Abstract
Human herpesviruses, classified into three subfamilies, are double-stranded DNA viruses that establish lifelong latent infections within most of the world’s population and can cause severe disease, especially in immunocompromised people. There is no cure, and current preventative and therapeutic options are limited. Therefore, understanding the biology of these viruses is essential for finding new ways to stop them. Capsids play a central role in herpesvirus biology. They are sophisticated vehicles that shelter the pressurized double-stranded-DNA genomes while ensuring their delivery to defined cellular destinations on the way in and out of the host cell. Moreover, the importance of capsids for multiple key steps in the replication cycle makes their assembly an attractive therapeutic target. Recent cryo-electron microscopy reconstructions of capsids from all three subfamilies of human herpesviruses revealed not only conserved features but also remarkable structural differences. Furthermore, capsid assembly studies have suggested subfamily-specific roles of viral capsid protein homologs. In this review, we compare capsid structures, assembly mechanisms, and capsid protein functions across human herpesvirus subfamilies, highlighting the differences.
Highlights
Herpesviruses are enveloped DNA viruses that infect almost all vertebrates and some invertebrates [1]
Capsid assembly is thought to be nucleated by the portal complex and mediated by the major capsid protein (MCP) and triplexes that form a spherical procapsid around the scaffold and the protease (Figure 2) [25,26,27]
For either Epstein–Barr virus (EBV) or Kaposi’s sarcoma herpes virus (KSHV), overexpression of the MCP, triplexes, small capsid protein (SCP), protease, and scaffold resulted in the assembly of B-capsids [21,22], which required the presence of the MCP and triplexes, to HSV-1 [19,20,21,22]
Summary
Herpesviruses are enveloped DNA viruses that infect almost all vertebrates and some invertebrates [1]. Once progeny genomes are replicated and encapsidated in the nucleus (reviewed in [3,4]), capsids traffic them across the nuclear envelope to the cytoplasmic viral assembly sites with the help of the nuclear egress complex [5]. To fulfill these functions, herpesviral capsids employ multifunctional proteins and have evolved specific properties. The main capsid building blocks (MCP, SCP, triplexes, protease, and scaffold) are conserved across human herpesviruses. We discuss the roles of the auxiliary capsid proteins in viral replication, highlighting both conserved and subfamily-specific roles
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