Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
Institut Max von Laue - Paul Langevin, 71 avenue des Martyrs, 38042 Grenoble, France.
Soft Matter. 2021 Sep 29;17(37):8506-8516. doi: 10.1039/d1sm00418b.
The formation of molecular assemblies in protein solutions is of strong interest both from a fundamental viewpoint and for biomedical applications. While ordered and desired protein assemblies are indispensable for some biological functions, undesired protein condensation can induce serious diseases. As a common cofactor, the presence of salt ions is essential for some biological processes involving proteins, and in aqueous suspensions of proteins can also give rise to complex phase diagrams including homogeneous solutions, large aggregates, and dissolution regimes. Here, we systematically study the cluster formation approaching the phase separation in aqueous solutions of the globular protein BSA as a function of temperature (), the protein concentration () and the concentrations of the trivalent salts YCl and LaCl (). As an important complement to structural, time-averaged, techniques we employ a dynamical technique that can detect clusters even when they are transient on the order of a few nanoseconds. By employing incoherent neutron spectroscopy, we unambiguously determine the short-time self-diffusion of the protein clusters depending on , and . We determine the cluster size in terms of effective hydrodynamic radii as manifested by the cluster center-of-mass diffusion coefficients . For both salts, we find a simple functional form (, , ) in the parameter range explored. The calculated inter-particle attraction strength, determined from the microscopic and short-time diffusive properties of the samples, increases with salt concentration and temperature in the regime investigated and can be linked to the macroscopic behavior of the samples.
蛋白质溶液中分子组装的形成无论从基础观点还是从生物医学应用的角度来看都具有很强的研究意义。虽然有序且所需的蛋白质组装对于某些生物功能是不可或缺的，但不需要的蛋白质凝聚会导致严重的疾病。作为一种常见的共因子，盐离子的存在对于涉及蛋白质的某些生物过程是必不可少的，并且在蛋白质的水悬浮液中也会产生包括均相溶液、大聚集体和溶解区的复杂相图。在这里，我们系统地研究了球形蛋白质 BSA 在水溶液中接近相分离时的簇形成，作为温度 (T)、蛋白质浓度 () 和三价盐 YCl 和 LaCl (C) 的函数。作为对结构、时间平均技术的重要补充，我们采用了一种动力学技术，即使在几个纳秒的时间尺度上，也可以检测到瞬态簇。通过使用非相干中子光谱，我们可以明确地确定蛋白质簇的短时间自扩散取决于 T、和 C。我们根据簇质心扩散系数来确定簇的尺寸，用有效流体力学半径表示为 。对于两种盐，我们在研究的参数范围内发现了一种简单的函数形式 (T, C, C)。从样品的微观和短时间扩散性质确定的粒子间吸引力强度随着盐浓度和温度的增加而增加在所研究的范围内，并可以与样品的宏观行为联系起来。
