Ubiquitin complex

The surface of UbcH7 that contacts c-Cbl does not overlap with the E2 surface that contacts ubiquitin (Figures. 5.4 and 5.5 see also Ref [108]), confirming that the E2/ubiquitin thiol ester can associate with a RING E3. The E2 surface that contacts c-Cbl does, however, overlap the E2 surface implicated in E1/E2 interactions (Section 5.6.1). Thus, the El may have to depart from the E2/ubiquitin complex before E2/E3 interactions can take place. 

Swanson, K. A., Kang, R. S., Stamenova, S. D., Hicke, L., and Radhakeishnan, 1. Solution structure of Vps27 UlM-ubiquitin complex important for endosomal sorting and receptor downregulation. Embo J 2003, 22, 4597-606. 

The three-dimensional structure of both UBA domains of the human Rad23a proteins have been solved and reveal a conserved three-helix bundle fold [50, 51], So far, no structure of a UBA-ubiquitin complex is known and we can only speculate on their mode of interaction. The original UBA structures revealed two... 

Figure 12.4A shows the interaction of the first CUE domain of Cue2 interacting with ubiquitin, which might serve as a general model for the interaction mode of other UBA-like domains. The CUE domain binds to the Ile-44 patch of ubiquitin, in accordance with the chemical shift perturbation results of the UBA ubiquitin interaction [52], On the side of the CUE domain, residues of the first and third helix participate in this interaction surface. These residues include the Phe-Pro and Leu-Leu motifs, which had been predicted to be important for ubiquitin binding, based on comparative sequence analysis of CUE-A and CUE-B domains [62]. Positions in close contact with ubiquitin are also indicated in the alignment of Figure 12.3. The two available structures of the CUE ubiquitin complexes offer little expla-...

Because previous studies demonstrated that both Radfi and Ubcl3 ubiquitination activities are required for their PRR functions, it is expected that the covalent modification of one or more critical targets by these two ubiquitination complexes signals for their respective PRR activities (Broomfield et aL, 2001). A recent study has clearly pointed to PCNA as such a critical target (Hoege et oL, 2002). 

FIGURE 4.49 Isolation of a complex protein conjugate on Toyopearl HW-50S. Column 22 mm X 83 cm. Sample Fraction from crude Tetrahymena H2A containing the ubiquitin-histone conjugate uH2A. Elution 10 nM HCI. Flow rate 0.1 ml/min. Detection UV at 230 nm. 

Chromatin is composed of nucleosomes, where each comprise 147 base pairs of DNA wrapped around an octamer oftwo copies of each histone H2A, H2B, H3, and H4. Nucleosomes are folded into higher-order structures that are stabilized by linker histones. Chromatin structure can be altered by enzymes that posttranslationally modify histones (e.g., through phosphorylation, acetylation, methylation, or ubiquitination) or by ATP-driven chromatin-remodeling complexes that alter nucleosome position and/or composition. 

Fujita Y, Krause G, Scheffner M et al (2002) Hakai, a c-Cbl-like protein, ubiquitinates and induces endo-cytosis of the E-cadherin complex. Nat Cell Biol 4(3) 222-231... 

Multiprotein complex that catalyses ATP-dependent degradation of proteins tagged with ubiquitin. 

The SCF, a ubiquitin ligase complex, consists of the piimaiy subunits Skpl, Cullin and Rbx/Rocl. While the Rbx/Cul components form the E3 ligase catalytic core... 

Hyperphosphorylation of ERAK-1 by itself and ERAK-4 causes ERAK-1 to dissociate from the membrane-bound complex. Tumour necrosis factor (TNF) receptor-associated factor-6 ( TRAF-6), a cytoplasmic protein, is activated by ERAK-1 and with TAB-2, another cytoplasmic protein, activates transforming growth factor-P (TFG-P)-activating kinase (TAK-1). During this process both TRAF-6 and TAK-1 become ubiquitinated. TAK-1 then promotes activation of the IkB kinases, or the IKK family, EKKa and EKK 3 (found in a complex with NFicB-essential modulator [NEMO]), which phosphorylate the IkB family, notably IkB-u. IkB-u is an inhibitor of NFkB as it sequesters NFkB in an... 

The core unit of the chromatin, the nucleosome, consists of histones arranged as an octamer consisting of a (H3/ H4)2-tetramer complexed with two histone H2A/H2B dimers. Accessibility to DNA-binding proteins (for replication, repair, or transcription) is achieved by posttranslational modifications of the amino-termini of the histones, the histone tails phosphorylation, acetylation, methylation, ubiquitination, and sumoyla-tion. Especially acetylation of histone tails has been linked to transcriptional activation, leading to weakened interaction of the core complexes with DNA and subsequently to decondensation of chromatin. In contrast, deacetylation leads to transcriptional repression. As mentioned above, transcriptional coactivators either possess HAT activity or recruit HATs. HDACs in turn act as corepressors. 

Protein modification by the covalent attachment of ubiquitin chains serves as a signal to mark proteins for the degradation by a multicatalytic proteinase complex called the proteasome. Thus the ubiquitin proteasome system (UPS) controls the stability of proteins in a... 

APC is active from mid-M phase (anaphase) to the end of G1 phase and required for disconnecting sister chromatids and exit from M-Phase to Gl. The complex mediates the ubiquitination of Securin and Cyclin B. Degradation of these proteins, which block mitotic progression, promotes anaphase onset and exit from mitosis. 

Ubiquitin modification of substrates can be sensed by proteins, which serve as ubiquitin receptors. These proteins harbor domains capable of ubiquitin binding and help to translate the signal into the proper physiological response by forming signaling complexes or activating downstream effectors. So far more than 15 different ubiquitin recognition motifs have been identified. 

Figure 1. The cell cycle as a Cdc2 cycle. Progression through the eukaryotic cell cycle is sensitive to the phosphorylation state of Cdc2. A block to DNA synthesis (S) prevents dephosphorylation, and hence activation, of Cdc2. Impaired spindle function will prevent deactivation of Cdc2 and thus blocks exit from M phase (Hoyt et al., 1991 Li and Murray, 1991 reviewed in Nurse, 1991). Exit from M phase requires destruction of the regulatory subunit, Cyc B. Dephosphorylation of Cdc2 at thr-161 may act to destabilize the Cdc2/Cyc B complex and thus allow the ubiquitination of Cyc B followed by its destruction.

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