Structural and functional studies of a 39,000-Mr immunodominant protein of vaccinia virus

Design, evaluation, and immune simulation of potentially universal multi-epitope mpox vaccine candidate: focus on DNA vaccine

Monkeypox (mpox) is a zoonotic infectious disease caused by the mpox virus. Mpox symptoms are similar to smallpox with less severity and lower mortality. As yet mpox virus is not characterized by as high transmissibility as some severe acute respiratory syndrome 2 (SARS-CoV-2) variants, still, it is spreading, especially among men who have sex with men (MSM). Thus, taking preventive measures, such as vaccination, is highly recommended. While the smallpox vaccine has demonstrated considerable efficacy against the mpox virus due to the antigenic similarities, the development of a universal anti-mpox vaccine remains a necessary pursuit. Recently, nucleic acid vaccines have garnered special attention owing to their numerous advantages compared to traditional vaccines. Importantly, DNA vaccines have certain advantages over mRNA vaccines. In this study, a potentially universal DNA vaccine candidate against mpox based on conserved epitopes was designed and its efficacy was evaluated via an immunoinformatics approach. The vaccine candidate demonstrated potent humoral and cellular immune responses in silico, indicating the potential efficacy in vivo and the need for further research.

Comparative sequence and structural analysis of the ORF095 gene, a vaccinia virus A4L homolog of capripoxvirus in sheep and goats

Sheeppox and goatpox are important transboundary animal viral diseases of sheep and goats caused by sheeppox virus (SPPV) and goatpox virus (GTPV), respectively, of the genus Capripoxvirus, family Poxviridae. Among the proteins encoded by the capripoxvirus (CaPV) genome, ORF095 (vaccinia virus A4L homolog) is an immunodominant virion core protein that plays a pivotal role in virus assembly and morphogenesis. In the present study, sequence analysis of the ORF095 genes of 27 SPPV and GTPV isolates or field samples from different geographical regions of India was performed, and structure was prediction was done by homology modeling. A multiple sequence alignment of different CaPV isolates revealed that CaPV-A4L is highly conserved, with several species-specific signature residues, namely A93, A216, A315, G136 and G146 in GTPV, G47, A63, A168 and A276 in SPPV, and G48 and C98 in lumpy skin disease virus (LSDV). Phylogenetically, the CaPV isolates were separated into three major clusters, GTPV, SPPV and LSDV, based on the complete coding sequence of the CaPV-A4L gene. Genus-specific clustering of poxviruses was observed in phylogenetic analysis based on A4L protein homologs of chordopoxviruses. A secondary structure prediction showed the presence of six α-helices and one β-sheet as well as some coils. The signature residues identified here are potentially useful for genotyping, and the predicted characteristics of the CaPV-A4L protein make it an ideal candidate for use as an immunogenic or diagnostic antigen for the development of immunoassays in  the sero-evaluation of CaPV in target hosts.

RNA interference targeting virion core protein ORF095 inhibits Goatpox virus replication in Vero cells

BACKGROUND

Goatpox is an economically important disease in goat and sheep-producing areas of the world. Many vaccine strategies developed to control the disease are not yet completely successful. Hairpin expression vectors have been used to induce gene silencing in a large number of studies on viruses. However, none of these studies has been attempted to study GTPV. In the interest of exploiting improved methods to control goat pox, it is participated that RNAi may provide effective protection against GTPV. In this study we show the suppression of Goatpox virus (GTPV) replication via knockdown of virion core protein using RNA interference.

RESULTS

Four short interfering RNA (siRNA) sequences (siRNA-61, siRNA-70, siRNA-165 and siRNA-296) against a region of GTPV ORF095 were selected. Sense and antisense siRNA-encoding sequences separated by a hairpin loop sequence were designed as short hairpin RNA (shRNA) expression cassettes under the control of a human U6 promoter. ORF095 amplicon was generated using PCR, and then cloned into pEGFP-N1 vector, named as p095/EGFP. p095/EGFP and each of the siRNA expression cassettes (p61, p70, p165 and p296) were co-transfected into BHK-21 cells. Fluorescence detection, flow cytometric analysis, retro transcription PCR (RT-PCR) and real time PCR were used to check the efficiency of RNAi. The results showed that the ORF095-specific siRNA-70 effectively down-regulated the expression of ORF095. When Vero cells were transfected with shRNA expression vectors (p61/GFP, p70/GFP, p165/GFP and p296/GFP) and then infected with GTPV, GTPV-ORF095-70 was found to be the most effective inhibition site in decreasing cytopathic effect (CPE) induced by GTPV. The results presented here indicated that DNA-based siRNA could effectively inhibit the replication of GTPV (approximately 463. 5-fold reduction of viral titers) on Vero cells.

CONCLUSIONS

This study demonstrates that vector-based shRNA methodology can effectively inhibit GTPV replication on Vero cells. Simultaneously, this work represents a strategy for controlling goatpox, potentially facilitating new experimental approaches in the analysis of both viral and cellular gene functions during of GTPV infection.

Genomic expression libraries for the identification of cross-reactive orthopoxvirus antigens

Increasing numbers of human cowpox virus infections that are being observed and that particularly affect young non-vaccinated persons have renewed interest in this zoonotic disease. Usually causing a self-limiting local infection, human cowpox can in fact be fatal for immunocompromised individuals. Conventional smallpox vaccination presumably protects an individual from infections with other Orthopoxviruses, including cowpox virus. However, available live vaccines are causing severe adverse reactions especially in individuals with impaired immunity. Because of a decrease in protective immunity against Orthopoxviruses and a coincident increase in the proportion of immunodeficient individuals in today's population, safer vaccines need to be developed. Recombinant subunit vaccines containing cross-reactive antigens are promising candidates, which avoid the application of infectious virus. However, subunit vaccines should contain carefully selected antigens to confer a solid cross-protection against different Orthopoxvirus species. Little is known about the cross-reactivity of antibodies elicited to cowpox virus proteins. Here, we first identified 21 immunogenic proteins of cowpox and vaccinia virus by serological screenings of genomic Orthopoxvirus expression libraries. Screenings were performed using sera from vaccinated humans and animals as well as clinical sera from patients and animals with a naturally acquired cowpox virus infection. We further analyzed the cross-reactivity of the identified immunogenic proteins. Out of 21 identified proteins 16 were found to be cross-reactive between cowpox and vaccinia virus. The presented findings provide important indications for the design of new-generation recombinant subunit vaccines.

Colocalization of transcription and translation within cytoplasmic poxvirus factories coordinates viral expression and subjugates host functions

Poxviruses are large DNA viruses that include the causal agent of human smallpox and vaccinia virus. Poxviruses replicate in cytoplasmic foci known as DNA factories. Here we show that a virus-encoded transcription factor, viral mRNA, cellular RNA-binding protein heterodimer G3BP/Caprin-1 (p137), translation initiation factors eIF4E and eIF4G, and ribosomal proteins are concentrated in the same subdomains of cytoplasmic DNA factories. Furthermore, a cell coinfected with two recombinant vaccinia viruses expressing a virus core protein fused to cyan or yellow fluorescent protein displayed separate cyan and yellow factories, indicating that each factory formed from a single genome and was the site of transcription and translation as well as DNA replication. Hijacking of the host translation apparatus within the factory likely enhances the efficiency of virus replication and contributes to the suppression of host protein synthesis, thereby facilitating poxvirus subjugation of the cell.

Protein composition of the vaccinia virus mature virion

The protein content of vaccinia virus mature virions, purified by rate zonal and isopycnic centrifugations and solubilized by SDS or a solution of urea and thiourea, was determined by the accurate mass and time tag technology which uses both tandem mass spectrometry and Fourier transform-ion cyclotron resonance mass spectrometry to detect tryptic peptides separated by high-resolution liquid chromatography. Eighty vaccinia virus-encoded proteins representing 37% of the 218 genes annotated in the complete genome sequence were detected in at least three analyses. Ten proteins accounted for approximately 80% of the virion mass. Thirteen identified proteins were not previously reported as components of virions. On the other hand, 8 previously described virion proteins were not detected here, presumably due to technical reasons including small size and hydrophobicity. In addition to vaccinia virus-encoded proteins, 24 host proteins omitting isoforms were detected. The most abundant of these were cytoskeletal proteins, heat shock proteins and proteins involved in translation.

In a nutshell: structure and assembly of the vaccinia virion

Poxviruses comprise a large family of viruses characterized by a large, linear dsDNA genome, a cytoplasmic site of replication and a complex virion morphology. The most notorious member of the poxvirus family is variola, the causative agent of smallpox. The laboratory prototype virus used for the study of poxviruses is vaccinia, the virus that was used as a live, naturally attenuated vaccine for the eradication of smallpox. Both the morphogenesis and structure of poxvirus virions are unique among viruses. Poxvirus virions apparently lack any of the symmetry features common to other viruses such as helical or icosahedral capsids or nucleocapsids. Instead poxvirus virions appear as "brick shaped" or "ovoid" membrane-bound particles with a complex internal structure featuring a walled, biconcave core flanked by "lateral bodies." The virion assembly pathway involves a remarkable fabrication of membrane-containing crescents and immature virions, which evolve into mature virions in a process that is unparalleled in virology. As a result of significant advances in poxvirus genetics and molecular biology during the past 15 years, we can now positively identify over 70 specific gene products contained in poxvirus virions, and we can describe the effects of mutations in over 50 specific genes on poxvirus assembly. This review summarizes these advances and attempts to assemble them into a comprehensible and thoughtful picture of poxvirus structure and assembly.

A vaccinia virus lacking A10L: viral core proteins accumulate on structures derived from the endoplasmic reticulum

The assembly of the intracellular mature virus (IMV) of vaccinia virus (VV), the prototype member of the poxviridae, is poorly understood and controversial. We have previously proposed that the IMV is composed of a continuous double-membraned cisterna derived from the smooth ER, whereby the genome-containing core is enwrapped by a part of this cisterna. In the present study we characterize a mutant virus in which the synthesis of the major core protein A10L can be conditionally expressed. Without A10L, IMVs are not made; immature viruses (IVs) and regularly stacked membrane structures that contain viral DNA, accumulate instead. By immunolabelling of thawed cryo-sections these stacks contain most of the viral core proteins and low levels of viral membrane proteins. Importantly, the stacked membranes could be labelled with antibodies to an ER marker protein, implying that they are derived from this cellular compartment. By electron tomography (ET) on semi-thin cryo-sections we show that the membranes of the stacks are continuous with the membranes of the IVs. Direct continuities with ER cisternae, to which the stacks are tightly apposed, were, however, not unequivocally seen. Finally, ET revealed how the IV membranes separated to become two-membrane profiles. Taken together, this study shows that VV core proteins and the viral DNA can coassemble onto ER-derived membranes that are continuous with the membranes of the IVs.

Identification and preliminary characterization of vaccinia virus (Dryvax) antigens recognized by vaccinia immune globulin

Using vaccinia immune globulin (VIG), a high-titer antibody preparation from immunized subjects, we demonstrate that the humoral immune response in humans is directed against numerous antigens in the Dryvax vaccine strain. Western blot and immunoprecipitation analyses revealed highly antigenic proteins associated with both the extracellular enveloped virus and intracellular mature virus forms. The modified vaccinia virus Ankara (MVA), a new generation smallpox vaccine that is attenuated for replication in humans, expresses most, but not all, of the major vaccinia antigens recognized by antibodies in VIG, lacking the highly antigenic protein corresponding to the A-type inclusion body protein. Since new-generation smallpox vaccines such as MVA will require extensive comparison to traditional smallpox vaccines in animal models of immunogenicity and protection, we compared the vaccinia virus antigens recognized by VIG to those recognized by sera from Dryvax and MVA immunized mice. The humoral immune response in immunized mice is qualitatively similar to that in humans.

Efficacy of novel plasmid DNA encoding vaccinia antigens in improving current smallpox vaccination strategy

We tested a DNA vaccine strategy in order to improve the efficacy and safety of the current live smallpox vaccine involving priming with DNA vaccines and boosting with live vaccinia virus (VacV). We generated DNA plasmids encoding the A4L, A27L and H5R VacV genes. A considerable increase in antigen-specific IFN-gamma responses, high proliferative and humoral antigen-specific responses were detected in experimental primed Balb/C mice compared to controls after VacV boost. The VacV-DNA plasmids elicited IFN-gamma production in HLA-A2.1 transgenic mice in response to predicted HLA-A2.1 restricted peptide epitopes, providing valuable data for further vaccine development.

Vaccinia virus cores are transported on microtubules

Infection with Vaccinia virus (VV) produces several distinct virions called intracellular mature virus (IMV), intracellular enveloped virus (IEV), cell-associated enveloped virus (CEV) and extracellular enveloped virus (EEV). In this report, we have investigated how incoming virus cores derived from IMV are transported within the cell. To do this, recombinant VVs (vA5L-EGFP-N and vA5L-EGFP-C) were generated in which the A5L virus core protein was fused with the enhanced green fluorescent protein (EGFP) at the N or C terminus. These viruses were viable, induced formation of actin tails and had a plaque size similar to wild-type. Immunoblotting showed the A5L-EGFP fusion protein was present in IMV particles and immunoelectron microscopy showed that the fusion protein was incorporated into VV cores. IMV made by vA5L-EGFP-N were used to follow the location and movement of cores after infection of PtK(2) cells. Confocal microscopy showed that virus cores were stained with anti-core antibody only after they had entered the cell and, once intracellular, were negative for the IMV surface protein D8L. These cores co-localized with microtubules and moved in a stop-start manner with an average speed of 51.8 (+/-3.9) microm min(-1), consistent with microtubular movement. Treatment of cells with nocodazole or colchicine inhibited core movement, but addition of cytochalasin D did not. These data show that VV cores derived from IMV use microtubules for intracellular transport after entry.

Analysis of the monkeypox virus genome

Monkeypox virus (MPV) belongs to the orthopoxvirus genus of the family Poxviridae, is endemic in parts of Africa, and causes a human disease that resembles smallpox. The 196,858-bp MPV genome was analyzed with regard to structural features and open reading frames. Each end of the genome contains an identical but oppositely oriented 6379-bp terminal inverted repetition, which similar to that of other orthopoxviruses, includes a putative telomere resolution sequence and short tandem repeats. Computer-assisted analysis was used to identify 190 open reading frames containing >/=60 amino acid residues. Of these, four were present within the inverted terminal repetition. MPV contained the known essential orthopoxvirus genes but only a subset of the putative immunomodulatory and host range genes. Sequence comparisons confirmed the assignment of MPV as a distinct species of orthopoxvirus that is not a direct ancestor or a direct descendent of variola virus, the causative agent of smallpox.

Chimeras between the human immunodeficiency virus (HIV-1) Env and vaccinia virus immunogenic proteins p14 and p39 generate in mice broadly reactive antibodies and specific activation of CD8+ T cell responses to Env

A vaccine based on the envelope protein (Env) of the human immunodeficiency virus type 1 (HIV-1) that triggers widely reactive antibodies might be a desirable approach to control virus infection. To expose epitopes which could induce broadly reactive antibodies against HIV-1 Env, we have generated vaccinia virus (VV) recombinants that express Env fused at its N- or C-terminus with two major antigenic proteins of VV, p14 (A27L gene) and p39 (A4L gene). Biochemical analysis of the chimeric proteins in cell cultures revealed that, in all cases, recombinant viruses expressed the correct fusion proteins. When p14 or p39 are fused at the N-terminus of Env the chimeric proteins are poorly glycosylated but when p14 or p39 are fused at the C-terminus of Env, the chimeric proteins are fully glycosylated. In Balb/c mice, immunisation with the referred VV recombinants induced similar levels of CD8+ T cell specific responses to Env as immunisation with the entire Env protein. The humoral immune response triggered by the fusion proteins was broader than in animals immunised with VV expressing the entire Env (VVEnv1), and was directed to epitopes outside of the V3 loop (V1/V2, C1, C2, C4). One of the chimeric constructs induced a better neutralising antibody response than VVEnv1. We conclude that fusing VV proteins p14 or p39 to Env provides an effective means to induce broadly reactive antibodies and CD8+ T cell responses to Env. This approach might have utility against HIV and other pathogens.

Characterization of vaccinia virus intracellular cores: implications for viral uncoating and core structure

The entry of vaccinia virus (VV) into the host cell results in the delivery of the double-stranded DNA genome-containing core into the cytoplasm. The core is disassembled, releasing the viral DNA in order to initiate VV cytoplasmic transcription and DNA replication. Core disassembly can be prevented using the VV early transcription inhibitor actinomycin D (actD), since early VV protein synthesis is required for core uncoating. In this study, VV intracellular cores were accumulated in the presence of actD and isolated from infected cells. The content of these cores was analyzed by negative staining EM and by Western blotting using a collection of antibodies to VV core and membrane proteins. By Western blot analyses, intracellular actD cores, as well as cores prepared by NP-40-dithiothreitol treatment of purified virions (NP-40/DTT cores), contained the core proteins p25 (encoded by L4R), 4a (A10L), 4b (A3L), and p39 (A4L) as well as small amounts of the VV membrane proteins p32 (D8L) and p35 (H3L). While NP-40/DTT cores contained the major putative DNA-binding protein p11 (F17R), actD cores entirely lacked this protein. Labeled cryosections of cells infected for different periods of time in the presence or absence of actD were subsequently used to follow the fate of VV core proteins by EM. These EM images confirmed that p11 was lost at the plasma membrane upon core penetration. The cores that accumulated in the presence of actD were labeled with antibodies to 4a, p39, p25, and DNA at all times examined. In the absence of the drug the cores gradually lost their electron-dense inner part, concomitant with the loss of p25 and DNA labeling. The remaining core shell still labeled with antibodies to p39 and 4a/4b, implying that these proteins are part of this structure. These combined data are discussed with respect to the structure of VV as well as core disassembly.

Alastrim smallpox variola minor virus genome DNA sequences

Alastrim variola minor virus, which causes mild smallpox, was first recognized in Florida and South America in the late 19th century. Genome linear double-stranded DNA sequences (186,986 bp) of the alastrim virus Garcia-1966, a laboratory reference strain from an outbreak associated with 0.8% case fatalities in Brazil in 1966, were determined except for a 530-bp fragment of hairpin-loop sequences at each terminus. The DNA sequences (EMBL Accession No. Y16780) showed 206 potential open reading frames for proteins containing >/=60 amino acids. The amino acid sequences of the putative proteins were compared with those reported for vaccinia virus strain Copenhagen and the Asian variola major strains India-1967 and Bangladesh-1975. About one-third of the alastrim viral proteins were 100% identical to correlates in the variola major strains and the remainder were >/=95% identical. Compared with variola major virus DNA, alastrim virus DNA has additional segments of 898 and 627 bp, respectively, within the left and right terminal regions. The former segment aligns well with sequences in other orthopoxviruses, particularly cowpox and vaccinia viruses, and the latter is apparently alastrim-specific.

The vaccinia virus 39-kDa protein forms a stable complex with the p4a/4a major core protein early in morphogenesis

The vaccinia virus (VV) 39-kDa protein, the product of the A4L gene, is a highly antigenic protein of the viral core. Pulse-chase and immunoprecipitation experiments have shown that the 39-kDa protein interacts with p4a (encoded by the A10L gene), the precursor of the most abundant virion protein. This interaction is maintained with the processed 4a form that arises during virion maturation. The controlled disruption of mature viral particles showed that the 39-kDa and 4a proteins are tightly bound within the virion. Immunoelectron microscopy showed that both proteins first localize within the cytoplasm and later accumulate inside the viral factories, reaching these locations via a mechanism apparently unrelated to cellular membranes. Double labeling experiments showed a colocalization of both proteins in all virus-induced structures.

Vaccinia virus WR gene A5L is required for morphogenesis of mature virions

The vaccinia virus WR A5L open reading frame (corresponding to open reading frame A4L in vaccinia virus Copenhagen) encodes an immunodominant late protein found in the core of the vaccinia virion. To investigate the role of this protein in vaccinia virus replication, we have constructed a recombinant virus, vA5Li, in which the endogenous gene has been deleted and an inducible copy of the A5 gene dependent on isopropyl-beta-D-thiogalactopyranoside (IPTG) for expression has been inserted into the genome. In the absence of inducer, the yield of infectious virus was dramatically reduced. However, DNA synthesis and processing, viral protein expression (except for A5), and early stages in virion formation were indistinguishable from the analogous steps in a normal infection. Electron microscopy revealed that the major vaccinia virus structural form present in cells infected with vA5Li in the absence of inducer was immature virions. Viral particles were purified from vA5Li-infected cells in the presence and absence of inducer. Both particles contained viral DNA and the full complement of viral proteins, except for A5, which was missing from particles prepared in the absence of inducer. The particles prepared in the presence of IPTG were more infectious than those prepared in its absence. The A5 protein appears to be required for the immature virion to form the brick-shaped intracellular mature virion.

Production and characterization of human monoclonal antibody Fab fragments to vaccinia virus from a phage-display combinatorial library

A combinatorial, phage-display library of human Fab antibody fragments was generated from IgG heavy chain (HC) and light chain (LC) genes cloned from the lymphocytes of a vaccinia virus (VACV)-immune donor. To ascertain the complexity of the library, nucleotide sequences of the variable regions of the HC and LC genes were determined. Fourteen distinct HC and 18 distinct LC (7 kappa and 11 lambda) that formed a combinatorial library of 22 Fabs were identified. Immune-precipitation of radiolabeled VACV revealed that at least six different VACV proteins were recognized by the antibodies. Plaque-reduction neutralization demonstrated that six of the Fabs neutralized VACV in the presence of anti-human antibody. ELISA studies indicated that 15 of the Fabs were cross-reactive with monkeypox virus.

An unconventional role for cytoplasmic disulfide bonds in vaccinia virus proteins

Previous data have shown that reducing agents disrupt the structure of vaccinia virus (vv). Here, we have analyzed the disulfide bonding of vv proteins in detail. In vv-infected cells cytoplasmically synthesized vv core proteins became disulfide bonded in the newly assembled intracellular mature viruses (IMVs). vv membrane proteins also assembled disulfide bonds, but independent of IMV formation and to a large extent on their cytoplasmic domains. If disulfide bonding was prevented, virus assembly was only partially impaired as shown by electron microscopy as well as a biochemical assay of IMV formation. Under these conditions, however, the membranes around the isolated particles appeared less stable and detached from the underlying core. During the viral infection process the membrane proteins remained disulfide bonded, whereas the core proteins were reduced, concomitant with delivery of the cores into the cytoplasm. Our data show that vv has evolved an unique system for the assembly of cytoplasmic disulfide bonds that are localized both on the exterior and interior parts of the IMV.

The 131-amino-acid repeat region of the essential 39-kilodalton core protein of fowlpox virus FP9, equivalent to vaccinia virus A4L protein, is nonessential and highly immunogenic

The immunodominant, 39,000-molecular weight core protein (39K protein) of fowlpox virus (FP9 strain), equivalent to the vaccinia virus A4L gene product, contains highly charged domains at each end of the protein and multiple copies of a 12-amino-acid serine-rich repeat sequence in the middle of the protein. Similar repeats were also detected in other fowlpox virus strains, suggesting that they might confer a selective advantage to the virus. The molloscum contagiosum virus homolog (MC107L) also contains repeats, unlike the vaccinia virus protein. The number of repeats in the fowlpox virus protein does not seem to be crucial, since some strains have a different number of repeats, as shown by the difference in the size of the protein in these strains. The repeat region could be deleted, indicating that it is not essential for replication in vitro. It was not possible to delete the entire 39K protein, indicating that it was essential (transcriptional control signals for the flanking genes were left intact). The repeat region is partly responsible for the immunodominance of the protein, but the C-terminal part of the protein also contains highly antigenic linear epitopes. A role for the 39K protein in immune system modulation is discussed.

Identification of the major membrane and core proteins of vaccinia virus by two-dimensional electrophoresis

Vaccinia virus assembly has been well studied at the ultrastructural level, but little is known about the molecular events that occur during that process. Towards this goal, we have identified the major membrane and core proteins of the intracellular mature virus (IMV). Pure IMV preparations were subjected to Nonidet P-40 (NP-40) and dithiothreitol (DTT) treatment to separate the core proteins from the membrane proteins. These proteins were subsequently separated by two-dimensional (2D) gel electrophoresis, and the major polypeptide spots, as detected by silver staining and 35S labeling, were identified by either matrix-assisted laser desorption/ionization mass spectrometry, N-terminal amino acid sequencing, or immunoprecipitation with defined antibodies. Sixteen major spots that partitioned into the NP-40-DTT-soluble fraction were identified; 11 of these were previously described virally encoded proteins and 5 were cellular proteins, mostly of mitochondrial origin. The core fraction revealed four major spots of previously described core proteins, two of which were also detected in the membrane fraction. Subsequently, the NP-40-DTT-soluble and -insoluble fractions from purified virus preparations, separated by 2D gels, were compared with postnuclear supernatants of infected cells that had been metabolically labeled at late times (6 to 8 h) postinfection. This relatively short labeling period as well as the apparent shutoff of host protein synthesis allowed the selective detection in such postnuclear supernatants of virus-encoded proteins. These postnuclear supernatants were subsequently treated with Triton X-114 or with sodium carbonate to distinguish the membrane proteins from the soluble proteins. We have identified the major late membrane and nonmembrane proteins of the IMV as they occur in the virus as well as in infected cells. This 2D gel map should provide an important reference for future molecular studies of vaccinia virus morphogenesis.

A vaccinia virus core protein, p39, is membrane associated

We describe herein the characterization of p39, the product of the A4L gene of vaccinia virus. By immunolabelling of thawed cryosections from infected HeLa cells, we show that this protein is initially located in the central region, or viroplasm, of the viral factories, as well as in the immature virions, with very small amounts of labelling observed on the surrounding membranes. The localization of p39 changes dramatically during the transition of the immature virion to the intracellular mature virus (IMV), coincident with the appearance of the core structure in the center of the IMV, with p39 located between this core and the surrounding membranes. Complementary biochemical data, such as partitioning into the Triton X-114 detergent phase and stripping of the viral membranes with Nonidet P-40 and dithiothreitol, suggest that p39 is associated with the innermost of the two membranes surrounding the core. Sodium carbonate treatment also indicates that p39 is associated with membranes, even at the early stages of viral assembly. However, following in vitro translation of p39 in the presence of microsomal membranes, we failed to detect any association of the independently expressed protein with membranes. We also failed to detect any posttranslational acylation of p39 with myristate or palmitate, suggesting that p39 does not achieve its membrane association through lipid anchors. Therefore, p39 is most likely membrane associated through an interaction with an integral membrane protein(s) present in the innermost of the two membranes surrounding the IMV. These data, together with our recent data showing that p39 colocalizes with the spike-like protrusions on the IMV core (N. Roos, M. Cyrklaff, S. Cudmore, R. Blasco, J. Krijnse-Locker, and G. Griffiths, EMBO J. 15:2343-2355, 1996), suggest that p39 may form part of this spike and that it possibly functions as a matrix-like linker protein between the core and the innermost of the two membranes surrounding the IMV.

The role of a 21-kDa viral membrane protein in the assembly of vaccinia virus from the intermediate compartment

We have recently provided morphological evidence that a key event in the assembly of vaccinia virus is the formation of a novel cisternal domain of the intermediate compartment (IC) between the endoplasmic reticulum and the Golgi complex (Sodeik, B., Doms, R. W., Ericsson, M., Hiller, G., Machamer, C. E., van't Hof, W., van Meer, G., Moss, B., and Griffiths, G. (1993) J. Cell Biol. 121, 521-541). This tightly apposed cisternal domain incompletely surrounds the spherical immature virus that matures into the first of the two distinct infectious forms of vaccinia, the intracellular mature virus (IMV). In this study we describe the characterization of an abundant membrane protein of the IMV, the gene product of A17L, a 21-kDa protein that has recently been shown to be essential for the formation of the viral membranes (Rodriguez, D., Esteban, M., and Rodriguez, J. R. (1995) J. Virol. 69, 4640-4648). Upon translation in vitro, p21 associated with rough microsomal membranes in a co-translational manner. Using NH2- and COOH-terminal specific antibodies, we show that both in vitro as well as in vivo, p21 adopts a topology where the NH2 and COOH termini are cytoplasmically orientated. Immunocytochemical experiments demonstrated that p21 is a component of the inner of the two cisternal membranes of the immature virus as well as of membranes of the IC, identified using antibodies against Rab1. Taken together, these data provide the first molecular evidence in support of our assembly model; they show that an essential membrane protein of the IMV inserts into the rough endoplasmic reticulum, but gets efficiently targeted to the IC and membranes of the viral factory.

Mycoplasma pneumoniae and Mycoplasma genitalium mixture in synovial fluid isolate

A mycoplasma cultured from synovial fluid specimens from a patient with pneumonia and subsequent polyarthritis was identified initially as Mycoplasma pneumoniae. In retrospective studies, the culture was shown also to contain Mycoplasma genitalium. In this paper, the laboratory techniques employed in the identification and separation of the two species are presented, and evidence to implicate postinfectious autoimmunity is provided. An increasing number of reports of M. genitalium in human tissue sites and difficulties in isolation and identification of the organism in the clinical laboratory suggest the need for more extensive application of rapid and specific detection systems for both M. genitalium and M. pneumoniae in the clinical laboratory.

Identification and characterization of vaccinia virus genes encoding proteins that are highly antigenic in animals and are immunodominant in vaccinated humans

Vaccinia virus (VV) is a potent immunogen, but the nature of VV proteins involved in the activation of the immune response of the host is not yet known. By screening a lambda gt11 expression library of rabbitpox virus DNA with serum from humans vaccinated against smallpox or with serum from VV-immunized animals, we identified several VV genes that encode highly antigenic viral proteins with molecular masses of 62, 39, 32, 25, 21, and 14 kDa. It was found that VV proteins of 62, 39, 25, and 21 kDa are part of the virus core, while proteins of 32 and 14 kDa are part of the virus envelope. All of these proteins were synthesized at late times postinfection. Proteins of 62 and 25 kDa were produced by cleavage of larger precursors of 95 kDa (p4a) and 28 kDa, respectively. The 21-kDa protein was the result of a cleavage of p4a, presumably at amino acid Gly-697. DNA sequence analysis, in comparison with the known nucleotide sequence of VV, provided identification of the corresponding open reading frames. Expression of the viral genes in Escherichia coli was used to monitor which of the viral antigens elicit immunodominant responses and the location of antigenic domains. Three viral antigens of 62, 39, and 32 kDa exhibited immunodominant characteristics. The most antigenic sites of 62 and 39 kDa were identified at the N terminus (amino acids 132 to 295) and C terminus (last 103 amino acids), respectively. Immunization of mice with the 62-, 39-, or 14-kDa antigenic proteins conferred different degrees of protection from VV challenge. Proteins of 32 and 14 kDa induced cellular proliferative responses in VV-infected mice. Our findings demonstrate the nature of VV proteins involved in the activation of host immune responses after vaccination, provide identification of the viral gene locus, and define structural and immunological properties of these antigenic VV proteins.

Vaccinia virus induces cell fusion at acid pH and this activity is mediated by the N-terminus of the 14-kDa virus envelope protein

The mechanism by which the large-size poxviruses enter animal cells is not known. In this investigation we show that acid pH treatment of wild-type vaccinia virus-infected cells triggers strong fusion of cells in culture, with an optimum at pH 4.8. We have identified the virus-induced fusion protein as a 14-kDa envelope protein, based on the ability of a 14-kDa specific monoclonal antibody (mAbC3) to block vaccinia virus-induced fusion-from-within and fusion-from-without. We provide genetic evidence for a role of the 14-kDa protein in cell fusion, since insertion of the 14-kDa encoding gene into the genome of nonfusogenic mutant viruses generates heterozygous viruses that now acquire acid pH-dependent fusion activity. DNA sequence analyses of the 14-kDa encoding gene of the mutant viruses, 65-16 and 101-14, reveal N-terminal deletions of 46 and 10 amino acids, respectively. These deletions remove a small hydrophobic region at the N-terminus of the 14-kDa protein and prevent fusion. Our findings demonstrate that vaccinia virus can induce strong fusion of cells in culture at acid pH implying some entry of the virus by endocytosis, that the 14-kDa virus envelope protein is the fusogenic protein, and that the N-terminal proximal region is involved in fusion.

Identification of the point mutations in two vaccinia virus nucleoside triphosphate phosphohydrolase I temperature-sensitive mutants and role of this DNA-dependent ATPase enzyme in virus gene expression

The biological function of the nucleoside triphosphate phosphohydrolase I (NTPase I) enzyme of vaccinia virus is not yet known. In this investigation we have identified the genetic lesion of two temperature-sensitive mutants of vaccinia virus, ts50 and ts36, as single point mutations contained within the 5'615 nucleotides of the NTPase I gene (ts50, G to A at position 131; ts36, C to T at position 556). The point mutations result in amino acid substitutions of Gly to Glu-44 (ts50) and Pro to Ser-186 (ts36). In monkey BSC-40 cells, ts50 and ts36 behave phenotypically like wild-type virus with respect to replication and synthesis of viral DNA but are defective in late polypeptide synthesis. However, these two ts mutants displayed a drastically different phenotype in virus-infected human HeLa cells at the restrictive temperature; viral DNA replication did not occur and late polypeptide synthesis was absent. Moreover, if the early block was overcome by a temperature shift-up, then HeLa cells infected with the ts mutants displayed a profile characteristic of defective late viral polypeptide synthesis. Our results reveal that vaccinia NTPase I enzyme functions early and late in the viral replication cycle and that the phenotype of these ts mutants is dependent upon the cell type.

Highly attenuated vaccinia virus mutants for the generation of safe recombinant viruses

An attenuated vaccinia virus mutant with specific genetic lesions has been used to develop a vehicle for safer live recombinant virus vaccines. The mutant virus 48-7 has an 8-MDa deletion starting 2.2 MDa from the left end of the viral genome and point mutations in the gene encoding the 14-kDa fusion protein that determines the plaque-size phenotype of the virus. Using the highly sensitive reporter gene luciferase, we have shown that this mutant can generate recombinant viruses that infect cultured cells and animals with normal vaccinia virus tropism. Insertion of the envelope and gag genes of human immunodeficiency virus type 1 into the attenuated vaccinia mutant resulted in their efficient expression and precursor processing in infected cultured cells. Infection of mice with human immunodeficiency virus-vaccinia recombinant viruses elicited human immunodeficiency virus-specific antibodies. Using mice pretreated with cyclophosphamide as a model for immunosuppression, the reduced virulence of the mutant recombinant virus was clearly evident. These findings demonstrate that the highly attenuated vaccinia virus mutant 48-7 can be used to generate effective and safer vaccines.