KPNA3
Description
The KPNA3 (karyopherin subunit alpha 3) is a protein-coding gene located on chromosome 13.
KPNA3, also known as karyopherin subunit alpha-3, is a human protein encoded by the KPNA3 gene. It plays a critical role in the transport of molecules between the nucleus and the cytoplasm. Eukaryotic cells utilize the nuclear pore complex (NPC), a large structure composed of 60-100 proteins, to facilitate this transport. Small molecules can passively diffuse through the NPC, while larger molecules require active transport. Most nuclear proteins contain nuclear localization signals (NLSs), short sequences of basic amino acids that facilitate their import into the nucleus. KPNA3 shares similarities with nuclear transport proteins in Xenopus and humans, suggesting its involvement in the nuclear transport system. KPNA3 has been shown to interact with KPNB1, another protein involved in nuclear transport.
KPNA3 is involved in the nuclear import of proteins. It acts as an adapter protein for the nuclear receptor KPNB1, binding specifically to substrates containing either a simple or bipartite NLS motif. The complex formed by KPNA3, its substrate, and KPNB1 docks to the nuclear pore complex (NPC) through KPNB1's interaction with nucleoporin FxFG repeats. This complex is then transported through the NPC in a Ran-dependent manner, requiring energy. Once inside the nucleus, Ran binds to KPNB1, causing the complex to disassemble. KPNA3 and KPNB1 are then exported back to the cytoplasm, where GTP hydrolysis releases Ran from KPNB1. This process is facilitated by an uneven distribution of Ran in its GTP- and GDP-bound forms between the cytoplasm and nucleus. In addition to its role in general nuclear import, KPNA3 has been shown to mediate the nuclear import of specific viral proteins, including human cytomegalovirus UL84 (recognizing a non-classical NLS) and influenza A virus nucleoprotein (likely through ARM repeats 7-9).
KPNA3 is also known as IPOA4, SPG88, SRP1, SRP1gamma, SRP4, hSRP1.
