Respiratory syncytial virus fusion glycoprotein: nucleotide sequence of mRNA, identification of cleavage activation site and amino acid sequence of N-terminus of F1 subunit

The RSV F p27 peptide: current knowledge, important questions

Respiratory syncytial virus (RSV) remains a leading cause of hospitalizations and death for young children and adults over 65. The worldwide impact of RSV has prioritized the search for an RSV vaccine, with most targeting the critical fusion (F) protein. However, questions remain about the mechanism of RSV entry and RSV F triggering and fusion promotion. This review highlights these questions, specifically those surrounding a cleaved 27 amino acids long peptide within F, p27.

Contribution of cysteine residues in the extracellular domain of the F protein of human respiratory syncytial virus to its function

The mature F protein of all known isolates of human respiratory syncytial virus (HRSV) contains fifteen absolutely conserved cysteine (C) residues that are highly conserved among the F proteins of other pneumoviruses as well as the paramyxoviruses. To explore the contribution of the cysteines in the extracellular domain to the fusion activity of HRSV F protein, each cysteine was changed to serine. Mutation of cysteines 37, 313, 322, 333, 343, 358, 367, 393, 416, and 439 abolished or greatly reduced cell surface expression suggesting these residues are critical for proper protein folding and transport to the cell surface. As expected, the fusion activity of these mutations was greatly reduced or abolished. Mutation of cysteine residues 212, 382, and 422 had little to no effect upon cell surface expression or fusion activity at 32 degrees C, 37 degrees C, or 39.5 degrees C. Mutation of C37 and C69 in the F2 subunit either abolished or reduced cell surface expression by 75% respectively. None of the mutations displayed a temperature sensitive phenotype.

Envelope targeting: hemagglutinin attachment specificity rather than fusion protein cleavage-activation restricts Tupaia paramyxovirus tropism

To engineer a targeting envelope for gene and oncolytic vector delivery, we characterized and modified the envelope proteins of Tupaia paramyxovirus (TPMV), a relative of the morbilli- and henipaviruses that neither infects humans nor has cross-reactive relatives that infect humans. We completed the TPMV genomic sequence and noted that the predicted fusion (F) protein cleavage-activation site is not preceded by a canonical furin cleavage sequence. Coexpression of the TPMV F and hemagglutinin (H) proteins induced fusion of Tupaia baby fibroblasts but not of human cells, a finding consistent with the restricted TPMV host range. To identify the factors restricting fusion of non-Tupaia cells, we initially analyzed F protein cleavage. Even without an oligo- or monobasic protease cleavage sequence, TPMV F was cleaved in F1 and F2 subunits in human cells. Edman degradation of the F1 subunit yielded the sequence IFWGAIIA, placing the conserved phenylalanine in position 2, a novelty for paramyxoviruses but not the cause of fusion restriction. We then verified whether the lack of a TPMV H receptor limits fusion. Toward this end, we displayed a single-chain antibody (scFv) specific for the designated receptor human carcinoembryonic antigen on the TPMV H ectodomain. The H-scFv hybrid protein coexpressed with TPMV F mediated fusion of cells expressing the designated receptor, proving that the lack of a receptor limits fusion and that TPMV H can be retargeted. Targeting competence and the absence of antibodies in humans define the TPMV envelope as a module to be adapted for ferrying ribonucleocapsids of oncolytic viruses and gene delivery vectors.

The compound DATEM inhibits respiratory syncytial virus fusion activity with epithelial cells

The effect of diacetyltartaric acid esters of mono and diglycerides (DATEM) on fusion of respiratory syncytial virus (RSV) with HEp-2 cells was studied using the R18 fluorescence dequenching fusion assay. At DATEM concentrations less than 2.0 microg/ml, the inhibition of fusion increased with the concentration of DATEM. At 2 microg/ml of DATEM, the fusion was suppressed by 80-90%. Studies examining possible mechanism of fusion-inhibition indicated that DATEM was likely adsorbed onto lipid membranes of both viral envelope and target cell membranes. Quantitative measurements of DATEM adsorption onto membranes were also performed using lipid monolayers and vesicles. The surface pressure of lipid monolayer formed at the air/aqueous interface increased as the concentration of DATEM in the monolayer subphase increased, suggesting that DATEM was inserted into the monolayer. As the concentration of DATEM in vesicle suspensions increased, electrophoretic mobility of initially uncharged lipid vesicles also increased, reflective of increased negative charge at vesicle surfaces. These results strongly suggest that the insertion of DATEM onto membranes inhibited viral fusion. DATEM may prove to be effective in limiting the infectivity of RSV by interference with the fusion of the viral envelope with target cell membranes.

MFP1, a novel plant filament-like protein with affinity for matrix attachment region DNA

The interaction of chromatin with the nuclear matrix via matrix attachment regions (MARs) on the DNA is considered to be of fundamental importance for higher order chromatin organization and regulation of gene expression. Here, we report a novel nuclear matrix-localized MAR DNA binding protein, designated MAR binding filament-like protein 1 (MFP1), from tomato. In contrast to the few animal MAR DNA binding proteins thus far identified, MFP1 contains a predicted N-terminal transmembrane domain and a long filament-like alpha-helical domain that is similar to diverse nuclear and cytoplasmic filament proteins from animals and yeast. DNA binding assays established that MFP1 can discriminate between animal and plant MAR DNAs and non-MAR DNA fragments of similar size and AT content. Deletion mutants of MFP1 revealed a novel, discrete DNA binding domain near the C terminus of the protein. MFP1 is an in vitro substrate for casein kinase II, a nuclear matrix-associated protein kinase. Its structure, MAR DNA binding activity, and nuclear matrix localization suggest that MFP1 is likely to participate in nuclear architecture by connecting chromatin with the nuclear matrix and potentially with the nuclear envelope.

Vaccination with a heterologous respiratory syncytial virus chimeric FG glycoprotein demonstrates significant subgroup cross-reactivity

A subunit vaccine candidate, termed FG, is a chimeric glycoprotein composed of the extracellular domains of the fusion (F) glycoprotein and the attachment (G) glycoproteins of a subgroup A respiratory syncytial virus (RSV). Two subgroups, A and B, of RSV differ primarily within the G glycoprotein. Therefore, it has been suggested that a subunit vaccine composed of the G glycoprotein would need to contain the G glycoproteins from both RSV subgroups. We have engineered a second chimeric glycoprotein, FGB, which is composed of the F glycoprotein from RSV subgroup A and the G glycoprotein from RSV subgroup B and is expressed in baculovirus. A comparison of protection between the two subunit vaccines (FG and FGB) was performed in cotton rats after homologous and heterologous virus challenge. FG and FGB appeared to afford the same degree of protection against either homologous or heterologous challenge. Serum neutralization titres against homologous or heterologous virus were nearly equivalent following FG or FGB vaccination. Radioimmunoprecipitation using sera from rats immunized with FG or FGB revealed cross-reactivity between the two G glycoproteins. Adsorption of anti-F antibody from serum of rats immunized with FG significantly reduced the RSV neutralizing activity of the serum suggesting that enhanced neutralization previously observed with FG antisera compared with F antisera alone may not be entirely attributed to antibodies against the G glycoprotein but may be attributed to a function associated with the G glycoprotein portion of FG which enhances the immunogenicity of the F portion of FG.

Protection of BALB/c mice from respiratory syncytial virus infection by immunization with a synthetic peptide derived from the G glycoprotein

A synthetic peptide homologous to amino acids 174-187 of the G glycoprotein of the A2 strain of human respiratory syncytial (RS) virus (G/174-187) was shown to induce protection from live virus challenge of BALB/c mice after immunization with three doses of 50 micrograms of peptide coupled to keyhole limpet hemocyanin. Immunized mice showed high levels of circulating RS-specific antibodies as detected by ELISA assay; however, no neutralizing antibodies were found. Moreover, an important short-term cytotoxic T-cell response was observed with lymphocytes isolated from the lungs but not from the spleen of immunized mice. This response was lost 24 weeks after immunization; however, mice remained protected against challenge with live RS virus. In addition, a monoclonal antibody that specifically binds to peptide G/174-187 was found efficient in conferring passive protection from challenge: this data further supports our results on the importance of the 174-187 region in protection. Another peptide, spanning amino acids 144 to 159, was shown to induce neutralizing antibodies but did not confer protection.

Characteristics of fusion of respiratory syncytial virus with HEp-2 cells as measured by R18 fluorescence dequenching assay

The characteristics of fusion of respiratory syncytial virus (RSV) with HEp-2 cells were studied by the R18 fluorescence dequenching assay of membrane fusion. A gradual increase in fluorescence intensity indicative of virion-cell fusion was observed when R18-labeled RSV was incubated with HEp-2 cells. Approximately 35% dequenching of the probe fluorescence was observed in 1 h at 37 degrees C. Fusion showed a temperature dependence, with significant dequenching occurring above 18 degrees C. The dequenching was also dependent on the relative concentration of target membrane. Thus, increasing the concentration of target membrane resulted in increased levels of dequenching. In addition, viral glycoproteins were shown to be involved in this interaction, since dequenching was significantly reduced by pretreatment of labeled virus at 70 degrees C for 5 min or by trypsinization of R18-labeled virions prior to incubation with HEp-2 cells at 37 degrees C. The fusion of RSV with HEp-2 cells was unaffected over a pH range of 5.5 to 8.5, with some increase seen at lower pH values. Treatment of HEp-2 cells with ammonium chloride (20 and 10 mM), a lysosomotropic agent, during early stages of infection did not inhibit syncytium formation or progeny virion production by RSV. At the same concentrations of ammonium chloride, the production of vesicular stomatitis virus was reduced approximately 4 log10 units. These results suggest that fusion of the virus with the cell surface plasma membrane is the principal route of entry.

Human influenza virus hemagglutinin with high sensitivity to proteolytic activation

To examine the prerequisites for cleavage activation of the hemagglutinin of human influenza viruses, a cDNA clone obtained from strain A/Port Chalmers/1/73 (serotype H3) was subjected to site-directed mutagenesis and expressed in CV-1 cells by using a simian virus 40 vector. The number of basic residues at the cleavage site, which consists of a single arginine with wild-type hemagglutinin, was increased by inserting two, three, or four additional arginines. Like wild-type hemagglutinin, mutants with up to three additional arginines were not cleaved in CV-1 cells, but insertion of four arginines resulted in activation. When the oligosaccharide at asparagine 22 of the HA1 subunit of the hemagglutinin was removed by site-directed mutagenesis of the respective glycosylation site, only three inserted arginines were required to obtain cleavage. Mutants containing a series of four basic residues were also generated by substituting arginine for uncharged amino acids immediately preceding the cleavage site. The observation that these mutants were not cleaved, even when the carbohydrate at asparagine 22 of HA1 was absent, underscores the fact that the basic peptide had to be generated by insertion to obtain cleavage. The data show that the hemagglutinin of a human influenza virus can acquire high cleavability, a property known to be an important determinant for the pathogenicity of avian influenza viruses. Factors important for cleavability are the number of basic residues at the cleavage site, the oligosaccharide at asparagine 22, and the length of the carboxy terminus of HA1.

Mapping of a fusion related epitope of the respiratory syncytial virus fusion protein

The region of the fusion glycoprotein of respiratory syncytial virus which reacts with a neutralizing and fusion inhibiting monoclonal antibody, was mapped using a deductive method derived from analysis of Western blot reactivity of proteolytic fragments. Reaction of the whole fusion protein was found to be so conformationally dependent, that complete digestion of the protein with a variety of proteases resulted in fragments which were not sufficiently reactive to permit mapping. For this reason, polyclonal antibodies to synthetic peptides which spanned the fusion protein sequence, were used to map the position of large peptides derived from partial digests, and these peptides were then analysed for their ability to react with the monoclonal antibody. Comparison of the peptides which were reactive with the monoclonal antibody to those which were not, identified a region of non-overlap between residues 283 and 327 in the F1 subunit of the fusion protein. Synthesis of a peptide within this region confirmed the placement of the epitope.

Synthetic peptides corresponding to the F protein of RSV stimulate murine B and T cells but fail to confer protection

We have previously located a major neutralization site of the fusion protein of respiratory syncytial virus (RSV) in the polypeptide region extending from amino acids Ile221 to Glu232. In this report, 8 peptides corresponding to the six major hydrophilic regions of the F1 subunit were selected to analyse their immunogenic and protective capacities as well as their ability to block the high neutralization activities of 4 monoclonal antibodies (MAbs). Only 5 of the 8 peptides tested induced specific antibodies while all induced an in vitro interleukin-2 response of splenocytes from immunized mice. Peptide 3 (Ile221-Phe237) was able to elicit neutralizing antibodies, confirming our previous hypothesis concerning the location of a neutralization site. However, immunization with the latter did not induce significant reduction of virus in lungs of BALB/c mice upon challenge, probably due to an inadequate level of circulating neutralizing antibodies. Interestingly, peptides 2 (Asn216-Glu232), 3 (Ile221-Phe237), and 5 (Ser275-Ile288) blocked in vitro neutralization by four different F1 specific MAbs. A hypothesis is proposed to explain these results.

Analysis of polypeptides synthesized in bovine respiratory syncytial virus-infected cells

Ten virus-specific polypeptides ranging in molecular weight from approximately 200k to 11k were identified in bovine respiratory syncytial virus (BRSV-)infected cells. Time course analysis of the induction of the viral polypeptides indicated that they could be detected as early as 30 min post-infection and their synthesis reached a plateau 12 h after infection. Cell free translation of total infected-cell mRNA in a rabbit reticulocyte system yielded 7 proteins corresponding in size to virus-specific proteins synthesized in BRSV-infected cells. The P protein was highly phosphorylated; G and F were identified as glycoproteins by [3H]glucosamine labeling. Glycosylation of G protein was largely resistant to tunicamycin, suggesting that the majority of the carbohydrate residues are attached via O-glycosidic bonds, whereas the F protein was N-linked glycosylated. Tunicamycin caused a drastic reduction in the yield of infectious virus titer indicating that the carbohydrate moieties serve a critical role in the infectious cycle of BRSV.

Location of a highly conserved neutralizing epitope in the F glycoprotein of human respiratory syncytial virus

Trypsin digestion of the purified F protein from human respiratory syncytial virus (Long strain) generated a set of fragments in the amino-terminal third of the F1 subunit which contained the epitope 47F involved in neutralization. Sequencing of five escape mutant viruses selected with monoclonal antibody 47F allowed us to map precisely two amino acid residues (262 and 268) of the F1 subunit which are essential for the integrity of this important epitope. The results are discussed in terms of the mechanisms involved in virus neutralization and the design of potential synthetic vaccines.

Interprotein disulfide bonding between F and G glycoproteins of human respiratory syncytial virus

The envelope glycoprotein G, of human respiratory virus was purified by immunoaffinity chromatography using a monoclonal antibody reacting with G glycoprotein. The purified material was analyzed for its protein patterns and by western blot for its reactivity with specific monoclonal antibodies. In addition to the G specific proteins at 90 and 55 kilodalton (kDa) range, high molecular weight species were coeluted with G protein. Three high molecular weight species were noticed: one (140 kDa) reacting with fusion protein (F) monoclonal antibody and two other species (230 and 195 kDa) reacting with both fusion protein and G protein monoclonal antibodies. The protein reacting only with F monoclonal antibody consists of fusion protein dimer. Western blot and two dimensional gel electrophoretic analysis revealed that each of the other two complexes is composed of two moles of F protein and one mole of G protein. These two complexes differ in their molecular sizes depending on whether G is in the form of 90 or 55 kDa. Upon heat denaturation, fusion protein monomer (70 kDa) is released from the complex, leaving the two complexes, consisting of one mole of F protein and one mole of G protein (160 and 125 kDa species respectively). Disulfide-reducing agents are required to break the monomers of F and G complexes. These results provide a direct evidence for the presence of envelope glycoprotein complexes linked by interprotein disulfide bonding. This may have implications on the structural and functional properties of envelope glycoproteins.

Analysis of the relationship between cleavability of a paramyxovirus fusion protein and length of the connecting peptide

The relationship between the length of the connecting peptide in a paramyxovirus F0 protein and cleavage of F0 into the F1 and F2 subunits has been examined by constructing a series of mutant F proteins via site-directed mutagenesis of a cDNA clone encoding the simian virus 5 F protein. The mutant F proteins had one to five arginine residues deleted from the connecting peptide. The minimum number of arginine residues required for cleavage-activation of the simian virus 5 F0 protein by host cell proteases was found to be four. F proteins with two or three arginine residues in the connecting peptide were not cleaved by host cell proteases but could be cleaved by exogenously added trypsin. The mutant F protein possessing a connecting peptide consisting of one arginine residue was not cleaved by trypsin. The altered F proteins were all transported to the infected-cell plasma membrane as shown by cell surface immunofluorescence or cell surface trypsinization. However, the only mutant F protein found to be biologically active as detected by syncytium formation was the F protein which has four arginine residues at the cleavage site. The results presented here suggest that in the paramyxovirus F protein the number of basic amino acid residues in the connecting peptide is important for cleavage of the precursor protein by host cell proteases but is not the only structural feature involved. In addition, the data indicate that cleavage of F0 into F1 and F2 does not necessarily result in biological activity and that the connecting peptide may affect the local conformation of the F polypeptide.

Comparison of caprine, human and bovine strains of respiratory syncytial virus

A new continuous ovine kidney cell line allowing the growth of caprine, human and bovine respiratory syncytial virus was used to minimize host cell related variations for the direct comparison of the viral ultrastructures, serological relationships and structural protein profiles. Results show that all three strains are closely related although a closer relationship was found between bovine and caprine RS.

Experimental polyvalent ISCOMs subunit vaccine induces antibodies that neutralize human and bovine respiratory syncytial virus

The purpose of the present study was to evaluate experimentally, in guinea-pigs, the immunogenicity of respiratory syncytial (RS) virus subunit vaccines. Immunostimulating complexes (ISCOMs), made from the surface proteins of both human (Long) and bovine (A-51908) RS strains adsorbed to the adjuvant Quil A, were assayed for their capacity to induce neutralizing antibodies, in comparison to experimental live virus vaccines. Serums from animals vaccinated with either the human or bovine RS subunit vaccines were equally efficient in neutralizing human or bovine RS virus. ISCOMs prepared with bovine RS virus proteins were significantly (p less than 0.05%) more efficient than their human counterpart, in inducing neutralizing antibodies, suggesting their greater potential as a subunit vaccine.

Nucleotide sequence of the fusion and phosphoprotein genes of human respiratory syncytial (RS) virus Long strain: evidence of subtype genetic heterogeneity

The nucleotide and deduced amino acid sequences of the fusion (F) and phosphoprotein (P) genes of the Long strain of human respiratory syncytial (RS) virus have been determined from cDNA copies cloned into pBSV9 shuttle vector. Comparison of these sequences with their counterparts of other strains reveals genetic heterogeneity within the same subtype. The percentage of nucleotide and amino acid changes occurring in both proteins is similar. Thus, the Long F and P proteins share 97.9% and 98.3% amino acid identity, respectively, with their homologs of the A2 strain. Nevertheless the F2 subunit of the fusion protein accumulates 3.1 times more amino acid changes than the F1 subunit. In addition, the percentage of nucleotide changes in the 3' extracistronic sequences is 6 times higher in the P than in the F gene. These results are discussed in terms of selective pressures operating in the evolution of RS virus in nature.

Structure, function, and intracellular processing of paramyxovirus membrane proteins

Paramyxoviruses are a fascinating group of viruses with diverse hosts and disease manifestations. They are valuable systems for studying viral pathogenesis, molecular mechanisms of negative strand viral replication, and glycoprotein structure and function. In the past few years this group of viruses has received increased attention and as a result there is a wealth of new information. For example, most of the genes of many paramyxoviruses have been cloned and sequenced. The recent availability of sequence information from a number of paramyxoviruses now allows the direct comparison of the amino acid sequence and determinants of secondary structure of analogous genes across the family of viruses. Such comparisons are revealing for two reasons. First, results provide clues to the evolution of these viruses. Second, and more importantly, comparisons of analogous genes may point to sequences and structural determinants that are central to the function of the individual proteins. Below is a comparison of five of the paramyxovirus genes with a discussion of the implications of common structural determinants for function, intracellular processing, and evolutionary origin. The focus is on the paramyxovirus membrane proteins, although other proteins are discussed briefly.

The molecular biology of influenza virus pathogenicity

It is an accepted concept that the pathogenicity of a virus is of polygenic nature. Because of their segmented genome, influenza viruses provide a suitable system to prove this concept. The studies employing virus mutants and reassortants have indicated that the pathogenicity depends on the functional integrity of each gene and on a gene constellation optimal for the infection of a given host. As a consequence, virtually every gene product of influenza virus has been reported to contribute to pathogenicity, but evidence is steadily growing that a key role has to be assigned to hemagglutinin. As the initiator of infection, hemagglutinin has a double function: (1) promotion of adsorption of the virus to the cell surface, and (2) penetration of the viral genome through a fusion process among viral and cellular membranes. Adsorption is based on the binding to neuraminic acid-containing receptors, and different virus strains display a distinct preference for specific oligosaccharides. Fusion capacity depends on proteolytic cleavage by host proteases, and variations in amino acid sequence at the cleavage site determine whether hemagglutinin is activated in a given cell. Differences in cleavability and presumably also in receptor specificity are important determinants for host tropism, spread of infection, and pathogenicity. The concept that proteolytic activation is a determinant for pathogenicity was originally derived from studies on avian influenza viruses, but there is now evidence that it may also be relevant for the disease in humans because bacterial proteases have been found to promote the development of influenza pneumonia in mammals.

Identification of a synthetic nonapeptide sequence that inhibits motility in culture of a melanoma subclone that possesses a high metastatic potential

A synthetic nonapeptide fragment of thrombin inhibits the cellular motility in culture of a human melanoma subclone that possesses a high metastatic potential in mice. Concomitant with the loss of ability to translocate in culture, these cells exhibit increases in the average length of actin cables and cellular surface area in contact with the substratum. The spreading activity is observed at a nonapeptide concentration of 1 nM within 1 hr of exposure at 37 degrees C. Pretreatment of cells with this nonapeptide does not block signal transduction through plasma membrane receptors for the following growth or differentiation factors: alpha-melanotropin (alpha-melanocyte-stimulating hormone), nerve growth factor, and transforming growth factor type beta. Results of the present study suggest an approach to cancer chemotherapy in which naturally occurring peptides from two functionally orthogonal classes may be used to perform two complementary functions: inhibition of metastasis and induction of differentiation.

Resistance of a measles virus mutant to fusion inhibitory oligopeptides is not associated with mutations in the fusion peptide

The nucleotide sequence and predicted amino acid sequence has been obtained for the fusion (F) protein gene of the R93 strain of measles virus and compared to that of the parental strain, Edmonston B. The R93 strain is a mutant measles virus which is able to grow and induce cell fusion in the presence of the fusion inhibiting oligopeptide, Z-D-Phe-L-Phe-L-(NO2)Arg (SV4814). Primer extension sequencing on isolated R93 mRNA demonstrated the presence of three nucleotide changes leading to three amino acid changes, none of which are in the hydrophobic NH2-terminal region of the F1 polypeptide.

Differential immunoglobulin G subclass antibody titers to respiratory syncytial virus F and G glycoproteins in adults

Two respiratory syncytial virus glycoproteins, F and G, which differ substantially in the amount of glycosylation were used as antigens in an enzyme-linked immunosorbent assay to determine immunoglobulin G (IgG) subclass titers in 30 experimentally infected healthy adults. The titers of antibodies to the F glycoprotein achieved in postinfection sera were highest in the IgG1 subclass, whereas those to the G glycoprotein were highest and comparable in the IgG1 and IgG2 subclasses. The high IgG2 response to the G glycoprotein suggests that it is seen by the immune system as a polysaccharide antigen, a hypothesis consistent with its large carbohydrate content.

Expression at the cell surface of native fusion protein of the Newcastle disease virus (NDV) strain Italien from cloned cDNA

A cDNA library was constructed with poly(A)+-mRNAs from NDV-Italien infected BHK-21 cells. A clone, that hybridized to the F gene mRNA, was sequenced. A long open reading frame encodes for a protein of 553 amino acids, with a calculated molecular weight of 59,153, consisting of twelve cysteine residues and six potential glycosylation sites. The protein sequence contains a hydrophobic region at the N-terminus of F1 and a presumptive long transmembrane fragment near the C-terminus. Comparison of the F proteins from NDV strains Italien and Australia-Victoria shows that the sequences are very similar, with conservation of most cysteine residues and of the potential glycosylation sites. The F coding sequence was inserted into the genome of vaccinia virus under the control of vaccinia P7.5 transcriptional regulatory sequences. Expression of F protein was demonstrated by indirect immunofluorescence with five anti-F monoclonal antibodies known to react with conformational epitopes.

Expression of the fusion protein of human respiratory syncytial virus from recombinant vaccinia virus vectors and protection of vaccinated mice

Vaccinia virus (VV) recombinants were constructed that contained full-length cDNA copies of the fusion (F) protein gene of human respiratory syncytial (RS) virus. The F protein gene was placed next to the strong early-late VV 7.5-kilodalton promoter and was located within the VV thymidine kinase (tk) gene. Full-length recombinant transcripts that initiated at both the tk and the 7.5-kilodalton promoters accumulated in cells early in infection, and one or more of these transcripts was translated to yield a glycoprotein which comigrated with Fo, the fusion protein precursor. This precursor was processed by proteolytic cleavage to produce the two disulfide-linked subunits F1 and F2, which were both glycosylated and of the same electrophoretic mobility as authentic F1 and F2. Immunofluorescence studies demonstrated that the mature F protein was transported to and expressed on the surface of recombinant VV-infected cells. Inoculation of rabbits with a recombinant vector expressing F resulted in the production of antiserum specific for the RS virus F protein. This antiserum neutralized virus infectivity and was capable of preventing fusion in RS virus-infected cells. Mice were vaccinated with recombinants expressing the F protein. At 3 weeks postinoculation, these animals had serum antibody against RS virus F protein. At 5 days after intranasal challenge with RS virus, the lungs of the mice previously vaccinated with recombinants expressing F protein were free of detectable RS virus, whereas the lungs of unvaccinated mice contained 10(4.2) PFU of virus per g.

Human respiratory syncytial virus glycoprotein G expressed from a recombinant vaccinia virus vector protects mice against live-virus challenge

Recombinant vaccinia virus vectors were constructed which expressed the major surface glycoprotein G of human respiratory syncytial (RS) virus. The biological activity of the G protein expressed from these vectors was assayed. Inoculation of rabbits with live recombinant virus induced high titers of antibody which specifically immunoprecipitated RS virus G protein and was capable of neutralizing RS virus infectivity. Immunization of mice by either the intranasal or the intraperitoneal route with recombinant virus that expressed only the G protein resulted in complete protection of the lower respiratory tract upon subsequent challenge with live RS virus.

Expression of the F glycoprotein of respiratory syncytial virus by a recombinant vaccinia virus: comparison of the individual contributions of the F and G glycoproteins to host immunity

A cDNA clone representing the mRNA coding sequence of the fusion glycoprotein (F) gene of human respiratory syncytial virus (RSV) was constructed and inserted into the thymidine kinase gene of vaccinia virus (WR strain) under the control of a vaccinia virus promoter. The resulting recombinant vaccinia virus, vaccinia F, expressed the F1 and F2 cleavage products (48 and 20 kDa, respectively) of the F glycoprotein in cell culture. F1 and F2 were indistinguishable from their authentic RSV counterparts with respect to glycosylation, disulfide linkage, electrophoretic mobility, cell-surface expression, and antigenic specificity. Cotton rats infected intradermally with vaccinia F developed a high titer of serum F-specific antibodies, which neutralized infectivity of RSV. This neutralizing antibody response exceeded that induced by infection of the respiratory tract with RSV and was 6-fold higher than that induced by vaccinia G, a recombinant vaccinia virus that expressed the RSV G glycoprotein gene. Immunization with vaccinia F stimulated almost complete resistance to replication of RSV in the lower respiratory tract as well as significant resistance in the upper respiratory tract. The degree of resistance conferred by vaccinia F exceeded that induced by vaccinia G.

Serum immunoglobulin G antibody subclass responses to respiratory syncytial virus F and G glycoproteins after primary infection

Because the immunoglobulin G (IgG) response to carbohydrate antigens is typically from the IgG2 subclass and the IgG response to protein antigens is typically from the IgG1 and sometimes the IgG3 subclass, two respiratory syncytial virus glycoproteins, F and G, which differ substantially in the amount of glycosylation, were used as antigens in an enzyme-linked immunosorbent assay to determine IgG subclass responses in 20 infants and young children with naturally acquired respiratory syncytial virus infection. Both glycoproteins elicited primarily IgG1 and IgG3 responses, indicating that the protein moieties of the glycoproteins may be immunodominant in this age group.

Conserved structures among the nucleocapsid proteins of the paramyxoviridae: complete nucleotide sequence of human parainfluenza virus type 3 NP mRNA

The nucleotide sequence of the mRNA coding for the nucleocapsid protein (NP) of the paramyxovirus, human parainfluenza virus type 3 (PIV-3), has been determined. The NP mRNA was found to contain 1642 bases, excluding poly(A), and encode a protein of 515 amino acids, with a molecular weight of 57,823. Amino acid residues 1 through 420 of PIV-3 NP protein showed extensive sequence homology with the corresponding amino acids of Sendai virus nucleocapsid protein. There was virtually no homology between the last 95 amino acids. Comparison of the NP proteins of PIV-3, Sendai virus, measles virus, and canine distemper virus revealed, from amino acid residues 160 through 390, some conserved areas between the corresponding proteins of these paramyxoviruses. The 5' terminal sequence of PIV-3 NP mRNA (5'-AGGATTAAAG-3') was similar to the conserved sequence (formula; see text) found at the 5' termini of Sendai virus mRNAs. Both PIV-3 NP and Sendai virus mRNAs had a common 3' terminal tetranucleotide (5'-TAAG-3') preceding the poly (A) tail.

Serum and nasal-wash immunoglobulin G and A antibody response of infants and children to respiratory syncytial virus F and G glycoproteins following primary infection

An enzyme-linked immunosorbent assay (ELISA) with immunoaffinity-purified fusion (F) or attachment (G) glycoprotein was used to measure the serum and secretory immune responses of 18 infants and children, 4 to 21 months of age, who underwent primary infection with respiratory syncytial virus (RSV). Most of the 10 older individuals (9 to 21 months of age) developed moderate levels of serum and nasal-wash immunoglobin A (IgA) and IgG F and G antibodies. These individuals developed a moderate level of serum or nasal-wash antibodies that neutralized virus infectivity. One of the eight younger individuals (4 to 8 months of age) failed to develop an F antibody response, while three failed to develop a G antibody response. The most notable difference in the responses of the two age groups involved the titer in convalescent sera of G, F, and neutralizing antibodies which were 8- to 10-fold lower in younger individuals. Most of the younger infants failed to develop a rise in serum or nasal-wash neutralizing antibody. It is possible that the presence of maternally derived antibody in the younger infants suppressed the immune response to RSV infection, and that this accounted, in part, for the low level of postinfection antibody titer in this group. This low level and the irregular response of the infants less than 8 months of age may contribute to the severity of their initial infection and may also be responsible, in part, for their failure to develop effective resistance to subsequent reinfection by RSV.

Resistance to human respiratory syncytial virus (RSV) infection induced by immunization of cotton rats with a recombinant vaccinia virus expressing the RSV G glycoprotein

A cDNA copy of the G glycoprotein gene of human respiratory syncytial virus (RSV) was placed under control of a vaccinia virus promoter and inserted into the thymidine kinase locus of the vaccinia virus genome. The recombinant vaccinia virus retained infectivity and expressed a 93-kDa protein that migrated with the authentic RSV G glycoprotein upon polyacrylamide gel electrophoresis. Glycosylation of the expressed protein and transport to the cell surface were demonstrated in the absence of other RSV proteins. Cotton rats that were inoculated intradermally with the infectious recombinant virus produced serum antibody to the G glycoprotein that neutralized RSV in vitro. Furthermore, the vaccinated animals were resistant to lower respiratory tract infection upon intranasal inoculation with RSV and had reduced titers of RSV in the nose.

Determination of the complete nucleotide sequence of the Sendai virus genome RNA and the predicted amino acid sequences of the F, HN and L proteins

We previously determined the 3' proximal 5,824 nucleotides of the Sendai virus genome RNA (Nucleic Acids Res. 11, 7317-7330, 1983; Nucleic Acids Res. 12, 7965-7973, 1984), and present here the sequence of the remaining 5' proximal 9,559 nucleotides. Thus, this is the first paramyxovirus to have its genome organization elucidated. The set of complementary DNA clones used was prepared by the method of Okayama and Berg from polyadenylylated viral genome RNA. We sequenced the region containing the 5' proximal half of the F gene, and the subsequent HN and L genes, and predicted the complete amino acid sequence of the products of these genes. Sequence analyses confirmed that all the genes are flanked by consensus sequences and suggest that the viral mRNAs are capable of forming stem-and-loop structures. Comparison of the F and HN glycoproteins of Sendai virus with those of simian virus 5 strongly suggests that the cysteine residues are highly important for maintenance of the molecular structures of these glycoproteins.

Human parainfluenza type 3 virus hemagglutinin-neuraminidase glycoprotein: nucleotide sequence of mRNA and limited amino acid sequence of the purified protein

The nucleotide sequence of mRNA for the hemagglutinin-neuraminidase (HN) protein of human parainfluenza type 3 virus obtained from the corresponding cDNA clone had a single long open reading frame encoding a putative protein of 64,254 daltons consisting of 572 amino acids. The deduced protein sequence was confirmed by limited N-terminal amino acid microsequencing of CNBr cleavage fragments of native HN that was purified by immunoprecipitation. The HN protein is moderately hydrophobic and has four potential sites (Asn-X-Ser/Thr) of N-glycosylation in the C-terminal half of the molecule. It is devoid of both the N-terminal signal sequence and the C-terminal membrane anchorage domain characteristic of the hemagglutinin of influenza virus and the fusion (F0) protein of the paramyxoviruses. Instead, it has a single prominent hydrophobic region capable of membrane insertion beginning at 32 residues from the N terminus. This N-terminal membrane insertion is similar to that of influenza virus neuraminidase and the recently reported structures of HN proteins of Sendai virus and simian virus 5.

Expression of the major glycoprotein G of human respiratory syncytial virus from recombinant vaccinia virus vectors

The major glycoprotein, G, of human respiratory syncytial (RS) virus is a Mr 84,000-90,000 species that has about 60% of its mass contributed by carbohydrate, most of which is in the form of O-linked oligosaccharides. The G protein contains neither a hydrophobic N-terminal signal sequence nor a hydrophobic C-terminal anchor region. Instead, its amino acid sequence reveals only one region with significant hydrophobic character, which is between residues 38 and 66. In order to study the synthesis, processing, and functions of this unusual viral glycoprotein, full-length cDNA copies of the G protein mRNA were inserted into the DNA genome of vaccinia virus (VV) in a position that was adjacent to a strong VV promoter and within the VV gene for thymidine kinase (TK). The resulting TK- recombinant viruses were selected, plaque-purified, and characterized by Southern blot analysis of restriction enzyme digests of the viral DNA. Recombinant RNA transcripts that contained both G-specific and VV-specific sequences accumulated in cells infected with recombinant viruses having the G protein gene in the positive orientation. The translation product of these transcripts in infected cells was a Mr 84,000-90,000 glycoprotein that was indistinguishable from authentic RS virus G protein. It could be detected in cell lysates after metabolic labeling with [3H]glucosamine and was immunoprecipitated by anti-RS-virus antiserum. Immunofluorescence studies showed that the G protein accumulated intracellularly with the perinuclear distribution that is characteristic of newly synthesized glycoproteins. Furthermore, the protein was also clearly detectable on the surface of recombinant-infected cells, showing that it was transported to and inserted into the plasma membrane.

Respiratory syncytial virus envelope glycoprotein (G) has a novel structure

Amino acid sequence of human respiratory syncytial virus envelope glycoprotein (G) was deduced from the DNA sequence of a recombinant plasmid and confirmed by limited amino acid microsequencing of purified 90K G protein. The calculated molecular mass of the protein encoded by the only long open reading frame of 298 amino acids was 32,588 daltons and was somewhat smaller than the 36K polypeptide translated in vitro from mRNA selected by this plasmid. Inspection of the sequence revealed a single hydrophobic domain of 23 amino acids capable of membrane insertion at 41 residues from the N-terminus. There was no N-terminal signal sequence and the hydrophilic N-terminal 20 residues probably represent the cytoplasmic tail of the protein. The N-terminally oriented membrane insertion was somewhat analogous to paramyxovirus hemagglutinin-neuraminidase (HN) and influenza neuraminidase (NA). The protein was moderately hydrophilic and rich in hydroxy-amino acids. It was both N- and O-glycosylated with the latter contributing significantly to the net molecular mass 90K.

Isolation and characterization of the measles virus F1 polypeptide: comparison with other paramyxovirus fusion proteins

Measles virus fusion (F) protein has been isolated by immunoadsorption to a complex of monoclonal antibodies bound to protein A-Sepharose. The 41-kDa F1 component of the fusion protein was obtained pure in high yield by preparative SDS-polyacrylamide gel electrophoresis. The amino acid composition of the F1 chain was determined and the N-terminal sequence was analyzed for 40 residues. The structure determined is largely hydrophobic, with 24 residues of Val, Ile, Leu, Met, Phe, or Ala. Comparison with previously published data on the F1 polypeptide of Sendai virus showed considerable similarity in amino acid composition. Extensive N-terminal sequence homologies with F1 polypeptides of different paramyxoviruses are also noticed, including a nine-residue segment strictly conserved among four F1 polypeptides studied, as well as a weaker but distinct and Gly-rich sequence homology with the influenza A and B virus HA2 polypeptides. The evolutionary conservation of the N-terminal region at the site of cleavage of surface glycoproteins of the two families of myxoviruses highlights its specialized function in membrane fusion.

Proteins associated with human parainfluenza virus type 3

The polypeptides associated with human parainfluenza virus type 3 were identified. Five proteins were present in detergent- and salt-resistant viral cores. Of these, three proteins designated NP0, NP1, and NP2 of 68,000, 58,000, and 52,000 daltons, respectively, were stably associated with 50S RNA in CsCl gradient-purified nucleocapsids. The amounts of NP1 and NP2 were variable, and these proteins were shown to be structurally related to the major nucleocapsid protein (NP0) by partial Staphylococcus aureus V8 protease mapping. The other core proteins included a 240K protein designated L (candidate for the viral polymerase) and an 84K protein designated as the phosphoprotein (P) on the basis of a predominant incorporation of Pi. The viral envelope had four prominent proteins (72, 53, 40, and 12K) under reducing conditions of electrophoresis. The 72 and 53K proteins were specifically labeled with [3H]glucosamine and [3H]mannose. When sulfhydryl reagents were removed, a new 62K protein was visualized in place of the 72, 53, and 12K proteins. The 53 and 12K proteins were interpreted to be the two subunits (F1 and F2) of the fusion protein, and the 72K protein was designated as the HN (hemagglutinin-neuraminidase) glycoprotein. The unglycosylated 40K protein represented the viral matrix protein (M). Immunoprecipitation of infected cell lysates with rabbit hyperimmune antiserum against purified virus confirmed the viral origin of these polypeptides.