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A study reports the first comprehensive investigation of the molecular dynamics of the C-terminus of membrane-associated full-length lapidated Ras protein determined by solid-state nuclear molecular resonance. The C-terminus of Ras shows a versatile dynamics with segmental fluctuations and axially symmetric overall motions on the membrane surface.

Structural and kinetic requirements for interaction of Ran with the Ran-binding domains from RanBP2 and importin-beta are discussed. It appears that the C-terminus of Ran acts like a loose tether in Ran.GTP complexes of importins or exportins leaving the nucleus. The flag is recognized by the multiple RanBDis at or near the nuclear pore complex. That makes efficient disassembly of the Ran.GTP complexes possible.

The crystal structure of the complex of the first Ran-binding domain of human Ran-binding protein 2 (RanBP2) with Ran bound to a non-hydrolysable GTP analogue indicates a molecular mechanism to explain the function of RanBPs in nuclear transport. It is likely that the main function of Ran-binding domains is to sequester the C-terminal extension of Ran. There is currently no structural model for Ran-transport-factor complexes, and this makes it hard to identify the function of RanBPs as a 'dissociator' of nuclear-export complexes.