Identification of mar mutations in herpes simplex virus type 1 glycoprotein B which alter antigenic structure and function in virus penetration.

Analysis of six monoclonal antibody-resistant (mar) mutants in herpes simplex virus type 1 glycoprotein B identified two type-common (II and III) and two type-specific (I and IV) antigenic sites on this molecule. To derive additional information on the location of these sites, mar mutations were mapped and nucleotide alterations were identified by DNA sequencing. Each mutant carried a single amino acid substitution resulting from a G-to-A base transition. Alterations affecting antibody neutralization were identified at residues 473, 594, 305, and 85 for mutants in sites I through IV, respectively. Two clonally distinct site II antibodies each selected mar mutants (Gly to Arg at residue 594) that exhibited a reduction in the rate of entry (roe) into host cells. A site II mar revertant that regained sensitivity to neutralization by site II antibodies also showed normal entry kinetics. DNA sequencing of this virus identified a single base reversion of the site II mar mutation, resulting in restoration of the wild-type sequence (Arg to Gly). This finding demonstrated that the mar and roe phenotypes were the result of a single mutation. To further define structures that contributed to antibody recognition, monoclonal antibodies specific for all four sites were tested for their ability to immune precipitate a panel of linker-insertion mutant glycoprotein B molecules. Individual polypeptides that contained single insertions of 2 to 28 amino acids throughout the external domain were not recognized or were recognized poorly by antibodies specific for sites II and III, whereas no insertion affected antibody recognition of sites I and IV. mar mutations affecting either site II or III were previously shown to cause temperature-sensitive defects in glycoprotein B glycosylation, and variants altered in both these sites were temperature sensitive for virus production. Taken together, the data indicate that antigenic sites II and III are composed of higher-order structures whose integrity is linked with the ability of glycoprotein B to function in virus infectivity.