Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7.
Phys Rev E. 2019 Nov;100(5-1):052404. doi: 10.1103/PhysRevE.100.052404.
Motivated by the idea that intrinsically disordered proteins (IDPs) condense into liquidlike droplets within cells, we carry out Monte Carlo simulations of a polymer lattice model to study the relationship between charge patterning and phase separation. Polymer chains containing neutral, positively charged, and negatively charged monomers are placed on a cubic lattice. Only nearest-neighbor interactions between charges are considered. We determine the phase diagram for a systematically varied set of sequences. We observe homogeneous fluids, liquid condensation, cluster phases, filaments, and crystal states. Of the six sequences we study, three form crystals at low temperatures. The other three sequences, which have lower charge densities, instead collapse into gel-like networks or unconnected finite clusters. Longer neutral patches along the sequence sterically limit the size and shape of low-energy structures, which is analogous to the effect of charge or limited valence in attractive colloids. Only one sequence clearly exhibits liquid behavior; this sequence has a reduced tendency to individually fold and crystallize compared to others of similar charge density and draws parallels to real IDP behavior.
受细胞内无规蛋白（IDP）凝聚成类似液体的液滴这一观点的启发，我们进行了高分子晶格模型的蒙特卡罗模拟，以研究电荷模式与相分离之间的关系。将含有中性、正电荷和负电荷单体的聚合物链置于立方晶格上。仅考虑电荷之间的最近邻相互作用。我们确定了一系列系统变化序列的相图。我们观察到均匀流体、液体冷凝、团相、纤维和晶体状态。在我们研究的六个序列中，有三个在低温下形成晶体。另外三个序列，其电荷密度较低，反而坍塌成凝胶状网络或不相连的有限团簇。序列中较长的中性片段在空间上限制了低能结构的大小和形状，这类似于吸引胶体中电荷或有限价的作用。只有一个序列明显表现出液体行为；与具有相似电荷密度的其他序列相比，该序列折叠和结晶的趋势较小，与真实 IDP 行为相似。
