Karyopherin Beta


Number of Polypeptide Chains in the Protein:   2

Chain Designation:  

Chain 1: A; Chain 2: B

Gene Names:  


PDB Deposition Title:  

Structure Of Importin Beta Bound To The IBB Domain Of Importin Alpha

Primary Citation Title:  

Structure of importin-beta bound to the IBB domain of importin-alpha

Citation Authors:  

Cingolani, G., Petosa, C., Weis, K., Muller, C.W

Citation Journal:  

(1999) Nature 399: 221-229

Related PDB Entries:  

1F59, 1IBR, 1M5N, 1O6O, 1O6P


Information for Chain A;  UniprotKB Accession Number:  Q14974

Primary Structure

Length of the Chain (from Uniprot Q14974):  876

FASTA Sequence for the chain (from Uniprot Q14974):

>sp|Q14974|IMB1_HUMAN Importin subunit beta-1 OS=Homo sapiens GN=KPNB1 PE=1 SV=2

Secondary Structures (DSSP defined; from RCSB PDB)

Helical Structures:  Number of Helices:  61;  Percentage of Residues:  76

Beta Strands:  Number of Strands:  0;  Percentage of Residues:  0

Secondary Structure Map:


Tertiary Structure

Number of Domains Along Chain A:  1

CATH Domain IDs:  A00

CATH Classes:  A00: Mainly Alpha

CATH Architectures:  A00: Alpha Horshoe

CATH Topologies:  A00: Leucine-rich Repeat Variant

Topological Diagrams:



Function and Ligand Binding Site

Excerpt from Abstract:

Cytosolic proteins bearing a classical nuclear localization signal enter the nucleus bound to a heterodimer of importin-alpha and importin-beta (also called karyopherin-alpha and -beta).

Description of Function from Uniprot:

Functions in nuclear protein import, either in association with an adapter protein, like an importin-alpha subunit, which binds to nuclear localization signals (NLS) in cargo substrates, or by acting as autonomous nuclear transport receptor. Acting autonomously, serves itself as NLS receptor. Docking of the importin/substrate complex to the nuclear pore complex (NPC) is mediated by KPNB1 through binding to nucleoporin FxFG repeats and the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin-beta and the three components separate and importin-alpha and -beta are re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran from importin. The directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Mediates autonomously the nuclear import of ribosomal proteins RPL23A, RPS7 and RPL5. Binds to a beta-like import receptor binding (BIB) domain of RPL23A. In association with IPO7 mediates the nuclear import of H1 histone. In vitro, mediates nuclear import of H2A, H2B, H3 and H4 histones. In case of HIV-1 infection, binds and mediates the nuclear import of HIV-1 Rev. Imports SNAI1 and PRKCI into the nucleus.

Selected Molecular Function GO Terms:

GO ID: 0008139, Name: Nuclear Localization Sequence Binding, Definition: Interacting selectively and non-covalently with a nuclear localization sequence, a specific peptide sequence that acts as a signal to localize the protein within the nucleus.


GO ID: 0008536, Name: Ran GTPase Binding, Definition: Interacting selectively and non-covalently with Ran, a conserved Ras-like GTP-binding protein, implicated in nucleocytoplasmic transport, cell cycle progression, spindle assembly, nuclear organization and nuclear envelope (NE) assembly.


GO ID: 0008565, Name: Protein Transporter Activity, Definition: Enables the directed movement of proteins into, out of or within a cell, or between cells.

EC Number:   N/A

EC Description:   


Major Organic Ligand:   Importin Alpha

Ligand Binding Residues:

Glu 281, Asp 288, Asp 339, Asp 340, Asp 426, Thr 426, Asn 469, Glu 530, Arg 593, Asp 627, Asp 676, Glu 767

Ligand Binding Site: