Two distinct trimeric conformations of natively membrane-anchored full-length herpes simplex virus 1 glycoprotein B
Two distinct trimeric conformations of natively membrane-anchored full-length herpes simplex virus 1 glycoprotein B
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DOI：
10.1073/pnas.1523234113
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发表时间：
2016-03
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通讯作者：
T. Zeev-Ben-Mordehai;D. Vasishtan;A. Durán;A. Durán;B. Vollmer;P. White;A. P. Pandurangan;C. A. Siebert;M. Topf;K. Grünewald
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作者：
T. Zeev-Ben-Mordehai;D. Vasishtan;A. Durán;A. Durán;B. Vollmer;P. White;A. P. Pandurangan;C. A. Siebert;M. Topf;K. Grünewald
成功感染宿主细胞需要病毒携带各种成分——最重要的是它们的基因组——穿过结合膜进入细胞质。对于包膜病毒来说，进入过程的关键部分是通过病毒膜与宿主膜的融合来实现的，这是一个由驻留在病毒包膜上的专门的病毒编码融合蛋白介导的过程。因此，这些表面病毒蛋白是抗病毒治疗和预防性疫苗开发的重要靶点。疱疹病毒是一种无处不在的机会性DNA病毒，它已经掌握了免疫系统的逃避，导致终身感染，并伴有间歇性的临床和亚临床病毒再激活。本文报道的有效糖蛋白B构象的结构信息为疱疹病毒进入的靶向干预开辟了迟来的机会。许多病毒被在组装过程中获得的脂质双分子层包裹着，这一层通常镶嵌着一种或两种类型的糖蛋白。这些病毒表面蛋白是病毒和宿主之间的主要界面。包膜病毒的进入依赖于特殊的融合原蛋白来帮助病毒膜与宿主膜融合。在多组分疱疹病毒融合机制中，糖蛋白B （gB）充当这种融合原。虽然已经确定了gB外结构域融合后构象的结构，但迄今为止，任何其他构象（例如融合前构象、中间构象）仍然难以捉摸，从而限制了开发抗病毒治疗和预防性疫苗的努力。在这里，我们通过在细胞源性囊泡上展示并使用电子冷冻层析技术，在天然膜中表征了全长1 gB的单纯疱疹病毒。除了已知的融合后构象外，还发现了一种新的构象。它的结构，在膜的背景下，是由亚体积平均确定的，发现是三聚体，像融合后的构象，但看起来更浓缩。结构域的层次约束密度拟合意外地揭示了这种构象中的融合环是分开的，并且指向远离锚定膜的地方。这一重要的观察结果是了解复杂的疱疹病毒融合机制的重要一步，并为更有针对性地干预疱疹病毒进入开辟了新的机会。
Significance Successful host cell infection requires that viruses get various components—most importantly, their genomes—across the bounding membranes into the cytosol. For enveloped viruses, this crucial part of the entry process is achieved by merging the viral membrane with the host membrane, a process mediated by specialized virus-encoded fusion proteins residing on the virus envelope. Accordingly, these surface viral proteins constitute important targets for antiviral treatments as well as for prophylactic vaccine development. Herpesviruses are ubiquitous, opportunistic DNA viruses that have mastered immune system evasion to cause lifelong infections, with intermittent clinical and subclinical viral reactivation. The structural information on an effective glycoprotein B conformation reported here opens up overdue opportunities for targeted interventions in herpesvirus entry. Many viruses are enveloped by a lipid bilayer acquired during assembly, which is typically studded with one or two types of glycoproteins. These viral surface proteins act as the primary interface between the virus and the host. Entry of enveloped viruses relies on specialized fusogen proteins to help merge the virus membrane with the host membrane. In the multicomponent herpesvirus fusion machinery, glycoprotein B (gB) acts as this fusogen. Although the structure of the gB ectodomain postfusion conformation has been determined, any other conformations (e.g., prefusion, intermediate conformations) have so far remained elusive, thus restricting efforts to develop antiviral treatments and prophylactic vaccines. Here, we have characterized the full-length herpes simplex virus 1 gB in a native membrane by displaying it on cell-derived vesicles and using electron cryotomography. Alongside the known postfusion conformation, a novel one was identified. Its structure, in the context of the membrane, was determined by subvolume averaging and found to be trimeric like the postfusion conformation, but appeared more condensed. Hierarchical constrained density-fitting of domains unexpectedly revealed the fusion loops in this conformation to be apart and pointing away from the anchoring membrane. This vital observation is a substantial step forward in understanding the complex herpesvirus fusion mechanism, and opens up new opportunities for more targeted intervention of herpesvirus entry.