Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.64 (MPP)
 1,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The major mitochondrial processing activity removing presequences from nuclear encoded precursor proteins is present in the soluble fraction of fungal and mammalian mitochondria. We found that in potato, this activity resides in the inner mitochondrial membrane. Surprisingly, the proteolytic activity co-purifies with cytochrome c reductase, a protein complex of the respiratory chain. The purified complex is bifunctional, as it has the ability to transfer electrons from ubiquinol to cytochrome c and to cleave off the presequences of mitochondrial precursor proteins. In contrast to the nine subunit fungal complex, cytochrome c reductase from potato comprises 10 polypeptides. Protein sequencing of peptides from individual subunits and analysis of corresponding cDNA clones reveals that subunit III of cytochrome c reductase (51 kDa) represents the general mitochondrial processing peptidase.
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PMID:The general mitochondrial processing peptidase from potato is an integral part of cytochrome c reductase of the respiratory chain. 132 69

The vast majority of proteins comprising the mitochondrion are encoded by nuclear genes, synthesized on ribosomes in the cytosol, and translocated into the various mitochondrial subcompartments. During this process proteins must cross the lipid membranes of the mitochondrion without interfering with the integrity or functions of the organelle. In recent years an approach combining biochemical, molecular, genetic, and morphological methodology has provided insights into various aspects of this complex process of intracellular protein sorting. In particular, a greater understanding of the molecular specificity and mechanism of targeting of mitochondrial preproteins has been reached, as a protein complex of the outer membrane which facilitates recognition and initial membrane insertion has been identified and characterized. Furthermore, pathways and components involved in the translocation of pre-proteins across the two mitochondrial membranes are being dissected and defined. The energetics of translocation and the processes of unfolding and folding of proteins during transmembrane transfer are closely linked to the function of a host of proteins known as heat-shock proteins or molecular chaperones, present both outside and inside the mitochondrion. In addition, the analysis of the process of folding of polypeptides in the mitochondrial matrix has allowed novel and unexpected insights into general pathways of protein folding assisted by folding factors. Pathways of sorting of proteins to the four different mitochondrial subcompartments--the outer membrane (OM), intermembrane space, inner membrane (IM) and matrix--are only partly understood and reveal an amazing complexity and variation. Many additional protein factors are involved in these latter processes, a few of which have been analyzed, such as cytochrome c heme lyase and cytochrome c1 heme lyase, enzymes that catalyze the covalent addition of the heme group to cytochrome c and c1 preproteins, and the mitochondrial processing peptidase which cleaves signal sequences after import of preproteins into the matrix. Thus, the study of transport of polypeptides through the mitochondrial membranes does not only contribute to the understanding of how biological membranes facilitate the penetration of macromolecules but also provides novel insights into the structure and function of this organelle.
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PMID:Heinrich Wieland--prize lecture. Transport of proteins across mitochondrial membranes. 804 71

The mitochondrial transition pore (MTP) is implicated as a mediator of cell injury and death in many situations. The MTP opens in response to stimuli including reactive oxygen species and inhibition of the electron transport chain. Sporadic Parkinson's disease (PD) is characterized by oxidative stress and specifically involves a defect in complex I of the electron transport chain. To explore the possible involvement of the MTP in PD models, we tested the effects of the complex I inhibitor and apoptosis-inducing toxin N-methyl-4-phenylpyridinium (MPP+) on cyclosporin A (CsA)-sensitive mitochondrial swelling and release of cytochrome c. In the presence of Ca2+ and Pi, MPP+ induced a permeability transition in both liver and brain mitochondria. MPP+ also caused release of cytochrome c from liver mitochondria. Rotenone, a classic non-competitive complex I inhibitor, completely inhibited MPP(+)-induced swelling and release of cytochrome c. The MPP(+)-induced permeability transition was synergistic with nitric oxide and the adenine nucleotide translocator inhibitor atractyloside, and additive with phenyl arsine oxide cross-linking of dithiol residues. MPP(+)-induced pore opening and cytochrome c release were blocked by CsA, the Ca2+ uniporter inhibitor ruthenium red, the hydrophobic disulfide reagent N-ethylmaleimide, butacaine, and the free radical scavenging enzymes catalase and superoxide dismutase. MPP+ neurotoxicity may derive from not only its inhibition of complex I and consequent ATP depletion, but also from its ability to open the MTP and to release mitochondrial factors including Ca2+ and cytochrome c known to be involved in apoptosis.
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PMID:The parkinsonian neurotoxin MPP+ opens the mitochondrial permeability transition pore and releases cytochrome c in isolated mitochondria via an oxidative mechanism. 998 45

A dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), can induce dopaminergic denervation and Parkinsonism in humans. The active metabolite of MPTP is the 1-methyl-4-phenylpyridinium ion (MPP(+)). Previously we reported that MPP(+) is incorporated via the dopamine transport system and causes delayed cell death in GH3 cells, a clonal strain from the rat anterior pituitary. In this study, we investigated whether MPP(+) induces apoptosis. GH3 cells cultured with MPP(+) exhibited DNA laddering and fragmentation in a time- and concentration-dependent manner. The effect of MPP(+) was inhibited in GH3 cells treated with a pan-caspase inhibitor (100 microM ZVAD-fmk), an antioxidant (25 mM N-acetyl-l-cysteine), or epidermal growth factor (EGF; 50 ng/mL). Because EGF stimulated tyrosine phosphorylation of the EGF receptor and tyrphostin AG1478 [4-(3-chloroanilino)-6,7-dimethoxyquinazoline; 5 microM, a specific inhibitor of EGF receptor kinase] abolished EGF inhibition, involvement of EGF receptor kinase is assumed. Protein kinase C-dependent processes and Bcl-2 protein expression were shown not to be involved in EGF inhibition. MPP(+) increased cytochrome c immunoreactivity in cytosolic fractions in GH3 cells. The addition of 200 microM MPP(+) to isolated mitochondrial fractions from GH3 cells stimulated the release of a 13-kDa protein that cross-reacted with anti-cytochrome c antibody. The release was inhibited in EGF-treated GH3 cells. Our findings demonstrated that (i) MPP(+) induces apoptosis of GH3 cells via cytochrome c release and caspase activation, and (ii) apoptosis by MPP(+) can be blocked by N-acetyl-l-cysteine or EGF treatment.
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PMID:Apoptosis induction by a dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP(+)), and inhibition by epidermal growth factor in GH3 cells. 1080 52

The chicken mitochondrial ubiquinol cytochrome c oxidoreductase (bc(1) complex) is inhibited by Zn(2+) ions, but with higher K(i) ( approximately 3 microM) than the corresponding bovine enzyme. When equilibrated with mother liquor containing 200 microM ZnCl(2) for 7 days, the crystalline chicken bc(1) complex specifically binds Zn(2+) at 4 sites representing two sites on each monomer in the dimer. These two sites are close to the stigmatellin-binding site, taken to be center Q(o) of the Q-cycle mechanism, and are candidates for the inhibitory site. One binding site is actually in the hydrophobic channel between the Q(o) site and the bulk lipid phase, and may interfere with quinone binding. The other is in a hydrophilic area between cytochromes b and c(1), and might interfere with the egress of protons from the Q(o) site to the intermembrane aqueous medium. No zinc was bound near the putative proteolytic active site of subunits 1 and 2 (homologous to mitochondrial processing peptidase) under these conditions.
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PMID:Crystallographic location of two Zn(2+)-binding sites in the avian cytochrome bc(1) complex. 1100 61

There is growing evidence that apoptotic mechanisms underlie the neurodegeneration leading to Parkinson's disease. 1-Methyl-4-phenylpyridinium ion (MPP(+)), the active metabolite of the parkinsonism-inducing drug MPTP, induced apoptosis in cultures of human SH-SY5Y neuroblastoma cells. Nuclear fragmentation, DNA laddering, and a 20% decrease in viability were seen after a 4-day incubation with 5 microM MPP(+). Cell viability decreased by 40% at 100 microM MPP(+), but the degree of apoptosis was not correlatively increased. The MPP(+)-induced apoptosis was completely prevented by the broad caspase inhibitor zVAD.fmk but not by the caspase-8 inhibitor IETD.fmk. Furthermore, MPP(+) had no effect on the levels of Fas or Fas-L, suggesting lack of activation of the Fas-L/Fas/caspase-8 pathway of apoptosis. There was no evidence of mitochondrial dysfunction at 5 microM MPP(+): No differences were seen in transmembrane potential or in cytochrome c release from controls. At 100 microM MPP(+), the mitochondrial potential decreased, and cytoplasmic cytochrome c and caspase-9 activation increased slightly. At both low and high concentrations of MPP(+), VDVADase and DEVDase activities increased. We conclude that MPP(+) can induce caspase-mediated apoptosis, which is prevented by caspase inhibition, at concentrations lower than those needed to trigger mitochondrial dysfunction and closer to those found in the brains of MPTP-treated animals.
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PMID:Low concentrations of 1-methyl-4-phenylpyridinium ion induce caspase-mediated apoptosis in human SH-SY5Y neuroblastoma cells. 1122 17

Bax is a proapoptotic member of the Bcl-2 family of proteins. It is believed to exert its action primarily by facilitating the release of cytochrome c from the mitochondrial intermembrane space into the cytosol, leading to caspase activation and cell death. Because alterations in mitochondrial respiratory function, caspase activation and cell death with morphologic features compatible with apoptosis have been observed post mortem in the brain of patients with Parkinson's disease, we tried to clarify the potential role of Bax in this process in an immunohistochemical study on normal and Parkinson's disease post-mortem brain and primary mesencephalic cell cultures treated with MPP(+). We found that Bax is expressed ubiquitously by dopaminergic (DA) neurons in post-mortem brain of normal and Parkinson's disease subjects as well as in vitro. Using an antibody to Bax inserted into the outer mitochondrial membrane as an index of Bax activation, no significant differences were observed between control and Parkinson's disease subjects, regardless of the mesencephalic subregion analysed. However, in Parkinson's disease subjects, the percentage of Bax-positive melanized SNpc neurons containing Lewy bodies, suggestive of DA neuronal suffering, was significantly higher than the overall percentage of Bax-positive neurons among melanized neurons. Furthermore, all melanized SNpc neurons in Parkinson's disease subjects with activated caspase-3 were also immunoreactive for Bax, suggesting that Bax anchored in the outer mitochondrial membrane of melanized SNpc neurons showing signs of neuronal suffering or apoptosis is increased compared with DA neurons that are apparently unaltered. Surprisingly, MPP(+) treatment of tyrosine hydroxylase (TH)-positive neurons in primary mesencephalic cultures did not cause redistribution of Bax, although cytochrome c was released from the mitochondria and nuclear condensation/fragmentation was induced. Taken together, these findings suggest that in the human pathology, Bax may be a cofactor in caspase activation, but our in vitro data fail to indicate a central role for Bax in apoptotic death of DA neurons in an experimental Parkinson's disease paradigm.
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PMID:Is Bax a mitochondrial mediator in apoptotic death of dopaminergic neurons in Parkinson's disease? 1125 96

Recently, it has been shown that release of cytochrome c from the mitochondria to the cytosol is required for activation of the caspase-3-dependent cascade in apoptosis, and also for alpha-synuclein aggregation. In the present study, we examined the effects of talipexole and pramipexole on the release of cytochrome c and alpha-synuclein, their aggregations, and activation of caspases. Treatment of human neuroblastoma SH-SY5Y cells with 1-methyl-4-phenylpyridinium (MPP(+), 1 mM) induced the first event, which was the release of cytochrome c from the organellar fraction to the cytosolic fraction, then came the DNA fragmentation, and caused the last event, which was the accumulation of alpha-synuclein protein in the cytosolic fraction. Talipexole and pramipexole at low concentration (0.1-1 mM) significantly inhibited the accumulation of cytochrome c or alpha-synuclein in the cytosolic fraction. These drugs at high concentration (3-10 mM) inhibited in vitro aggregation of cytochrome c by hydrogen peroxide or that of alpha-synuclein by cytochrome c and hydrogen peroxide. In addition, in vitro activation of caspase-3 induced by cytochrome c and/or dATP was also inhibited by drugs at high concentration (5-10 mM). These results suggest that talipexole and pramipexole may have protective effects against the neurodegeneration, which is induced by intracellular accumulation of cytochrome c and alpha-synuclein.
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PMID:Release and aggregation of cytochrome c and alpha-synuclein are inhibited by the antiparkinsonian drugs, talipexole and pramipexole. 1130 Oct 60

Two cysteine protease families, caspase and calpain, are known to participate in cell death. We investigated whether a stress-specific protease activation pathway exists, and to what extent Bcl-2 plays a role in preventing drug-induced protease activity and cell death in a dopaminergic neuronal cell line, MN9D. Staurosporine (STS) induced caspase-dependent apoptosis while a dopaminergic neurotoxin, MPP(+) largely induced caspase-independent necrotic cell death as determined by morphological and biochemical criteria including cytochrome c release and fluorogenic caspase cleavage assay. At the late stage of both STS- and MPP(+)-induced cell death, Bax was cleaved into an 18-kDa fragment. This 18-kDa fragment appeared only in the mitochondria-enriched heavy membrane fraction of STS-treated cells, whereas it was detected exclusively in the cytosolic fraction of MPP(+)-treated cells. This proteolytic cleavage of Bax appeared to be mediated by calpain as determined by incubation with [(35)S]methionine-labelled Bax. Thus, cotreatment of cells with calpain inhibitor blocked both MPP(+)- and STS-induced Bax cleavage. Intriguingly, overexpression of baculovirus-derived inhibiting protein of caspase, p35 or cotreatment of cells with caspase inhibitor blocked STS- but not MPP(+)-induced Bax cleavage. This appears to indicate that calpain activation may be either dependent or independent of caspase activation within the same cells. However, cotreatment with calpain inhibitor rescued cells from MPP(+)-induced but not from STS-induced neuronal cell death. In these paradigms of dopaminergic cell death, overexpression of Bcl-2 prevented both STS- and MPP(+)-induced cell death and its associated cleavage of Bax. Thus, our results suggest that Bcl-2 may play a protective role by primarily blocking drug-induced caspase or calpain activity in dopaminergic neuronal cells.
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PMID:Cleavage of Bax is mediated by caspase-dependent or -independent calpain activation in dopaminergic neuronal cells: protective role of Bcl-2. 1141 36

Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity are both associated with dopaminergic neuron death in the substantia nigra (SN). Apoptosis has been implicated in this cell loss; however, whether or not it is a major component of disease pathology remains controversial. Caspases are a major class of proteases involved in the apoptotic process. To evaluate the role of caspases in PD, we analyzed caspase activation in MPTP-treated mice, in cultured dopaminergic cells, and in postmortem PD brain tissue. MPTP was found to elicit not only the activation of the effector caspase-3 but also the initiators caspase-8 and caspase-9, mitochondrial cytochrome c release, and Bid cleavage in the SN of wild-type mice. These changes were attenuated in transgenic mice neuronally expressing the general caspase inhibitor protein baculoviral p35. These mice also displayed increased resistance to the cytotoxic effects of the drug. MPTP-associated toxicity in culture was found temporally to involve cytochrome c release, activation of caspase-9, caspase-3, and caspase-8, and Bid cleavage. Caspase-9 inhibition prevented the activation of both caspase-3 and caspase-8 and also inhibited Bid cleavage, but not cytochrome c release. Activated caspase-8 and caspase-9 were immunologically detectable within MPP(+)-treated mesencephalic dopaminergic neurons, dopaminergic nigral neurons from MPTP-treated mice, and autopsied Parkinsonian tissue from late-onset sporadic cases of the disease. These data demonstrate that MPTP-mediated activation of caspase-9 via cytochrome c release results in the activation of caspase-8 and Bid cleavage, which we speculate may be involved in the amplification of caspase-mediated dopaminergic cell death. These data suggest that caspase inhibitors constitute a plausible therapeutic for PD.
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PMID:Caspase-9 activation results in downstream caspase-8 activation and bid cleavage in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease. 1173 63


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