title: Functional Comparison of Mx1 from Two Different Mouse Species Reveals the Involvement of Loop L4 in the Antiviral Activity against Influenza A Viruses.
abstract: The interferon-induced Mx1 gene is an important part of the mammalian defense against influenza viruses. Mus musculus Mx1 inhibits influenza A virus replication and transcription by suppressing the polymerase activity of viral ribonucleoproteins (vRNPs). Here, we compared the anti-influenza virus activity of Mx1 from Mus musculus A2G with that of its ortholog from Mus spretus. We found that the antiviral activity of M. spretus Mx1 was less potent than that of M. musculus Mx1. Comparison of the M. musculus Mx1 sequence with the M. spretus Mx1 sequence revealed 25 amino acid differences, over half of which were present in the GTPase domain and 2 of which were present in loop L4. However, the in vitro GTPase activity of Mx1 from the two mouse species was similar. Replacement of one of the residues in loop L4 in M. spretus Mx1 by the corresponding residue of A2G Mx1 increased its antiviral activity. We also show that deletion of loop L4 prevented the binding of Mx1 to influenza A virus nucleoprotein and, hence, abolished the antiviral activity of mouse Mx1. These results indicate that loop L4 of mouse Mx1 is a determinant of antiviral activity. Our findings suggest that Mx proteins from different mammals use a common mechanism to inhibit influenza A viruses.
  
  
  OBJECTIVE
  Mx proteins are evolutionarily conserved in vertebrates and inhibit a wide range of viruses. Still, the exact details of their antiviral mechanisms remain largely unknown. Functional comparison of the Mx genes from two species that diverged relatively recently in evolution can provide novel insights into these mechanisms. We show that both Mus musculus A2G Mx1 and Mus spretus Mx1 target the influenza virus nucleoprotein. We also found that loop L4 in mouse Mx1 is crucial for its antiviral activity, as was recently reported for primate MxA. This indicates that human and mouse Mx proteins, which have diverged by 75 million years of evolution, recognize and inhibit influenza A viruses by a common mechanism.
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
authors: Judith
authors: J
authors: Verhelst
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
authors: Jan
authors: J
authors: Spitaels
authors: Institute of Virology, University Medical Center Freiburg, Freiburg, Germany Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, Germany Faculty of Biology, University of Freiburg, Freiburg, Germany.
authors: Cindy
authors: C
authors: Nürnberger
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
authors: Dorien
authors: D
authors: De Vlieger
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
authors: Tine
authors: T
authors: Ysenbaert
authors: Institute of Virology, University Medical Center Freiburg, Freiburg, Germany.
authors: Peter
authors: P
authors: Staeheli
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.
authors: Walter
authors: W
authors: Fiers
authors: Medical Biotechnology Center, VIB, Ghent, Belgium Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium xavier.saelens@vib-ugent.be.
authors: Xavier
authors: X
authors: Saelens
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000998:Antiviral Agents / Q000276:immunology* / Q000494:pharmacology; D001483:Base Sequence; D005434:Flow Cytometry; D005822:Genetic Vectors / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D009980:Influenza A virus / Q000187:drug effects*; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D064547:Myxovirus Resistance Proteins / Q000235:genetics* / Q000276:immunology* / Q000494:pharmacology; D009698:Nucleoproteins / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D012044:Regression Analysis; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D000998:Antiviral Agents; C579070:Mx1 protein, mouse; D064547:Myxovirus Resistance Proteins; D009698:Nucleoproteins