Nucleocapsid assembly in pneumoviruses is regulated by conformational switching of the N protein.
Nucleocapsid assembly in pneumoviruses is regulated by conformational switching of the N protein.
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DOI：
10.7554/elife.12627
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发表时间：
2016-02-15
期刊：
影响因子：
7.7
通讯作者：
Grimes JM
中科院分区：
文献类型：
--
作者：
Renner M;Bertinelli M;Leyrat C;Paesen GC;Saraiva de Oliveira LF;Huiskonen JT;Grimes JM
不分段的(-)RNA病毒会导致严重的人类疾病。人类偏肺病毒（HMPV）是该病毒目（单链病毒目）的一种新兴病原体，是儿童呼吸道疾病的主要原因之一。为了帮助阐明核衣壳（由核蛋白 N 包装的病毒 RNA 基因组）的组装机制，我们展示了 HMPV N 在其组装的 RNA 结合状态和单体状态下的晶体结构，与聚合酶辅因子 P 结合。我们的结构揭示了 P 如何抑制 N 自组装以及 N 如何在无 RNA 和 RNA 结合之间转换的分子细节 构象状态。值得注意的是，我们观察到 N 的 C 端延伸通过折叠到 RNA 结合裂缝中，直接防止 RNA 过早摄取。我们的结构提出了核衣壳生长如何协调的共同机制，并突出了代表抗病毒药物重要靶点的相互作用位点。 DOI：http://dx.doi.org/10.7554/eLife.12627.001 人类偏肺病毒（简称 HMPV）是气道和肺部感染的主要原因，尤其是儿童、老年人和免疫系统较弱的人。与所有病毒一样，HMPV 无法单独生存。相反，它必须侵入并劫持细胞，以便复制自己的遗传物质并形成新病毒。在 HMPV 中，这种遗传信息以 RNA 链的形式存在，并受到称为核衣壳的壳状结构的保护。因此，破坏核衣壳的药物可能有助于杀死病毒并治疗它们引起的疾病。核衣壳是由一种称为核蛋白的蛋白质的许多副本构成的，该蛋白质与一条 RNA 链结合。然而，病毒核衣壳只能由与病毒 RNA 结合的核蛋白构建。核蛋白可能会与 HMPV 感染的细胞的 RNA 结合，然后它们就会陷入死胡同。为了防止这种类型的无效结合，在核衣壳形成之前，核蛋白在另一种称为聚合酶辅因子的蛋白质的帮助下保持未组装状态。然而，目前尚不清楚聚合酶辅因子如何帮助维持这种未组装状态。 Renner 等人使用冷冻电子显微镜和 X 射线晶体学技术。研究了核蛋白与 RNA 结合或未组装并与聚合酶辅因子结合时形成的结构。比较这些结构表明，RNA 通常与核蛋白中的特定裂口结合。然而，当核蛋白与聚合酶辅因子结合时，一部分核蛋白会折叠到这个裂缝中，从而阻止 RNA 的插入。这可以防止核蛋白与错误的 RNA 结合，从而使核蛋白保持未组装状态，直到病毒需要它为止。雷纳等人。还发现 HMPV 的核蛋白和聚合酶辅因子之间的相互作用发生在其他几种相关病毒（例如埃博拉病毒）中也发现的位点。因此，针对这个共同区域可能是开发新抗病毒药物的良好策略。 DOI：http://dx.doi.org/10.7554/eLife.12627.002
Non-segmented, (-)RNA viruses cause serious human diseases. Human metapneumovirus (HMPV), an emerging pathogen of this order of viruses (Mononegavirales) is one of the main causes of respiratory tract illness in children. To help elucidate the assembly mechanism of the nucleocapsid (the viral RNA genome packaged by the nucleoprotein N) we present crystallographic structures of HMPV N in its assembled RNA-bound state and in a monomeric state, bound to the polymerase cofactor P. Our structures reveal molecular details of how P inhibits the self-assembly of N and how N transitions between the RNA-free and RNA-bound conformational state. Notably, we observe a role for the C-terminal extension of N in directly preventing premature uptake of RNA by folding into the RNA-binding cleft. Our structures suggest a common mechanism of how the growth of the nucleocapsid is orchestrated, and highlight an interaction site representing an important target for antivirals. DOI: http://dx.doi.org/10.7554/eLife.12627.001 Human metapneumovirus (HMPV for short) is a major cause of infections of the airways and lungs, particularly in children, elderly individuals and people with weakened immune systems. As for all viruses, HMPV cannot survive on its own. Instead, it must invade and hijack cells in order to replicate its own genetic material and form new viruses. In HMPV, this genetic information is in the form of a strand of RNA, and is protected by a shell-like structure called a nucleocapsid. Drugs that disrupt the nucleocapsid may therefore help to kill the viruses and treat the illnesses that they cause. Nucleocapsids are built out of many copies of a protein called nucleoprotein, which binds to a strand of RNA. However, viral nucleocapsids can only be built from nucleoproteins that are bound to viral RNA. Potentially, nucleoproteins could instead bind to RNA belonging to the cells that HMPV infects and they would then be trapped in a dead-end state. To prevent this type of unproductive binding, before the nucleocapsid is formed the nucleoprotein is kept unassembled with the help of another protein called the polymerase cofactor. However, it was not clear exactly how the polymerase cofactor helps to maintain this unassembled state. Using techniques called cryo-electron microscopy and X-ray crystallography, Renner et al. studied the structures formed when nucleoproteins are either bound to RNA or are unassembled and bind to the polymerase cofactor. Comparing these structures revealed that RNA normally binds to a specific cleft in the nucleoprotein. However, when nucleoprotein is bound to the polymerase cofactor a portion of the nucleoprotein folds into this cleft instead, blocking the insertion of RNA. This prevents the nucleoprotein from associating with the wrong RNA, allowing the nucleoprotein to remain in an unassembled state until it is needed for the virus. Renner et al. also found that the interactions between the nucleoprotein and the polymerase cofactor of HMPV occur at sites that are also found in several other related viruses, such as Ebola. Targeting this common region could therefore be a good strategy for developing new antiviral drugs. DOI: http://dx.doi.org/10.7554/eLife.12627.002