A molecular switch between alternative conformational states in the complex of Ran and importin beta1

Nat Struct Biol. 2003 Jul;10(7):553-7. doi: 10.1038/nsb940.


Several million macromolecules are exchanged each minute between the nucleus and cytoplasm by receptor-mediated transport. Most of this traffic is controlled by the small GTPase Ran, which regulates assembly and disassembly of the receptor-cargo complexes in the appropriate cellular compartment. Here we applied dynamic force spectroscopy to study the interaction of Ran with the nuclear import receptor importin beta1 (impbeta) at the single-molecule level. We found that the complex alternates between two distinct conformational states of different adhesion strength. The application of an external mechanical force shifts equilibrium toward one of these states by decreasing the height of the interstate activation energy barrier. The other state can be stabilized by a functional Ran mutant that increases this barrier. These results support a model whereby functional control of Ran-impbeta is achieved by a population shift between pre-existing alternative conformations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Guanosine Diphosphate / metabolism
  • Guanosine Triphosphate / metabolism
  • Microscopy, Atomic Force
  • Protein Binding
  • Protein Conformation
  • beta Karyopherins / chemistry*
  • beta Karyopherins / metabolism
  • ran GTP-Binding Protein / chemistry*
  • ran GTP-Binding Protein / metabolism


  • KPNB1 protein, human
  • beta Karyopherins
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • ran GTP-Binding Protein