Amino acid substitutions in a conserved region in the stalk of the Newcastle disease virus HN glycoprotein spike impair its neuraminidase activity in the globular domain.
The ectodomain of the paramyxovirus haemagglutinin-neuraminidase (HN) glycoprotein spike can be divided into two regions: a membrane-proximal, stalk-like structure and a terminal globular domain. The latter contains all the antibody recognition sites of the protein, as well as its receptor recognition and neuraminidase (NA) active sites. These two activities of the protein can be separated by monoclonal antibody functional inhibition studies and mutations in the globular domain. Herein, we show that mutation of several conserved residues in the stalk of the Newcastle disease virus HN protein markedly decrease its NA activity without a significant effect on receptor recognition. Thus, mutations in the stalk, distant from the NA active site in the globular domain, can also separate attachment and NA. These results add to an increasing body of evidence that the NA activity of this protein is dependent on an intact stalk structure. (+info)
Pathogenesis of Newcastle disease in chickens experimentally infected with viruses of different virulence.
Groups of 4-week-old White Rock chickens were inoculated intraconjunctivally with nine isolates of Newcastle disease virus representing all pathotypes. Birds were monitored clinically and euthanatized sequentially, with collection of tissues for histopathologic examination and in situ hybridization using an anti-sense digoxigenin-labeled riboprobe corresponding to the sequence of the gene coding for the matrix protein. Disease was most severe with velogenic viscerotropic pathotypes and was characterized by acute systemic illness with extensive necrosis of lymphoid areas in the spleen and intestine. Viral nucleic acid was detected in multiple tissues but most prominently in macrophages associated with lymphoid tissue. Velogenic neurotropic isolates caused central nervous system disease despite minimal amounts of viral nucleic acid detected in neural tissue. Mesogenic and lentogenic pathotypes caused no overt disease; however, viral nucleic acid was present in myocardium and air sac epithelium following infection with these isolates. Compromise of air sac and myocardium may predispose mesogen- and lentogen-infected chickens to secondary infection and/or decreased meat and egg production. (+info)
Isolation and characterization of monoclonal antibodies directed against murine FRP-1/CD98/4F2 heavy chain: murine FRP-1 is an alloantigen and amino acid change at 129 (P<-->R) is related to the alloantigenicity.
Nineteen mAb directed against murine fusion regulatory protein-1 (mFRP-1)/4F2/CD98 were isolated and their biological properties were analysed. Intriguingly, mFRP-1 was found to be an alloantigen, namely, FRP-1.1 (DBA/2 and CBA mice type) and FRP-1.2 (BALB/c, C57BL/6 and C3H/He mice type). The nucleotide sequences of FRP-1.1 and FRP-1.2 were determined, demonstrating that amino acid change at 129 (P<-->R) is related to the alloantigenicity. mFRP-1 is expressed on thymocytes, on spleen cells, on peripheral lymphocytes and on blood monocytes, suggesting that the physiological role in vivo of murine FRP-1 is different from that of human FRP-1. The biological activities of antimFRP-1 mAbs showed by the present study are: (i) enhancement of Newcastle disease virus-induced cell fusion; (ii) suppression of HIVgp160-mediated cell fusion; and (iii) induction of aggregation and multinucleated giant cells of monocytes/macrophages. (+info)
Mutational analysis of heptad repeats in the membrane-proximal region of Newcastle disease virus HN protein.
For most paramyxoviruses, syncytium formation requires the expression of both surface glycoproteins (HN and F) in the same cell, and evidence suggests that fusion involves a specific interaction between the HN and F proteins (X. Hu et al., J. Virol. 66:1528-1534, 1992). The stalk region of the Newcastle disease virus (NDV) HN protein has been implicated in both fusion promotion and virus specificity of that activity. The NDV F protein contains two heptad repeat motifs which have been shown by site-directed mutagenesis to be critical for fusion (R. Buckland et al., J. Gen. Virol. 73:1703-1707, 1992; T. Sergel-Germano et al., J. Virol. 68:7654-7658, 1994; J. Reitter et al., J. Virol. 69:5995-6004, 1995). Heptad repeat motifs mediate protein-protein interactions by enabling the formation of coiled coils. Upon analysis of the stalk region of the NDV HN protein, we identified two heptad repeats. Secondary structure analysis of these repeats suggested the potential for these regions to form alpha helices. To investigate the importance of this sequence motif for fusion promotion, we mutated the hydrophobic a-position amino acids of each heptad repeat to alanine or methionine. In addition, hydrophobic amino acids in other positions were also changed to alanine. Every mutant protein retained levels of attachment activity that was greater than or equal to the wild-type protein activity and bound to conformation-specific monoclonal as well as polyclonal antisera. Neuraminidase activity was variably affected. Every mutation, however, showed a dramatic decrease in fusion promotion activity. The phenotypes of these mutant proteins indicate that individual amino acids within the heptad repeat region of the stalk domain of the HN protein are important for the fusion promotion activity of the protein. These data are consistent with the idea that the HN protein associates with the F protein via specific interactions between the heptad repeat regions of both proteins. (+info)
Rescue of Newcastle disease virus from cloned cDNA: evidence that cleavability of the fusion protein is a major determinant for virulence.
A full-length cDNA clone of Newcastle disease virus (NDV) vaccine strain LaSota was assembled from subgenomic overlapping cDNA fragments and cloned in a transcription plasmid between the T7 RNA polymerase promoter and the autocatalytic hepatitis delta virus ribozyme. Transfection of this plasmid into cells that were infected with a recombinant fowlpoxvirus that expressed T7 RNA polymerase, resulted in the synthesis of antigenomic NDV RNA. This RNA was replicated and transcribed by the viral NP, P, and L proteins, which were expressed from cotransfected plasmids. After inoculation of the transfection supernatant into embryonated specific-pathogen-free eggs, infectious virus derived from the cloned cDNA was recovered. By introducing three nucleotide changes in the cDNA, we generated a genetically tagged derivative of the LaSota strain in which the amino acid sequence of the protease cleavage site (GGRQGR downward arrowL) of the fusion protein F0 was changed to the consensus cleavage site of virulent NDV strains (GRRQRR downward arrowF). Pathogenicity tests in day-old chickens showed that the strain derived from the unmodified cDNA was completely nonvirulent (intracerebral pathogenicity index [ICPI] = 0.00). However, the strain derived from the cDNA in which the protease cleavage site was modified showed a dramatic increase in virulence (ICPI = 1.28 out of a possible maximum of 2.0). Pulse-chase labeling of cells infected with the different strains followed by radioimmunoprecipitation of the F protein showed that the efficiency of cleavage of the F0 protein was greatly enhanced by the amino acid replacements. These results demonstrate that genetically modified NDV can be recovered from cloned cDNA and confirm the supposition that cleavage of the F0 protein is a key determinant in virulence of NDV. (+info)
Local immunity in the respiratory tract of the chicken. I. Transudation of circulating antibody in normal and virus-infected birds.
Three-week-old chickens were given sheep erythrocytes or bovine serum albumin intravenously. Seven days later their tears and saliva possessed low levels of antibody to those antigens. Concurrent infection with lentogenic Newcastle disease virus (NDV) caused a significant increase in transuded antibody in those fluids. In chickens with circulating antibody to NDV, induced by parenterally administered inactivated vaccine, respiratory infection with heterologous infectious bronchitis virus resulted in limited transudation of anti-NDV. In contrast, the tears, saliva and tracheal fluid of non-vaccinated chickens undergoing primary infection with NDV acquired considerable levels of specific anti-NDV. The difference between the two groups is attributed to locally synthesized antibody. (+info)
Purification of two components of mouse L cell interferon: electrophoretic demonstration of interferon proteins.
Mouse L cell interferon induced by Newcastle disease virus was purified by the procedure described previously (Yamamoto et al. 1974) followed by gel filtration. The two fractions obtained containing interferon species S (36000 daltons) and F (24000 daltons), respectively, were analysed electrophoretically at pH 4-3, or in the presence of sodium dodecyl sulphate (SDS) at pH 7-2. In both fractions, interferon activity was invariably associated with distinct protein bands. In the F-containing fraction there were essentially no other proteins, and in the S-containing fraction, impurity proteins were well separated from the interferon activity. The apparent mol. wt. determined by SDS-gel electrophoresis showed little or no dependence on gel concentration, suggesting that the interferons had low carbohydrate contents, and did not change after reduction with thiol reagents in SDS and urea. (+info)
The production and action of interferon in Chinese hamster cells.
The interferon system has been investigated in primary cell cultures established from Chinese hamster embryos and new born pups. Interferon synthesis was induced with Sindbis virus, ultraviolet inrradiated Newcastle disease virus (u.v.-NDV) and with polyriboinosine acid-polyribocytidylic acid complex [poly (rI). poly (rC)]. Only u.v.-NDV induced significant production of interferon, maximum amounts being produced in 'aged' cells. Its apparent mol. wt. was 25000. CHO-KI cells, an established line of Chinese hamster cells, did not synthesize interferon in response to viruses, but were sensitive to its action. (+info)