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arXiv 1609.08205q-bio.BMcond-mat.soft
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随机相近似理论用于内在无序蛋白的序列依赖性生物功能性液液相分离

Random-phase-approximation theory for sequence-dependent, biologically functional liquid-liquid phase separation of intrinsically disordered proteins

Yi-Hsuan Lin, Jianhui Song, Julie D. Forman-Kay, Hue Sun Chan

摘要:

内在无序蛋白(IDP)的非极性/疏水性通常较低,但极性、带电和芳香族氨基酸组成相对较高。一些IDP在活细胞的水性环境中经历液液相分离。具有增强的IDP浓度的所得相可以作为无膜细胞器的主要组分,其通过创建其自身的富含IDP的微环境来刺激关键的生物功能。IDP相行为受其氨基酸序列的控制。为了在理解这种序列-相位关系方面取得进展,我们报告了最近引入的随机相位近似(RPA)杂聚物理论应用的进一步进展,以解释IDP相分离中的序列特异性静电。在这里,我们研究计算的变化相行为相对于块长度和电荷密度的模型聚两性电解质的交替等长的电荷块,以深入了解在IDP相分离中观察到的趋势。作为一个现实生活中的例子,该理论被应用到合理化/预测的236个残基的N-末端无序区域的RNA解旋酶Ddx 4和其电荷乱序突变体的实验数据是可用的双节和spinodal相行为。RPA预测的相图和平均场Flory-Huggins和Overbeek-Voorn/Debye-Hückel理论预测的相图之间存在根本差异。在RPA的背景下,物理上合理的依赖于蛋白质浓度的相对介电常数可以产生有利于IDP-IDP吸引的协同效应,从而显着增加相分离的趋势。这些研究结果的分歧为IDP相分离理论的未来发展进行了讨论。

英文摘要:

Intrinsically disordered proteins (IDPs) are typically low in nonpolar/hydrophobic but relatively high in polar, charged, and aromatic amino acid compositions. Some IDPs undergo liquid-liquid phase separation in the aqueous milieu of the living cell. The resulting phase with enhanced IDP concentration can function as a major component of membraneless organelles that, by creating their own IDP-rich microenvironments, stimulate critical biological functions. IDP phase behaviors are governed by their amino acid sequences. To make progress in understanding this sequence-phase relationship, we report further advances in a recently introduced application of random-phase-approximation (RPA) heteropolymer theory to account for sequence-specific electrostatics in IDP phase separation. Here we examine computed variations in phase behavior with respect to block length and charge density of model polyampholytes of alternating equal-length charge blocks to gain insight into trends observed in IDP phase separation. As a real-life example, the theory is applied to rationalize/predict binodal and spinodal phase behaviors of the 236-residue N-terminal disordered region of RNA helicase Ddx4 and its charge-scrambled mutant for which experimental data are available. Fundamental differences are noted between the phase diagrams predicted by RPA and those predicted by mean-field Flory-Huggins and Overbeek-Voorn/Debye-Hückel theories. In the RPA context, a physically plausible dependence of relative permittivity on protein concentration can produce a cooperative effect in favor of IDP-IDP attraction and thus a significant increased tendency to phase separate. Ramifications of these findings for future development of IDP phase separation theory are discussed.

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