Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, California, USA.
California NanoSystems Institute, UCLA, Los Angeles, California, USA.
J Virol. 2024 Nov 19;98(11):e0119424. doi: 10.1128/jvi.01194-24. Epub 2024 Oct 29.
Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are classified into the gammaherpesvirus subfamily of , which stands out from its alpha- and betaherpesvirus relatives due to the tumorigenicity of its members. Although structures of human alpha- and betaherpesviruses by cryogenic electron tomography (cryoET) have been reported, reconstructions of intact human gammaherpesvirus virions remain elusive. Here, we structurally characterize extracellular virions of EBV and KSHV by deep learning-enhanced cryoET, resolving both previously known monomorphic capsid structures and previously unknown pleomorphic features beyond the capsid. Through subtomogram averaging and subsequent tomogram-guided sub-particle reconstruction, we determined the orientation of KSHV nucleocapsids from mature virions with respect to the portal to provide spatial context for the tegument within the virion. Both EBV and KSHV have an eccentric capsid position and polarized distribution of tegument. Tegument species span from the capsid to the envelope and may serve as scaffolds for tegumentation and envelopment. The envelopes of EBV and KSHV are less densely populated with glycoproteins than those of herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV), representative members of alpha- and betaherpesviruses, respectively. Also, we observed fusion protein gB trimers exist within triplet arrangements in addition to standalone complexes, which is relevant to understanding dynamic processes such as fusion pore formation. Taken together, this study reveals nuanced yet important differences in the tegument and envelope architectures among human herpesviruses and provides insights into their varied cell tropism and infection.
Discovered in 1964, Epstein-Barr virus (EBV) is the first identified human oncogenic virus and the founding member of the gammaherpesvirus subfamily. In 1994, another cancer-causing virus was discovered in lesions of AIDS patients and later named Kaposi's sarcoma-associated herpesvirus (KSHV), the second human gammaherpesvirus. Despite the historical importance of EBV and KSHV, technical difficulties with isolating large quantities of these viruses and the pleiomorphic nature of their envelope and tegument layers have limited structural characterization of their virions. In this study, we employed the latest technologies in cryogenic electron microscopy (cryoEM) and tomography (cryoET) supplemented with an artificial intelligence-powered data processing software package to reconstruct 3D structures of the EBV and KSHV virions. We uncovered unique properties of the envelope glycoproteins and tegument layers of both EBV and KSHV. Comparison of these features with their non-tumorigenic counterparts provides insights into their relevance during infection.
爱泼斯坦-巴尔病毒 (EBV) 和卡波济肉瘤相关疱疹病毒 (KSHV) 被归类为 的γ疱疹病毒亚科，由于其成员的致瘤性，它与α和β疱疹病毒的亲缘关系明显不同。虽然已经报道了人类α和β疱疹病毒的低温电子断层扫描 (cryoET) 结构，但完整的人类γ疱疹病毒病毒体的重建仍然难以捉摸。在这里，我们通过深度学习增强的 cryoET 对 EBV 和 KSHV 的细胞外病毒体进行结构表征，解析了以前已知的单形衣壳结构和衣壳之外以前未知的多形特征。通过亚断层平均和随后的断层引导子颗粒重建，我们确定了成熟病毒体中 KSHV 核衣壳相对于门的取向，为病毒体内的被膜提供了空间背景。EBV 和 KSHV 的衣壳位置都偏心，被膜呈极化分布。被膜种类从衣壳延伸到包膜，可能作为被膜化和包膜的支架。与疱疹单纯病毒 1 (HSV-1) 和人类巨细胞病毒 (HCMV) 相比，EBV 和 KSHV 的包膜上糖蛋白的密度较低，HSV-1 和 HCMV 分别是α和β疱疹病毒的代表成员。此外，我们观察到融合蛋白 gB 三聚体除了单独的复合物外，还存在于三聚体排列中，这与理解融合孔形成等动态过程有关。总之，这项研究揭示了人类疱疹病毒在被膜和包膜结构上的细微但重要的差异，并为它们不同的细胞嗜性和感染提供了深入了解。
爱泼斯坦-巴尔病毒 (EBV) 于 1964 年发现，是第一种被发现的人类致癌病毒，也是 γ疱疹病毒亚科的创始成员。1994 年，在艾滋病患者的病变中发现了另一种致癌病毒，并随后命名为卡波济肉瘤相关疱疹病毒 (KSHV)，这是第二种人类 γ疱疹病毒。尽管 EBV 和 KSHV 具有历史重要性，但由于难以分离大量这些病毒，以及其包膜和被膜层的多形性，限制了对其病毒体的结构表征。在这项研究中，我们采用了最新的低温电子显微镜 (cryoEM) 和断层扫描 (cryoET) 技术，并辅以人工智能驱动的数据处理软件包，重建了 EBV 和 KSHV 病毒体的 3D 结构。我们揭示了 EBV 和 KSHV 包膜糖蛋白和被膜层的独特性质。将这些特征与非致瘤性对应物进行比较，为它们在感染过程中的相关性提供了线索。
