National High Magnetic Field Laboratory (NHMFL), 1800 East, Paul Dirac Dr., Tallahassee, FL, 32310, USA.
Sci Rep. 2019 Jan 10;9(1):33. doi: 10.1038/s41598-018-37230-1.
Characterization of small oligomers formed at an early stage of amyloid formation is critical to understanding molecular mechanism of pathogenic aggregation process. Here we identified and characterized cytotoxic oligomeric intermediates populated during transthyretin (TTR) aggregation process. Under the amyloid-forming conditions, TTR initially forms a dimer through interactions between outer strands. The dimers are then associated to form a hexamer with a spherical shape, which serves as a building block to self-assemble into cytotoxic oligomers. Notably, wild-type (WT) TTR tends to form linear oligomers, while a TTR variant (G53A) prefers forming annular oligomers with pore-like structures. Structural analyses of the amyloidogenic intermediates using circular dichroism (CD) and solid-state NMR reveal that the dimer and oligomers have a significant degree of native-like β-sheet structures (35-38%), but with more disordered regions (~60%) than those of native TTR. The TTR variant oligomers are also less structured than WT oligomers. The partially folded nature of the oligomeric intermediates might be a common structural property of cytotoxic oligomers. The higher flexibility of the dimer and oligomers may also compensate for the entropic loss due to the oligomerization of the monomers.
在淀粉样形成的早期阶段形成的小寡聚体的特征对于理解致病聚集过程的分子机制至关重要。在这里，我们鉴定并表征了转甲状腺素蛋白（TTR）聚集过程中形成的细胞毒性寡聚体中间产物。在淀粉样形成条件下，TTR 最初通过外部链之间的相互作用形成二聚体。然后，这些二聚体缔合形成具有球形的六聚体，作为自组装成细胞毒性寡聚体的构建块。值得注意的是，野生型（WT）TTR 倾向于形成线性寡聚体，而 TTR 变体（G53A）则倾向于形成具有孔状结构的环形寡聚体。使用圆二色性（CD）和固态 NMR 对淀粉样中间产物进行结构分析表明，二聚体和寡聚体具有相当程度的天然β-折叠结构（35-38%），但与天然 TTR 相比，无序区域更多（~60%）。TTR 变体寡聚体的结构也不如 WT 寡聚体。寡聚体中间产物的部分折叠性质可能是细胞毒性寡聚体的共同结构特性。二聚体和寡聚体的较高灵活性也可能补偿由于单体寡聚化而导致的熵损失。
