The importin beta binding domain modulates the avidity of importin beta for the nuclear pore complex

J Biol Chem. 2010 Apr 30;285(18):13769-80. doi: 10.1074/jbc.M109.095760. Epub 2010 Mar 1.


Importin beta mediates active passage of cellular substrates through the nuclear pore complex (NPC). Adaptors such as importin alpha and snurportin associate with importin beta via an importin beta binding (IBB) domain. The intrinsic structural flexibility of importin beta allows its concerted interactions with IBB domains, phenylalanine-glycine nucleoporins, and the GTPase Ran during transport. In this paper, we provide evidence that the nature of the IBB domain modulates the affinity of the import complex for the NPC. In permeabilized cells, importin beta imports a cargo fused to the snurportin IBB (sIBB) with approximately 70% reduced energy requirement as compared with the classical importin alpha IBB. At the molecular level, this is explained by approximately 200-fold reduced affinity of importin beta for Nup62, when bound to the sIBB. Consistently, in vivo, the importin beta.sIBB complex has greatly reduced persistence inside the central channel of the NPC. We propose that by controlling the degree of strain in the tertiary structure of importin beta, the IBB domain modulates the affinity of the import complex for nucleoporins, thus dictating its persistence inside the NPC.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • HeLa Cells
  • Humans
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism
  • Nuclear Pore / genetics
  • Nuclear Pore / metabolism*
  • Nuclear Pore Complex Proteins
  • Protein Structure, Tertiary
  • RNA Cap-Binding Proteins / genetics
  • RNA Cap-Binding Proteins / metabolism
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • alpha Karyopherins / genetics
  • alpha Karyopherins / metabolism
  • beta Karyopherins / genetics
  • beta Karyopherins / metabolism*
  • ran GTP-Binding Protein / genetics
  • ran GTP-Binding Protein / metabolism


  • Membrane Glycoproteins
  • Nuclear Pore Complex Proteins
  • RAN protein, human
  • RNA Cap-Binding Proteins
  • Receptors, Cytoplasmic and Nuclear
  • SNUPN protein, human
  • alpha Karyopherins
  • beta Karyopherins
  • nuclear pore protein p62
  • ran GTP-Binding Protein