Varicella Zoster Virus: Proteins and Enzymes

Varicella Zoster Virus (VZV), a member of the human herpes virus family, causes two distinct clinical manifestations: childhood chickenpox(Varicella) and shingles (zoster). Varicella is the outcome of the primary infection with VZV, whereas, zoster is the result of VZV reactivation from latently infected sensory ganglia which occurs predominantly in aging and immunosuppressed individuals. VZV is closely related to the herpes simplex viruses (HSV), sharing much genome homology. The known envelope glycoproteins (gB, gC, gE, gH, gI, gK, gL) correspond with those in HSV, however there is no equivalent of HSV gD. VZV virons are spherical and 150-200 nm in diameter. Its lipid envelope encloses the nucleocapsid of 162 capsomeres arranged in a hexagonal form. Its DNA is a single linear, double strand molecule, 125,000 nt long. Glycoprotein E (gE), a 623 amino acid type I integral membrane protein, is expressed on plasma membranes and in the cytoplasm of VZV infected cells, where it is presumed to be present in the membranes of intracellular vesicles or organelles. VZV gE complexes with gI in the rough endoplasmic reticulum, and most gE exists in the form of gE to gI heterodimers in infected cells. VZV gE is also a predominant component of the virion envelope. The functions of gE, which is encoded by ORF68, are of particular interest because it has been demonstrated that ORF68 is essential for VZV replication. In contrast, the genes for gE proteins can be deleted from herpes simplex virus and pseudorabies virus, albeit with significant reductions in infectivity in cell culture and in animal models. Since the VZV genome does not encode a homologue of gD, VZV gE may have functions that are usually segregated between gD and gE, or the gE to gI complex, in other alphaherpesviruses.