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

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 2 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 2 strains were identical, and only 5 amino acid 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 the fusion-promotion activity caused by a slight decrease in receptor-binding activity. The slight increase in the 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.