A point mutation in the polymerase protein PB2 allows a reassortant H9N2 influenza isolate of wild-bird origin to replicate in human cells.
H9N2 influenza A viruses are on the list of potentially pandemic subtypes. Therefore, it is important to understand how genomic reassortment and genetic polymorphisms affect phenotypes of H9N2 viruses circulating in the wild bird reservoir. A comparative genetic analysis of North American H9N2 isolates of wild bird origin identified a naturally occurring reassortant virus containing gene segments derived from both North American and Eurasian lineage ancestors. The PB2 segment of this virus encodes 10 amino acid changes that distinguish it from other H9 strains circulating in North America. G590S, one of the 10 amino acid substitutions observed, was present in ~12% of H9 viruses worldwide. This mutation combined with R591 has been reported as a marker of pathogenicity for human pandemic 2009 H1N1 viruses. Screening by polymerase reporter assay of all the natural polymorphisms at these two positions identified G590/K591 and S590/K591 as the most active, with the highest polymerase activity recorded for the SK polymorphism. Rescued viruses containing these two polymorphic combinations replicated more efficiently in MDCK cells and they were the only ones tested that were capable of establishing productive infection in NHBE cells. A global analysis of all PB2 sequences identified the K591 signature in six viral HA/NA subtypes isolated from several hosts in seven geographic locations. Interestingly, introducing the K591 mutation into the PB2 of a human-adapted H3N2 virus did not affect its polymerase activity. Our findings demonstrate that a single point mutation in the PB2 of a low pathogenic H9N2 isolate could have a significant effect on viral phenotype and increase its propensity to infect mammals. However, this effect is not universal, warranting caution in interpreting point mutations without considering protein sequence context.
Department of Biological Engineering and Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, MA, USA.
Islam T M
ITM
Hussein
Department of Biological Engineering and Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, MA, USA.
Eric J
EJ
Ma
Department of Biological Engineering and Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, MA, USA.
Nichola J
NJ
Hill
U.S. Geological Survey, Alaska Science Center, Anchorage, AK 99508, USA.
Brandt W
BW
Meixell
Institute of Arctic Biology, University of Alaska Fairbanks, AK 99775, USA.
Mark
M
Lindberg
Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York City, NY, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York City, NY, USA.
Randy A
RA
Albrecht
Center for Infectious Diseases, The University of Texas School of Public Health, Houston, TX, USA.
Justin
J
Bahl
Department of Biological Engineering and Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, MA, USA. Electronic address: jrun@mit.edu.
Jonathan A
JA
Runstadler
D019943:Amino Acid Substitution; D000818:Animals; D001717:Birds / Q000821:virology; D001980:Bronchi / Q000473:pathology / Q000821:virology; D004285:Dogs; D004847:Epithelial Cells / Q000473:pathology / Q000821:virology; D015870:Gene Expression; D057809:HEK293 Cells; D058507:Host Specificity; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D053122:Influenza A Virus, H3N2 Subtype / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D053127:Influenza A Virus, H9N2 Subtype / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D061985:Madin Darby Canine Kidney Cells; D010802:Phylogeny; D017354:Point Mutation; D011110:Polymorphism, Genetic; D016865:Reassortant Viruses / Q000235:genetics* / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D014779:Virus Replication
C502893:PB2 protein, influenza virus; D014764:Viral Proteins; D008239:Lysine
H9N2; Influenza; PB2; Polymorphisms; Viral polymerase