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)

The proteasome is a multicatalytic protease complex that plays a key role in diverse cellular functions. The peptide vinyl sulfone, carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z-L3VS) covalently inhibits the trypsin-like, chymotrypsin-like and, unlike lactacystin, also the peptidylglutamyl peptidase activity in isolated proteasomes, and blocks their function in living cells. Although described as a class of mechanism-based inhibitors for cysteine proteases, the peptide vinyl sulfone Z-L3VS and a 125I-labeled nitrophenol derivative (125I-NIP-L3VS) covalently modify the active site threonine of the catalytic beta subunits of the proteasome. Modification of Thermoplasma proteasomes demonstrates the requirement for a hydroxyl amino acid (threonine, serine) as nucleophile at the beta subunit's NH2 terminus. 125I-NIP-L3VS covalently modifies the HslV subunit of the Escherichia coli protease complex HslV/HslU, a reaction that requires ATP, and supports a catalytic mechanism shared with that of the eukaryotic proteasome.
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PMID:Covalent modification of the active site threonine of proteasomal beta subunits and the Escherichia coli homolog HslV by a new class of inhibitors. 919 16

We have studied the mechanism of inhibition of the recombinant Rhodococcus proteasome by four different chemical classes of active site-directed small molecule inhibitors. Clasto-lactacystin beta-lactone is a time-dependent inhibitor of the Rhodococcus proteasome's ability to hydrolyze Suc-Leu-Leu-Val-Tyr-AMC, a substrate for this proteasome's single type of active site, and proceeds with a kinact/[I] of 1,700 M-1 s-1. Using peptide mapping of tryptic digests, LC/MS, and amino acid sequence analysis, we have established that the Ogamma of the hydroxyl group on the N-terminal threonine of the beta-subunit is the sole modification made by the beta-lactone. Active site titrations of the Rhodococcus proteasome with reversible peptide aldehydes show the expected stoichiometry of one inhibitor molecule per beta-subunit. Prior modification with beta-lactone completely abrogates the binding of peptidyl boronic acid inhibitors, suggesting that these inhibitors also inactivate the enzyme by reacting with the Ogamma moiety on Thr1. High performance liquid chromatography analysis of peptidyl vinyl sulfone-modified intact Rhodococcus proteasome beta-subunit and its tryptic peptides suggests that the peptidyl vinyl sulfone modifies a residue in the N-terminal 20 amino acids. This modification is also blocked by prior treatment with beta-lactone.
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PMID:Active site-directed inhibitors of Rhodococcus 20 S proteasome. Kinetics and mechanism. 933 74

Hitherto the biology of proteolysis in prokaryotes, particularly in archaea, is only poorly understood. We have used the tri-peptide vinyl sulfone inhibitor carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z-L3VS) to study the in vivo function of proteasomes in Thermoplasma acidophilum. Z-L3VS is a potent inhibitor of the Thermoplasma proteasome and is capable of modifying 75 to 80% of the proteasomal beta-subunits in cell cultures. Inhibition of proteasomes has only marginal effects under normal growth conditions. Under heat shock conditions, however, the effects of proteasome inhibition are much more severe, to the extent of complete cell growth arrest. These data suggest that other proteolytic systems may exist that can compensate for the loss of proteasome function in T. acidophilum.
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PMID:Proteasome function is dispensable under normal but not under heat shock conditions in Thermoplasma acidophilum. 954 Oct 12

20S proteasomes were purified from Streptomyces coelicolor A3(2) and shown to be built from one alpha-type subunit (PrcA) and one beta-type subunit (PrcB). The enzyme displayed chymotrypsin-like activity on synthetic substrates and was sensitive to peptide aldehyde and peptide vinyl sulfone inhibitors and to the Streptomyces metabolite lactacystin. Characterization of the structural genes revealed an operon-like gene organization (prcBA) similar to Rhodococcus and Mycobacterium spp. and showed that the beta subunit is encoded with a 53-amino-acid propeptide which is removed during proteasome assembly. The upstream DNA region contains the conserved orf7 and an AAA ATPase gene (arc).
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PMID:The 20S proteasome of Streptomyces coelicolor. 976 79

Several studies on disposal of nonsecreted Ig L chains have identified the endoplasmic reticulum as the site of degradation. Here, we examine degradation of a nonsecreted Ig L chain, T15L, and an experimentally endoplasmic reticulum-retained secretion-competent L chain, D16L, in the absence of H chains. We demonstrate that 1) degradation is specifically impaired by the proteasome-specific inhibitors carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z-L3VS) and lactacystin, 2) L chain degradation occurs early in the biosynthetic pathway, and 3) degradation does not require vesicular transport. Our findings indicate that previous assertions of L chain disposal within the endoplasmic reticulum must be modified. To our knowledge, we provide the first direct evidence supporting a new paradigm for removal of nonsecreted Ig L chains via dislocation to cytosolic proteasomes.
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PMID:Cutting edge: proteasome involvement in the degradation of unassembled Ig light chains. 1038 92

The proteasome regulates cellular processes as diverse as cell cycle progression and NF-kappaB activation. In this study, we show that the potent antitumor natural product epoxomicin specifically targets the proteasome. Utilizing biotinylated-epoxomicin as a molecular probe, we demonstrate that epoxomicin covalently binds to the LMP7, X, MECL1, and Z catalytic subunits of the proteasome. Enzymatic analyses with purified bovine erythrocyte proteasome reveal that epoxomicin potently inhibits primarily the chymotrypsin-like activity. The trypsin-like and peptidyl-glutamyl peptide hydrolyzing catalytic activities also are inhibited at 100- and 1,000-fold slower rates, respectively. In contrast to peptide aldehyde proteasome inhibitors, epoxomicin does not inhibit nonproteasomal proteases such trypsin, chymotrypsin, papain, calpain, and cathepsin B at concentrations of up to 50 microM. In addition, epoxomicin is a more potent inhibitor of the chymotrypsin-like activity than lactacystin and the peptide vinyl sulfone NLVS. Epoxomicin also effectively inhibits NF-kappaB activation in vitro and potently blocks in vivo inflammation in the murine ear edema assay. These results thus define epoxomicin as a novel proteasome inhibitor that likely will prove useful in exploring the role of the proteasome in various in vivo and in vitro systems.
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PMID:Epoxomicin, a potent and selective proteasome inhibitor, exhibits in vivo antiinflammatory activity. 1046 20

The human immunodeficiency virus, type I protease inhibitor Ritonavir has been used successfully in AIDS therapy for 4 years. Clinical observations suggested that Ritonavir may exert a direct effect on the immune system unrelated to inhibition of the human immunodeficiency virus, type I protease. In fact, Ritonavir inhibited the major histocompatibility complex class I restricted presentation of several viral antigens at therapeutically relevant concentrations (5 microM). In search of a molecular target we found that Ritonavir inhibited the chymotrypsin-like activity of the proteasome whereas the tryptic activity was enhanced. In this study we kinetically analyzed how Ritonavir modulates proteasome activity and what consequences this has on cellular functions of the proteasome. Ritonavir is a reversible effector of proteasome activity that protected the subunits MB-1 (X) and/or LMP7 from covalent active site modification with the vinyl sulfone inhibitor(125)I-NLVS, suggesting that they are the prime targets for competitive inhibition by Ritonavir. At low concentrations of Ritonavir (5 microM) cells were more sensitive to canavanine but proliferated normally whereas at higher concentrations (50 microM) protein degradation was affected, and the cell cycle was arrested in the G(1)/S phase. Ritonavir thus modulates antigen processing at concentrations at which vital cellular functions of the proteasome are not yet severely impeded. Proteasome modulators may hence qualify as therapeutics for the control of the cytotoxic immune response.
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PMID:How an inhibitor of the HIV-I protease modulates proteasome activity. 1058 54

The 26S proteasome is a non-lysosomal multicatalytic protease complex for degrading intracellular proteins by ATP/ubiquitin-dependent proteolysis. Tightly ordered proteasomal degradation of proteins critical for cell cycle control implies a role of the proteasome in maintaining cell proliferation and cell survival. In this study, we demonstrate that cell-permeable proteasome inhibitors, lactacystin, benzyloxycarbonyl(Z)-leucyl-leucyl-leucinal (ZLLLal; MG-132) and 4-hydroxy-5-iodo-3-nitrophenylacetyl-leucyl-leucyl-leucine vinyl sulfone (NLVS), induce apoptosis abundantly in p53-defective leukemic cell lines CCRF-CEM, U937 and K562 as well as in myelogenic and lymphatic leukemic cells obtained from adult individuals with relapsed acute leukemias. Leukemic cell apoptosis induced by the proteasome inhibitors was dependent on activation of caspase-3 and related caspase family proteases, because caspase-3 inhibitor N-acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspartal (Ac-DEVD-cho) and, more effectively, the general caspase-inhibitor N-benzyloxycarbonyl-L-valyl-L-alanyl-L-aspartate fluoromethylketone (Z-VAD-fmk) were capable of blocking apoptosis induced by lactacystin, ZLLLal or NLVS. Induction of apoptosis by lactacystin or ZLLLal was accompanied by cell cycle arrest at G2/M phase and by accumulation and stabilization of cyclin-dependent kinase inhibitor p21WAF1/Cip and tumor suppressor protein p53. A role of p53 in mediating apoptosis or induction of p21WAF1/Cip1 was ruled out since CCRF-CEM and U937 cells express non-functional mutant p53, and K562 cells lack expression of p53. Viability and hematopoietic outgrowth of human CD34+ progenitor cells treated with lactacystin were slightly reduced, whereas treatment of CD34 + cells with ZLLLal or the cytostatic drugs doxorubicin and gemcitabine resulted in markedly reduced viability and hematopoietic outgrowth. These results demonstrate a basic role of the proteasome in maintaining survival of human leukemic cells, and may define cell-permeable proteasome inhibitors as potently anti-leukemic agents which exhibit a moderate hematopoietic toxicity in vitro.
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PMID:Proteasome inhibitors induced caspase-dependent apoptosis and accumulation of p21WAF1/Cip1 in human immature leukemic cells. 1107 63

The proteasome is the primary protease used by cells for degrading proteins and generating peptide ligands for class I molecules of the major histocompatibility complex. Based on the properties of cells adapted to grow in the presence of the proteasome inhibitor 4-hydroxy-5-iodo-3-nitrophenylacetyl-Leu-Leu-leucinal-vinyl sulfone (NLVS), it was proposed that proteasomes can be replaced by alternative proteolytic systems, particularly a large proteolytic complex with a tripeptidyl peptidase II activity. Here we show that NLVS-adapted cells retain sensitivity to a number of highly specific proteasome inhibitors with regard to antigenic peptide generation, accumulation of polyubiquitinated proteins, degradation of p53, and cell viability. In addition, we show that in the same assays (with a single minor exception), NLVS-adapted cells are about as sensitive as nonselected cells to Ala-Ala-Phe-chloromethylketone, a specific inhibitor of tripeptidyl peptidase II activity. Based on these findings, we conclude that proteasomes still have essential proteolytic functions in adapted cells that are not replaced by Ala-Ala-Phe-chloromethylketone-sensitive proteases.
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PMID:Cells adapted to the proteasome inhibitor 4-hydroxy- 5-iodo-3-nitrophenylacetyl-Leu-Leu-leucinal-vinyl sulfone require enzymatically active proteasomes for continued survival. 1114 39

The proteasome is a large protease complex consisting of multiple catalytic subunits that function simultaneously to digest protein substrates. This complexity has made deciphering the role each subunit plays in the generation of specific protein fragments difficult. Positional scanning libraries of peptide vinyl sulfones were generated in which the amino acid located directly at the site of hydrolysis (P1 residue) was held constant and sequences distal to that residue (P2, P3, and P4 positions) were varied across all natural amino acids (except cysteine and methionine). Binding information for each of the individual catalytic subunits was obtained for each library under a variety of different conditions. The resulting specificity profiles indicated that substrate positions distal to P1 are critical for directing substrates to active subunits in the complex. Furthermore, specificity profiles of IFN-gamma-regulated subunits closely matched those of their noninducible counterparts, suggesting that subunit swapping may modulate substrate processing by a mechanism that does require a change in the primary sequence specificity of individual catalytic subunits in the complex. Finally, specificity profiles were used to design specific inhibitors of a single active site in the complex. These reagents can be used to further establish the role of each subunit in substrate processing by the proteasome.
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PMID:Global analysis of proteasomal substrate specificity using positional-scanning libraries of covalent inhibitors. 1124 15


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