A single-amino-acid mutation at position 225 in hemagglutinin attenuates H5N6 influenza virus in mice

• Published in: Emerging microbes & infections 2021-01, Vol.10 (1), p.2052-2061
• Main Authors: Kong, Xingtian, Guan, Lizheng, Shi, Jianzhong, Kong, Huihui, Zhang, Yaping, Zeng, Xianying, Tian, Guobin, Liu, Liling, Li, Chengjun, Kawaoka, Yoshihiro, Deng, Guohua, Chen, Hualan
• Format: Article
• Language: English
• Subjects: Animals; Female; Genome, Viral; H5N6 subtype; Hemagglutinin Glycoproteins, Influenza Virus - genetics; Hemagglutinin Glycoproteins, Influenza Virus - metabolism; Humans; Influenza A virus - genetics; Influenza A virus - metabolism; Influenza A virus - pathogenicity; Influenza virus; Influenza, Human - virology; Mice; Mice, Inbred BALB C; molecular basis; Mutation, Missense; pathogenicity; Virulence
• ISSN: 2222-1751; 2222-1751
• DOI: 10.1080/22221751.2021.1997340

The highly pathogenic avian influenza H5N6 viruses are widely circulating in poultry and wild birds, and have caused 38 human infections including 21 deaths; however, the key genetic determinants of the pathogenicity of these viruses have yet to be fully investigated. Here, we characterized two H5N6 avian influenza viruses - A/duck/Guangdong/S1330/2016 (GD/330) and A/environment/Fujian/S1160/2016 (FJ/160) - that have similar viral genomes but differ markedly in their lethality in mice. GD/330 is highly pathogenic with a 50% mouse lethal dose (MLD 50 ) of 2.5 log 10 50% egg infectious doses (EID 50 ), whereas FJ/160 exhibits low pathogenicity with an MLD 50 of 7.4 log 10 EID 50 . We explored the molecular basis for the difference in virulence between these two viruses. By using reverse genetics, we created a series of reassortants and mutants in the GD/330 background and assessed their virulence in mice. We found that the HA gene of FJ/160 substantially attenuated the virulence of GD/330 and that the mutation of glycine (G) to tryptophan (W) at position 225 (H3 numbering) in HA played a key role in this function. We further found that the amino acid mutation G225W in HA decreased the acid and thermal stability and increased the pH of HA activation, thereby attenuating the H5N6 virus in mice. Our study thus identifies a novel molecular determinant in the HA protein and provides a new target for the development of live attenuated vaccines and antiviral drugs against H5 influenza viruses.