title: Structural basis for nuclear import complex dissociation by RanGTP.
abstract: Nuclear protein import is mediated mainly by the transport factor importin-beta that binds cytoplasmic cargo, most often via the importin-alpha adaptor, and then transports it through nuclear pore complexes. This active transport is driven by disassembly of the import complex by nuclear RanGTP. The switch I and II loops of Ran change conformation with nucleotide state, and regulate its interactions with nuclear trafficking components. Importin-beta consists of 19 HEAT repeats that are based on a pair of antiparallel alpha-helices (referred to as the A- and B-helices). The HEAT repeats stack to yield two C-shaped arches, linked together to form a helicoidal molecule that has considerable conformational flexibility. Here we present the structure of full-length yeast importin-beta (Kap95p or karyopherin-beta) complexed with RanGTP, which provides a basis for understanding the crucial cargo-release step of nuclear import. We identify a key interaction site where the RanGTP switch I loop binds to the carboxy-terminal arch of Kap95p. This interaction produces a change in helicoidal pitch that locks Kap95p in a conformation that cannot bind importin-alpha or cargo. We suggest an allosteric mechanism for nuclear import complex disassembly by RanGTP.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Rd, Cambridge CB2 2QH, UK.
authors.forename: Soo Jae
authors.initials: SJ
authors.lastname: Lee
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Matsuura
authors.forename: Sai Man
authors.initials: SM
authors.lastname: Liu
authors.forename: Murray
authors.initials: M
authors.lastname: Stewart
mesh_terms: D021581:Active Transport, Cell Nucleus; D000494:Allosteric Regulation; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae; D013329:Structure-Activity Relationship; D028961:beta Karyopherins / Q000737:chemistry* / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein