IPO5
Description
The IPO5 (importin 5) is a protein-coding gene located on chromosome 13.
Importin-5 is a protein that in humans is encoded by the IPO5 gene. The protein encoded by this gene is a member of the importin beta family. Structurally, the protein adopts the shape of a right hand solenoid and is composed of 24 HEAT repeats.
== Function == Nuclear transport, a signal- and energy-dependent process, takes place through nuclear pore complexes embedded in the nuclear envelope. The import of proteins containing a nuclear localization signal (NLS) requires the NLS import receptor, a heterodimer of importin alpha and beta subunits also known as karyopherins. 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. IPO5 facilitates cytoplasmic polyadenylation element-binding protein (CPEB)3 translocation by binding to RRM1 motif of CPEB3 in neurons.
IPO5 functions as a nuclear transport receptor, facilitating the movement of proteins into the nucleus. It recognizes and binds to nuclear localization signals (NLS) present on cargo proteins, forming a complex that docks at the nuclear pore complex (NPC). This docking is mediated through interactions with nucleoporins. The importin/substrate complex then translocates through the NPC via an energy-dependent, Ran-mediated mechanism. Once inside the nucleus, Ran binds to the importin, leading to the dissociation of the complex and the re-export of the importin back to the cytoplasm. This directional movement is regulated by the differential distribution of Ran in its GTP- and GDP-bound forms between the cytoplasm and nucleus. Specifically, IPO5 is known to mediate the nuclear import of ribosomal proteins RPL23A, RPS7, and RPL5, and in vitro studies have shown its involvement in importing histones H2A, H2B, H3, and H4. Furthermore, IPO5 binds to CPEB3, facilitating its nuclear import following neuronal stimulation. In the context of HIV-1 infection, IPO5 binds to and mediates the nuclear import of HIV-1 Rev. These interactions highlight the diverse roles of IPO5 in nuclear transport and its potential involvement in various cellular processes.
IPO5 is also known as IMB3, KPNB3, Pse1, RANBP5, imp5.
