Amino acids 473V and 598P of PB1 from an avian-origin influenza A virus contribute to polymerase activity, especially in mammalian cells

Abstract

It has been reported that the avian-origin influenza A virus PB1 protein (avian PB1) enhances influenza A virus polymerase activity in mammalian cells when it replaces the human-origin PB1 protein (human PB1). Characterization of the amino acid residues that contribute to this enhancement is needed. In this study, it was found that PB1 from an avian-origin influenza A virus [A/Cambodia/P0322095/2005, H5N1 (Cam)] could enhance the polymerase activity of an attenuated human isolated virus, A/WSN/33, carrying the PB2 K627E mutation (WSN627E) in vitro. Furthermore, 473V and 598P in the Cam PB1 were identified as the residues responsible for this enhanced activity. The results from recombinant virus experiments demonstrated the contribution of PB1 amino acids 473V and 598P to polymerase activity in mammalian cells and in mice. Interestingly, 473V is conserved in pH1N1 viruses from the 2009 pandemic. Substitution of 473V by leucine in pH1N1 PB1 led to a decreased viral polymerase activity and a lower growth rate in mammalian cells, suggesting that the PB1 473V also plays a role in maintaining efficient virus replication of the pH1N1 virus. Thus, it was concluded that two amino acids in avian-origin PB1, 473V and 598P, contribute to the polymerase activity of the H5N1 virus, especially in mammalian cells, and that 473V in PB1 also contributes to efficient replication of the pH1N1 strain.

Adaptation of Avian Influenza A Virus Polymerase in Mammals To Overcome the Host Species Barrier

“…Interestingly, the N terminus of PA is also associated with viral genome promoter binding (41, 133) and regulation of cRNA/ vRNA synthesis (134), although it remains to be shown whether these mutations might affect the RNA-binding feature of PA. While additional mutations were identified at various positions in PA, including 336M, 552S, and 615N (3,11,14,(16)(17)(18), in PB1 only mutations at positions 473 and 598 were shown to increase polymerase activity of avian polymerases in mammalian cells (15).…”

Identification of Rare PB2-D701N Mutation from a Patient with Severe Influenza: Contribution of the PB2-D701N Mutation to the Pathogenicity of Human Influenza

“…PB1 has a role in pathogenicity and polymerase activity and two mutations in PB1, PB1-L473V and L598P, compensated for the absence of PB2-627K within an attenuated reassortant virus containing the H5N1 polymerase in a WSN background, both in cell culture and in the mouse model (Xu et al, 2012). The minimal set of mutations required for airborne transmission of a H5N1 virus among ferrets included, in addition of the PB2-E627K change, mutation PB1-H99Y (Linster et al, 2014), both mutations together had a synergistic effect, increasing viral polymerase activity and virus replication in mammalian cells.…”

Full-Genome Analysis of Avian Influenza A(H5N1) Virus from a Human, North America, 2013

“…The PB1 protein showed the P598L mutation reported to enhance polymerase activity in mammalian cells and mice ( 3 ). This change has been reported to enhance the polymerase activity of an attenuated human virus carrying the PB2 K627E mutation ( 15 ). Of the polymerase mutations hypothesized to increase the RNA polymerase activity of HPAI A(H5N1) viruses, namely P149S, R226H, K357I, and T515S, only two, 149S and 357T, were present in the A/Alberta/01/2014 isolate ( 3 ).…”