humans have about 40 E2s that are involved in the transfer of Ub or Ub-like (Ubl) proteins (e.g. SUMO and NEDD8). Common functional and structural features that define unifying themes among E2s, overview. Highly specific chain builders such as Ube2N, Ube2S, and Ube2R1 can only transfer their conjugated Ub to another Ub molecule. This leads to a division of labor among E2s in which one E2 initiates or primes chain synthesis and a second E2 builds and extends the polyUb chain
ubiquitin-conjugating enzyme E2 O (UBE2O) is a member of the E2 family of the ubiquitin-proteasome system (UPS). Unlike most members of this family which are about 20 to 25 kDa in molecular weight, UBE2O is unusually large, with a molecular weight of 141 kDa
a UCP mutant in which Cys118 is changed to alanine (UCPC118A) does not form a polyubiquitin chain but strongly accumulates mono- and di-ubiquitin via auto-ubiquitination
inhibition of UBE2O or depletion of UBE2O leads to the reduced growth of breast and prostate cancer cells, but inactivation of AMPKalpha2 abrogates the beneficial effect caused by the UBE2O loss
UBE2O knockdown elevates the amplitude of the circadian clock in human osteosarcoma U2OS cells. Full-length UBE2O and the CR2 truncation rescue the effect of UBE2O knockdown on the BMAL1 protein level
the ubiquitin-proteasome system is an important regulatory machinery involved in proteostasis and cellular signaling. Proteins are ubiquitinated via the concerted action of E1 ubiquitin-activating enzymes, E2 ubiquitin-conjugating enzymes, and E3 ubiquitin ligases. UBE2O is an E2/E3 hybrid enzyme and exhibits both the E2 and E3 activities. Role of UBE2O in the development of hematological disorders and cancers, overview
UBE2O is a critical regulator in the ubiquitin-proteasome system, which modulates BMAL1 transcriptional activity and circadian function by promoting BMAL1 ubiquitination and degradation under normal physiological conditions. UBE2O regulates BMAL1 protein level and stability
ubiquitin-conjugating enzymes (E2s) are the central players in the trio of enzymes responsible for the attachment of ubiquitin (Ub) to cellular proteins. E2 regulation mechanisms, overview
the enzyme forms a labile ubiquitin adduct in the presence of E1, ubiquitin, and MgATP and catalyzes the conjugation of ubiquitin to protein substrates, independent of E3
E2 enzyme HIP2-ubiquitin thioester complexes remain predominantly monomeric in solution. Models of the HIP2-ubiquitin complex show an open or backbent conformation similar to UbcH5b-ubiquitin where the ubiquitin-associated UBA domain and covalently attached ubiquitin reside on opposite ends of the catalytic domain. Full length HIP2 exhibits a fivefold increase in the formation rate of diubiquitin compared to a HIP2 lacking the UBA domain
dysregulation of the circadian rhythm is associated with many diseases, including diabetes, obesity, and cancer. Aryl hydrocarbon receptor nuclear translocator-like protein 1 (Arntl or Bmal1) is the only clock gene whose loss disrupts circadian locomotor behavior in constant darkness. BMAL1 transcription factor levels are affected by proteasomal inhibition and by several enzymes in the ubiquitin-proteasome system. Specific interaction between BMAL1 and ubiquitin-conjugating enzyme E2 O (UBE2O), an E3-independent E2 ubiquitin-conjugating enzyme (i.e. hybrid E2/E3 enzyme) is detetcted, UBE2O expression reduces BMAL1 levels by promoting its ubiquitination and degradation. UBE2O expression/knockdown diminishes/increases, respectively, BMAL1-mediated transcriptional activity but does not affect BMAL1 gene expression. The conserved region 2 (CR2) in UBE2O significantly enhances BMAL1 ubiquitination and decreases BMAL1 protein levels. The CR2 domain alone can enhance BMAL1 ubiquitination and its protein level
humans have about 40 E2s that are involved in the transfer of Ub or Ub-like (Ubl) proteins (e.g. SUMO and NEDD8). Although the majority of E2s are only twice the size of Ub, this remarkable family of enzymes performs a variety of functional roles
the ubiquitin-conjugating enzyme E2 O (UBE2O) is an E3-independent E2 (i.e. an E2/E3 hybrid enzyme), can directly mediate the ubiquitination of many substrates, e.g. 5'-AMP-activated protein kinase catalytic subunit alpha2 (AMPKalpha2), tumor suppressor ubiquitin carboxyl-terminal hydrolase BAP1, mixed-lineage leukemia (MLL) protein, SMAD family member 6 (SMAD6), transcription factor c-Maf and aryl hydrocarbon receptor nuclear translocator-like protein 1 (ARNTL or BMAL1), and free ribosomal proteins, which are ubiquitinated in distinct ways, thereby associating UBE2O with a variety of biological functions. The presence of multifunctional domains in UBE2O suggests that it might act on a broad spectrum of targets and execute diverse biological functions. Although UBE2O is first identified as an E2 enzyme, it is subsequently discovered that it also functions as an E2/E3 hybrid enzyme. UBE2O also functions as an E3 enzyme which is fused to an E2 enzyme and carries out the E3-independent ubiquitination. UBE2O may involve an intramolecular thiol relay mechanism. UBE2O mediates monoubiquitination, multi-monoubiquitination, and polyubiquitination of different substrates and thereby performs its diverse functions. UBE2O specifically targets AMPKalpha2 but not AMPKalpha1 for the formation of K48-linked polyubiquitin chains and for its subsequent degradation by the 26S proteasome, importance of UBE2O-mediated ubiquitination of AMPKalpha2 on tumor cell growth
UCP possesses not only E2 ubiquitin conjugating enzyme activity but also E3 ubiquitin ligase activity, and Cys118 is critical for polyubiquitin chain formation
homology modeling of UBE2O, using the recombinant enzyme and structure of the MZM-REP domains of Mind bomb 1 (Mib1, PDB ID 4XI6) and the UBC domain of baculoviral IAP repeat-containing protein 6 (BIRC6, PDB ID 3CEG), respectively, overview. UBE2O also displays nonenzymatic functions, and as a protein-interacting partner it can block protein ubiquitination. The N-terminus of UBE2O interacts efficiently with the TRAF domain in TNF receptor-associated factor 6 (TRAF6), prevents its K63-linked polyubiquitination, competes with myeloid differentiation primary response protein MyD88 for TRAF6, and thus suppresses the activation of NF-kappaB induced by lipopolysaccharide and interleukin-1beta. Loss of the UBC domain in UBE2O does not affect this regulation, indicating that its nonenzymatic function prevents TRAF6 ubiquitination
homology modeling of UBE2O, using the recombinant enzyme and structure of the MZM-REP domains of Mind bomb 1 (Mib1, PDB ID 4XI6) and the UBC domain of baculoviral IAP repeat-containing protein 6 (BIRC6, PDB ID 3CEG), respectively, overview. UBE2O also displays nonenzymatic functions, and as a protein-interacting partner it can block protein ubiquitination. The N-terminus of UBE2O interacts efficiently with the TRAF domain in TNF receptor-associated factor 6 (TRAF6), prevents its K63-linked polyubiquitination, competes with myeloid differentiation primary response protein MyD88 for TRAF6, and thus suppresses the activation of NF-kappaB induced by lipopolysaccharide and interleukin-1beta. Loss of the UBC domain in UBE2O does not affect this regulation, indicating that its nonenzymatic function prevents TRAF6 ubiquitination
UCP ubiquitinates itself independent of E3 ubiquitin ligase in vitro using mixed lysine linkages. E2-EPF ubiquitin carrier protein (UCP) possesses E3 ubiquitin ligase activity via its cysteine 118 residue. E2-EPF UCP elongates E3-independent polyubiquitin chains on the lysine residues of von Hippel-Lindau protein (pVHL) and its own lysine residues both in vitro and in vivo. The initiation of the ubiquitin reaction depends on not only Lys11 linkage but also the Lys6, Lys48 and Lys63 residues of ubiquitin, which are involved in polyubiquitin chain formation on UCP itself. UCP self-association occurred through the UBC domain, which also contributes to the interaction with pVHL. The polyubiquitin chains appears on the N-terminus of UCP in vivo, which indicates that the N-terminus of UCP contains target lysines for polyubiquitination. The Lys76 residue of UCP is the most critical site for auto-ubiquitination, whereas the polyubiquitin chain formation on pVHL occurrs on all three of its lysines (Lys159, Lys171 and Lys196). Polyubiquitin chain formation requires the coordination of Cys95 and Cys118 between two interacting molecules. The mechanism of the polyubiquitin chain reaction of UCP may involve the transfer of ubiquitin from Cys95 to Cys118 by trans-thiolation, with polyubiquitin chains forming at Cys118 by reversible thioester bonding. The polyubiquitin chains are then moved to the lysine residues of the substrate by irreversible isopeptide bonding. During the elongation of the ubiquitin chain, an active Cys118 residue is required in both parts of UCP, namely, the catalytic enzyme and the substrate. Residue Cys118 plays a key role in the autoubiquitination of UCP. Reaction mechanism, overview