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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)

The 26 S proteasome complex catalyzing ATP-dependent breakdown of ubiquitin-ligated proteins was purified from spinach leaves to near homogeneity by chromatography on DEAE-cellulose, gel filtration on Biogel A-1.5, and glycerol density gradient centrifugation. The purified enzyme was shown to degrade multi-ubiquitinated, but not unmodified, lysozymes in an ATP-dependent fashion coupled with ATPase activity supplying energy for proteolysis and isopeptidase activity to generate free ubiquitin. By nondenaturing electrophoresis, the purified enzyme was separated into two distinct forms of the 26 S complex, named 26 S alpha and 26 S beta proteasomes, with different electrophoretic mobilities. The 26 S proteasome was found to consist of multiple polypeptides with molecular masses of 23-35 and 39-115 kDa, which were thought to be those of a 20 S proteasome with multicatalytic proteinase activity and an associated regulatory part with ATPase and deubiquitinating activities, respectively. The subunit multiplicity of the spinach 26 S proteasome closely resembled that of rat liver with minor differences in certain components. No sulfhydryl bond was involved in the assembly of this multicomponent polypeptide complex. Electron microscopy showed that the 26 S proteasome complex had a "caterpillar"-like shape, consisting of four central protein layers, assumed to be the 20 S proteasome, with asymmetric V-shaped layers at each end. These structural and functional characteristics of the spinach 26 S proteasome showed marked similarity to those of the mammalian 26 S proteasomes reported recently, suggesting that the 26 S proteasome is widely distributed in eukaryotic cells and is of general importance for catalyzing the soluble energy- and ubiquitin-dependent proteolytic pathway.
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PMID:Purification and characterization of the 26 S proteasome from spinach leaves. 792 95

Exposure of HT4 cells (a mouse neuronal cell line) to a new potent permeable peptidyl aldehyde inhibitor of the chymotrypsin-like activity of the multicatalytic proteinase complex (MPC) causes accumulation of ubiquitinylated proteins. In contrast, inhibition of calpain or treatment with a lysosomotropic agent failed to produce detectable ubiquitin-protein conjugates. The appearance of such conjugates is not a nonspecific phenomenon because incubation with the peptidyl alcohol analogue of the inhibitor does not produce accumulation of ubiquitinylated proteins. The MPC inhibitor may therefore be a useful tool for identification and study of physiological pathways involving MPC. Furthermore, the inhibitor may help develop a model for the study of neurodegeneration where accumulation of ubiquitin-protein conjugates is commonly detected in abnormal brain inclusions.
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PMID:A new inhibitor of the chymotrypsin-like activity of the multicatalytic proteinase complex (20S proteasome) induces accumulation of ubiquitin-protein conjugates in a neuronal cell. 793 14

In rat muscle metabolic acidosis increases ATP-dependent protein degradation and levels of mRNAs for ubiquitin (Ub) and proteasome subunits. Because adrenalectomy (ADX) abolishes the proteolytic response to acidosis in muscle, we examined whether glucocorticoids (GCs) are necessary for acidosis-induced changes in Ub and proteasome mRNAs in muscles. Total RNA content of the white fiber extensor digitorum longus or mixed fiber gastrocnemius muscles were lowest in muscles of ADX rats given acid plus GCs. In contrast, the abundance of Ub and C2 and C9 proteasome subunits mRNAs were increased in muscles from this group compared with untreated ADX rats or ADX rats given acid or GCs alone. Because total RNA is reduced, the increase in these mRNAs in muscles of ADX rats receiving acid plus GCs provides evidence for a specific activation of the ATP-dependent-Ub-proteasome pathway. Thus, GCs are required but not sufficient to produce the coordinated increase in mRNAs encoding ubiquitin and proteasome subunits occurring in muscles of acidotic rats.
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PMID:Acidosis and glucocorticoids concomitantly increase ubiquitin and proteasome subunit mRNAs in rat muscle. 794 91

Rapid degradation of specific regulatory proteins plays a role in a wide range of cellular phenomena, including cell cycle progression and the regulation of cell growth and differentiation. A major mechanism of selective protein turnover in vivo involves a large multi-subunit protease known as the proteasome or multi-catalytic proteinase. At the same time, the degradation of many cellular proteins requires their covalent ligation to the polypeptide ubiquitin. Here we show that the yeast S. cerevisiae MAT alpha 2 repressor, which is known to be ubiquitinylated in vivo, requires the proteasome for its rapid intracellular proteolysis.
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PMID:Degradation of the yeast MAT alpha 2 transcriptional regulator is mediated by the proteasome. 795

Evidence indicates that a component of the multicatalytic proteinase complex (MPC) that preferentially cleaves bonds after branched chain amino acids (BrAAP) is a major factor responsible for the protein-degrading activity of the MPC. We report here the synthesis of substrate-related peptidyl aldehydes that inhibit the activity of this component toward both synthetic peptide substrates and proteins. The most potent of the inhibitors, Cbz-Gly-Pro-Phe-leucinal (Cbz-GPFL-CHO) inhibits competitively with a Ki of 1.5 microM. The peptidyl aldehydes also inhibit the small neutral amino acid preferring and the peptidylglutamyl-peptide hydrolyzing activities of the MPC. The chymotrypsin-like activity is only weakly inhibited, and the trypsin-like activity is moderately activated. The importance of a Pro residue in the P3 position and a leucinal residue in the P1 position for inhibition of the BrAAP component is indicated by the finding that replacement of these residues by a glycine or phenylalaninal, respectively, markedly increases the Ki. Cbz-GPFL-CHO inhibited the BrAAP activity with the same Ki both before and after activation of this component by exposure of the MPC to 3,4-dichloroisocoumarin, suggesting that the peptidyl aldehyde is an effective inhibitor of both the overt and latent proteolytic activities of the MPC. Incubation of a human breast cancer cell line (MCF-7) in culture with the inhibitors of the BrAAP component led to an accumulation of ubiquitin-protein conjugates, indicating inhibition of the ubiquitin-dependent proteolytic pathway.
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PMID:Inhibition of the proteolytic activity of the multicatalytic proteinase complex (proteasome) by substrate-related peptidyl aldehydes. 796 80

20 S proteasomes are cylinder-shaped protein complexes that play an important role in intracellular protein degradation in eukaryotes and certain archaebacteria. Although 20 S proteasomes were first described many years ago, it has been discovered only recently that these particles can assemble with other protein complexes, presumably of regulatory function. One of the macromolecular assemblies formed, the 26 S proteasome complex, functions as an ATP-dependent protease in the ubiquitin pathway, which has been implicated in the degradation of abnormal proteins, degradation of short-lived regulatory proteins and antigen presentation.
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PMID:Proteasomes: protein degradation machines of the cell. 798 32

Proteasomes are the essential components of complexes involved in an extralysosomal energy- and ubiquitin-dependent proteolytic pathway. The first alpha-type proteasome subunit in plants has recently been described. In this work, the sequence of the first beta-type proteasome subunit in plants, isolated from Arabidopsis thaliana cDNA libraries is reported. The mRNA accumulation of both subunits was analysed and compared with those of the ubiquitin and histone mRNAs, in different tissues and during re-initiation of mitotic activity. It is demonstrated that in plants, as in animal cells, the transcripts of both the alpha-type and beta-type proteasome subunits accumulate to high levels during cell proliferation, in parallel with mRNAs coding for a ubiquitin fusion protein and several polyubiquitins, but earlier than those coding for histone H4 whose expression is known to be coupled to DNA synthesis. These results suggest that, as in animal cells, proteasomes may be involved in the progression of the cell cycle.
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PMID:Molecular characterization of a beta-type proteasome subunit from Arabidopsis thaliana co-expressed at a high level with an alpha-type proteasome subunit early in the cell cycle. 798 12

The molecular properties of an ATP/ubiquitin-dependent "26S" proteasome complex purified from rat liver were examined by physicochemical, biochemical, and morphological analyses. On ultracentrifugation, the proteasome complex sedimented as almost a single component with a sedimentation coefficient of 30.3S. Dynamic light-scattering measurements indicated that it has a diffusion coefficient of 1.38 x 10(-7) cm2/sec and a Stokes radius of 15.5 nm. From these two coefficients, the protein complex was estimated to have the high molecular weight of 2.02 x 10(6). Static light-scattering analysis indicated a molecular weight of 1.91 x 10(6) and a radius of gyration of 16.8 nm. The proteasome complex was found to be composed of multiple subunits of the 20S proteasome with molecular weights of 2.1-3.1 x 10(4) and 15-20 protein species with molecular weights of 3.5-11.0 x 10(4), which were directly associated with the 20S proteasome. The electron micrographic finding that the 26S proteasome complex had a caterpillar shape, direct electronmicroscopic observations on the subunit arrangement of the 20S proteasome, and classification of the subunits of the latter into two groups with respect to sequence homology suggested that the 26S complex is a symmetrical assembly of two domains, each containing a large terminal subset and half the central 20S subset of components. For clarification of the molecular structure of the 26S proteasome complex in solution, its physicochemical parameters were calculated theoretically using a model based on this caterpillar-shaped complex. The values obtained for the Stokes radius and radius of gyration of 12.2 and 14.9 nm were consistent with the experimental values. These results provide evidence that the 26S proteasome complex is a cylindrical caterpillar-like structure of "30S" in solution, consisting of a 20S proteasome component with proteolytic function and multiple other components, which possibly have regulatory roles.
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PMID:Molecular characterization of the "26S" proteasome complex from rat liver. 800 81

Eukaryotic cells contain a major intracellular proteolytic activity known as the proteasome. The proteasome is a strongly conserved cylindrical structure of high molecular weight (650 kDa, approximately 20 S) and demonstrates multiple endopeptidase activities. The general structural, biochemical and genetic features of the proteasome are conserved from archaebacteria through yeast to humans. This structure fulfills an essential role by functioning as the proteolytic core of a 26 S multienzyme complex responsible for the energy-dependent degradation of ubiquitinated proteins. The bulk of intracellular proteolysis appears to be through the ubiquitin-dependent pathway. Incorporation of the proteasome into the 26 S multienzyme complex appears to confer both a specificity for ubiquitinated proteins as well as a means to tightly regulate proteolytic activity. Thus, one function of the proteasome is required for the degradation of either abnormal or certain regulatory proteins by the ubiquitin pathway. Proteasome subunits appear to be encoded by a related gene family as defined by extensive sequence similarities. The gene products are confined to either of two general classes: alpha-type which appear to be structural and beta-type which may be catalytic. Genes encoding at least two proteasome subunits map to the Major Histocompatibility Complex. Accumulating evidence points to the proteasome (or a specialized form) participating in the cytosolic degradation of these viral proteins upon cellular infection.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The role of the proteasome in cellular protein degradation. 800 15

The ATP-ubiquitin-dependent proteolytic pathway (ubiquitin pathway) is believed to be involved in the formation of various neuronal inclusion bodies including Lewy bodies (LBs), a pathological hallmark of Parkinson disease and diffuse Lewy body disease (DLBD). Since multicatalytic proteinase (MCP) is involved in the ubiquitin pathway, an investigation of whether MCP is involved in neuronal inclusion bodies would provide a clue to the mechanism underlying the formation of neuronal inclusion bodies as well as to the pathogenesis of degenerative neurological disorders. In this study, we investigated detailed immunolocalization of MCP in LBs in DLBD brains using light and electron microscopy. We raised three different monoclonal antibodies against purified human MCP. Each of them recognized different sets of MCP subunits on Western blotting. Immunohistochemically, anti-MCP antibodies recognized all ubiquitin-positive cortical LBs in situ as well as those isolated from frozen DLBD cortices, suggesting that MCP is present in LBs as a whole molecule exhibiting protease activity. In electron microscopy, MCP immunoreactivity (MCP-IR) was exclusively localized on a characteristic oval structure with an approximate diameter of 100 nm. This structure was distributed throughout the LBs and was devoid of ubiquitin immunoreactivity. Treatment of isolated LBs with 2% SDS, but not with 0.5% Triton X-100, removed this structure from LBs in which fibrous materials predominated. Ubiquitin immunoreactivity was also decreased in isolated LBs treated with 2% SDS, suggesting that the fibrous structures in LBs were not ubiquitinated in situ. Thus, it is suggested that LBs are subjected to a proteolytic process in which MCP plays a role via processing of specific components of LBs.
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PMID:Multicatalytic proteinase is associated with characteristic oval structures in cortical Lewy bodies: an immunocytochemical study with light and electron microscopy. 802 94


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