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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)

An endogenous activator of 20S proteasome was purified from human platelets and its effect on three peptidase activities of proteasome was studied. This activator had a molecular weight of 170 kDa, and was composed of 32 kDa polypeptides as determined by SDS-PAGE. It was highly labile upon heat treatment (56 degrees C, 20 s) and proteinase (pronase CB) digestion. Suc-LLVY-MCA degrading activity of the platelet proteasome showed positive cooperativity between two or more catalytic sites because the coefficient was 1.54 when analyzed by use of the Hill plot. The endogenous activator increased Vmax and caused a loss of cooperativity. The plot of reaction velocity as a function of activator concentration yielded a saturation curve, implying the binding of the activator to proteasome. Boc-LTR-MCA degrading activity followed Michaelis-Menten kinetics. The activator enhanced the activity by increasing Vmax and decreasing Km. In contrast, CBz-LLE-2NA degrading activity could not be analyzed according to any kinetic scheme reported so far. The activator stimulated this activity at lower substrate concentrations (below 200 microM), while it inhibited the activity at higher substrate concentrations (400-800 microM). It is concluded from these findings that the endogenous protein activator may regulate the intracellular proteasome activity by functioning as a positive allosteric effector.
J Biochem 1993 Sep
PMID:Purification and characterization of endogenous protein activator of human platelet proteasome. 828 19

Proteasomes are highly conserved macromolecular structures which function as endopeptidases. They are found in the cytoplasm and nucleus of eukaryotic tissues and consist of at least 14 non-identical subunits with molecular masses ranging from approximately 20 to 32K. Proteasomes are essential in the selective degradation of ubiquitinated and certain non-ubiquitinated proteins, acting as the proteolytic core of an energy-dependent 26S (1,500K) proteolytic complex. Two proteasome subunits, LMP2 and LMP7 (refs 4-7), are encoded within the major histocompatibility complex (MHC), implicating proteasomes in antigen processing. Here we determine the function of these two MHC-linked subunits by comparing the proteolytic activities of purified proteasomes containing (LMP+) or lacking (LMP-) these components. We find that proteasomes of both types have endopeptidase activity against substrates bearing hydrophobic, basic or acidic residues immediately preceding the cleavage site (the P1 position) and at sites following asparagine, glycine and proline residues. The activity of LMP+ proteasomes is much higher than that of LMP- proteasomes against substrates with hydrophobic, basic or asparagine residues at P1, whereas their activities are comparable when acidic and glycine residues are present at P1. The MHC-linked LMP2 and LMP7 subunits therefore function to amplify specific endopeptidase activities of the proteasome.
Nature 1993 Sep 16
PMID:MHC-linked LMP gene products specifically alter peptidase activities of the proteasome. 837 76

Among various protease inhibitors, chymostatin (an inhibitor of sperm chymotrypsin-like protease) strongly inhibited the binding of sperm to the vitelline coat of glycerinated eggs of the ascidian Halocynthia roretzi, whereas leupeptin (an inhibitor for sperm acrosin), antipain, and soybean trypsin inhibitor had no significant inhibitory effects. Dansyl-Val-Pro-argininal (an inhibitor of the sperm trypsin-like protease, spermosin) had an inhibitory effect on the binding of sperm that was much smaller than its effects on fertilization. Since the sperm chymotrypsin-like protease that is involved in ascidian fertilization has been identified as a proteasome (multicatalytic proteinase complex), we tested the effects of several peptidyl argininals, inhibitors of the activities of proteasomes, on this binding process. The ranking of the inhibitory effects of these compounds on the binding of sperm was the same as that of their effects on the chymotrypsin-like activity of the proteasome, reported previously. The potent inhibitors of binding used in these studies had no or minimal effects on sperm motility. These results suggest that a sperm chymotrypsin-like protease (most probably the chymotrypsin-like protease in the proteasome) plays a key role in binding of sperm to the vitelline coat of the ascidian egg.
J Exp Zool 1993 Sep 15
PMID:Effects of protease inhibitors on binding of sperm to the vitelline coat of ascidian eggs: implications for participation of a proteasome (multicatalytic proteinase complex). 837 53

The presentation of intracellular proteins to the immune system requires their degradation to small peptides that then become associated with major histocompatibility complex (MHC) class I molecules. The generation of these peptides may involve the 20S or 26S proteasome particles, which contain multiple proteolytic activities including distinct sites that preferentially cleave small peptides on the carboxyl side of hydrophobic, basic or acidic residues. Degradation of most cell proteins requires their conjugation to ubiquitin before hydrolysis by the 26S proteasome. This large complex contains the 20S proteasome as its proteolytic core. This ubiquitin-dependent proteolytic pathway is implicated in MHC class I presentation. gamma-Interferon (gamma-IFN), a stimulator of antigen presentation, induces a subclass of proteasomes that contain two MHC-encoded subunits, LMP2 and 7 (refs 5-10). Here we show that gamma-interferon alters the peptidase activities of the 20S and 26S proteasomes without affecting the rates of breakdown of proteins or of ubiquitinated proteins. By enhancing the expression of MHC genes, gamma-IFN increases the proteasomes' capacity to cleave small peptides after hydrophobic and basic residues but reduces cleavage after acidic residues. Moreover, proteasomes of mutants lacking LMP subunits show decreased rates of cleavage after hydrophobic and basic residues. Thus, gamma-IFN and expression of these MHC genes should favour the production by proteasomes of the types of peptides found on MHC class I molecules, which terminate almost exclusively with hydrophobic or basic residues.
Nature 1993 Sep 16
PMID:Gamma-interferon and expression of MHC genes regulate peptide hydrolysis by proteasomes. 837 76

Proteasomes are abundant, multisubunit protein complexes found in the cytoplasm and nucleus of eukaryotic cells that catalyze both ubiquitin-dependent and ubiquitin-independent protein degradation. In addition to their role in normal protein turnover, proteasomes are believed to be involved in the production of most antigenic peptides presented to T cells by major histocompatibility complex (MHC) class I molecules. A distinct subset of mouse proteasomes contain a subunit called LMP-2, which is encoded within the MHC. Here we demonstrate that a previously isolated proteasome cDNA clone encodes the LMP-2 subunit, and that two distinct forms of this subunit may be found in the proteasome complex. One form probably corresponds to the primary translation product, whereas the second form appears to be post-translationally processed by removal of the amino-terminal 20 amino acids. Determination of the location of intron/exon boundaries in the Lmp-2 gene indicated that these residues correspond precisely to the first exon of the gene.
Mol Immunol 1993 Sep
PMID:Post-translational processing of a major histocompatibility complex-encoded proteasome subunit, LMP-2. 841 22

Clathrin is the structural protein of coated membranes involved in receptor-mediated endocytosis and aspects of Golgi sorting in eukaryotic cells. We have now detected a stoichiometric complex of clathrin with a novel protein of M(r) approximately 100,000 (100K) in lysates of different mammalian cells. Formation of the complex, which also includes the 70K heat-shock protein Hsc70, occurs within 15 min of synthesis. The 100K protein has been identified as valosin-containing protein (VCP; ref. 1), an early substrate for tyrosine phosphorylation on T-cell receptor activation. Further, VCP is the mammalian homologue of yeast Cdc48p (ref. 3) and is a member of a larger gene family that includes putative ATP-binding proteins involved in vesicle transport and fusion, 26S proteasome function, regulation of the expression of human immunodeficiency virus, and assembly of peroxisomes. The association with clathrin and the morphological and catalytic similarity to the chaperonin proteins indicate that VCP may modulate protein-protein interactions in membrane transport processes.
Nature 1993 Sep 30
PMID:Valosin-containing protein, VCP, is a ubiquitous clathrin-binding protein. 841 90

The crystal structure of the unliganded alkaline protease from Pseudomonas aeruginosa IFO3080 has been determined at 2.0 A resolution by the X-ray method. The enzyme consists of N-terminal catalytic and C-terminal beta-helix domains. On structural comparison between the present unliganded enzyme and structurally- known liganded enzyme, some structural changes were observed around the active site. In the unliganded enzyme, Y216 serves as the fifth ligand for the active site zinc ion. On ligand binding, Y216 may move to form a hydrogen-bond with the carbonyl oxygen of the P1 residue of a ligand peptide. D191 in the flexible loop, Y190 to D196, over the active site cleft forms hydrogen-bonds with the backbone atoms of the P1 and P2 residues of the ligand to close the entrance to the cleft. The water molecule which is the fourth ligand for the zinc ion is replaced by the carbonyl oxygen of the P1 residue. These structural changes around the active site may reflect the substrate-binding mode during the enzymatic reaction.
J Biochem 1995 Sep
PMID:Crystal structure of the unliganded alkaline protease from Pseudomonas aeruginosa IFO3080 and its conformational changes on ligand binding. 869 Jul 4

STAT proteins (signal transducers and activators of transcription) are latent cytoplasmic transcription factors that are phosphorylated by Janus kinases in response to cytokines. Phosphorylated STAT proteins translocate to the nucleus, where they transiently turn on specific sets of cytokine-inducible genes. The mechanism that controls the amounts of activated STAT proteins is not understood. STAT1 proteins activated by interferon-gamma treatment in HeLa cells were shown to be stabilized by a proteasome inhibitor and ubiquitinated in vivo. Thus, the amount of activated STAT1 may be negatively regulated by the ubiquitin-proteasome pathway.
Science 1996 Sep 20
PMID:Regulation of interferon-gamma-activated STAT1 by the ubiquitin-proteasome pathway. 878 Dec 35

Secretion of proteins is initiated by their uptake into the endoplasmic reticulum (ER), which possesses a proteolytic system able to degrade misfolded and nonassembled proteins. The ER degradation system was studied with yeast mutants defective in the breakdown of a mutated soluble vacuolar protein, carboxypeptidase yscY (CPY*). The ubiquitin-conjugating enzyme Ubc7p participated in the degradation process, which was mediated by the cytosolic 26S proteasome. It is likely that CPY* entered the ER, was glycosylated, and was then transported back out of the ER lumen to the cytoplasmic side of the organelle, where it was conjugated with ubiquitin and degraded.
Science 1996 Sep 20
PMID:ER degradation of a misfolded luminal protein by the cytosolic ubiquitin-proteasome pathway. 878 Dec 38

Recent work suggests that the proteolytic degradation of the nuclear lamins is a common event in apoptosis, although the nature of the proteases involved is still not clear. Our previous work showed that the degradation of lamin B1 in glucocorticoid-treated thymocytes occurs via a Ca2+-sensitive mechanism and that exogenous Ca2+ promotes lamin degradation in isolated thymocyte nuclei from untreated cells. Here we demonstrate that peptide-based inhibitors of the interleukin 1beta-converting enzyme family of cysteine proteases (Tyr-Val-Ala-Asp fluoromethyl ketone) and of the nuclear scaffold multicatalytic proteinase (Ala-Pro-Phe chloromethyl ketone) block the degradation of lamin B1 to a 21-kDa fragment in thymocytes treated with glucocorticoid, the Ca2+-mobilizing agent thapsigargin, or antibodies to the T cell receptor. However, among a panel of inhibitors specific for several different proteases implicated in apoptosis, only tosylphenylalanyl chloromethyl ketone and the nuclear scaffold protease inhibitor block lamin degradation, histone H1 cleavage, and DNA fragmentation in isolated thymocyte nuclei incubated with Ca2+. Overexpression of human BCL-2 in nuclei by stable transfection resulted in an inhibition of Ca2+-stimulated lamin degradation and DNA fragmentation, suggesting that endogenous nuclear BCL-2 regulates activation of the nuclear scaffold protease. The results demonstrate the existence of an alternative pathway of lamin degradation and DNA fragmentation mediated by a resident Ca2+-stimulated nuclear protease that is not directly dependent upon activation of the interleukin 1beta-converting enzyme family of cell death regulators.
J Biol Chem 1996 Sep 13
PMID:Calcium-dependent, interleukin 1-converting enzyme inhibitor-insensitive degradation of lamin B1 and DNA fragmentation in isolated thymocyte nuclei. 879 2


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