Role of surgery in infective endocarditis

One-hundred-and-thirteen patients with endocarditis and valvular insufficiency were studied retrospectively with special regard to indications for operation and the optimum time for cardiac valve surgery. Thirty patients (group I) had acute, 63 (group II) subacute and 20 (group III) prosthetic valve endocarditis. Group I: Eleven patients underwent surgery in the acute stage, 8 while bacteremic; 5 of the latter died perioperatively. Of the 19 patients treated medically, 16 died. Group II: All patients underwent operation in a bacteria-free state. The mortality was 5%. Group III: Eight patients had early (less than 60 days postoperatively) and 12 late endocarditis. Total mortality was 40% (71% early and 25% late mortality). Ten patients underwent reoperation, with a mortality of 20%, compared with 60% in the medically treated group. The results support the indication for early operation in acute endocarditis with progressive cardiac failure and renal failure and prosthetic valve endocarditis, even during bacteremia.

The constitutive photomorphogenesis 9 signalosome directs vascular endothelial growth factor production in tumor cells

Angiogenesis is a prerequisite for solid tumor growth and metastasis. Elucidation of the signaling pathways that control tumor angiogenesis constitutes the basis for a rational antiangiogenic tumor therapy. Here we show that the production of vascular endothelial growth factor (VEGF) in HeLa and HL-60 cells is directed by the constitutive photomorphogenesis 9 signalosome (CSN). The CSN is a kinase complex that cooperates with the ubiquitin/26S proteasome system in regulating the stability of proteins involved in signal transduction. VEGF expression is controlled by the transcription factors activator protein (AP)-1, AP-2, SP-1, and hypoxia-inducible factor 1. Inhibition of CSN kinase activity by 50 microM curcumin for 2 h decreases the cellular c-Jun concentration, resulting in a reduction of the VEGF production by approximately 75%. The removal of the inhibitor from the cells led to a time-dependent recovery of endogenous c-Jun that is paralleled by increasing VEGF production. Elevated cellular CSN activity induced by CSN subunit 2 overexpression causes increased VEGF production in HeLa cells. A competitor of CSN-dependent c-Jun phosphorylation, the NH(2)-terminal c-Jun fragment Deltac-Jun(1-226), inhibits VEGF production in HeLa cells. The transcription factors AP-2 and SP-1 act independently of the CSN. They contribute less than a quarter to basal VEGF production. Under our experimental conditions, hypoxia-inducible factor 1alpha protein was not detected. Overexpression of the tumor suppressor p53 reduces VEGF production in HeLa cells. p53 competes with c-Jun for CSN-specific phosphorylation with the consequence of c-Jun destabilization. We conclude that CSN-directed c-Jun signaling mediates high VEGF production in HeLa and HL-60 cells. The data provide an explanation for the known antiangiogenic and antitumorigenic activities of curcumin. Because the CSN regulates the major part of VEGF production in the tested tumor cells, it constitutes a potentially important target for tumor therapy.

Protein stability: the COP9 signalosome gets in on the act

The COP9 signalosome is a multiprotein complex somewhat similar to the lid component of the 26S proteasome. Recent studies suggest that it regulates the stability of proteins by interfering with the ubiquitin-proteasome pathway via deneddylation and phosphorylation.

Interaction between interferon consensus sequence-binding protein and COP9/signalosome subunit CSN2 (Trip15). A possible link between interferon regulatory factor signaling and the COP9/signalosome

Interferon consensus sequence-binding protein (ICSBP) is a member of the interferon regulatory factors (IRF) that has a pivotal role in mediating resistance to pathogenic infections in mice and in promoting the differentiation of myeloid cells. ICSBP exerts some of its transcriptional activities via association with other factors that enable its binding to a variety of promoters containing DNA composite elements. These interactions are mediated through a specific COOH-terminal domain termed IAD (IRF association domain). To gain a broader insight of the capacity of ICSBP to interact with other factors, yeast two-hybrid screens were performed using ICSBP-IAD as a bait against a B-cell cDNA library. Trip15 was identified as a specific interacting factor with ICSBP in yeast cells, which was also confirmed by in vitro glutathione S-transferase pull-down assays and by coimmunoprecipitation studies in COS7 cells. Trip15 was recently identified as a component of the COP9/signalosome (CSN) complex composed of eight evolutionary conserved subunits and thus termed CSN2. This complex has a role in cell-signaling processes, which is manifested by its associated novel kinase activity and by the involvement of its subunits in regulating multiple cell-signaling pathways and cell-cycle progression. We show that in vitro association of ICSBP with the CSN leads to phosphorylation of ICSBP at a unique serine residue within its IAD. The phosphorylated residue is essential for efficient association with IRF-1 and thus for the repressor activity of ICSBP exerted on IRF-1. This suggests that the CSN has a role in integrating incoming signals that affect the transcriptional activity of ICSBP.

Electron microscopy and subunit-subunit interaction studies reveal a first architecture of COP9 signalosome

The COP9 signalosome is involved in signal transduction, whereas the 26 S proteasome lid is a regulatory subcomplex of the 26 S proteasome responsible for degradation of ubiquitinated proteins. COP9 signalosome and lid possess significant sequence homologies among their eight core subunits and are likely derived from a common ancestor. Surprisingly, from our two-dimensional electron microscopy data, a common architectural plan for the two complexes could not be deduced. None-the-less, the two particles have structural features in common. Both COP9 signalosome and lid lack any symmetry in subunit arrangement and exhibit a central groove, possibly qualified for scaffolding functions.Filter-binding assays with recombinant COP9 signalosome components revealed a multitude of subunit-subunit interactions, supporting the asymmetrical appearance of the complex in electron microscopy. On the basis of two-dimensional images and subunit interaction studies, a first architectural model of COP9 signalosome was created. The fact that four distinct classes of particle views were identified and that only 50 % of the selected particles could be classified indicates a high degree of heterogeneity in electron microscopic images. Different orientations with respect to the viewing axis and conformational variety, presumably due to different grades of phosphorylation, are possible reasons for the heterogeneous appearance of the complex. Our biochemical data show that recombinant COP9 signalosome subunits 2 and 7 are phosphorylated by the associated kinase activity. The modification of COP9 signalosome subunit 2 might be essential for c-Jun phosphorylation. Dephosphorylation does not inactivate the associated kinase activity. Although substrate phosphorylation by COP9 signalosome is significantly decreased by lambda protein phosphatase treatment, "autophosphorylation" is increased.

Analysis of a gene encoding Rpn10 of the fission yeast proteasome reveals that the polyubiquitin-binding site of this subunit is essential when Rpn12/Mts3 activity is compromised

Substrates are targeted for proteolysis by the ubiquitin pathway by the addition of a polyubiquitin chain before being degraded by the 26 S proteasome. Previously, a subunit of the proteasome, S5a, was identified that was able to bind to polyubiquitin in vitro and thus proposed to act as a substrate recognition component. Deletion of the corresponding Saccharomyces cerevisiae gene, MCB1/RPN10, rendered cells viable indicating that other proteasomal polyubiquitin receptors must exist. In this study, we describe pus1(+), the fission yeast homologue of RPN10. This gene is also not required for cell viability; however, the Deltapus1 mutant is synthetically lethal with mutations in other proteasomal component-encoding genes, namely mts3, pad1, and mts4 (RPN12, RPN11, and RPN1). Overexpression of pus1(+) is able to rescue mts3-1 at 32 degrees C but overexpression of a cDNA encoding a version of Pus1 that does not bind to polyubiquitin cannot and leads to greatly reduced viability when used to rescue the mts3-1Deltapus1 double mutant. The Mts3 protein was unable to bind to polyubiquitin in vitro, but the Pus1 and Mts3 proteins were found to bind to one another in vitro, which taken together with the genetic data suggests that they are also closely associated in vivo.

Regulatory subunit interactions of the 26S proteasome, a complex problem

The 26S proteasome is the major non-lysosomal protease in eukaryotic cells. This multimeric enzyme is the integral component of the ubiquitin-mediated substrate degradation pathway. It consists of two subcomplexes, the 20S proteasome, which forms the proteolytic core, and the 19S regulator (or PA700), which confers ATP dependency and ubiquitinated substrate specificity on the enzyme. Recent biochemical and genetic studies have revealed many of the interactions between the 17 regulatory subunits, yielding an approximation of the 19S complex topology. Inspection of interactions of regulatory subunits with non-subunit proteins reveals patterns that suggest these interactions play a role in 26S proteasome regulation and localization.

COP9 signalosome-directed c-Jun activation/stabilization is independent of JNK

The basic region-leucine zipper transcription factor c-Jun regulates gene expression and cell function. It participates in the formation of homo- or heterodimeric complexes that specifically bind to DNA sequences called activating protein 1 (AP-1) sites. The stability and activity of c-Jun is regulated by phosphorylation within the N-terminal activation domain. Mitogen- and stress-activated c-Jun N-terminal kinases (JNKs) were previously the only described enzymes phosphorylating c-Jun at the N terminus in vivo. In this report we demonstrate a JNK-independent activation of c-Jun in vivo directed by the constitutive photomorphogenesis (COP9) signalosome. The overexpression of signalosome subunit 2 (Sgn2), a subunit of the COP9 signalosome, leads to de novo assembly of the complex with a partial incorporation of the overexpressed subunit. The de novo formation of COP9 signalosome parallels an increase of c-Jun protein resulting in elevated AP-1 transcriptional activity. The c-Jun activation caused by Sgn2 overexpression is independent of JNK and mitogen-activated protein kinase kinase 4. The data demonstrate the existence of a novel COP9 signalosome-directed c-Jun activation pathway.

Hemizygosity for the COP9 signalosome subunit gene, SGN3, in the Smith-Magenis syndrome

Smith-Magenis syndrome (SMS) is a multiple congenital anomaly/mental retardation syndrome associated with an interstitial deletion of chromosome band 17p11.2. The critical region is extremely gene-rich and spans approximately 1.5-2.0 Mb of DNA. Here we report the localization and partial characterization of the gene for subunit 3 of the COP9 signalosome, SGN3. SGN3 maps to the distal portion of the SMS critical interval, between SREBF1 and cCI17-638. We assessed the potential effect of haploinsufficiency of SGN3 in SMS patient lymphoblastoid cell lines through transfection studies and western analysis. Our results indicate that the COP9 signalosome assembles properly in these cells and appears to have normal expression and a kinase function intact. However, because the role of the COP9 signalosome in embryogenesis or differentiation is still uncertain, we cannot rule out the involvement of this gene in the Smith-Magenis syndrome.

Ubiquitin pathway: another link in the polyubiquitin chain?

Polyubiquitin has long been recognised as an intracellular signal. It now appears that different lysine linkages between the ubiquitin moieties are recognised as distinct signals and act in different cell processes. The generation of these different polyubiquitin chains may play an important part in the life of a cell.

Comparison of human COP9 signalsome and 26S proteasome lid'

The human core COP9 signalosome consists of eight subunits which have been identified, cloned and sequenced. The components of COP9 signalosome possess homologies with eight non-ATPase regulatory subunits of the 26S proteasome. These polypeptides of the 19S regulator form a reversibly binding subcomplex called the 'lid'. We isolated the 'lid' from human red blood cells and compared it with the COP9 signalosome complex. In addition to the non-ATPase regulatory polypeptides, we found a high molecular mass ATPase copurifying with the human 'lid'. The COP9 signalosome-associated kinase activity is either not at all or only weakly affected by common kinase inhibitors such as 1-(5-Isoquinolinesulfonyl)-2-methyl-piperazine (H7), 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) or Wortmannin. Curcumin, a tumor suppressor and effector of AP-1 activation, is a potent inhibitor of the COP9 signalosome kinase activity with a Ki of about 10 microM. Since curcumin is known as an inhibitor of the c-Jun N-terminal kinase (JNK) signaling pathway acting upstream of the MAP kinase kinase kinase level, one site of action of the COP9 signalosome might be proximal to regulators on that level.

The Pad1+ gene encodes a subunit of the 26 S proteasome in fission yeast

We have isolated a fission yeast mutant, mts5-1, in a screen for mutations that confer both methyl 2-benzimidazolecarbamate resistance (MBCR) and temperature sensitivity (ts) on Schizosaccharomyces pombe. This screen has previously isolated mutations in the 26 S proteasome subunits Mts2, Mts3, and Mts4. We show that the mutation in the mts5-1 strain occurs in the pad1(+) gene. pad1(+) was originally isolated on a multicopy plasmid that was capable of conferring staurosporine resistance on a wild type strain. mts5-1/pad1-1 has a similar phenotype to 26 S proteasome mutants previously isolated in the same screen and we show that Pad1 interacts genetically with two of these subunits, Mts3 and Mts4. In this study we describe the identification of Pad1 as a subunit of the 26 S proteasome in fission yeast.

A novel protein complex involved in signal transduction possessing similarities to 26S proteasome subunits

A novel protein complex has been identified in human cells that has a molecular mass of approximately 450 kDa. It consists of at least eight different subunits including JAB1, the Jun activation-domain binding protein 1, and Trip15, the thyroid hormone receptor-interacting protein 15. The purified complex contains COP9 and COP11 protein homologs and is very similar, if not identical, to the plant COP9 complex involved in light-mediated signal transduction. The isolated JAB1-containing particle has kinase activity that phosphorylates IkappaBalpha, the carboxy terminus of p105, and Ser63 and/or Ser73 of the amino-terminal activation domain of c-Jun. The phosphorylation of c-Jun requires the carboxy terminus of the protein containing the DNA binding and dimerization domains. Three subunits of the new complex--Sgn3, Sgn5/JAB1, and Sgn6--exhibit sequence similarities to regulatory components of the 26S proteasome, which could indicate the existence of common substrate binding sites. Immunofluorescence staining reveals that the new complex shows a subcellular distribution similar to that of the 26S proteasome. The functional relationship of the two particles in regulating transcriptional activity is discussed. Considering the putative role of the complex in signal transduction and its widespread occurrence, we suggest the name JAB1-containing signalosome.

Evidence for a novel ATP-dependent protease from the rat liver mitochondrial intermembrane space: purification and characterisation

An ATP-dependent protease in the intermembrane space of rat liver mitochondria, MISP I (mitochondrial intermembrane space protease), was partially purified and characterised. The protease complex has a molecular mass of 200 kDa and appears to be an oligomeric enzyme complex. The proteolytic activity of the enzyme can be stimulated up to 3-fold by Mg2+ATP. The Km for ATP is 200 microM. Nucleoside triphosphates, but not ADP, AMP, or nonhydrolysable ATP analogues, can substitute for ATP. The protease exhibits multicatalytic properties with chymotrypsin-like, peptidyl-glutamyl-hydrolysing, and trypsin-like activities. Of the latter the trypsin-like activity is not enhanced by ATP. In addition to the hydrolysis of fluorogenic peptide substrates the protease is able to degrade radiolabeled model proteins. The ATP-dependent mitochondrial protease was characterised as a cysteine protease sensitive to hemine. The cross reactivity of an anti-human-S4 antibody raised against an ATPase subunit of the PA700 complex with a component of MISP I indicated a structural relationship. Furthermore, ATP-agarose-binding assays revealed the connection of the peptide hydrolysing activity with an ATP binding domain. The data presented here and a comparison with known ATP-dependent mitochondrial proteases demonstrated that MISP I represents a novel ATP-dependent protease in the mitochondrial intermembrane space of rat liver.

Resistance to diverse drugs and ultraviolet light conferred by overexpression of a novel human 26 S proteasome subunit

We have investigated the usefulness of the fission yeast Schizosaccharomyces pombe as a model organism for the discovery of novel modes of drug resistance in human cells. In fission yeast, overexpression of the essential pad1(+) gene confers pleiotropic drug resistance through a pathway involving an AP-1 transcription factor encoded by pap1(+). We have identified POH1, a human pad1 homologue that can substitute fully for pad1(+) and induce AP-1-dependent drug resistance in fission yeast. POH1 also confers P-glycoprotein-independent resistance to taxol (paclitaxel), doxorubicin, 7-hydroxystaurosporine, and ultraviolet light when transiently overexpressed in mammalian cells. Poh1 is a previously unidentified component of the human 26 S proteasome, a multiprotein complex that degrades proteins targeted for destruction by the ubiquitin pathway. Hence, Poh1 is part of a conserved mechanism that determines cellular susceptibility to cytotoxic agents, perhaps by influencing the ubiquitin-dependent proteolysis of transcription factors.

Mts4, a non-ATPase subunit of the 26 S protease in fission yeast is essential for mitosis and interacts directly with the ATPase subunit Mts2

We have isolated a fission yeast gene, mts4(+), by complementation of a temperature-sensitive mutation and show that it encodes subunit 2 (S2) of the 19 S regulatory complex of the 26 S protease. mts4(+) is an essential gene, and we show that loss of this subunit causes cells to arrest in metaphase, illustrating the importance of S2 for mitosis. The Mts4 protein is 48% identical to S2 of the human 26 S protease, and the lethal phenotype of the null mts4 allele can be rescued by the human cDNA encoding S2. We provide genetic and physical evidence to suggest that the Mts4 protein interacts with the product of the mts2(+) gene, an ATPase which has previously been shown to be subunit 4 of the 26 S protease.

HIV-1 tat inhibits the 20 S proteasome and its 11 S regulator-mediated activation

The proteasomal system consists of a proteolytic core, the 20 S proteasome, which associates in an ATP-dependent reaction with the 19 S regulatory complex to form the functional 26 S proteasome. In the absence of ATP, the 20 S proteasome forms a complex with the gamma-interferon-inducible 11 S regulator. Both the 20 S proteasome and the 11 S regulator have been implied in the generation of antigenic peptides. The human immunodeficiency virus (HIV)-1 Tat protein causes a number of different effects during acquired immunodeficiency syndrome (AIDS). Here we show that HIV-1 Tat protein strongly inhibits the peptidase activity of the 20 S proteasome and that it interferes with formation of the 20 S proteasome-11 S regulator complex. In addition, it slightly increases the activity of purified 26 S proteasome. These results may explain the mechanism by which HIV-1-infected cells escape cytotoxic T lymphocyte response and at least in part immunodeficiency in AIDS patients.

The 26S proteasome: a dynamic structure

The proteasomal system consists of a proteolytic core, the 20S proteasome, which associates in ATP-dependent and independent reactions with endogenous regulators providing specific substrate binding sites, chaperone function and regulation of activity to the protease. The best known regulators of the 20S proteasome are the 11S and the 19S complexes. Three subunits of the 20S proteasome and the two subunits of the 11S regulator are induced by gamma-Interferon. However, there are no indications for an influence of gamma-interferon on the subunit composition of the 19S regulator and only a few data exist about the dynamics of this complex. The analysis of 19S regulator subunits from yeast mutants reveals that the ATPases appear to be stringently organized in the 26S complex, while peripheral non-ATPases, such as S5a, might serve as subunits which shuttle substrates to the enzyme. A novel non-ATPase has been cloned, sequenced and identified in a complex besides the 19S regulator, the function of which is presently unknown. The dynamic structure of the 26S proteasome is also characterized by transient associations with components such as the modulator and isopeptidases. Certain viral proteins can also be associated with components of the proteasomal system and alter enzymatic activities.

Characteristics of 26 S proteases from fission yeast mutants, which arrest in mitosis

We have isolated the 26 S protease from the fission yeast Schizosaccharomyces pombe. The affinity-purified enzyme contains the two regulatory ATPases mts2+, a homolog of human S4, and CIM5, a homolog of human MSS1 = S7. We show that mts3+, a homolog of the budding yeast NIN1 protein and human S14, is a true component of the 19 S regulatory complex from the fission yeast. The 26 S proteases purified from two thermosensitive mutants, mts2-1 and mts3-1, which arrest in cell cycle at the restrictive temperature (37 degrees C), have been compared with the wild-type enzyme after growing cells at permissive (25 degrees C) and non-permissive temperatures. We demonstrate that mutated mts2 protein is integrated into the protease complex prepared from mts2 cells, whereas mutated mts3 is not present in the 19 S regulatory complex from mts3 cells. The two mutant 26 S proteases isolated after growing cells at 37 degrees C remain stable for two hours at 37 degrees C as measured by ATP-dependent cleavage of the fluorogenic peptide sucLLVY-MCA. At the restrictive temperature, the mutant 26 S proteases do not degrade ubiquitin-[125I]lysozyme conjugates in an ATP-dependent manner, indicating that mts2+ and mts3+ are essential for ubiquitin conjugate degradation. This explains the conditional lethality of the mutants and the cell-cycle arrest in metaphase to anaphase transition. In addition, our data demonstrate that the ATPases of the 26 S enzyme are not redundant.

Identification of a novel ATP-dependent proteolytic activity in mitochondrial intermembrane space

The formation of primary amines via proteolysis was monitored in isolated rat liver, kidney cortex and heart mitochondria in the presence and in the absence of ATP. The highest proteolytic activity was detected in kidney cortex mitochondria with about 120 nmoles primary amines/hour x mg protein. The formation rates of liver mitochondria amounted to about 100 nmoles primary amines/hour x mg protein and in heart mitochondria about 60 nmoles primary amines/hour x mg protein. In all mitochondria investigated an ATP-dependent proteolysis of 20-40 nmoles primary amines/hour x mg protein was detected. The effects of various protease inhibitors were tested in rat liver mitochondria and thiol-specific reagents showed a 35-70% inhibition. The ATP stimulable portion of proteolysis was blocked by hemin, a known inhibitor of ATP-dependent proteases. The localization of the proteolytic activity was tested by fractionation of the compartments of rat liver mitochondria using the flourogenic peptide suc-Leu-Leu-Val-Tyr-MCA as substrate. About 90% of the ATP-dependent peptide cleavage activity were found in the mitochondrial intermembrane space. The characteristics of the enzyme were compared to those of other known mitochondrial ATP-dependent proteases and it was concluded that it represents a novel proteolytic system of the intermembrane space.

Molecular cloning and expression of subunit 12: a non-MCP and non-ATPase subunit of the 26 S protease

A cDNA encoding subunit 12 (S12) of human erythrocyte 26 S protease has been isolated, sequenced and expressed. The cDNA contains an open reading frame that encodes a 36.6 kDA protein 96% identical to mouse Mov-34 and 67% identical to its Drosophila melanogaster homolog. Based on the high degree of sequence identity between human S12, mouse and Drosophila Mov-34 proteins, we conclude that the Mov-34 gene product is a component of the 26 S protease. Antibodies produced against two S12 fragments, Met1-Tyr95 (S12f95) and Met1-Leu205 (S12f205), react with S12 transferred to nitrocellulose from SDS-PAGE. In contrast, after transfer from native gels, the epitope(s) recognized by anti-S12f205 is exposed in the regulatory complex but appears to be masked when the regulatory complex associates with the multicatalytic protease.

Molecular cloning and expression of a gamma-interferon-inducible activator of the multicatalytic protease

The multicatalytic protease (MCP) can be activated by two distinct multisubunit complexes. One is the regulatory component of the 26 S protease, which contains at least 15 distinct subunits. The other is a hexameric activator composed of 31- and 29-kDa subunits. A cDNA for the smaller subunit has been cloned and sequenced. The cDNA encodes a protein of 249 amino acids. Embedded between sequences typical of globular protein domains is a stretch of 28 "alternating" lysine and glutamic acid residues. Similar regions, which we call KEKE motifs, are also found in two MCP subunits, in subunit 12 of the 26 S protease and in a variety of chaperonins including hsp90, hsp70, and calnexin. Expression of the activator cDNA in Escherichia coli produced a functional protein virtually indistinguishable from MCP activator purified directly from red blood cells. The recombinant protein formed three isoelectric species on two-dimensional polyacrylamide gel electrophoresis, and it reacted with antibodies to red blood cell activator. Recombinant activator also bound the multicatalytic protease and stimulated cleavage at the carboxyl terminus of hydrophobic or charged residues. Synthesis of the activator subunit was induced by gamma interferon treatment of HeLa cells. These last two findings have implications for antigen presentation by class I major histocompatibility receptors.

Tat-binding protein 7 is a subunit of the 26S protease

Subunit 6 (S6), an integral component of the 26S protease from human erythrocytes, has been studied by SDS-PAGE, peptide mapping and sequence analysis. S6 was cleaved with CNBr and three internal peptides were sequenced. A comparison with known proteins in Genbank revealed that all three S6 peptides match the predicted sequence of TBP7, Tat-binding protein 7. Based on peptide matches covering more than 10% of the TBP7 sequence, and the fact that the migration of S6 on SDS-PAGE is consistent with the estimated molecular mass for TBP7, we conclude that subunit 6 of the 26S protease is TBP7.

Peptide sequencing identifies MSS1, a modulator of HIV Tat-mediated transactivation, as subunit 7 of the 26 S protease

Subunit 7 is an integral component of the human erythrocyte 26 S protease. Peptide sequence analysis reveals that 22 amino acids from the N-terminus of subunit 7 correspond exactly to the N-terminus of MSS1, a modulator of HIV gene expression. Additional internal peptides from subunit 7 obtained by CNBr cleavage also match 100% with the deduced amino acid sequence of MSS1. Based on the fact that directly sequenced peptides from subunit 7 are identical to more than 12% of the hypothetical translation product of MSS1, and the fact that the molecular weight of subunit 7 (49 kDa) corresponds to the predicted molecular weight of MSS1 (48,633 Da), we conclude that subunit 7 is MSS1.

Subunit 4 of the 26 S protease is a member of a novel eukaryotic ATPase family

Ubiquitinated proteins are degraded by a 26 S ATP-dependent protease. SDS-polyacrylamide gel electrophoresis analysis of the purified 26 S enzyme reveals more than 20 polypeptides ranging in apparent molecular masses from 20 to 110 kDa. Although many of the subunits smaller than 30 kDa are members of the multicatalytic protease family, the identity and function of the larger polypeptides have remained unknown. We report here the cDNA sequence for subunit 4, a 51-kDa chain of the 26 S protease. Subunit 4 belongs to a recently identified eukaryotic ATPase family, which includes proteins involved in peroxisome formation, secretion, and human immunodeficiency virus gene expression. Subunit 4 also shows weak similarity to ClpA, the ATP-binding subunit of the Escherichia coli protease, Clp.

Purification of an 11 S regulator of the multicatalytic protease

We have identified and purified a protein complex from human red blood cells that activates the multicatalytic protease (MCP). The complex, which we call the regulator, sediments at 11 S and is composed of 30-kDa subunits. The regulator does not hydrolyze fluorogenic peptides, but when multicatalytic protease and regulator are combined, MCP cleaves succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin and Leu-Leu-Glu-p-nitroanilide as much as 60-fold faster. Hydrolysis of several other fluorogenic peptides is stimulated to a lesser extent, and activated MCP does not degrade ubiquitin-lysozyme conjugates, bovine serum albumin, or lysozyme. Latent and activated forms of MCP display similar sensitivity to protease inhibitors, suggesting that activation does not generate new kinds of catalytic sites. In addition, ATP suppresses peptide hydrolysis by activated and latent MCPs to the same extent. Activation involves binding of regulator to MCP, and activated MCP migrates slower on native acrylamide gels. Dissociation of the MCP regulator complex during prolonged sedimentation on glycerol gradients releases active regulator and MCP molecules capable of being reactivated. Moreover, two-dimensional electrophoresis does not reveal changes in MCP or regulator subunits following activation. Thus, activation appears to result from reversible association of regulator subunits with MCP.

The catabolism of endogenous adenine nucleotides in rat liver mitochondria

The degradation of intramitochondrial adenine nucleotides to nucleosides and bases was investigated by incubating isolated rat liver mitochondria at 37 degrees C under non-phosphorylating conditions in the presence of oligomycin and carboxyatractyloside. Within 30 min the adenine nucleotides were degraded by about 25 per cent. The main products formed were adenosine and inosine the contents of which increased five- to sevenfold. Compartmentation studies revealed that about 50 to 60 per cent of the adenosine formed remained inside the organelles whereas inosine was almost completely released into the surrounding medium. Outside the mitochondria only very small amounts of adenine nucleotides were detected. Similar incubations in the presence of [14C]-adenosine yielded no [14C]-inosine ruling out extramitochondrial adenosine deamination. It is concluded that endogenous adenine nucleotides can be degraded in mitochondria via AMP dephosphorylation and subsequent adenosine deamination. A purine nucleoside transport system mediating at least the efflux of inosine from the mitochondria is suggested.

Adenosine formation by isolated rat kidney mitochondria

Isolated rat kidney mitochondria are able to generate extraordinary amounts of adenosine. About one-third of the adenosine formed only results from the degradation of adenine nucleotides. Pyridine nucleotides may contribute to adenosine formation. Nevertheless, there must be an additional, as yet unidentified, acid-insoluble compound in mitochondria which is able to form a significant portion of adenosine.

ATP-dependent peptide release from mitochondria of reticulocytes

ATP-dependent release of TCA-precipitable peptides from mitochondria-containing stroma (MCS) is described. The process is independent of ubiquitin, but is sensitive to hemin and to heat treatment. Neither chloramphenicol nor EGTA inhibit. 50% of the activity is dependent on charged tRNA. The peptides released from MCS possess a molecular mass of about 1-5 kDa and are degraded to TCA-soluble compounds by a cytosolic protease system (fraction II) without ubiquitin.

Mitochondrial metabolism of guanine nucleotides. Possible role of guanosine

The catabolism of intramitochondrial guanine nucleotides was examined. During 30 min incubation of rat liver mitochondria at 37 degrees C in the presence of oligomycin and carboxyatractyloside, guanine and xanthine were formed and appeared in the medium. Under these conditions, the direct conversion of GMP to guanine by hypoxanthine-guanine phosphoribosyltransferase is suggested to be the main catabolic route within the organelles. Only very small amounts of guanosine were produced and detected both inside and outside the organelles. [14C]Guanosine and [14C]inosine were taken up by the mitochondria. Therefore, guanosine is suggested to be a precursor of intramitochondrial guanine nucleotides.

Identification and characteristics of a novel mitochondrial 5'-nucleotidase in rat liver

In rat liver mitochondria there exists an AMP-dephosphorylating activity which converts external 5'-AMP to adenosine. It exhibits a pH optimum of 7.5 and a Km(AMP) of 0.085 mM. Furthermore, this activity is stimulated by magnesium (Km = 0.5 mM) and seems to be not affected by low concentrations of ATP or ADP. From the characteristics of the enzyme the existence of a 5'-nucleotidase in rat liver mitochondria which is localized on the outer surface of the inner mitochondrial membrane was concluded. The enzyme may be important for the production of cellular adenosine.

Optimization of the ion-pair high-performance liquid chromatographic separation of purine derivatives in erythrocytes, thymocytes and liver mitochondria

Various methods are described for the analysis of purine derivatives in biological samples by ion-pair high-performance liquid chromatography (HPLC) with both gradient and isocratic systems. A new approach is proposed that is suitable for the separation of nuclei acid constituents in different cells with a specific enzymatic activity pattern. The ion-pair HPLC methods were developed for the analysis of erythrocytes, lymphocytes and mitochondria acid-soluble fractions in clinical and experimental studies of normal and altered nucleotide metabolism. The results of studies of purine metabolite redistribution in mouse liver mitochondria during a 30-min incubation at 37 degrees C and data on purine metabolic alterations in mouse thymocytes during hepatoma growth are discussed.

Kinetics of 125I-ubiquitin conjugation with and liberation from rabbit reticulocyte stroma

The breakdown of mitochondria-containing stroma of rabbit reticulocytes is an ATP- and ubiquitin-dependent process and there is no evidence for an ATP-dependent but ubiquitin-independent proteolysis in these cells. The ubiquitin conjugate formation with heat-denatured stroma proteins is about one-fifth of that with native stroma. In reticulocytes there exist two mechanisms of ubiquitin liberation from its conjugates with stroma proteins: an ATP-dependent and hemin-resistant release of ubiquitin, which is assumed to be the first step in the degradation of ubiquitin conjugates by the protease system, and a release of ubiquitin catalyzed by an isopeptidase activity.

A mathematical model to study short-term regulation of mitochondrial energy transduction

A mathematical model is presented which includes the following elementary process of mitochondrial energy transduction: hydrogen supply, proton translocation by the respiratory chain, proton-driven ATP synthesis by the F0F1-ATPase, passive back-flow of protons (leak) and carrier-mediated exchange of adenine nucleotides and phosphate. For these processes empirical rate laws are used. The model is applied to calculate time-dependent states of energy transduction in isolated rat liver mitochondria. From the general agreement of the computational results with experimental data (Ogawa, S. and Lee, T.M. (1984) J. Biol. Chem. 259, 10004-10011) the following conclusions can be drawn. (1) The length of the time interval during which mitochondria are able to maintain a relatively high and constant delta pH in the absence of oxygen (anaerobiosis) is limited by the availability of intramitochondrial ATP. (2) The overshoot kinetics of delta pH which appear when reoxigenating mitochondria after a preceeding anaerobiosis might be due to a lag phase kinetics of the F0F1-ATPase. (3) In phosphorylating mitochondria the homeostasis of delta pH is brought about by a high sensitivity of the respiration rate and the rate of the F0F1-ATPase as to changes of delta pH. (4) Analysis of the mean transient times shows that the rate of ATP synthesis in State 3 is controlled to almost the same extent by the hydrogen supply, the respiratory chain, the adenine nucleotide translocator and the proton leak.

Accounting for the ATP-consuming processes in rabbit reticulocytes

The report deals with a detailed balance of ATP production and consumption of the rabbit reticulocyte. The sum-total of ATP produced amounts to 135 mmol . 1-1 . h-1. About 70% of the ATP consumption has been accounted for by specific processes. The main contributing processes are the globin synthesis with about 28%, the Na+, K+-ATPase with 23% and the proteolysis with more than 15%. 30% of ATP consumption has not been accounted for. Cycloheximide (20 microM) leads to a dissociation between synthesis and degradation of proteins, which argues against any obligatory connection between these processes. More than 90% of the lysine liberated from mitochondria by proteolysis were reutilized for the globin synthesis demonstrating the high nitrogen economy of reticulocytes. Each of the ATP-consuming processes studied appears to control ATP production in an independent manner without competition with each other.

Calcium exerts an indirect effect on ATP-dependent proteolysis of rat liver mitochondria

The ATP-dependent proteolysis of rat liver mitochondria prepared in electrolyte-poor sucrose media requires the presence of Ca2+. Lanthanum, an inhibitor of Ca2+ uptake, inhibits the proteolysis. In contrast, proteolysis of mitochondria prepared in a salt medium does not require Ca2+, nor is it inhibited by lanthanum. It is concluded that Caa+ exerts its effect in an indirect manner, by causing swelling and thereby increasing the accessibility of the membrane proteins of the inner mitochondrial membrane.

Determination and characteristics of energy-dependent proteolysis in rabbit reticulocytes

1. A method is reported, based on the isotopic dilution of lysine, which is suitable for the measurement of the degradation of stroma proteins of reticulocytes. 2. Proteolysis is extensive and time-limited. It may reach 50% of the stroma in 2 h at pH 7.6 and 37 degrees C. It is strongly dependent on pH and temperature, being small at low pH and temperatures. Proteolysis is largely ATP-dependent. The extent of proteolysis is nearly proportional to the degree of reticulocytosis. 3. The proteolytic system may be reconstructed in hemolysates if ATP is produced or supplied. It is assumed that the system is identical and that studied by Goldberg et al. and Hershko et al. on abnormal or denatured proteins as substrates. The main significance of the proteolytic system appears to be the degradation of mitochondria during maturation of the red cell.