快速形成的早期中间结构决定了衣壳装配的途径。

StephenW

J Am Chem Soc. 2020 Apr 1. doi: 10.1021/jacs.0c01092. [Epub ahead of print]
Rapidly Forming Early Intermediate Structures Dictate the Pathway of Capsid Assembly.
Asor R, Schlicksup CJ, Zhao Z, Zlotnick A, Raviv U.
Abstract

There are ∽1030 possible intermediates on the assembly path from hepatitis B capsid protein dimers to the 120-dimer capsid. If every intermediate was tested, assembly would often get stuck in an entropic trap and essentially every capsid would follow a unique assembly path. Yet, capsids assemble rapidly with minimal trapped intermediates, a realization of the Levinthal paradox. To understand the fundamental mechanisms of capsid assembly it is critical to resolve the early stages of the reaction. We have used Time-Resolved Small Angle X-ray Scattering, which is sensitive to solute size and shape and has millisecond temporal resolution. Scattering curves were fit to a thermodynamically curated library of assembly intermediates, using the principle of maximum entropy. Maximum entropy also provides a physical rationale for the selection of species. We found that the capsid assembly pathway was exquisitely sensitive to initial assembly conditions. With the mildest conditions tested, the reaction appeared two-state from dimer to 120-dimer capsid with some dimers-of-dimers and trimers-of-dimers. In slightly more aggressive conditions, we observed transient accumulation of a decamer-of-dimers and appearance of 90-dimer capsids. In conditions where there is measurable kinetic trapping, we found that a highly diverse early intermediates accumulated within a fraction of a second and propagated into long-lived kinetically trapped states (≧90-mer). In all cases, intermediates between 35 and 90 subunits did not accumulate. These results are consistent with the presence of low barrier paths that connect early and late intermediates and direct the ultimate assembly path to late intermediates where assembly can be paused.

PMID:
    32233479
DOI:
    10.1021/jacs.0c01092

StephenW

J Am Chem Soc。 2020年4月1日。doi：10.1021 / jacs.0c01092。 [Epub提前发行]
快速形成的早期中间结构决定了衣壳装配的途径。
Asor R，Schlicksup CJ，Zhao Z，Zlotnick A，Raviv U.
抽象

从乙型肝炎衣壳蛋白二聚体到120二聚体衣壳的组装过程中，存在约1030种可能的中间体。如果对每个中间体进行了测试，则组装常常会卡在熵阱中，并且基本上每个衣壳都将遵循唯一的组装路径。然而，衣壳以最少的被捕获的中间体快速组装，实现了列文萨尔悖论。要了解衣壳装配的基本机制，解决反应的早期阶段至关重要。我们使用了时间分辨小角度X射线散射，它对溶质的大小和形状敏感，时间分辨率为毫秒。使用最大熵原理，将散射曲线拟合到装配中间体的热力学规划库中。最大熵还为选择物种提供了物理原理。我们发现衣壳装配路径对初始装配条件非常敏感。在最温和的条件下，反应从二聚体到120二聚体衣壳出现了两个状态，其中包含一些二聚体和三聚体。在更具侵略性的条件下，我们观察到二聚体十聚体的短暂积累和90二聚体衣壳的出现。在存在可测量的动力学俘获的条件下，我们发现高度多样化的早期中间体在不到一秒的时间内积累，并传播到长寿命的动力学俘获状态（≥90-mer）。在所有情况下，35到90个亚基之间的中间体都不会积聚。这些结果与连接早期和晚期中间体并将最终组装路径引导至可以暂停组装的晚期中间体的低阻隔路径的存在是一致的。

PMID：
32233479
DOI：
10.1021 /江淮0C01092