Laboratory of Structural Biology Research, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Advanced Imaging Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA.
mBio. 2021 Mar 16;12(2):e03575-20. doi: 10.1128/mBio.03575-20.
Herpes simplex virus 1 (HSV-1) requires seven proteins to package its genome through a vertex in its capsid, one of which is the portal protein, pUL6. The portal protein is also thought to facilitate assembly of the procapsid. While the portal has been visualized in mature capsids, we aimed to elucidate its role in the assembly and maturation of procapsids using cryo-electron tomography (cryoET). We identified the portal vertex in individual procapsids, calculated a subtomogram average, and compared that with the portal vertex in empty mature capsids (A-capsids). The resulting maps show the portal on the interior surface with its narrower end facing outwards, while maintaining close contact with the capsid shell. In the procapsid, the portal is embedded in the underlying scaffold, suggesting that assembly involves a portal-scaffold complex. During maturation, the capsid shell angularizes with a corresponding outward movement of the vertices. We found that in A-capsids, the portal translocates outward further than the adjacent capsomers and strengthens its contacts with the capsid shell. Our methodology also allowed us to determine the number of portal vertices in each capsid, with most having one per capsid, but some none or two, and rarely three. The predominance of a single portal per capsid supports facilitation of the assembly of the procapsid. Herpes simplex virus 1 (HSV-1) infects a majority of humans, causing mostly mild disease but in some cases progressing toward life-threatening encephalitis. Understanding the life cycle of the virus is important to devise countermeasures. Production of the virion starts with the assembly of an icosahedral procapsid, which includes DNA packaging proteins at a vertex, one of which is the dodecameric portal protein. The procapsid then undergoes maturation and DNA packaging through the portal, driven by a terminase complex. We used cryo-electron tomography to visualize the portal in procapsids and compare them to mature empty capsids. We found the portal located inside one vertex interacting with the scaffold protein in the procapsid. On maturation, the scaffold is cleaved and dissociates, the capsid angularizes, and the portal moves outward, interacting closely with the capsid shell. These transformations may provide a basis for the development of drugs to prevent HSV-1 infections.
单纯疱疹病毒 1（HSV-1）需要七种蛋白质将其基因组包装到衣壳的一个顶点中，其中一种是门户蛋白 pUL6。门户蛋白也被认为有助于原衣壳的组装。虽然已经在成熟衣壳中观察到了门户，但我们旨在使用冷冻电子断层扫描（cryoET）阐明其在原衣壳组装和成熟过程中的作用。我们在单个原衣壳中鉴定了门户顶点，计算了子断层平均，并将其与空的成熟衣壳（A-衣壳）中的门户顶点进行了比较。得到的地图显示门户位于内部表面，其较窄的一端向外，同时与衣壳壳保持紧密接触。在原衣壳中，门户嵌入在基础支架中，表明组装涉及门户-支架复合物。在成熟过程中，衣壳壳的角向化伴随着顶点的相应向外运动。我们发现，在 A-衣壳中，门户向外迁移的距离超过相邻的衣壳小体，并且与衣壳壳的接触更加紧密。我们的方法还使我们能够确定每个衣壳中的门户顶点的数量，大多数衣壳每个衣壳一个，但有些衣壳没有或两个，很少有三个。每个衣壳中主要存在一个门户，这支持了原衣壳组装的促进。单纯疱疹病毒 1（HSV-1）感染大多数人类，引起大多数轻度疾病，但在某些情况下会进展为威胁生命的脑炎。了解病毒的生命周期对于制定对策很重要。病毒粒子的产生始于二十面体原衣壳的组装，其中包括顶点处的 DNA 包装蛋白，其中一种是十二聚体门户蛋白。然后，原衣壳通过门户经历成熟和 DNA 包装，由端酶复合物驱动。我们使用冷冻电子断层扫描术可视化原衣壳中的门户，并将其与成熟的空衣壳进行比较。我们发现门户位于一个顶点内部，与原衣壳中的支架蛋白相互作用。在成熟过程中，支架被切割并解离，衣壳角向化，门户向外移动，与衣壳壳紧密相互作用。这些转化可能为开发预防 HSV-1 感染的药物提供基础。
