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Tjhin ET, Hayward JA, McFadden GI, van Dooren GG. Characterization of the apicoplast-localized enzyme TgUroD in Toxoplasma gondii reveals a key role of the apicoplast in heme biosynthesis. J Biol Chem 2020; 295:1539-1550. [PMID: 31914409 PMCID: PMC7008375 DOI: 10.1074/jbc.ra119.011605] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 12/21/2019] [Indexed: 12/29/2022] Open
Abstract
Apicomplexan parasites such as Toxoplasma gondii possess an unusual heme biosynthesis pathway whose enzymes localize to the mitochondrion, cytosol, or apicoplast, a nonphotosynthetic plastid present in most apicomplexans. To characterize the involvement of the apicoplast in the T. gondii heme biosynthesis pathway, we investigated the role of the apicoplast-localized enzyme uroporphyrinogen III decarboxylase (TgUroD). We found that TgUroD knockdown impaired parasite proliferation, decreased free heme levels in the parasite, and decreased the abundance of heme-containing c-type cytochrome proteins in the parasite mitochondrion. We validated the effects of heme loss on mitochondrial cytochromes by knocking down cytochrome c/c1 heme lyase 1 (TgCCHL1), a mitochondrial enzyme that catalyzes the covalent attachment of heme to c-type cytochromes. TgCCHL1 depletion reduced parasite proliferation and decreased the abundance of c-type cytochromes. We further sought to characterize the overall importance of TgUroD and TgCCHL1 for both mitochondrial and general parasite metabolism. TgUroD depletion decreased cellular ATP levels, mitochondrial oxygen consumption, and extracellular acidification rates. By contrast, depletion of TgCCHL1 neither diminished ATP levels in the parasite nor impaired extracellular acidification rate, but resulted in specific defects in mitochondrial oxygen consumption. Together, our results indicate that the apicoplast has a key role in heme biology in T. gondii and is important for both mitochondrial and general parasite metabolism. Our study highlights the importance of heme and its synthesis in these parasites.
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Affiliation(s)
- Edwin T Tjhin
- Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Jenni A Hayward
- Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Geoffrey I McFadden
- School of BioSciences University of Melbourne, Parkville, VIC 3010, Australia
| | - Giel G van Dooren
- Research School of Biology, Australian National University, Canberra, ACT 2601, Australia.
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2
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Backes S, Herrmann JM. Protein Translocation into the Intermembrane Space and Matrix of Mitochondria: Mechanisms and Driving Forces. Front Mol Biosci 2017; 4:83. [PMID: 29270408 PMCID: PMC5725982 DOI: 10.3389/fmolb.2017.00083] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 11/24/2017] [Indexed: 11/17/2022] Open
Abstract
Mitochondria contain two aqueous subcompartments, the matrix and the intermembrane space (IMS). The matrix is enclosed by both the inner and outer mitochondrial membranes, whilst the IMS is sandwiched between the two. Proteins of the matrix are synthesized in the cytosol as preproteins, which contain amino-terminal matrix targeting sequences that mediate their translocation through translocases embedded in the outer and inner membrane. For these proteins, the translocation reaction is driven by the import motor which is part of the inner membrane translocase. The import motor employs matrix Hsp70 molecules and ATP hydrolysis to ratchet proteins into the mitochondrial matrix. Most IMS proteins lack presequences and instead utilize the IMS receptor Mia40, which facilitates their translocation across the outer membrane in a reaction that is coupled to the formation of disulfide bonds within the protein. This process requires neither ATP nor the mitochondrial membrane potential. Mia40 fulfills two roles: First, it acts as a holdase, which is crucial in the import of IMS proteins and second, it functions as a foldase, introducing disulfide bonds into newly imported proteins, which induces and stabilizes their natively folded state. For several Mia40 substrates, oxidative folding is an essential prerequisite for their assembly into oligomeric complexes. Interestingly, recent studies have shown that the two functions of Mia40 can be experimentally separated from each other by the use of specific mutants, hence providing a powerful new way to dissect the different physiological roles of Mia40. In this review we summarize the current knowledge relating to the mitochondrial matrix-targeting and the IMS-targeting/Mia40 pathway. Moreover, we discuss the mechanistic properties by which the mitochondrial import motor on the one hand and Mia40 on the other, drive the translocation of their substrates into the organelle. We propose that the lateral diffusion of Mia40 in the inner membrane and the oxidation-mediated folding of incoming polypeptides supports IMS import.
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Affiliation(s)
- Sandra Backes
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
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3
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Wenger C, Oeljeklaus S, Warscheid B, Schneider A, Harsman A. A trypanosomal orthologue of an intermembrane space chaperone has a non-canonical function in biogenesis of the single mitochondrial inner membrane protein translocase. PLoS Pathog 2017; 13:e1006550. [PMID: 28827831 PMCID: PMC5584982 DOI: 10.1371/journal.ppat.1006550] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 09/05/2017] [Accepted: 07/24/2017] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial protein import is essential for Trypanosoma brucei across its life cycle and mediated by membrane-embedded heterooligomeric protein complexes, which mainly consist of trypanosomatid-specific subunits. However, trypanosomes contain orthologues of small Tim chaperones that escort hydrophobic proteins across the intermembrane space. Here we have experimentally analyzed three novel trypanosomal small Tim proteins, one of which contains only an incomplete Cx3C motif. RNAi-mediated ablation of TbERV1 shows that their import, as in other organisms, depends on the MIA pathway. Submitochondrial fractionation combined with immunoprecipitation and BN-PAGE reveals two pools of small Tim proteins: a soluble fraction forming 70 kDa complexes, consistent with hexamers and a second fraction that is tightly associated with the single trypanosomal TIM complex. RNAi-mediated ablation of the three proteins leads to a growth arrest and inhibits the formation of the TIM complex. In line with these findings, the changes in the mitochondrial proteome induced by ablation of one small Tim phenocopy the effects observed after ablation of TbTim17. Thus, the trypanosomal small Tims play an unexpected and essential role in the biogenesis of the single TIM complex, which for one of them is not linked to import of TbTim17.
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Affiliation(s)
- Christoph Wenger
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, Bern, Switzerland
| | - Silke Oeljeklaus
- Department of Biochemistry and Functional Proteomics, Institute of Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestr. 18, Freiburg, Germany
| | - Bettina Warscheid
- Department of Biochemistry and Functional Proteomics, Institute of Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestr. 18, Freiburg, Germany
| | - André Schneider
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, Bern, Switzerland
- * E-mail:
| | - Anke Harsman
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, Bern, Switzerland
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Ghosh A, Stuehr DJ. Regulation of sGC via hsp90, Cellular Heme, sGC Agonists, and NO: New Pathways and Clinical Perspectives. Antioxid Redox Signal 2017; 26:182-190. [PMID: 26983679 PMCID: PMC5278824 DOI: 10.1089/ars.2016.6690] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
SIGNIFICANCE Soluble guanylate cyclase (sGC) is an intracellular enzyme that plays a primary role in sensing nitric oxide (NO) and transducing its multiple signaling effects in mammals. Recent Advances: The chaperone heat shock protein 90 (hsp90) associates with signaling proteins in cells, including sGC, where it helps to drive heme insertion into the sGC-β1 subunit. This allows sGC-β1 to associate with a partner sGC-α1 subunit and mature into an NO-responsive active form. CRITICAL ISSUES In this article, we review evidence to date regarding the mechanisms that modulate sGC activity by a pathway where binding of hsp90 or sGC agonist to heme-free sGC dictates the assembly and fate of an active sGC heterodimer, both by NO and heme-dependent or heme-independent pathways. FUTURE DIRECTIONS We discuss some therapeutic implications of the NO-sGC-hsp90 nexus and its potential as a marker of inflammatory disease. Antioxid. Redox Signal. 26, 182-190.
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Affiliation(s)
- Arnab Ghosh
- Department of Pathobiology, Lerner Research Institute , Cleveland Clinic, Cleveland, Ohio
| | - Dennis J Stuehr
- Department of Pathobiology, Lerner Research Institute , Cleveland Clinic, Cleveland, Ohio
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Babbitt SE, Sutherland MC, San Francisco B, Mendez DL, Kranz RG. Mitochondrial cytochrome c biogenesis: no longer an enigma. Trends Biochem Sci 2015; 40:446-55. [PMID: 26073510 DOI: 10.1016/j.tibs.2015.05.006] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 05/13/2015] [Accepted: 05/18/2015] [Indexed: 12/31/2022]
Abstract
Cytochromes c (cyt c) and c1 are heme proteins that are essential for aerobic respiration. Release of cyt c from mitochondria is an important signal in apoptosis initiation. Biogenesis of c-type cytochromes involves covalent attachment of heme to two cysteines (at a conserved CXXCH sequence) in the apocytochrome. Heme attachment is catalyzed in most mitochondria by holocytochrome c synthase (HCCS), which is also necessary for the import of apocytochrome c (apocyt c). Thus, HCCS affects cellular levels of cyt c, impacting mitochondrial physiology and cell death. Here, we review the mechanisms of HCCS function and the roles of heme and residues in the CXXCH motif. Additionally, we consider concepts emerging within the two prokaryotic cytochrome c biogenesis pathways.
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Affiliation(s)
- Shalon E Babbitt
- Department of Biology, Washington University, St Louis, MO 63130, USA
| | | | | | - Deanna L Mendez
- Department of Biology, Washington University, St Louis, MO 63130, USA
| | - Robert G Kranz
- Department of Biology, Washington University, St Louis, MO 63130, USA.
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6
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Respiration triggers heme transfer from cytochrome c peroxidase to catalase in yeast mitochondria. Proc Natl Acad Sci U S A 2014; 111:17468-73. [PMID: 25422453 DOI: 10.1073/pnas.1409692111] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In exponentially growing yeast, the heme enzyme, cytochrome c peroxidase (Ccp1) is targeted to the mitochondrial intermembrane space. When the fermentable source (glucose) is depleted, cells switch to respiration and mitochondrial H2O2 levels rise. It has long been assumed that CCP activity detoxifies mitochondrial H2O2 because of the efficiency of this activity in vitro. However, we find that a large pool of Ccp1 exits the mitochondria of respiring cells. We detect no extramitochondrial CCP activity because Ccp1 crosses the outer mitochondrial membrane as the heme-free protein. In parallel with apoCcp1 export, cells exhibit increased activity of catalase A (Cta1), the mitochondrial and peroxisomal catalase isoform in yeast. This identifies Cta1 as a likely recipient of Ccp1 heme, which is supported by low Cta1 activity in ccp1Δ cells and the accumulation of holoCcp1 in cta1Δ mitochondria. We hypothesized that Ccp1's heme is labilized by hyperoxidation of the protein during the burst in H2O2 production as cells begin to respire. To test this hypothesis, recombinant Ccp1 was hyperoxidized with excess H2O2 in vitro, which accelerated heme transfer to apomyoglobin added as a surrogate heme acceptor. Furthermore, the proximal heme Fe ligand, His175, was found to be ∼ 85% oxidized to oxo-histidine in extramitochondrial Ccp1 isolated from 7-d cells, indicating that heme labilization results from oxidation of this ligand. We conclude that Ccp1 responds to respiration-derived H2O2 via a previously unidentified mechanism involving H2O2-activated heme transfer to apoCta1. Subsequently, the catalase activity of Cta1, not CCP activity, contributes to mitochondrial H2O2 detoxification.
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Babbitt SE, San Francisco B, Bretsnyder EC, Kranz RG. Conserved residues of the human mitochondrial holocytochrome c synthase mediate interactions with heme. Biochemistry 2014; 53:5261-71. [PMID: 25054239 PMCID: PMC4139152 DOI: 10.1021/bi500704p] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
C-type cytochromes are distinguished by the covalent attachment of a heme cofactor, a modification that is typically required for its subsequent folding, stability, and function. Heme attachment takes place in the mitochondrial intermembrane space and, in most eukaryotes, is mediated by holocytochrome c synthase (HCCS). HCCS is the primary component of the eukaryotic cytochrome c biogenesis pathway, known as System III. The catalytic function of HCCS depends on its ability to coordinate interactions between its substrates: heme and cytochrome c. Recent advancements in the recombinant expression and purification of HCCS have facilitated comprehensive analyses of the roles of conserved residues in HCCS, as demonstrated in this study. Previously, we proposed a four-step model describing HCCS-mediated cytochrome c assembly, identifying a conserved histidine residue (His154) as an axial ligand to the heme iron. In this study, we performed a systematic mutational analysis of 17 conserved residues in HCCS, and we provide evidence that the enzyme contains two heme-binding domains. Our data indicate that heme contacts mediated by residues within these domains modulate the dynamics of heme binding and contribute to the stability of the HCCS-heme-cytochrome c steady state ternary complex. While some residues are essential for initial heme binding (step 1), others impact the subsequent release of the holocytochrome c product (step 4). Certain HCCS mutants that were defective in heme binding were corrected for function by exogenous aminolevulinic acid (ALA, the precursor to heme). This chemical "correction" supports the proposed role of heme binding for the corresponding residues.
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Affiliation(s)
- Shalon E Babbitt
- Department of Biology, Washington University , St. Louis, Missouri 63130, United States
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8
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Zhang Y, Stevens JM, Ferguson SJ. Substrate recognition of holocytochrome c synthase: N-terminal region and CXXCH motif of mitochondrial cytochrome c. FEBS Lett 2014; 588:3367-74. [PMID: 25084480 PMCID: PMC4158909 DOI: 10.1016/j.febslet.2014.07.026] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 07/18/2014] [Accepted: 07/22/2014] [Indexed: 11/25/2022]
Abstract
Holocytochrome c synthase (HCCS) does not attach heme to cytochromes lacking the histidine in the CXXCH motif. HCCS can recognise C-terminally truncated cytochromes c. The aromatic nature of, or possibly shape complementarity to, F15 in cytochrome c is important for recognition by HCCS. The spacing of the phenylalanine relative to the CXXCH is a recognition feature.
Holocytochrome c synthase (HCCS) attaches heme covalently to mitochondrial respiratory cytochromes c. Little is known about the reaction of heme attachment to apocytochromes c by HCCS, although recently it has been established that the CXXCH motif and the N-terminus of the apocytochrome polypeptide are important protein–protein recognition motifs. Here, we explore further the important features of the N-terminal sequence and investigate what variations in the CXXCH residues are productively recognised by HCCS in its substrate.
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Affiliation(s)
- Yulin Zhang
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Julie M Stevens
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
| | - Stuart J Ferguson
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
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9
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Abstract
Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), an endogenous neurotoxin, is known to perform a role in the pathogenesis of Parkinson’s disease (PD). In this study, we
evaluated oxidative modification of cytochrome c occurring after incubation with salsolinol. When cytochrome c was incubated with salsolinol, protein aggregation increased in a dosedependent manner. The formation of carbonyl compounds and the release of iron were obtained in salsolinol- treated cytochrome c. Salsolinol also led to the release of iron from cytochrome c. Reactive oxygen species (ROS) scavengers and iron specific chelator inhibited the salsolinol-mediated cytochrome c modification and carbonyl compound formation. It is suggested that oxidative damage of cytochrome c by salsolinol might induce the increase of iron content in cells, subsequently leading to the deleterious condition which was observed. This mechanism may, in part, provide an explanation for the deterioration of organs under neurodegenerative disorders such as PD. [BMB Reports 2013; 46(2): 119-123]
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Affiliation(s)
- Jung Hoon Kang
- Department of Genetic Engineering, Cheongju University, Cheongju 360-764, Korea.
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10
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Abstract
The mitochondrion is arguably the most complex organelle in the budding yeast cell cytoplasm. It is essential for viability as well as respiratory growth. Its innermost aqueous compartment, the matrix, is bounded by the highly structured inner membrane, which in turn is bounded by the intermembrane space and the outer membrane. Approximately 1000 proteins are present in these organelles, of which eight major constituents are coded and synthesized in the matrix. The import of mitochondrial proteins synthesized in the cytoplasm, and their direction to the correct soluble compartments, correct membranes, and correct membrane surfaces/topologies, involves multiple pathways and macromolecular machines. The targeting of some, but not all, cytoplasmically synthesized mitochondrial proteins begins with translation of messenger RNAs localized to the organelle. Most proteins then pass through the translocase of the outer membrane to the intermembrane space, where divergent pathways sort them to the outer membrane, inner membrane, and matrix or trap them in the intermembrane space. Roughly 25% of mitochondrial proteins participate in maintenance or expression of the organellar genome at the inner surface of the inner membrane, providing 7 membrane proteins whose synthesis nucleates the assembly of three respiratory complexes.
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11
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Huang YH, Wu HY, Wu KM, Liu TT, Liou RF, Tsai SF, Shiao MS, Ho LT, Tzean SS, Yang UC. Generation and analysis of the expressed sequence tags from the mycelium of Ganoderma lucidum. PLoS One 2013; 8:e61127. [PMID: 23658685 PMCID: PMC3642047 DOI: 10.1371/journal.pone.0061127] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Accepted: 03/07/2013] [Indexed: 12/24/2022] Open
Abstract
Ganoderma lucidum (G. lucidum) is a medicinal mushroom renowned in East Asia for its potential biological effects. To enable a systematic exploration of the genes associated with the various phenotypes of the fungus, the genome consortium of G. lucidum has carried out an expressed sequence tag (EST) sequencing project. Using a Sanger sequencing based approach, 47,285 ESTs were obtained from in vitro cultures of G. lucidum mycelium of various durations. These ESTs were further clustered and merged into 7,774 non-redundant expressed loci. The features of these expressed contigs were explored in terms of over-representation, alternative splicing, and natural antisense transcripts. Our results provide an invaluable information resource for exploring the G. lucidum transcriptome and its regulation. Many cases of the genes over-represented in fast-growing dikaryotic mycelium are closely related to growth, such as cell wall and bioactive compound synthesis. In addition, the EST-genome alignments containing putative cassette exons and retained introns were manually curated and then used to make inferences about the predominating splice-site recognition mechanism of G. lucidum. Moreover, a number of putative antisense transcripts have been pinpointed, from which we noticed that two cases are likely to reveal hitherto undiscovered biological pathways. To allow users to access the data and the initial analysis of the results of this project, a dedicated web site has been created at http://csb2.ym.edu.tw/est/.
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Affiliation(s)
- Yen-Hua Huang
- Department of Biochemistry, Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
- Center for Systems and Synthetic Biology, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
| | - Hung-Yi Wu
- Department of Plant Pathology and Microbiology, National Taiwan University, Taipei City, Taiwan, R.O.C.
| | - Keh-Ming Wu
- VYM Genome Research Center, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
| | - Tze-Tze Liu
- VYM Genome Research Center, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
| | - Ruey-Fen Liou
- Department of Plant Pathology and Microbiology, National Taiwan University, Taipei City, Taiwan, R.O.C.
| | - Shih-Feng Tsai
- VYM Genome Research Center, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
| | - Ming-Shi Shiao
- Medical Research and Education Department, Taipei Veterans General Hospital, Taipei City, Taiwan, R.O.C.
| | - Low-Tone Ho
- Medical Research and Education Department, Taipei Veterans General Hospital, Taipei City, Taiwan, R.O.C.
| | - Shean-Shong Tzean
- Department of Plant Pathology and Microbiology, National Taiwan University, Taipei City, Taiwan, R.O.C.
| | - Ueng-Cheng Yang
- Institute of Biomedical Informatics, College of Life Science, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
- Center for Systems and Synthetic Biology, National Yang-Ming University, Taipei City, Taiwan, R.O.C.
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Indrieri A, Conte I, Chesi G, Romano A, Quartararo J, Tatè R, Ghezzi D, Zeviani M, Goffrini P, Ferrero I, Bovolenta P, Franco B. The impairment of HCCS leads to MLS syndrome by activating a non-canonical cell death pathway in the brain and eyes. EMBO Mol Med 2013; 5:280-93. [PMID: 23239471 PMCID: PMC3569643 DOI: 10.1002/emmm.201201739] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 12/03/2012] [Accepted: 12/04/2012] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial-dependent (intrinsic) programmed cell death (PCD) is an essential homoeostatic mechanism that selects bioenergetically proficient cells suitable for tissue/organ development. However, the link between mitochondrial dysfunction, intrinsic apoptosis and developmental anomalies has not been demonstrated to date. Now we provide the evidence that non-canonical mitochondrial-dependent apoptosis explains the phenotype of microphthalmia with linear skin lesions (MLS), an X-linked developmental disorder caused by mutations in the holo-cytochrome c-type synthase (HCCS) gene. By taking advantage of a medaka model that recapitulates the MLS phenotype we demonstrate that downregulation of hccs, an essential player of the mitochondrial respiratory chain (MRC), causes increased cell death via an apoptosome-independent caspase-9 activation in brain and eyes. We also show that the unconventional activation of caspase-9 occurs in the mitochondria and is triggered by MRC impairment and overproduction of reactive oxygen species (ROS). We thus propose that HCCS plays a key role in central nervous system (CNS) development by modulating a novel non-canonical start-up of cell death and provide the first experimental evidence for a mechanistic link between mitochondrial dysfunction, intrinsic apoptosis and developmental disorders.
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A model system for mitochondrial biogenesis reveals evolutionary rewiring of protein import and membrane assembly pathways. Proc Natl Acad Sci U S A 2012; 109:E3358-66. [PMID: 23151513 DOI: 10.1073/pnas.1206345109] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The controlled biogenesis of mitochondria is a key cellular system coordinated with the cell division cycle, and major efforts in systems biology currently are directed toward understanding of the control points at which this coordination is achieved. Here we present insights into the function, evolution, and regulation of mitochondrial biogenesis through the study of the protein import machinery in the human fungal pathogen, Candida albicans. Features that distinguish C. albicans from baker's yeast (Saccharomyces cerevisiae) include the stringency of metabolic control at the level of oxygen consumption, the potential for ATP exchange through the porin in the outer membrane, and components and domains in the sorting and assembling machinery complex, a molecular machine that drives the assembly of proteins in the outer mitochondrial membrane. Analysis of targeting sequences and assays of mitochondrial protein import show that components of the electron transport chain are imported by distinct pathways in C. albicans and S. cerevisiae, representing an evolutionary rewiring of mitochondrial import pathways. We suggest that studies using this pathogen as a model system for mitochondrial biogenesis will greatly enhance our knowledge of how mitochondria are made and controlled through the course of the cell-division cycle.
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Human mitochondrial holocytochrome c synthase's heme binding, maturation determinants, and complex formation with cytochrome c. Proc Natl Acad Sci U S A 2012; 110:E788-97. [PMID: 23150584 DOI: 10.1073/pnas.1213897109] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Proper functioning of the mitochondrion requires the orchestrated assembly of respiratory complexes with their cofactors. Cytochrome c, an essential electron carrier in mitochondria and a critical component of the apoptotic pathway, contains a heme cofactor covalently attached to the protein at a conserved CXXCH motif. Although it has been known for more than two decades that heme attachment requires the mitochondrial protein holocytochrome c synthase (HCCS), the mechanism remained unknown. We purified membrane-bound human HCCS with endogenous heme and in complex with its cognate human apocytochrome c. Spectroscopic analyses of HCCS alone and complexes of HCCS with site-directed variants of cytochrome c revealed the fundamental steps of heme attachment and maturation. A conserved histidine in HCCS (His154) provided the key ligand to the heme iron. Formation of the HCCS:heme complex served as the platform for interaction with apocytochrome c. Heme was the central molecule mediating contact between HCCS and apocytochrome c. A conserved histidine in apocytochrome c (His19 of CXXCH) supplied the second axial ligand to heme in the trapped HCCS:heme:cytochrome c complex. We also examined the substrate specificity of human HCCS and converted a bacterial cytochrome c into a robust substrate for the HCCS. The results allow us to describe the molecular mechanisms underlying the HCCS reaction.
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15
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Schreiner B, Westerburg H, Forné I, Imhof A, Neupert W, Mokranjac D. Role of the AAA protease Yme1 in folding of proteins in the intermembrane space of mitochondria. Mol Biol Cell 2012; 23:4335-46. [PMID: 22993211 PMCID: PMC3496608 DOI: 10.1091/mbc.e12-05-0420] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We show here that the i-AAA protease Yme1 has a role in folding of proteins in the intermembrane space of mitochondria and identify a number of endogenous proteins that aggregate in its absence. Thus the function of Yme1 in mitochondrial proteostasis extends beyond its role in proteolytic removal of misfolded and nonassembled inner membrane proteins. The vast majority of mitochondrial proteins are synthesized in the cytosol and transported into the organelle in a largely, if not completely, unfolded state. The proper function of mitochondria thus depends on folding of several hundreds of proteins in the various subcompartments of the organelle. Whereas folding of proteins in the mitochondrial matrix is supported by members of several chaperone families, very little is known about folding of proteins in the intermembrane space (IMS). We targeted dihydrofolate reductase (DHFR) as a model substrate to the IMS of yeast mitochondria and analyzed its folding. DHFR can fold in this compartment, and its aggregation upon heat shock can be prevented in an ATP-dependent manner. Yme1, an AAA (ATPases associated with diverse cellular activities) protease of the IMS, prevented aggregation of DHFR. Analysis of protein aggregates in mitochondria lacking Yme1 revealed the presence of a number of proteins involved in the establishment of mitochondrial ultrastructure, lipid metabolism, protein import, and respiratory growth. These findings explain the pleiotropic effects of deletion of YME1 and suggest an important role for Yme1 as a folding assistant, in addition to its proteolytic function, in the protein homeostasis of mitochondria
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Affiliation(s)
- Bernadette Schreiner
- Adolf Butenandt Institute, Physiological Chemistry, University of Munich, 81377 Munich, Germany
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16
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The multiple functions of cytochrome c and their regulation in life and death decisions of the mammalian cell: From respiration to apoptosis. Mitochondrion 2011; 11:369-81. [PMID: 21296189 DOI: 10.1016/j.mito.2011.01.010] [Citation(s) in RCA: 384] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Revised: 01/26/2011] [Accepted: 01/28/2011] [Indexed: 02/06/2023]
Abstract
Cytochrome c (Cytc) is essential in mitochondrial electron transport and intrinsic type II apoptosis. Mammalian Cytc also scavenges reactive oxygen species (ROS) under healthy conditions, produces ROS with the co-factor p66(Shc), and oxidizes cardiolipin during apoptosis. The recent finding that Cytc is phosphorylated in vivo underpins a model for the pivotal role of Cytc regulation in making life and death decisions. An apoptotic sequence of events is proposed involving changes in Cytc phosphorylation, increased ROS via increased mitochondrial membrane potentials or the p66(Shc) pathway, and oxidation of cardiolipin by Cytc followed by its release from the mitochondria. Cytc regulation in respiration and cell death is discussed in a human disease context including neurodegenerative and cardiovascular diseases, cancer, and sepsis.
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Tamura Y, Iijima M, Sesaki H. Mdm35p imports Ups proteins into the mitochondrial intermembrane space by functional complex formation. EMBO J 2010; 29:2875-87. [PMID: 20622808 DOI: 10.1038/emboj.2010.149] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2010] [Accepted: 06/09/2010] [Indexed: 11/09/2022] Open
Abstract
Ups1p, Ups2p, and Ups3p are three homologous proteins that control phospholipid metabolism in the mitochondrial intermembrane space (IMS). The Ups proteins are atypical IMS proteins in that they lack the two major IMS-targeting signals, bipartite presequences and cysteine motifs. Here, we show that Ups protein import is mediated by another IMS protein, Mdm35p. In vitro import assays show that import of Ups proteins requires Mdm35p. Loss of Mdm35p led to a decrease in steady state levels of Ups proteins in mitochondria. In addition, mdm35Delta cells displayed a similar phenotype to ups1Deltaups2Deltaups3Delta cells. Interestingly, unlike typical import machineries, Mdm35p associated stably with Ups proteins at a steady state after import. Demonstrating that Mdm35p is a functional component of Ups-Mdm35p complexes, restoration of Ups protein levels in mdm35Delta mitochondria failed to restore phospholipid metabolism. These findings provide a novel mechanism in which the formation of functional protein complexes drives mitochondrial protein import.
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Affiliation(s)
- Yasushi Tamura
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
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18
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Vempati UD, Han X, Moraes CT. Lack of cytochrome c in mouse fibroblasts disrupts assembly/stability of respiratory complexes I and IV. J Biol Chem 2008; 284:4383-91. [PMID: 19075019 DOI: 10.1074/jbc.m805972200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytochrome c (cyt c) is a heme-containing protein that participates in electron transport in the respiratory chain and as a signaling molecule in the apoptotic cascade. Here we addressed the effect of removing mammalian cyt c on the integrity of the respiratory complexes in mammalian cells. Mitochondria from cyt c knockout mouse cells lacked fully assembled complexes I and IV and had reduced levels of complex III. A redox-deficient mutant of cyt c was unable to rescue the levels of complexes I and IV. We found that cyt c is associated with both complex IV and respiratory supercomplexes, providing a potential mechanism for the requirement for cyt c in the assembly/stability of complex IV.
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Affiliation(s)
- Uma D Vempati
- Department of Neurology and Department of Cell Biology and Anatomy, University of Miami Miller School of Medicine, Miami, Florida 33136, USA
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19
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Latypov RF, Maki K, Cheng H, Luck SD, Roder H. Folding mechanism of reduced Cytochrome c: equilibrium and kinetic properties in the presence of carbon monoxide. J Mol Biol 2008; 383:437-53. [PMID: 18761351 DOI: 10.1016/j.jmb.2008.08.025] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 08/08/2008] [Accepted: 08/13/2008] [Indexed: 11/26/2022]
Abstract
Despite close structural similarity, the ferric and ferrous forms of cytochrome c differ greatly in terms of their ligand binding properties, stability, folding, and dynamics. The reduced heme iron binds diatomic ligands such as CO only under destabilizing conditions that promote weakening or disruption of native methionine-iron linkage. This makes CO a useful conformational probe for detecting partially structured states that cannot be observed in the absence of endogenous ligands. Heme absorbance, circular dichroism, and NMR were used to characterize the denaturant-induced unfolding equilibrium of ferrocytochrome c in the presence and in the absence of CO. In addition to the native state (N), which does not bind CO, and the unfolded CO complex (U-CO), a structurally distinct CO-bound form (M-CO) accumulates to high levels (approximately 75% of the population) at intermediate guanidine HCl concentrations. Comparison of the unfolding transitions for different conformational probes reveals that M-CO is a compact state containing a native-like helical core and regions of local disorder in the segment containing the native Met80 ligand and adjacent loops. Kinetic measurements of CO binding and dissociation under native, partially denaturing, and fully unfolded conditions indicate that a state M that is structurally analogous to M-CO is populated even in the absence of CO. The binding energy of the CO ligand lowers the free energy of this high-energy state to such an extent that it accumulates even under mildly denaturing equilibrium conditions. The thermodynamic and kinetic parameters obtained in this study provide a fully self-consistent description of the linked unfolding/CO binding equilibria of reduced cytochrome c.
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20
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Role of heme in the antifungal activity of the azaoxoaporphine alkaloid sampangine. EUKARYOTIC CELL 2007; 7:387-400. [PMID: 18156292 DOI: 10.1128/ec.00323-07] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Sampangine, a plant-derived alkaloid found in the Annonaceae family, exhibits strong inhibitory activity against the opportunistic fungal pathogens Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. In the present study, transcriptional profiling experiments coupled with analyses of mutants were performed in an effort to elucidate its mechanism of action. Using Saccharomyces cerevisiae as a model organism, we show that sampangine produces a transcriptional response indicative of hypoxia, altering the expression of genes known to respond to low-oxygen conditions. Several additional lines of evidence obtained suggest that these responses could involve effects on heme. First, the hem1Delta mutant lacking the first enzyme in the heme biosynthetic pathway showed increased sensitivity to sampangine, and exogenously supplied hemin partially rescued the inhibitory activity of sampangine in wild-type cells. In addition, heterozygous mutants with deletions in genes involved in five out of eight steps in the heme biosynthetic pathway showed increased susceptibility to sampangine. Furthermore, spectral analyses of pyridine extracts indicated significant accumulation of free porphyrins in sampangine-treated cells. Transcriptional profiling experiments were also performed with C. albicans to investigate the response of a pathogenic fungal species to sampangine. Taking into account the known differences in the physiological responses of C. albicans and S. cerevisiae to low oxygen, significant correlations were observed between the two transcription profiles, suggestive of heme-related defects. Our results indicate that the antifungal activity of the plant alkaloid sampangine is due, at least in part, to perturbations in the biosynthesis or metabolism of heme.
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21
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Wimplinger I, Morleo M, Rosenberger G, Iaconis D, Orth U, Meinecke P, Lerer I, Ballabio A, Gal A, Franco B, Kutsche K. Mutations of the mitochondrial holocytochrome c-type synthase in X-linked dominant microphthalmia with linear skin defects syndrome. Am J Hum Genet 2006; 79:878-89. [PMID: 17033964 PMCID: PMC1698567 DOI: 10.1086/508474] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Accepted: 08/15/2006] [Indexed: 12/23/2022] Open
Abstract
The microphthalmia with linear skin defects syndrome (MLS, or MIDAS) is an X-linked dominant male-lethal disorder almost invariably associated with segmental monosomy of the Xp22 region. In two female patients, from two families, with MLS and a normal karyotype, we identified heterozygous de novo point mutations--a missense mutation (p.R217C) and a nonsense mutation (p.R197X)--in the HCCS gene. HCCS encodes the mitochondrial holocytochrome c-type synthase that functions as heme lyase by covalently adding the prosthetic heme group to both apocytochrome c and c(1). We investigated a third family, displaying phenotypic variability, in which the mother and two of her daughters carry an 8.6-kb submicroscopic deletion encompassing part of the HCCS gene. Functional analysis demonstrates that both mutant proteins (R217C and Delta 197-268) were unable to complement a Saccharomyces cerevisiae mutant deficient for the HCCS orthologue Cyc3p, in contrast to wild-type HCCS. Moreover, ectopically expressed HCCS wild-type and the R217C mutant protein are targeted to mitochondria in CHO-K1 cells, whereas the C-terminal-truncated Delta 197-268 mutant failed to be sorted to mitochondria. Cytochrome c, the final product of holocytochrome c-type synthase activity, is implicated in both oxidative phosphorylation (OXPHOS) and apoptosis. We hypothesize that the inability of HCCS-deficient cells to undergo cytochrome c-mediated apoptosis may push cell death toward necrosis that gives rise to severe deterioration of the affected tissues. In summary, we suggest that disturbance of both OXPHOS and the balance between apoptosis and necrosis, as well as the X-inactivation pattern, may contribute to the variable phenotype observed in patients with MLS.
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Affiliation(s)
- Isabella Wimplinger
- Institut fur Humangenetik, Universitatsklinikum Hamburg-Eppendorf, Butenfeld 42, Hamburg, Germany
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22
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Liao TSV, Call GB, Guptan P, Cespedes A, Marshall J, Yackle K, Owusu-Ansah E, Mandal S, Fang QA, Goodstein GL, Kim W, Banerjee U. An efficient genetic screen in Drosophila to identify nuclear-encoded genes with mitochondrial function. Genetics 2006; 174:525-33. [PMID: 16849596 PMCID: PMC1569793 DOI: 10.1534/genetics.106.061705] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We conducted a screen for glossy-eye flies that fail to incorporate BrdU in the third larval instar eye disc but exhibit normal neuronal differentiation and isolated 23 complementation groups of mutants. These same phenotypes were previously seen in mutants for cytochrome c oxidase subunit Va. We have molecularly characterized six complementation groups and, surprisingly, each encodes a mitochondrial protein. Therefore, we believe our screen to be an efficient method for identifying genes with mitochondrial function.
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Affiliation(s)
- T S Vivian Liao
- Molecular Biology Institute, University of California, Los Angeles, California 90095, USA
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23
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Chacinska A, Pfannschmidt S, Wiedemann N, Kozjak V, Sanjuán Szklarz LK, Schulze-Specking A, Truscott KN, Guiard B, Meisinger C, Pfanner N. Essential role of Mia40 in import and assembly of mitochondrial intermembrane space proteins. EMBO J 2004; 23:3735-46. [PMID: 15359280 PMCID: PMC522791 DOI: 10.1038/sj.emboj.7600389] [Citation(s) in RCA: 344] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2004] [Accepted: 08/09/2004] [Indexed: 11/08/2022] Open
Abstract
Mitochondria import nuclear-encoded precursor proteins to four different subcompartments. Specific import machineries have been identified that direct the precursor proteins to the mitochondrial outer membrane, inner membrane or matrix, respectively. However, a machinery dedicated to the import of mitochondrial intermembrane space (IMS) proteins has not been found so far. We have identified the essential IMS protein Mia40 (encoded by the Saccharomyces cerevisiae open reading frame YKL195w). Mitochondria with a mutant form of Mia40 are selectively inhibited in the import of several small IMS proteins, including the essential proteins Tim9 and Tim10. The import of proteins to the other mitochondrial subcompartments does not depend on functional Mia40. The binding of small Tim proteins to Mia40 is crucial for their transport across the outer membrane and represents an initial step in their assembly into IMS complexes. We conclude that Mia40 is a central component of the protein import and assembly machinery of the mitochondrial IMS.
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Affiliation(s)
- Agnieszka Chacinska
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
| | - Sylvia Pfannschmidt
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
- Fakultät für Biologie, Universität Freiburg, Freiburg, Germany
| | - Nils Wiedemann
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
| | - Vera Kozjak
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
- Fakultät für Biologie, Universität Freiburg, Freiburg, Germany
| | - Luiza K Sanjuán Szklarz
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
- Fakultät für Biologie, Universität Freiburg, Freiburg, Germany
| | | | - Kaye N Truscott
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
| | - Bernard Guiard
- Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l'Université Pierre et Marie Curie, Gif-sur-Yvette, France
| | - Chris Meisinger
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
| | - Nikolaus Pfanner
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Freiburg, Germany
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, 79104 Freiburg im Breisgau, Germany. Tel.: +49 761 203 5224; Fax: +49 761 203 5261; E-mail:
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24
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Maurer-Stroh S, Gouda M, Novatchkova M, Schleiffer A, Schneider G, Sirota FL, Wildpaner M, Hayashi N, Eisenhaber F. MYRbase: analysis of genome-wide glycine myristoylation enlarges the functional spectrum of eukaryotic myristoylated proteins. Genome Biol 2004; 5:R21. [PMID: 15003124 PMCID: PMC395771 DOI: 10.1186/gb-2004-5-3-r21] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Revised: 12/17/2003] [Accepted: 01/08/2004] [Indexed: 11/25/2022] Open
Abstract
We evaluated the evolutionary conservation of glycine myristoylation within eukaryotic sequences. Our large-scale cross-genome analyses, available as MYRbase, show that the functional spectrum of myristoylated proteins is currently largely underestimated. We give experimental evidence for in vitro myristoylation of selected predictions. Furthermore, we classify five membrane-attachment factors that occur most frequently in combination with, or even replacing, myristoyl anchors, as some protein family examples show.
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Affiliation(s)
- Sebastian Maurer-Stroh
- IMP Research Institute of Molecular Pathology, Dr, Bohr-Gasse 7, A-1030 Vienna, Austria.
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25
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Lutz T, Neupert W, Herrmann JM. Import of small Tim proteins into the mitochondrial intermembrane space. EMBO J 2003; 22:4400-8. [PMID: 12941692 PMCID: PMC202364 DOI: 10.1093/emboj/cdg421] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Proteins of the intermembrane space (IMS) of mitochondria are typically synthesized without presequences. Little is known about their topogenesis. We used Tim13, a member of the 'small Tim protein' family, as model protein to investigate the mechanism of translocation into the IMS. Tim13 contains four conserved cysteine residues that bind a zinc ion as cofactor. Import of Tim13 did not depend on the membrane potential or ATP hydrolysis. Upon import into mitochondria Tim13 adopted a stably folded conformation in the IMS. Mutagenesis of the cysteine residues or pretreatment with metal chelators interfered with folding of Tim13 in vitro and impaired its import into mitochondria. Upon depletion of metal ions or modification of cysteine residues, imported Tim13 diffused back out of the IMS. We propose an import pathway in which (1) Tim13 can pass through the TOM complex into and out of the IMS in an unfolded conformation, and (2) cofactor acquisition stabilizes folding on the trans side of the outer membrane and traps Tim13 in the IMS, and drives unidirectional movement of the protein across the outer membrane of mitochondria.
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Affiliation(s)
- Thomas Lutz
- Institut für Physiologische Chemie, Universität München, Butenandtstrasse 5, 81377 München, Germany
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26
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Wang X, Han X, Jia S, Yang F. Change of apocytochrome c translocation across membrane in consequence of hydrophobic segment deletion. Mol Cell Biochem 2002; 233:39-47. [PMID: 12083378 DOI: 10.1023/a:1015502800914] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Wild-type apocytochrome c and its hydrophobic segment deleted mutants, named delta28-39, delta72-86 and delta28-29/72-86 were constructed, expressed and highly purified respectively. Insertion ability into phospholipid monolayer, inducing leakage of entrapped fluorescent dye fluorescein sulfonate (FS) from liposomes, and translocation across model membrane system showed that the wild-type apoprotein and delta28-39 almost exhibited the same characteristics, while mutants with segment 72-86 deletion did not. Furthermore, CD spectra, intrinsic fluorescence emission spectra, and the accessibility of the protein to the fluorescence quenchers: KI, acrylamide and HB demonstrated that the segment 72-86 deletion has a significant effect on the conformational changes of apocytochrome c following its interaction with phospholipid. On the basis of these results it is postulated that the C-terminal hydrophobic segment 72-86 plays an important role in the translocation of apocytochrome c across membrane.
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Affiliation(s)
- Xiaoping Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, The Chinese Academy of Sciences, Beijing
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27
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Diekert K, de Kroon AI, Ahting U, Niggemeyer B, Neupert W, de Kruijff B, Lill R. Apocytochrome c requires the TOM complex for translocation across the mitochondrial outer membrane. EMBO J 2001; 20:5626-35. [PMID: 11598006 PMCID: PMC125676 DOI: 10.1093/emboj/20.20.5626] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The import of proteins into the mitochondrial intermembrane space differs in various aspects from the classical import pathway into the matrix. Apocytochrome c defines one of several pathways known to reach the intermembrane space, yet the components and pathways involved in outer membrane translocation are poorly defined. Here, we report the reconstitution of the apocytochrome c import reaction using proteoliposomes harbouring purified components. Import specifically requires the protease-resistant part of the TOM complex and is driven by interactions of the apoprotein with internal parts of the complex (involving Tom40) and the 'trans-side receptor' cytochrome c haem lyase. Despite the necessity of TOM complex function, the translocation pathway of apocytochrome c does not overlap with that of presequence-containing preproteins. We conclude that the TOM complex is a universal preprotein translocase that mediates membrane passage of apocytochrome c and other preproteins along distinct pathways. Apocytochrome c may provide a paradigm for the import of other small proteins into the intermembrane space such as factors used in apoptosis and protection from stress.
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Affiliation(s)
| | - Anton I.P.M. de Kroon
- Institut für Zytobiologie und Zytopathologie der Philipps-Universität Marburg, Robert-Koch-Strasse 5, 35033 Marburg,
Adolf-Butenandt-Institut für Physiologische Chemie der Universität München, Butenandtstrasse 5, 81377 München, Germany and
Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Corresponding author e-mail:
| | - Uwe Ahting
- Institut für Zytobiologie und Zytopathologie der Philipps-Universität Marburg, Robert-Koch-Strasse 5, 35033 Marburg,
Adolf-Butenandt-Institut für Physiologische Chemie der Universität München, Butenandtstrasse 5, 81377 München, Germany and
Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Corresponding author e-mail:
| | | | - Walter Neupert
- Institut für Zytobiologie und Zytopathologie der Philipps-Universität Marburg, Robert-Koch-Strasse 5, 35033 Marburg,
Adolf-Butenandt-Institut für Physiologische Chemie der Universität München, Butenandtstrasse 5, 81377 München, Germany and
Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Corresponding author e-mail:
| | - Ben de Kruijff
- Institut für Zytobiologie und Zytopathologie der Philipps-Universität Marburg, Robert-Koch-Strasse 5, 35033 Marburg,
Adolf-Butenandt-Institut für Physiologische Chemie der Universität München, Butenandtstrasse 5, 81377 München, Germany and
Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Corresponding author e-mail:
| | - Roland Lill
- Institut für Zytobiologie und Zytopathologie der Philipps-Universität Marburg, Robert-Koch-Strasse 5, 35033 Marburg,
Adolf-Butenandt-Institut für Physiologische Chemie der Universität München, Butenandtstrasse 5, 81377 München, Germany and
Department Biochemistry of Membranes, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Corresponding author e-mail:
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28
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Miao Q, Han X, Yang F. Phosphatidic acid-phosphatidylethanolamine interaction and apocytochrome c translocation across model membranes. Biochem J 2001; 354:681-8. [PMID: 11237873 PMCID: PMC1221700 DOI: 10.1042/0264-6021:3540681] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The translocation of apocytochrome c (apocyt.c) across large unilamellar vesicles (LUVs) constructed from mixtures of anionic and zwitterionic phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), has been studied. It was shown that the import ratio of horse heart apocyt.c in LUVs composed of phosphatidic acid (PA) combined with PE and PC (62+/-10%) was much higher than that in LUVs made of PE and PC plus any other acidic phospholipid species (20+/-5%). This feature was shared by tuna heart and chicken heart apocyt.c. In addition, the greater efficiency of the PA/PE/PC system versus others in facilitating apocyt.c translocation was maintained using synthetic anionic phospholipids with the same acyl chains. Besides, apocyt.c induces more leakage of entrapped fluorescein sulphonate (FS) from the interior of PA/PC/PE vesicles compared with phosphatidylglycerol (PG)/PC/PE ones. By measuring the intrinsic fluorescence emission spectrum and the accessibility of the preprotein to the fluorescence quencher, acrylamide, differences could be detected in the conformational changes of apocyt.c as a consequence of its interaction with PA/PE/PC and PG/PE/PC vesicles, respectively. Particularly notable is that PE is indispensable for the PA/PE/PC system to most efficiently facilitate apocyt.c translocation across the model membranes. With the fraction of PE increasing from 0 to 30 mol%, the translocation efficiency of apocyt.c as well as its ability to induce FS efflux was significantly enhanced in PA-containing LUVs, whereas this was not observed in the case of replacement of PA by PG or phosphatidylserine. It is also interesting to note that in LUVs containing PA, dioleoyl-PE, but not dielaidoyl-PE, can exert such influences, indicative of the role of non-bilayer formation propensity. On the basis of these results it is postulated that PA might increase the bilayer-destabilizing effects of PE, and hence increase the translocation efficiency of apocyt.c and its leakage-induction ability.
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Affiliation(s)
- Q Miao
- National Laboratory of Biomacromolecules, Institute of Biophysics, The Chinese Academy of Sciences, Beijing 100101, China
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29
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Abstract
The gene CYC2 from the yeast Saccharomyces cerevisiae was previously shown to affect levels of mitochondrial cytochrome c by acting at a posttranslational step in cytochrome c biosynthesis. We report here the cloning and identification of the CYC2 gene product as a protein involved in import of cytochrome c into mitochondria. CYC2 encodes a 168-amino-acid open reading frame with at least two potential transmembrane segments. Antibodies against a synthetic peptide corresponding to the carboxyl terminus of the predicted sequence were raised. These antibodies recognize multiple bands on immunoblots of mitochondrial extracts. The intensities of these bands vary according to the gene dosage of CYC2 in various isogenic strains. Immunoblotting of subcellular fractions suggests that the CYC2 gene product is a mitochondrial protein. Deletion of CYC2 leads to accumulation of apocytochrome c in the cytoplasm. However, strains with deletions of this gene still import low levels of cytochrome c into mitochondria. The effects of cyc2 mutations are more pronounced in rho- strains than in rho+ strains, even though rho- strains that are CYC2+ contain normal levels of holocytochrome c. cyc2 mutations affect levels of iso-1-cytochrome c more than they do levels of iso-2-cytochrome c, apparently because of the greater susceptibility of apo-iso-1-cytochrome c to degradation in the cytoplasm. We propose that CYC2 encodes a factor that increases the efficiency of cytochrome c import into mitochondria.
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30
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Dumont ME, Schlichter JB, Cardillo TS, Hayes MK, Bethlendy G, Sherman F. CYC2 encodes a factor involved in mitochondrial import of yeast cytochrome c. Mol Cell Biol 1993; 13:6442-51. [PMID: 8413243 PMCID: PMC364703 DOI: 10.1128/mcb.13.10.6442-6451.1993] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The gene CYC2 from the yeast Saccharomyces cerevisiae was previously shown to affect levels of mitochondrial cytochrome c by acting at a posttranslational step in cytochrome c biosynthesis. We report here the cloning and identification of the CYC2 gene product as a protein involved in import of cytochrome c into mitochondria. CYC2 encodes a 168-amino-acid open reading frame with at least two potential transmembrane segments. Antibodies against a synthetic peptide corresponding to the carboxyl terminus of the predicted sequence were raised. These antibodies recognize multiple bands on immunoblots of mitochondrial extracts. The intensities of these bands vary according to the gene dosage of CYC2 in various isogenic strains. Immunoblotting of subcellular fractions suggests that the CYC2 gene product is a mitochondrial protein. Deletion of CYC2 leads to accumulation of apocytochrome c in the cytoplasm. However, strains with deletions of this gene still import low levels of cytochrome c into mitochondria. The effects of cyc2 mutations are more pronounced in rho- strains than in rho+ strains, even though rho- strains that are CYC2+ contain normal levels of holocytochrome c. cyc2 mutations affect levels of iso-1-cytochrome c more than they do levels of iso-2-cytochrome c, apparently because of the greater susceptibility of apo-iso-1-cytochrome c to degradation in the cytoplasm. We propose that CYC2 encodes a factor that increases the efficiency of cytochrome c import into mitochondria.
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Affiliation(s)
- M E Dumont
- Department of Biochemistry, University of Rochester School of Medicine and Dentistry, New York 14642
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31
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Abstract
Apocytochrome b5 from rabbit liver was studied by scanning calorimetry, limited proteolysis, circular dichroism, second derivative spectroscopy, and size exclusion chromatography. The protein is able to undergo a reversible two-state thermal transition. However, transition temperature, denaturational enthalpy, and heat capacity change are reduced compared with the holoprotein. Apocytochrome b5 stability in terms of Gibbs energy change at protein unfolding (delta G) amounts to delta G = 7 +/- 1 kJ/mol at 25 degrees C (pH 7.4) compared with delta G = 25 kJ/mol for the holoprotein. Apocytochrome b5 is a compact, native-like protein. According to the spectral data, the cooperative structure is mainly based in the core region formed by residues 1-35 and 79-90. This finding is in full agreement with NMR data (Moore, C.D. & Lecomte, J.T.J., 1993, Biochemistry 32, 199-207).
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Affiliation(s)
- W Pfeil
- Max-Delbrück-Center for Molecular Medicine, Berlin-Buch, Germany
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32
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Barker PD, Ferrer JC, Mylrajan M, Loehr TM, Feng R, Konishi Y, Funk WD, MacGillivray RT, Mauk AG. Transmutation of a heme protein. Proc Natl Acad Sci U S A 1993; 90:6542-6. [PMID: 8341666 PMCID: PMC46968 DOI: 10.1073/pnas.90.14.6542] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Residue Asn57 of bovine liver cytochrome b5 has been replaced with a cysteine residue, and the resulting variant has been isolated from recombinant Escherichia coli as a mixture of four major species: A, BI, BII, and C. A combination of electronic spectroscopy, 1H NMR spectroscopy, resonance Raman spectroscopy, electrospray mass spectrometry, and direct electrochemistry has been used to characterize these four major cytochrome derivatives. The red form A (E(m) = -19 mV) is found to possess a heme group bound covalently through a thioether linkage involving Cys57 and the alpha carbon of the heme 4-vinyl group. Form BI has a covalently bound heme group coupled through a thioether linkage involving the beta carbon of the heme 4-vinyl group. Form BII is similar to BI except that the sulfur involved in the thioether linkage is oxidized to a sulfoxide. The green form C (E(m) = 175 mV) possesses a noncovalently bound prosthetic group with spectroscopic properties characteristic of a chlorin. A mechanism is proposed for the generation of these derivatives, and the implications of these observations for the biosynthesis of cytochrome c and naturally occurring chlorin prosthetic groups are discussed.
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Affiliation(s)
- P D Barker
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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33
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Gu Z, Moerschell RP, Sherman F, Goldfarb DS. NIP1, a gene required for nuclear transport in yeast. Proc Natl Acad Sci U S A 1992; 89:10355-9. [PMID: 1332047 PMCID: PMC50337 DOI: 10.1073/pnas.89.21.10355] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Cytochrome c with a nuclear localization signal added at the N terminus was mistargeted to the nucleus, resulting in a yeast strain deficient in mitochondrial cytochrome c. Reversion of this strain allowed the isolation of temperature-conditional mutants defective in nuclear transport, as demonstrated with one of these mutants, nip1-1, that was shown to be defective in nuclear accumulation of a LacZ protein containing a nuclear localization signal of the yeast ribosomal protein L29. The NIP1+ gene was cloned and shown to encode a 93,143-Da protein. Furthermore, an epitope-labeled NIP1 protein migrated in SDS/polyacrylamide gels with a mass of approximately 100,000 Da and was shown by immunofluorescence to localize mainly in the cytoplasm. NIP1+ was shown to be an essential gene by gene disruption experiments. Intriguingly, NIP1 has a serine-rich acidic N-terminal region that is similar in this regard to the N-terminal region of a previously described nuclear localization signal-binding protein, NSR1.
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Affiliation(s)
- Z Gu
- Department of Biology, University of Rochester, NY 14627
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