title: Identification of a conserved loop in Mog1 that releases GTP from Ran.
abstract: Ran regulates nuclear import and export pathways by coordinating the assembly and disassembly of transport complexes. These transport reactions are linked to the GTPase cycle and subcellular distribution of Ran. Mog1 is an evolutionarily conserved nuclear protein that binds RanGTP and stimulates guanine nucleotide release, suggesting Mog1 regulates the nuclear transport functions of Ran. In the present study, we have characterized the nuclear import pathway of Mog1, and we have defined the domain in Mog1 that stimulates GTP release from Ran. In permeabilized cells, nuclear import of Mog1 is independent of exogenously added factors, and is inhibited by wheat germ agglutinin, indicating that translocation of Mog1 involves physical interactions with the nuclear pore complex. In contrast to RanGEF, which is restricted to the nucleus, Mog1 shuttles between the nucleus and the cytoplasm. Single-point mutations in acidic residues of Mog1 (Asp25, Asp34, Glu37) dramatically reduce GTP release and Ran binding activity, whereas mutation of a single basic residue (Arg30) renders Mog1 hyperactive for GTP release. These mutations map within a conserved, solvent-exposed loop in Mog1 that is functionally similar to the beta-wedge used by RanGEF to promote nucleotide release from Ran. These data suggest that Mog1 and RanGEF use similar mechanisms to facilitate guanine nucleotide release from Ran.
authors.affiliation: Center for Cell Signaling, Department of Biochemistry and Molecular Genetics, and Cell and Molecular Biology Program, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Steggerda
authors.forename: B M
authors.initials: BM
authors.lastname: Paschal
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D017931:DNA Primers; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014909:Wheat Germ Agglutinins / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; D014909:Wheat Germ Agglutinins; C498736:Rangnrf protein, mouse; D020931:ran GTP-Binding Protein