加州大学Z. Hong Zhou研究团队取得一项新突破。他们提出了单纯性疱疹病毒1型病毒粒子的顶端入口和包装基因组的低温电镜结构。这一研究成果发表在2019年5月29日出版的国际学术期刊《自然》上。

为更好地定义单纯疱疹病毒1型基因组组织和包装的结构基础，研究团队开发了连续的局部分类和对称松弛方法，来处理1型单纯疱疹病毒粒子的低温冷冻电子显微镜（冷冻电镜）的图像，使他们能够分离和重构伪二十面体衣壳内的异源对称和不对称元素。该课题组研究人员提出了病毒唯一的顶端入口，基因组末端和衣壳内缠绕在一个无序dsDNA核心上的有序的dsDNA线圈的原位结构。该团队鉴定出了覆盖于病毒粒子顶端入口的触手状螺旋和一个球形复合物，此类结构从未在在噬菌体中被观察到过，这表明在dna包装过程中，疱疹病毒具有特异性的适应性。最后，他们建立的顶端入口元素的原子模型揭示了五重相关衣壳是如何适应十二聚体入口所带来的的对称性不匹配的(二十面体病毒中一个长期存在的谜)，并为基因组包装中可能涉及的dna序列识别和头部感知通路提供了信息。这项工作展示了如何去解决一个大型真核病毒对称不匹配的元素，并提供了对疱疹病毒基因组包装机制的深入认识。

据了解，疱疹病毒是带有包膜的病毒，在人类中普遍存在，并与多种疾病有关，包括唇疱疹、先天缺陷和癌症。它们的特征都是一个三角化数(T)等于16的高度密封的伪二十面体衣壳，里面紧密包裹病毒的双链DNA (dsDNA)基因组。疱疹病毒生命周期中的一个关键过程包括将一个ATP驱动的末端酶招募到一个唯一的顶端入口，以识别、包装和切割多联体双链DNA，最终生成一个密闭的、含有基因组的病毒粒子。虽然这个过程已经在双链DNA噬菌体上获得研究验证，而且疱疹病毒与其也有一些相似之处，但是由于缺乏基因组组装机制的高分辨率的原位结构，因此大大阻碍了需要在一个集成环境下和多因子紧密配合才能完成的基因组组装多步反应的阐明。
 

附：英文原文

Title: Cryo-EM structures of herpes simplex virus type 1 portal vertex and packaged genome

Author: Yun-Tao Liu, Jonathan Jih, Xinghong Dai, Guo-Qiang Bi, Z. Hong Zhou

Issue&Volume: Volume 570 Issue 7760, 13 June 2019

Abstract: Herpesviruses are enveloped viruses that are prevalent in the human population and are responsible for diverse pathologies, including cold sores, birth defects and cancers. They are characterized by a highly pressurized pseudo-icosahedral capsid—with triangulation number (T) equal to 16—encapsidating a tightly packed double-stranded DNA (dsDNA) genome. A key process in the herpesvirus life cycle involves the recruitment of an ATP-driven terminase to a unique portal vertex to recognize, package and cleave concatemeric dsDNA, ultimately giving rise to a pressurized, genome-containing virion. Although this process has been studied in dsDNA phages—with which herpesviruses bear some similarities—a lack of high-resolution in situ structures of genome-packaging machinery has prevented the elucidation of how these multi-step reactions, which require close coordination among multiple actors, occur in an integrated environment. To better define the structural basis of genome packaging and organization in herpes simplex virus type 1 (HSV-1), we developed sequential localized classification and symmetry relaxation methods to process cryo-electron microscopy (cryo-EM) images of HSV-1 virions, which enabled us to decouple and reconstruct hetero-symmetric and asymmetric elements within the pseudo-icosahedral capsid. Here we present in situ structures of the unique portal vertex, genomic termini and ordered dsDNA coils in the capsid spooled around a disordered dsDNA core. We identify tentacle-like helices and a globular complex capping the portal vertex that is not observed in phages, indicative of herpesvirus-specific adaptations in the DNA-packaging process. Finally, our atomic models of portal vertex elements reveal how the fivefold-related capsid accommodates symmetry mismatch imparted by the dodecameric portal—a longstanding mystery in icosahedral viruses—and inform possible DNA-sequence recognition and headful-sensing pathways involved in genome packaging. This work showcases how to resolve symmetry-mismatched elements in a large eukaryotic virus and provides insights into the mechanisms of herpesvirus genome packaging.

DOI: https://doi.org/10.1038/s41586-019-1248-6

Source: https://www.nature.com/articles/s41586-019-1248-6