Limited proteolysis of herpes simplex virus glycoproteins that occurs during their extraction from vero cells

Detergent extraction of herpes simplex virus type 1 glycoprotein D by zwitterionic and non-ionic detergents and purification by ion-exchange high-performance liquid chromatography

Detergents (surfactants) are the key reagents in the extraction and purification of integral membrane proteins. Zwitterionic and non-ionic detergents were used for the extraction of recombinant glycoprotein D (gD-1) of herpes simplex virus type 1 (HSV-1) from insect cells infected with recombinant baculovirus. The highest yield was obtained with the two alkyl carboxybetaine detergents (N-dodecyl-N,N-dimethylammonio)undecanoate [DDMAU, critical micelle concentration (CMC) = 0.13 mM] and (N-dodecyl-N,N-dimethylammonio)butyrate (DDMAB, CMC = 4.3 mM). Therefore these zwitterionic detergents were used as additives to the elution buffers in ion-exchange high-performance liquid chromatography (HPIEC) to purify gD-1 of HSV-1 from the extracts. The non-ionic detergent pentaethyleneglycol monodecyl ether (C10E5) that was used in earlier studies [R.A. Damhof, M. Feijlbrief, S. Welling-Wester, G.W. Welling, J. Chromatogr. A, 676 (1994) 43] was used for comparison. Two columns were used, Mono Q and Resource Q, at 1 and 5 ml/min flow-rates, respectively. The results show that the detergents DDMAU and C10E5 are superior to DDMAB, when the detergents were used as additives to the elution buffers at 0.2% (w/v). With 0.2% DDMAB in the eluent, purification of HSV gD-1 was not possible. Detergents with a high CMC may be less suitable as additives in elution buffers. HPIEC at flow-rates of 1 and at 5 ml/min showed satisfactory results. At 5 ml/min HSV gD-1 was mainly concentrated in two eluent fractions. The highest recovery of gD-1 was obtained either by chromatography of a C10E5 extract using a Mono Q column at a flow-rate of 1 ml/min or by chromatography of a DDMAU extract using a Resource Q column at a flow-rate of 5 ml/min.

Discrete cleavage patterns of pseudorabies virus immediate early protein (IE180) seen in some cell lines upon extraction after cycloheximide reversal

Pseudorabies virus (PrV) encodes for a single and essential immediate early phosphoprotein designated IE180. In this study, IE180 was examined in lysates from various cell lines infected at high multiplicities under cycloheximide inhibition of protein synthesis and subsequent reversal. Three distinct protein patterns of IE180 which were cell-specific and dependant on the extraction procedure were revealed. Detergent lysates of PrV infected MDBK cells yielded almost exclusively wild type IE molecule (180 kDa). In contrast, SSG/94 cells, VERO or CV-1 cells did not yield 180 kDa molecules but predominantly a shorter variant of approximately 60 kDa in molecular mass. Additional bands of about 50/55 kDa were also detected in lysates of SSG/94 and VERO cells by immunoprecipitation. Lysates of CV-1 and MDBK cells also yielded a 120 kDa molecule. The smaller molecular mass bands occurred in the presence of PMSF and aprotinin however, cleavage was blocked completely by addition of N alpha-p-Tosyl-L-lysine chloromethyl ketone (TLCK) into the lysis buffer. Moreover, an ability of the shorter IE180 variants to bind heparin was also revealed in the study. These data provide useful insights on protease profiles encountered among different PrV susceptible cells and indicates the use of appropriate protease inhibitors such as TLCK to protect IE180 under these experimental conditions.

Induction in vitro of primary cytotoxic T-lymphocyte responses with DNA encoding herpes simplex virus proteins

Vaccines which successfully protect against virus infections usually need to induce a broadly reactive immune response which includes the induction of cytotoxic T lymphocytes (CTL). In this study, we have used a convenient in vitro approach to investigate if plasmid DNAs encoding proteins of herpes simplex virus (HSV) are capable of inducing primary CD8+ CTL. Dendritic cells or macrophages were transfected with either plasmid DNA encoding glycoprotein B or DNA encoding the immediate-early protein ICP27. These antigen-presenting cells (APC) were then used to stimulate enriched populations of naive T cells in microcultures for 5 days in vitro. Antigen-specific CD8+ CTL which reacted both with specific protein-expressing targets and with syngeneic targets infected with HSV could be demonstrated. Dendritic cells, as APC, generated the maximal responses, but such cells needed to be transfected with DNA in the presence of a cationic lipid. However, macrophages could act as APC when they were exposed to purified DNA. HSV-primed splenocytes were also shown to generate specific CTL responses when they were stimulated with purified DNA encoding ICP27. The novel approach described in this paper promises to be extremely useful, since defining immunogenicity profiles and identifying epitopes on viral proteins should be easier and more convenient when working with DNA and investigating variables in vitro. This is particularly the case with complex viruses such as HSV, most of whose encoded proteins have yet to be isolated in sufficient quantity or purity to perform in vivo immunological studies.

Expression and characterization of baculovirus expressed herpes simplex virus type 1 glycoprotein L

We have constructed a recombinant baculovirus expressing high levels of the herpes simplex virus type 1 (HSV-1) glycoprotein L (gL) in Sf9 cells. Sf9 cells infected with this recombinant virus synthesized three polypeptides of 26-27 kDa 28 kDa, and 31 kDa. The 28 and 31 kDa species were sensitive to tunicamycin and N-glycosidase F (PNGase F) treatment, suggesting that they were glycosylated. As shown by both indirect immunofluorescence and Western blot analysis, using polyclonal antibodies to synthetic gL peptides indicated that the baculovirus expressed gL was abundant on the surface of baculovirus gL infected Sf9 cells. A small fraction of the 31 kDa polypeptide was secreted into the extracellular medium as judged by Western blot analysis. The secreted form of gL was completely resistant to Endoglycosidase H (Endo-H), while the membrane associated form of gL was only partially resistant to Endo-H treatment, suggesting that the secreted gL represented a subpopulation of the membrane bound gL. Mice vaccinated with baculovirus expressed gL produced serum antibodies that reacted with authentic HSV-1 gL. However, these mice produced no HSV-1 neutralizing antibody (titer < 1:10) and they were not protected from lethal intraperitoneal or lethal ocular challenge with HSV-1. Thus, when used as a vaccine in the mouse model, gL, similar to our findings with HSV-1 gH, but unlike our results with the other 6 HSV-1 glycoproteins that we have expressed in this baculovirus system, did not provide any protection against HSV-1 challenge.

Purification of the integral membrane glycoproteins D of herpes simplex virus types 1 and 2, produced in the recombinant baculovirus expression system, by ion-exchange high-performance liquid chromatography

Selective elution of Sendai virus integral membrane proteins by ion-exchange high-performance liquid chromatography (HPIEC) using different detergent concentrations was reported before [S. Welling-Wester, M. Freijlbrief, D.G.A.M. Koedijk, M.A. Braaksma, B.R.K. Douma and G.W. Welling, J. Chromatogr., 646 (1993) 37]. In the present study this novel approach was applied to the purification of the integral membrane glycoprotein D of Herpes simplex virus type 1 and 2. The glycoproteins D of types 1 (gD-1) and 2 (gD-2) were cloned into the baculovirus expression system and produced in protein-free cultured insect cells. Detergent extracts of recombinant baculovirus-infected insect cells containing gD-1 or gD-2 were prepared using pentaethyleneglycol monodecyl ether, for extraction (final concentration 2%, w/v). The same detergent was used as additive in the elution buffers for HPIEC on a Mono Q HR 5/5 column. At low (0.005%) detergent concentration, most of the proteins present in the extract including part of gD were eluted with the sodium chloride gradient whereas a subsequent blank run using the same gradient at higher detergent concentration (0.1%) resulted in selective elution of pure gD.

Glycoprotein gB (gII) of pseudorabies virus can functionally substitute for glycoprotein gB in herpes simplex virus type 1

Glycoproteins homologous to gB of herpes simplex virus (HSV) constitute the most highly conserved family of herpesvirus glycoproteins. All gB homologs analyzed so far have been shown to play essential roles in penetration and direct viral cell-to-cell spread. In studies aimed at assessing whether the high sequence homology is also indicative of functional homology, we analyzed the ability of the gB-homologous glycoprotein (former designation gII) of pseudorabies virus (PrV) to complement a gB- HSV type 1 (HSV-1) mutant and vice versa. The results show that a PrV gB-expressing cell line phenotypically complemented the lethal defect in gB- HSV-1 whereas reciprocal complementation of a gB- PrV mutant by HSV-1 gB was not observed.

Immunoprecipitation of viral polypeptides of equid herpesvirus 1 and 4 by serum from experimentally infected ponies

Sera from two sibling groups of ponies experimentally infected with Equid herpesvirus 1 or 4 (EHV-1 or 4) were used to investigate which viral polypeptides (VPs) of EHV-1 and EHV-4 were recognised. Recognition was detected as early as 8 d.p.i. and thereafter. The polypeptides of EHV-1 (labelled with 35S-methionine) immunoprecipitated (IIP) by sera from both groups had Mr of 148, 138, 123, 117, 110, 77-79, 70, 55, 49-50, 47, 40 and 35-37 kDa respectively. Of these VP148K (VP9 nucleocapsid) gave the maximum precipitation, followed by 117 and 77-79 kDa. The latter were confirmed by monoclonal antibodies as the gB homologue of Herpes-simplex virus (HSV). With EHV-4 the homologous VPs precipitated were similar to those of EHV-1. However, instead of the precipitated VP55K of EHV-1, there were two faint bands of Mr 60 and 55 kDa, neither of significant density. Bands at 123 and 70 kDa were absent. High MW polypeptides (>200 kDa) were not significant and infrequently seen with both viruses. Labelling EHV-1 with 3H glucosamine indicated that viral glycoproteins (VGPs) at an Mr of 79-88 kDa (equivalent to gB and gC) were most commonly recognised in homologous EHV-1 IIP and at 83 kDa (gC) in heterologous IIP. The EHV-4 immunoprecipitated VGPs were at 230-300 kDa with bands at 290 kDa and 250 kDa. Also detected were bands at 100, 123, 79-88, 58-61K and 54-55 kDa. The 79-88 kDa polypeptides gave maximum density and were considered as homologues of HSV gB and gC. Thus the overall profile indicated that following experimental infection the major nucleocapsid protein of 148K, and the gB analogues of 117 and 77 kDa were the most antigenic in experimental infections of ponies with either EHV-1 or 4 and that these showed reciprocal precipitation.

A comparison of T cell responses to glycoprotein B (gB-1) of herpes simplex virus type 1 and its non-glycosylated precursor protein, pgB-1

The ability of non-glycosylated precursor glycoprotein B (pgB) to induce T cell responses in herpes simplex virus (HSV) infected mice was compared with fully glycosylated glycoprotein B (gB) and with whole virus. pgB was as effective as gB in priming for virus- and glycoprotein-specific T cells. pgB could also re-stimulate virus or glycoprotein primed cells in vitro as efficiently as gB. In addition, priming with pgB protected mice against a lethal challenge with HSV type 1 (HSV-1) and could induce the early in vivo production of IL-2 and IL-3 in infected mice. In all of these responses, pgB was as effective as gB. Thus, the carbohydrate side chains on gB do not appear to be necessary for T cell recognition of this protein.

Immunoselection of recombinant baculoviruses expressing high levels of biologically active herpes simplex virus type 1 glycoprotein D

The DNA sequence encoding the complete herpes simplex virus type 1 (HSV-1) glycoprotein D (gD) was inserted into a baculovirus transfer vector under control of the polyhedrin gene promoter of the baculovirus Autographa california nuclear polyhedrosis virus (AcNPV). After co-transfection of Spodoptera frugiperda (Sf9) insect cells with wild-type AcNPV DNA and the recombinant transfer vector DNA, polyhedrin-negative recombinants that expressed high levels of HSV-1 gD were isolated using immunoaffinity selection with antibody coated magnetic particles followed by plaque purification. These recombinant baculoviruses expressed a protein that was slightly smaller than virion HSV-1 gD made in Vero cells. This recombinant protein was expressed at high levels. The expressed protein was glycosylated, was found on the membrane of Sf9 cells, and reacted with gD specific antibodies. Antibodies raised in mice to the recombinant gD neutralized HSV-1 as measured by plaque reduction assays. Mice inoculated with the recombinant baculovirus were completely protected from lethal challenge with HSV-1.

Effect of an amber mutation in the herpes simplex virus thymidine kinase gene on polypeptide synthesis and stability

KG111 is a mutant of herpes simplex virus (HSV), strain KOS, that exhibits temperature-dependent drug resistance. For example, it is almost as resistant as a thymidine kinase (tk)-deficient virus at 39 degrees, but is relatively sensitive to acyclovir at 34 degrees, Using marker transfer techniques, we have mapped the mutation conferring temperature-dependent drug resistance in KG111 to the 5' portion of the tk gene. Sequencing of this region revealed an amber mutation at codon 44, which lies between the first and second methionine codons of the tk polypeptide. This mutation is identical to that found in TK4, an HSV mutant derived from Cl 101 (L. Haarr et al., 1985, J. Virol. 56, 512-519). Analyses of immunoprecipitated tk proteins from KG111- and TK4-infected cells showed that KG111 and TK4 do not synthesize full-length tk polypeptides, but instead produce a truncated form of the protein. Small amounts of a similar truncated tk polypeptide are also produced in wild-type-infected cells and are thought to arise from initiation at a downstream AUG. The relative amounts and size of the mutant tk proteins compared with those of the wild-type are consistent with the amber mutation eliminating translation of full-length polypeptide and causing a four- to fivefold increase in the utilization of downstream AUG codons for initiation. The truncated polypeptides specified by KG111 and TK4 are less stable than the full-length polypeptide at 39 degrees, which may contribute to the conditional drug-resistant phenotype. On the other hand, the truncated polypeptides normally expressed by wild-type virus at low levels and the more highly expressed truncated tk polypeptides from a deletion mutant are relatively stable at 39 degrees. These results suggest that stability of the truncated tk polypeptide is influenced by the amount of tk present.

Effect of recombinant hybrid human interferon on replication and morphogenesis of HSV-1 in monkey cells

Human recombinant alpha interferon, A/D, significantly reduced the replication and cell fusion induced by herpes simplex virus type 1 in monkey cells. Thin-section electron microscopy of interferon-treated monkey cells showed distinct assembly of nucleocapsids within the nucleus. Analysis of virus-specific proteins by the immunoblot technique confirmed that A/D interferon had no significant effect on the expression of major nucleocapsid proteins, although the expression of glycoproteins B and D was reduced in interferon-treated cells. The possibility of an interferon-induced block at a late stage in virus morphogenesis is discussed.

Functional cross-reactivity between the glycoprotein B of herpes simplex virus type 1 and Epstein-Barr virus

A monoclonal antibody (T157) directed against gB-1, the glycoprotein B (gB) of herpes simplex virus-1 (HSV-1) shows positive indirect immunoflourescent staining with an Epstein-Barr virus (EBV)-transformed lymphoblastoid cell line B95-8. SDS PAGE and Western blot analysis show that B95-8 cells contain a 110,000 MW protein that co-migrates with the 110,000-115,000 MW gB-1. The gB-1 homologue of EBV (gB-EBV), immunopurified using a T157 affinity column, cross-stimulates HSV-1 immune T cells to proliferate in vitro. Mice immunized by a single subcutaneous injection of 30 microg gB-EBV in saline developed significant protection against HSV-1 challenge infection. Therefore gB-EBV can be considered a potential candidate vaccine and as an antigen to examine the cell-mediated immune response mounted by the host to limit virus spread during productive infection. The significance of a better understanding of the immune response to this and other EBV proteins of productive infection as an alternative to limit tumour growth by preventing virus spread is discussed.

Herpes simplex viruses lacking glycoprotein D are unable to inhibit virus penetration: quantitative evidence for virus-specific cell surface receptors

Herpes simplex virus (HSV) glycoprotein D (gD) plays an essential role in the entry of virus into cells. HSV mutants unable to express gD were constructed. The mutants can be propagated on VD60 cells, which supply the viruses with gD; however, virus particles lacking gD were produced in mutant-infected Vero cells. Virus particles with or without gD adsorbed to a large number (greater than 4 x 10(4] of sites on the cell surface; however, virions lacking gD did not enter cells. Cells pretreated with UV-inactivated virions containing gD (approximately 5 x 10(3) particles per cell) were resistant to infection with HSV type 1 (HSV-1) and HSV-2. In contrast, cells pretreated with UV-inactivated virions lacking gD could be infected with HSV-1 and HSV-2. If infectious HSV-1 was added prior to UV-inactivated virus particles containing gD, the infectious virus entered cells and replicated. Therefore, virus particles containing gD appear to block specific cell surface receptors which are very limited in number. Particles lacking gD are presumably unable to interact with these receptors, suggesting that gD is an essential receptor-binding polypeptide.

Synthesis and processing of the Marek's disease herpesvirus B antigen glycoprotein complex

The Marek's disease herpesvirus B antigen (MDHV-B) complex was previously immunologically identified and molecularly characterized as a set of three glycoproteins designated gp100, gp60, and gp49 on the basis of apparent molecular weight and immunoprecipitation with both polyclonal and monoclonal antibodies. Immunoprecipitation analysis, previously with polyclonal and more recently with monoclonal antibodies, of infected cell lysates labeled with [35S]methionine in the presence of tunicamycin, an inhibitor of N-linked glycosylation, revealed two putative precursor molecules of 88,000 daltons (pr88) and 44,000 daltons (pr44). High-resolution pulse-chase studies revealed that gp100 was a glycosylated intermediate which was processed to yield gp60 and gp49. This cleavage was inhibited by monensin, an inhibitor of glycoprotein processing. Endo-beta-N-acetylglucosaminidases F and H (endo-F, endo-H) reduced gp100 to pr88, indicating that the latter is an intermediate in the biosynthetic pathway. These same enzymes reduced gp49, and to a lesser extent gp60, to pr44, suggesting that pr44 is their polypeptide backbone. Significant support for this concept is the fact that the same monoclonal antibody recognized all three molecules, gp60, gp49, and pr44. In the presence of monensin, terminal addition of complex sugars was also prevented, since gp60 was replaced by a slightly faster migrating component which was insensitive to both endo-F and endo-H. Cell-free translation of infected-cell mRNA, followed by immunoprecipitation analysis with either polyclonal or monoclonal antibody, resulted in detection of a putative unglycosylated precursor polypeptide of 44,000 daltons. Since pr88 was not the initial precursor polypeptide of the MDHV-B complex, its existence may have resulted from dimerization of pr44. Again, detection of both pr88 and pr44 with the same monoclonal antibody is consistent with this interpretation. These collective data obtained from the cell-free and in vivo studies with polyclonal and monoclonal antibodies reactive with MDHV-B are consistent with the concept that pr44, the initial gene product, dimerizes to form pr88 and demonstrate that pr88 is actually a processing intermediate glycosylated to gp100, another processing intermediate, which is then processed to gp60 and gp49.

Immunological properties of an N-terminal fragment of herpes simplex virus type 1 glycoprotein D expressed in Escherichia coli

The N-terminal fragment, comprising residues -5 to 55 of herpes simplex virus type 1 glycoprotein D was expressed as a beta-galactosidase fusion protein in Escherichia coli. This gD-fusion protein reacts with monoclonal antibody LP 14 directed against glycoprotein D of HSV. Antisera obtained after immunization of rabbits with purified gD-fusion protein react with HSV-1 gD in a Western blot and with N-terminal synthetic peptides of gD. In addition, these antisera are able to neutralize viral infectivity in vitro.

Abundant expression of herpes simplex virus glycoprotein gB using an adenovirus vector

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is a major component of infected cell membranes and virion envelopes. Glycoprotein B is known to be essential for entry of viruses into cells and may play important roles in virus-induced cell fusion and other alterations in cell morphology. In order to study the biochemical and immunological properties of gB in isolation from other HSV-1 polypeptides we have constructed human adenovirus vectors capable of expressing high levels of gB. The gB gene was coupled to the SV40 early promoter and inserted into the E3 region of two adenovirus vectors, one in which the E1 region was deleted (AdgB-1) and another which contained E1 sequences (AdgB-2). In AdgB-1 the orientation of the chimeric gB-SV40 gene was right to left, i.e., opposite to the direction of late and E3 mRNA transcription, whereas in AdgB-2 the orientation was left to right. Human 293 cells which express E1 functions supported replication of AdgB-1 and gB was expressed in these cells but not in mouse cells and only at very low levels in human cells other than 293. Replication of AdgB-2 was not limited to 293 cells and the virus was able to induce synthesis of gB at levels equal to or higher than those expressed in HSV-1-infected human or mouse cells. Microscopic examination of AdgB-2-infected cells revealed extensive vacuolization in a manner completely uncharacteristic of adenovirus-infected cells, and fluorescent antibody staining indicated that gB was not only present at the cell surface but also concentrated in the cytoplasmic vacuoles.

Antibodies against synthetic peptides of herpes simplex virus type 1 glycoprotein D and their capability to neutralize viral infectivity in vitro

Peptides corresponding to residues 1-13, 9-21, 18-30, 82-93, 137-150, 181-197, 232-243, 235-243, 267-281, 271-281 and 302-315 of glycoprotein D of herpes simplex virus type 1 (HSV-1) were chemically synthesized. These peptides were coupled to carrier proteins, and the resulting conjugates were used to immunize rabbits. An enzyme-linked immunosorbent assay was used to determine antipeptide antibody titers in serum collected after immunization. All peptides appeared to be immunogenic in rabbits. Western immunoblot analysis with detergent extracts of HSV-1-infected Vero cells showed that antibodies against each of the peptides were able to react with the parent glycoprotein under denaturing conditions. Antisera against peptides 1-13, 9-21, and 18-30 neutralized HSV-1 infectivity in vitro, peptide 9-21 being the most successful in this respect. Immunization with a mixture of peptides 9-21 and 267-281 yielded antisera which reacted strongly with glycoprotein gD in Western blot analysis and showed a more solid virus-neutralizing activity in vitro.

The characterization of equine herpes virus-1-infected cell polypeptides recognized by equine lymphocytes

Ponies, without evidence of previous exposure to Equine herpes virus-1 (EHV-1), were experimentally infected with EHV-1 subtype 2 and investigated for lymphocyte transformation to virus-infected cell polypeptides, as shown by separation with gel electrophoresis. Animals made significant responses to Western blot fractions that corresponded to molecular weights of approximately 30,000, 40,000-45,000, 60,000-65,000, 80,000-95,000 and 100,000-140,000 MW. These molecular weight ranges correlated with the positions of major EHV-1 subtype 2 glycoproteins that were found at migration distances approximating to 137,000, 111,000, 90,000, 65,000 and 47,000 MW. Responses were also made to a subset of similar points on the subtype 1 profile. Hyperimmune equine serum precipitated numerous infected-cell proteins of both subtypes; in particular the recognition of polypeptides with MW of 142,000, 132,000, 114,000, and 46,000 was in agreement with the mitogenic responses. Labelling with 125I indicated that immunoprecipitated greater than 250,000, 182,000, 142,000, 132,000, 75,000, 46,000 and 32,000/34,000 MW products were exposed on the surface of infected cells.

Characterization of herpesvirus sylvilagus glycoproteins released into the culture medium of infected cells: antisera to gp13 and gp32 neutralize viral infectivity in vitro and identify antigens on plasma membranes of infected cells

Polypeptides released into the culture medium of herpesvirus sylvilagus-infected cells were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of extracellular fluid from [35S]methionine- and [3H]glucosamine-labeled cell cultures. Virus-induced glycoproteins 31, 32, and 33 (molecular weights of 62,000, 59,000, and 54,000, respectively) were the most abundant species and appeared predominantly in the culture medium. This observation, together with the known cell-associated nature of herpesvirus sylvilagus, suggested that virus-induced glycoproteins 31, 32, and 33 were specifically released. Immunization of rabbits with virus-induced glycoproteins 13 (molecular weight of 130,000) and 32 resulted in the production of antibodies that neutralized viral infectivity in vitro. Both antiserum to gp13 and antiserum to gp32 immunoprecipitated gp13, gp26, gp33a, gp45, and virus-induced polypeptide 39 (molecular weights of 130,000, 77,000, 49,000, 27,000, and 36,000, respectively) from [35S]methionine-labeled cell extracts as well as virus-induced glycoproteins 31, 32, and 33 from the culture medium. In addition, membrane immunofluorescence assays indicate that an antigen(s) reactive with anti-gp13/32 serum was located on the plasma membrane of infected cells.

In situ detection of alkaline nuclease activity in cells infected with herpes simplex virus type 1 (HSV-1)

An in situ assay for detection of alkaline nuclease activities has been adapted to the herpes simplex virus type 1 (HSV-1) system. Six major nuclease activities which migrate with molecular weights of 90,000, 85,000, 80,000, 76,000, 71,000 and 65,000, and six minor species of molecular weights 87,000, 81,000, 57,000, 18,500, 17,500 and 16,500 were detected in lysates of HSV-1 infected cells following SDS-polyacrylamide gel electrophoresis and enzyme activation in situ. An ELISA assay and an immunoprecipitation study indicated that the six major HSV-induced nuclease species are virus-specific. Moreover, a reconstruction experiment in which 14C-labelled protein markers were incubated with mock- and HSV-infected cell lysates demonstrates that the nuclease fractions detected in situ were not due to endogenous proteolytic activity. The 80,000, 76,000, 71,000 and 65,000 species were first detected at 4 h post-infection, whereas all others were detectable by 6 h post-infection. The activities of the major cellular nucleases of molecular weights 50,000. 48,000 and 45,000 decreased as a function of time post-infection. The level of expression of each of the virus-induced species was dependent upon the multiplicity of infection, and all virus-induced activities exhibited biochemical properties characteristic of purified HSV-1 alkaline nuclease, including activation and inhibition by specifications. The 76,000 HSV-induced alkaline nuclease species was also demonstrated to possess endonucleolytic activity.

Induced proteins in cells infected with pseudorabies virus

New proteins appearing after infection of cultured L929 cells with pseudorabies virus (PRV) were analyzed by SDS polyacrylamide gel electrophoresis. Analysis was facilitated by using a virus-cell system with marked inhibition of host protein synthesis after infection. Infected cells were pulsed during successive two hour periods through the infectious cycle with 35S-methionine. Proteins were extracted with detergent and analyzed on high resolution reducing gels. Thirty-four protein bands were resolved on gels of different concentrations that varied from 7 to 15 percent. Calculated apparent molecular weights of the protein peaks were not dependent on gel concentration except for very large or small sized proteins. Eight glycoproteins were resolved after labeling with 14C-glucosamine. The time course of incorporation of label was used as a measure of protein synthesis allowing the grouping of proteins according to the time of maximal synthesis. Several proteins shifted in MW during the course of infection, indicating possible post-translational cleavage or other minor modification.

Identification of a novel herpes simplex virus type 1-induced glycoprotein which complexes with gE and binds immunoglobulin

We detected a glycoprotein on the surface of cells infected with herpes simplex virus type 1 (HSV-1) which, in conjunction with gE, binds immunoglobulin G (IgG). The novel glycoprotein, which has an apparent molecular mass of 70 kilodaltons and was provisionally named g70, was first detected in extracts of HSV-1-infected cells labeled by lactoperoxidase-catalyzed iodination and precipitated with rabbit sera or IgG and protein A-Sepharose. In subsequent experiments, g70 and gE were coprecipitated from extracts of HSV-1-infected cells labeled with [35S]methionine, [35S]cysteine, or 14C-amino acids. We were unable to precipitate a polypeptide analogous to g70 or gE from extracts of HSV-2-infected cells with rabbit IgG and protein A-Sepharose. Partial proteolytic peptide analysis indicated that g70 is structurally distinct from gE and gI). In addition, g70 was electrophoretically distinct from the HSV-1 Us4 glycoprotein gG. HSV-1 gE, expressed in mouse cells transfected with the gE gene, was not precipitated with rabbit IgG, nor could these cells bind radiolabeled IgG, suggesting that gE alone cannot act as an IgG (Fc) receptor. This result, coupled with the findings that gE and g70 are coprecipitated with IgG and with an anti-gE monoclonal antibody, suggests that gE and g70 form a complex which binds IgG. The electrophoretic mobilities of g70 molecules induced by different strains of HSV-1 differed markedly, arguing that g70 is encoded by the virus and is not a cellular protein induced by virus infection.

The herpes simplex virus type 1 ribonucleotide reductase is a tight complex of the type alpha 2 beta 2 composed of 40K and 140K proteins, of which the latter shows multiple forms due to proteolysis

We have isolated two monospecific monoclonal mouse antibodies directed against the HSV-1 ribonucleotide reductase. When immobilized to Sepharose, both antibodies remove enzyme activity from solution. However, on immunoblots of crude extracts of HSV-1-infected cells, one antibody only detects a 140K protein and the other antibody only a 40K protein. Neither antibody recognizes the cellular ribonucleotide reductase or the related pseudorabies virus-induced enzyme. Therefore, our data strongly suggest that the HSV-1 ribonucleotide reductase consists of a 140K and a 40K protein. The 140K protein is sequentially degraded to 110K, 93K, and 81K proteins by a Vero cell-specific, N alpha-p-tosyl-L-lysine chloromethyl ketone-sensitive protease. Of the different proteolytic products, at least the 93K species seems to be enzymatically active, suggesting that part of the 140K protein may have functions not related to ribonucleotide reduction. There is a very high affinity between the 140K and 40K proteins as evident from affinity chromatography on antibody-Sepharose and sedimentation velocity centrifugation in a glycerol gradient. The 140K and 40K proteins cosediment with the HSV-1 ribonucleotide reductase activity at 17 S. This indicates that the active form of the HSV-1 reductase consists of the 140K and 40K proteins forming a tight complex of the alpha 2 beta 2 type.

Stages in the nuclear association of the herpes simplex virus transcriptional activator protein ICP4

The nuclear localization of the herpes simplex virus transcriptional activator protein ICP4 was studied by indirect immunofluorescence. At early times after viral infection, ICP4 quickly localized to a diffuse intranuclear distribution. ICP4 later concentrated in globular compartments within the nucleus. The redistribution to the compartments was dependent on viral DNA replication. Double staining for ICP4 and ICP8, the early major DNA-binding protein, revealed that both were found in the same intranuclear globular compartments at late times. These were previously named "replication compartments" (M. P. Quinlan, L. B. Chen, and D. M. Knipe, Cell 36:857-868, 1984). Because ICP4 and ICP8 are known to function in transcriptional activation and DNA replication, respectively, both DNA replication and late transcription may occur in these compartments. The association of ICP4 and ICP8 with the replication compartments appeared to be independent in that the retention of ICP8 in the compartments required ongoing viral DNA synthesis, while the association of ICP4 was independent of viral DNA synthesis once the compartments were formed. Because ICP4 shows a different distribution at early and late times, stimulation of transcription by ICP4 may involve different molecular events or contacts during these two periods of the replicative cycle.

The processing of pseudorabies virus glycoprotein gX in infected cells and in an uninfected cell line

Pseudorabies virus (PRV) produces a glycoprotein, gX, that accumulates in the medium of infected cells. The gX gene was expressed in Chinese hamster ovary cells (CHOgX cells) using the cytomegalovirus Towne major immediate early promoter. Like PRV-infected cells, CHOgX cells produced gX and exported it into the medium. Tunicamycin reduced the molecular weight of the gX in the medium to 89 kDa, compared with 99 kDa for gX made in the absence of drug. In the presence of tunicamycin gX produced by both PRV-infected cells and CHOgX cells was still glycosylated, as indicated by incorporation of [14C]glucosamine. The most likely form of this glycosylation is O-linked. In a pulse-chase experiment, gX first appeared in a 90-kDa form, then a 115-kDa form. This 115-kDa form is probably cleaved to give the 99-kDa form of gX that is released into the medium. The 115-kDa form was much more persistent in the PRV-infected Vero cells than in the CHOgX cells. In both cell types, gX was labeled by [35S]sulfate in the presence and absence of tunicamycin.

Synthesis and processing of the envelope gp55-116 complex of human cytomegalovirus

The envelope of human cytomegalovirus has been reported to contain between three and eight glycoproteins. Major constituents of the envelope include two abundant glycoproteins with estimated molecular weights of 55,000 (gp55) and 116,000 (gp116). These two glycoproteins have been shown to exist as a disulfide-linked complex (gp55-116) within the envelope of mature virions. Utilizing a panel of monoclonal antibodies reactive with the gp55-116 complex, we characterized the synthesis and processing of these two virion proteins. Infected cells were shown to contain two glycosylated proteins of 160,000 and 150,000 daltons as well as the mature gp55 and gp116. Pulse-chase analysis indicated that gp150 was a precursor protein of gp160. The mature gp55 and gp116 were generated, in turn, by cleavage of gp160. Antigenic and structural analysis revealed that gp55 and gp116 shared little structural homology and no detectable antigenic cross-reactivity. The results of this study are discussed in relation to the synthesis of envelope proteins of other herpesviruses.

Isolation of herpes simplex virus regulatory protein ICP4 as a homodimeric complex

The viral polypeptide ICP4 (or Vmw175) is synthesized during the immediate early phase of infection by herpes simplex virus and regulates the transcription of delayed early and late viral genes. We obtained a partially purified preparation of soluble ICP4 under nondenaturing conditions. Physical constants for native ICP4 were empirically determined by molecular sieve chromatography and sucrose density gradient ultracentrifugation. The Stokes radius of native ICP4 was 8.72 X 10(-7) cm. The sedimentation coefficient of native ICP4 was 9.00S. From these values, the calculated molecular weight of native ICP4 was 342,000, a value which is twice that of monomeric ICP4, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The failure of any other polypeptides to specifically coprecipitate with native ICP4 in the presence of anti-ICP4 antibody indicates that the 342,000-dalton complex is a homodimer of ICP4. The frictional coefficient ratio of native ICP4, which is 1.9, indicates that the homodimer is a highly elongated molecule.

Isolation by high-performance liquid chromatography and partial characterization of a 57,000-dalton herpes simplex virus type 1 polypeptide

A Nonidet P-40 extract of HSV-1-purified virions was fractionated by reversed-phase high-performance liquid chromatography (RP-HPLC). The first peak fraction eluted at 25% organic solvent. Polyacrylamide gel electrophoresis showed that it contained a 57,000-dalton polypeptide. The polypeptide was characterized by determination of the amino acid composition and the N-terminal amino acid sequence. Adsorption of the detergent extract before RP-HPLC showed that the polypeptide reacted with monoclonal antibodies LP1 directed against herpes simplex virus polypeptide VP-16.

Evidence for post-translational glycosylation of a nonglycosylated precursor protein of herpes simplex virus type 1

Incubation of herpes simplex virus type 1-infected Vero and HEp-2 cells at a reduced temperature (34 degrees C) enhanced the detection of the nonglycosylated precursors (pgB97 and pgC75) to the gB and gC glycoproteins in the cytoplasmic and nuclear fractions. Relative to the fully glycosylated and high-mannose forms detected, the nonglycosylated precursors were the predominant components associated with the nuclear fraction of infected cells. Furthermore, addition of protease inhibitors to the fractionation buffers did not affect the distribution or abundance of the nonglycosylated precursors, suggesting that the presence of pgB97 and pgC75 was not the result of proteolysis. When infected Vero or HEp-2 cells were harvested at various times postinfection, the nonglycosylated precursors were detected after the initial appearance of the high mannose components (pgB110 and pgC105). In Vero cells, pgB97 and pgC75 were detected simultaneously at 8 h postinfection, whereas detection was not apparent in HEp-2 cells until 20 h postinfection. Conditions which favored detection of appreciable amounts of nonglycosylated precursors provided an unique approach to probe possible post-translational modifications in the absence of inhibitors of glycosylation. In nuclear fractions isolated from cycloheximide-treated HEp-2 or Vero cells, numerous discrete gC-immunoreactive bands migrating with decreased electrophoretic mobility relative to the nonglycosylated precursor pgC75 were observed. This series of one to four additional bands was eliminated by digestion with endoglycosidase H, and the appearance of these bands was blocked by the addition of tunicamycin. Collectively, the data suggest that high-mannose core oligosaccharides may be added to the nonglycosylated precursor of the gC glycoprotein of herpes simplex virus type 1 in a post-translational fashion.