KPNA2
Description
The KPNA2 (karyopherin subunit alpha 2) is a protein-coding gene located on chromosome 17.
Importin subunit alpha-1 is a protein that in humans is encoded by the KPNA2 gene. The import of proteins into the nucleus is a process that involves at least 2 steps. The first is an energy-independent docking of the protein to the nuclear envelope and the second is an energy-dependent translocation through the nuclear pore complex. Imported proteins require a nuclear localization sequence (NLS) which generally consists of a short region of basic amino acids or 2 such regions spaced about 10 amino acids apart. Proteins involved in the first step of nuclear import are members of the alpha importin family of karyopherins such as importin subunit alpha-1. These include the Xenopus protein importin and its yeast homolog, SRP1 (a suppressor of certain temperature-sensitive mutations of RNA polymerase I in Saccharomyces cerevisiae), which bind to the NLS. KPNA2 protein interacts with the NLSs of DNA helicase Q1 and SV40 T antigen and may be involved in the nuclear transport of proteins.
KPNA2, also known as Importin subunit alpha-1, functions as an adapter protein in nuclear protein import, specifically working with nuclear receptor KPNB1. It directly binds to substrates possessing either a simple or bipartite NLS motif. KPNB1 facilitates 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 NPC via an energy-dependent, Ran-mediated process. At the nucleoplasmic side of the NPC, Ran binds to importin-beta, causing the complex to dissociate. Importin-alpha and -beta are then re-exported back to the cytoplasm, where GTP hydrolysis releases Ran from importin. The asymmetric distribution of GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus is believed to dictate the directionality of nuclear import.
KPNA2 is also known as IPOA1, PTAC58, QIP2, RCH1, SRP1-alpha, SRP1alpha.
