Npap60/Nup50 Is a Tri-Stable Switch That Stimulates Importin-Alpha:beta-Mediated Nuclear Protein Import

Cell. 2002 Aug 9;110(3):349-60. doi: 10.1016/s0092-8674(02)00836-x.

Abstract

Many nuclear-targeted proteins are transported through the nuclear pore complex (NPC) by the importin-alpha:beta receptor. We now show that Npap60 (also called Nup50), a protein previously believed to be a structural component of the NPC, is a Ran binding protein and a cofactor for importin-alpha:beta-mediated import. Npap60 is a tri-stable switch that alternates between binding modes. The C terminus binds importin-beta through RanGTP. The N terminus binds the C terminus of importin-alpha, while a central domain binds importin-beta. Npap60:importin-alpha:beta binds cargo and can stimulate nuclear import. Endogenous Npap60 can shuttle and is accessible from the cytoplasmic side of the nuclear envelope. These results identify Npap60 as a cofactor for importin-alpha:beta nuclear import and as a previously unidentified subunit of the importin complex.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Active Transport, Cell Nucleus / genetics*
  • Cell Compartmentation / physiology
  • Cellular Apoptosis Susceptibility Protein / genetics
  • Cellular Apoptosis Susceptibility Protein / metabolism
  • Cytoplasm / genetics
  • Cytoplasm / metabolism
  • Dimerization
  • Eukaryotic Cells / cytology
  • Eukaryotic Cells / metabolism*
  • GTPase-Activating Proteins / genetics
  • GTPase-Activating Proteins / metabolism
  • HeLa Cells
  • Humans
  • Macromolecular Substances
  • Molecular Structure
  • Nuclear Pore / genetics
  • Nuclear Pore / metabolism*
  • Nuclear Pore Complex Proteins / genetics
  • Nuclear Pore Complex Proteins / metabolism*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Binding / genetics
  • Protein Structure, Tertiary / genetics
  • Signal Transduction / genetics
  • alpha Karyopherins / genetics
  • alpha Karyopherins / metabolism*
  • beta Karyopherins / genetics
  • beta Karyopherins / metabolism*
  • ran GTP-Binding Protein / genetics
  • ran GTP-Binding Protein / metabolism

Substances

  • Cellular Apoptosis Susceptibility Protein
  • GTPase-Activating Proteins
  • KPNB1 protein, human
  • Macromolecular Substances
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • RANGAP1 protein, human
  • alpha Karyopherins
  • beta Karyopherins
  • karyopherin alpha 2
  • ran-binding protein 1
  • ran GTP-Binding Protein