Importin subunit beta-1

Importin subunit beta-1 (KPNB1) is a core component of the nuclear import machinery that mediates the transport of proteins into the nucleus. It functions both as an adapter-independent nuclear transport receptor and as a partner to importin-alpha, recognizing nuclear localization signals (NLS) on cargo proteins and docking complexes at the nuclear pore through interactions with FxFG repeat-containing nucleoporins (UniProt: Q14974). The protein catalyzes Ran-GTP-dependent translocation across the nuclear envelope and participates in importing diverse substrates including ribosomal proteins, histones, and transcription factors.

KPNB1 is ubiquitously expressed and plays a fundamental housekeeping role in nucleocytoplasmic trafficking. Its substrates include regulatory proteins such as MRTFA, SNAI1, and PRKCI, linking nuclear import to gene expression control (UniProt: Q14974). The protein is also exploited by HIV-1 for nuclear import of the viral Rev protein during infection.

In Alzheimer's disease, KPNB1 shows ambiguous regulation across subcellular brain fractions, with a mean log2 fold-change of −0.11 relative to age-matched controls in post-mortem tissue analyzed by quantitative proteomics (Chaparral AD proteomics). This modest, variable signal suggests either subtle dysregulation or compartment-specific changes that warrant further investigation into whether nuclear import deficits contribute to AD pathogenesis.