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J. Virol., Jan 1997, 110-119, Vol 71, No. 1
JK Olson, GA Bishop and C Grose
Varicella-zoster virus (VZV) glycoprotein gE is the predominant viral cell
surface molecule; it behaves as an Fc receptor for immunoglobulin G, but
its central function may be more closely related to viral egress and
cell-to-cell spread. To further analyze the receptor properties of VZV gE,
the gE gene (also called open reading frame 68) was expressed by a
baculovirus vector in insect cells. The recombinant baculovirus gE product
had a molecular mass of 64 kDa, smaller than the previously documented 98
kDa of mature gE expressed in mammalian cells. The major reason for the
lowered molecular mass was diminished glycosylation. In addition to the
64-kDa form, a larger (130-kDa) form was observed in insect cells and
represented dimerized 64-kDa molecules. Both the monomeric and dimeric gE
forms were highly phosphorylated in insect cells. Protein kinase assays
conducted in vitro with [gamma-32P]ATP and [gamma-32P]GTP indicated that
endogenous casein kinase II was phosphorylating monomeric gE, while the
dimeric gE form was phosphorylated by another kinase which did not utilize
[gamma-32P]GTP. When immobilized recombinant gE molecules were probed with
a monoclonal antibody which specifically recognizes a phosphotyrosine
linkage, the gE dimer was found to be tyrosine phosphorylated whereas the
monomer was not similarly modified. When recombinant gE produced in HeLa
cells was probed with the same antiphosphotyrosine antibody, a dimeric gE
form at 130 kDa was detected on the cell surface. These results suggested
that VZV gE closely resembled other cell surface receptors, being modified
on its various forms by both serine/threonine and tyrosine protein kinases.
In this case, tyrosine phosphorylation occurred on a previously
unrecognized and underglycosylated VZV gE dimeric product.
Copyright © 1997, American Society for Microbiology
Varicella-zoster virus Fc receptor gE glycoprotein: serine/threonine and tyrosine phosphorylation of monomeric and dimeric forms
Department of Microbiology and Immunology Program, University of Iowa College of Medicine, Iowa City 52242, USA.
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