Phase separation of immiscible fluids is a common phenomenon in polymer chemistry, and is recognized as an important mechanism by which cells compartmentalize their biochemical reactions. Biomolecular condensates are condensed fluid droplets in cells that form by liquid–liquid phase separation of intrinsically-disordered proteins. They have a wide range of functions and are associated with chronic neurodegenerative diseases in which they become pathologically rigid. However, it remains unclear how their material properties depend on the molecular structure of the proteins. Here we explore the phase behaviour and structure of a model biomolecular condensate composed of semi-flexible polymers with attractive end-caps using coarse-grained simulations. The model contains the minimal molecular features that are sufficient to observe liquid–liquid phase separation of soluble polymers into a porous, three-dimensional network in which their end-caps reversibly bind at junctions. The distance between connected junctions scales with the polymer length as a self-avoiding random walk over a wide range of concentration with a weak affinity-dependent prefactor. By contrast, the average number of polymers that meet at the junctions depends on the end-cap affinity but only weakly on the polymer length. The structured porosity of the condensed phase suggests a mechanism for cells to regulate biomolecular condensates. Protein interaction sites may be turned on or off to modulate the condensate's porosity and therefore the diffusion and interaction of additional proteins.

中文翻译：

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模型生物分子冷凝物的相行为和结构。

不混溶流体的相分离是聚合物化学中的常见现象，并且被认为是细胞分隔其生化反应的重要机制。生物分子冷凝物是细胞内的冷凝液滴，这些液滴是通过本质上紊乱的蛋白质的液相液相分离形成的。它们具有广泛的功能，并且与慢性神经退行性疾病有关，在慢性神经退行性疾病中它们变得病理僵化。但是，尚不清楚它们的材料特性如何取决于蛋白质的分子结构。在这里，我们使用粗粒度模拟研究由半柔性聚合物组成的具有吸引力的端盖的模型生物分子冷凝物的相行为和结构。该模型包含的最小分子特征足以观察到可溶性聚合物的液相-液相分离成多孔的三维网络，其中它们的端盖可逆地结合在结合处。连接的连接点之间的距离与聚合物的长度成比例，这是在较弱的亲和力依赖性因子的较大浓度范围内进行的自规随机游走。相比之下，在连接处相遇的聚合物的平均数量取决于封端的亲和力，而仅取决于聚合物的长度。冷凝相的结构化孔隙率表明细胞调节生物分子冷凝物的机制。可以打开或关闭蛋白质相互作用位点，以调节冷凝液的孔隙率，从而调节其他蛋白质的扩散和相互作用。