Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In eukaryotic cells, the ubiquitin-proteasome pathway is the major mechanism for the targeted degradation of proteins with short half-lives. The covalent attachment of ubiquitin to lysine residues of targeted proteins is a signal for the recognition and rapid degradation by the proteasome, a large multi-subunit protease. In this report, we demonstrate that the human estrogen receptor (ER) protein is rapidly degraded in mammalian cells in an estradiol-dependent manner. The treatment of mammalian cells with the proteasome inhibitor MG132 inhibits activity of the proteasome and blocks ER degradation, suggesting that ER protein is turned over through the ubiquitin-proteasome pathway. In addition, we show that in vitro ER degradation depends on ubiquitin-activating E1 enzyme (UBA) and ubiquitin-conjugating E2 enzymes (UBCs), and the proteasome inhibitors MG132 and lactacystin block ER protein degradation in vitro. Furthermore, the UBA/UBCs and proteasome inhibitors promote the accumulation of higher molecular weight forms of ER. The UBA and UBCs, which promote ER degradation in vitro, have no significant effect on human progesterone receptor and human thyroid hormone receptor beta proteins.
...
PMID:Proteasome-dependent degradation of the human estrogen receptor. 1005 59

Addition of ammonium ions to yeast cells growing on proline as the sole nitrogen source induces internalization of the general amino acid permease Gap1p and its subsequent degradation in the vacuole. An essential step in this down-regulation is Gap1p ubiquitination through a process requiring the Npi1p/Rsp5p ubiquitin ligase. We show in this report that NPI2, a second gene required for NH4+-induced down-regulation of Gap1p, codes for the ubiquitin hydrolase Doa4p/Ubp4p/Ssv7p and that NH4+-induced Gap1p ubiquitination is strongly reduced in npi2 cells. The npi2 mutation results in substitution of an aromatic amino acid located in a 33-residue sequence shared by some ubiquitin hydrolases of the Ubp family. In this mutant, as in doa4(delta) cells, the amount of free monomeric ubiquitin is at least four times lower than in wild-type cells. Both ubiquitination and down-regulation of the permease can be restored in npi2 cells by over-expression of ubiquitin. In proline-grown wild-type and npi2/doa4 cells overproducing ubiquitin, Gap1p appears to be mono-ubiquitinated at two lysine acceptor sites. Addition of NH4+ triggers rapid poly-ubiquitination of Gap1p, the poly-ubiquitin chains being specifically formed by linkage through the lysine 63 residue of ubiquitin. Gap1p is thus ubiquitinated differently from the proteins targeted by ubiquitination for proteolysis by the proteasome, but in the same manner as the uracil permease, also subject to ubiquitin-dependent endocytosis. When poly-ubiquitination through Lys63 is blocked, the Gap1p permease still undergoes NH4+-induced down-regulation, but to a lesser extent.
...
PMID:NH4+-induced down-regulation of the Saccharomyces cerevisiae Gap1p permease involves its ubiquitination with lysine-63-linked chains. 1019 16

Two proteasome activators PA28alpha and beta, which have been implicated in antigen processing for loading class I MHC molecules, are synthesized in response to Ifn-gamma. The human genes encoding these activators (PSME1 and PSME2, respectively) were analyzed by sequencing. Each gene comprised 11 exons, consistent with gene duplication during vertebrate evolution. The intron/exon organization of both genes was highly conserved, the major difference being the absence of the exon encoding the lysine and glutamic acid-rich 'KEKE' motif in PA28beta. Two other genes of relevance to the immune system were located close to those for PA28 at 14q11.2 including ISGF3G, a protein involved in transcription after IFNalpha signalling. These sequences were also characterized.
...
PMID:Organization of the genes encoding the human proteasome activators PA28alpha and beta. 1019 20

The ubiquitin proteolytic system plays a major role in a variety of basic cellular processes. In the majority of these processes, the target proteins are completely degraded. In one exceptional case, generation of the p50 subunit of the transcriptional regulator NF-kappaB, the precursor protein p105 is processed in a limited manner: the N-terminal domain yields the p50 subunit, whereas the C-terminal domain is degraded. The identity of the mechanisms involved in this unique process have remained elusive. It has been shown that a Gly-rich region (GRR) at the C-terminal domain of p50 is an important processing signal. Here we show that the GRR does not interfere with conjugation of ubiquitin to p105 but probably does interfere with the processing of the ubiquitin-tagged precursor by the 26S proteasome. Structural analysis reveals that a short sequence containing a few Gly residues and a single essential Ala is sufficient to generate p50. Mechanistically, the presence of the GRR appears to stop further degradation of p50 and to stabilize the molecule. It appears that the localization of the GRR within p105 plays an important role in directing processing: transfer of the GRR within p105 or insertion of the GRR into homologous or heterologous proteins is not sufficient to promote processing in most cases, which is probably due to the requirement for an additional specific ubiquitination and/or recognition domain(s). Indeed, we have shown that amino acid residues 441 to 454 are important for processing. In particular, both Lys 441 and Lys 442 appear to serve as major ubiquitination targets, while residues 446 to 454 are independently important for processing and may serve as the ubiquitin ligase recognition motif.
...
PMID:Structural motifs involved in ubiquitin-mediated processing of the NF-kappaB precursor p105: roles of the glycine-rich region and a downstream ubiquitination domain. 1020 90

The intracellular level of p27(Kip1), a cyclin-dependent kinase (CDK) inhibitory protein, is rapidly reduced at the G1/S transition phase when the cell cycle pause ceases. In this study, we demonstrated that two posttranslational mechanisms were involved in p27(Kip1) breakdown: degradation via the ubiquitin (Ub)-proteasome pathway and proteolytic processing that rapidly eliminates the cyclin-binding domain. We confirmed that p27(Kip1) was ubiquitinated in vitro as well as in vivo. The p27(Kip1) -ubiquitination activity was higher at the G1/S boundary than during the G0/G1 phase, and p27(Kip1) ubiquitination was reduced significantly when the lysine residues at positions 134, 153, and 165 were replaced by arginine, suggesting that these lysine residues are the targets for Ub conjugation. In parallel with its Ub-dependent degradation, p27(Kip1) was processed rapidly at its N terminus, reducing its molecular mass from 27 to 22 kDa, by a ubiquitination-independent but adenosine triphosphate (ATP)-dependent mechanism with higher activity during the S than the G0/G1 phase. This 22-kDa intermediate had no cyclin-binding domain at its N terminus and virtually no CDK2 kinase inhibitory activity. These results suggest that p27(Kip1) is eliminated by two independent mechanisms, ubiquitin-mediated degradation and ubiquitin-independent processing, during progression from the G1 to S phase.
...
PMID:Down-regulation of p27(Kip1) by two mechanisms, ubiquitin-mediated degradation and proteolytic processing. 1031 97

MyoD is a tissue-specific transcriptional activator involvd in skeletal muscle differentiation. It is induced during transition from proliferating, non-differentiated myoblasts to the resting and well differentiated myotubes. Like many other transcriptional regulators, it is short-lived, however, the targeting proteolytic pathway and the underlying regulatory mechanisms involved have remained obscure. Here we show that MyoD is degraded by the ubiquitin system both in vivo and in vitro. In cells, degradation is inhibited by lactacystin, a specific inhibitor of the 20S proteasome. Inhibition is accompanied by accumulation of MyoD-ubiquitin conjugates. In a cell free system, the proteolytic process requires both ATP and ubiquitin and is preceded by formation of MyoD-ubiquitin adducts. Interestingly, the process is inhibited by the specific DNA sequence to which MyoD binds. Analysis of the ubiquitination site has revealed that the N-terminal residue of MyoD is sufficient and essential to promote conjugation and subsequent degradation of the protein: conjugation to internal Lys residues is not necessary. Substitution of all Lys residues did not affect significantly its degradation either in intact cells or in a reconstituted cell free system. Degradation was inhibited by specific proteasome inhibitors and was accompanied by accumulation of ubiquitinated species of the protein. We concluded that the first ubiquitin moiety is attached via its C-terminal Gly to the N-terminal residue of MyoD, and the polyubiquitin chain is then synthesized on Lys48 of this moiety.
...
PMID:Degradation of MyoD by the ubiquitin pathway: regulation by specific DNA-binding and identification of a novel site for ubiquitination. 1036 48

The HTLV-1 singly spliced open reading frame I protein, p12(I), is highly unstable and appears to be necessary for persistent infection in rabbits. Here we demonstrate that p12(I) forms dimers through two putative leucine zipper domains and that its stability is augmented by specific proteasome inhibitors. p12(I) is ubiquitylated, and mutations of its unique carboxy-terminus lysine residue to an arginine greatly enhance its stability. Interestingly, analysis of 53 independent HTLV-1 strains revealed that the natural p12(I) alleles found in ex vivo samples of tropical spastic paraparesis-HTLV-1-associated myelopathy patients contain a Lys at position 88 in some cases, whereas arginine is consistently found at position 88 in HTLV-1 strains from all adult T-cell leukemia-lymphoma (ATLL) cases and healthy carriers studied. This apparent segregation of different alleles in tropical spastic paraparesis-HTLV-associated myelopathy and ATLL or healthy carriers may be relevant in vivo, since p12(I) binds the interleukin-2 receptor beta and gammac chains, raising the possibility that the two natural alleles might affect differently the regulation of these molecules.
...
PMID:A lysine-to-arginine change found in natural alleles of the human T-cell lymphotropic/leukemia virus type 1 p12(I) protein greatly influences its stability. 1040 Jul 40

Polyubiquitin (Ub) chains linked through Lys-48-Gly-76 isopeptide bonds represent the principal signal by which substrates of the Ub-dependent protein degradation pathway are targeted to the 26 S proteasome, but the mechanism(s) whereby these chains are assembled on substrate proteins is poorly understood. Nor have assembly mechanisms or definitive functions been assigned to polyubiquitin chains linked through several other lysine residues of ubiquitin. We show that rabbit reticulocyte lysate harbors enzymatic components that catalyze the assembly of unanchored Lys-29-linked polyubiquitin chains. This reaction can be reconstituted using the ubiquitin-conjugating enzyme (E2) known as UbcH5A, a 120-kDa protein(s) that behaves as a ubiquitin-protein ligase (E3), and ubiquitin-activating enzyme (E1). The same partially purified E3 preparation also catalyzes the assembly of unanchored chains linked through Lys-48. Kinetic studies revealed a K(m) of approximately 9 microM for the acceptor ubiquitin in the synthesis of diubiquitin; this value is similar to the concentration of free ubiquitin in most cells. Similar kinetic behavior was observed for conjugation to Lys-48 versus Lys-29 and for conjugation to tetraubiquitin versus monoubiquitin. The properties of these enzymes suggest that there may be distinct pathways for ubiquitin-ubiquitin ligation versus substrate-ubiquitin ligation in vivo.
...
PMID:E2/E3-mediated assembly of lysine 29-linked polyubiquitin chains. 1048 Sep 50

We have used solid-phase chemistry to synthesize proteins equivalent to a human ubiquitin precursor (ubiquitin-52-amino-acid ribosomal protein fusion; UBICEP52) and representative of isopeptide-linked ubiquitin-protein conjugates [ubiquitin-(epsilonN)-lysine]; these proteins were precisely cleaved by a purified recombinant Drosophila deubiquitinating enzyme (DUB), UCH-D. Along with the previously synthesized ubiquitin-(alphaN)-valine, these synthetic proteins were used as substrates to assess the catalytic capacities of a number of diverse DUBs expressed in Escherichia coli: human HAUSP; mouse Unp; and yeast Ubps 1p, 2p, 3p, 6p, 11p, and 15p and Yuh1p. Distinct specificities of these enzymes were detected; notably, in addition to UCH-D, isopeptidase activity [ubiquitin-(epsilonN)-lysine cleavage] was only associated with Yuh1p, Unp, Ubp1p, and Ubp2p. Additionally, human placental 26S proteasomes were only able to cleave UBICEP52 and ubiquitin-(epsilonN)-lysine, suggesting that 26S proteasome-associated DUBs are class II-like. This work demonstrates that the synthetic approach offers an alternative to recombinant methods for the production of small proteins in vitro.
...
PMID:Chemically synthesized ubiquitin extension proteins detect distinct catalytic capacities of deubiquitinating enzymes. 1052 95

It is assumed that increased oxidative stress contributes to the development of complications in diabetes. In this study, several markers of protein structural modifications directly induced by free radicals were investigated in the liver and kidney cytosolic fractions of rats with streptozotocin-induced diabetes. Sulfydryl residue and side-chain amino group analyses, as well as immunoblotting and chromatographic measurements of protein-bound carbonyl, suggest that protein oxidative modification is not increased by diabetes, with the exception of sulfydryl groups in renal cytosol. The levels of the glycation-derived carbonyl N epsilon-fructosyl-lysine are significantly increased by diabetes. Furthermore, unchanged proteolytic activity against in vivo-oxidized proteins, significant decreases both in activity against H2O2-modified proteins and in proteasome activity, measured by the degradation of a specific fluorogenic substrate, suggest that the unchanged oxidative protein modification in the diabetic state cannot be attributed to an increased cytosolic proteolytic activity in these tissues. These results provide evidence against a generalized increase in protein oxidative damage and demonstrate a diabetes-induced alteration in cytosolic proteolytic pathways, suggesting that proteasome activity may be impaired in these organs.
...
PMID:Diabetes induces an impairment in the proteolytic activity against oxidized proteins and a heterogeneous effect in nonenzymatic protein modifications in the cytosol of rat liver and kidney. 1053 57


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---