Screening and mechanistic study of key sites of the hemagglutinin-neuraminidase protein related to the virulence of Newcastle disease virus

ABSTRACT Newcastle disease is a kind of avian infectious disease caused by Newcastle disease virus (NDV). The virulence of NDV is dependent mainly on the fusion (F) protein and hemagglutinin-neuraminidase (HN) protein. The genomes of two viruses, NDV-Blackbird and NDV-Dove, are 99.9% similar, while NDV-Blackbird is a velogenic virus, and NDV-Dove is a lentogenic virus. Further analysis revealed that the F proteins of the two strains were identical, and only five amino acid (aa) sites on the HN proteins were inconsistent. Five different HN mutant plasmids were constructed and analyzed in this study. The results showed that the mutation F110L caused a significant increase in fusion promotion activity caused by an increase in neuraminidase activity. Because of the increase in receptor-binding activity caused by G116R, there was a significant increase in fusion promotion activity. The mutation G54S resulted in a slight decrease in fusion promotion activity caused by a slight decrease in receptor-binding activity. The slight increase in fusion promotion activity caused by A469V was associated with a significant increase in neuraminidase activity. Therefore, the amino acids L110 and R116 played a key role in determining the virulence difference between NDV-Blackbird and NDV-Dove, which could lay a foundation for illuminating the virulence differences of NDV strains, as well as the development of attenuated vaccines.