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Title: A single amino acid substitution in the hemagglutinin-neuraminidase protein of Newcastle disease virus results in increased fusion and decreased neuraminidase activities without changes in virus pathotype

Author
item Estevez, Carlos
item King, Daniel
item LOU, MING - University Of Alabama
item Yu, Qingzhong

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2010
Publication Date: 3/1/2011
Citation: Estevez, C., King, D.J., Lou, M., Yu, Q. 2011. A single amino acid substitution in the hemagglutinin-neuraminidase protein of Newcastle disease virus results in increased fusion and decreased neuraminidase activities without changes in virus pathotype. Journal of General Virology. 92:544-551.

Interpretive Summary: Newcastle disease virus (NDV) is an important poultry pathogen that can cause severe economical losses to the poultry industry. To better understand how these viruses infect poultry, we studied the molecular mechanisms of virus attachment and invasion. Using genetic manipulation, the specific sites on the viral protein responsible for attachment to host cells, the hemagglutinin-neuraminidase (HN) protein, were altered. The resulting viruses were tested for the ability to infect cultured cells and chickens. The results showed that changing the amino acid sequence of the HN protein resulted in decrease of virus attachment, but increased virus penetration into the host cells. Results of these studies demonstrate the importance of amino acid sequence of the HN protein in the early steps of virus infection.

Technical Abstract: Newcastle disease virus (NDV) attachment to the host cell is mediated by the hemagglutinin-neuraminidase (HN), a multifunctional protein that has receptor recognition, neuraminidase and fusion promotion activities. The process that correlates receptor binding and fusion triggering is poorly understood and amino acid residues important for the protein functions remain to be fully determined. During the process of generation of an infectious clone of the Anhinga strain of NDV, we were able to rescue a NDV virus with highly increased fusogenic activity in vitro and decreased hemagglutinating activity, as compared with the wild type parental strain. Sequencing of this recombinant virus showed a single mutation at amino acid position 192 of the HN protein (Ile-Met). This work characterizes that single amino acid substitution in three strains of NDV by assessing the neuraminidase activity and fusogenic potential of the mutated versus wild-type proteins in cell cultures. The original recombinant NDV harboring the mutation in the HN gene was also used to characterize the phenotype of the virus in cell cultures, embryonated chicken eggs and day-old chickens. Mutation Ile 192 Met results in low neuraminidase activity and highly increased cell fusion in vitro, without changes in viral pathotype of recombinant viruses harboring the mutation in vivo. The results obtained suggest that multiple regions of the HN protein globular head are important for fusion promotion, and that wild type levels of neuraminidase activity are not absolutely required for viral infection.