The hemagglutinating and neuraminidase protein of a paramyxovirus: interaction with neuraminic acid in affinity chromatography

Sendai virus as a backbone for vaccines against RSV and other human paramyxoviruses

Human paramyxoviruses are the etiological agents for life-threatening respiratory virus infections of infants and young children. These viruses, including respiratory syncytial virus (RSV), the human parainfluenza viruses (hPIV1-4) and human metapneumovirus (hMPV), are responsible for millions of serious lower respiratory tract infections each year worldwide. There are currently no standard treatments and no licensed vaccines for any of these pathogens. Here we review research with which Sendai virus, a mouse parainfluenza virus type 1, is being advanced as a Jennerian vaccine for hPIV1 and as a backbone for RSV, hMPV and other hPIV vaccines for children.

Newcastle disease virus: macromolecules and opportunities

Over the past two decades, enormous advances have occurred in the structural and biological characterization of Newcastle disease virus (NDV). As a result, not only the complete sequence of the viral genome has been fully determined, but also a clearer understanding of the viral proteins and their respective roles in the life cycle has been achieved. This article reviews the progress in the molecular biology of NDV with emphasis on the new technologies. It also identifies the fundamental problems that need to be addressed and attempts to predict some research opportunities in NDV that can be realized in the near future for the diagnosis, prevention and treatment of disease(s).

Functions of surface glycoproteins of myxoviruses and paramyxoviruses and their inhibition

Two glycoproteins, HN and F, are present on the surface of paramyxoviruses. HN has receptor-binding amd neuraminidase activities. F is involved in viral penetration, cell fusion and haemolysis and is activated by proteolytic cleavage by a host enzyme into two disulphide-bonded subunits (f1 and F2). The ability of the virus to initiate infection and undergo multiple cycle replication depends on the presence of an activating protease in the host; thus cleavage of F is a major determinant of pathogenesis. The new N-terminus generated on F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 is hydrophobic and highly conserved among para-myxoviruses. In an attempt to design specific inhibitors, oligopeptides and analogous to this region were synthesized and found to be highly active, specific inhibitors of viral penetration, cell fusion and haemolysis. Inhibition is amino-acid-sequence-specific and affected by peptide length, steric configuration and addition of groups to the n-terminal and C-terminal amino acids. Replication of influenza virus was also specifically inhibited by oligopeptides resembling the N-terminus of the HA2 polypeptide. Like that of F1 protein the N-terminus of HA2 is generated by a proteolytic cleavage that activates infectivity. These results have provided information on the action of proteins in viral penetration and membrane fusion and they suggest a possible new approach to chemical inhibition of viral replication. Studies with specific antibodies to each of the paramyxovirus glycoproteins have shown that antibodies to the F protein are essential for effective prevention of the spread of infection. Antibodies to the HN protein, although capable of neutralizing released virus, do not prevent spread to adjacent cells through membrane fusion mediated by the F protein. These findings have implications for the design of effective vaccines against paramyxoviruses and also provided additional insight into the mechanisms involved in the atypical and severe infections observed in individuals who received inactivated paramyxovirus vaccines and were later infected.

Mutation at residue 523 creates a second receptor binding site on human parainfluenza virus type 1 hemagglutinin-neuraminidase protein

The paramyxovirus hemagglutinin-neuraminidase (HN) is a multifunctional protein mediating hemagglutination (HA), neuraminidase (NA), and fusion promotion activities. It has been a matter of debate whether HN contains combined or separate sites for HA and NA activities. To clear the issue, we determined the presence of the second binding site on human parainfluenza virus (hPIV) type 1, 2, and 3 and Sendai virus (SeV) HN proteins. Results of virus elution from erythrocytes at an elevated temperature and HA inhibition by NA inhibitor BCX-2798 suggest that all hPIVs bind to the receptor only through the NA catalytic site, while SeV HN has an additional receptor binding site. Comparison of SeV and hPIV1 HN sequences revealed two amino acid differences at residues 521 and 523 in the region close to the second binding site identified in Newcastle disease virus HN. We mutated hPIV1 HN at position 523 from Asn to the residue of SeV HN, Asp, and rescued a recombinant SeV that carries the mutated hPIV1 HN by a reverse genetics system. The hPIV1 HN with Asp at position 523 hemagglutinated in the presence of BCX-2798, suggesting that the amino acid difference at position 523 is critical for the formation of a second binding site. Creation of the second binding site on hPIV1 HN, however, did not significantly affect the growth or fusion activity of the recombinant virus. Our study indicates that the presence and requirement of a second binding site vary among paramyxoviruses.

Structural studies of the parainfluenza virus 5 hemagglutinin-neuraminidase tetramer in complex with its receptor, sialyllactose

The paramyxovirus hemagglutinin-neuraminidase (HN) functions in virus attachment to cells, cleavage of sialic acid from oligosaccharides, and stimulating membrane fusion during virus entry into cells. The structural basis for these diverse functions remains to be fully understood. We report the crystal structures of the parainfluenza virus 5 (SV5) HN and its complexes with sialic acid, the inhibitor DANA, and the receptor sialyllactose. SV5 HN shares common structural features with HN of Newcastle disease virus (NDV) and human parainfluenza 3 (HPIV3), but unlike the previously determined HN structures, the SV5 HN forms a tetramer in solution, which is thought to be the physiological oligomer. The sialyllactose complex reveals intact receptor within the active site, but no major conformational changes in the protein. The SV5 HN structures do not support previously proposed models for HN action in membrane fusion and suggest alternative mechanisms by which HN may promote virus entry into cells.

T-cell cytotoxicity in the absence of viral protein synthesis in target cells

Cytotoxic T cells lyse only those virus infected target cells in vitro which express, in addition to the viral antigen(s), those K or D region products of the major histocompatibility complex (MHC) which were present during anti-viral sensitisation in vivo. This 'associative recognition' by cytotoxic T cells could reflect the interaction of two T-cell receptors with specificity for target K or D gene products and independently for the viral antigen, or one receptor with specificity for virally altered K or D region products (see ref. 1 and refs therein). There are various ways that the MHC antigens could be altered, including 'modification from within', where the virus modifies host protein synthesis by interfering with transcription, translation or post-translational glycosylation; or 'modification from without' where enzymic or chemical alteration of cell membrane proteins are induced by virus activity at the cell surface. In this report we show that inactivated Sendai virus or isolated Sendai virus envelopes can serve to modify a cell and make it a specific target for Sendai-immune T-cell killing, thus excluding the possibility of 'modification from within' in this system.

Mutations in multiple domains activate paramyxovirus F protein-induced fusion

SER virus, a paramyxovirus that is closely related to simian virus 5 (SV5), is unusual in that it fails to induce syncytium formation. The SER virus F protein has an unusually long cytoplasmic tail (CT), and it was previously observed that truncations or specific mutations of this domain result in enhanced syncytium formation. In addition to the long CT, the SER F protein has nine amino acid differences from the F protein of SV5. We previously observed only a partial suppression of fusion in a chimeric SV5 F protein with a CT derived from SER virus, indicating that these other amino acid differences between the SER and SV5 F proteins also play a role in regulating the fusion phenotype. To examine the effects of individual amino acid differences, we mutated the nine SER residues individually to the respective residues of the SV5 F protein. We found that most of the mutants were expressed well and were transported to the cell surface at levels comparable to that of the wild-type SER F protein. Many of the mutants showed enhanced lipid mixing, calcein transfer, and syncytium formation even in the presence of the long SER F protein CT. Some mutants, such as the I310 M, T438S, M489I, T516V, and N529K mutants, also showed fusion at lower temperatures of 32, 25, and 18 degrees C. The residue Asn529 plays a critical role in the suppression of fusion activity, as the mutation of this residue to lysine caused a marked enhancement of fusion. The effect of the N529K mutation on the enhancement of fusion by a previously described mutant, L539,548A, as well as by chimeric SV5/SER F proteins was also dramatic. These results indicate that activation to a fusogenic conformation is dependent on the interplay of residues in the ectodomain, the transmembrane domain, and the CT domain of paramyxovirus F proteins.

Crystal structure of the Ebola virus membrane fusion subunit, GP2, from the envelope glycoprotein ectodomain

We have determined the structure of GP2 from the Ebola virus membrane fusion glycoprotein by X-ray crystallography. The molecule contains a central triple-stranded coiled coil followed by a disulfide-bonded loop homologous to an immunosuppressive sequence in retroviral glycoproteins, which reverses the chain direction and connects to an alpha helix packed antiparallel to the core helices. The structure suggests that fusion peptides near the N termini form disulfide-bonded loops at one end of the molecule and that the C-terminal membrane anchors are at the same end. In this conformation, GP2 could both bridge two membranes and facilitate their apposition to initiate membrane fusion. We also find a heptad irregularity like that in low-pH-induced influenza HA2 and a solvent ion trapped in a coiled coil like that in retroviral TMs.

Quantitative measurement of paramyxovirus fusion: differences in requirements of glycoproteins between simian virus 5 and human parainfluenza virus 3 or Newcastle disease virus

To compare the requirements for paramyxovirus-mediated cell fusion, the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of simian virus 5 (SV5), human parainfluenza virus 3 (HPIV-3), and Newcastle disease virus (NDV) were expressed individually or coexpressed in either homologous or heterologous combinations in CV-1 or HeLa-T4 cells, using the vaccinia virus-T7 polymerase transient expression system. The contribution of individual glycoproteins in virus-induced membrane fusion was examined by using a quantitative assay for lipid mixing based on the relief of self-quenching (dequenching) of fluorescence of the lipid probe octadecyl rhodamine (R18) and a quantitative assay for content mixing based on the cytoplasmic activation of a reporter gene, beta-galactosidase. In these assays, expression of the individual F glycoproteins did not induce significant levels of cell fusion and no cell fusion was observed in experiments when cells individually expressing homologous F or HN proteins were mixed. However, coexpression of homologous F and HN glycoproteins resulted in extensive cell fusion. The kinetics of fusion were found to be very similar for all three paramyxoviruses studied. With NDV and HPIV-3, no cell fusion was detected when F proteins were coexpressed with heterologous HN proteins or influenza virus hemagglutinin (HA). In contrast, SV5 F protein exhibited a considerable degree of fusion activity when coexpressed with either NDV or HPIV-3 HN or with influenza virus HA, although the kinetics of fusion were two- to threefold higher when the homologous SV5 F and HN proteins were coexpressed. Thus, these data indicate that among the paramyxoviruses tested, SV5 has different requirements for cell fusion.

The haemagglutinin-neuraminidase glycoprotein of the porcine paramyxovirus LPMV: comparison with other paramyxoviruses revealed the closest relationship to simian virus 5 and mumps virus

The complete nucleotide sequence of the haemagglutinin-neuraminidase (HN) gene of the porcine paramyxovirus LPMV, was determined from cDNA derived from viral genomic RNA. The gene was 1906 nucleotides long including a putative gene end and poly A signal. One long open reading frame was found encoding a protein of 576 amino acids with a calculated molecular weight of 63,324. The protein contains four potential N-glycosylation sites and a major hydrophobic region near the N-terminal, suggesting a membrane anchor domain. Comparison of the deduced amino acid sequence of the LPMV HN protein with that of other paramyxovirus HN proteins, revealed the highest amino acid identity to simian virus 5 of 43% and mumps virus of 41%.

Mutation of the HANA protein of Sendai virus by passage in eggs

A study was made to elucidate the effect of host cells on the HANA protein of Sendai virus. Two strains of Sendai virus were isolated from an epidemic in an animal laboratory by inoculating the lung homogenate of a moribund mouse either into LLC-MK2 cells (Oh-L) or into the allantoic cavity of embryonated eggs (Oh-E). Oh-E agglutinated chicken red blood cells at 37 degrees (HA37+), while Oh-L did not (HA37-). When Oh-L was passaged in eggs, conversion of the HA37- virus to the HA37+ virus readily occurred. A single point mutation was recognized on the HANA protein of the HA37+ virus either at position 525 (Gln----Arg) or at position 198 (Leu----Phe). Hl test with monoclonal antibody revealed conformational changes around the receptor binding site. Neuraminidase activity was also affected by these mutations. The changes in these biological activities of the HANA protein seemed to allow the HA37+ virus to replicate in eggs. On the contrary, the HA37+ virus replicates as efficiently as the HA37- virus in LLC-MK2 cells and no reversion to the HA37- virus was observed. The overall results indicate that the passage of Sendai virus in eggs resulted in selection of viruses possessing a specific mutation on the HANA protein. The pneumopathogenicity in mice was not significantly different between the HA37- virus and the HA37+ virus, suggesting the existence of genes other than the HANA gene that determine mouse pathogenicity.

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.

The E3 protein of bovine coronavirus is a receptor-destroying enzyme with acetylesterase activity

In addition to members of the Orthomyxoviridae and Paramyxoviridae, several coronaviruses have been shown to possess receptor-destroying activities. Purified bovine coronavirus (BCV) preparations have an esterase activity which inactivates O-acetylsialic acid-containing receptors on erythrocytes. Diisopropyl fluorophosphate (DFP) completely inhibits this receptor-destroying activity of BCV, suggesting that the viral enzyme is a serine esterase. Treatment of purified BCV with [3H]DFP and subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins revealed that the E3 protein was specifically phosphorylated. This finding suggests that the esterase/receptor-destroying activity of BCV is associated with the E3 protein. Furthermore, treatment of BCV with DFP dramatically reduced its infectivity in a plaque assay. It is assumed that the esterase activity of BCV is required in an early step of virus replication, possibly during virus entry or uncoating.

Cell surface expression and orientation in membranes of the 44-amino-acid SH protein of simian virus 5

Antiserum was raised against a synthetic peptide containing the N-terminal hydrophilic domain of the small hydrophobic protein (SH) of simian virus 5 (SV5) and used to characterize properties of the SH protein. SH demonstrated properties of an integral membrane protein. Indirect immunofluorescence experiments showed that the protein is involved in the exocytotic pathway, and isolation of plasma membranes from SV5-infected cells showed an enrichment of SH, indicating that SH is transported to the infected-cell surface. Biochemical analysis of the orientation of SH in membranes by proteolysis of intact SV5-infected cell surfaces and intracellular microsomal vesicles indicated that SH is oriented in membranes with its N-terminal hydrophilic domain exposed on the cytoplasmic face of the plasma membrane and the C terminus of approximately five amino acid residues exposed at the cell surface. These data are discussed with respect to positive-acting signals being necessary in the ectodomain of SH for cell surface expression.

Localization of functional sites on the hemagglutinin-neuraminidase glycoprotein of Sendai virus by sequence analysis of antigenic and temperature-sensitive mutants

To locate the various functions associated with the hemagglutinin-neuraminidase (HN) glycoprotein of Sendai virus in the primary structure of the protein, a temperature-sensitive (ts) mutant and seven antigenic mutants were sequenced. The ts mutant was defective in its ability to agglutinate erythrocytes and infect host cells, while its neuraminidase activity was normal. Its sequence revealed two closely spaced amino acid substitutions (residues 262 and 264) and one distant substitution (residue 461). Revertants could not be isolated, suggesting that more than one of the substitutions is responsible for the defective hemagglutinating activity. The antigenic mutants were selected with monoclonal antibodies that delineate four nonoverlapping antigenic sites (I-IV) and separately inhibit hemagglutinating, neuraminidase, and hemolysis activities. Mutants selected with antibodies to antigenic sites I-III were used to map these functions on the primary sequence of HN. Each antigenic mutant had a single point mutation in the HN gene that resulted in an amino acid substitution in the protein. A site II mutant selected with an antibody which inhibits hemolysin activity had a substitution at amino acid 420, while a mutant selected with antibody that inhibits only erythrocyte binding (site III) had a substitution at amino acid 541. Two antigenic mutants selected with an antibody that inhibits hemagglutination and neuraminidase activities (site I) had amino acid substitutions in close proximity (residues 277 and 279) to the two closely spaced substitutions of the ts mutant. These findings suggest that the region defined by the ts mutant and these two antigenic mutants is involved in host cell binding. Antigenic mutants selected with another site I antibody had amino acid changes at residue 184, indicating that antigenic site I is discontinuous in the primary sequence. This antibody blocks only hemagglutination, but mutants selected with it had a decreased neuraminidase activity. This finding supports the idea that the neuraminidase site is close to, but distinct from, the hemagglutination site.

Comparison of the relative roles of the F and HN surface glycoproteins of the paramyxovirus simian virus 5 in inducing protective immunity

To compare the relative roles of the paramyxovirus simian virus 5 (SV5) major surface glycoproteins, fusion (F) and hemagglutinin-neuraminidase (HN), in inducing protective immunity, two recombinant vaccinia viruses were constructed. The F and HN polypeptides expressed by the recombinant viruses were indistinguishable from their authentic SV5 counterparts in electrophoretic mobility, glycosylation, and, for the F protein, cleavage of the precursor, F0, to the disulfide-linked subunits F1 and F2. Injection of rabbits and hamsters with live recombinant virus elicited an antibody response to either F or HN and provided a source of monospecific polyclonal antisera to the SV5 proteins. The vaccinia virus-SV5 F (vaccinia-F) recombinant induced higher levels of neutralizing antibody than did the vaccinia-HN recombinant, but animals inoculated with vaccinia-HN were better protected from challenge with SV5. Animals infected with both the vaccinia-HN and vaccinia-F viruses were nearly as well protected from challenge as were animals infected with SV5.

Characterization of influenza virus neuraminidase with hemagglutinin activity and its comparison with that of viral neuraminidase

The neuraminidase associated with the bifunctional protein, hemagglutinin-neuraminidase, of influenza virus has been characterized. The enzyme has a pH optimum of 4.5, does not require Ca2+ and is inactivated (98%) by incubation at 50 degrees C. The enzyme has a Km of 2.00 X 10(-3) M and 0.06 X 10(-3) M with the substrates 2-(3-methoxyphenyl)-N-acetylneuraminic acid and fetuin, respectively. The Ki is 400 X 10(-6) with the inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid. The incorporation of labeled cysteine, valine and leucine in the hemagglutinin-neuraminidase protein is different from that of viral neuraminidase. A comparison of the properties of the neuraminidase associated with protein hemagglutinin-neuraminidase with that of viral neuraminidase or sialidase showed that the former is biochemically different and an antigenically distinct enzyme. The unique feature of the new enzyme is that it has the hemagglutinin activity as well. The two biological activities could not be separated from each other in all systems used. Apparently, protein hemagglutinin-neuraminidase is genetically transferable and it is detectable in a laboratory recombinant virus E-2971 (H3 Aichi X N7). These results suggest that protein hemagglutinin-neuraminidase is a unique surface protein of the influenza virus A/Aichi/2/68 (H3N2).

Expression at the cell surface of biologically active fusion and hemagglutinin/neuraminidase proteins of the paramyxovirus simian virus 5 from cloned cDNA

cDNAs encoding the mRNAs for the fusion protein (F) and the hemagglutinin/neuraminidase protein (HN) of the paramyxovirus simian virus 5 have been inserted into a eukaryotic expression vector under the control of the simian virus 40 late promoter. The F and HN proteins synthesized in recombinant infected cells are indistinguishable in terms of electrophoretic mobility and glycosylation from the proteins synthesized in simian virus 5-infected cells. In addition, the expressed F and HN proteins have been shown to be anchored in the plasma membrane in a biologically active form by indirect live cell immunofluorescence, the F-mediated formation of syncytia, and the ability of HN to cause the hemadsorption of erythrocytes to the infected cell surface.

Hemagglutinin-neuraminidase protein of the paramyxovirus simian virus 5: nucleotide sequence of the mRNA predicts an N-terminal membrane anchor

The nucleotide sequence of a cloned cDNA copy of the mRNA coding for the hemagglutinin-neuraminidase of the paramyxovirus SV5 was determined. There was a single large open reading frame on the mRNA which encoded a protein of 565 amino acids with a molecular weight of 62,134. The deduced amino acid sequence indicated that the only major hydrophobic region in the protein sufficiently long to anchor the protein in the membrane is located near the N terminus (amino acids 18 to 36). It is suggested that, like the influenza virus neuraminidase, hemagglutinin-neuraminidase of paramyxoviruses is oriented with its N terminus inserted into the membrane.

Analysis and gene assignment of mRNAs of a paramyxovirus, simian virus 5

Polypeptides synthesized by the paramyxovirus SV5 in infected CV-1 cells were readily identified when the host cell was treated with actinomycin D. The unglycosylated forms of HN and Fo synthesized in infected cells in the presence of tunicamycin and HN and Fo synthesized in vitro were identified by immunoprecipitation with specific antibodies. Separation of SV5-specific poly(A)-containing RNAs on methyl-mercury agarose gels and in vitro translation of fractions, indicated that the viral polypeptides were translated from individual mRNAs except P (Mr approximately 44K) and the nonstructural polypeptide V (Mr approximately 24K) for which the mRNAs could not be separated. cDNA copies of SV5-specific mRNAs were synthesized and cloned in plasmid pBR322. Clones to NP, P + V, M, F, and HN were identified by hybrid-arrest and hybrid-selection translation of SV5 mRNAs. Tryptic peptide mapping of polypeptides P and V indicated that the peptides of V were a subset of those of P. Hybridization of cDNA probes to infected cell mRNAs separated on agarose gels permitted identification of the NP, P + V, M, F, and HN mRNAs and presumptive polycistronic mRNAs. The sizes and sequence homologies of these polycistronic mRNAs were used to derive a likely gene order on the SV5 50 S genome RNA.

Influenza virus neuraminidase with hemagglutinin activity

Isolated intact influenza virus neuraminidase (NA) molecules of the N9 subtype have been found to possess hemagglutinin (HA) activity which, at equivalent protein concentration, was fourfold higher than that of isolated hemagglutinin molecules of the H3 subtype. The amino-terminal sequence of the N9 NA is the same as in neuraminidases of the eight other influenza A virus NA subtypes previously reported. Viruses possessing N9 NA therefore have two different HA activities and antibody to either HA or NA alone was incapable of inhibiting hemagglutination by the virus. However, antibody to the HA of an H1N9 virus neutralized its infectivity as effectively as it neutralized H1N1 or H1N2 viruses whose neuraminidases have no HA activity. (Antibodies to N9 NA did not neutralize the infectivity of viruses with N9 neuraminidase). 2-deoxy-2,3-dehydro-N-acetyl-neuraminic acid inhibited N9 NA activity but had no effect on the HA activity of the isolated N9 NA. One interpretation of this result would be that the HA and NA activities are located in separate sites. Pronase-released N9 NA heads form crystals suitable for X-ray diffraction studies and preliminary data to 2.9 A establish the space group as cubic, I432 with cell dimension a = 184 A. Data extend to beyond 1.9 A resolution, and these will be collected in the future.

Resolution of two surface glycoproteins from human parainfluenza-3 virus by crossed immunoelectrophoresis

The technique of two-dimensional crossed immunoelectrophoresis (CIE) was used to resolve two glycoproteins from purified human parainfluenza type 3 virus. Virus preparations were extracted with Triton X-100 and fractionated by centrifugation in a Beckman airfuge. Two immunoprecipitates were detected by CIE in the supernatant fractions, but were not found in the pellets from extracted virus. Viral glycoproteins labeled with [35S]methionine were isolated by affinity chromatography on concanavalin A (Con A) agarose columns, resolved by CIE and detected by autoradiography. Resolution of two glycoprotein peaks from as little as 4.5 micrograms of protein from extracted virus is consistent with results from polyacrylamide gel patterns showing two unique glycoproteins with molecular weights of 48 kd and 65 kd.

Monoclonal antibodies against a paramyxovirus isolated from Japanese Sparrow-Hawks

Five monoclonal antibodies against the haemagglutinin-neuraminidase (HN) molecule of Taka virus, a variant of Newcastle disease virus (NDV), were established to compare the antigenicities of several avian paramyxoviruses including NDV. From the results of the cross haemagglutination-inhibition (HI) test with the monoclonal antibodies, the HN molecule of Taka virus seemed to have at least three different antigenic determinants; one was specific for all NDV strains tested, the second was for Taka virus and Komarov strain of NDV and the third was for Taka virus, Komarov strain, Bangor and Yucaipa. Furthermore, the differences in the ratio of HI to neuraminidase-inhibition titers suggested that the separate active sites involved in haemagglutinin and neuraminidase activities might exist at least in close proximity.

Differentiation of mumps virus strains with monoclonal antibody to the HN glycoprotein

A hybridoma cell line secreting antibody of the immunoglobulin G3 isotype with kappa light chains and with activity against the HN glycoprotein of the Kilham strain of mumps virus was established. The antibody exhibited structural homogeneity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and had a microheterogeneous isoelectric spectrum characteristic of an antibody of monoclonal origin. The specificity of the monoclonal antibody, shown by immunoprecipitation performed with radiolabeled virus and infected cell lysates, was for the larger mumps virus glycoprotein. In functional assays the antibody inhibited the hemagglutinating and neuraminidase activities and neutralized the infectivity of the homologous Kilham strain of virus and clearly differentiated this strain from two heterologous strains, Enders and O'Take. The antibody was markedly less effective with the O'Take strain than with either the Kilham or Enders strain in inhibiting both hemagglutination and neuraminidase activity against the macromolecular substrate fetuin. The inhibition of the neuraminidase activity of the Kilham strain was independent of substrate size, the antibody inhibiting the hydrolysis of both fetuin and the trisaccharide neuraminlactose. By contrast, the antibody did not inhibit the hydrolysis of neuraminlactose by the two heterologous mumps strains. These results provide the first demonstration of antigenic differences between mumps virus strains and highlight the utility of monoclonal antibody in analyzing the structural basis underlying functional activities of the HN glycoproteins.

Microinjection of arginase into enzyme-deficient cells with the isolated glycoproteins of Sendai virus as fusogen

A method of introducing enzymes into the cytoplasm of fibroblasts in culture is described. Erythrocytes obtained from normal and arginase-deficient individuals were loaded with arginase in vitro and fused to arginase-deficient mouse and human fibroblasts. Erythrocyte ghost-fibroblast fusion was quantified by a 14C-radioactive assay for arginase in solubilized fibroblasts. Fusion was successfully induced by Sendai virus and also by the isolated glycoproteins of Sendai virus. After fusion the arginase activity associated with the Fibroblasts was 700--1500 U of arginase/mg of cell protein; this enzyme activity was 5- to 10-times higher than that normally found in the fibroblasts. The enrichment in arginase activity indicated that between four and ten ghosts had fused per fibroblast. The use of isolated viral proteins to mediate the transfer of enzymes into cells in vivo might alleviate clinical complications inherent in the use of whole virions. The enzyme replacement technique described in this report for a hyperargininemic model cell system should be applicable to the group of inborn errors of metabolism characterized by deficiency of an enzyme normally localized in the cytoplasmic compartment of cells.

Separation of Sendai virus glycoproteins by using glutaraldehyde-treated erythrocytes and preparation of monospecific antisera against the glycoproteins

Sendai virus hemagglutinin-neuraminidase (HN) and fusion (F) glycoproteins, F and HN, were separated from Triton X-100- or Nonidet P-40-solubilized envelopes as unadsorbed and eluted fractions, respectively, by using glutaralde-hyde-treated chicken erythrocytes. These separated glycoproteins were biologically active. Monospecific antisera (in terms of monoreactivity to virus glycoproteins in gel diffusion precipitation patterns) were prepared by using these fractions as immunogens. Anti-HN rabbit serum inhibited all of the viral activities tested (infectivity, neuraminidase, hemagglutinating, and viral hemolysis), whereas anti-F serum definitely inhibited viral hemolysis only, although the two antisera enhanced neutralization in the presence of complement. The advantages and disadvantages of this separation method were discussed.