Kim Sieun, Sureka Hursh V, Kayitmazer A Basak, Wang Gang, Swan James W, Olsen Bradley D
Department of Chemical Engineering, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts, United States.
Department of Chemistry, Boğaziçi University, Bebek, 34342 Istanbul, Turkey.
Biomacromolecules. 2020 Aug 10;21(8):3026-3037. doi: 10.1021/acs.biomac.0c00346. Epub 2020 Jul 16.
Charge anisotropy or the presence of charge patches at protein surfaces has long been thought to shift the coacervation curves of proteins and has been used to explain the ability of some proteins to coacervate on the "wrong side" of their isoelectric point. This work makes use of a panel of engineered superfolder green fluorescent protein mutants with varying surface charge distributions but equivalent net charge and a suite of strong and weak polyelectrolytes to explore this concept. A patchiness parameter, which assessed the charge correlation between points on the surface of the protein, was used to quantify the patchiness of the designed mutants. Complexation between the polyelectrolytes and proteins showed that the mutant with the largest patchiness parameter was the most likely to form complexes, while the smallest was the least likely to do so. The patchiness parameter was found to correlate well with the phase behavior of the protein-polymer mixtures, where both macrophase separation and the formation of soluble aggregates were promoted by increasing the patchiness depending on the polyelectrolyte with which the protein was mixed. Increasing total charge and increasing strength of the polyelectrolyte promote interactions for oppositely charged polyelectrolytes, while charge regulation is also key to interactions for similarly charged polyelectrolytes, which must interact selectively with oppositely charged patches.
电荷各向异性或蛋白质表面电荷斑块的存在长期以来一直被认为会改变蛋白质的凝聚曲线，并被用于解释一些蛋白质在其等电点“错误一侧”凝聚的能力。这项工作利用了一组经过工程改造的超级折叠绿色荧光蛋白突变体，它们具有不同的表面电荷分布但净电荷相等，以及一系列强电解质和弱电解质来探索这一概念。一个斑块参数用于评估蛋白质表面各点之间的电荷相关性，以量化设计突变体的斑块程度。聚电解质与蛋白质之间的络合表明，斑块参数最大的突变体最有可能形成复合物，而最小的则最不可能。发现斑块参数与蛋白质-聚合物混合物的相行为密切相关，其中根据与蛋白质混合的聚电解质不同，通过增加斑块程度既促进宏观相分离又促进可溶性聚集体的形成。增加总电荷和聚电解质的强度会促进带相反电荷的聚电解质之间的相互作用，而电荷调节对于带相同电荷的聚电解质之间的相互作用也是关键，它们必须与带相反电荷的斑块选择性地相互作用。
