Insulin Degrading Enzyme Induces a Conformational Change in Varicella-Zoster Virus gE, and Enhances Virus Infectivity and Stability

Abstract

Varicella-zoster virus (VZV) glycoprotein E (gE) is essential for virus infectivity and binds to a cellular receptor, insulin-degrading enzyme (IDE), through its unique amino terminal extracellular domain. Previous work has shown IDE plays an important role in VZV infection and virus cell-to-cell spread, which is the sole route for VZV spread in vitro. Here we report that a recombinant soluble IDE (rIDE) enhances VZV infectivity at an early step of infection associated with an increase in virus internalization, and increases cell-to-cell spread. VZV mutants lacking the IDE binding domain of gE were impaired for syncytia formation and membrane fusion. Pre-treatment of cell-free VZV with rIDE markedly enhanced the stability of the virus over a range of conditions. rIDE interacted with gE to elicit a conformational change in gE and rendered it more susceptible to proteolysis. Co-incubation of rIDE with gE modified the size of gE. We propose that the conformational change in gE elicited by IDE enhances infectivity and stability of the virus and leads to increased fusogenicity during VZV infection. The ability of rIDE to enhance infectivity of cell-free VZV over a wide range of incubation times and temperatures suggests that rIDE may be useful for increasing the stability of varicella or zoster vaccines.

Molecular mechanisms of varicella zoster virus pathogenesis

“…Although gE typically forms a heterodimer with gI via a cysteine-rich ectodomain region at residues 208–236, this interaction is not needed to infect T cells 38,39 . In addition, amino acid residues 27–90 are required for binding to insulin-degrading enzyme (IDE), which is a cellular protein that contributes to VZV replication in melanoma cells in vitro and is a proposed entry receptor 41 . However, disrupting these interactions by mutating gE does not affect T cell-xenograft infection, which indicates that IDE is not needed for T cell entry.…”

“…Deleting gI interferes with gE trafficking and secondary envelopment of virions in vitro and completely blocks infection of skin and T cells in vivo , which can be attributed to defective virion assembly 41,71 . Ensuring that gI expression levels are sufficient for normal skin pathogenesis depends on the enhancing effect of the ORF29 DNA-binding protein for IE62 transactivation 43 .…”

In vitro system using human neurons demonstrates that varicella-zoster vaccine virus is impaired for reactivation, but not latency

“…Neurons were infected with VZV at the somal (cell body) or axonal compartment for 2 h at 37°C using a multiplicity of infection (MOI) based on the titer of virus obtained in MRC-5 cells. After 2 h, the virus inoculum was removed, cells were washed with medium and treated with low pH buffer [40 mM sodium citrate, 10 mM potassium chloride, 135 mM sodium chloride (pH 3.2)] for 30 s to inactivate virus that had not entered the cells as described previously (27), and neural differentiation medium was added. For virus reactivation, anti-NGF Ab (AB1528SP; EMD Millipore) was added to the somal and axonal compartments at a final concentration of 50 μg/mL and cultured for 7 d. IgG isotype control Ab (Purified Sheep IgG; R&D Systems) was used as a negative control.…”

Pathogenesis and Current Approaches to Control of Varicella-Zoster Virus Infections

“…In contrast, neither heparin nor mannose 6-phosphate interferes with the cell-to-cell spread of cell-associated VZV. That process requires the insulin-degrading enzyme (IDE), which is cytosolic but is expressed near cell surfaces and can interact with gE (15,16).…”