The Primary Enveloped Virion of Herpes Simplex Virus 1: Its Role in Nuclear Egress.
The Primary Enveloped Virion of Herpes Simplex Virus 1: Its Role in Nuclear Egress.
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DOI：
10.1128/mbio.00825-17
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发表时间：
2017-06-13
期刊：
影响因子：
6.4
通讯作者：
Steven AC
中科院分区：
文献类型：
--
作者：
Newcomb WW;Fontana J;Winkler DC;Cheng N;Heymann JB;Steven AC
许多病毒在不同的细胞区室之间迁移，以进行连续的组装阶段。HSV-1衣壳在细胞核中组装，然后转移到细胞质中。首先，衣壳芽穿过内核膜，变得被核出口复合物（NEC）蛋白包被。这产生了初级包膜病毒体（PEV），其包膜与外核膜融合，将衣壳释放到细胞质中。我们研究了相关的分子机制，从US 3空感染的细胞中分离PEVs，并通过冷冻电子显微镜和断层扫描对其进行成像。(pUS3是一种病毒蛋白激酶，在没有PEV的情况下，PEV积聚在核周空间中。与成熟的细胞外病毒体不同，PEV具有非常少的糖蛋白刺突。PEV比成熟病毒粒子小约20%，并且衣壳和NEC层之间可用的空间很小，这表明大多数被膜蛋白在出口途径中较晚获得。以前的研究已经提出，NEC是组织为六聚体在蜂窝状阵列的PEV，但我们发现阵列的七聚体环提取物从US 3空感染的细胞。在PEV中，NEC主要通过位于衣壳顶点附近的pUL 17/pUL 25复合物接触衣壳。最后，NEC层从衣壳解离，因为它离开细胞核，可能在响应pUS 3介导的磷酸化。总的来说，核出口是一个由多个弱相互作用程序驱动的过程。在其成熟途径中，新形成的HSV-1核衣壳必须穿过核膜，同时尊重该屏障的完整性。核衣壳（直径125 nm）太大，无法通过进行大多数核质运输的核孔复合体。现在广泛接受的是，该过程涉及一个关键中间体-初级包膜病毒体的包封/去包封。在野生型感染中，PEV的寿命很短，这阻碍了研究。使用一个突变体，积累PEVs在核周空间，我们能够分离PEVs在足够数量的结构分析，冷冻电子显微镜和断层扫描。这些发现不仅阐明了一种重要的人类病原体的成熟途径，而且对涉及大分子复合物运输的细胞过程也有影响。
Many viruses migrate between different cellular compartments for successive stages of assembly. The HSV-1 capsid assembles in the nucleus and then transfers into the cytoplasm. First, the capsid buds through the inner nuclear membrane, becoming coated with nuclear egress complex (NEC) protein. This yields a primary enveloped virion (PEV) whose envelope fuses with the outer nuclear membrane, releasing the capsid into the cytoplasm. We investigated the associated molecular mechanisms by isolating PEVs from US3-null-infected cells and imaging them by cryo-electron microscopy and tomography. (pUS3 is a viral protein kinase in whose absence PEVs accumulate in the perinuclear space.) Unlike mature extracellular virions, PEVs have very few glycoprotein spikes. PEVs are ~20% smaller than mature virions, and the little space available between the capsid and the NEC layer suggests that most tegument proteins are acquired later in the egress pathway. Previous studies have proposed that NEC is organized as hexamers in honeycomb arrays in PEVs, but we find arrays of heptameric rings in extracts from US3-null-infected cells. In a PEV, NEC contacts the capsid predominantly via the pUL17/pUL25 complexes which are located close to the capsid vertices. Finally, the NEC layer dissociates from the capsid as it leaves the nucleus, possibly in response to pUS3-mediated phosphorylation. Overall, nuclear egress emerges as a process driven by a program of multiple weak interactions. On its maturation pathway, the newly formed HSV-1 nucleocapsid must traverse the nuclear envelope, while respecting the integrity of that barrier. Nucleocapsids (125 nm in diameter) are too large to pass through the nuclear pore complexes that conduct most nucleocytoplasmic traffic. It is now widely accepted that the process involves envelopment/de-envelopment of a key intermediate—the primary enveloped virion. In wild-type infections, PEVs are short-lived, which has impeded study. Using a mutant that accumulates PEVs in the perinuclear space, we were able to isolate PEVs in sufficient quantity for structural analysis by cryo-electron microscopy and tomography. The findings not only elucidate the maturation pathway of an important human pathogen but also have implications for cellular processes that involve the trafficking of large macromolecular complexes.