Roberts D, Keeling R, Tracka M, van der Walle C F, Uddin S, Warwicker J, Curtis R
School of Chemical Engineering and Analytical Science, The University of Manchester , Sackville Street, Manchester M13 9PL, U.K.
Mol Pharm. 2014 Jul 7;11(7):2475-89. doi: 10.1021/mp5002334. Epub 2014 Jun 18.
Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.
为了更好地控制蛋白质溶液行为，需要了解蛋白质-蛋白质相互作用如何依赖于缓冲液、盐、离子强度和pH值的选择。在这里，我们根据从动态光散射获得的相互作用参数kD和通过静态光散射测量的渗透第二维里系数B22，表征了蛋白质-蛋白质相互作用对pH值和离子强度的依赖性。基于巴克斯特粘附势和双电层力的简化蛋白质-蛋白质相互作用模型用于区分长程静电相互作用和短程吸引力的贡献。对于pH值为6.5及以下的溶液，使用德亚金-朗道-弗韦-奥弗贝克（DLVO）势来描述双层力，可以准确地捕捉蛋白质-蛋白质相互作用对离子强度的依赖性。在pH值为9的溶液中，在5-275 mM的离子强度范围内会出现有吸引力的静电作用。在中间pH值（7.25至8.5）时，存在一种交叉效应，其特征是蛋白质-蛋白质相互作用对离子强度的依赖性非单调，这可以通过低离子强度下长程排斥双层力和在临界离子强度以上占主导地位的较短程静电吸引力的竞争效应来解释。相互作用从排斥到吸引的变化表明蛋白质-蛋白质相互作用的角度依赖性从各向同性到各向异性的相应变化。在论文的第二部分，我们展示了如何使用巴克斯特粘附势通过拟合B22测量值来预测kD值，从而为两个蛋白质-蛋白质相互作用参数之间的线性相关性提供分子基础。
