Summary for IκBα (NES ID: 37)

Full Name
NF-kappa-B inhibitor alpha     UniProt    
Alternative Names
Major histocompatibility complex enhancer-binding protein MAD3   
Organism
Homo sapiens (Human)    
Experimental Evidence for CRM1-mediated Export
LMB Sensitive,  Binds CRM1,  Mislocalization in Xpo1-1 temperature sensitive strains Ref.1An N-terminal nuclear export signal is required for the nucleocytoplasmic shuttling of IκBα, Johnson et al., EMBO J, 1999 Ref.2Nuclear retention of IκBα protects it from signal-induced degradation and inhibits nuclear factor kappaB transcriptional activation, Rodriguez et al., J Biol Chem, 1999 Ref.3The N-terminal nuclear export sequence of IkappaBalpha is required for RanGTP-dependent binding to CRM1, Lee et al., J Biol Chem, 2001 Ref.4A nuclear export signal in the N-terminal regulatory domain of IkappaBalpha controls cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes, Huang et al., Proc Natl Acad Sci, 2000 Ref.5Cytoplasmic sequestration of rel proteins by IkappaBalpha requires CRM1-dependent nuclear export, Tam et al., Mol Cell Biol, 2000 Ref.6Evidence for a role of CRM1 in signal-mediated nuclear protein export., Nazari et al., Science, 1997
Mutations That Affect Nuclear Export
*highlighted yellow in the full sequence
I52A/L54A, M45A/V46A/L49A/I52A, L49A/I52A/L54A, L269A, /L272A/L274A/L277A Ref.1An N-terminal nuclear export signal is required for the nucleocytoplasmic shuttling of IκBα, Johnson et al., EMBO J, 1999 Ref.4A nuclear export signal in the N-terminal regulatory domain of IkappaBalpha controls cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes, Huang et al., Proc Natl Acad Sci, 2000 Ref.5Cytoplasmic sequestration of rel proteins by IkappaBalpha requires CRM1-dependent nuclear export, Tam et al., Mol Cell Biol, 2000 Ref.6Evidence for a role of CRM1 in signal-mediated nuclear protein export., Nazari et al., Science, 1997
Mutations That Affect CRM1 Binding
*shown as red residues in the full sequence
M45A/L49A/I52A/L54A Ref.3The N-terminal nuclear export sequence of IkappaBalpha is required for RanGTP-dependent binding to CRM1, Lee et al., J Biol Chem, 2001
Functional Export Signals
*shown as underlined residues in the full sequence
1MFQAAERPQEWAMEGPRDGLKKERLLDDRHDSGLDSMKDEEYEQMVKELQEIRLE55 Ref.1An N-terminal nuclear export signal is required for the nucleocytoplasmic shuttling of IκBα, Johnson et al., EMBO J, 1999 Ref.4A nuclear export signal in the N-terminal regulatory domain of IkappaBalpha controls cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes, Huang et al., Proc Natl Acad Sci, 2000
Secondary Structure of Export Signal
Unknown
Other Residues Important for Export
Unknown
Sequence
Show FASTA Format Show Domain Info by CDD Show Secondary Structure by PSIPRED Show Conservation Score by AL2CO 
        10         20         30         40         50         60 
MFQAAERPQE WAMEGPRDGL KKERLLDDRH DSGLDSMKDE EYEQMVKELQ EIRLEPQEVP 

        70         80         90        100        110        120 
RGSEPWKQQL TEDGDSFLHL AIIHEEKALT MEVIRQVKGD LAFLNFQNNL QQTPLHLAVI 

       130        140        150        160        170        180 
TNQPEIAEAL LGAGCDPELR DFRGNTPLHL ACEQGCLASV GVLTQSCTTP HLHSILKATN 

       190        200        210        220        230        240 
YNGHTCLHLA SIHGYLGIVE LLVSLGADVN AQEPCNGRTA LHLAVDLQNP DLVSLLLKCG 

       250        260        270        280        290        300 
ADVNRVTYQG YSPYQLTWGR PSTRIQQQLG QLTLENLQML PESEDEESYD TESEFTEFTE 

       310                                                        
DELPYDDCVF GGQRLTL
3D Structures in PDB
Not Available
Comments
The transcriptional activities of nuclear factor kappa B (NF-κB) are mediated by its inhibitor IκB proteins. IκBα binds to a heterodimer of p65/p50, masking its NLS, which results in the cytoplasmic retention of p65/p50. But recent crystallographic data failed to reveal such a masking and LMB treatment caused the NF-κB/IκBα complex to accumulate in the nucleus, suggesting that the cytoplasmic retention of the complex is a result of active export. Under certain extracellular stimuli, IκBα is phosphorylated and degraded. With its NLS unmasked, NF-κB travels to the nucleus, and initiates target gene transcription. However, NF-κB activation will induce IκBα expression. The newly synthesized IκBα enters the nucleus, binds to NF-κB, and mediate its export to the cytoplasm, thereby, establishing an auto-regulatory loop. Using an HIV-1 Rev NES deletion complementation assay, Johnson et al. examined several fragments of IκBα and found that aa 22-72 can restore the export function of Rev. Double mutations I52A/L54A abolish export its function. The putative NES is located from 45-54. Huang demonstrated that aa 1-55, when fused with GFP, is able to export the fusion protein out of the nucleus following microinjection. The export activity is sensitive to LMB treatment. The previous proposed C-terminal NES failed to export. The NLS of IκBα is located within the central ankyrin repeat domain. Another point to mention is that it has benn shown that IκBα shuttle with NF-κB as a complex and the export requires the NES of IκBα. However p65 has been shown to contain an NES and can mediate the export of the complex with its own NES (even when the NES of IκBα was mutated). Lee et al. verified the presence of this NES in IκBα of Gallus gallus (UniProt: Q91974)
Doubt about C-terminal NES: The C-terminal NES of IκBα was introduced by Sossareh-Nazari et al. . They showed that CRM1 bound to NES affinity column (CIQQQLGQLTLENL). Mutations of key leucine residues abolished the binding. They also showed that the interaction between CRM1 and NES is LMB sensitive. However, later studies by Lee et al. (2001) and Johnson et al. (1999) showed that the C-terminal part of IκBα is not required for the formation of ternary complex of RanGTP-CRM1-IκBα.
References
[1]. "An N-terminal nuclear export signal is required for the nucleocytoplasmic shuttling of IκBα"
Johnson, C., Van Antwerp, D., Hope, T.J. (1999) EMBO J, 18:6682-6693 PubMed
[2]. "Nuclear retention of IκBα protects it from signal-induced degradation and inhibits nuclear factor kappaB transcriptional activation"
Rodriguez, M.S., Thompson, J., Hay, R.T., Dargemont, C. (1999) J Biol Chem, 274:9108-9115 PubMed
[3]. "The N-terminal nuclear export sequence of IkappaBalpha is required for RanGTP-dependent binding to CRM1"
Lee SH, Hannink M. (2001) J Biol Chem, 276:23599-23606 PubMed
[4]. "A nuclear export signal in the N-terminal regulatory domain of IkappaBalpha controls cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes"
Huang TT, Kudo N, Yoshida M, Miyamoto S (2000) Proc Natl Acad Sci, 97:1014-1019 PubMed
[5]. "Cytoplasmic sequestration of rel proteins by IkappaBalpha requires CRM1-dependent nuclear export"
Tam WF, Lee LH, Davis L, Sen R (2000) Mol Cell Biol, 20:2269-2284 PubMed
[6]. "Evidence for a role of CRM1 in signal-mediated nuclear protein export."
Ossareh-Nazari B, Bachelerie F, Dargemont C. (1997) Science, 278:141-4 PubMed
User Input
Accurate identification of NESs is difficult because many sequences in the genome match the NES consensus. Therefore, some published NESs may be mistakenly identified. Please help us improve the accuracy of NESdb by providing either a positive or negative flag for the NES in this entry. Supporting comments are required to process the flag.

Supporting comments *

Flag this NES *

Positive
Negative

E-mail: