| Structural highlights
Function
[UBC_HUMAN] Ubiquitin exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.[1] [2] [TNAP3_HUMAN] Ubiquitin-editing enzyme that contains both ubiquitin ligase and deubiquitinase activities. Involved in immune and inflammatory responses signaled by cytokines, such as TNF-alpha and IL-1 beta, or pathogens via Toll-like receptors (TLRs) through terminating NF-kappa-B activity. Essential component of a ubiquitin-editing protein complex, comprising also RNF11, ITCH and TAX1BP1, that ensures the transient nature of inflammatory signaling pathways. In cooperation with TAX1BP1 promotes disassembly of E2-E3 ubiquitin protein ligase complexes in IL-1R and TNFR-1 pathways; affected are at least E3 ligases TRAF6, TRAF2 and BIRC2, and E2 ubiquitin-conjugating enzymes UBE2N and UBE2D3. In cooperation with TAX1BP1 promotes ubiquitination of UBE2N and proteasomal degradation of UBE2N and UBE2D3. Upon TNF stimulation, deubiquitinates 'Lys-63'-polyubiquitin chains on RIPK1 and catalyzes the formation of 'Lys-48'-polyubiquitin chains. This leads to RIPK1 proteasomal degradation and consequently termination of the TNF- or LPS-mediated activation of NF-kappa-B. Deubiquinates TRAF6 probably acting on 'Lys-63'-linked polyubiquitin. Upon T-cell receptor (TCR)-mediated T-cell activation, deubiquitinates 'Lys-63'-polyubiquitin chains on MALT1 thereby mediating disassociation of the CBM (CARD11:BCL10:MALT1) and IKK complexes and preventing sustained IKK activation. Deubiquinates NEMO/IKBKG; the function is facilitated by TNIP1 and leads to inhibition of NF-kappa-B activation. Upon stimulation by bacterial peptidoglycans, probably deubiquitinates RIPK2. Can also inhibit I-kappa-B-kinase (IKK) through a non-catalytic mechanism which involves polyubiquitin; polyubiquitin promotes association with IKBKG and prevents IKK MAP3K7-mediated phosphorylation. Targets TRAF2 for lysosomal degradation. In vitro able to deubiquitinate both 'Lys-48'- and 'Lys-63' polyubiquitin chains. Inhibitor of programmed cell death. Has a role in the function of the lymphoid system.[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Publication Abstract from PubMed
LUBAC (linear ubiquitin chain assembly complex) activates the canonical NF-kappaB pathway through linear polyubiquitination of NEMO (NF-kappaB essential modulator, also known as IKKgamma) and RIP1. However, the regulatory mechanism of LUBAC-mediated NF-kappaB activation remains elusive. Here, we show that A20 suppresses LUBAC-mediated NF-kappaB activation by binding linear polyubiquitin via the C-terminal seventh zinc finger (ZF7), whereas CYLD suppresses it through deubiquitinase (DUB) activity. We determined the crystal structures of A20 ZF7 in complex with linear diubiquitin at 1.70-1.98 A resolutions. The crystal structures revealed that A20 ZF7 simultaneously recognizes the Met1-linked proximal and distal ubiquitins, and that genetic mutations associated with B cell lymphomas map to the ubiquitin-binding sites. Our functional analysis indicated that the binding of A20 ZF7 to linear polyubiquitin contributes to the recruitment of A20 into a TNF receptor (TNFR) signalling complex containing LUBAC and IkappaB kinase (IKK), which results in NF-kappaB suppression. These findings provide new insight into the regulation of immune and inflammatory responses.
Specific recognition of linear polyubiquitin by A20 zinc finger 7 is involved in NF-kappaB regulation.,Tokunaga F, Nishimasu H, Ishitani R, Goto E, Noguchi T, Mio K, Kamei K, Ma A, Iwai K, Nureki O EMBO J. 2012 Oct 3;31(19):3856-70. doi: 10.1038/emboj.2012.241. Epub 2012 Aug 28. PMID:23032187[14]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Huang F, Kirkpatrick D, Jiang X, Gygi S, Sorkin A. Differential regulation of EGF receptor internalization and degradation by multiubiquitination within the kinase domain. Mol Cell. 2006 Mar 17;21(6):737-48. PMID:16543144 doi:S1097-2765(06)00120-1
- ↑ Komander D. The emerging complexity of protein ubiquitination. Biochem Soc Trans. 2009 Oct;37(Pt 5):937-53. doi: 10.1042/BST0370937. PMID:19754430 doi:10.1042/BST0370937
- ↑ Song HY, Rothe M, Goeddel DV. The tumor necrosis factor-inducible zinc finger protein A20 interacts with TRAF1/TRAF2 and inhibits NF-kappaB activation. Proc Natl Acad Sci U S A. 1996 Jun 25;93(13):6721-5. PMID:8692885
- ↑ De Valck D, Heyninck K, Van Criekinge W, Vandenabeele P, Fiers W, Beyaert R. A20 inhibits NF-kappaB activation independently of binding to 14-3-3 proteins. Biochem Biophys Res Commun. 1997 Sep 18;238(2):590-4. PMID:9299557 doi:10.1006/bbrc.1997.7343
- ↑ Eliopoulos AG, Blake SM, Floettmann JE, Rowe M, Young LS. Epstein-Barr virus-encoded latent membrane protein 1 activates the JNK pathway through its extreme C terminus via a mechanism involving TRADD and TRAF2. J Virol. 1999 Feb;73(2):1023-35. PMID:9882303
- ↑ Evans PC, Ovaa H, Hamon M, Kilshaw PJ, Hamm S, Bauer S, Ploegh HL, Smith TS. Zinc-finger protein A20, a regulator of inflammation and cell survival, has de-ubiquitinating activity. Biochem J. 2004 Mar 15;378(Pt 3):727-34. PMID:14748687 doi:10.1042/BJ20031377
- ↑ Wertz IE, O'Rourke KM, Zhou H, Eby M, Aravind L, Seshagiri S, Wu P, Wiesmann C, Baker R, Boone DL, Ma A, Koonin EV, Dixit VM. De-ubiquitination and ubiquitin ligase domains of A20 downregulate NF-kappaB signalling. Nature. 2004 Aug 5;430(7000):694-9. Epub 2004 Jul 18. PMID:15258597 doi:10.1038/nature02794
- ↑ Mauro C, Pacifico F, Lavorgna A, Mellone S, Iannetti A, Acquaviva R, Formisano S, Vito P, Leonardi A. ABIN-1 binds to NEMO/IKKgamma and co-operates with A20 in inhibiting NF-kappaB. J Biol Chem. 2006 Jul 7;281(27):18482-8. Epub 2006 May 9. PMID:16684768 doi:10.1074/jbc.M601502200
- ↑ Li L, Soetandyo N, Wang Q, Ye Y. The zinc finger protein A20 targets TRAF2 to the lysosomes for degradation. Biochim Biophys Acta. 2009 Feb;1793(2):346-53. doi: 10.1016/j.bbamcr.2008.09.013., Epub 2008 Oct 8. PMID:18952128 doi:10.1016/j.bbamcr.2008.09.013
- ↑ Duwel M, Welteke V, Oeckinghaus A, Baens M, Kloo B, Ferch U, Darnay BG, Ruland J, Marynen P, Krappmann D. A20 negatively regulates T cell receptor signaling to NF-kappaB by cleaving Malt1 ubiquitin chains. J Immunol. 2009 Jun 15;182(12):7718-28. doi: 10.4049/jimmunol.0803313. PMID:19494296 doi:10.4049/jimmunol.0803313
- ↑ Skaug B, Chen J, Du F, He J, Ma A, Chen ZJ. Direct, noncatalytic mechanism of IKK inhibition by A20. Mol Cell. 2011 Nov 18;44(4):559-71. doi: 10.1016/j.molcel.2011.09.015. PMID:22099304 doi:10.1016/j.molcel.2011.09.015
- ↑ Komander D, Barford D. Structure of the A20 OTU domain and mechanistic insights into deubiquitination. Biochem J. 2008 Jan 1;409(1):77-85. PMID:17961127 doi:10.1042/BJ20071399
- ↑ Lin SC, Chung JY, Lamothe B, Rajashankar K, Lu M, Lo YC, Lam AY, Darnay BG, Wu H. Molecular basis for the unique deubiquitinating activity of the NF-kappaB inhibitor A20. J Mol Biol. 2008 Feb 15;376(2):526-40. Epub 2007 Dec 4. PMID:18164316 doi:http://dx.doi.org/10.1016/j.jmb.2007.11.092
- ↑ Tokunaga F, Nishimasu H, Ishitani R, Goto E, Noguchi T, Mio K, Kamei K, Ma A, Iwai K, Nureki O. Specific recognition of linear polyubiquitin by A20 zinc finger 7 is involved in NF-kappaB regulation. EMBO J. 2012 Oct 3;31(19):3856-70. doi: 10.1038/emboj.2012.241. Epub 2012 Aug 28. PMID:23032187 doi:http://dx.doi.org/10.1038/emboj.2012.241
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