Importin-beta is a GDP-to-GTP exchange factor of Ran: implications for the mechanism of nuclear import. 2009

Thierry G Lonhienne, and Jade K Forwood, and Mary Marfori, and Gautier Robin, and Bostjan Kobe, and Bernard J Carroll
Australian Research Council Centre of Excellence for Integrative Legume Research, School of Chemistry and Molecular Biosciences, University of Queensland, QLD 4072, St. Lucia, Australia. t.lonhienne@uq.edu.au

Ran-GTP interacts strongly with importin-beta, and this interaction promotes the release of the importin-alpha-nuclear localization signal cargo from importin-beta. Ran-GDP also interacts with importin-beta, but this interaction is 4 orders of magnitude weaker than the Ran-GTP.importin-beta interaction. Here we use the yeast complement of nuclear import proteins to show that the interaction between Ran-GDP and importin-beta promotes the dissociation of GDP from Ran. The release of GDP from the Ran-GDP-importin-beta complex stabilizes the complex, which cannot be dissociated by importin-alpha. Although Ran has a higher affinity for GDP compared with GTP, Ran in complex with importin-beta has a higher affinity for GTP. This feature is responsible for the generation of Ran-GTP from Ran-GDP by importin-beta. Ran-binding protein-1 (RanBP1) activates this reaction by forming a trimeric complex with Ran-GDP and importin-beta. Importin-alpha inhibits the GDP exchange reaction by sequestering importin-beta, whereas RanBP1 restores the GDP nucleotide exchange by importin-beta by forming a tetrameric complex with importin-beta, Ran, and importin-alpha. The exchange is also inhibited by nuclear-transport factor-2 (NTF2). We suggest a mechanism for nuclear import, additional to the established RCC1 (Ran-guanine exchange factor)-dependent pathway that incorporates these results.

UI MeSH Term Description Entries
D009687 Nuclear Proteins Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus. Nucleolar Protein,Nucleolar Proteins,Nuclear Protein,Protein, Nuclear,Protein, Nucleolar,Proteins, Nuclear,Proteins, Nucleolar
D011485 Protein Binding The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments. Plasma Protein Binding Capacity,Binding, Protein
D002850 Chromatography, Gel Chromatography on non-ionic gels without regard to the mechanism of solute discrimination. Chromatography, Exclusion,Chromatography, Gel Permeation,Chromatography, Molecular Sieve,Gel Filtration,Gel Filtration Chromatography,Chromatography, Size Exclusion,Exclusion Chromatography,Gel Chromatography,Gel Permeation Chromatography,Molecular Sieve Chromatography,Chromatography, Gel Filtration,Exclusion Chromatography, Size,Filtration Chromatography, Gel,Filtration, Gel,Sieve Chromatography, Molecular,Size Exclusion Chromatography
D002851 Chromatography, High Pressure Liquid Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed. Chromatography, High Performance Liquid,Chromatography, High Speed Liquid,Chromatography, Liquid, High Pressure,HPLC,High Performance Liquid Chromatography,High-Performance Liquid Chromatography,UPLC,Ultra Performance Liquid Chromatography,Chromatography, High-Performance Liquid,High-Performance Liquid Chromatographies,Liquid Chromatography, High-Performance
D006153 Guanosine Diphosphate A guanine nucleotide containing two phosphate groups esterified to the sugar moiety. GDP,Guanosine 5'-Diphosphate,Guanosine 5'-Trihydrogen Diphosphate,5'-Diphosphate, Guanosine,5'-Trihydrogen Diphosphate, Guanosine,Diphosphate, Guanosine,Diphosphate, Guanosine 5'-Trihydrogen,Guanosine 5' Diphosphate,Guanosine 5' Trihydrogen Diphosphate
D006160 Guanosine Triphosphate Guanosine 5'-(tetrahydrogen triphosphate). A guanine nucleotide containing three phosphate groups esterified to the sugar moiety. GTP,Triphosphate, Guanosine
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D020662 Guanine Nucleotide Exchange Factors Protein factors that promote the exchange of GTP for GDP bound to GTP-BINDING PROTEINS. GDP Exchange Factors,GDP-GTP Reversing Factors,Guanine Nucleotide Releasing Factors,GDP Dissociation Factor,GDP Dissociation Stimulators,GDP-GTP Exchange Protein,Guanine Nucleotide Exchange Factor,Guanine-Nucleotide-Releasing Factor,Exchange Factors, GDP,Factors, GDP Exchange,Factors, GDP-GTP Reversing,GDP GTP Exchange Protein,GDP GTP Reversing Factors,Guanine Nucleotide Releasing Factor,Reversing Factors, GDP-GTP
D020931 ran GTP-Binding Protein A monomeric GTP-binding protein involved in nucleocytoplasmic transport of proteins into the nucleus and RNA into the cytoplasm. This enzyme was formerly listed as EC 3.6.1.47. TC4 Protein,ran Protein,ran Proteins,ras-Related Nuclear Protein,GTP-Binding Protein, ran,Nuclear Protein, ras-Related,ran GTP Binding Protein,ras Related Nuclear Protein
D021581 Active Transport, Cell Nucleus Gated transport mechanisms by which proteins or RNA are moved across the NUCLEAR MEMBRANE. Nuclear Export,Nuclear Import,Nuclear Transport,Nucleocytoplasmic Transport,Nucleo-cytoplasmic Transport,Export, Nuclear,Import, Nuclear,Nucleo cytoplasmic Transport,Transport, Nuclear,Transport, Nucleo-cytoplasmic,Transport, Nucleocytoplasmic,Transports, Nucleo-cytoplasmic

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