| Interferon-mediated host responses are key features for regulating influenza A virus（IAV）infections.It is well-known that the interferon-induced Mx proteins are the thriving antiviral potent against a number of viruses including IAV.Viral polymerases are a notable part essential for viral replication.The cellular protein Mx1 has been previously found to interact with viral nucleoprotein（NP）,influence polymerase activity and provide interspecies restriction.We did evolutionary analysis and found great diversities in NP sequences of different hosts.Considering the diversity of Mx1 proteins and the different activities on viruses from different hosts,we hypothesized the NP from equine viruses might have evolved a specific signature of adaptation to counter equine Mx1（eqMx1）,andthis“signature”of the equine virus may not be able to overcome the restriction of humanMxA（huMxA）.We estimated the difference in antiviral activities of hu Mx A&eq Mx1proteins against a broad range of IAV strains.We found that huMxA possesses the antiviral potential against the IAV strains from non-human species whereas eqMx1 could only inhibit the polymerase activity of non-equine species.In general,avian influenza viruses were found to be better inhibited than human or equine strains.Exchange of the viral components in a minireplicon system between two different strains of IAV identified the viral nucleoprotein as the main target structure of Mx1.Next,we identified adaptive mutations in the NP of strains A/equine/Jilin/1/1989(H3N8 JL89)and H7N9A/chicken/Zhejiang/DTID-ZJU01/2013(H7N9ZJ13)that confer eqMx1 resistance and sensitivity respectively.We found two positions which could be the possible target for H3N8 JL89 IAV.We demonstrated that in H3N8 JL89 NP,a significant decrease in Mx1resistance was observed for the mutations G34S and H52N and the reverse mutations in the H7N9ZJ13 NP showed the reverse effect of mutations at site 52（N52H）and make it able to escape the eqMx1 restriction.Interestingly,mutating S34G in the H7NZJ13 NP does not lose its activity completely,but slightly altered.In conclusion,our current research evaluates anti-influenza activities of eqMx1 and identifies key sites on H3N8JL89 NP to antagonize the effect of eqMx1,which gives us a better understanding of the sequence-specific interaction between IAV and eqMx1.Collectively,it can be summarized that eqMx1 is a crucial gene in the evolution of influenza viral NP.The present study postulates that continuous monitoring of amino acid sequences is mandatory in order to predict the pandemic potential of emerging IAVs in the future. |
