Department of Chemical and Biomolecular Engineering. University of Delaware , Newark, Delaware 19716, United States.
J Phys Chem B. 2017 May 11;121(18):4756-4767. doi: 10.1021/acs.jpcb.7b02183. Epub 2017 Apr 27.
Protein interactions of α-chymotrypsinogen A (aCgn) were quantified using light scattering from low to high protein concentrations. Static light scattering (SLS) was used to determine the excess Rayleigh ratio (R) and osmotic second virial coefficients (B) as a function of pH and total ionic strength (TIS). Repulsive (attractive) protein-protein interactions (PPI) were observed at pH 5 (pH 7), with decreasing repulsions (attractions) upon increasing TIS. Simple colloidal potential of mean force models (PMF) that account for short-range nonelectrostatic attractions and screened electrostatic interactions were used to fit model parameters from data for B vs TIS at both pH values. The parameters and PMF models from low-concentration conditions were used as the sole input to transition matrix Monte Carlo simulations to predict high concentration R behavior. At conditions where PPI are repulsive to slightly attractive, experimental R data at high concentrations could be predicted quantitatively by the simulations. However, accurate predictions were challenging when PPI were strongly attractive due to strong sensitivity to changes in PMF parameter values. Additional simulations with higher-resolution coarse-grained molecular models suggest an approach to qualitatively predict cases when anisotropic surface charge distributions will lead to overall attractive PPI at low ionic strength, without assumptions regarding electrostatic "patches" or multipole expansions.
使用低至高蛋白质浓度的光散射来定量测定α-糜蛋白酶原 A (aCgn) 的蛋白质相互作用。静态光散射 (SLS) 用于确定过量瑞利比 (R) 和渗透压第二维里系数 (B) 作为 pH 和总离子强度 (TIS) 的函数。在 pH 5（pH 7）处观察到排斥（吸引）的蛋白质-蛋白质相互作用 (PPI)，随着 TIS 的增加，排斥（吸引）作用减弱。简单胶体平均力势能模型 (PMF) 用于拟合 B 与 TIS 在两种 pH 值下的数据，这些模型考虑了短程非静电吸引和屏蔽静电相互作用。从低浓度条件获得的参数和 PMF 模型被用作过渡矩阵蒙特卡罗模拟的唯一输入，以预测高浓度 R 行为。在 PPI 具有排斥性或略微吸引力的条件下，模拟可以定量预测高浓度下的实验 R 数据。然而，当 PPI 具有很强的吸引力时，由于对 PMF 参数值变化的强烈敏感性，准确的预测具有挑战性。具有更高分辨率的粗粒度分子模型的附加模拟表明，一种方法可以定性预测在低离子强度下各向异性表面电荷分布将导致整体吸引 PPI 的情况，而无需关于静电“补丁”或多极展开的假设。
