title: Structure of the nuclear transport complex karyopherin-beta2-Ran x GppNHp.
abstract: Transport factors in the karyopherin-beta (also called importin-beta) family mediate the movement of macromolecules in nuclear-cytoplasmic transport pathways. Karyopherin-beta2 (transportin) binds a cognate import substrate and targets it to the nuclear pore complex. In the nucleus, Ran x GTP binds karyopherin-beta2 and dissociates the substrate. Here we present the 3.0 A structure of the karyopherin-beta2-Ran x GppNHp complex where GppNHp is a non-hydrolysable GTP analogue. Karyopherin-beta2 contains eighteen HEAT repeats arranged into two continuous orthogonal arches. Ran is clamped in the amino-terminal arch and substrate-binding activity is mapped to the carboxy-terminal arch. A large loop in HEAT repeat 7 spans both arches. Interactions of the loop with Ran and the C-terminal arch implicate it in GTPase-mediated dissociation of the import-substrate. Ran x GppNHp in the complex shows extensive structural rearrangement, compared to Ran GDP, in regions contacting karyopherin-beta2. This provides a structural basis for the specificity of the karyopherin-beta family for the GTP-bound state of Ran, as well as a rationale for interactions of the karyopherin-Ran complex with the regulatory proteins ranGAP, ranGEF and ranBP1.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10021, USA.
authors.forename: Y M
authors.initials: YM
authors.lastname: Chook
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D028884:Karyopherins; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D020931:ran GTP-Binding Protein
chemical_list: D028884:Karyopherins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein