Novel Polymerase Gene Mutations for Human Adaptation in Clinical Isolates of Avian H5N1 Influenza Viruses

PLoS Pathog. 2016 Apr 20;12(4):e1005583. doi: 10.1371/journal.ppat.1005583. eCollection 2016 Apr.


A major determinant in the change of the avian influenza virus host range to humans is the E627K substitution in the PB2 polymerase protein. However, the polymerase activity of avian influenza viruses with a single PB2-E627K mutation is still lower than that of seasonal human influenza viruses, implying that avian viruses require polymerase mutations in addition to PB2-627K for human adaptation. Here, we used a database search of H5N1 clade 2.2.1 virus sequences with the PB2-627K mutation to identify other polymerase adaptation mutations that have been selected in infected patients. Several of the mutations identified acted cooperatively with PB2-627K to increase viral growth in human airway epithelial cells and mouse lungs. These mutations were in multiple domains of the polymerase complex other than the PB2-627 domain, highlighting a complicated avian-to-human adaptation pathway of avian influenza viruses. Thus, H5N1 viruses could rapidly acquire multiple polymerase mutations that function cooperatively with PB2-627K in infected patients for optimal human adaptation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / genetics*
  • Animals
  • Blotting, Western
  • DNA-Directed RNA Polymerases / genetics*
  • Disease Models, Animal
  • Female
  • Humans
  • Influenza A Virus, H5N1 Subtype
  • Influenza, Human / genetics*
  • Mice
  • Mice, Inbred BALB C
  • Mutagenesis, Site-Directed
  • Mutation
  • Real-Time Polymerase Chain Reaction
  • Transfection
  • Viral Proteins / genetics*


  • PB2 protein, influenza virus
  • Viral Proteins
  • DNA-Directed RNA Polymerases

Grant support

This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (KAKENHI Grant Numbers 15K08497 and 15H05295; The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.