Interactions and aggregation of apoferritin molecules in solution: Effects of added electrolytes
Interactions and aggregation of apoferritin molecules in solution: Effects of added electrolytes
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DOI：
10.1016/s0006-3495(00)76753-1
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发表时间：
2000-04-01
影响因子：
3.4
通讯作者：
Vekilov, PG
中科院分区：
文献类型：
--
作者：
Petsev, DN;Thomas, BR;Vekilov, PG
我们已经研究了蛋白质物种的结构和蛋白质-蛋白质相互作用的溶液中含有两个脱铁铁蛋白分子形式，单体和二聚体，在Na+和Cd 2+离子的存在下。我们使用色谱，静态和动态光散射技术，和原子力显微镜（AFM）。使用尺寸排阻色谱分离这两种蛋白质级分。通过动态光散射和原子力显微镜测定了单体和二聚体的尺寸和形状。虽然单体是一个明显的球体，其直径对应于先前的X射线晶体学测定，但二聚体的形状对应于两个结合的单体球体。应用静态光散射技术研究了单体和二聚体溶质分子间的相互作用。单体的结果表明，Na+离子引起强烈的分子间排斥，即使在浓度高于0.15 M，相反的预测，通常应用的Derjaguin-Landau-Verwey-Overbeek理论。我们认为，这种行为的原因是水化力，由于在钠离子的帮助下，在蛋白质分子周围形成水壳。即使加入少量的Cd 2+，也会将排斥相互作用变为吸引相互作用，但不会导致寡聚体形成，至少在所用的蛋白质浓度下不会。因此，这两种离子提供了它们与蛋白质分子相互作用的强特异性的实例。在脱铁铁蛋白二聚体的溶液中，即使在仅存在Na+的情况下，分子也吸引，表明脱铁铁蛋白分子的表面发生了变化。考虑到单体之间的强排斥，这表明二聚体和高级寡聚体仅在一些脱铁铁蛋白单体部分变性后形成。这些观察结果表明，蛋白质分子或分子亚基的聚集和自组装可能是由那些负责结晶和蛋白质溶液中的其他相变以外的力驱动的。
We have studied the structure of the protein species and the protein-protein interactions in solutions containing two apoferritin molecular forms, monomers and dimers, in the presence of Na+ and Cd2+ ions. We used chromatographic, and static and dynamic light scattering techniques, and atomic force microscopy (AFM). Size-exclusion chromatography was used to isolate these two protein fractions. The sizes and shapes of the monomers and dimers were determined by dynamic light scattering and AFM. Although the monomer is an apparent sphere with a diameter corresponding to previous x-ray crystallography determinations, the dimer shape corresponds to two, bound monomer spheres. Static light scattering was applied to characterize the interactions between solute molecules of monomers and dimers in terms of the second osmotic virial coefficients. The results for the monomers indicate that Na+ ions cause strong intermolecular repulsion even at concentrations higher than 0.15 M, contrary to the predictions of the commonly applied Derjaguin-Landau-Verwey-Overbeek theory. We argue that the reason for such behavior is hydration force due to the formation of a water shell around the protein molecules with the help of the sodium ions. The addition of even small amounts of Cd2+ changes the repulsive interactions to attractive but does not lead to oligomer formation, at least at the protein concentrations used. Thus, the two ions provide examples of strong specificity of their interactions with the protein molecules, in solutions of the apoferritin dimer, the molecules attract even in the presence of Na+ only, indicating a change in the surface of the apoferritin molecule. in view of the strong repulsion between the monomers, this indicates that the dimers and higher oligomers form only after partial denaturation of some of the apoferritin monomers. These observations suggest that aggregation and self-assembly of protein molecules or molecular subunits may be driven by forces other than those responsible for crystallization and other phase transitions in the protein solution.