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)

It is known that two types of high-molecular-mass protease complexes are present in the cytosol of mammalian cells; a 20S latent multicatalytic proteinase named the proteasome, and a large proteolytic complex with an apparent sedimentation coefficient of 26S that catalyzes ATP-dependent breakdown of proteins conjugated with ubiquitin. In this work, we first demonstrated that a low concentration of SDS was required for activation of the latent proteasome, whereas the 26S complex degraded substrates for proteasomes in the absence of SDS. Moreover, the 26S complex was greatly stabilized in the presence of 2 mM ATP and 20% glycerol. Based on these characteristics, we next devised a novel procedure for purification of the 26S proteolytic complexes from human kidney. In this procedure, the proteolytic complexes were precipitated from cytoplasmic extracts by ultracentrifugation for 5 h at 105000 x g, and the large 26S complexes were clearly separated from the 20S proteasomes by molecular-sieve chromatography on a Biogel A-1.5 m column. The 26S enzyme was then purified to apparent homogeneity by successive chromatographies on hydroxyapatite and Q Sepharose, then by glycerol density-gradient centrifugation. Electrophoretic and immunochemical analyses showed that the purified human 26S complex consisted of multiple subunits of proteasomes with molecular masses of 21-31 kDa and 13-15 protein components ranging in molecular mass over 35-110 kDa, which were directly associated with the proteasome. The purified 26S proteolytic complex degraded 125I-labeled lysozyme-ubiquitin conjugates in an ATP-dependent manner. The 26S enzyme also showed high ATPase activity, which was copurified with the complex. Vanadate and hemin strongly inhibited not only ATP cleavage, but also ATP-dependent breakdown of ubiquitinligated proteins, suggesting that the 26S complex hydrolyzes ATP and ubiquitinated proteins by closely linked mechanisms. These findings indicate that the 26S complex consists of a proteasome with proteolytic function and multiple other components including an ATPase that regulates energy-dependent, ubiquitin-mediated protein degradation.
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PMID:Demonstration that a human 26S proteolytic complex consists of a proteasome and multiple associated protein components and hydrolyzes ATP and ubiquitin-ligated proteins by closely linked mechanisms. 131 98

The energy-requirement for intracellular proteolysis is due largely to the involvement of large multimeric proteases whose function requires ATP hydrolysis. The best-studied such enzyme is protease La from E coli. This tetrameric protease is inhibited in vivo until the binding of an unfolded protein allostericically activates its peptidase and ATPase functions. This mechanism and tight transcriptional regulation prevent non-specific or excessive proteolysis. E. coli contains another ATP-hydrolyzing protease, Ti (Clp), which contains distinct ATPase and proteolytic subunits. Enzymes homologous to La and Ti exist in mitochondria and chloroplasts. In eukaryotic cells, a major neutral proteolytic activity is the 650 kDa proteasome. This multicatalytic structure can function as an ATP-dependent protease or as part of the ATP-dependent complex that degrades ubiquitinated proteins. In mammalian muscle this 1300 kDa complex is formed by an ATP-dependent association of the proteasome with another ATP-dependent protease complex, multipain. Much remains to be learned about the physiological roles and mechanisms of these novel proteases.
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PMID:ATP-dependent proteases in prokaryotic and eukaryotic cells. 210 93

The multicatalytic proteinase complex (MPC) (proteasome) is a high-molecular-weight proteolytic enzyme found in eukaryotic cells and archaebacteria. Regulatory proteins that inhibit or activate the MPC have been described. Association with an ATPase complex alters the specificity of the multicatalytic proteinase complex to permit cleavage of ubiquitinylated proteins. Unidentified proteins have been observed in highly purified preparations of the multicatalytic proteinase complex. Based on immunoreactivity and N-terminal sequencing, we have identified heat-shock protein 90 as a major component of the multicatalytic proteinase complex prepared from 1-month, but not 2-year bovine lenses. alpha-Crystallin, a lens structural protein with chaperone activity, is also found in multicatalytic proteinase complex preparations. Both heat-shock protein 90 and alpha-crystallin inhibit hydrolysis of Cbz-Leu-Leu-Leu-MCA by the multicatalytic proteinase complex at a stoichiometry of 1 mol heat-shock protein per mole of MPC. Heat-shock proteins may interact with denatured proteins and facilitate their degradation. These studies give evidence for the involvement of heat-shock proteins in proteolysis by direct interaction with the multicatalytic proteinase complex.
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PMID:Age-dependent association of isolated bovine lens multicatalytic proteinase complex (proteasome) with heat-shock protein 90, an endogenous inhibitor. 748 11

The multicatalytic and multisubunit proteasomal complexes have been implicated in the processing of antigens to peptides presented by class I major histocompatibility complex molecules. Two structural complexes of this proteinase, 20 S and 26 S proteasomes, have been isolated from cells. By analyzing in vivo assembly of the proteasomal complexes we show that the 20 S proteasomal complexes are irreversibly assembled via 15 S assembly intermediates containing unprocessed beta-type subunits. The 20 S proteasomes further associate reversibly with proteasome activators PA28 or pre-existing ATPase complexes to form 26 S proteasomal complexes. Our findings that not all of the 20 S proteasomal complexes are assembled into 26 S proteasomal complexes within cells and that all of PA28 and ATPase complexes are associated with 20 S proteasomes strongly suggest that all proteasomal complexes coexist within cells. We further demonstrate that 26 S proteasomal complexes are predominantly present in the cytoplasm and a significant portion of the 20 S proteasomal complexes is associated with the endoplasmic reticulum membrane. Taken together, our findings suggest that depending upon their associated regulatory components, 26 S and 20 S-PA28 proteasomal complexes serve different housekeeping functions within the cells, while they degrade antigens in a cooperative manner in antigen processing.
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PMID:In vivo assembly of the proteasomal complexes, implications for antigen processing. 749 35

The 26S proteasome is the central protease of the ubiquitin-dependent pathway of protein degradation. The molecule has a molecular mass of approximately 2000 kD and has a highly conserved structure in eukaryotes. The 26S proteasome is formed by a barrel-shaped 20S core complex and two polar 19S complexes. The 20S complex has C2 symmetry and is formed by four seven-membered rings of which the outer rings (alpha-type subunits) are rotated by 25.7 degrees relative to the inner rings while the inner rings (beta-type subunits) are in register. From a comparison of the activity and regulation of the 26S and 20S particles it can be deduced that the 20S particle contains the protease activity while the 19S complex contains isopeptidase, ATPase and protein unfolding activities. In this article we describe the structures of various proteasome complexes as determined by electron microscopy and discuss structural implications of their subunit sequences.
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PMID:Structural features of archaebacterial and eukaryotic proteasomes. 756 58

We have cloned and sequenced a non-ATPase subunit of the regulatory complex of the Drosophila 26S protease. The gene is present in a single copy in the Drosophila genome. By comparing the nucleotide sequence of the genomic and cDNA clones three exons and two introns were localized. Two transcription start sites were identified 9 bp apart. The deduced protein sequence shows no significant similarity to any other protein in the database. In Drosophila embryos where the 26S protease is present in high concentration, the pool of free subunits of the regulatory complex is very low. Among the free subunits of the regulatory complex the cloned subunit is present in very large excess. This observation raises the possibility that this subunit is in a dynamic equilibrium, exchanging between a free and a particle-bound form, which may have important implications concerning its function.
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PMID:Cloning and sequencing a non-ATPase subunit of the regulatory complex of the Drosophila 26S protease. 764 73

Proteasomes are large multicatalytic protease complexes found in the cytoplasm and nucleus of all eukaryotic cells. 20S proteasomes are cylindrically shaped particles composed of a set of different subunits arranged in a stack of 4 rings with 7-fold symmetry. In yeast 14 different genes are known, which are proposed to code for the complete set of 20S proteasomal subunits. They can be divided in 7 alpha- and 7 beta-type subunits. 26S proteasomes are even larger proteinase complexes which contain the 20S proteasome as the functional proteolytic core. They degrade ubiquitinylated proteins in vitro. Several yeast 26S proteasome subunits have been characterized as members of a novel ATPase family. Studies with yeast 20S and 26S proteasome mutants uncovered the function of proteasomes in stress-dependent and ubiquitin-mediated proteolytic pathways. Proteasomes are important for cellular regulation, cell differentiation, adaptation to environmental changes and are involved in cell cycle control.
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PMID:Studies on the yeast proteasome uncover its basic structural features and multiple in vivo functions. 769 19

The 26S proteasome is the central protease of the ubiquitin-dependent pathway of protein degradation and has a highly conserved structure from slime molds to humans. The elongated molecule which has a molecular mass of approximately 2,000 kD is formed by a barrel-shaped 20S core complex and two polar 19S complexes. The 20S complex has C2 symmetry and is built by four seven-membered rings of which the outer rings are rotated by 26 degrees relative to the inner rings while the inner rings are in register. The 19S cap complex is asymmetric and therefore considerably less well understood on a structural level. From a comparison of the activity and regulation of the 26S and 20S particles, it can be deduced that the 20S particle contains the protease activity while the 19S complex is supposed to contain isopeptidase, oxidoreductase, ATPase and protein-unfolding activities. In this article we describe the structure of various proteasome complexes as determined by electron microscopy and discuss structural implications of their subunit sequences.
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PMID:Structural features of 26S and 20S proteasomes. 769 24

The function of the proteasome is controlled by a variety of specific regulatory proteins including activators, inhibitors, and modulators. Two recently discovered activators, termed PA28 and PA700, bind to the terminal rings of the proteasome to form proteasome-regulatory complexes which display greatly increased proteolytic activity. PA28 is a high-affinity activator of the proteasome's multiple peptidase activities. The carboxyl terminus of PA28 is required for its binding to the proteasome. PA700 binds to the proteasome via an ATP-dependent mechanism. PA700 has ATPase activity, and at least four of PA700's 16 subunits are members of a protein family containing a concensus sequence for ATP binding. Proteasome-PA700 complexes are activated with respect to both the hydrolysis of peptide substrates and the hydrolysis of ubiquitinated proteins.
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PMID:Regulatory proteins of the proteasome. 769 29

Escherichia coli FtsH is an essential integral membrane protein that has an AAA-type ATPase domain at its C-terminal cytoplasmic part, which is homologous to at least three ATPase subunits of the eukaryotic 26S proteasome. We report here that FtsH is involved in degradation of the heat-shock transcription factor sigma 32, a key element in the regulation of the E. coli heat-shock response. In the temperature-sensitive ftsH1 mutant, the amount of sigma 32 at a non-permissive temperature was higher than in the wild-type under certain conditions due to a reduced rate of degradation. In an in vitro system with purified components, FtsH catalyzed ATP-dependent degradation of biologically active histidine-tagged sigma 32. FtsH has a zinc-binding motif similar to the active site of zinc-metalloproteases. Protease activity of FtsH for histidine-tagged sigma 32 was stimulated by Zn2+ and strongly inhibited by the heavy metal chelating agent o-phenanthroline. We conclude that FtsH is a novel membrane-bound, ATP-dependent metalloprotease with activity for sigma 32. These findings indicate a new mechanism of gene regulation in E. coli.
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PMID:Escherichia coli FtsH is a membrane-bound, ATP-dependent protease which degrades the heat-shock transcription factor sigma 32. 778 8


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