SUMMARYIn contrast to other viral glycoproteins, the herpes simplex virus (HSV) glycoprotein C (gC) binds to the N-acetylgalactosamine-specific Helix pomatia lectin (HPA). In the present paper gC was purified by affinity chromatography with monospecific antibodies and the purified glycoprotein was subjected to protease digestion. HPAbinding protease-resistant glycopeptides were isolated by lectin affinity chromatography. The isolated structures did not bind to concanavalin A and seemed to lack charged groups as determined by ion-exchange chromatography. In gel filtration, the glycopeptides appeared in two peaks with molecular weights higher than 4000. The HPA-binding structures of gC were synthesized in the presence of tunicamycin, indicating that they belong to the O-glycosyl class of oligosaccharides. In addition to HPA-binding oligosaccharides, synthesis of tunicamycin-resistant wheat germ lectinbinding gC oligosaccharides was demonstrable. These were sensitive to sialidase and apparently unrelated to the HPA-binding oligosaccharides.

In the present study we investigated to what extent the peripheral carbohydrate structure of N-linked glycans influences the antigenic properties of human immunodeficiency virus type 1 glycoprotein 120 (gpl20). Recombinant gpl20 was purified from GMK cells infected with a recombinant vaccinia virus expressing gpl20. Purified gpl20 was then coated onto 96-well ELISA microplates and subjected to sequential removal of peripheral monosaccharide units. Modified or unmodified gpl20 was then incubated with monoclonal antibodies recognizing specific epitopes of gpl20 and with a reporter lectin to determine the extent of carbohydrate elimination. Antibody and lectin binding was quantified in an enzyme-linked system. We found that the carbohydrate structure NeuAc-Galfl(1-4) of N-linked glycans, defined both by lectin reactivity and by specific glycosidases, is involved in modulating the binding of antibody to a number of epitopes of peptide nature. The binding of antibody to one class of epitopes, situated in a region between amino acids 200 and 230, was strongly increased by removal of NeuAc-Galfl(1-4), whereas the binding to epitopes in the V3 region was decreased and the binding to epitopes in the far N-terminal region was not altered by the treatment. These results suggested that peripheral structures of N-glycans are involved in modulating the overall conformation of gp 120.

SUMMARYThe carbohydrate dependence of epitopes in the herpes simplex virus type 1-specified glycoprotein C (gC) was studied using a new solid-phase assay procedure. Glycoprotein C, coated on 96-well microtitre plates, was treated with sialidase and increasing concentrations of periodate. A sequential removal of peripheral monosaccharides from the oligosaccharides of gC was ascertained by an enzyme-linked lectin assay. By using a panel of gC-specific monoclonal antibodies in ELISA, it was found that gC contained two types of epitopes differing in their dependence on terminal galactose and sialic acid for expression. Control experiments indicated that the carbohydrate-dependent epitopes were peptide structures and that the carbohydrates did not directly participate in the antibody-binding reaction. The carbohydrate-dependent epitopes were mapped to antigenic site II, according to the proposed nomenclature, whereas those expressed also in the absence of peripheral sugars were located mainly in antigenic site I. These results were compatible with the relative distribution of oligosaccharides in the gC molecule.

We have previously shown that the herpes simplex virus type 1 (HSV-1)-specified glycoprotein C (gC-1) produced in epitheloid cells contains epitopes of peptide nature, which are dependent on galactose of oligosaccharides for their expression. In the present communication we report that these epitopes are expressed in a mouse neuroblastoma cell line (C1300) with low levels of galactosyl transferases. However, in place of galactose the glycoprotein from C1300 cells was found to contain oligosaccharides with additional fucose units. Fucosidase treatment, but not galactosidase treatment, abolished the antigenic activity of the carbohydrate-dependent epitopes. Altogether the resuits indicated that the carbohydrate-dependent epitopes of gC-1 from C1300 cells were stabilized by peripheral sugars of N-linked oligosaccharides rather than O-linked ones and that fucose could substitute for terminal galactose in promoting the activity of the carbohydrate-dependent epitopes. This is the first demonstration of the involvement of fucose in the establishment of a carbohydrate-dependent epitope of peptide nature. The results also demonstrated that reversible carbohydrate-peptide interactions were responsible for the activity of the carbohydrate-dependent epitopes.

We have described two types of oligosaccharide modification influencing the antigenicity of the herpes simplex virus type 1 (HSV-1)-specified glycoprotein C (gC-1). First, the expression of several epitopes belonging to antigenic site II of gC-1 is dependent on the peripheral galactose of N-linked oligosaccharides. We have also shown that treatment of HSV-1-infected cells with 5-n-propyl-2'-deoxyuridine (PdU) under certain circumstances results in other modifications of peripheral carbohydrate determinants, which are associated with increased antigenic activity of gC-1. In the present study we have mapped and characterized the epitopes susceptible to PdU induction by analysing the reactivity to a number of monoclonal antibodies defining several epitopes of antigenic sites I and II. The results indicate that the strict galactose dependence of epitopes and the PdU-induced increase of antigenic activity are independent and unrelated phenomena. Thus, we identified galactose-dependent epitopes that were not PdU-inducible and vice versa, and some epitopes were both galactose-dependent and PdUinducible. The results support a model where PdU treatment blocks synthesis of an antigen-masking carbohydrate determinant. In addition, PdU treatment of HSV-l-infected cells seemed to increase the antigenic activity of other HSV-1 glycoproteins.