Abstract
Alphaherpesviruses like herpes simplex virus are large DNA viruses characterized by their ability to establish lifelong latent infection in neurons. As for all herpesviruses, alphaherpesvirus virions contain a protein-rich layer called “tegument” that links the DNA-containing capsid to the glycoprotein-studded membrane envelope. Tegument proteins mediate a diverse range of functions during the virus lifecycle, including modulation of the host-cell environment immediately after entry, transport of virus capsids to the nucleus during infection, and wrapping of cytoplasmic capsids with membranes (secondary envelopment) during virion assembly. Eleven tegument proteins that are conserved across alphaherpesviruses have been implicated in the formation of the tegument layer or in secondary envelopment. Tegument is assembled via a dense network of interactions between tegument proteins, with the redundancy of these interactions making it challenging to determine the precise function of any specific tegument protein. However, recent studies have made great headway in defining the interactions between tegument proteins, conserved across alphaherpesviruses, which facilitate tegument assembly and secondary envelopment. We summarize these recent advances and review what remains to be learned about the molecular interactions required to assemble mature alphaherpesvirus virions following the release of capsids from infected cell nuclei.
Highlights
The herpesviruses are classified into three subfamilies, the alpha, beta- and gammaherpesviruses, all of which share a common virion morphology and a group of approximately 40 conserved genes that play key roles during virus replication [1]
Three alphaherpesviruses are capable of infecting humans: herpes simplex virus (HSV)-1 and HSV-2, which usually cause only mild orofacial or genital lesions, respectively, but can cause more severe disease in neonates or the immunocompromised, and varicella-zoster virus (VZV), the etiological agent of chickenpox and shingles [1]
Designated as the portal vertex associated tegument (PVAT), this feature appears to maintain a constant distance between the portal vertex and the viral membrane, meaning that for virions with a large diameter the portal vertex typically corresponds with the proximal pole
Summary
The herpesviruses are classified into three subfamilies, the alpha-, beta- and gammaherpesviruses, all of which share a common virion morphology and a group of approximately 40 conserved genes that play key roles during virus replication [1]. Primary alphaherpesvirus infection occurs in epithelial cells and is frequently asymptomatic. Viruses 2015, 7, 5084–5114 Viruses 2015, 7, page–page resulting in reettrrooggrraaddee ttrraannssppoorrtt ooff ccaappssiiddss ttoo tthhee cceellll bbooddyy dduurriinngg vviirraall eennttrryy ((FFiigguurree 11)). The movement of viral particles along axons during entry and egress is bidirectional and saltatory suggesting tthhaatt bbootthh ddyynneeiinn aanndd kkiinneessiinn mmoottoorr pprrootteeiinnss mmaayy bbee ininvvoolvlveedd. The focus of this review will be on the latter cytoplasmic stages of maturation, tegumentation and secondary envelopment; for reviews of nuclear egress see [12,13,15]. Tegument proteins are generally designated as belonging to either “inner” or “outer” tegument depending on their preferential association with either the capsid or viral membranes during entry and egress, and based on their fractionation be5h0a8v6iour after virion lysis with non-ionic detergents [13,20,21]. More recently the localization of specific tegument proteins within the tegument layer of
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