Nucleotide sequence of the gene encoding the Newcastle disease virus fusion protein and comparisons of paramyxovirus fusion protein sequences

Epitope Peptide-Based Predication and Other Functional Regions of Antigenic F and HN Proteins of Waterfowl and Poultry Avian Avulavirus Serotype-1 Isolates From Uganda

Uganda is a Newcastle disease (ND) endemic country where the disease is controlled by vaccination using live LaSota (genotype II) and I₂ (genotype I) vaccine strains. Resurgent outbreak episodes call for an urgent need to understand the antigenic diversity of circulating wild Avian Avulavirus serotype-1 (AAvV-1) strains. High mutation rates and the continuous emergence of genetic and antigenic variants that evade immunity make non-segmented RNA viruses difficult to control. Antigenic and functional analysis of the key viral surface proteins is a crucial step in understanding the antigen diversity between vaccine lineages and the endemic wild ND viruses in Uganda and designing ND peptide vaccines. In this study, we used computational analysis, phylogenetic characterization, and structural modeling to detect evolutionary forces affecting the predicted immune-dominant fusion (F) and hemagglutinin-neuraminidase (HN) proteins of AAvV-1 isolates from waterfowl and poultry in Uganda compared with that in LaSota vaccine strain. Our findings indicate that mutational amino acid variations at the F protein in LaSota strain, 25 poultry wild-type and 30 waterfowl wild-type isolates were distributed at regions including the functional domains of B-cell epitopes or N-glycosylation sites, cleavage site, fusion site that account for strain variations. Similarly, conserved regions of HN protein in 25 Ugandan domestic fowl isolates and the representative vaccine strain varied at the flanking regions and potential linear B-cell epitope. The fusion sites, signal peptides, cleavage sites, transmembrane domains, potential B-cell epitopes, and other specific regions of the two protein types in vaccine and wild viruses varied considerably at structure by effective online epitope prediction programs. Cleavage site of the waterfowl isolates had a typical avirulent motif of ¹¹¹GGRQGR'L¹¹⁷ with the exception of one isolate which showed a virulent motif of ¹¹¹GGRQKR'F¹¹⁷. All the poultry isolates showed the ¹¹¹GRRQKR'F¹¹⁷ motif corresponding to virulent strains. Amino acid sequence variations in both HN and F proteins of AAvV-1 isolates from poultry, waterfowl, and vaccine strain were distributed over the length of the proteins with no detectable pattern, but using the experimentally derived 3D structure data revealed key-mapped mutations on the surfaces of the predicted conformational epitopes encompassing the experimental major neutralizing epitopes. The phylogenic tree constructed using the full F gene and partial F gene sequences of the isolates from poultry and waterfowl respectively, showed that Ugandan ND aquatic bird and poultry isolates share some functional amino acids in F sequences yet do remain unique at structure and the B-cell epitopes. Recombination analyses showed that the C-terminus and the rest of the F gene in poultry isolates originated from prevalent velogenic strains. Altogether, these could provide rationale for antigenic diversity in wild ND isolates of Uganda compared with the current ND vaccine strains.

Genetic diversity of Newcastle disease viruses isolated from domestic poultry species in Eastern China during 2005-2008

Seventy-nine Newcastle disease viruses (NDV) isolated from clinical specimens of different poultry species including chickens, pigeons (Columba livia), geese and ostriches in Eastern China during 2005-2008 were characterized biologically and phylogenetically. The results showed genetic diversity of these viruses: three class I viruses and one genotype I and 12 genotype II viruses of class II circulating in chickens were avirulent; four genotype VIb viruses isolated from pigeons were moderately virulent; and two genotype III viruses and 57 genotype VIId viruses were highly virulent. The three class I viruses were further classified as genotypes 2 and 3. The very high F protein sequence identity of one genotype I virus with strain Queensland V4 and 12 genotype II viruses with strain La Sota indicated that these viruses originated from the two vaccine strains. Two genotype III viruses shared greater than 99% sequence identity with the moderately virulent vaccine strain Mukteswar but exhibited significantly higher virulence, suggesting that they evolved from the vaccine virus and that the Mukteswar vaccine should be banned in China. Fifty-seven of the 63 virulent NDVs in this study belonged to genotype VIId, indicating its predominance in Eastern China. Genotype VIId viruses could be further classified into two subgroups. Four of the five NDVs isolated from pigeons belonged to genotype VIb, indicating its host-specific preference. Both the genotype VIb and VIId NDVs showed low amino acid similarity to the vaccine strains currently used in China, implying the urgent need to develop better vaccines against the most prevalent NDVs in China.

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).

Role of sequence and structure of the Hendra fusion protein fusion peptide in membrane fusion

Viral fusion proteins are intriguing molecular machines that undergo drastic conformational changes to facilitate virus-cell membrane fusion. During fusion a hydrophobic region of the protein, termed the fusion peptide (FP), is inserted into the target host cell membrane, with subsequent conformational changes culminating in membrane merger. Class I fusion proteins contain FPs between 20 and 30 amino acids in length that are highly conserved within viral families but not between. To examine the sequence dependence of the Hendra virus (HeV) fusion (F) protein FP, the first eight amino acids were mutated first as double, then single, alanine mutants. Mutation of highly conserved glycine residues resulted in inefficient F protein expression and processing, whereas substitution of valine residues resulted in hypofusogenic F proteins despite wild-type surface expression levels. Synthetic peptides corresponding to a portion of the HeV F FP were shown to adopt an α-helical secondary structure in dodecylphosphocholine micelles and small unilamellar vesicles using circular dichroism spectroscopy. Interestingly, peptides containing point mutations that promote lower levels of cell-cell fusion within the context of the whole F protein were less α-helical and induced less membrane disorder in model membranes. These data represent the first extensive structure-function relationship of any paramyxovirus FP and demonstrate that the HeV F FP and potentially other paramyxovirus FPs likely require an α-helical structure for efficient membrane disordering and fusion.

Analysis of the fusion protein gene of Newcastle disease viruses isolated in Japan

The complete nucleotide sequences of the fusion (F) protein gene of Newcastle disease viruses (NDV) isolated in Japan from 1930 to 2007 (45 strains total) were determined and genetically analyzed. In the deduced amino acid sequences of fusion protein, the 5 potential asparagine-linked glycosylation sites and 10 cysteine residues were all conserved in the NDV examined in this study. The major epitopes involved in virus neutralization are conserved in most of the NDV strains isolated in Japan except a few strains. By virus neutralization test, no major antigenic differences were observed among representative strains of each genotype in Japan. All chickens vaccinated with the B1 strain survived without clinical signs after challenge with 2 NDV strains isolated in Japan (velogenic strains, JP/Ibaraki/2000 and JP/Kagoshima/91), which possess amino acids substitutions involved in virus neutralization in the F protein gene.

Assembly and biological and immunological properties of Newcastle disease virus-like particles

Virus-like particles (VLPs) released from avian cells expressing the Newcastle disease virus (NDV) strain AV proteins NP, M, HN (hemagglutinin-neuraminidase), and F were characterized. The VLP-associated HN and F glycoproteins directed the attachment of VLPs to cell surfaces and fusion of VLP membranes with red blood cell membranes, indicating that they were assembled into VLPs in an authentic conformation. These particles were quantitatively prepared and used as an immunogen, without adjuvant, in BALB/c mice. The resulting immune responses, detected by enzyme-linked immunosorbent assay (ELISA), virus neutralization, and intracellular cytokine staining, were comparable to the responses to equivalent amounts of inactivated NDV vaccine virus. HN and F proteins from another strain of NDV, strain B1, could be incorporated into these VLPs. Foreign peptides were incorporated into these VLPs when fused to the NP or HN protein. The ectodomain of a foreign glycoprotein, the Nipah virus G protein, fused to the NDV HN protein cytoplasmic and transmembrane domains was incorporated into ND VLPs. Thus, ND VLPs are a potential NDV vaccine candidate. They may also serve as a platform to construct vaccines for other pathogens.

Characterization of newly emerging Newcastle disease viruses isolated during 2002-2008 in Taiwan

To elucidate the epidemiological relationships between ND outbreaks and genetic lineages, a portion of the F gene (535 bp) and the full-length HN gene (1922 bp) of recent Taiwanese NDVs isolated in 2002-2008 was amplified by reverse transcription (RT)-polymerase chain reaction (PCR) and sequenced. Only a portion of above amplified PCR products of the F and HN genes (374 and 1713 bp) and their deduced amino acid residues were compared with the other 60 NDVs retrieved from GenBank. Most (29/30) of the recent Taiwanese isolates were clustered in subgenotype VIIe while only one isolate was classified as subgenotype VIIc. All the 29 isolates of subgenotype VIIe were further subclassified and termed provisionally as sub-subgenotypes VIIe2 (13 isolates), VIIe3 (5 isolates), and VIIe4 (11 isolates). The sub-subgenotype VIIe2 isolates possessing the motif (112)R-R-Q-K-R-F(117) and amino acid residue substitutions at positions 23 (L to F) and 90 (T to A) were collected during 2002-2005. The sub-subgenotype VIIe3 isolates possessing the motif (112)R-R-K-K-R-F(117) and amino acid residue substitutions at positions 74 (E to G) and 75 (A to G) within epitopes and 114 (Q to K) within cleavage site of F protein were collected during 2003-2006. The sub-subgenotype VIIe4 isolates possessing the motif (112)R-R-Q-K-R-F(117) and amino acid residue substitutions at positions 23 (L to F), 26 (I to T), and 90 (T to A) were collected during 2007-2008. All the NDV isolates in this study exhibited a high intra-cerebral pathogenicity index (ICPI), they were all classified as velogenic type of NDVs. The sub-subgenotype VIIe2 and VIIe4 viruses are now dominant and have been implicated in most of the recent ND outbreaks in Taiwan. Phylogenetic analysis of these isolates revealed that they may have evolved from previously reported local strains (VIIe1). This finding is essential for improving the disease control strategies and development of vaccines for ND.

A conserved region in the F(2) subunit of paramyxovirus fusion proteins is involved in fusion regulation

Paramyxoviruses utilize both an attachment protein and a fusion (F) protein to drive virus-cell and cell-cell fusion. F exists functionally as a trimer of two disulfide-linked subunits: F(1) and F(2). Alignment and analysis of a set of paramyxovirus F protein sequences identified three conserved blocks (CB): one in the fusion peptide/heptad repeat A domain, known to play important roles in fusion promotion, one in the region between the heptad repeats of F(1) (CBF(1)) (A. E. Gardner, K. L. Martin, and R. E. Dutch, Biochemistry 46:5094-5105, 2007), and one in the F(2) subunit (CBF(2)). To analyze the functions of CBF(2), alanine substitutions at conserved positions were created in both the simian virus 5 (SV5) and Hendra virus F proteins. A number of the CBF(2) mutations resulted in folding and expression defects. However, the CBF(2) mutants that were properly expressed and trafficked had altered fusion promotion activity. The Hendra virus CBF(2) Y79A and P89A mutants showed significantly decreased levels of fusion, whereas the SV5 CBF(2) I49A mutant exhibited greatly increased cell-cell fusion relative to that for wild-type F. Additional substitutions at SV5 F I49 suggest that both side chain volume and hydrophobicity at this position are important in the folding of the metastable, prefusion state and the subsequent triggering of membrane fusion. The recently published prefusogenic structure of parainfluenza virus 5/SV5 F (H. S. Yin et al., Nature 439:38-44, 2006) places CBF(2) in direct contact with heptad repeat A. Our data therefore indicate that this conserved region plays a critical role in stabilizing the prefusion state, likely through interactions with heptad repeat A, and in triggering membrane fusion.

A conserved region between the heptad repeats of paramyxovirus fusion proteins is critical for proper F protein folding

Paramyxoviruses are a diverse family that utilizes a fusion (F) protein to enter cells via fusion of the viral lipid bilayer with a target cell membrane. Although certain regions of the F protein are known to play critical roles in membrane fusion, the function of much of the protein remains unclear. Sequence alignment of a set of paramyxovirus F proteins and analysis utilizing Block Maker identified a region of conserved amino acid sequence in a large domain between the heptad repeats of F1, designated CBF1. We employed site-directed mutagenesis to analyze the function of completely conserved residues of CBF1 in both the simian virus 5 (SV5) and Hendra virus F proteins. The majority of CBF1 point mutants were deficient in homotrimer formation, proteolytic processing, and transport to the cell surface. For some SV5 F mutants, proteolytic cleavage and surface expression could be restored by expression at 30 degrees C, and varying levels of fusion promotion were observed at this temperature. In addition, the mutant SV5 F V402A displayed a hyperfusogenic phenotype at both 30 and 37 degrees C, indicating that this mutation allows for efficient fusion with only an extremely small amount of cleaved, active protein. The recently published prefusogenic structure of PIV5/SV5 F (Yin, H. S., et al. (2006) Nature 439, 38-44) indicates that residues within and flanking CBF1 interact with the fusion peptide domain. Together, these data suggest that CBF1-fusion peptide interactions are critical for the initial folding of paramyxovirus F proteins from this important viral family and can also modulate subsequent membrane fusion promotion.

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.

A Goose-Sourced Paramyxovirus Isolated from Southern China

We report the isolation and characterization of a paramyxovirus from geese in South China during 1997. The isolate, designated as goose paramyxovirus/QingYuan 1997-1 (GPMV/QY97-1), showed pathogenicity to geese and could agglutinate chicken erythrocytes. Its hemagglutinating activity was inhibited by antiavian paramyxovirus serotype 1 (APMV-1) serum. The F gene of isolate was amplified by reverse transcription polymerase chain reaction, and sequence analysis proved that its sequence conformed to that reported in the literature, encoding an F0 protein of 553 amino acids with 13 cysteine residues and 6 potential glycosylation sites. It also contained multiple basic amino acids at the deduced cleavage site of the fusion protein, which is a typical feature of highly virulent APMV-1 strains. Sequences analysis of the F gene of GPMV/QY97-1 revealed a homology with other APMV-1 isolates, with its identity ranging from 84.1% to 99.9% on a nudeotide basis and from 88.8% to 99.6% on an amino acid basis. Phylogenetic analysis of the APMV-1 isolates showed that this isolate most closely resembled the reference APMV-1 strain GD/1/98/Go, which was originally isolated from geese in 1998.

Newcastle disease virus fusion and haemagglutinin-neuraminidase gene motifs as markers for viral lineage

Reverse transcriptase polymerase chain reaction was used to generate sequence data for 91 Australian Newcastle disease viruses (NDV) isolated from 1932 to 2000 covering the cleavage site of the fusion (F) protein and the C-terminus of the haemagglutinin-neuraminidase (HN) protein. Comparison of sequences at these two sites indicates distinct evolutionary relationships between these viruses. Typically, HN gene relationships revealed by phylogenetic analyses were also maintained in comparisons between F gene cleavage sites; however, the former analyses appeared to give a clearer indication of the lineage of a virus isolate. This data supports and extends earlier observations in that there is no evidence for gene exchange by recombination but that different strains appear to have evolved through synonymous mutations. Inter-relationships, especially between Australian NDV isolates, appear to be associated with lineages having the same C-terminal HN extensions rather than associated with virulence of the virus. A proposed mechanism for this observation is discussed.

Mutations in the putative HR-C region of the measles virus F2 glycoprotein modulate syncytium formation

The fusion (F) glycoproteins of measles virus strains Edmonston (MV-Edm) and wtF (MV-wtF) confer distinct cytopathic effects and strengths of hemagglutinin (H) interaction on a recombinant MV-Edm virus. They differ in just two amino acids, V94 and V101 in F-Edm versus M94 and F101 in F-wtF, both of which lie in the relatively uncharacterized F(2) domain. By comparing the sequence of MV F with those of the parainfluenza virus SV5 and Newcastle disease virus (NDV) F proteins, the structures of which are known, we show that MV F(2) also possesses a potential heptad repeat (HR) C domain. In NDV, the N-terminal half of HR-C interacts with HR-A in F(1) while the C-terminal half is induced to kink outward by a central proline residue. We found that this proline is part of an LXP motif conserved in all three viruses. Folding and transport of MV F require this motif to be intact and also require covalent interaction of cysteine residues that probably support the potential HR-A-HR-C interaction. Amino acids 94 and 101, both located in "d" positions of the HR-C helical wheel, lie in the potentially outwardly kinked region. We demonstrate that their effect on MV fusogenicity and glycoprotein interaction is mediated solely by amino acid 94. Substitutions at position 94 with polar or charged amino acids are tolerated poorly or not at all, while changes to smaller and more hydrophilic amino acids are tolerated in both transiently expressed F protein and recombinant virus. MV F V94A and MV F V94G viruses induce extensive syncytium formation and are relatively, or almost completely, resistant to a known inhibitor of MV glycoprotein-induced fusion. We propose that the conformational changes in MV F protein required to expose the fusion peptide involve the C-terminal half of the HR-C helix, specifically amino acid 94.

Evidence for mixed membrane topology of the newcastle disease virus fusion protein

The synthesis of the Newcastle disease virus (NDV) fusion (F) protein in a cell-free protein-synthesizing system containing membranes was characterized. The membrane-associated products were in at least two different topological forms with respect to the membranes. The properties of one form were consistent with the expected membrane insertion as a classical type 1 glycoprotein. This form of the protein was fully glycosylated, and sequences amino terminal to the transmembrane domain were protected from protease digestion by the membranes. The second form of membrane-associated F protein was partially glycosylated and partially protected from protease digestion by the membranes. Protease digestion resulted in a 23-kDa protease-protected polypeptide derived from F2 sequences and sequences from the amino-terminal end of the F1 domain. Furthermore, a 10-kDa polypeptide derived from the cytoplasmic domain (CT) was also protected from protease digestion by the membranes. Protease resistance of the 23- and 10-kDa polypeptides suggested that this second form of F protein inserted in membranes in a polytopic conformation with both the amino-terminal end and the carboxyl-terminal end translocated across membranes. To determine if this second form of the fusion protein could be found in cells expressing the F protein, two different approaches were taken. A polypeptide with the size of the partially translocated F protein was detected by Western analysis of proteins in total-cell extracts of NDV strain B1 (avirulent)-infected Cos-7 cells. Using antibodies raised against a peptide with sequences from the cytoplasmic domain, CT sequences were detected on surfaces of F protein-expressing Cos-7 cells by immunofluorescence and by flow cytometry. This antibody also inhibited the fusion of red blood cells to cells expressing F and HN proteins. These results suggest that NDV F protein made both in a cell-free system and in Cos-7 cells may exist in two topological forms with respect to membranes and that the second form of the protein may be involved in cell-cell fusion.

Newcastle disease virus HN protein alters the conformation of the F protein at cell surfaces

Conformational changes in the Newcastle disease virus (NDV) fusion (F) protein during activation of fusion and the role of HN protein in these changes were characterized with a polyclonal antibody. This antibody was raised against a peptide with the sequence of the amino-terminal half of the F protein HR1 domain. This antibody immunoprecipitated both F(0) and F(1) forms of the fusion protein from infected and transfected cell extracts solubilized with detergent, and precipitation was unaffected by expression of the HN protein. In marked contrast, this antibody detected significant conformational differences in the F protein at cell surfaces, differences that depended upon HN protein expression. The antibody minimally detected the F protein, either cleaved or uncleaved, in the absence of HN protein expression. However, when coexpressed with HN protein, an uncleaved mutant F protein bound the anti-HR1 antibody, and this binding depended upon the coexpression of specifically the NDV HN protein. When the cleaved wild-type F protein was coexpressed with HN protein, the F protein bound anti-HR1 antibody poorly although significantly more than F protein expressed alone. Anti-HR1 antibody inhibited the fusion of R18 (octadecyl rhodamine B chloride)-labeled red blood cells to syncytia expressing HN and wild-type F proteins. This inhibition showed that fusion-competent F proteins present on surfaces of syncytia were capable of binding anti-HR1. Furthermore, only antibody which was added prior to red blood cell binding could inhibit fusion. These results suggest that the conformation of uncleaved cell surface F protein is affected by HN protein expression. Furthermore, the cleaved F protein, when coexpressed with HN protein and in a prefusion conformation, can bind anti-HR1 antibody, and the anti-HR1-accessible conformation exists prior to HN protein attachment to receptors on red blood cells.

Characterization of newly emerging Newcastle disease virus isolates from the People's Republic of China and Taiwan

Seven Newcastle disease (ND) virus (NDV) isolates which were recovered from ND outbreaks in chicken and pigeon flocks in China and Taiwan between 1996 and 2000 were genotypically and pathotypically characterized. By phylogenetic analysis of the fusion protein genes, isolates Ch-A7/96, Ch/98-3, Ch/99, Ch/2000, and TW/2000 were placed into two novel subgenotypes, VIIc and VIId. Isolate Ch/98-1 was grouped into subgenotype VIb, while Ch-W6/96 was proven to be a mixture of isolates Ch-A7/96 and Ch/98-1. These isolates were pathotyped as viscerotropic velogenic for Ch/98-3, Ch/99, Ch/2000, and TW/2000; neurotropic velogenic for Ch-A7/96; and mesogenic for Ch/98-1. Three separate, comparative, genetic analyses of the F genes, including genetic distance measurement, phylogenetic tree analysis, and residue substitution analysis, were performed with our isolates and selected NDV strains from GenBank. Results showed that the close genetic similarity provided evidence for the epidemiological linkage between the outbreaks in China and Taiwan and that the 1990s outbreaks in Asia, the Middle East, Africa, and Europe constituted the fourth panzootic of ND. In combination with epidemiological analysis, an evolutionary model of the NDV strains, representative of the direction of transmission within the NDV strains, was proposed, and epidemiology of NDV transmission was evaluated with emphasis on molecular aspects. Finally, a cross-protective experiment indicated that at least one strain (Ch-A7/96) among our NDV isolates was an antigenic variant, responsible for recent outbreaks of ND in vaccinated chicken flocks.

Molecular evolution of viral fusion and matrix protein genes and phylogenetic relationships among the Paramyxoviridae

Phylogenetic relationships among the Paramyxoviridae, a broad family of viruses whose members cause devastating diseases of wildlife, livestock, and humans, were examined with both fusion (F) and matrix (M) protein-coding sequences. Neighbor-joining trees of F and M protein sequences showed that the Paramyxoviridae was divided into the two traditionally recognized subfamilies, the Paramyxovirinae and the Pneumovirinae. Within the Paramyxovirinae, the results also showed groups corresponding to three currently recognized genera: Respirovirus, Morbillivirus, and Rubulavirus. The relationships among the three genera of the Paramyxovirinae were resolved with M protein sequences and there was significant bootstrap support (100%) showing that members of the genus Respirovirus and the genus Morbillivirus were more closely related to each other than to members of the genus Rubulavirus. Both F and M phylogenies showed that Newcastle disease virus (NDV) was more closely related to the genus Rubulavirus than to the other two genera but were consistent with the proposal (B. S. Seal et al., 2000, Virus Res. 66, 1-11) that NDV be classified as a separate genus within the Paramyxovirinae. Both F and M phylogenies were also consistent with the proposal (L. Wang et al., 2000, J. Virol 74, 9972-9979) that Hendra virus be classified as a new genus closely related and basal to the genus Morbillivirus. Rinderpest was most closely related to measles and a more derived virus than to canine distemper virus, phocine distemper virus, or dolphin morbillivirus.

Carbohydrate modifications of the NDV fusion protein heptad repeat domains influence maturation and fusion activity

The amino acid sequence of the fusion protein (F) of Newcastle disease virus (NDV) has six potential N-linked glycosylation addition sites, five in the ectodomain (at amino acids 85, 191, 366, 447, and 471) and one in the cytoplasmic domain at amino acid 542. Two of these sites, at positions 191 and 471, are within heptad repeat (HR) domains implicated in fusion activity of the protein. To determine glycosylation site usage as well as the function of added carbohydrate, each site was mutated by substituting alanine for the serine or threonine in the addition signal. The sizes of the resulting mutant proteins, expressed in Cos cells, showed that sites at amino acids 85, 191, 366, and 471 are used. This conclusion was verified by comparing sizes of mutant proteins missing all four used sites with that of unglycosylated F protein. The role of each added oligosaccharide in the structure and function of the F protein was determined by characterizing stability, proteolytic cleavage, surface expression, and fusion activity of the mutant proteins. Elimination of the site in F(2) at amino acid 85 had the most detrimental effect, decreasing cleavage, stability, and surface expression as well as fusion activity. The protein missing the site at 191, at the carboxyl terminus of the HR1 domain, also showed modestly reduced surface expression and negligible fusion activity. Proteins missing sites at 366 and 471 (within HR2) were expressed at nearly wild-type levels but had decreased fusion activity. These results suggest that all carbohydrate side chains, individually, influence the folding or activity of the NDV F protein. Importantly, carbohydrate modifications of the HR domains impact fusion activity of the protein.

Phylogenetic relationships among highly virulent Newcastle disease virus isolates obtained from exotic birds and poultry from 1989 to 1996

Newcastle disease virus [NDV (avian paramyxovirus type 1 [APMV1])] isolates were recovered from imported exotic birds confiscated following importation into the United States, from waterbirds in the United States, and from poultry. The exotic birds probably originated from Central and South America, Asia, and Africa. The NDV isolates were initially characterized as highly virulent because of a short mean death time in embryonated chicken eggs. The isolates were typed as neurotropic or viscerotropic velogenic by intracloacal inoculation of adult chickens. Intracerebral pathogenicity index values for the virulent NDV isolates ranged from 1.54 to 1.90, compared to a possible maximum value of 2.0. These isolates had a dibasic amino acid motif in the fusion protein cleavage site sequence required for host systemic replication. Sequence differences were detected surrounding the fusion protein cleavage site and the matrix protein nuclear localization signal, indicating evolution of highly virulent NDV. Phylogenetically, these isolates were categorized with other highly virulent NDV strains that caused outbreaks in southern California poultry during 1972 and in cormorants in the north central United States and southern Canada during 1990 and 1992. These isolates are related to NDV that may have the APMV1 strain chicken/Australia/AV/32 or a related virus as a possible progenitor. Recent virulent NDV isolates and those recovered during disease outbreaks since the 1970s are phylogenetically distinct from current vaccine viruses and standard challenge strains.

The transmembrane domain in viral fusion: essential role for a conserved glycine residue in vesicular stomatitis virus G protein

The transmembrane (TM) domains of viral fusion proteins are required for fusion, but their precise role is unknown. G protein, the fusion protein of vesicular stomatitis virus, was previously shown to lose syncytia-forming ability if six residues (GLIIGL) were deleted from its TM domain. The 20-residue TM domain of wild-type (TM20) G protein was thus changed into a TM domain of 14 residues (TM14). To assess possible sequence specificity for this loss of function, the two Gly residues in TM20 were replaced with either Ala or Leu. Both mutations resulted in complete loss of fusion activity, as measured by fusion-dependent reporter gene transfer. Single substitutions decreased activity by about half. TM14 was weakly active (15%) but reintroduction of a Gly residue into TM14 by a single Ile --> Gly substitution increased activity to 80%. All mutants retained normal hemifusion activity, i.e., lipid mixing between the outer leaflets of the reacting membranes. Thus, at least one TM Gly residue is required for a late step in fusion mediated by G protein. Gly residues were significantly (2.6-fold; P = 0.004) more abundant in the TM domains of viral fusion proteins than in those of nonfusion proteins and were distributed differently within the TM domain. Thus, Gly residues in the TM domain of other viral fusion proteins may also prove to be important for fusion activity.

Pathogenicity and phylogenetic evaluation of the variant Newcastle disease viruses termed "pigeon PMV-1 viruses" based on the nucleotide sequence of the fusion protein gene

The nucleotide sequences of the entire F genes of two isolates of the pigeon PMV-1 (PPMV-1) variant of Newcastle disease virus (NDV) were determined using RTPCR. The deduced amino acid sequences of the F0 protein showed four differences between isolate 760/83 which had been passaged 4 times in chickens and gave an intravenous pathogenicity index in chickens (IVPI) of 2.01 and isolate 1168/84 which had received six passages in chickens and had an IVPI of 0.00. The F genes of virus from two passage levels of isolate 1447/84, 0 with IVPI value 0.00 and six with IVPI value 0.58, were partially sequenced to cover the areas of variation between 760/83 and 1168/84. The two passage levels of 1447/84 showed identical sequences in these areas which in turn were identical of those of 760/83. It was concluded that the recorded differences in intravenous pathogenicity were unlikely to be associated with differences in the primary structure of the F0 protein. Phylogenetic comparisons of the F gene sequences of the two PPMV-1 viruses with those published for other NDV strains and isolates showed that the PPMV-1 viruses formed a new fourth lineage but were closely related to strain Warwick with which they presumably shared a common origin.

Identification and grouping of Newcastle disease virus strains by restriction site analysis of a region from the F gene

A 75% region of the F gene (between nucleotides 334 and 1682) of Newcastle disease virus (NDV) RNA was amplified by reverse transcription polymerase chain reaction (RT-PCR). PCR products were cleaved by three restriction endonucleases and the positions of thirty cleavage sites were mapped in more than 200 NDV strains. Restrictions site analysis established six major groups of NDV isolates and unique fingerprints of vaccine strains. Group I comprised lentogenic strains isolated mainly from waterfowl with some from chickens. "Old" (prior to 1960s) North American isolates of varying virulence including lentogenic and mesogenic vaccine strains belonged to group II. Group III included two early isolates from the Far East. Early European strains (Herts 33 and Italien) of the first panzootic (starting in the late 1920s) and their descendants with some modifications were placed into group IV. NDV strains isolated during the second panzootic of chickens (starting in the early 1960s) were classified into two groups. Group V included strains originating in imported psittacines and in epizootics of chickens in the early 1970s. Group V1 comprised strains from the Middle East in the late 1960s and later isolates from Asia and Europe. Pigeon paramyxovirus-1 strains that were responsible for the third panzootic formed a distinct subgroup in group V1. Our grouping of NDV strains has confirmed group differences established by monoclonal antibodies. It is concluded that restriction site analysis of F gene PCR amplicons is a relatively fast, simple and reliable method for the differentiation and identification of NDV strains.

Characterization of Newcastle disease virus isolates by reverse transcription PCR coupled to direct nucleotide sequencing and development of sequence database for pathotype prediction and molecular epidemiological analysis

Degenerate oligonucleotide primers were synthesized to amplify nucleotide sequences from portions of the fusion protein and matrix protein genes of Newcastle disease virus (NDV) genomic RNA that could be used diagnostically. These primers were used in a single-tube reverse transcription PCR of NDV genomic RNA coupled to direct nucleotide sequencing of the amplified product to characterize more than 30 NDV isolates. In agreement with previous reports, differences in the fusion protein cleavage sequence that correlated genotypically with virulence among various NDV pathotypes were detected. By using sequences generated from the matrix protein gene coding for the nuclear localization signal, lentogenic viruses were again grouped phylogenetically separate from other pathotypes. These techniques were applied to compare neurotropic velogenic viruses isolated from an outbreak of Newcastle disease in cormorants and turkeys. Cormorant NDV isolates and an NDV isolate from an infected turkey flock in North Dakota had the fusion protein cleavage sequence 109SRGRRQKRFVG119. The R-for-G substitution at position 110 may be unique for the cormorant-type isolates. Although the amino acid sequences from the fusion protein cleavage site were identical, nucleotide sequence data correlate the outbreak in turkeys to a cormorant virus isolate from Minnesota and not to a cormorant virus isolate from Michigan. On the basis of sequence information, the cormorant isolates are virulent viruses related to isolates of psittacine origin, possibly genotypically distinct from other velogenic NDV isolates. These techniques can be used reliably for Newcastle disease epidemiology and for prediction of pathotypes of NDV isolates without traditional live-bird inoculations.

Analysis of matrix protein gene nucleotide sequence diversity among Newcastle disease virus isolates demonstrates that recent disease outbreaks are caused by viruses of psittacine origin

Nucleotide sequence analysis was completed for isolates of Newcastle disease virus (NDV; avian paramyxovirus 1) from 1992 outbreaks in cormorants and turkeys. These isolates were of the neurotropic velogenic type. The cormorant and turkey NDV isolates had the fusion protein cleavage sequence 109SRGRRQKR/FVG119, as opposed to the consensus sequence 109SGGRRQKR/FIG119 of most known velogenic NDV isolates. The R for G substitution at position 110 may be unique for the cormorant and turkey isolates. For comparative purposes, nucleotide sequencing and analysis of the conserved matrix protein gene coding region were completed for isolates representing all pathotypes. Phylogenetic relationships demonstrated that there are two major groups of NDV isolates. One group includes viruses found in North America and worldwide, such as B1, LaSota, Texas/GB, and Beaudette/C. The second group contains isolates, such as ulster/2C, Australia/Victoria, and Herts/33, considered exotic to North America. Within this second group are viruses of psittacine origin. The viruses from 1992 outbreaks of Newcastle disease in North America, and an isolate thought to have caused the major outbreak in southern California during the 1970s, are most closely related to an NDV isolate of psittacine origin.

Intracellular processing of the paramyxovirus F protein: critical role of the predicted amphipathic alpha helix adjacent to the fusion domain

At a nonpermissive temperature, the group D temperature-sensitive mutants of Newcastle disease virus strain Australia-Victoria (AV) are defective in plaque formation, in inducing infected cells to fuse, and in incorporating the cleaved fusion glycoprotein, F1 + F2, into virus particles. In this study, the F protein of AV, expressed in chicken embryo cells, was able to complement these mutants in a plaque assay, identifying the F gene as the gene containing the group D temperature-sensitive lesions. The F genes of mutants D1, D2, and D3 were found to contain single mutations relative to the AV sequence, clustered within a predicted amphipathic alpha helix (AAH) adjacent to the hydrophobic amino terminus of F1. These mutant F proteins were inefficiently processed at the permissive temperature, a problem that was exacerbated at the nonpermissive temperature. Surprisingly, the AV F protein was also found to be partially temperature sensitive in processing. Its AAH is predicted to contain a break in the helix close to the D mutation sites, which are themselves predicted to further weaken the helix at this point. Interestingly, six revertants of the group D mutants were found to have an additional lesion in the AAH, repairing both the AV and mutant helices, resulting in a predicted perfect helix. The F protein of these revertants had overcome both the processing defects of the mutants and the temperature sensitivity of AV, indicating that the AAH region is critical for F protein processing. The lesions of a second group of revertants were localized within F2, suggesting an interaction with the F1 AAH region containing the original lesion.

Biological activity of paramyxovirus fusion proteins: factors influencing formation of syncytia

The fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of the paramyxovirus simian virus 5 (SV5) were expressed individually or coexpressed in CV-1 cells by using SV40-based vectors and recombinant vaccinia viruses. The extent of detectable fusion in a syncytium formation assay was found to be affected by the expression system used. In addition, when HN was coexpressed with F, it was found that the expression vector system influenced the contribution of HN in forming syncytia. The abilities of the SV5, human parainfluenza virus type 3, and Newcastle disease virus F glycoproteins to cause fusion, when expressed alone or coexpressed with HN, were directly compared by using the SV40-based vector system in CV-1 cells. The F proteins exhibited various degrees of fusion activity independent of HN expression, but the formation of syncytia could be enhanced to different extents by the coexpression of the homotypic HN protein.

Studies on the fusion peptide of a paramyxovirus fusion glycoprotein: roles of conserved residues in cell fusion

The role of residues in the conserved hydrophobic N-terminal fusion peptide of the paramyxovirus fusion (F) protein in causing cell-cell fusion was examined. Mutations were introduced into the cDNA encoding the simian virus 5 (SV5) F protein, the altered F proteins were expressed by using an eukaryotic vector, and their ability to mediate syncytium formation was determined. The mutant F proteins contained both single- and multiple-amino-acid substitutions, and they exhibited a variety of intracellular transport properties and fusion phenotypes. The data indicate that many substitutions in the conserved amino acids of the simian virus 5 F fusion peptide can be tolerated without loss of biological activity. Mutant F proteins which were not transported to the cell surface did not cause cell-cell fusion, but all of the mutants which were transported to the cell surface were fusion competent, exhibiting fusion properties similar to or better than those of the wild-type F protein. Mutant F proteins containing glycine-to-alanine substitutions had altered intracellular transport characteristics, yet they exhibited a great increase in fusion activity. The potential structural implications of this substitution and the possible importance of these glycine residues in maintaining appropriate levels of fusion activity are discussed.

Antipeptide antibodies for analysis of pathotype-specific variations in cleavage activation of the membrane glycoprotein precursors of Newcastle disease virus isolates in cultured cells

Antipeptide antibodies have been produced which target regions either side of the cleavage activation sites of Newcastle disease virus (NDV) membrane glycoprotein precursors. Use of complementary pairs of antibodies in Western blot analysis of mercaptoethanol-reduced extracts of NDV-infected BHK-21 cells enabled analysis of the susceptibilities of NDV fusion protein precursors (Fo-proteins) to cleavage activation in these cells. In addition, it was possible to determine whether or not isolates produce haemagglutinin-neuraminidase (HN)-proteins in precursor forms (HNo-proteins). This assay system has been evaluated with a series of Australian isolates of NDV with well defined virulence properties in order to validate its use in pathotyping NDV isolates. Less well defined isolates also produced data consistent with their biological properties and an isolate was characterised which, hitherto, was not known to be present in Australian poultry. The applicability of this assay system in fundamental studies of the processes of cleavage activation of NDV Fo- and HNo-proteins and formatting of the antisera into ELISA systems are discussed.

Detection of Newcastle disease virus RNA in infected allantoic fluids by in vitro enzymatic amplification (PCR)

The Polymerase Chain Reaction (PCR) procedure was applied in order to identify the Newcastle disease virus (NDV), an avian paramyxovirus (A-PMV 1). The sequence selected for amplification consists of 238 bp lying in the gene encoding the fusion protein F. A pair of 19-mer and 18-mer oligonucleotides, flanking this sequence, were used as primers. Following RNA extraction by the proteinase K method, a cDNA was prepared using the previous 19-mer oligonucleotide as the primer. The amplification reaction product was analyzed by electrophoresis and ethidium bromide staining, using the restriction enzymes HaeIII, Mbo II, and Nar I. The PCR was performed on cDNA prepared from 30 A-PMV 1 and 3 other strains (A-PMV2, A-PMV3, A-PMV4). It was thereby demonstrated that the selected sequence was highly specific and constant. However, two of the PMV1 strains isolated from feral ducks, are thought to present a deletion of about 25 bp inside this fragment as shown by the smaller length of the corresponding amplified product and the disappearance of the NarI restriction site. The advantages of this technique, as a first step in evaluating virulence by means of molecular biology, is discussed.

Complementation between avirulent Newcastle disease virus and a fusion protein gene expressed from a retrovirus vector: requirements for membrane fusion

The cDNA derived from the fusion gene of the virulent AV strain of Newcastle disease virus (NDV) was expressed in chicken embryo cells by using a retrovirus vector. The fusion protein expressed in this system was transported to the cell surface and was efficiently cleaved into the disulfide-linked F1-F2 form found in infectious virions. The cells expressing the fusion gene grew normally and could be passaged many times. Monolayers of these cells would plaque, in the absence of trypsin, avirulent NDV strains (strains which encode a fusion protein which is not cleaved in tissue culture). Fusion protein-expressing cells would not fuse if mixed with uninfected cells or uninfected cells expressing the hemagglutinin-neuraminidase (HN) protein. However, the fusion protein-expressing cells, if infected with avirulent strains of NDV, would fuse with uninfected cells, suggesting that fusion requires both the fusion protein and another viral protein expressed in the same cell. Fusion was also seen after transfection of the HN protein gene into fusion protein-expressing cells. Thus, the expressed fusion protein gene is capable of complementing the virus infection, providing an active cleaved fusion protein required for the spread of infection. However, the fusion protein does not mediate cell fusion unless the cell also expresses the HN protein. Fusion protein-expressing cells would not plaque influenza virus in the absence of trypsin, nor would influenza virus-infected fusion protein-expressing cells fuse with uninfected cells. Thus, the influenza virus HA protein will not substitute for the NDV HN protein in cell-to-cell fusion.

Comparison of the positions and efficiency of cleavage activation of fusion protein precursors of virulent and avirulent strains of Newcastle disease virus: insights into the specificities of activating proteases

The F1- and F2-polypeptide components of in ovo activated fusion proteins of one virulent (AV or Australia-Victoria) strain, one low-virulence (EG or Eaves-Grimes) strain, and two avirulent (V4 or Queensland and WA2116) strains of Newcastle disease virus (NDV) were isolated and subjected to structural analysis. This included complementary application of amino acid analysis, fast atom bombardment-mass spectrometry, and N-terminal sequence analysis to fragments isolated from AspN protease digests of the F2-polypeptides using HPLC. As a result, the complete sequences of the F2-polypeptides were determined, including documentation of glycosylation of asparagine 54. The sequence of the cleavage-activation site of the WA2116 F0-protein was found to be distinctly different from this site in any other NDV F0-protein. Cleavage activation at the C termini of the F2-polypeptide regions was found to have occurred to approximately equivalent extents at arginines 82 and 85 of the AV and EG strains, but was restricted largely to arginine 85 of the V4 strain and completely to arginine 85 of the WA2116 strain. In each case cleavage activation was apparently succeeded by trimming of the basic residues from the newly formed C termini. Immunochemical analysis with antipeptide antisera showed that the extent of cleavage was influenced by amino acids adjacent to these arginines. These data provide insight into the substrate specificities of the enzymes involved in cleavage activation of the fusion protein precursors.

Avian Paramyxoviridae--recent developments

This paper reviews the recent developments related to members of the Paramyxoviridae family which infect avian species. These developments include: (1) The identification of the virus responsible for the diseases turkey rhinotracheitis and swollen head syndrome in chickens as a member of the Pneumovirus genus, the first of this type to be isolated from birds. (2) The use of monoclonal antibodies prepared against Newcastle disease virus (NDV) and other avian paramyxoviruses which has enabled more exact and rapid diagnosis and greater understanding of the epizootiology of these viruses. (3) The nucleotide sequencing of the genome of NDV and subsequent amino acid sequencing of the major virus proteins have resulted in greater understanding of the pathogenicity of this economically important virus.

Newcastle disease virus fusion protein expressed in a fowlpox virus recombinant confers protection in chickens

A cDNA copy of the RNA encoding the fusion (F) protein of Newcastle disease virus (NDV) strain Texas, a velogenic strain of NDV, was obtained and the sequence was determined. The 1,792-base-pair sequence encodes a protein of 553 amino acids which has essential features previously established for the F protein of virulent NDV strains. These include the presence of three strongly hydrophobic regions and pairs of dibasic amino acids in the pentapeptide Arg-Arg-Gln-Arg-Arg preceding the putative cleavage site. When inserted into a fowlpox virus vector, a glycosylated protein was expressed and presented on the surface of infected chicken embryo fibroblast cells. The F protein expressed by the recombinant fowlpox virus was cleaved into two polypeptides. When inoculated into susceptible birds by a variety of routes, an immunological response was induced. Ocular or oral administration of the recombinant fowlpox virus gave partial protection, whereas both intramuscular and wing-web routes of inoculation gave complete protection after a single inoculation.

A host range mutant of Newcastle disease virus with an altered cleavage site for proteolytic activation of the F protein

The primary structure of the F protein of a host range mutant of the Ulster strain of Newcastle Disease virus (NDV) has been determined by nucleotide sequence analysis and compared to that of the wild type and other NDV strains. The cleavage site of the mutant had the sequence Gly-Lys-Gln-Arg-Arg as compared to two isolated basic amino acids [Gly-Lys(Arg)-Gln-Gly-Arg] with the apathogenic strains and two pairs of basic amino acids [Arg-Arg-Gln-Lys(Arg)-Arg] with the pathogenic strains. The data indicate that the cleavability of the F protein of NDV increases with the number of arginine and lysine residues at the cleavage site and that the susceptibility of the pathogenic strains to ubiquitous host proteases depends on both pairs of basic amino acids.

Newcastle disease virus evolution. II. Lack of gene recombination in generating virulent and avirulent strains

Sequence analysis and comparison of the fusion glycoprotein genes of 11 Newcastle disease virus (NDV) isolates indicated a high degree of functional and structural constraint exerted on the change of the glycoprotein. However, synonymous nucleotide substitutions occurred frequently throughout the coding region. Facilitated by an analysis of synonymous difference (Ks) in pairwise strain comparison, we defined the branching orders of the strains and identified three distinct evolutionary lineages correlating with the virulence as expressed by mean death time (MDT) for chick embryo. The typically virulent strains with MDT of about 50 hr were associated with one lineage, while the typically nonvirulent strains with MDT of infinity were of another lineage. The third lineage consisted of both virulent and avirulent strains whose MDTs lay on a continuum from 50 to 120 hr. Synonymous substitutions were found to occur with almost the same rates in the adjacent hemagglutinin-neuraminidase and membrane protein genes as in the fusion protein gene, and the branching orders based upon the Ks for these genes were essentially identical to those derived from the fusion protein gene. Therefore, no gene exchange by recombination seems to have occurred to generate the strains of distinct lineages. Rather, the different strains appear to have evolved through various degrees of accumulation of point mutations. Besides these evolutionary features, the present study strongly supports the importance of the previously identified signals for gene expression and for the proteolytic activation of the gene product.

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.

Mutations located on both F1 and F2 subunits of the Newcastle disease virus fusion protein confer resistance to neutralization with monoclonal antibodies

The fusion gene sequence of six Newcastle disease virus escape mutants revealed that residues important for the integrity of antigenic site 1 and antigenic site 2 were located, respectively, on the F2 subunit and within the cysteine-rich domain of the F1 subunit. We further report the antibody-binding capacity of these mutants.

Identification of amino acids relevant to three antigenic determinants on the fusion protein of Newcastle disease virus that are involved in fusion inhibition and neutralization

Nucleotide sequence analysis of F protein antigenic variants of Newcastle disease virus mapped three distinct antigenic determinants to positions 343, 72, and 161 on the protein. The high fusion-inhibiting and neutralizing capacities of all of the monoclonal antibodies used for selection suggested close functional and structural relationships of the three positions with the fusion-inducing N-terminal region of the F1 subunit. The former two positions were located at the cysteine cluster domain near the C terminus of the F1 subunit and at the major hydrophilic domain in the F2 subunit, respectively, and both domains appeared to represent the major antigenic determinants of paramyxovirus F protein.

Association of soluble matrix protein of Newcastle disease virus with liposomes is independent of ionic conditions

An immunoaffinity method was designed for purification of a soluble form of the matrix (M) protein of Newcastle disease virus. The resulting M protein sedimented in a sucrose gradient as a small complex. This purified M protein associated with liposomes containing a net neutral, negative, or positive charge. The liposomes were composed of phosphatidylcholine, cholesterol, and a third lipid which provided the charge. The M protein-liposome associations were not prevented by high salt conditions. These observations are consistent with a nonelectrostatic association between the M protein and liposomes. Monoclonal antibodies to three separate epitopes of the M protein were all able to bind M protein complexed with liposomes, suggesting that the three M protein epitopes are not directly involved in the interaction between the M protein and liposomes. The M protein was also able to associate with liposomes lacking cholesterol implying that cholesterol does not play a substantial role in the M protein-liposome interaction.

The P protein and the nonstructural 38K and 29K proteins of Newcastle disease virus are derived from the same open reading frame

The nucleotide sequence of cloned cDNA copies of the mRNA encoding the Newcastle disease virus (NDV), strain AV, phosphoprotein (P) was determined. The sequence of 1443 nucleotides contains one long open reading frame which could encode a protein with a molecular weight of 42,126, and two smaller open reading frames which could encode proteins with molecular weights of 11,178 and 13,935. Full-length cDNA clones were constructed in an SP6 vector, mRNA was transcribed in a cell-free system using the SP6 polymerase, and the mRNA was translated in a wheat germ cell-free extract. The P mRNA directed the synthesis of, primarily, four products. One, with a molecular weight of 53,000 Da, comigrated with authentic P protein made in infected cells and was precipitable with antisera with specificity for the NDV P protein. The other products of the cell-free reaction had molecular weights of 38,000, 29,000 and 12,000. The 29,000- and the 38,000-Da polypeptides were also precipitable with anti-P protein antibody. Using truncated cDNA clones, evidence is presented that the 38,000- and 29,000-Da proteins are derived from initiation at AUG triplets in the same reading frame as the P protein. Infected cells also contain these polypeptides which may be analogous to C proteins of other paramyxoviruses. Thus the NDV P protein mRNA is different than most other paramyxovirus P protein mRNAs which are translated in two different reading frames to yield the P and C proteins.

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.