Increase in the Neuraminidase Activity of a Nonpathogenic Newcastle Disease Virus Isolate during Passaging in Chickens

Abstract

ABSTRACT. A pathogenic mutant of the Newcastle disease virus (NDV) was previously generated by passaging a non-pathogenic isolate from wild waterfowl. Velogenic mutant 9a5b (IVPI=2.67) contains three amino acid substitutions (128H, 495K and 573stop) in the hemagglutinin-neuraminidase (HN) protein, as compared with nonpathogenic waterfowl isolate 415/91 strain, and two of these (128H and 495K) were introduced after mesogenic 9a3b (IVPI=1.88). To investigate the role of the HN protein in NDV virulence, the function of HN protein such as neuraminidase (NA), Hemadsorption (HAd) and fusion promotion activities was examined by introducing the point mutations observed in passaged mutants into the HN gene cDNAs. In vitro functional assay using mutant protein expression demonstrated that the 128H substitution markedly increases NA activity and 573stop substitution increase NA and HAd activities. On the other hand, 495K substitution had little effect on any activities. These results indicate that a single amino acid substitution (128P to H) in the NDV HN protein affects the neuraminidase activity and is possibly correlated with the virulence.KEY WORDS: hemagglutinin-neuraminidase protein, IVPI, Newcastle disease virus, passage, pathogenicity.J. Vet. Med. Sci. 72(4): 453-457, 2010 Newcastle disease virus (NDV) is classified as a member of the genus Avulavirus, belonging to the family Paramyxoviridae [12,16]. It causes a highly contagious respiratory, neurological or enteric disease in all species of birds, and is responsible for significant economic losses in the commercial poultry industry worldwide. Strains of NDV can be differentiated on the basis in their pathogenicity in chickens into strains of high (velogenic), intermediate (mesogenic) and low (lentogenic) virulence [1,2,24].NDV has two surface glycoproteins, a fusion (F) protein and a hemagglutinin-neuraminidase (HN) protein [11]. The F protein mediates fusion of the virion envelope with the cellular plasma membrane. It is synthesized as an inactive precursor, F 0 , which must be proteolytically cleaved to form a disulfide-linked heterodimer of F 1 and F 2 in order to activate membrane fusion activity. The F proteins of virulent strains differ from those of avirulent strains with regard to the presence of a pair of dibasic amino acids at the carboxyl (C) terminus of F 2 [5,20,22]. Whereas the F protein of virulent strains is cleaved by furin or other ubiquitous intracellular host cell proteases, the F protein of avirulent strains is cleaved by trypsin-like enzymes found in limited tissue. As a result, avirulent strains can only replicate in areas with trypsin-like enzymes, such as the respiratory and intestinal tracts, whereas virulent strains can replicate in a range of tissues and organs, resulting in fatal systemic infection [20,21].The HN protein possesses both the receptor recognition and neuraminidase (NA) activities associated with the virus. It is responsible for the attachment of virus particles to sialic acid-containing receptors of the host cell, it p...

Structure of the Newcastle disease virus hemagglutinin-neuraminidase (HN) ectodomain reveals a four-helix bundle stalk

“…Third, functional studies have implicated HN stalk residues through approximately residue 141 (12-16) in determining Fprotein specificity, and five residues between 125 and 138 form part of the observed interface. Fourth, analysis of pathogenic mutants of NDV indicates that substitution of residue 128 from proline to histidine increases NA activity and may influence virulence (24). Residue 128 is adjacent to residues in the NA domain that pack against the stalk, and substitution may affect the local structure of the protein and stalk interactions (Fig.…”

Molecular epidemiology of Newcastle disease virus isolates from vaccinated commercial poultry farms in non-epidemic areas of Japan

“…Different NDV strains vary greatly in pathogenicity [ 12 - 14 ]. NDV isolates can be broadly grouped into five pathotypes on the basis of clinical signs in infected chickens.…”

“…NDV isolates can be broadly grouped into five pathotypes on the basis of clinical signs in infected chickens. ND may manifest as viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic and asymptomatic enteric [ 14 , 15 ]. Other factors, such as host species, host immune status and age, environmental stress, coinfection with other organisms, viral dose and route of exposure, may also influence the severity of the disease [ 15 ].…”

Differential Features of Fusion Activation within the Paramyxoviridae

“…Given that category II mutations-which occur exclusively in the hydrophobic core-have an impact on tetramerization, whereas category I mutations-which occur on the exposed surface of the 4HB-do not, the differing phenotypes further support the solo involvement of the hydrophobic core in tetramerization. Moreover, category II mutations are linked to lowered pathogenicity, suggesting the tetrameric integrity of RBP plays a role in NDV pathogenesis [110].…”