title: The C terminus of the nuclear RAN/TC4 GTPase stabilizes the GDP-bound state and mediates interactions with RCC1, RAN-GAP, and HTF9A/RANBP1.
abstract: Ran/TC4 is a member of the Ras superfamily of GTPases. It is unusual in being predominantly nuclear and because it possesses an acidic -DEDDDL sequence instead of a consensus prenylation domain at the C terminus. Ran is required for nuclear protein import and cell cycle progression, and has been implicated in mRNA processing and export and DNA replication. The inhibition of cell cycle progression by a dominant gain-of-function mutant of Ran has been shown to be abrogated by removal of the -DEDDDL sequence, suggesting that this domain is essential for Ran function. We demonstrate here that the -DEDDDL sequence stabilizes GDP binding to Ran, and that the domain is required for high affinity interaction with a Ran-binding protein, HTF9A/RanBP1. HTF9A functions as a co-stimulator of Ran-GAP (GTPase activating protein) activity on wild-type Ran, but in the absence of the acidic C terminus of Ran, HTF9A behaves as a Ran-GAP inhibitor. An antibody directed against the C-terminal region preferentially recognizes the GTP-bound form of Ran, suggesting that this domain undergoes a nucleotide-dependent conformational change. The results suggest that the acidic C-terminal domain is important in modulating the interaction of Ran with regulatory factors, and implicate Ran-binding proteins in mediating the effects of Ran on cell cycle progression.
authors.affiliation: Department of Pathology, University of Vermont Medical College, Burlington 05405-0068, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Richards
authors.forename: K M
authors.initials: KM
authors.lastname: Lounsbury
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000201:enzymology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006868:Hydrolysis; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011506:Proteins / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D020931:ran GTP-Binding Protein; D020703:ras GTPase-Activating Proteins
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; D011506:Proteins; D016601:RNA-Binding Proteins; C091775:ran-binding protein 1; D020703:ras GTPase-Activating Proteins; D006153:Guanosine Diphosphate; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein