Structure-function Profiles of Nine Varicella-Zoster Virus Glycoproteins: Endocytosis, Entry And Egress
Charles Grose, Susan Vleck, Odd Andre Karlsen and Eduardo A. Montalvo
from: Alphaherpesviruses: Molecular Virology (Edited by: Sandra K. Weller). Caister Academic Press, U.K. (2011)
Varicella zoster virus has a smaller genome than herpes simplex virus and therefore encodes fewer glycoproteins. In this chapter, nine VZV glycoproteins are profiled, including gE, gI, gC, gH, gL, gB, gK, gM, and gN. Although all VZV glycoproteins have HSV homologs, functions occasionally have greatly shifted. For example, VZV gE is the predominant VZV glycoprotein and exists as a monomer, dimer and trimer, as well as a gE/gI complex. VZV gE is essential, unlike HSV gE. Even though essential, mutations in gE had been detected in wild type VZV strains that exhibit an accelerated cell-spread phenotype. The VZV gC glycoprotein differs from HSV gC in that both transcription and translation of VZV gC are remarkably delayed in cultured cells; often VZV gC protein is difficult to detect altogether. The VZV gH/gL complex resembles the HSV gH/gL complex is that both are critical for virus induced fusion. Fusion is a prominent feature of VZV infected cells. Neutralization antibody to VZV gH dramatically reduces the spread of virus and limits pathogenesis in the skin. The VZV gB glycoprotein is also involved in virus-induced fusion. Of interest, four VZV glycoproteins (gE, gI, gH and gB) have functional endocytosis motifs in their cytoplasmic tail. Thus, all four are internalized from the cell surface in clathrin coated vesicles. This pathway appears critical for the process of virion envelopment in the assembly compartment. Even though abundant amounts of most glycoproteins are produced in cell culture, assembly of fully enveloped and infectious VZV particles rarely occurs. The particle:plaque forming unit ratio remains an extremely high 40,000:1. Likewise, the aberrant assembly process severely limits any assessment of egress mechanisms read more ...