KPNB1
Description
The KPNB1 (karyopherin subunit beta 1) is a protein-coding gene located on chromosome 17.
Importin subunit beta-1 is a protein that in humans is encoded by the KPNB1 gene.
== Function == Nucleocytoplasmic transport, a signal- and energy-dependent process, takes place through nuclear pore complexes embedded in the nuclear envelope. The import of proteins containing a classical nuclear localization signal (NLS) requires the NLS import receptor, a heterodimer of importin alpha and beta subunits. Each of these subunits are part of the karyopherin family of proteins. Importin alpha binds the NLS-containing cargo in the cytoplasm and importin beta docks the complex at the cytoplasmic side of the nuclear pore complex. In the presence of nucleoside triphosphates and the small GTP binding protein Ran, the complex moves into the nuclear pore complex and the importin subunits dissociate. Importin alpha enters the nucleoplasm with its passenger protein and importin beta remains at the pore. Interactions between importin beta and the FG repeats of nucleoporins are essential in translocation through the pore complex. The protein encoded by this gene is a member of the importin beta family.
KPNB1, also known as Importin-90, Karyopherin subunit beta-1, Nuclear factor p97, or Pore targeting complex 97 kDa subunit, plays a crucial role in nuclear protein import. It can function either in association with an adapter protein like importin-alpha, which binds to nuclear localization signals (NLS) in cargo substrates, or autonomously as a nuclear transport receptor. In its autonomous role, KPNB1 itself serves as an NLS receptor. KPNB1 mediates the docking of the importin/substrate complex to the nuclear pore complex (NPC) by binding to nucleoporin FxFG repeats. The complex is then translocated through the pore via an energy-requiring, Ran-dependent mechanism. Upon reaching the nucleoplasmic side of the NPC, Ran binds to importin-beta, leading to the separation of the three components. Importin-alpha and -beta are re-exported from the nucleus to the cytoplasm, where GTP hydrolysis releases Ran from importin. This asymmetric distribution of GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus is believed to dictate the directionality of nuclear import. KPNB1 autonomously mediates the nuclear import of ribosomal proteins RPL23A, RPS7, and RPL5. In conjunction with IPO7, it facilitates the nuclear import of H1 histone. In vitro studies show its involvement in the nuclear import of histones H2A, H2B, H3, and H4. In the context of HIV-1 infection, KPNB1 binds and mediates the nuclear import of HIV-1 Rev. It also imports SNAI1 and PRKCI into the nucleus.
KPNB1 is also known as IMB1, IPO1, IPOB, Impnb, NTF97.
