Structural and biochemical characterization of the Importin-β • Ran • GTP • RanBD1 complex

Here we present the crystal structure of Importin-beta(1-462) center dot Ran center dot GTP center dot RanBDIAN as solved by molecular replacement. HPLC dissociation measurements on this complex show, that the N-terminus of RanBD may be involved in the release of the hydrolysis- and dissociation-block of Ran by Transportin/Importin-beta. We could identify a pair of amino acids which - upon mutation - weaken the interaction between Ran and Importin-beta specifically to allow dissociation without RanBD. These findings support the hypothesis that a ternary complex of Importin-beta center dot Ran center dot GTP center dot RanBD exists in the final step of the export of Importin-beta from the nucleus and that interaction of the N-terminus of RanBD with Ran plays a crucial role in disassembly of this complex. (c) 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.