title: Restriction of HIV-1 Requires the N-Terminal Region of MxB as a Capsid-Binding Motif but Not as a Nuclear Localization Signal.
abstract: The interferon alpha (IFN-α)-inducible restriction factor MxB blocks HIV-1 infection after reverse transcription but prior to integration. Fate-of-capsid experiments have correlated the ability of MxB to block HIV-1 infection with stabilization of viral cores during infection. We previously demonstrated that HIV-1 restriction by MxB requires capsid binding and oligomerization. Deletion and gain-of-function experiments have mapped the HIV-1 restriction ability of MxB to its N-terminal 25 amino acids. This report reveals that the N-terminal 25 amino acids of MxB exhibit two separate functions: (i) the ability of MxB to bind to HIV-1 capsid and (ii) the nuclear localization signal of MxB, which is important for the ability of MxB to shuttle into the nucleus. To understand whether MxB restriction of HIV-1 requires capsid binding and/or nuclear localization, we genetically separated these two functions and evaluated their contributions to restriction. Our experiments demonstrated that the (11)RRR(13) motif is important for the ability of MxB to bind capsid and to restrict HIV-1 infection. These experiments suggested that capsid binding is necessary for the ability of MxB to block HIV-1 infection. Separately from the capsid binding function of MxB, we found that residues (20)KY(21) regulate the ability of the N-terminal 25 amino acids of MxB to function as a nuclear localization signal; however, the ability of the N-terminal 25 amino acids to function as a nuclear localization signal was not required for restriction.
  
  
  OBJECTIVE
  MxB/Mx2 blocks HIV-1 infection in cells from the immune system. MxB blocks infection by preventing the uncoating process of HIV-1. The ability of MxB to block HIV-1 infection requires that MxB binds to the HIV-1 core by using its N-terminal domain. The present study shows that MxB uses residues (11)RRR(13) to bind to the HIV-1 core during infection and that these residues are required for the ability of MxB to block HIV-1 infection. We also found that residues (20)KY(21) constitute a nuclear localization signal that is not required for the ability of MxB to block HIV-1 infection.
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Bianca
authors.initials: B
authors.lastname: Schulte
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Cindy
authors.initials: C
authors.lastname: Buffone
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Silvana
authors.initials: S
authors.lastname: Opp
authors.affiliation: Institut Pasteur, Unité Virus et Immunité, CNRS 3015, Paris, France.
authors.forename: Francesca
authors.initials: F
authors.lastname: Di Nunzio
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Daniel Augusto
authors.initials: DA
authors.lastname: De Souza Aranha Vieira
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Alberto
authors.initials: A
authors.lastname: Brandariz-Nuñez
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA Felipe.Diaz-Griffero@einstein.yu.edu.
authors.forename: Felipe
authors.initials: F
authors.lastname: Diaz-Griffero
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D015153:Blotting, Western; D002213:Capsid / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D019084:Fluorescent Antibody Technique, Indirect; D005822:Genetic Vectors / Q000235:genetics; D015658:HIV Infections / Q000378:metabolism / Q000517:prevention & control*; D015497:HIV-1 / Q000378:metabolism*; D006801:Humans; D008156:Luciferases; D064547:Myxovirus Resistance Proteins / Q000235:genetics / Q000378:metabolism*; D019913:Nuclear Localization Signals / Q000235:genetics; D011485:Protein Binding; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; C579068:MX2 protein, human; D064547:Myxovirus Resistance Proteins; D019913:Nuclear Localization Signals; D008156:Luciferases