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importin alpha-1 subunit (karyopherin alpha-1 subunit, KPNA1, suppressor of RNA polymerase 1 mutation, SRP1, SRP1-beta, recombination activating gene (RAG) cohort protein 2, RCH2, nucleoprotein interactor 1, NPI-1)
Function:
- nuclear protein import as an adapter protein for nuclear receptor KPNB1
- binds specifically & directly to substrates containing either a simple or bipartite NLS motif
- docking of the importin/substrate complex to the nuclear pore complex is mediated by KPNB1 through binding to nucleoporin FxFG repeats
- the complex is subsequently translocated through the pore by an energy requiring, Ran- dependent mechanism
- at the nucleoplasmic side of the nuclear pore complex, Ran binds to importin-beta & the 3 components separate
- importin-alpha & importin-beta are re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran from importin
- directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- & GDP-bound forms of Ran between the cytoplasm & nucleus
- forms a complex with importin subunit beta-1
- found in a complex with CSE1L/XPO2, Ran & KPNA2
- interacts with CSE1L/XPO2 & NBN
- interacts with ANP32E (putative)
- forms a complex with importin subunit beta-1
Structure:
- consists of
a) N-terminal hydrophilic region
b) hydrophobic central region composed of 10 repeats
c) short hydrophilic C-terminus
- N-terminal hydrophilic region contains the importin beta binding domain (IBB domain), which is sufficient for binding importin beta & essential for nuclear protein import
- the IBB domain is thought to act as an intrasteric autoregulatory sequence by interacting with the internal autoinhibitory NLS
- binding of KPNB1 probably overlaps the internal NLS & contributes to a high affinity for cytoplasmic NLS- containing cargo substrates
- after dissociation of the importin/substrate complex in the nucleus, the internal autohibitory NLS contributes to a low affinity for nuclear NLS- containing proteins (putative)
- the major & minor NLS binding sites
a) mainly involved in recognition of simple or bipartite NLS motifs
b) structurally located within in a helical surface groove
c) they contain several conserved Trp & Asn of the corresponding 3rd helices (H3) of ARM repeats which mainly contribute to binding
- belongs to the importin alpha family
- contains 10 ARM repeats
- contains 1 IBB domain
Compartment: cytoplasm. nucleus
Expression: expressed ubiquitously
Pathology:
- in vitro, mediates nuclear import of human cytomegalovirus UL84 by recognizing a non-classical NLS
- interacts with the nucleoprotein of influenza A viruses
- binds to HCMV (human cytomegalovirus) UL84, HIV-1 Vpr & to ebolavirus VP24
General
phosphoprotein
protein subunit
Properties
SIZE: entity length = 538 aa
MW = 60 kD
COMPARTMENT: cytoplasm
cell nucleus
MOTIF: IBB {1-57}
MOTIF: Thr phosphorylation site {T3}
arginine-rich region {25-28}
MOTIF: arginine residue (SEVERAL)
nuclear translocation signal {42-51}
ARM repeat {77-117}
ARM repeat {118-161}
NLS binding site (major) {149-241}
MOTIF: ARM repeat {162-206}
ARM repeat {207-245}
Binding to RAG1 {245-437}
MOTIF: ARM repeat {246-290}
ARM repeat {291-330}
NLS binding site (minor) {318-406}
ARM repeat {331-372}
ARM repeat {373-412}
ARM repeat {413-457}
ARM repeat {460-504}
Database Correlations
OMIM 600686
UniProt P52294
Entrez Gene 3836
Kegg hsa:3836
References
- Nigg EA, Baeuerle PA, Luhrmann R.
Nuclear import-export: in search of signals and mechanisms.
Cell. 1991 Jul 12;66(1):15-22. Review. No abstract available.
PMID: 1712670
- Vandromme M et al
Regulation of transcription factor localization: fine-tuning
of gene expression.
Trends Biochem Sci. 1996 Feb;21(2):59-64. Review.
PMID: 8851662
- UniProt :accession P52294