Towards a mechanistic model of herpes simplex virus primary envelopment mediated by the nuclear egress complex

疱疹病毒在包括人类在内的多种脊椎动物中引起终身潜伏感染。潜伏感染的重新激活导致单轮或多轮疾病，并使新的感染成为可能。再活化的中心是病毒外出，这是一个从感染细胞中组装和释放多个子代病毒体的过程。这一复杂的过程涉及多种病毒和宿主蛋白之间的一系列特异性蛋白质-蛋白质相互作用。病毒外出的一些关键特征已被阐明，然而，仍然缺少对该过程的详细机制理解。这一建议的重点是核出口，这涉及病毒衣壳在内核膜（INM）的包裹和随后在外核膜（ONM）的脱包裹。结果，衣壳从细胞核重新定位到细胞质，在细胞质中，最终在高尔基体网络衍生的囊泡中发生。两个保守的疱疹病毒蛋白质是必不可少的核出口，并形成核出口复合物（NEC）。NEC通过一种未知的机制使病毒衣壳能够在内核膜上进行初级修饰。病毒逃逸的这一步骤在所有疱疹病毒亚科中是保守的，并且是病毒复制所必需的。在单纯疱疹病毒（HSV）中，NEC由UL 31和UL 34蛋白组成。本文拟对HSV UL 31和UL 34蛋白及其复合物NEC进行生物化学、生物药理学和结构表征，以确定初级衣壳蛋白的分子机制。UL 31与UL 34的相互作用以及该复合物引起膜变形的能力需要进一步分析，因为它是所有疱疹病毒核出口的关键特征。到目前为止，只有非常有限的生化数据，没有详细的结构信息，UL 31和UL 34。因此，这两种蛋白质使衣壳蛋白化的详细机制仍然未知。该研究旨在更详细地了解疱疹病毒核出口的结构方面和分子机制。对这一过程的精确理解有助于开发阻止病毒逃逸和重新激活的抗病毒治疗方法。

Herpesviruses cause lifelong latent infections in a wide range of vertebrates including humans. Reactivation of a latent infection leads to a single or multiple rounds of disease and enables new infections. At the center of reactivation is viral egress a process of assembly and release of multiple progeny virions from an infected cell. This complex process involves a range of specific protein-protein interactions among multiple viral and host proteins. Some key features of viral egress have been elucidated; however, a detailed mechanistic understanding of the process is still missing. This proposal focuses on nuclear egress, which involves envelopment of viral capsids at the inner nuclear membrane (INM) and the subsequent de-envelopment at the outer nuclear membrane (ONM). As a result, the capsids get relocated from the nucleus to the cytoplasm where final envelopment takes place at Trans-Golgi-Network-derived vesicles. Two conserved herpesvirus proteins are essential for nuclear egress and form the nuclear egress complex (NEC). The NEC enables the primary envelopment of viral capsids at the inner nuclear membrane by a yet unknown mechanism. This step in viral egress is conserved among all herpesvirus subfamilies and is required for viral replication. In herpes simplex viruses (HSVs), the NEC consists of proteins UL31 and UL34.Here, I propose to biochemically, biophysically and structurally characterize the HSV proteins UL31 and UL34 and their complex, the NEC, with the goal of determining the molecular mechanism of primary capsid envelopment. The interaction of UL31 with UL34, as well as the proposed ability of membrane deformation by this complex requires further analysis as it is a key feature in nuclear egress of all herpesviruses. To date, only very limited biochemical data and no detailed structural information is available on UL31 and UL34. As a result, the detailed mechanism by which these two proteins enable capsid envelopment remains unknown. The proposed research aims to understand the structural aspects and molecular mechanism of nuclear egress of herpesviruses in more detail. A precise understanding of this process should aid the development of antiviral therapeutics that hinder egress and thus viral reactivation.