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

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

FAT10 is an interferon-gamma-inducible ubiquitin-like protein that consists of two ubiquitin-like domains. FAT10 bears a diglycine motif at its C terminus that can form isopeptide bonds to so far unidentified target proteins. Recently we found that FAT10 and its conjugates are rapidly degraded by the proteasome and that the N-terminal fusion of FAT10 to a long lived protein markedly reduces its half-life. FAT10 may hence direct target proteins to the proteasome for degradation. In this study we report a new interaction partner of FAT10 that may link FAT10 to the proteasome. A yeast two-hybrid screen identified NEDD8 ultimate buster-1L (NUB1L) as a non-covalent binding partner of FAT10, and this interaction was confirmed by coimmunoprecipitation and glutathione S-transferase pull-down experiments. NUB1L is also an interferon-inducible protein that has been reported to interact with the ubiquitin-like protein NEDD8, thus leading to accelerated NEDD8 degradation. Here we show that NUB1L binds to FAT10 much stronger than to NEDD8 and that NEDD8 cannot compete with FAT10 for NUB1L binding. The interaction of FAT10 and NUB1L is specific as green fluorescent fusion proteins containing ubiquitin or SUMO-1 do not bind to NUB1L. The coexpression of NUB1L enhanced the degradation rate of FAT10 8-fold, whereas NEDD8 degradation was only accelerated 2-fold. Because NUB1 was shown to bind to the proteasome subunit RPN10 in vitro and to be contained in 26 S proteasome preparations, it may function as a linker that targets FAT10 for degradation by the proteasome.
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PMID:NEDD8 ultimate buster-1L interacts with the ubiquitin-like protein FAT10 and accelerates its degradation. 1475 70

NEDD8 is a ubiquitin-like protein that controls vital biological events through its conjugation to target proteins. Previously, we identified a negative regulator of the NEDD8 conjugation system, NEDD8 ultimate buster-1 (NUB1), that recruits NEDD8 and its conjugates to the proteasome for degradation. Recently, we performed yeast two-hybrid screening with NUB1 as bait and isolated a ubiquitin precursor UbC1 that is composed of nine tandem repeats of a ubiquitin unit through alpha-peptide bonds. Interestingly, NUB1 interacted with UbC1 through its UBA domain. Further study revealed that the UBA domain interacted with alpha-peptide bond-linked polyubiquitin, but not with isopeptide bond-linked polyubiquitin, indicating that the UBA domain of NUB1 is a specific acceptor for the linear ubiquitin precursor. A functional study revealed that an unidentified protein that was immunoprecipitated with NUB1 served as a ubiquitin C-terminal hydrolase for UbC1. Thus, NUB1 seems to form a protein complex with the unidentified ubiquitin C-terminal hydrolase and recruit UbC1 to this complex. This might allow the ubiquitin C-terminal hydrolase to hydrolyze UbC1, in order to generate ubiquitin monomers. Northern blot analysis showed that the mRNAs of both NUB1 and UbC1 were enriched in the testis. Furthermore, in situ hybridization showed that both mRNAs were strongly expressed in seminiferous tubules of the testis. These results may imply that the UbC1 hydrolysis mediated by NUB1 is involved in cellular functions in the seminiferous tubules such as spermatogenesis.
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PMID:NUB1-mediated targeting of the ubiquitin precursor UbC1 for its C-terminal hydrolysis. 1500 9

In the ubiquitin system, a target substrate is modified by ubiquitin or a ubiquitin-like protein. This modification remodels the surface of the target proteins, affecting, among other properties, their stability, interactions with other proteins, activity, and subcellular localization. At least 10 different modifiers have been described in mammalian cells and conjugation of each modifier to its target may result in a different biological effect. In many cases proteins are modified by multiple moieties of ubiquitin that generate a branched polyubiquitin chain. For most proteins, this modification leads to their degradation by the 26S proteasome. Yet, dependent on the character of the internal linkage between the ubiquitin moieties, it can also lead to activation of transcriptional regulators. Modification by a single moiety of ubiquitin can target proteins for degradation in the lysosome/vacuole. Conjugation of ubiquitin or ubiquitin-like proteins can serve a variety of non-proteolytic functions, such as activation of enzymes, modulation of membrane dynamics, or routing of the tagged proteins to their sub-cellular destination. Ubiquitination of cellular proteins is a highly complex, temporally controlled, and tightly regulated process that targets, in a specific manner, thousands of cellular proteins. It is carried out by a modular cascade of enzymes with high specificity towards defined structural motifs in the target proteins. It has emerged as a critically important post-translational modification that plays major roles in regulating a broad array of basic cellular processes, such as cell division, differentiation, signal transduction, trafficking, and quality control. Not surprisingly, aberrations in the system have been implicated in the pathogenesis of many diseases, certain malignancies, neurodegenerative disorders and pathologies of the inflammatory and immune response among them. Understanding of the underlying mechanisms involved is important for the development of novel, mechanism-based drugs.
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PMID:The ubiquitin system: from basic mechanisms to the patient bed. 1523 Mar 46

The ataxin-1 interacting ubiquitin-like protein (A1Up) contains an amino-terminal ubiquitin-like (UbL) region, four stress-inducible, heat shock chaperonin-binding motifs (STI1), and an ubiquitin-associated domain (UBA) at the carboxyl terminus of A1Up. Although proteins that have both an UbL and UBA domain are thought to play a crucial role in proteasome-mediated activities, few are characterized, except for hHR23A/B. Similar to other UbL-containing proteins, the UbL of A1Up is essential for the interaction of A1Up with the S5a subunit of the 19S proteasome. Importantly, the interaction with the 19S proteasome was disrupted in the presence of the polyglutamine repeat protein, ataxin-1. The UbL domain of A1Up is ubiquitinated by both Lys(48)-linked and Lys(63)-linked chains. Intact A1Up is stable, suggesting that ubiquitination of A1Up is important for degradation-independent targeting of A1Up to the 19S proteasome. The UBA domain of A1Up binds polyubiquitin chains and has a role in the stability of A1Up and in the subcellular localization of A1Up. When the UBA domain was deleted, the localization of A1Up was entirely cytoplasmic, and it co-localized with the proteasome. Interestingly, the interaction between A1Up and mutant ataxin-1-(82Q) increased the half-life of A1Up, whereas nonpathogenic wild-type ataxin-1-(30Q) or ataxin-1-(82Q)-A776 did not.
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PMID:The effects of the polyglutamine repeat protein ataxin-1 on the UbL-UBA protein A1Up. 1528 Mar 65

Attachment of ubiquitin to proteins is a crucial step in many cellular regulatory mechanisms and contributes to numerous biological processes, including embryonic development, the cell cycle, growth control, and prevention of neurodegeneration. In these diverse regulatory settings, the most widespread mechanism of ubiquitin action is probably in the context of protein degradation. Polyubiquitin attachment targets many intracellular proteins for degradation by the proteasome, and (mono)ubiquitination is often required for down-regulating plasma membrane proteins by targeting them to the vacuole (lysosome). Ubiquitin-protein conjugates are highly dynamic structures. While an array of enzymes directs the conjugation of ubiquitin to substrates, there are also dozens of deubiquitinating enzymes (DUBs) that can reverse the process. Several lines of evidence indicate that DUBs are important regulators of the ubiquitin system. These enzymes are responsible for processing inactive ubiquitin precursors, proofreading ubiquitin-protein conjugates, removing ubiquitin from cellular adducts, and keeping the 26S proteasome free of inhibitory ubiquitin chains. The present review focuses on recent discoveries that have led to a better understanding the mechanisms and physiological roles of this diverse and still poorly understood group of enzymes. We also discuss briefly some of the proteases that act on ubiquitin-like protein (UBL) conjugates and compare them to DUBs.
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PMID:Mechanism and function of deubiquitinating enzymes. 1557 15

NEDD8 (neural precursor cell expressed, developmentally down-regulated 8) is a ubiquitin-like protein that controls vital biological events through its conjugation to members of the cullin family, which are components of certain ubiquitin E3 ligases. Recent studies have shown that NEDD8 is incorporated into Lewy bodies (LBs) in Parkinson's disease, Mallory bodies in alcoholic liver disease and Rosenthal fibres in astrocytoma. In order to examine whether NEDD8 plays a role in the formation of ubiquitinated inclusions, we performed immunohistochemical staining of brain tissue from patients with various neurodegenerative disorders, using an affinity-purified polyclonal antibody raised against NEDD8 that did not cross-react with ubiquitin. In LB disease, NEDD8 immunoreactivity was present in almost all of the LBs and Lewy neurites. Moreover, NEDD8 immunoreactivity was found in a variety of ubiquitinated inclusions, including neuronal and oligodendroglial inclusions in multiple system atrophy, neurofibrillary tangles in Alzheimer's disease, ubiquitinated inclusions in motor neurone disease, and intranuclear inclusions in triplet repeat diseases. These findings suggest that NEDD8 is involved in the formation of various ubiquitinated inclusions via the ubiquitin-proteasome system.
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PMID:Accumulation of NEDD8 in neuronal and glial inclusions of neurodegenerative disorders. 1563 31

Cullin-based E3 ubiquitin ligases play important roles in the regulation of diverse developmental processes and environmental responses in eukaryotic organisms. Recently, it was shown in Schizosaccharomyces pombe, Caenorhabditis elegans, and mammals that Cullin3 (CUL3) directly associates with RBX1 and BTB domain proteins in vivo to form a new family of E3 ligases, with the BTB protein subunit functioning in substrate recognition. Here, we demonstrate that Arabidopsis thaliana has two redundant CUL3 (AtCUL3) genes that are essential for embryo development. Besides supporting anticipated specific AtCUL3 interactions with the RING protein AtRBX1 and representative Arabidopsis proteins containing a BTB domain in vitro, we show that AtCUL3 cofractionates and specifically associates with AtRBX1 and a representative BTB protein in vivo. Similar to the AtCUL1 subunit of the SKP1-CUL1-F-box protein-type E3 ligases, the AtCUL3 subunit of the BTB-containing E3 ligase complexes is subjected to modification and possible regulation by the ubiquitin-like protein Related to Ubiquitin in vivo. Together with the presence of large numbers of BTB proteins with diverse structural features and expression patterns, our data suggest that Arabidopsis has conserved AtCUL3-RBX1-BTB protein E3 ubiquitin ligases to target diverse protein substrates for degradation by the ubiquitin/proteasome pathway.
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PMID:Arabidopsis has two redundant Cullin3 proteins that are essential for embryo development and that interact with RBX1 and BTB proteins to form multisubunit E3 ubiquitin ligase complexes in vivo. 1577 80

Eps15 and its related protein Eps15R are key components of the clathrin-mediated endocytic pathway. We searched for new binding partners of Eps15 using a yeast two-hybrid screen. We report here that ubiquilin (hPLIC1), a type-2 ubiquitin-like protein containing a ubiquitin-like domain (UBL) and a ubiquitin-associated domain (UBA), interacts with both Eps15 and Eps15R. Using glutathione-S-transferase pull-down experiments, we show that the first ubiquitin-interacting motif of Eps15 (UIM1) interacts directly with the UBL domain of ubiquilin, whereas it does not bind to ubiquitinated proteins. The second UIM of Eps15 (UIM2) binds poorly to the UBL domain but does bind to ubiquitinated proteins. Two other UIM-containing endocytic proteins, Hrs and Hbp, also interact with ubiquilin in a UIM-dependent manner, whereas epsin does not. Immunofluorescence analysis showed that endogenous Eps15 and Hrs, but not epsin, colocalize with green-fluorescent-protein-fused ubiquilin in cytoplasmic aggregates that are not endocytic compartments. We have characterized these green-fluorescent-protein-fused-ubiquilin aggregates as ubiquitin-rich intracytoplasmic inclusions that are recruited to aggresomes upon proteasome inhibition. Moreover, we show that endogenous Eps15 and endogenous ubiquilin colocalize to cytoplasmic aggregates and aggresomes. Finally, we show that the recruitment of Eps15 into ubiquilin-positive aggregates is UIM dependent. Altogether, our data identify ubiquilin as the first common UIM-binding partner of a subset of UIM-containing endocytic proteins. We propose that this UIM/UBL-based interaction is responsible for the sequestration of certain UIM-containing endocytic proteins into cytoplasmic ubiquitin-rich protein aggregates.
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PMID:Ubiquilin recruits Eps15 into ubiquitin-rich cytoplasmic aggregates via a UIM-UBL interaction. 1615 59

NUB1 interacts with a ubiquitin-like protein NEDD8 to target the NEDD8 monomer and neddylated proteins to the proteasome for degradation. Therefore, NUB1 is thought to be a potent downregulator of NEDD8 conjugation system. Since NUB1 possesses a UBL domain, which was previously shown to be an S5a-interacting motif in RAD23/HHR23, we initially hypothesized that NUB1 interacts with the S5a subunit of the proteasome through its UBL domain. To examine this, we performed an in vitro GST pull-down assay and a yeast two-hybrid assay. Unexpectedly, our studies revealed that NUB1 directly interacts with the S5a subunit through its C-terminal region between amino acid residues 536 and 584, not through its UBL domain. Although the UBL domain was not an S5a-interacting motif in NUB1, our further studies revealed that the UBL domain is required for the function of NUB1.
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PMID:Interaction of NUB1 with the proteasome subunit S5a. 1617 79

The ubiquitin-proteasome pathway is the major nonlysosomal proteolytic system in eukaryotic cells responsible for regulating the level of many key regulatory molecules within the cells. Modification of cellular proteins by ubiquitin and ubiquitin-like proteins, such as small ubiquitin-like modifying protein (SUMO), plays an essential role in a number of biological schemes, and ubiquitin pathway enzymes have become important therapeutic targets. Ubiquitination is a dynamic reversible process; a multitude of ubiquitin ligases and deubiquitinases (DUBs) are responsible for the wide-ranging influence of this pathway as well as its selectivity. The DUB enzymes serve to maintain adequate pools of free ubiquitin and regulate the ubiquitination status of cellular proteins. Using SUMO fusions, a novel assay system, based on poliovirus RNA-dependent RNA polymerase activity, is described here. The method simplifies the isopeptidase assay and facilitates high-throughput analysis of these enzymes. The principle of the assay is the dependence of the viral polymerase on a free N terminus for activity; accordingly, the polymerase is inactive when fused at its N terminus to SUMO or any other ubiquitin-like protein. The assay is sensitive, reproducible, and adaptable to a high-throughput format for use in screens for inhibitors/activators of clinically relevant SUMO proteases and deubiquitinases.
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PMID:Small ubiquitin-like modifying protein isopeptidase assay based on poliovirus RNA polymerase activity. 1635 62


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