Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The RAD6 postreplication repair and mutagenesis pathway is the only major radiation repair pathway yet to be extensively characterized. It has been previously speculated that the RAD6 pathway consists of two parallel subpathways, one error free and another error prone (mutagenic). Here we show that the RAD6 group genes can be exclusively divided into three rather than two independent subpathways represented by the RAD5, POL30, and REV3 genes; the REV3 pathway is largely mutagenic, whereas the RAD5 and the POL30 pathways are deemed error free. Mutants carrying characteristic mutations in each of the three subpathways are phenotypically indistinguishable from a single mutant such as rad18, which is defective in the entire RAD6 postreplication repair/tolerance pathway. Furthermore, the rad18 mutation is epistatic to all single or combined mutations in any of the above three subpathways. Our data also suggest that MMS2 and UBC13 play a key role in coordinating the response of the error-free subpathways; Mms2 and Ubc13 form a complex required for a novel polyubiquitin chain assembly, which probably serves as a signal transducer to promote both RAD5 and POL30 error-free postreplication repair pathways. The model established by this study will facilitate further research into the molecular mechanisms of postreplication repair and translesion DNA synthesis. In view of the high degree of sequence conservation of the RAD6 pathway genes among all eukaryotes, the model presented in this study may also apply to mammalian cells and predicts links to human diseases.
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PMID:The Saccharomyces cerevisiae RAD6 group is composed of an error-prone and two error-free postreplication repair pathways. 1092 62

TRAF6 is a signal transducer in the NF-kappaB pathway that activates IkappaB kinase (IKK) in response to proinflammatory cytokines. We have purified a heterodimeric protein complex that links TRAF6 to IKK activation. Peptide mass fingerprinting analysis reveals that this complex is composed of the ubiquitin conjugating enzyme Ubc13 and the Ubc-like protein Uev1A. We find that TRAF6, a RING domain protein, functions together with Ubc13/Uev1A to catalyze the synthesis of unique polyubiquitin chains linked through lysine-63 (K63) of ubiquitin. Blockade of this polyubiquitin chain synthesis, but not inhibition of the proteasome, prevents the activation of IKK by TRAF6. These results unveil a new regulatory function for ubiquitin, in which IKK is activated through the assembly of K63-linked polyubiquitin chains.
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PMID:Activation of the IkappaB kinase complex by TRAF6 requires a dimeric ubiquitin-conjugating enzyme complex and a unique polyubiquitin chain. 2941 May 30

Polyubiquitin chains assembled through lysine 48 (Lys-48) of ubiquitin act as a signal for substrate proteolysis by 26 S proteasomes, whereas chains assembled through Lys-63 play a mechanistically undefined role in post-replicative DNA repair. We showed previously that the products of the UBC13 and MMS2 genes function in error-free post-replicative DNA repair in the yeast Saccharomyces cerevisiae and form a complex that assembles Lys-63-linked polyubiquitin chains in vitro. Here we confirm that the Mms2.Ubc13 complex functions as a high affinity heterodimer in the chain assembly reaction in vitro and report the results of a kinetic characterization of the polyubiquitin chain assembly reaction. To test whether a Lys-63-linked polyubiquitin chain can signal degradation, we conjugated Lys-63-linked tetra-ubiquitin to a model substrate of 26 S proteasomes. Although the noncanonical chain effectively signaled substrate degradation, the results of new genetic epistasis studies agree with previous genetic data in suggesting that the proteolytic activity of proteasomes is not required for error-free post-replicative repair.
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PMID:In vitro assembly and recognition of Lys-63 polyubiquitin chains. 1136 80

While the signaling properties of ubiquitin depend on the topology of polyubiquitin chains, little is known concerning the molecular basis of specificity in chain assembly and recognition. UEV/Ubc complexes have been implicated in the assembly of Lys63-linked polyubiquitin chains that act as a novel signal in postreplicative DNA repair and I kappa B alpha kinase activation. The crystal structure of the Mms2/Ubc13 heterodimer shows the active site of Ubc13 at the intersection of two channels that are potential binding sites for the two substrate ubiquitins. Mutations that destabilize the heterodimer interface confer a marked UV sensitivity, providing direct evidence that the intact heterodimer is necessary for DNA repair. Selective mutations in the channels suggest a molecular model for specificity in the assembly of Lys63-linked polyubiquitin signals.
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PMID:Molecular insights into polyubiquitin chain assembly: crystal structure of the Mms2/Ubc13 heterodimer. 1144 Jul 14

TRAF6 is a signal transducer that activates IkappaB kinase (IKK) and Jun amino-terminal kinase (JNK) in response to pro-inflammatory mediators such as interleukin-1 (IL-1) and lipopolysaccharides (LPS). IKK activation by TRAF6 requires two intermediary factors, TRAF6-regulated IKK activator 1 (TRIKA1) and TRIKA2 (ref. 5). TRIKA1 is a dimeric ubiquitin-conjugating enzyme complex composed of Ubc13 and Uev1A (or the functionally equivalent Mms2). This Ubc complex, together with TRAF6, catalyses the formation of a Lys 63 (K63)-linked polyubiquitin chain that mediates IKK activation through a unique proteasome-independent mechanism. Here we report the purification and identification of TRIKA2, which is composed of TAK1, TAB1 and TAB2, a protein kinase complex previously implicated in IKK activation through an unknown mechanism. We find that the TAK1 kinase complex phosphorylates and activates IKK in a manner that depends on TRAF6 and Ubc13-Uev1A. Moreover, the activity of TAK1 to phosphorylate MKK6, which activates the JNK-p38 kinase pathway, is directly regulated by K63-linked polyubiquitination. We also provide evidence that TRAF6 is conjugated by the K63 polyubiquitin chains. These results indicate that ubiquitination has an important regulatory role in stress response pathways, including those of IKK and JNK.
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PMID:TAK1 is a ubiquitin-dependent kinase of MKK and IKK. 2941 May 30

The ubiquitin conjugating enzyme complex Mms2-Ubc13 plays a key role in post-replicative DNA repair in yeast and the NF-kappaB signal transduction pathway in humans. This complex assembles novel polyubiquitin chains onto yet uncharacterized protein targets. Here we report the crystal structure of a complex between hMms2 (Uev1) and hUbc13 at 1.85 A resolution and a structure of free hMms2 at 1.9 A resolution. These structures reveal that the hMms2 monomer undergoes a localized conformational change upon interaction with hUbc13. The nature of the interface provides a physical basis for the preference of Mms2 for Ubc13 as a partner over a variety of other structurally similar ubiquitin-conjugating enzymes. The structure of the hMms2-hUbc13 complex provides the conceptual foundation for understanding the mechanism of Lys 63 multiubiquitin chain assembly and for its interactions with the RING finger proteins Rad5 and Traf6.
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PMID:Crystal structure of the human ubiquitin conjugating enzyme complex, hMms2-hUbc13. 1147 44

Tumor necrosis factor (TNF)-induced activation of apoptosis signal-regulating kinase 1 (ASK1) and germinal center kinases (GCKs) and the subsequent activation of stress-activated protein kinases (SAPKs and c-Jun NH(2)-terminal kinases) requires TNF receptor-associated factor 2 (TRAF2). Although the TRAF2 TRAF domain binds ASK1, GCK, and the highly related kinase GCKR, the RING finger domain is needed for their activation. Here, we report that TNF activates GCKR and the SAPK pathway in a manner that depends upon TRAF2 and Ubc13, a member along with Uev1A of a dimeric ubiquitin-conjugating enzyme complex. Interference with Ubc13 function or expression inhibits both TNF- and TRAF2-mediated GCKR and SAPK activation, but has a minimal effect on ASK1 activation. TNF signaling leads to TRAF2 polyubiquitination and oligomerization and to the oligomerization, ubiquitination, and activation of GCKR, all of which are sensitive to the disruption of Ubc13 function. These results indicate that the assembly of a TRAF2 lysine 63-linked polyubiquitin chain by Ubc13/Uev1A is required for TNF-mediated GCKR and SAPK activation, but may not be required for ASK1 activation.
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PMID:Tumor necrosis factor (TNF)-induced germinal center kinase-related (GCKR) and stress-activated protein kinase (SAPK) activation depends upon the E2/E3 complex Ubc13-Uev1A/TNF receptor-associated factor 2 (TRAF2). 1259 26

Lys(63)-linked polyubiquitin (poly-Ub) chains appear to play a nondegradative signaling and/or recruitment role in a variety of key eukaryotic cellular processes, including NF-kappaB signal transduction and DNA repair. A protein heterodimer composed of a catalytically active ubiquitin-conjugating enzyme (Ubc13) and its homologue (Mms2 or Uev1a) forms a catalytic scaffold upon which a noncovalently associated acceptor Ub and thiolester-linked donor Ub are oriented such that Lys(63)-linked poly-Ub chain synthesis is facilitated. In this study, we have used (1)H-(15)N nuclear magnetic resonance spectroscopy, in combination with isothermal titration calorimetry, to determine the thermodynamics and kinetics of the interactions between various components of the Lys(63)-linked poly-Ub conjugation machinery. Mms2 and Uev1a interact in vitro with acceptor Ub to form 1/1 complexes with macroscopic dissociation constants of 98 +/- 15 and 213 +/- 14 microM, respectively, and appear to bind Ub in a similar fashion. Interestingly, the Mms2.Ubc13 heterodimer associates with acceptor Ub in a 1/1 complex and binds with a dissociation constant of 28 +/- 6 microM, significantly stronger than the binding of Mms2 alone. Furthermore, a dissociation constant of 49 +/- 7 nM was determined for the interaction between Mms2 and Ubc13 using isothermal titration calorimetry. In connection with previous structural studies for this system, the thermodynamics and kinetics of acceptor Ub binding to the Mms2.Ubc13 heterodimer described in detail in this study will allow for a more thorough rationalization of the mechanism of formation of Lys(63)-linked poly-Ub chains.
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PMID:Energetics and specificity of interactions within Ub.Uev.Ubc13 human ubiquitin conjugation complexes. 1283 44

We recently described a novel checkpoint pathway that functions early in mitosis to delay chromosome condensation in response to microtubule poisons. The only gene implicated so far in this checkpoint pathway is chfr, whose protein product contains a RING domain and has ubiquitin ligase activity in vitro. The significance of this activity in vivo is unclear. A recent report suggested that the Chfr protein targets itself for proteasome-dependent degradation in mitotic cells through autoubiquitination. However, we observe that in mitosis Chfr exhibits a phosphorylation-dependent electrophoretic mobility shift with no change in overall protein levels. Further analysis of its ubiquitin ligase activity revealed that Chfr can catalyse the formation of noncanonical Lys63-linked polyubiquitin chains with Ubc13-Mms2 acting as the ubiquitin-conjugating enzyme. Ubc13-Mms2 and Lys63-polyubiquitin chains are not associated with targeting proteins to the proteasome, but rather with signaling cellular stress. We propose that Chfr may have a role in signaling the presence of mitotic stress induced by microtubule poisons.
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PMID:The Chfr mitotic checkpoint protein functions with Ubc13-Mms2 to form Lys63-linked polyubiquitin chains. 1456 38

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a crucial signaling transducer that regulates a diverse array of physiological processes, including adaptive immunity, innate immunity, and bone metabolism. Importantly, it is essential for activating NF-kappaB signaling pathway in response to interleukin-1 and Toll-like receptor ligands. Previously, we characterized TRAF6 to be a ubiquitin ligase. In combination with the ubiquitin conjugating enzyme complex Ubc13/Uev1A, TRAF6 could catalyze the formation on itself of unique Lys-63 linked polyubiquitin chain that positively regulated NF-kappaB signaling pathway. However, it remains unknown how this auto-ubiquitination process is regulated. In this study, we found that the coiled-coil domain of TRAF6 was essential for its auto-ubiquitination and activating NF-kappaB signaling pathway. This domain served not as the specific target where the polyubiquitin chain was linked, but as a specific bridge to recruit Ubc13/Uev1A.
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PMID:The coiled-coil domain of TRAF6 is essential for its auto-ubiquitination. 1546 37


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