Ubiquitin Molecule (ubiquitin + molecule)

Distribution by Scientific Domains
Distribution within Chemistry

Selected Abstracts

Ubiquitination of E3 ubiquitin ligase TRIM5, and its potential role

FEBS JOURNAL, Issue 7 2008
Keiko Yamauchi
HIV-1 efficiently infects susceptible cells and causes AIDS in humans. Although HIV can also enter the cells of Old World monkeys, it encounters a block before reverse transcription. Data have shown that this species-specific restriction is mediated by tripartite motif (TRIM)5,, whose molecular function is still undefined. Here, we show that TRIM5, functions as a RING-finger-type E3 ubiquitin ligase both in vitro and in vivo and ubiquitinates itself in cooperation with the E2 ubiquitin-conjugating enzyme UbcH5B. In addition to the self-ubiquitination, we show that TRIM5, is ubiquitinated by another E3 ubiquitin ligase, Ro52, and deubiquitinated by YopJ, one of the pathogenic proteins derived from Yersinia species. Thus, the ubiquitination of TRIM5, is catalyzed by itself and Ro52 and downregulated by YopJ. Unexpectedly, although TRIM5, is ubiquitinated, our results have revealed that the proteasome inhibitors MG115 and MG132 do not stabilize it in HeLa cells, suggesting that the ubiquitination of TRIM5, does not lead to proteasomal degradation. Importantly, TRIM5, is clearly conjugated by a single ubiquitin molecule (monoubiquitination). Our monoubiquitin-fusion assay suggests that monoubiquitination is a signal for TRIM5, to translocate from cytoplasmic bodies to the cytoplasm. [source]

Structure of full-length ubiquitin-conjugating enzyme E2-25K (huntingtin-interacting protein 2)

Randall C. Wilson
The ubiquitin-conjugating enzyme E2-25K has been identified as a huntingtin (the key protein in Huntington's disease) interacting protein and has been shown to play a role in mediating the toxicity of A,, the principal protein involved in Alzheimer's disease pathogenesis. E2-25K is a dual-domain protein with an ubiquitin-associated (UBA) domain as well as a conserved ubiquitin-conjugating (UBC) domain which catalyzes the formation of a covalent bond between the C-terminal glycine of an ubiquitin molecule and the ,-amine of a lysine residue on the acceptor protein as part of the ubiquitin-proteasome pathway. The crystal structures of E2-25K M172A mutant protein at pH 6.5 and pH 8.5 were determined to 1.9 and 2.2, resolution, respectively. Examination of the structures revealed domain,domain interactions between the UBC and UBA domains which have not previously been reported. [source]

Immunosuppressory activity of ubiquitin fragments containing retro-RGD sequence

BIOPOLYMERS, Issue 5 2004
Zbigniew Szewczuk
Abstract A peptide fragment corresponding to the ubiquitin50,59 sequence (LEDGRTLSDY) (U50,59) possesses a very high immunosuppressory activity, comparable to that of cyclosporine, both in the cellular and humoral immune responses. We found that the pentapeptide DGRTL (U52,56) is the shortest, effective immunosuppressory fragment of ubiquitin, although its potency is weaker than that of U50,59. Replacement of each consecutive residue with alanine in U52,56 allowed identification of essential amino acids involved in the immunosuppression. We also evaluated the roles of its N- and C-terminal groups by their acetylation and/or amidation, respectively. The active sequence is located in the external loop of the molecule and therefore it may serve as an important functional epitope for intermolecular binding. Based on the crystal structure of ubiquitin molecule, we designed and synthesized the cyclic analogue with a restricted conformation, cyclo(Glt,Gln,Leu,Glu,Asp,Gly,Arg,Thr,Leu,Ser,Asp,Lys),NH2 (Glt = glutaryl) by reacting the C-terminal Lys side chain with the glutarylated N-terminus. The peptide was designed to mimic the ubiquitin48,59 loop, in order to obtain the ligand that may interact with hypothetical receptors of the loop. The cyclization product selectively but strongly suppresses the cellular immune response. The results indicate that the 48,59 loop may serve as an important functional epitope in the ubiquitin molecule for intermolecular binding. 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source]

Structural basis for distinct roles of Lys63- and Lys48-linked polyubiquitin chains

GENES TO CELLS, Issue 10 2004
Takeshi Tenno
Ubiquitination, a modification in which single or multiple ubiquitin molecules are attached to a protein, serves as a signalling function that controls a wide variety of cellular processes. To date, two major forms of polyubiquitin chain have been functionally characterized, in which the isopeptide bond linkages involve Lys48 or Lys63. Lys48-linked polyubiquitin tagging is mostly used to target proteins for degradation by the proteasome, whereas Lys63-linked polyubiquitination has been linked to numerous cellular events that do not rely on degradative signalling via the proteasome. Apparently linkage-specific conformations of polyubiquitin chains are important for these cellular functions, but the structural bases distinguishing Lys48- and Lys63-linked chains remain elusive. Here, we report NMR and small-angle X-ray scattering (SAXS) studies on the intersubunit interfaces and conformations of Lys63- and Lys48-linked di- and tetraubiquitin chains. Our results indicate that, in marked contrast to Lys48-linked chains, Lys63-linked chains are elongated molecules with no stable non-covalent intersubunit interfaces and thus adopt a radically different conformation from that of Lys48-linked chains. [source]

Structure of a new crystal form of tetraubiquitin

Cynthia L. Phillips
Polyubiquitin chains, in which the C-terminus and a lysine side chain of successive ubiquitin molecules are linked by an isopeptide bond, function to target substrate proteins for degradation by the 26S proteasome. Chains of at least four ubiquitin moieties appear to be required for efficient recognition by the 26S proteasome, although the conformations of the polyubiquitin chains recognized by the proteasome or by other enzymes involved in ubiquitin metabolism are currently unknown. A new crystal form of tetraubiquitin, which has two possible chain connectivities that are indistinguishable in the crystal, is reported. In one possible connectivity, the tetraubiquitin chain is extended and packs closely against the antiparallel neighbor chain in the crystal to conceal a hydrophobic surface implicated in 26S proteasome recognition. In the second possibility, the tetraubiqutitin forms a closed compact structure, in which that same hydrophobic surface is buried. Both of these conformations are quite unlike the structure of tetraubiquitin that was previously determined in a different crystal form [Cook et al. (1994), J. Mol. Biol.236, 601,609]. The new structure suggests that polyubiquitin chains may possess a substantially greater degree of conformational flexibility than has previously been appreciated. [source]

Purification, crystallization and preliminary crystallographic studies of Lys48-linked polyubiquitin chains

Daichi Morimoto
Post-translational modification of proteins by covalent attachment of ubiquitin regulates diverse cellular events. A Lys48-linked polyubiquitin chain is formed via an isopeptide bond between Lys48 and the C-terminal Gly76 of different ubiquitin molecules. The chain is attached to a lysine residue of a substrate protein, which leads to proteolytic degradation of the protein by the 26S proteasome. In order to reveal the chain-length-dependent higher order structures of polyubiquitin chains, Lys48-linked polyubiquitin chains were synthesized enzymatically on a large scale and the chains were separated according to chain length by cation-exchange column chromatography. Subsequently, crystallization screening was performed using the hanging-drop vapour-diffusion method, from which crystals of tetraubiquitin, hexaubiquitin and octaubiquitin chains were obtained. The crystals of the tetraubiquitin and hexaubiquitin chains diffracted to 1.6 and 1.8, resolution, respectively. The tetraubiquitin crystals belonged to space group C2221, with unit-cell parameters a = 58.795, b = 76.966, c = 135.145,. The hexaubiquitin crystals belonged to space group P21, with unit-cell parameters a = 51.248, b = 102.668, c = 51.161,. Structural analysis by molecular replacement is in progress. [source]