CHARACTERIZATION OF REGIONS OF HERPES-SIMPLEX VIRUS TYPE-1 GLYCOPROTEIN-E INVOLVED IN BINDING THE FC DOMAIN OF MONOMERIC IGG AND IN FORMINGA COMPLEX WITH GLYCOPROTEIN-I

Glycoprotein E (gE) and glycoprotein I (gl) of herpes simplex virus ty pe 1 form a molecular complex that binds the Fc domain of monomeric Ig G. Two approaches were used to define regions of gE-1 involved in mono meric IgG binding and complex formation with gl-1. First, we construct ed 22 in-frame gE-1 linker-insertion mutants and, in cotransfection ex periments with gl-1, assayed each mutant for IgG monomer binding and t he ability to complex with gl-1. Nine mutants with insertions between gE-1 amino acids 235 and 380 failed to bind IgG monomers, whereas muta nts outside this region retained binding activity. Each mutant reacted with several gE-1 mAbs, was detected at the cell surface, and was ful ly processed. Only two gE-1 mutants with insertions at residues 235 an d 264 lost the ability to co-immunoprecipitate with gl-1, wh ich defin es a region of gE-1 that comp teres with gl-1. As an additional approa ch, we assayed 8 gE-1/gD-1 fusion proteins containing large overlappin g gE-1 peptides inserted within the ectodomain of gD-1 for binding of IgG monomers and complex formation with gl-1. Three fusion proteins co ntaining gE-1 peptides that overlap at residues 183-402 bound monomeri c IgG. This region of gE-1 includes the Fc binding region defined by l inker insertion mutagenesis. Five fusion proteins containing gE-1 pept ides that overlap at residues 183-288 were co-immunoprecipitated with gl-1, confirming results of gE-1 linker insertion mutagenesis. These s tudies define two regions on gE-1 involved in Fc binding activity, one that interacts with gl-1, and another that binds IgG.