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arXiv 1802.05211cond-mat.softphysics.bio-ph
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单个病毒衣壳围绕其RNA基因组的自组装动力学的测量

Measurements of the self-assembly kinetics of individual viral capsids around their RNA genome

Rees F. Garmann, Aaron M. Goldfain, Vinothan N. Manoharan

摘要:

病毒衣壳的形成是自组装的典型例子。病毒衣壳是围绕病毒基因组的高度有序的蛋白质外壳。许多正义RNA病毒的衣壳在体外由外壳蛋白和RNA的混合物自发组装而成。考虑到它们的结构复杂性,组装的适当衣壳的高产率是显着的:180个相同的蛋白质必须排列成三个不同的局部构型以形成三角形数为3(T = 3)的二十面体衣壳。尽管从结构研究和模拟中获得了大量数据,但即使是关于这些结构如何组装的最基本问题也仍未得到解决。实验还没有确定组装途径是否涉及聚集或成核,或者RNA如何控制这一过程。在这里,我们使用干涉散射显微镜直接观察在体外组装动力学的个别,未标记的衣壳的噬菌体MS2。通过测量从1 ms到900 s的时间尺度上有多少外壳蛋白与单个MS2 RNA链结合,我们发现组装的开始在时间上分布很广,随后结合蛋白的数量迅速增加。这些测量为成核和生长途径提供了强有力的证据。我们还发现,当第一个核生长完成之前,同一RNA上出现多个核时,畸形结构就会组装起来。我们的测量揭示了RNA周围病毒衣壳的复杂组装途径的定量细节,包括成核阈值,成核时间,生长时间和限制的临界核大小。这些结果可能为工程合成衣壳或破坏致病病毒组装的策略提供信息。

英文摘要:

The formation of a viral capsid -- the highly-ordered protein shell that surrounds the genome of a virus -- is the canonical example of self-assembly. The capsids of many positive-sense RNA viruses spontaneously assemble from in vitro mixtures of the coat protein and RNA. The high yield of proper capsids that assemble is remarkable, given their structural complexity: 180 identical proteins must arrange into three distinct local configurations to form an icosahedral capsid with a triangulation number of 3 (T = 3). Despite a wealth of data from structural studies and simulations, even the most fundamental questions about how these structures assemble remain unresolved. Experiments have not determined whether the assembly pathway involves aggregation or nucleation, or how the RNA controls the process. Here we use interferometric scattering microscopy to directly observe the in vitro assembly kinetics of individual, unlabeled capsids of bacteriophage MS2. By measuring how many coat proteins bind to individual MS2 RNA strands over time scales from 1 ms to 900 s, we find that the start of assembly is broadly distributed in time and is followed by a rapid increase in the number of bound proteins. These measurements provide strong evidence for a nucleation-and-growth pathway. We also find that malformed structures assemble when multiple nuclei appear on the same RNA before the first nucleus has finished growing. Our measurements reveal the complex assembly pathways for viral capsids around RNA in quantitative detail, including the nucleation threshold, nucleation time, growth time, and constraints on the critical nucleus size. These results may inform strategies for engineering synthetic capsids or for derailing the assembly of pathogenic viruses.

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