Molecular basis of type-specificity in herpes simplex virus glycoprotein C.

Abstract

Herpes simplex virus (HSV) is a human herpesvirus which is found in two serotypes. Studies of the immune response to HSV have revealed that many of the antibodies elicited react with both serotypes. Of the major envelope glycoproteins, glycoprotein C (gC) is unique in that most antibodies to this glycoprotein react with only one serotype. gC-1 (type 1) and gC-2 (type 2) share a significant amount of homology; therefore the antibody responses they elicit must recognize epitopes that are different between the two. Previous studies have identified two antigenic sites in gC-1 through the use of a panel of monoclonal antibodies (MAbs). The objective of this dissertation was to study the antigenic structure of gC-1 and gC-2 and identify components important to serotype specificity and therefore important to particular epitopes. Initially, chimeric genes expressing gC-1/gC-2 hybrid proteins were constructed and introduced into HSV-1. Antigenic structure of these proteins was studied by testing them with several gC-1 and gC-2 MAbs by immunoprecipitation from extracts of infected cells, neutralization assays and flow cytometry. All MAbs were able to bind one or the other hybrid protein, indicating that the structures of the antigenic sites are independent. Site-directed mutagenesis was used to introduce point mutations into site I of gC-1 and gC-2 so that residues from the heterotypic serotype were introduced. The mutants were assayed in the same way as the hybrid proteins. A mutation which resulted in binding of a MAb specific for the heterotypic serotype identified a residue necessary to an epitope and important for type-specificity. A single amino acid position in both gC-1 and gC-2 was identified which was responsible for type-specificity in both cases and three additional amino acid positions were responsible for another example of type-specificity. Binding of some gC-2 MAbs to site I was not altered, indicating that type-specificity of site I is not restricted to the region of the mutated residues. This study allowed the identification of a small number of amino acids which are important for type-specificity of gC. The results provide insight into the molecular basis of antigenicity in gC, particularly for site I. This work also contributes to the understanding of glycoprotein epitopes at the amino acid level and antigenic features of proteins.