Mapping of the structural gene for the herpes simplex virus type 2 counterpart of herpes simplex virus type 1 glycoprotein C and identification of a type 2 mutant which does not express this glycoprotein

Virus-Encoded Complement Regulators: Current Status

Viruses require a host for replication and survival and hence are subjected to host immunological pressures. The complement system, a crucial first response of the host immune system, is effective in targeting viruses and virus-infected cells, and boosting the antiviral innate and acquired immune responses. Thus, the system imposes a strong selection pressure on viruses. Consequently, viruses have evolved multiple countermeasures against host complement. A major mechanism employed by viruses to subvert the complement system is encoding proteins that target complement. Since viruses have limited genome size, most of these proteins are multifunctional in nature. In this review, we provide up to date information on the structure and complement regulatory functions of various viral proteins.

Herpes simplex virus Membrane Fusion

Herpes simplex virus mediates multiple distinct fusion events during infection. HSV entry is initiated by fusion of the viral envelope with either the limiting membrane of a host cell endocytic compartment or the plasma membrane. In the infected cell during viral assembly, immature, enveloped HSV particles in the perinuclear space fuse with the outer nuclear membrane in a process termed de-envelopment. A cell infected with some strains of HSV with defined mutations spread to neighboring cells by a fusion event called syncytium formation. Two experimental methods, the transient cell-cell fusion approach and fusion from without, are useful surrogate assays of HSV fusion. These five fusion processes are considered in terms of their requirements, mechanism, and regulation. The execution and modulation of these events require distinct yet often overlapping sets of viral proteins and host cell factors. The core machinery of HSV gB, gD, and the heterodimer gH/gL is required for most if not all of the HSV fusion mechanisms.

Widely Used Herpes Simplex Virus 1 ICP0 Deletion Mutant Strain dl1403 and Its Derivative Viruses Do Not Express Glycoprotein C Due to a Secondary Mutation in the gC Gene

Herpes simplex virus 1 (HSV-1) ICP0 is a multi-functional phosphoprotein expressed with immediate early kinetics. An ICP0 deletion mutant, HSV-1 dl1403, has been widely used to study the roles of ICP0 in the HSV-1 replication cycle including gene expression, latency, entry and assembly. We show that HSV-1 dl1403 virions lack detectable levels of envelope protein gC, and that gC is not synthesized in infected cells. Sequencing of the gC gene from HSV-1 dl1403 revealed a single amino acid deletion that results in a frameshift mutation. The HSV-1 dl1403 gC gene is predicted to encode a polypeptide consisting of the original 62 N-terminal amino acids of the gC protein followed by 112 irrelevant, non-gC residues. The mutation was also present in a rescuant virus and in two dl1403-derived viruses, D8 and FXE, but absent from the parental 17+, suggesting that the mutation was introduced during the construction of the dl1403 virus, and not as a result of passage in culture.

Virus–complement interactions: an assiduous struggle for dominance

The complement system is a major component of the innate immune system that recognizes invading pathogens and eliminates them by means of an array of effector mechanisms, in addition to using direct lytic destruction. Viruses, in spite of their small size and simple composition, are also deftly recognized and neutralized by the complement system. In turn, as a result of years of coevolution with the host, viruses have developed multiple mechanisms to evade the host complement. These complex interactions between the complement system and viruses have been an area of focus for over three decades. In this article, we provide a broad overview of the field using key examples and up-to-date information on the complement-evasion strategies of viruses.

Viral mimicry of the complement system

The complement system is a potent innate immune mechanism consisting of cascades of proteins which are designed to fight against and annul intrusion of all the foreign pathogens. Although viruses are smaller in size and have relatively simple structure, they are not immune to complement attack. Thus, activation of the complement system can lead to neutralization of cell-free viruses, phagocytosis of C3b-coated viral particles, lysis of virus-infected cells, and generation of inflammatory and specific immune responses. However, to combat host responses and succeed as pathogens, viruses not only have developed/adopted mechanisms to control complement, but also have turned these interactions to their own advantage. Important examples include poxviruses, herpesviruses, retroviruses, paramyxoviruses and picornaviruses. In this review, we provide information on the various complement evasion strategies that viruses have developed to thwart the complement attack of the host. A special emphasis is given on the interactions between the viral proteins that are involved in molecular mimicry and the complement system.

Kinetic analysis of glycoprotein C of herpes simplex virus types 1 and 2 binding to heparin, heparan sulfate, and complement component C3b

Glycoprotein C (gC) from herpes simplex virus (HSV) facilitates virus entry by attaching the virion to host cell-surface heparan sulfate (HS). Although gC from HSV-1 (gC1) and from HSV-2 (gC2) bind to heparin, gC2 is believed to play a less significant role than gC1 in attachment of virus to cells. This attachment step is followed by the binding of gD to one of several cellular receptors. gC also plays an important role in immune evasion by binding to the C3b fragment of the third component of the host complement system. Yet, although both gC1 and gC2 protect HSV against complement-mediated neutralization, only gC on HSV-1-infected cells acts as a receptor for C3b. We used optical biosensor technology to quantitate the affinities (K(D)) and the stabilities (k(off)) between both serotypes of gC with heparin, HS, and C3b to address three questions concerning gC interactions. First, can differences in affinity or stability account for differences between the contributions of HSV-1 and HSV-2 gC in attachment? Our data show that the gC2-HS complex is highly unstable (k(off) = 0.2 s(-1)) compared to the gC1-HS complex (k(off) = 0.003 s(-1)), suggesting why gC2 may not play an important role in attachment of virus to cells as does gC1. Second, does gC2 have a lower affinity for C3b than does gC1, thereby explaining the lack of C3b-receptor activity on HSV-2 infected cells? Surprisingly, gC2 had a 10-fold higher affinity for C3b compared to gC1, so this functional difference in serotypes cannot be accounted for by affinity. Third, do differences in gC-HS and gD-receptor affinities support a model of HSV entry in which the gC-HS interaction is of lower affinity than the gD-receptor interaction? Our biosensor results indicate that gC has a higher affinity for HS than gD does for cellular receptors HveA (HVEM) and HveC (nectin-1).

Herpes simplex virus type 2 glycoprotein G-negative clinical isolates are generated by single frameshift mutations

Herpes simplex virus (HSV) codes for several envelope glycoproteins, including glycoprotein G-2 (gG-2) of HSV type 2 (HSV-2), which are dispensable for replication in cell culture. However, clinical isolates which are deficient in such proteins occur rarely. We describe here five clinical HSV-2 isolates which were found to be unreactive to a panel of anti-gG-2 monoclonal antibodies and therefore considered phenotypically gG-2 negative. These isolates were further examined for expression of the secreted amino-terminal and cell-associated carboxy-terminal portions of gG-2 by immunoblotting and radioimmunoprecipitation. The gG-2 gene was completely inactivated in four isolates, with no expression of the two protein products. For one isolate a normally produced secreted portion and a truncated carboxy-terminal portion of gG-2 were detected in virus-infected cell medium. Sequencing of the complete gG-2 gene identified a single insertion or deletion of guanine or cytosine nucleotides in all five strains, resulting in a premature termination codon. The frameshift mutations were localized within runs of five or more guanine or cytosine nucleotides and were dispersed throughout the gene. For the isolate for which a partially inactivated gG-2 gene was detected, the frameshift mutation was localized upstream of but adjacent to the nucleotides coding for the transmembranous region. Thus, this study demonstrates the existence of clinical HSV-2 isolates which do not express an envelope glycoprotein and identifies the underlying molecular mechanism to be a single frameshift mutation.

Disulfide bond structure determination and biochemical analysis of glycoprotein C from herpes simplex virus

A biochemical analysis of glycoprotein C (gC of herpes simplex virus was undertaken to further characterize the structure of the glycoprotein and to determine its disulfide bond arrangement. We used three recombinant forms of gC, gC1(457t), gC1(delta33-123t), and gC2(426t), each truncated prior to the transmembrane region. The proteins were expressed and secreted by using a baculovirus expression system and have been shown to bind to monoclonal antibodies which recognize discontinuous epitopes and to complement component C3b in a dose-dependent manner. We confirmed the N-terminal residues of each mature protein by Edman degradation and confirmed the internal deletion in gC1(delta33-123t). The molecular weight and extent of glycosylation of gC1 (457t), gC1(delta33-123t), and gC2(426t) were determined by treating each protein with endoglycosidases and then subjecting it to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric analysis. The data indicate that eight to nine of the predicted N-linked oligosaccharide sites on gC1(457t) are occupied by glycans of approximately 1,000 Da. In addition, O-linked oligosaccharides are present on gC1(457t), primarily localized to the N-terminal region (amino acids [aa] 33 to 123) of the protein. gC2(426t) contains N-linked oligosaccharides, but no O-linked oligosaccharides were detected. To determine the disulfide bond arrangement of the eight cysteines of gC1(457t),the protein was cleaved with cyanogen bromide. SDS-PAGE analysis followed by Edman degradation identified three cysteine-containing fragments which are not connected by disulfide linkages. Chemical modification of cysteines combined with matrix-assisted laser desorption ionization mass spectrometry identified disulfide bonds between cysteine 1 (aa 127) and cysteine 2 (aa 144) and between cysteine 3 (aa 286) and cysteine 4 (aa 347). Further proteolysis of the cyanogen bromide-generated fragment containing cysteine 5 through cysteine 8, combined with mass spectrometry and Edman degradation, showed that disulfide bonds link cysteine 5 (aa 386) to cysteine 8 (aa 442) and cysteine 6 (aa 390) to cysteine 7 (aa 419). A similar disulfide bond arrangement is postulated to exist in gC homologs from other herpesviruses.

Interaction of herpes simplex virus glycoprotein gC with mammalian cell surface molecules

The entry of herpes simplex virus (HSV) into mammalian cells is a multistep process beginning with an attachment step involving glycoproteins gC and gB. A second step requires the interaction of glycoprotein gD with a cell surface molecule. We explored the interaction between gC and the cell surface by using purified proteins in the absence of detergent. Truncated forms of gC and gD, gC1(457t), gC2(426t), and gD1(306t), lacking the transmembrane and carboxyl regions were expressed in the 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 monoclonal antibodies and to human complement component C3b, indicating that they maintained the same conformation of gC proteins expressed in mammalian 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 gD, 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 gD binding. Moreover, binding of gC to two heparan sulfate-deficient L-cell lines, gro2C and sog9, both of which are mostly resistant to HSV infection, was markedly reduced. Purified gD1 (306t), however, bound equally well to the two mutant cell lines. In contrast, saturating amounts of gC1(457t) interfered with HSV-1 attachment to cells but failed to block plaque formation, suggesting a role for gC in attachment but not penetration. A mutant form of gC lacking residues 33 to 123, gC1(delta 33-123t), expressed in the baculovirus system, bound significantly less well to cells than did gC1(457t) and competed poorly with biotinylated gC1(457t) for binding. These results suggest that residues 33 to 123 are important for gC attachment to cells. In contrast, both the mutant and wild-type forms of gC bound to immobilized heparin, indicating that binding 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 several properties of a mutant HSV-1 which contains gC lacking amino acids 33 to 123 to those of its parental virus, which contains full-length gC. The mutant bound less well to cells than the parental virus but exhibited normal growth properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of the contributions of herpes simplex virus type 1 membrane proteins to the induction of cell-cell fusion

The contributions of a set of herpes simplex virus type 1 membrane proteins towards the process of cell-cell fusion were examined with a series of deletion mutants into which a syncytial mutation had been introduced at codon 855 of the glycoprotein B (gB) gene. Analysis of the fusion phenotypes of these recombinant viruses in Vero cells revealed that while gC, gG, US5, and UL43 are dispensable for syncytium formation at both high and low multiplicities of infection, gD, gHgL, gE, gI, and gM were all required for the fusion of cellular membranes. These data confirm that the requirements for virion entry and cell-cell fusion are not identical. gD and gHgL, like gB, are essential for both processes. gG, gI, and gM, on the other hand, are dispensable for virus penetration, yet play a role in cell-to-cell spread by the direct contact route, at least on an SC16 gBANG background.

The herpes simplex virus type 1 particle: structure and molecular functions. Review article

This review is a summary of our present knowledge with respect to the structure of the virion of herpes simplex virus type 1. The virion consists of a capsid into which the DNA is packaged, a tegument and an external envelope. The protein compositions of the structures outside the genome are described as well as the functions of individual proteins. Seven capsid proteins are identified, and two of them are mainly present in precursors of mature DNA-containing capsids. The protein components of the 150 hexamers and 12 pentamers in the icosahedral capsid are known. These capsomers all have a central channel and are connected by Y-shaped triplexes. In contrast to the capsid, the tegument has a less defined structure in which 11 proteins have been identified so far. Most of them are phosphorylated. Eleven virus-encoded glycoproteins are present in the envelope, and there may be a few more membrane proteins not yet identified. Functions of these glycoproteins include attachment to and penetration of the cellular membrane. The structural proteins, their functions, coding genes and localizations are listed in table form.

Antigenic specificities of human CD4+ T-cell clones recovered from recurrent genital herpes simplex virus type 2 lesions

Lesions resulting from recurrent genital herpes simplex virus (HSV) infection are characterized by infiltration of CD4+ lymphocytes. We have investigated the antigenic specificity of 47 HSV-specific CD4+ T-cell clones recovered from the HSV-2 buttock and thigh lesions of five patients. Clones with proliferative responses to recombinant truncated glycoprotein B (gB) or gD of HSV-2 or purified natural gC of HSV-2 comprised a minority of the total number of HSV-specific clones isolated from lesions. The gC2- and gD2-specific CD4+ clones had cytotoxic activity. The approximate locations of the HSV-2 genes encoding HSV-2 type-specific CD4+ antigens have been determined by using HSV-1 x HSV-2 intertypic recombinant virus and include the approximate map regions 0.30 to 0.46, 0.59 to 0.67, 0.67 to 0.73, and 0.82 to 1.0 units. The antigenic specificity of an HLA DQ2-restricted, HSV-2 type-specific T-cell clone was mapped to amino acids 425 to 444 of VP16 of HSV-2 by sequential use of an intertypic recombinant virus containing VP16 of HSV-2 in an HSV-1 background, recombinant VP16 fusion proteins, and synthetic peptides. Each of the remaining four patients also yielded at least one type-specific T-cell clone reactive with an HSV-2 epitope mapping to approximately 0.67 to 0.73 map units. The antigenic specificities of lesion-derived CD4+ T-cell clones are quite diverse and include at least 10 epitopes. Human T-cell clones reactive with gC and VP16 are reported here for the first time.

Detection of immunoglobulin M antibodies to glycoprotein G-2 by western blot (immunoblot) for diagnosis of initial herpes simplex virus type 2 genital infections

Western blots (immunoblots) for the detection of immunoglobulin M (IgM) antibodies specific for herpes simplex virus type 1 (HSV-1) and HSV-2 in patients' sera were developed. The locations of the type-specific glycoprotein G (gpG-2) of HSV-2 (92- and 140-kDa forms) and glycoprotein C of HSV-1 (gpC-1), which carries mostly type-specific antigenic epitopes, were checked with specific monoclonal antibodies. Western blot assays for IgM antibody to gpC-1 or gpG-2 were performed after depletion of IgG by precipitation with anti-human IgG. In patients with primary HSV-2 genital infections, seroconversion of IgM and IgG antibodies to both the 92- and 140-kDa forms of gpG-2 was observed, although both antibodies appeared in convalescent-phase serum after the first week. IgM and IgG antibodies to low-molecular-size polypeptides (40 to 65 kDa) were the first antibodies observed in patients with primary infection, but these antibodies were cross-reactive with HSV-1 and HSV-2. However, in patients with recurrent HSV-2 infections, IgG antibodies to both forms of gpG-2 and the low-molecular-size polypeptides were found no matter how early after onset the patient was bled, and IgM to gpG-2 did not appear. In patients with nonprimary initial genital HSV-2 infections, IgG antibody to HSV-1 was demonstrated in the first serum specimen, and HSV-2-specific IgM was found in 39% of the serum specimens. Hence, the Western blot assay can be used to test for IgM antibody to gpG-2, allowing for the retrospective diagnosis of inital HSV-2 infections and its use as a supplementary test to the gpG-2 IgG enzyme-linked immunosorbent assays developed elsewhere. In contrast, IgM antibody to gpG-2 is not usually detected in patients with recurrent HSV-2 infections.

Genetic analysis of type-specific antigenic determinants of herpes simplex virus glycoprotein C

Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC-1) elicits a largely serotype-specific immune response directed against previously described determinants designated antigenic sites I and II. To more precisely define these two immunodominant antigenic regions of gC-1 and to determine whether the homologous HSV-2 glycoprotein (gC-2) has similarly situated antigenic determinants, viral recombinants containing gC chimeric genes which join site I and site II of the two serotypes were constructed. The antigenic structure of the hybrid proteins encoded by these chimeric genes was studied by using gC-1- and gC-2-specific monoclonal antibodies (MAbs) in radioimmunoprecipitation, neutralization, and flow cytometry assays. The results of these analyses showed that the reactivity patterns of the MAbs were consistent among the three assays, and on this basis, they could be categorized as recognizing type-specific epitopes within the C-terminal or N-terminal half of gC-1 or gC-2. All MAbs were able to bind to only one or the other of the two hybrid proteins, demonstrating that gC-2, like gC-1, contains at least two antigenic sites located in the two halves of the molecule and that the structures of the antigenic sites in both molecules are independent and rely on limited type-specific regions of the molecule to maintain epitope structure. To fine map amino acid residues which are recognized by site I type-specific MAbs, point mutations were introduced into site I of the gC-1 or gC-2 gene, which resulted in recombinant mutant glycoproteins containing one or several residues from the heterotypic serotype in an otherwise homotypic site I background. The recognition patterns of the MAbs for these mutant molecules demonstrated that (i) single amino acids are responsible for the type-specific nature of individual epitopes and (ii) epitopes are localized to regions of the molecule which contain both shared and unshared amino acids. Taken together, the data described herein established the existence of at least two distinct and structurally independent antigenic sites in gC-1 and gC-2 and identified subtle amino acid sequence differences which contribute to type specificity in antigenic site I of gC.

Structural basis of C3b binding by glycoprotein C of herpes simplex virus

Glycoproteins C (gC) from herpes simplex virus type 1 (HSV-1) and HSV-2, gC-1 and gC-2, bind the human complement fragment C3b, although the two glycoproteins differ in their abilities to act as C3b receptors on infected cells and in their effects on the alternative complement pathway. Previously, we identified three regions of gC-2 (I, II, and III) which are important for C3b binding. In this study, our goal was to identify C3b-binding sites on gC-1 and to continue our analysis of gC-2. We constructed a large panel of mutants by using the cloned gC-1 and gC-2 genes. Most of the mutant proteins were transported to the surface of transiently transfected L cells and reacted with one or more monoclonal antibodies to discontinuous epitopes. By using 31 linker insertion mutants spread across the coding region of gC-1, we identified four regions in the ectodomain of gC-1 which are important for C3b binding, three of which are similar in position to C3b-binding regions I, II, and III of gC-2. Region III shares some similarities with the short consensus repeat found in CR1, the human complement receptor. These were, in part, the targets for construction of 20 single amino acid changes in region III of gC-1 and gC-2. These mutants identified similarities and differences in the C3b-binding properties of gC-1 and gC-2 and suggest that the amino half of region III is more important for C3b binding. However, our results do not support the concept of a structural relationship between the short consensus repeat of CR1 and gC, since mutations of some of the conserved residues, including three of four cysteines in region III, had no effect on C3b binding. Finally, we constructed four deletion mutants of gC-1, including one which lacked residues 33 to 123, as well as residues 367 to 449. This severely truncated molecule, lacking four cysteines and five potential N-linked glycosylation sites, was transported to the cell surface and retained its ability to bind monoclonal antibodies as well as C3b. Thus, the four distinct C3b-binding regions of gC-1 and several epitopes within two different antigenic sites are localized within residues 124 to 366.

The HSV-1 latency associated transcript (LAT) variants 1704 and 1705 are glycoprotein C negative

The latency associated transcripts (LAT) of herpes simplex virus type 1 (HSV-1) are encoded by diploid genes that are expressed during latent infections. Two LAT variant viruses, 1704 and 1705, were compared with the parental strain 17+. Variant 1705 has a deletion affecting one copy of the LAT genes, expresses LATs during latent infection and reactivates normally. Variant 1704 has deletions affecting both LAT gene copies, does not express LATs during latent infection, and its reactivation is impaired (Steiner et al., 1989). Comparison of infected cell proteins by immunoprecipitation and Western blot analysis revealed one significant difference between HSV-1 strain 17+, 1704 and 1705; glycoprotein C (gC) was not synthesized by 1704 or 1705. Since both 1704 and 1705 are gC minus, the reactivation defect of 1704 is most likely related to the absence of the LATs, and not to the absence of gC.

Coexpression by vaccinia virus recombinants of equine herpesvirus 1 glycoproteins gp13 and gp14 results in potentiated immunity

The equine herpesvirus 1 glycoprotein 14 (EHV-1 gp14) gene was cloned, sequenced, and expressed by vaccinia virus recombinants. Recombinant virus vP613 elicited the production of EHV-1-neutralizing antibodies in guinea pigs and was effective in protecting hamsters from subsequent lethal EHV-1 challenge. Coexpression of EHV-1 gp14 in vaccinia virus recombinant vP634 along with EHV-1 gp13 (P. Guo, S. Goebel, S. Davis, M. E. Perkus, B. Languet, P. Desmettre, G. Allen, and E. Paoletti, J. Virol. 63:4189-4198, 1989) greatly enhanced the protective efficacy in the hamster challenge model over that obtained with single recombinants. The inoculum doses (log10) required for protection of 50% of hamsters were 6.1 (EHV-1 gp13), 5.2 (EHV-1 gp14), and less than 3.6 (vaccinia virus recombinant expressing both EHV-1 glycoproteins [gp13 and gp14]).

Identification of C3b-binding regions on herpes simplex virus type 2 glycoprotein C

Glycoprotein C from herpes simplex viruses types 1 and 2 (gC-1 and gC-2) acts as a receptor for the C3b fragment of the third component of complement. Our goal is to identify domains on gC involved in C3b receptor activity. Here, we used in-frame linker-insertion mutagenesis of the cloned gene for gC-2 to identify regions of the protein involved in C3b binding. We constructed 41 mutants of gC-2, each having a single, double, or triple insertion of four amino acids at sites spread across the protein. A transient transfection assay was used to characterize the expressed mutant proteins. All of the proteins were expressed on the transfected cell surface, exhibited processing of N-linked oligosaccharides, and bound one or more monoclonal antibodies recognizing distinct antigenic sites on native gC-2. This suggested that each of the mutant proteins was folded into a native structure and that a loss of C3b binding by any of the mutants could be attributed to the disruption of a specific functional domain. When the panel of insertion mutants was assayed for C3b receptor activity, we identified three distinct regions that are important for C3b binding, since an insertion within those regions abolished C3b receptor activity. Region I was located between amino acids 102 and 107, region II was located between residues 222 and 279, and region III was located between residues 307 and 379. In addition, region III has some structural features similar to a conserved motif found in complement receptor 1, the human C3b receptor. Finally, blocking experiments indicated that gC-1 and gC-2 bind to similar locations on the C3b molecule.

Characterization of the gene encoding herpesvirus of turkeys gp57-65: comparison to Marek's disease virus gp57-65 and herpes simplex virus glycoprotein C

A gene encoding herpesvirus of turkeys (HVT) strain FC 126 gp57-65 has been mapped to the viral genome and sequenced. The HVT (FC 126) gp57-65 gene maps to BamHI fragments K1 and M, colinear with the gene from Marek's disease virus (MDV) strain GA. HVT gp57-65 gene sequences were compared to the MDV strain GA gp57-65 gene that we sequenced previously. Overall, the two sequences are 66% identical, with greater similarity in the 3' proximal two thirds of the genes. HVT gp57-65 gene sequences have a slightly higher overall guanosine plus cytosine (G + C) content than MDV gp57-65 gene sequences (46% vs. 41%, respectively). A single, long open reading frame capable of encoding 523 amino acids was identified within the HVT gp57-65 gene region. The predicted precursor polypeptide derived from this open reading frame would have a calculated molecular weight of 58,587. The predicted HVT gp57-65 amino acid sequences contain six potential N-linked glycosylation sites (asn-x-ser/thr). Five of these six potential N-linked glycosylation sites are conserved between the HVT and MDV predicted amino acid sequences. Hydropathic analysis of the predicted HVT gp57-65 amino acid sequences indicate the presence of an amino-terminal hydrophobic sequence, which may function as a signal peptide, and a hydrophobic carboxyl terminal sequence, which may function as a membrane anchor sequence. Overall, MDV gp57-65 and HVT gp57-65 precursor polypeptide sequences are 73% homologous and share many potential antigenic epitopes. Predicted MDV and HVT gp57-65 protein sequences are similar to those of herpes simplex virus glycoprotein C (gC) and gC-like proteins from other herpes-viruses. Similarities are scattered throughout the molecule, with a primary concentration near the carboxyl half of the molecule. One stretch of 60 amino acids (HVT amino acids 378-437 and MDV amino acids 350-410) are relatively well conserved among gC-like proteins from six herpesviruses. The possible implications of these homologies and the potential roles of gC-like proteins in virus infection, growth, and replication are discussed.

Localization on the herpes simplex virus type 1 genome of a region encoding proteins involved in adsorption to the cellular receptor

We have previously shown that aminoglycosides such as neomycin and the polyamino acids polylysine and polyarginine selectively inhibit the binding of herpes simplex virus type 1 (HSV-1) to the cellular receptor, whereas HSV-2 infection is unaffected. In the present study we took advantage of this difference between HSV-1 and HSV-2 by using HSV(-1)-HSV(-2) intertypic recombinants to locate a region on the HSV-1 genome encoding proteins affecting the binding of the virion to the cellular receptor. The results were consistent with those obtained by marker rescue experiments. The identified region, which mapped between coordinates 0.580 and 0.687, contains two partial and eight complete genes, including the glycoprotein C (gC) gene and two others with potential transmembrane sequences. Various gC monoclonal antibody-resistant mutants of HSV-1 as well as a mutant completely lacking gC were found to be fully sensitive to neomycin, suggesting that gC is not the site of drug sensitivity and is not essential for adsorption of virus to the cellular receptor. However, the rate of adsorption was reduced in the absence of gC, indicating a facilitating function of the glycoprotein. The universal nature of this HSV-1 receptor binding was revealed by the similarity in drug sensitivity of infectivity in four different cell lines from various tissues and species.

Expression in recombinant vaccinia virus of the equine herpesvirus 1 gene encoding glycoprotein gp13 and protection of immunized animals

The equine herpesvirus 1 (EHV-1) gene encoding glycoprotein 13 (gp13) was cloned into the hemagglutinin (HA) locus of vaccinia virus (Copenhagen strain). Expression of the gp13 gene was driven by the early/late vaccinia virus H6 promoter. Metabolically radiolabeled polypeptides of approximately 47 and 44 kilodaltons and 90 kilodaltons (glycosylated form) were precipitated with both polyclonal and gp13-specific monoclonal antibodies. Presentation of gp13 on the cytoplasmic membrane of cells infected with the recombinant gp13 vaccinia virus was demonstrated by immunofluorescence of unfixed cells. Inoculation of the recombinant gp13 vaccinia virus into guinea pigs induced neutralizing antibodies to both EHV-1 and vaccinia virus. Hamsters vaccinated with the recombinant gp13 vaccinia virus survived a lethal challenge with the hamster-adapted Kentucky strain of EHV-1. These results indicate that expression in vaccinia virus vectors of EHV-1 gp13, the glycoprotein homolog of herpes simplex virus gC-1 and gC-2, pseudorabies virus gIII, and the varicella-zoster virus gpV may provide useful vaccine candidates for equine herpesvirus infections.

C3b receptor activity on transfected cells expressing glycoprotein C of herpes simplex virus types 1 and 2

Glycoprotein C from herpes simplex virus type 1 (gC-1 from HSV-1) acts as a receptor for the C3b fragment of the third component of complement on HSV-1-infected cell surfaces. Direct binding assays with purified gC-1 and C3b demonstrate that other viral and cellular proteins are not required for this interaction. Although C3b receptor activity is not expressed on HSV-2-infected cell surfaces, purified gC-2 specifically binds C3b in direct binding assays, suggesting that gC-1 and gC-2 are functionally similar. Here, we used a transient transfection system to further characterize the role of gC-1 and gC-2 as C3b receptors and to localize the site(s) on gC involved in C3b binding. The genes for gC-1 and gC-2 were each cloned into a eucaryotic expression vector containing the Rous sarcoma virus long terminal repeat as the promoter and transfected into NIH 3T3 cells. The expressed proteins were similar in molecular size, extent of carbohydrate processing, and antigenic properties to gC-1 and gC-2 purified from infected cells. Using a double-label immunofluorescence assay, we found that both gC-1 and gC-2 were expressed on the surfaces of transfected cells and bound C3b. These results suggest that other proteins expressed during HSV-2 infection prevent receptor activity. We constructed three in-frame deletion mutants of gC-2 to identify domains on the protein important for C3b receptor activity. These mutants lacked amino acids 26 to 73, 219 to 244, or 318 to 346. The mutant protein lacking residues 26 to 73 was reactive with two monoclonal antibodies recognizing distinct epitopes, showed a wild-type pattern of carbohydrate processing, and bound C3b on the transfected cell surface. These results suggest that residues 26 to 73 are not involved in C3b binding. The other two mutant proteins were present on the cell surface, but did not bind C3b. In addition, these mutant proteins showed altered patterns of carbohydrate processing, formed aggregates, and were no longer recognized by the monoclonal antibodies. These properties indicate that removal of residues 219 to 244 or 318 to 346 disrupted the native conformation of gC-2, possibly owing to an alteration in the spacing between critical cysteine residues.

Characterization of an equine herpesvirus type 1 gene encoding a glycoprotein (gp13) with homology to herpes simplex virus glycoprotein C

The molecular structure of the equine herpesvirus type 1 (EHV-1) gene encoding glycoprotein 13 (gp13) was analyzed. The gene is contained within a 1.8-kilobase AccI-EcoRI restriction fragment mapping at map coordinates 0.136 to 0.148 in the UL region of the EHV-1 genome and is transcribed from right to left. Determination of the nucleotide sequence of the DNA fragment revealed a complete transcriptional unit composed of typical regulatory promoter elements upstream to a long open reading frame (1,404 base pairs) that encoded a 468-amino-acid primary translation product of 51 kilodaltons. The predicted protein has the characteristic features of a membrane-spanning protein: an N-terminal signal sequence, a hydrophobic membrane anchor region, a charged C-terminal cytoplasmic tail, and an exterior domain with nine potential N-glycosylation sites. The EHV-1 DNA sequences expressed in lambda gt11 as gp13 epitopes were present in the open reading frame. Amino acid sequences composing a major antigenic site, recognized by 35% of a panel of 42 anti-gp13 monoclonal antibodies, were identified in the N-terminal surface domain of the deduced gp13 molecule. Comparison of the EHV-1 gp13 DNA sequence with that encoding glycoproteins of other alphaherpesviruses revealed no detectable homology. However, a search for homology at the amino acid level showed regions of significant sequence similarity between the amino acids of the carboxy half of EHV-1 gp13 and those of the same region of gC-like glycoproteins of herpes simplex virus (gC-1 and gC-2), pseudorabies herpesvirus (gIII), and varicella-zoster virus (gp66). The sequences of the N-terminal portion of gp13, by contrast, were much less conserved. The results of these studies indicate that EHV-1 gp13 is the structural homolog of herpes simplex virus glycoprotein C and further suggest that the epitope-containing N-terminal amino acid sequences of the herpesvirus gC-like glycoproteins have undergone more extensive evolutionary divergence than the C-terminal sequences.

Attachment of human polymorphonuclear leukocytes to herpes simplex virus-infected fibroblasts mediated by antibody-independent complement activation

Herpes simplex virus (HSV)-infected cells can activate the human complement system without interference of specific anti-HSV antibodies. Analysis by flow cytometry showed that C3-like molecules were deposited on the membrane of the infected cell when incubated with human serum without specific antibodies. Depletion of calcium to block the classical pathway of the complement system had no effect on fluorescence intensity. The complement activation could be blocked by chelating both calcium and magnesium or by heating the serum. Furthermore, in the fluid phase C3 was converted to C3b by infected cells and not by uninfected cells. The antibody-independent activation did not lead to lysis of the virus-infected fibroblasts, indicating that the complement cascade is abrogated before formation of the membrane attack complex. This was also confirmed by measurement of the 50% hemolytic complement activities for total and alternative pathways. Polymorphonuclear leukocytes attached to infected fibroblasts after incubation of these fibroblasts with intact complement. This is most probably mediated by complement receptor binding of C3b and C3bi which is deposited on the membrane of the HSV-infected cell. Both type 1 and type 2 HSVs showed the same characteristics in complement activation and thereby mediated polymorphonuclear leukocyte adherence.

Complement component C3b binds directly to purified glycoprotein C of herpes simplex virus types 1 and 2

Cells infected with herpes simplex virus type 1 (HSV-1), but not HSV-2, express on their surfaces a receptor for the complement component C3b. Receptor activity is markedly enhanced by treatment of the infected cells with neuraminidase. Employing a direct binding assay, consisting of purified HSV glycoproteins immobilized on nitrocellulose and iodinated C3b as a probe, we found that C3b binds directly to gC-1, as well as to gC-2, but not to gB or gD from either serotype. C3b binding was enhanced by treatment of gC-1 or gC-2 with neuraminidase. Endo F or endo H treatment of gC-1 had no effect on C3b binding. However, treatment of gC-2 with these endoglycosidases had a marked negative effect on C3b binding. These results suggest that N-linked oligosaccharides are involved in binding of C3b to gC-2, but not gC-1. Alternatively, removal of N-linked oligosaccharides from gC-2 might adversely affect polypeptide conformation. Glycoprotein C-2 also differs from gC-1 in its effects on the complement cascade. Whereas gC-1 accelerated the decay of the alternative pathway C3 convertase and impaired the efficiency of lysis by the components C5 through C9, gC-2 stabilized the active C3 convertase and had little effect on the late-acting components. The dissimilarity of gC-1 and gC-2 with regard to their effects on the complement cascade may have implications regarding the role of these glycoproteins in confronting the host immune response.

Herpes simplex virus glycoproteins gC-1 and gC-2 bind to the third component of complement and provide protection against complement-mediated neutralization of viral infectivity

Cells infected with herpes simplex virus type 1 (HSV-1) form rosettes with C3b-coated erythrocytes, whereas cells infected with herpes simplex virus type 2 (HSV-2) or other herpes viruses do not. It was reported that glycoprotein C of HSV-1 (gC-1) mediates the binding of C3b-coated erythrocytes to infected cells and has regulatory (decay-accelerating) activity for the alternative pathway C3 convertase of human complement. We show here that solubilized gC-1 binds to iC3-Sepharose affinity columns. We also report that solubilized gC-2, the genetically related glycoprotein specified by HSV-2, binds to iC3-Sepharose. mAb specific for gC-1 or gC-2 and mutant viral strains were used to identify the C3-binding glycoproteins. In other experiments, HSV-1 mutant strains and recombinants, differing only in their expression of gC, were tested for sensitivity to neutralization by human complement in the presence or absence of antibodies specific for HSV gD. In either case the gC- strain was most sensitive. Expression of gC-1 or gC-2 by isogenic insertion mutants provided protection against complement-mediated neutralization. These results indicate that the genetically and structurally related gC-1 and gC-2 share the functional activity of binding to human C3 and enhance viral infectivity.

Bovine herpesvirus type 1 gp87 mediates both attachment of virions to susceptible cells and hemagglutination

The 87,000-dalton glycoprotein (gp87) of bovine herpesvirus type 1 (BHV-1) was found to selectively attach to susceptible cells. The attachment of gp87 to the cells was markedly decreased by the prior adsorption of intact virions. Anti-gp87 (site Ia) monoclonal antibody, which inhibited BHV-1 adsorption to the cells and neutralized the virus without complement [Okazaki et al., Virology 250: 260-264], was effective in inhibiting the adsorption of gp87. Only the same antibody was able to inhibit the hemagglutination activity of BHV-1. Other monoclonal antibodies to the glycoproteins of BHV-1, including antibodies directed to sites Ib and Ic on gp87, were ineffective in inhibiting either virus adsorption or hemagglutination. The results of this study indicate that site Ia of gp87 molecule is the critical site of virus attachment for initiation of infection as well as the hemagglutination of BHV-1.

Variability of pseudorabies virus glycoprotein I expression

The 130,000 mol wt glycoprotein I (gI) derived from two approx 80-kDa precursors is one of the major constituents of the envelope of pseudorabies virus (PRV) strain Phylaxia. Recently, gI has been shown to be nonessential for PRV replication since several PRV vaccine strains with deletions in the region of the genome encoding the gI gene have been described. In this paper we demonstrate that other alterations affecting gI expression can occur. We describe a PRV field isolate which expresses a single gI precursor molecule pgI of 64,000 mol wt. This precursor is processed into 60,000 mol wt gI. In contrast to PRV Phylaxia, the gI-expressing isolate is not neutralized by anti-gI monoclonal antibodies. Virions expressing the pgI also emerged after serial in vitro passages of the wild-type PRV strain NIA-5 which initially expressed wild-type pgI. Concomitant with the appearance of pgI the pgI disappeared and the resistance of the virus population to neutralization by anti-gI monoclonal antibodies increased. Furthermore, the amount of expression of gI and pgI in single plaque isolates of the PRV strain Ka was found to be highly variable among different plaque isolates and correlated with a different susceptibility to neutralization by anti-gI monoclonal antibodies. In single plaque isolates of strain Phylaxia, however, gI expression appeared to be stable. In all cases, no genomic or transcriptional alterations could be observed. Thus, viruses resistant to anti-gI antibodies occur spontaneously in vivo and in vitro, which argues against the use of gI as a subunit vaccine.

The single base pair substitution responsible for the Syn phenotype of herpes simplex virus type 1, strain MP

Nucleotide sequences were determined for portions of the genomes of the syncytial (Syn) mutant of herpes simplex virus type 1, strain MP, and the related wild-type strain mP. Comparisons of the nucleotide sequences showed only 1 bp difference between the DNAs of strains MP and mP in the region to which the Syn mutation of MP had previously been mapped. This base pair substitution in MP (at map coordinate 0.737) eliminates a ThaI restriction endonuclease recognition site that is present in mP DNA. Analyses of MP X mP recombinant viruses showed that presence of the ThaI site correlates with the Syn+ phenotype and absence of the ThaI site correlates with the Syn phenotype as predicted. We conclude that the base pair substitution at map coordinate 0.737 is responsible for the Syn phenotype of MP. This mutation could alter translation in four of the six reading frames, causing amino acid substitutions. From only one of these reading frames is a product likely to be expressed. The 338-amino acid polypeptide that could be expressed has features characteristic of membrane-associated proteins, including hydrophobic domains, potential sites for the attachment of N-linked carbohydrate, and a potential cleavable signal sequence.

Herpes simplex virus type 1 glycoprotein E is not indispensable for viral infectivity

A mutant of the herpes simplex virus type 1 Angelotti was isolated in which 87% of the coding region of glycoprotein E (gE) was deleted and replaced by a functional neomycin resistance gene of the Tn5 transposon. The mutant was characterized by restriction enzyme analyses and Southern blotting. Western blotting of proteins and immunofluorescence assays revealed that gE was completely absent and that the Fc receptor was not expressed in cells infected with the mutant. The fact that this mutant was viable and that it replicated to a slightly lower titer than did the wild-type virus suggests that the presence of gE is not a prerequisite of viral infectivity in tissue culture.

Putative glycoprotein gene of varicella-zoster virus with variable copy numbers of a 42-base-pair repeat sequence has homology to herpes simplex virus glycoprotein C

A strain variation of varicella-zoster virus that maps to the UL region of the genome was found to be due to different copy numbers of a high GC 42-base-pair repeat. DNA sequence analysis of this variable region showed the sequence to be 5-GCGGGATCGGGCTTTCGGG(A/T)AGCGGCCGAGGTGGGCGCGACG-3. Strains Scott and Webster both contain 7 and 32/42 copies of the repeat, whereas strain Oka has exactly 4 copies less. Microheterogeneity exists within the repeated sequences, depending on the strain and the repeat number. Sequencing of the entire EcoRI P fragment (which contains the repeated sequences) and part of the adjacent EcoRI M and EcoRI Q fragments from strain Scott showed that the repeats are part of a large open reading frame that could code for a polypeptide core with a molecular weight of 66,000. Several potential TATA boxes exist upstream and two polyadenylation signals are found downstream of the open reading frame. The predicted protein bears several characteristics of a glycoprotein. The region is transcriptionally active in varicella-zoster virus-infected cells, specifying at least three RNA species of 1.7, 1.95, and 2.5 kilobases, which are transcribed from the same DNA strand. Part of the predicted protein has a high degree of homology to the herpes simplex virus type 1 glycoprotein gC.

Studies on herpes simplex virus type 1 glycoproteins using monoclonal antibodies

Monoclonal antibodies against herpes simplex virus type 1 glycoproteins were isolated and utilized to study the synthesis and processing of glycoproteins B, C, and D (gB, gC, gD, respectively). Monoclonal antibodies against both gB and gD had higher virus-neutralizing activity when compared to that of gC. Differences among these glycoproteins were observed in their time of appearance in the virus-infected cells. The presence of gD was detected at a very early stage of infection when compared to gB and gC. The localization of these glycoproteins during their synthesis and processing was studied.

Multiple adjacent or overlapping loci affecting the level of gC and cell fusion mapped by intratypic recombinants of HSV-1

We have prepared and analyzed 40 HSV-1 intratypic recombinants with regard to plaque morphology and glycoprotein C(gC) phenotypes. Vero cells have been cotransfected with the intact genome of HSV-1(F) and cloned or uncloned DNA fragments from HSV-1(MP) and recombinants inducing the fusion of Vero cells [syncytial (Syn) recombinants] have been selected and purified. Marker transfer of the Syn phenotype has been observed with the cloned BamHI L and B fragments (0.706-0.745 and 0.745-0.810 map units, respectively) as well as with the uncloned HpaI TXO fragment (0.710-0.761) from MP DNA. No marker transfer has been observed with F DNA alone or with the cloned BamHI N fragment (0.863-0.898 map units). When viruses expressing the Syn phenotype in Vero cells were tested in HEp-2 cells, three kinds of recombinants were observed. Members of the first class expressed a wild type, cytoaggregating (Syn+), plaque morphology in these cells. Members of the second class induced the complete fusion (Syn phenotype) of the cells. Members of the third class induced an intermediate plaque morphology, characterized by the formation of groups of polykaryocytes (fused cells) but without formation of a complete syncytium. All recombinants expressing the Syn+ phenotype in HEp-2 cells were also gC+, whereas recombinants expressing the Syn phenotype in these cells were gC- with one exception, in which low levels of gC could be detected (but clearly less than with HSV-1(F]. Concerning polykaryocytic class of recombinants, some of them were gC+ while others expressed only low amounts of gC; no gC- virus was observed within this class of recombinants. The three classes of recombinants were observed with each of the cloned BamHI L and B fragments and also with the HpaI TXO fragment, suggesting the existence of multiple adjacent or overlapping loci affecting plaque morphology and the control of the accumulation or the synthesis of gC at both sides of 0.745 map units.

Characterization and mapping of a nonessential pseudorabies virus glycoprotein

Antigenic variants of pseudorabies virus (PRV) containing mutations in a viral glycoprotein with a molecular weight of 82,000 (gIII) were isolated by selecting for resistance to a complement-dependent neutralizing monoclonal antibody (MCA82-2) directed against gIII. These mutants were completely resistant to neutralization with MCA82-2 in the presence of complement. Two mutants selected for further studies either did not express gIII or expressed an improperly processed form of the glycoprotein. The mutations were also associated with an altered plaque morphology (syncytium formation). The gIII gene was mapped by marker rescue of a gIII- mutant with cloned restriction enzyme fragments to the long unique region of the PRV genome between 0.376 and 0.383 map units. This corresponds to the map location of a glycoprotein described by Robbins et al. (J. Mol. Appl. Gen. 2:485-496, 1984). Since gIII is nonessential for viral replication in cell culture and has several other characteristics in common with the herpes simplex virus glycoprotein gC, gIII may represent the PRV equivalent to herpes simplex virus gC.

Pathogenicity in mice of herpes simplex virus type 2 mutants unable to express glycoprotein C

Herpes simplex virus type 2 (HSV-2) mutants that were unable to express glycoprotein C (gC-2) were isolated. Deletions were made in a cloned copy of the gC-2 gene, and recombinant viruses containing these deletions were screened by using an immunoreactive plaque selection protocol. The viruses did not display a syncytial phenotype. Intravaginal inoculation of BALB/cJ mice with one of the HSV-2 gC-2- viruses produced local inflammation followed by a lethal spread of the viral infection into the nervous system in a manner identical to that produced by parental HSV-2 strain 333. Similarly, intracerebral inoculation of DBA-2 mice with the gC-2- virus produced a lethal neurological disease paralleling that caused by HSV-2 strain 333. These results indicate that gC-2 is not required for the spread of HSV-2 infections in mice.

Specificities of monoclonal and polyclonal antibodies that inhibit adsorption of herpes simplex virus to cells and lack of inhibition by potent neutralizing antibodies

Polyclonal and monoclonal antibodies to individual herpes simplex virus (HSV) glycoproteins were tested for ability to inhibit adsorption of radiolabeled HSV type 1 (HSV-1) strain HFEMsyn [HSV-1(HFEM)syn] to HEp-2 cell monolayers. Polyclonal rabbit antibodies specific for glycoprotein D (gD) or gC and three monoclonal mouse antibodies specific for gD-1 or gC-1 most effectively inhibited HSV-1 adsorption. Antibodies of other specificities had less or no inhibitory activity despite demonstrable binding of the antibodies to virions. Nonimmune rabbit immunoglobulin G and Fc fragments partially inhibited adsorption when used at relatively high concentrations. These results suggest involvement of gD, gC, and perhaps gE (the Fc-binding glycoprotein) in adsorption. The monoclonal anti-gD antibodies that were most effective at inhibiting HSV-1 adsorption had only weak neutralizing activity. The most potent anti-gD neutralizing antibodies had little effect on adsorption at concentrations significantly higher than those required for neutralization. This suggests that, although some anti-gD antibodies can neutralize virus by blocking adsorption, a more important mechanism of neutralization by anti-gD antibodies may be interference with a step subsequent to adsorption, possibly penetration.

Synthesis and processing of glycoprotein gG of herpes simplex virus type 2

Monoclonal antibody 13 alpha C5-1-A11 immunoprecipitated two major polypeptides of molecular weights 108,000 and 120,000 from extracts of herpes simplex virus type 2-infected BHK-21 cells labeled with [35S]methionine or [3H]glucosamine. In pulse-chase experiments, both labels were chased from the 120,000-molecular-weight peptide (120K peptide) into the 108K molecule. Endoglycosidase H (endo H) reduced the 120K peptide to a 112K peptide but did not affect the 108K peptide. Similar profiles were obtained with monoclonal antibody AP-1 which reacts with a 92K glycoprotein, gG, which maps to the short unique region of the genome. Cross-absorption experiments indicated that both antibodies reacted with the same peptides, suggesting that the 120K peptide is a partially glycosylated high-mannose-type precursor of gG (pgG1). Immunoprecipitation from monensin-treated cells indicated that pgG1(120K) may undergo peptide cleavage to form a 74K high-mannose-type peptide (pgG2) and that this 74K peptide may be further processed into an endo H-resistant 110K to 116K peptide. In the presence of tunicamycin, gG(108K) was replaced by 110K and 105K peptides which were resistant to both endo H and endoglycosidase F. The 105K peptide was the only molecule labeled by [3H]galactose or [3H]glucosamine in the presence of tunicamycin, and none of the peptides were labeled with [3H]mannose, indicating the probable presence of O-linked sugars in the 105K peptide. Our results imply that cotranslational glycosylation of the unglycosylated precursor 110K peptide results in the high-mannose-type pgG1(120K), which probably undergoes peptide cleavage. This putative cleavage product may then mature into gG (108K) by the trimming of sugars and the addition of complex and probably O-linked sugars; the high-mannose-type pgG2(74K) is probably an intermediate peptide formed in this process.

Enzyme-linked immunosorbent assay for determination of antibodies against herpes simplex virus types 1 and 2 in human sera

A rapid and reproducible enzyme-linked immunosorbent assay (ELISA) is described for determining antibodies in human sera against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). The sera were absorbed for 30 min with heterologous virus-infected-cell extracts to remove cross-reacting antibodies and then were applied to ELISA plates containing the target antigens, immunoaffinity-purified HSV-1 glycoproteins gC and gD and HSV-2 glycoproteins gD and gF. The absorbance index, defined as the ratio of A414 generated by a serum sample absorbed with a heterologous virus-infected-cell extract versus the A414 of a serum sample absorbed with an uninfected-cell extract, was used to determine the presence or absence of antibodies to HSV-1 and HSV-2. Results of the ELISA for detecting antibodies against HSV-2, when compared with results obtained for the same sera by the microneutralization test, showed an index of overall agreement of 91%. Results of the ELISA for detecting antibodies against HSV-1, when compared with microneutralization test results for sera negative for HSV-2 antibodies but positive for HSV antibodies by ELISA, showed an index of agreement of 99%.

Characterization of virus obtained from MDBK cells persistently infected with a variant of herpes simplex virus type 1 strain MP [HSV-1(MP)]

Virus clones which express glycoprotein gC (gC+) were obtained from two persistently infected (p.i.) MDBK cell lines which had been independently established by infection with HSV-1(MP)10311, a gC- syncytial (syn) variant of herpes simplex virus type 1 strain MP [HSV-1(MP)]. The gC+ revertants were syn in MDBK, HEp-2, and Vero cell lines and in primary human fibroblasts; this offers further evidence that glycoprotein gC does not inhibit cell fusion. The gC+ revertants represented from 70 to 100 percent of the virions present in the virus populations examined, thus suggesting a possible selective advantage of the gC+ revertants in this system of persistent infection.

Characterization of the gene encoding herpes simplex virus type 2 glycoprotein C and comparison with the type 1 counterpart

The gene encoding the glycoprotein C (gC) of herpes simplex virus type 1 maps to the region of the viral genome from 0.62 to 0.64. Recently, a herpes simplex virus type 2 glycoprotein previously designated gF and now designated gC was mapped to a homologous location. Analysis of the herpes simplex virus type 2 mRNA species encoded in this region revealed a major transcript of 2.5 kilobases, a 0.73-kilobase transcript (the 5' ends of which were mapped by primer extension), and several minor species, all nearly identical to the herpes simplex virus type 1 pattern. A polypeptide of ca. 60,000 daltons was identified by in vitro translation of hybrid-selected mRNA. A smaller protein of ca. 20,000 daltons was also mapped to this region. The nucleotide sequence of a 3.4-kilobase segment of DNA encompassing gC was determined, and an open reading frame of 1,440 nucleotides specifying a 480-amino acid protein with properties consistent with that of a glycoprotein was identified. Comparative DNA sequence analysis showed regions of limited homology within the coding sequences for gC and a deletion which results in 31 fewer amino acids in the gC-2 near the amino terminus of the protein. The carboxy termini of gC-1 and gC-2 are very similar, as are the 20,000-dalton proteins.

Novel rearrangements of herpes simplex virus DNA sequences resulting from duplication of a sequence within the unique region of the L component

We constructed insertion mutants of herpes simplex virus type 1 that contained a duplication of DNA sequences from the BamHI-L fragment (map units 0.706 to 0.744), which is located in the unique region of the L component (UL) of the herpes simplex virus type 1 genome. The second copy of the BamHI-L sequence was inserted in inverted orientation into the viral thymidine kinase gene (map units 0.30 to 0.32), also located within UL. A significant fraction of the progeny produced by these insertion mutants had genomes with rearranged DNA sequences, presumably resulting from intramolecular or intermolecular recombination between the BamHI-L sequences at the two different genomic locations. The rearranged genomes either had an inversion of the DNA sequence flanked by the duplication or were recombinant molecules in which different regions of the genome had been duplicated and deleted. Genomic rearrangements similar to those described here have been reported previously but only for herpes simplex virus insertion mutants containing an extra copy of the repetitive a sequence. Such rearrangements have not been reported for insertion mutants that contain duplications of herpes simplex virus DNA sequences from largely unique regions of the genome. The implications of these results are discussed.

Expression in bacteria of gB-glycoprotein-coding sequences of Herpes simplex virus type 2

A plasmid with an insert that encodes the glycoprotein B(gB) gene of Herpes simplex virus type 2 (HSV-2) has been isolated. DNA sequences coding for a portion of the HSV-2 gB peptide were cloned into a bacterial lacZ alpha expression vector and used to transform Escherichia coli. Upon induction of lacZpo-promoted transcription, some of the bacteria became filamentous and produced inclusion bodies containing a large amount of a 65-kDal peptide that was shown to be precipitated by broad-spectrum antibodies to HSV-2 and HSV-1. The HSV-2 insert of one of these clones specifies amino acid residues corresponding to 135 through 629 of the gB of HSV-1 [Bzik et al., Virology 133 (1984) 301-314].

Expression of Herpes simplex virus type 1 glycoprotein C antigens in Escherichia coli

DNA fragments encoding structural information of the Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC) gene were cloned into pUC plasmids [Vieira and Messing, Gene 19 (1982) 259-268]. None of the hybrid plasmids were able to direct the synthesis of significant amounts of gC related peptides. Several of the plasmid-bearing strains, however, exhibited inhibition characteristics which can be correlated with the presence on the plasmid of specific gC gene sequences. After insertion of gC DNA fragments into expression vector pMF2 between phage lambda repressor gene cI and lacZ, significant amounts of cI::gC::beta-galactosidase fusion proteins are synthesized. These tripartite fusion proteins are immunologically reactive with anti-HSV-1 antisera. The expression system based on pMF2 can be generally used to identify and express foreign antigens in Escherichia coli.

Herpes simplex virus type 1 glycoprotein C-negative mutants exhibit multiple phenotypes, including secretion of truncated glycoproteins

A virus-neutralizing monoclonal antibody specific for glycoprotein C (gC) of herpes simplex virus type 1 strain KOS was used to select a number of neutralization-resistant mutants. A total of 103 of these mutants also were resistant to neutralization by a pool of gC-specific antibodies and thus were operationally defined as gC-. Analysis of mutant-infected cell mRNA showed that a 2.7-kilobase mRNA, comparable in size to the wild-type gC mRNA, was produced by nearly all mutants. However, six mutants, gC-5, gC-13, gC-21, gC-39, gC-46, and gC-98, did not produce the normal-size gC mRNA but rather synthesized a novel 1.1-kilobase RNA species. These mutants had deletions of 1.6 kilobases in the coding sequence of the gC structural gene, which explains their gC- phenotype. Despite the production of an apparently normal mRNA by the remaining 97 mutants, only 7 mutants produced a detectable gC polypeptide. In contrast to wild-type gC, which is a membrane-bound glycoprotein with an apparent molecular weight of 130,000 (130K), five of these mutants quantitatively secreted proteins of lower molecular weight into the culture medium. These were synLD70 (101K), gC-8 (109K), gC-49 (112K), gC-53 (108K), and gC-85 (106K). The mutant gC-3 secreted a protein that was indistinguishable in molecular weight from wild-type KOS gC. Another mutant, gC-44, produced a gC protein which also was indistinguishable from wild-type gC by molecular weight and which remained cell associated. Pulse-labeling of infected cells in the presence and absence of the glycosylation inhibitor tunicamycin demonstrated that these proteins were glycosylated and provided estimates of the molecular weights of the nonglycosylated primary translation products. The smallest of these proteins was produced by synLD70 and was 48K, about two-thirds the size of the wild-type polypeptide precursor (73K). Physical mapping of the mutations in synLD70 and gC-8 by marker rescue placed these mutations in the middle third of the gC coding sequence. Mapping of the mutations in other gC- mutants, including two in which no protein product was detected, also placed these mutations within or very close to the gC gene. The biochemical and genetic data available on mutants secreting gC gene products suggest that secretion is due to the lack of a functional transmembrane anchor sequence on these mutant glycoproteins.

Binding to cells of virosomes containing herpes simplex virus type 1 glycoproteins and evidence for fusion

Envelope proteins and lipids were extracted from purified herpes simplex virus type 1 virions with octyl glucoside and mixed with phosphatidylcholine for preparation of virosomes by removal of the detergent. Greater than 85% of the extracted envelope proteins, including all the glycoproteins and the nonglycosylated protein designated VP16, were associated with virosomes, which ranged in density from ca. 1.07 to 1.13 g/cm3. All the glycoproteins except gC were as susceptible to degradation by added protease in virosomes as in virions, indicating similar orientations in both. Approximately 30 to 40% of radiolabel incorporated into virosomes bound to HEp-2 cells within 1.5 h at either 4 or 37 degrees C. The cell-bound virosomes were enriched for gB and deficient in other glycoproteins, in comparison with unbound or total virosomes. Binding of virosomes to HEp-2 cells could be inhibited by purified virus, heparin, and monospecific antiviral antibodies. Polyclonal and monoclonal anti-gB antibodies were more effective at inhibiting virosome binding than were anti-gD or anti-gC antibodies. Virosomes depleted of gB or gD did not bind to cells as efficiently as did virosomes containing all the extracted enveloped components; this loss of binding activity was especially pronounced on depletion of gB. The binding of herpes simplex virus type 1 virosomes to cells is discussed in relation to possible heterogeneity of the virosomes and comparisons with binding of virions to cells. We also present electron microscopic evidence that bound virosomes can fuse with the cell surface.

Extensive homology between the herpes simplex virus type 2 glycoprotein F gene and the herpes simplex virus type 1 glycoprotein C gene

The region of the herpes simplex virus type 2 (HSV-2) genome which maps colinearly with the HSV-1 glycoprotein C (gC) gene has been cloned, and the DNA sequence of a 2.29-kilobase region has been determined. Contained within this sequence is a major open reading frame of 479 amino acids. The carboxyterminal three-fourths of the derived HSV-2 protein sequence showed a high degree of sequence homology to the HSV-1 gC amino acid sequence reported by Frink et al. (J. Virol. 45:634-647, 1983). The amino-terminal region of the HSV-2 sequence, however, showed very little sequence homology to HSV-1 gC. In addition, the HSV-1 gC sequence contained 27 amino acids in the amino-terminal region which were missing from the HSV-2 protein. Computer-assisted analysis of the hydrophilic and hydrophobic properties of the derived HSV-2 sequence demonstrated that the protein contained structures characteristic of membrane-bound glycoproteins, including an amino-terminal signal sequence and carboxy-terminal hydrophobic transmembrane domain and charged cytoplasmic anchor. The HSV-2 protein sequence also contained seven putative N-linked glycosylation sites. These data, in conjunction with mapping studies of Para et al. (J. Virol. 45:1223-1227, 1983) and Zezulak and Spear (J. Virol. 49:741-747, 1984), suggest that the protein sequence derived from the HSV-2 genome corresponds to gF, the HSV-2 homolog of HSV-1 gC.

Molecular basis of the glycoprotein-C-negative phenotype of herpes simplex virus type 1 macroplaque strain

The basis for the inability of the macroplaque (MP) strain of herpes simplex virus type 1 to express mature glycoprotein C (gC) was examined. RNA transfer (Northern) blot analysis with hybridization probes from the region of the herpes simplex virus type 1 DNA known to encode the gC gene indicated that gC mRNA was produced in MP-infected HeLa cells at levels relative to other mRNAs comparable with that seen in KOS-infected cells. Comparative nucleotide sequence analysis of the gC gene from the MP and KOS strains, coupled with the results of recently reported marker rescue experiments, indicates that the inability of MP to produce gC is due to a frameshift mutation in the gC-coding sequence. Because two different (out-of-phase) open reading frames overlap the gC-coding sequence in the region of the mutation, MP mRNA can encode two gC-related polypeptides. Two polypeptides of the predicted size and precipitable by anti-gC antibodies were produced by in vitro translation of MP mRNA. These polypeptides have not been detected in extracts from infected cells with the same antibodies. Comparative nucleotide sequence analyses led to several corrections in the published sequence for the gC gene and the 17,800-molecular-weight polypeptide gene just to the right in KOS DNA. These relatively minor effects on the predicted amino code sequence of gC are tabulated.