Importin subunit beta-1 is a protein that in humans is encoded by the KPNB1 gene.
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.
In neurons of the peripheral nervous system, Importin ò1 has an additional role in retrograde injury signaling. Following axonal injury, Importin ò1 mRNA undergoes local translation within axons, contributing to the formation of signaling complexes that are transported retrogradely to the cell body. This localized protein synthesis enables Importin ò1 to participate in cytoplasmic injury-response pathways independently of its essential housekeeping functions in nucleocytoplasmic transport. An axon-localizing element within the 3â² untranslated region (UTR) of the Importin ò1 transcript has been identified as necessary for its selective localization and translation in axons. Subcellular depletion of Importin ò1 from axons of peripheral neurons attenuates injury-induced signaling to the cell body and delays functional recovery, demonstrating that local translation of Importin ò1 is required for efficient retrograde signaling in injured neurons. Similarly, subcellular depletion of the importin ò1 3â²UTR causes hippocampus-dependent memory deficits in mice, specific alteration of presynaptic long-term potentiation, and reduced local protein synthesis at mossy fiber terminals, revealing additional non-canonical roles for axonal importin ò1 in presynaptic organization beyond growth and regeneration, for the establishment and long-term maintenance of neuronal circuits.
KPNB1 has been shown to interact with: