Influenza A viruses with different amino acid residues at PB2-627 display distinct replication properties in vitro and in vivo: Revealing the sequence plasticity of PB2-627 position

- Influenza A virus has a high sequence plasticity at the PB2-627 position.
- The selection pressures imposed by in vitro and in vivo conditions on this position are different.
- A PB2-D309N mutation can enhance viral polymerase activity.

Sequence analyses of influenza PB2 sequences indicate that the 627 position almost exclusively contains either lysine (K) or glutamic acid (E), suggesting a high sequence constraint at this genetic marker. Here, we used a site-directed random mutagenesis method to demonstrate that PB2-627 position has a high sequence plasticity. Recombinant viruses carrying various amino acid residues at this position are viable in cell cultures. These PB2-627 mutants showed various polymerase activities and replication kinetics in mammalian and avian cells as well as pathogenicity in mice. Serially passaging these mutants in MDCK cells generated some compensatory PB2 mutations that can restore polymerase activities of the PB2-627 mutants. Of these, PB2-D309N was identified as a novel one. Besides showing that influenza virus can tolerate a wide range of amino acid residues at the PB2-627 position, this study also demonstrates a potential strategy to identify novel mutations that can enhance viral polymerase.