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

Here we present the crystal structure of Importin-β(1-462) · Ran · GTP · RanBD1ΔN 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-β. We could identify a pair of amino acids which - upon mutation - weaken the interaction between Ran and Importin-β specifically to allow dissociation without RanBD. These findings support the hypothesis that a ternary complex of Importin-β · Ran · GTP · RanBD exists in the final step of the export of Importin-β from the nucleus and that interaction of the N-terminus of RanBD with Ran plays a crucial role in disassembly of this complex.