Abstract
Glycoprotein E (gE) and glycoprotein I (gI) are expressed as a heterodimer on the surface of Herpes simplex virus (HSV). Glycoprotein E binds Fc domain of immunoglobulin G (IgG) and inhibits activities mediated by the IgG Fc domain, contributing to immune evasion by HSV. It has been reported that HSV type 1 gE (gE-1) is capable of binding IgG Fc as a monomer and in a heterodimeric complex with gI, with the heterodimer having 50- to100-fold greater affinity for Fc than gE alone. We report the production of both a soluble form of HSV type 2 gE (gE-2) and a soluble HSV-2 gE/gI heterodimer (gE-2/gI-2). Characterization of soluble gE-2 by surface plasmon resonance (SPR) demonstrates that it is incapable of binding human IgG or the IgG Fc domain. Co-expression with HSV-2 gI (gI-2) and purification of the gE-2/gI-2 heterodimer enable gE-2 to bind human IgG through its Fc domain. We hypothesize that functional epitopes of wildtype gE-2 may be masked by plasma IgG Fc and affect the immunogenicity of the gE-2/gI-2 heterodimer as a vaccine antigen. A series of gE-2 mutations within the surface-exposed Fc:gE-2 interface was designed, and gE-2 mutants were co-expressed with gI-2. Evaluation of twelve gE-2 mutant heterodimers by SPR assay identified nine gE-2 mutations which abrogated or reduced Fc binding while maintaining heterodimer formation with gI. Vaccinating rabbits with the four most Fc-binding deficient gE-2/gI-2 heterodimers elicited comparable anti-heterodimer binding antibody titers and statistically significantly higher serum neutralization antibody levels than wildtype heterodimers. Taken together, these data support the concept of rational antigen design for improved vaccine candidates.
Highlights
Herpes simplex virus type 2 (HSV-2) is an enveloped, double-stranded DNA virus and is the primary cause of genital ulcers in the United States [1]
To gain insight into the properties and function of HSV-2 glycoproteins Glycoprotein E (gE)-2 and glycoprotein I (gI)-2, we explored the ability of gE-2 to associate with immunoglobulin G (IgG) Fc either alone or as part of the heterodimer with gI-2
The requirement of the formation of gE-2/gI-2 complex for IgG binding observed here, taken together with previous data on gE-1/gI-1 showing increased IgG Fc-binding, suggests that gI plays an important role within the gE/gI heterodimer with respect to IgG Fc binding for both HSV-1 and HSV-2. gI may induce conformational changes within gE upon complex formation and thereby increase its affinity for IgG Fc
Summary
Herpes simplex virus type 2 (HSV-2) is an enveloped, double-stranded DNA virus and is the primary cause of genital ulcers in the United States [1]. A distinguishing feature of herpesviruses, HSV-2 included, is the establishment of a latent infection by the virus in peripheral nervous system neurons. Despite a primed immune system, reactivation of the virus is frequent, often leading to lesions at the original site of infection. The HSV-2 genome encodes multiple glycoproteins that are expressed on the virus surface. Glycoprotein E (gE) and glycoprotein I (gI) are expressed as a heterodimer on the surface of virions and infected cells [2]. The gE/gI heterodimer is responsible for cell-to-cell spread of the virus [3,4]. Glycoprotein E plays a role in immune evasion of the virus. It has been shown that gE binds to the Fc domain of immunoglobulin
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