Modeling the Early Stages of Phase Separation in Disordered Elastin-like Proteins.
Modeling the Early Stages of Phase Separation in Disordered Elastin-like Proteins.
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模拟无序弹性蛋白样蛋白相分离的早期阶段。
DOI：
10.1016/j.bpj.2018.01.045
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发表时间：
2018
影响因子：
3.4
通讯作者：
Fitzkee,NicholasC
中科院分区：
文献类型：
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作者：
Zhang,Yue;Zai-Rose,Valeria;Price,CodyJ;Ezzell,NicholasA;Bidwell,GeneL;Correia,JohnJ;Fitzkee,NicholasC
已知弹性蛋白样蛋白（ELPs）在浓度依赖的转变温度以上可进行可逆的液-液相分离。先前的研究表明，随着温度的升高，elp的i型β转变倾向增加。然而，ELPs在相变温度下的表现仍然难以捉摸。在此，我们研究了β-turn形成在ELP自关联早期阶段的重要性。我们研究了两个ELP的行为，一个是之前研究过的150重复结构（ELP[V5G3A2-150]），另一个是适用于核磁共振测量的新的40重复结构（ELP40）。ELP40的结构分析显示其无序构象，整个序列的化学位移对20°C以上的温度变化不敏感。然而，仅凭化学变化不能排除β-转构象的低种群。为了研究β-匝数在ELP中的结构影响，我们生成了一系列的ELP结构集合[V5G3A2-150]，在整个链中包含不同数量的β-匝数偏倚。为了模拟相变的早期阶段，两个单体配对，假设在β-转区优先相互作用。这种方法是合理的，因为在蛋白质数据库中通常观察到埋藏的疏水转弯相互作用。二聚化后，计算了各β转偏度下的系综平均水动力性能，并与不同温度下的解析性超离心实验结果进行了比较。我们发现沉积系数的温度依赖性可以通过增加结构系综中β-turn的含量来重现。这种分析使我们能够估计在实验条件下β-turn和弱关联的存在。由于无序蛋白质在二级结构倾向上经常表现出微弱的偏差，这些实验驱动的系综计算可以补充现有的无序蛋白质建模方法。
Elastin-like proteins (ELPs) are known to undergo liquid-liquid phase separation reversibly above a concentration-dependent transition temperature. Previous studies suggested that, as temperature increases, ELPs experience an increased propensity for type IIβ-turns. However, how the ELPs behave below the phase transition temperature itself is still elusive. Here, we investigate the importance ofβ-turn formation during the early stages of ELP self-association. We examined the behavior of two ELPs, a 150-repeat construct that had been investigated previously (ELP[V5G3A2-150] as well as a new 40-repeat construct (ELP40) suitable for nuclear magnetic resonance measurements. Structural analysis of ELP40 reveals a disordered conformation, and chemical shifts throughout the sequence are insensitive to changes in temperature over 20°C. However, a low population ofβ-turn conformation cannot be ruled out based on chemical shifts alone. To examine the structural consequences ofβ-turns in ELPs, a series of structural ensembles of ELP[V5G3A2-150] were generated, incorporating differing amounts ofβ-turn bias throughout the chain. To mimic the early stages of the phase change, two monomers were paired, assuming preferential interaction atβ-turn regions. This approach was justified by the observation that buried hydrophobic turns are commonly observed to interact in the Protein Data Bank. After dimerization, the ensemble-averaged hydrodynamic properties were calculated for each degree ofβ-turn bias, and the results were compared with analytical ultracentrifugation experiments at various temperatures. We find that the temperature dependence of the sedimentation coefficient (s20,wo) can be reproduced by increasing theβ-turn content in the structural ensemble. This analysis allows us to estimate the presence ofβ-turns and weak associations under experimental conditions. Because disordered proteins frequently exhibit weak biases in secondary structure propensity, these experimentally-driven ensemble calculations may complement existing methods for modeling disordered proteins generally.