A small-angle scattering study on equilibrium clusters in lysozyme solutions.
A small-angle scattering study on equilibrium clusters in lysozyme solutions.
复制标题
溶菌酶溶液中平衡簇的小角散射研究。
DOI：
10.1021/jp0639804
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
P. Schurtenberger
中科院分区：
文献类型：
--
作者：
A. Stradner;F. Cardinaux;P. Schurtenberger
我们使用小角散射实验来研究溶菌酶水溶液的结构特性，在该条件下最近已经证明了平衡簇的存在（Nature 2004，432，492）。我们还讨论了可能出现的低角度散射的贡献，最近引起了人们的兴趣，由于其外观在各种蛋白质的解决方案。我们证明，在我们的实验条件下，在溶菌酶的解决方案，这种上升的低q强度只能在特殊情况下观察到，因此不能归因于存在一个普遍的长程吸引力。然后，我们专注于作为蛋白质浓度，温度和离子强度的函数的平衡集群的结构特性。我们表明，从散射测量得到的实验结构因子表现出典型的簇-簇峰q（c），反映带电簇之间的平均距离，以及单体-单体峰q（m），这代表了单体在一个单一的集群内的最近邻壳。形成这些结构的基本原理是两种相反的力共存，即短程吸引力和由于残余电荷而产生的长程排斥力。我们可以通过应用一个简单的平衡团簇模型来定量分析我们的散射数据，并计算平均团簇聚集数N（c）。由此得到的团簇聚集数随体积分数线性增加。我们还观察到随着温度的降低和剩余电荷屏蔽的增加，N（c）也在增加。我们指出的重要性，存在的平衡集群和这种现象的普遍性，在自然界中观察到的自组装过程。最后，我们讨论了我们的简单球状星团模型的局限性，鉴于最近的研究结果从计算机模拟。
We use small-angle scattering experiments to investigate the structural properties of aqueous lysozyme solutions under conditions where the existence of equilibrium clusters has recently been demonstrated (Nature 2004, 432, 492). We also discuss the possible emergence of a low angle scattering contribution, which recently attracted interest due to its appearance in solutions of various proteins. We demonstrate that in lysozyme solutions under our experimental conditions such rising low q intensities can only be observed under special circumstances and can thus not be attributed to the existence of a universal long-range attraction. We then focus on the structural properties of the equilibrium clusters as a function of protein concentration, temperature, and ionic strength. We show that the experimental structure factors obtained from the scattering measurements exhibit the typical cluster-cluster peak q(c) reflecting the mean distance between charged clusters as well as a monomer-monomer peak q(m), which represents the nearest neighbor shell of monomers within a single cluster. The underlying principle for the formation of these structures is the coexistence of two opposing forces, a short-range attraction and a long-range repulsion due to residual charges. We can quantitatively analyze our scattering data by applying a simple equilibrium cluster model and calculate an average cluster aggregation number, N(c). The thus obtained cluster aggregation number increases linearly with volume fraction. We also observe an increasing N(c) as temperature decreases and as the screening of residual charges increases. We point out the importance of the existence of equilibrium clusters and the universality of this phenomenon for self-assembling processes observed in nature. Finally, we discuss the limitations of our simple globular cluster model in view of recent findings from computer simulations.