Summary: Importin-beta N-terminal domain
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Importin Edit Wikipedia article
|Importin beta binding domain|
mouse importin alpha-nucleoplasmin nls peptide complex
|Importin-beta N-terminal domain|
structure of the karyopherin beta2-ran gppnhp nuclear transport complex
Importin is a type of protein that moves other protein molecules into the nucleus by binding to a specific recognition sequence, called the nuclear localization signal (NLS). Importin is classified as a karyopherin.
Importin has two subunits, importin α and importin β. Members of the importin-beta family can bind and transport cargo by themselves, or can form heterodimers with importin-alpha. As part of a heterodimer, importin-beta mediates interactions with the pore complex, while importin-alpha acts as an adaptor protein to bind the nuclear localisation signal (NLS) on the cargo through the classical NLS import of proteins. The NLS-Importin α-Importin β trimer dissociates after binding to Ran GTP inside the nucleus. Proteins can contain one (monopartite) or two (bipartite) NLS motifs. Importin-alpha contains several armadillo (ARM) repeats, which produce a curving structure with two NLS-binding sites, a major one close to the N terminus and a minor one close to the C terminus. Importin alpha also contains an N-terminal importin beta binding domain that contains an auto-regulatory region. Importin-beta is a helicoidal molecule constructed from 19 HEAT repeats. Many nuclear pore proteins contain FG sequence repeats that can bind to HEAT repeats within importins, which is important for importin-beta mediated transport.
Ran GTPase helps to control the unidirectional transfer of cargo. The cytoplasm contains primarily RanGDP and the nucleus RanGTP through the actions of RanGAP and RanGEF, respectively. In the nucleus, RanGTP binds to importin-beta within the importin/cargo complex, causing a conformational change in importin-beta that releases it from importin-alpha-bound cargo. The N-terminal importin-beta-binding (IBB) domain of importin-alpha contains an auto-regulatory region that mimics the NLS motif. The release of importin-beta frees the auto-regulatory region on importin-alpha to loop back and bind to the major NLS-binding site, causing the cargo to be released.
Human importin genes
- Importin: IPO4, IPO5, IPO7, IPO8, IPO9, IPO11, IPO13
- Karyopherin-α: KPNA1, KPNA2, KPNA3, KPNA4, KPNA5, KPNA6
- Karyopherin-β: KPNB1
- Görlich D, Prehn S, Laskey RA, Hartmann E (1994). "Isolation of a protein that is essential for the first step of nuclear protein import". Cell 79 (5): 767–78. doi:10.1016/0092-8674(94)90067-1. PMID 8001116.
- Mattaj IW, Englmeier L (1998). "Nucleocytoplasmic transport: the soluble phase". Annu. Rev. Biochem. 67: 265–306. doi:10.1146/annurev.biochem.67.1.265. PMID 9759490.
- Moroianu J, Blobel G, Radu A (1996). "The binding site of karyopherin alpha for karyopherin beta overlaps with a nuclear localization sequence.". Proc Natl Acad Sci U S A 93 (13): 6572–6. doi:10.1073/pnas.93.13.6572. PMC 39066. PMID 8692858.
- Bayliss R, Littlewood T, Strawn LA, Wente SR, Stewart M (December 2002). "GLFG and FxFG nucleoporins bind to overlapping sites on importin-beta". J. Biol. Chem. 277 (52): 50597–606. doi:10.1074/jbc.M209037200. PMID 12372823.
- Isgro TA, Schulten K (February 2007). "Association of nuclear pore FG-repeat domains to NTF2 import and export complexes". J. Mol. Biol. 366 (1): 330–45. doi:10.1016/j.jmb.2006.11.048. PMID 17161424.
- Lange A, Mills RE, Lange CJ, Stewart M, Devine SE, Corbett AH (February 2007). "Classical nuclear localization signals: definition, function, and interaction with importin alpha". J. Biol. Chem. 282 (8): 5101–5. doi:10.1074/jbc.R600026200. PMID 17170104.
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Importin-beta N-terminal domain Provide feedback
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External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR001494
Karyopherins are a group of proteins involved in transporting molecules through the pores of the nuclear envelope. Karyopherins, which may act as importins or exportins, are part of the Importin-beta super-family, which all share a similar three-dimensional structure.
Members of the importin-beta (karyopherin-beta) family can bind and transport cargo by themselves, or can form heterodimers with importin-alpha. As part of a heterodimer, importin-beta mediates interactions with the pore complex, while importin-alpha acts as an adaptor protein to bind the nuclear localisation signal (NLS) on the cargo through the classical NLS import of proteins. Importin-beta is a helicoidal molecule constructed from 19 HEAT repeats. Many nuclear pore proteins contain FG sequence repeats that can bind to HEAT repeats within importins [PUBMED:12372823, PUBMED:17161424], which is important for importin-beta mediated transport.
Ran GTPase helps to control the unidirectional transfer of cargo. The cytoplasm contains primarily RanGDP and the nucleus RanGTP through the actions of RanGAP and RanGEF, respectively. In the nucleus, RanGTP binds to importin-beta within the importin/cargo complex, causing a conformational change in importin-beta that releases it from importin-alpha-bound cargo. As a result, the N-terminal auto-inhibitory region on importin-alpha is free to loop back and bind to the major NLS-binding site, causing the cargo to be released [PUBMED:17170104]. There are additional release factors as well.
This entry represents the N-terminal domain of karyopherins that is important for the binding of the Ran protein [PUBMED:10367892].
More information about these proteins can be found at Protein of the Month: Importins [PUBMED:].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||protein transporter activity (GO:0008565)|
|Biological process||intracellular protein transport (GO:0006886)|
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Tetratricopeptide-like repeats are found in a numerous and diverse proteins involved in such functions as cell cycle regulation, transcriptional control, mitochondrial and peroxisomal protein transport, neurogenesis and protein folding.
The clan contains the following 117 members:Adaptin_N Alkyl_sulf_dimr Apc3 Apc5 API5 Arm Arm_2 Avirulence BTAD CAS_CSE1 ChAPs CLASP_N Clathrin Clathrin-link Clathrin_propel Cnd1 Cnd3 Coatomer_E Cohesin_HEAT Cohesin_load CRM1_C Cse1 DNA_alkylation Drf_FH3 Drf_GBD DUF1822 DUF2225 DUF3385 DUF3458 DUF3808 DUF3856 EST1_DNA_bind FAT Fis1_TPR_C Fis1_TPR_N Foie-gras_1 GUN4 HAT HEAT HEAT_2 HEAT_EZ HEAT_PBS HemY_N IBB IBN_N IFRD KAP Leuk-A4-hydro_C LRV LRV_FeS MA3 MIF4G MIF4G_like MIF4G_like_2 MMS19_C Mo25 MRP-S27 NARP1 Neurochondrin Nro1 NSF Paf67 ParcG PC_rep PHAT PI3Ka PPP5 PPR PPR_1 PPR_2 PPR_3 Proteasom_PSMB PUF Rab5-bind Rapsyn_N RPN7 Sel1 SHNi-TPR SNAP SPO22 ST7 Suf SusD SusD-like SusD-like_2 SusD-like_3 Tcf25 TOM20_plant TPR_1 TPR_10 TPR_11 TPR_12 TPR_14 TPR_15 TPR_16 TPR_17 TPR_18 TPR_19 TPR_2 TPR_20 TPR_21 TPR_3 TPR_4 TPR_5 TPR_6 TPR_7 TPR_8 TPR_9 Upf2 V-ATPase_H_C V-ATPase_H_N Vac14_Fab1_bd Vitellogenin_N Vps39_1 W2 Xpo1 YfiO
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Curation and family details
|Number in seed:||52|
|Number in full:||2930|
|Average length of the domain:||72.40 aa|
|Average identity of full alignment:||20 %|
|Average coverage of the sequence by the domain:||7.63 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||14|
|Download:||download the raw HMM for this family|
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