INTERACTION OF HERPES-SIMPLEX VIRUS GLYCOPROTEIN GC WITH MAMMALIAN-CELL SURFACE MOLECULES

The entry of herpes simplex virus (HSV) into mammalian cells is a mult istep process beginning with an attachment step involving glycoprotein s gC and gB. A second step requires the interaction of glycoprotein go with a cell surface molecule. We explored the interaction between gC and the cell surface by using purified proteins in the absence of dete rgent. Truncated forms of gC and go, gC1(457t), gC2(426t), and gD(306t ), lacking the transmembrane and carboxyl regions were expressed in th e baculovirus system. We studied the ability of these proteins to bind to mammalian cells, to bind to immobilized heparin, to block HSV type 1 (HSV-1) attachment to cells, and to inhibit plaque formation by HSV -1. Each of these gC proteins bound to conformation-dependent monoclon al antibodies and to human complement component C3b, indicating that t hey maintained the same conformation of gC proteins expressed in mamma lian cells. Biotinylated gC1(457t) and gC2(426t) each bind to several cell lines. Binding was inhibited by an excess of unlabeled gC but not by go, indicating specificity. The attachment of gC to cells involves primarily heparan sulfate proteoglycans, since heparitinase treatment of cells reduced gC binding by 50% but had no effect on go binding. M oreover, binding of gC to two heparan sulfate-deficient L-cell lines, gro2C and sog9, both of which are mostly resistant to HSV infection, w as markedly reduced. Purified gD1(306t), however, bound equally well t o the two mutant cell lines. In contrast, saturating amounts of gC1(45 7t) interfered with HSV-1 attachment to cells but failed to block plaq ue formation, suggesting a role for gC in attachment but not penetrati on. A mutant form of gC lacking residues 33 to 123, gC1(Delta 33-123t) , expressed in the baculovirus system, bound significantly less well t o cells than did gC1(457t) and competed poorly with biotinylated gC1(4 57t) for binding. These results suggest that residues 33 to 123 are im portant for gC attachment to cells. In contrast, both the mutant and w ild-type forms of gC bound to immobilized heparin, indicating that bin ding of these proteins to the cell surface involves more than a simple interaction with heparin. To determine that the contribution of the N -terminal region of gC is important for HSV attachment, we compared se veral properties of a mutant HSV-1 which contains gC lacking amino aci ds 33 to 123 to those of its parental virus, which contains full-lengt h gC. The mutant bound less well to cells than the parental virus but exhibited normal growth properties. While we cannot rule out the possi bility that other regions of gC contribute to its function in attachme nt, our studies show that the N terminus of gC is important for effici ent attachment to cells.