Soft Matter. 2014 Mar 28;10(12):2059-68. doi: 10.1039/c3sm52532e.
The assembly kinetics of intermediate filament (IF) proteins from tetrameric complexes to single filaments and networks depends on the protein concentration, temperature and the ionic composition of their environment. We systematically investigate how changes in the concentration of monovalent potassium and divalent magnesium ions affect the internal organization of the resulting filaments. Small angle X-ray scattering (SAXS) is very sensitive to changes in the filament cross-section such as diameter or compactness. Our measurements reveal that filaments formed in the presence of magnesium chloride differ distinctly from filaments formed in the presence of potassium chloride. The principle multi-step assembly mechanism from tetramers via unit-length filaments (ULF) to elongated filaments is not changed by the valency of ions. However, the observed differences indicate that the magnesium ions free the head domains of tetramers from unproductive interactions to allow assembly but at the same time mediate strong inter-tetrameric interactions that impede longitudinal annealing of unit-length filaments considerably, thus slowing down filament growth.
中间丝（IF）蛋白从四聚体复合物到单丝和网络的组装动力学取决于蛋白质浓度、温度和环境的离子组成。我们系统地研究了单价钾离子和二价镁离子浓度的变化如何影响形成的纤维的内部组织。小角 X 射线散射（SAXS）对纤维横截面的变化（如直径或紧凑性）非常敏感。我们的测量结果表明，在氯化镁存在下形成的纤维与在氯化钾存在下形成的纤维明显不同。从四聚体通过单元长度纤维（ULF）到伸长纤维的主要多步组装机制不受离子价的影响。然而，观察到的差异表明，镁离子使四聚体的头部结构域从非生产性相互作用中释放出来，从而允许组装，但同时介导强的四聚体间相互作用，这极大地阻碍了单元长度纤维的纵向退火，从而减缓了纤维的生长。
