Diffusion in protein solutions: the effect of crowding, temperature and charges

我们提出了一个关于蛋白质在溶液中的扩散作为蛋白质体积分数、温度和重要的蛋白质表面电荷状态的函数的研究项目。我们将特别关注电荷调谐和拥挤的动态效应。通过在溶液中加入合适的盐（单价和多价），我们可以创建不同程度的筛选，也可以反转与聚集现象相关的蛋白质表面电荷，包括结晶。这种电荷调整不仅对蛋白质溶液的静态（时间平均）结构因子有显著影响，而且对它们的动力学也有显著影响。特别是，动态密度波动可能通过形成动态或瞬态蛋白质簇作为聚集的前兆而出现。预计这些动态簇的寿命敏感地依赖于电荷模式。为了探索这些动态现象，我们将系统地研究蛋白质在这些系统中的扩散作为电荷态的函数。主要的实验途径是利用中子后向散射测量蛋白质溶液的非相干散射函数，以确定其短时自扩散。将从中子自旋回波技术、动态光散射、核磁共振和分子动力学模拟中获得补充信息。

We propose a research project on protein diffusion in solution as a function of the protein volume fraction, temperature, and importantly protein surface charge state. We will in particular focus on the dynamic effects of charge tuning and crowding. By adding suitable salts (both monovalent and multivalent) to the solutions, we can create different degrees of screening and also an inversion of the protein surface charge relevant for aggregation phenomena including crystallization. This charge-tuning has significant impact not only on the static (time-averaged) structure factor of the protein solutions, but also on their dynamics.In particular, dynamic density fluctuations may emerge through the formation of dynamic or transient protein clusters as a precursor of aggregation. It is expected that the lifetime of these dynamic clusters sensitively depends on the charge patterns. To explore these dynamic phenomena, we will systematically study the protein diffusion in these systems as a function of the charge state. The main experimental pathway will be to measure the incoherent scattering function of the protein solutions using neutron backscattering, to determine the short-time self-diffusion. Complementary information will be gained from neutron spin echo technique, dynamic light scattering, NMR and molecular dynamics simulations.