Cell fusion induced by plasmids expressing homologous or heterologous mixtures of the HSV-1 or HSV-2 glycoproteins. The cell fusion assay was performed by transfecting CHO effector cells with plasmids expressing the indicated glycoproteins or vector alone (neg). The effector cells were mixed with CHO target cells expressing only the CHO endogenous receptor or also nectin-2, nectin-1, or HVEM. Effector cells transfected with an homologous set of HSV-1 or HSV-2 glycoproteins are the controls. The glycoprotein substituted is indicated with a minus (−), and the substituting protein is indicated with a plus (+). Cell fusion was quantified by measurements of luciferase activity (arbitrary units divided by 10 to give the numbers shown on the y axis). The values shown are means and standard deviations from one experiment performed in triplicate. The results presented are representative of at least two other additional experiments.

Cell fusion induced by gD2/1 or gD1/2 hybrid molecules in combination with the other HSV-1 or HSV-2 glycoproteins. These hybrids have the first 66 amino acids from gD1 or gD2 and the remainder from gD2 or gD1, respectively. The CHO effector cells were transfected with plasmids expressing the indicated glycoproteins or vector alone (neg). Effector cells were mixed with CHO target cells expressing only the CHO endogenous receptor or also nectin-2, nectin-1, or HVEM. Cell fusion was quantified by measurements of luciferase activity (arbitrary units divided by 100 to give the numbers shown on the y axis). The values shown are means and standard deviations from one experiment performed in triplicate. The results presented are representative of at least two other additional experiments.

(A) Alignment of the 66 N-terminal amino acids of HSV-1(KOS) gD and HSV-2(333) gD. Dots indicate identity. The positions where the amino acids differ are indicated. (B) Backbone trace of the crystal structure of gD1 bound to HVEM (1). HVEM is shown in black, and gD1 is shown in gray. Residues that have been substituted in the gD1 mutants are displayed in different colors.