Wesley C. Wilcox

Structure and Function of Glycoprotein D of Herpes Simplex Virus

Glycoprotein D (gD) is a structural component of the herpes simplex virus (HSV) envelope which is essential for virus penetration into host cells. The function of this protein is highly dependent on its structure, and its structure, in turn, is dependent on maintenance of three intact disulfide bonds. Our goal has been to relate structural features of this glycoprotein to its function in virus infection. We have constructed a detailed antigenic map of the protein. A large panel of gD mutants was assayed for gD function using a complementation assay. At least one antigenic site, which binds antibodies with high titers of virus-neutralizing activity, overlaps a portion of the functional domain of gD. In addition, we constructed mutants which lacked one or all three sites for addition of N-linked oligosaccharides (N-CHO). We found that a triple mutant lacking all three N-CHO sites is able to function normally in virus infection and when recombined back into the virus genome had very little effect on the phenotype of the resulting recombinant. Thus, it appears that N-CHO are not necessary for gD function, though there were some changes in gD structure. In contrast, removal of any of the cysteine residues which participate in disulfide bonding has drastic effects on gD structure and function. Using a combination of genetic and biochemical approaches, we showed that the disulfide bond pattern of gD is Cys 1 (aa 66) to Cys 5 (aa 189), Cys 2 (aa 106) to Cys 6 (aa 202), and Cys 3 (aa 118) to Cys 4 (aa 127). We postulate that a similar disulfide bond arrangement exists in other gD homologs and that gD is part of a superfamily of herpes proteins that includes HSV gI (and its homologs) and HSV gG (and its homologs), all with similar disulfide bonding to gD.

The Poxvirus Antigens

Only a short time has elapsed since the poxvirus literature was reviewed in a most thorough and comprehensive fashion (Joklik, 1966). It is the purpose of this communication to focus in somewhat more detail on a single facet of the overall picture, the poxvirus-coded proteins or antigens. The reader will note that not every investigation bearing on this subject has been cited. The preponderance of our effort has been to review the more recent literature most extensively, with a view towards emphasizing what seems to us are emerging patterns of function. We do not apologize for this approach for although it is intrinsically somewhat arbitrary it has the merit of making the subject more manageable. It also should be apparent to the reader that at least one entire area of investigation, the poxvirus hemagglutinins, has not been mentioned. Relatively little has been done in this field in very recent times and, inasmuch as this subject has been adequately reviewed in 1966 (Joklik, 1966), there seems to be little profit in repetition at this time.