Strauss Mike, Schotte Lise, Karunatilaka Krishanthi S, Filman David J, Hogle James M
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
Department of Pharmaceutical Biotechnology and Molecular Biology, Center for Neurosciences, Vrije Universiteit Brussel, Brussels, Belgium.
J Virol. 2017 Jan 18;91(3). doi: 10.1128/JVI.01443-16. Print 2017 Feb 1.
By using cryo-electron microscopy, expanded 80S-like poliovirus virions (poliovirions) were visualized in complexes with four 80S-specific camelid VHHs (Nanobodies). In all four complexes, the VHHs bind to a site on the top surface of the capsid protein VP3, which is hidden in the native virus. Interestingly, although the four VHHs bind to the same site, the structures of the expanded virus differ in detail in each complex, suggesting that each of the Nanobodies has sampled a range of low-energy structures available to the expanded virion. By stabilizing unique structures of expanded virions, VHH binding permitted a more detailed view of the virus structure than was previously possible, leading to a better understanding of the expansion process that is a critical step in infection. It is now clear which polypeptide chains become disordered and which become rearranged. The higher resolution of these structures also revealed well-ordered conformations for the EF loop of VP2, the GH loop of VP3, and the N-terminal extensions of VP1 and VP2, which, in retrospect, were present in lower-resolution structures but not recognized. These structural observations help to explain preexisting mutational data and provide insights into several other stages of the poliovirus life cycle, including the mechanism of receptor-triggered virus expansion.
When poliovirus infects a cell, it undergoes a change in its structure in order to pass RNA through its protein coat, but this altered state is short-lived and thus poorly understood. The structures of poliovirus bound to single-domain antibodies presented here capture the altered virus in what appear to be intermediate states. A careful analysis of these structures lets us better understand the molecular mechanism of infection and how these changes in the virus lead to productive-infection events.
通过使用冷冻电子显微镜，在与四种80S特异性骆驼科VHH（纳米抗体）形成的复合物中观察到了扩展的类80S脊髓灰质炎病毒颗粒（脊髓灰质炎病毒颗粒）。在所有四种复合物中，VHH均结合到衣壳蛋白VP3顶表面上的一个位点，该位点在天然病毒中是隐藏的。有趣的是，尽管这四种VHH结合到相同的位点，但在每个复合物中，扩展病毒的结构在细节上有所不同，这表明每个纳米抗体都采样了一系列扩展病毒体可利用的低能量结构。通过稳定扩展病毒体的独特结构，VHH结合使得对病毒结构的观察比以前更详细，从而更好地理解了作为感染关键步骤的扩展过程。现在已经清楚哪些多肽链变得无序，哪些发生了重排。这些结构的更高分辨率还揭示了VP2的EF环、VP3的GH环以及VP1和VP2的N端延伸的有序构象，回想起来，这些构象存在于较低分辨率的结构中，但未被识别。这些结构观察有助于解释先前存在的突变数据，并为脊髓灰质炎病毒生命周期的其他几个阶段提供见解，包括受体触发的病毒扩展机制。
当脊髓灰质炎病毒感染细胞时，它会经历结构变化以便将RNA穿过其蛋白衣壳，但这种改变的状态是短暂的，因此了解甚少。此处展示的与单域抗体结合的脊髓灰质炎病毒结构捕获了处于似乎是中间状态的改变后的病毒。对这些结构的仔细分析使我们能够更好地理解感染的分子机制以及病毒中的这些变化如何导致有效感染事件。
