Virus-specific polypeptides of human parainfluenza virus type 4 and their synthesis in infected cells

Synthesis of human parainfluenza virus 4 nucleocapsid-like particles in yeast and their use for detection of virus-specific antibodies in human serum

The aim of this study was to produce human parainfluenza virus type 4 (HPIV4) nucleocapsid (N) protein in yeast Saccharomyces cerevisiae expression system, to explore its structural and antigenic properties and to evaluate its applicability in serology. The use of an optimized gene encoding HPIV4 N protein amino acid (aa) sequence GenBank AGU90031.1 allowed high yield of recombinant N protein forming nucleocapsid-like particles (NLPs) in yeast. A substitution L332D disrupted self-assembly of NLPs, confirming the role of this position in the N proteins of Paramyxovirinae. Three monoclonal antibodies (MAbs) were generated against the NLP-forming HPIV4 N protein. They recognised HPIV4-infected cells, demonstrating the antigenic similarity between the recombinant and virus-derived N proteins. HPIV4 N protein was used as a coating antigen in an indirect IgG ELISA with serum specimens of 154 patients with respiratory tract infection. The same serum specimens were tested with previously generated N protein of a closely related HPIV2, another representative of genus Rubulavirus. Competitive ELISA was developed using related yeast-produced viral antigens to deplete the cross-reactive serum antibodies. In the ELISA either without or with competition using heterologous HPIV (2 or 4) N or mumps virus N proteins, the seroprevalence of HPIV4 N-specific IgG was, respectively, 46.8, 39.6 and 40.3% and the seroprevalence of HPIV2 N-specific IgG-47.4, 39.0 and 37.7%. In conclusion, yeast-produced HPIV4 N protein shares structural and antigenic properties of the native virus nucleocapsids. Yeast-produced HPIV4 and HPIV2 NLPs are prospective tools in serology.

Association of rabies virus nominal phosphoprotein (P) with viral nucleocapsid (NC) is enhanced by phosphorylation of the viral nucleoprotein (N)

We investigated possible role(s) of N protein phosphorylation in the rabies virus replication process. A large amount of P proteins are associated with the viral nucleocapsid (NC) in the infected cell, the amount which was greatly decreased by phosphatase-treatment of the isolated NC, indicating that the phosphate group of N and/or P proteins is essential for their stable association with the NC. Immunoprecipitation studies were performed on the coexpressed normal N or phosphorylation deficient N(S389A) and P proteins, demonstrating that the P protein associated with phosphorylation-deficient NC-like structures was much less in amount than that associated with the wild type NC. Similar results were also obtained with a mutant P protein, PDeltaN19, which lacked the N-terminal 19 amino acids and was capable of binding to the NC-like structures but incapable of forming the RNA-free N-P complexes. Immunoprecipitation studies with mAb #402-13 further suggested that the NC-specific linear 402-13 epitope was exposed even on the P proteins which were associated with the phosphorylation-deficient NC-like structures, but such association was very weak as demonstrated by greatly decreased amounts of coprecipitated NC-like structures. From these results, we assume that the phosphorylation of N protein enhances the association between the 402-13 epitope-positive P protein and the NC probably by stabilizing such P-NC binding.

Time-resolved fluoroimmunoassays with monoclonal antibodies for rapid identification of parainfluenza type 4 and mumps viruses

Monoclonal antibodies were prepared to the F and M proteins of parainfluenza 4A and 4B and to mumpsvirus to obtain reagents that could be configured into type-specific yet broadly-reactive IFA, EIA, and TR-FIA tests. Several antibodies to parainfluenza 4A also detected subtype 4B, although to a somewhat lower signal, and thus were well suited to generic parainfluenza type 4 tests that were comparable to similar tests previously described for parainfluenza types 1, 2, and 3. Monoclonals to subtype 4B were less able to detect 4A because of high background problems in one or another test. Monoclonals to mumpsvirus F protein were completely type-specific. These antibodies were screened by IFA and EIA for broad reactivity with diverse strains of each virus and were configured into optimized EIA and TR-FIA tests. The all-monoclonal tests were then compared to polyclonal tests in terms of their ability to detect virus in clinical specimens. The all-monoclonal TR-FIA was uniformly the most sensitive, detecting virus in 80% of culture-positive parainfluenza 4A specimens, 67% of parainfluenza 4B specimens, and 90% of mumps specimens, compared to 40-67% for the monoclonal EIA tests and 33-60% for the polyclonal EIA tests. For parainfluenza 4 TR-FIA, mean P/N values were 379 for subtype 4A cell culture fluids (228 for subtype 4B cultures) and 57 for 4A clinical specimens (43 for 4B specimens). For mumpsvirus TR-FIA, mean P/N values were 27 for culture fluids and 32 for clinical specimens. The sensitivities of the TR-FIA were determined with purified virus to be 0.28 ng virus per well for parainfluenza 4A and 0.70 ng virus per well for mumpsvirus.

Immunological relationships between parainfluenza virus type 4 and other paramyxoviruses studied by use of monoclonal antibodies

These results demonstrated that cross-reactions between mumps virus, PIV-2, PIV-4, and SV5 involve both internal components and surface glycoproteins and that these viruses form a separate group within the paramyxovirus genus.

Sequence analysis of the phosphoprotein (P) genes of human parainfluenza type 4A and 4B viruses and RNA editing at transcript of the P genes: the number of G residues added is imprecise

We cloned and sequenced the cDNAs against genomic RNAs and mRNAs for phosphoproteins (Ps) of human parainfluenza virus types 4A (PIV-4A) and 4B (PIV-4B). The PIV-4A and -4B P genes were 1535 nucleotides including poly(A) tract and were found to have two small open reading frames, neither of which was apparently large enough to encode the P protein. A cluster of G residues was found in genomic RNA and the number of G residues was 6 in both PIV-4A and -4B. However, the number of G residues at the corresponding site in the mRNAs to the genomic RNA was not constant. Three different mRNA cDNA clones were obtained; the first type of mRNA encodes a larger (P) protein of 399 amino acids, the second type encodes V protein of 229 or 230 amino acids, and the third type encodes the smallest protein (156 amino acids). Comparisons on the nucleotide and the amino acid sequences P and V proteins between these two subtypes revealed extensive homologies. However, these homology degrees are lower than that of NP protein. The C-terminal regions of the P and V proteins of PIV-4s could be aligned with all other Paramyxoviruses, PIV-2, mumps virus (MuV), simian virus 5 (SV 5), Newcastle disease virus (NDV), measles virus (MV), canine distemper virus (CDV), Sendai virus (SV), and PIV-3. On the other hand, the P-V common (N-terminal) regions showed no homology with MV, CDV, SV, and PIV-3. Seven phylogenetic trees of Paramyxoviruses were constructed from the entire and partial regions of P and V proteins.

Sequence analysis of P gene of human parainfluenza type 2 virus: P and cysteine-rich proteins are translated by two mRNAs that differ by two nontemplated G residues

We cloned and sequenced the cDNAs against genomic RNA and mRNA for phosphoprotein (P) of human parainfluenza type 2 virus (PIV-2). cDNA clone from genomic RNA was 1439 nucleotides in length excluding poly(A) and was found to have two small open reading frames encoding proteins of 233 and 249 amino acids. Two different mRNA cDNA clones were obtained; that is, one mRNA contained a smaller reading frame coding 225 amino acids, V protein, and the other mRNA contained a larger reading frame coding 395 amino acids, P protein. Both mRNAs had G cluster in coding frame. The former mRNA contained seven G residues, and two extra G residues were inserted in the latter mRNA. Ten cDNA clones from the genomic RNA were identical and were composed of seven G residues, indicating that genomes analyzed here were a homogeneous population. Therefore, V protein is encoded by faithfully copied mRNA and P protein is translated from mRNA in which two additional G residues are nontemplately inserted immediately after seven genomically encoded G residues. The V and P proteins are amino coterminal proteins and have different C termini. The C terminus of V protein is cysteine-rich and bears some resemblance to metal-binding protein of the zinc finger-type motif. P protein sequence of PIV-2 showed high homologies with SV 5 (40.4%) and mumps virus (35.5%), and a moderate homology with Newcastle disease virus (20.6%). On the other hand, very little homology was found between PIV-2 and other paramyxoviruses including Sendai virus, PIV-3, and measles virus. The cysteine-rich region in V protein was found to be highly conserved in PIV-2, SV 5, and measles virus, suggesting that V protein of paramyxoviruses plays important roles in transcription and/or replication. The predicted cysteine-rich V protein was detected in virus-infected cells using antiserum directed against an oligopeptide specific for the predicted V polypeptide.

Molecular cloning and sequence analysis of human parainfluenza type 4A virus HN gene: its irregularities on structure and activities

We cloned the cDNA of human parainfluenza type 4A virus (PIV-4A) HN gene by reverse-transcription of virus-specific mRNAs and genomic RNA, and determined the complete nucleotide sequence of the HN gene. The predicted HN protein sequence of PIV-4A showed significant relatedness with those of other paramyxoviruses, SV5, NDV, MuV, PIV-3, BPIV-3, indicating a common ancestor. The homologies between the viruses suggested that PIV-4A is more closely related to NDV, SV5, and MuV than to the parainfluenza viruses, PIV-3, bovine parainfluenza type 3 virus (BPIV-3), and Sendai virus (SV). Sixty amino acids were commonly conserved among the viruses, other than PIV-4A. Two of these amino acids were substituted in PIV-4A HN and are predicted to be located near the active site of the neuraminidase. The analysis of neuraminidase of PIV-4 revealed that the activity is hardly detectable, suggesting the significant effect of the substituted amino acid sites on neuraminidase activity.

Sequencing analyses and comparison of parainfluenza virus type 4A and 4B NP protein genes

The nucleotide sequences of the cDNA copies of the mRNA coding for the nucleocapsid proteins (NPs) of human parainfluenza viruses type 4A (PIV-4A) and type 4B (PIV-4B) were determined. The copy of PIV-4A NP mRNA contained 1885 nucleotides encoding a protein with a calculated molecular weight of 62,561. The same number of amino acids with a similar molecular weight (62,425) were predicted for the PIV-4B NP protein. Comparisons on the nucleotide sequence and the amino acid sequence of NP protein between these two subtypes revealed extensive homologies in the nucleotide sequence (87%) and in the amino acid sequence (93%). Furthermore, a conserved region with about 100 amino acids was observed between PIV-4s and other paramyxoviruses, Newcastle disease virus (NDV), Sendai virus, mumps virus (MuV), PIV-3, BPIV-3, measles virus (MV), and canine distemper virus (CDV), indicating a common ancestor for these nine viruses. Our data also indicated that the PIV-4 NP proteins were more closely related to MuV and NDV than to other parainfluenza viruses, PIV-3, BPIV-3, and Sendai virus. Interestingly, the NP protein homology between PIV-4s and the morbillivirus group, MV and CDV, was slightly higher than that between PIV-4s and the parainfluenza viruses, PIV-3, BPIV-3, and Sendai virus.