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Uncoupling Proteins and Regulated Proton Leak in Mitochondria. Int J Mol Sci 2022; 23:ijms23031528. [PMID: 35163451 PMCID: PMC8835771 DOI: 10.3390/ijms23031528] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 01/26/2022] [Indexed: 12/17/2022] Open
Abstract
Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field.
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Bround MJ, Bers DM, Molkentin JD. A 20/20 view of ANT function in mitochondrial biology and necrotic cell death. J Mol Cell Cardiol 2020; 144:A3-A13. [PMID: 32454061 DOI: 10.1016/j.yjmcc.2020.05.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 04/16/2020] [Accepted: 05/20/2020] [Indexed: 12/25/2022]
Abstract
The adenosine nucleotide translocase (ANT) family of proteins are inner mitochondrial membrane proteins involved in energy homeostasis and cell death. The primary function of ANT proteins is to exchange cytosolic ADP with matrix ATP, facilitating the export of newly synthesized ATP to the cell while providing new ADP substrate to the mitochondria. As such, the ANT proteins are central to maintaining energy homeostasis in all eukaryotic cells. Evidence also suggests that the ANTs constitute a pore-forming component of the mitochondrial permeability transition pore (MPTP), a structure that forms in the inner mitochondrial membrane that is thought to underlie regulated necrotic cell death. Additionally, emerging studies suggest that ANT proteins are also critical for mitochondrial uncoupling and for promoting mitophagy. Thus, the ANTs are multifunctional proteins that are poised to participate in several aspects of mitochondrial biology and the greater regulation of cell death, which will be discussed here.
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Affiliation(s)
- Michael J Bround
- Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH 45229, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA 95616, USA
| | - Jeffery D Molkentin
- Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH 45229, USA; Howard Hughes Medical Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
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3
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Ogunbona OB, Claypool SM. Emerging Roles in the Biogenesis of Cytochrome c Oxidase for Members of the Mitochondrial Carrier Family. Front Cell Dev Biol 2019; 7:3. [PMID: 30766870 PMCID: PMC6365663 DOI: 10.3389/fcell.2019.00003] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Accepted: 01/10/2019] [Indexed: 12/11/2022] Open
Abstract
The mitochondrial carrier family (MCF) is a group of transport proteins that are mostly localized to the inner mitochondrial membrane where they facilitate the movement of various solutes across the membrane. Although these carriers represent potential targets for therapeutic application and are repeatedly associated with human disease, research on the MCF has not progressed commensurate to their physiologic and pathophysiologic importance. Many of the 53 MCF members in humans are orphans and lack known transport substrates. Even for the relatively well-studied members of this family, such as the ADP/ATP carrier and the uncoupling protein, there exist fundamental gaps in our understanding of their biological roles including a clear rationale for the existence of multiple isoforms. Here, we briefly review this important family of mitochondrial carriers, provide a few salient examples of their diverse metabolic roles and disease associations, and then focus on an emerging link between several distinct MCF members, including the ADP/ATP carrier, and cytochrome c oxidase biogenesis. As the ADP/ATP carrier is regarded as the paradigm of the entire MCF, its newly established role in regulating translation of the mitochondrial genome highlights that we still have a lot to learn about these metabolite transporters.
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Affiliation(s)
- Oluwaseun B. Ogunbona
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
- Department of Pathology & Laboratory Medicine, School of Medicine, Emory University, Atlanta, GA, United States
| | - Steven M. Claypool
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
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4
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Board M, Lopez C, van den Bos C, Callaghan R, Clarke K, Carr C. Acetoacetate is a more efficient energy-yielding substrate for human mesenchymal stem cells than glucose and generates fewer reactive oxygen species. Int J Biochem Cell Biol 2017; 88:75-83. [PMID: 28483672 PMCID: PMC5497396 DOI: 10.1016/j.biocel.2017.05.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 04/05/2017] [Accepted: 05/04/2017] [Indexed: 12/28/2022]
Abstract
Stem cells have been assumed to demonstrate a reliance on anaerobic energy generation, suited to their hypoxic in vivo environment. However, we found that human mesenchymal stem cells (hMSCs) have an active oxidative metabolism with a range of substrates. More ATP was consistently produced from substrate oxidation than glycolysis by cultured hMSCs. Strong substrate preferences were shown with the ketone body, acetoacetate, being oxidised at up to 35 times the rate of glucose. ROS-generation was 45-fold lower during acetoacetate oxidation compared with glucose and substrate preference may be an adaptation to reduce oxidative stress. The UCP2 inhibitor, genipin, increased ROS production with either acetoacetate or glucose by 2-fold, indicating a role for UCP2 in suppressing ROS production. Addition of pyruvate stimulated acetoacetate oxidation and this combination increased ATP production 27-fold, compared with glucose alone, which has implications for growth medium composition. Oxygen tension during culture affected metabolism by hMSCs. Between passages 2 and 5, rates of both glycolysis and substrate-oxidation increased at least 2-fold for normoxic (20% O2)- but not hypoxic (5% O2)-cultured hMSCs, despite declining growth rates and no detectable signs of differentiation. Culture of the cells with 3-hydroxybutyrate abolished the increased rates of these pathways. These findings have implications for stem cell therapy, which necessarily involves in vitro culture of cells, since low passage number normoxic cultured stem cells show metabolic adaptations without detectable changes in stem-like status.
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Affiliation(s)
- Mary Board
- Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3 PG, United Kingdom.
| | | | | | - Richard Callaghan
- Research School of Biology, ANU College of Medicine, Biology and the Environment, Australian National University, Canberra, Australia
| | - Kieran Clarke
- Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3 PG, United Kingdom
| | - Carolyn Carr
- Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3 PG, United Kingdom
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5
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Adenine nucleotide translocase, mitochondrial stress, and degenerative cell death. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:146860. [PMID: 23970947 PMCID: PMC3732615 DOI: 10.1155/2013/146860] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Revised: 06/14/2013] [Accepted: 06/24/2013] [Indexed: 12/18/2022]
Abstract
Mitochondria are intracellular organelles involved in ATP synthesis, apoptosis, calcium signaling, metabolism, and the synthesis of critical metabolic cofactors. Mitochondrial dysfunction is associated with age-related degenerative diseases. How mitochondrial dysfunction causes cell degeneration is not well understood. Recent studies have shown that mutations in the adenine nucleotide translocase (Ant) cause aging-dependent degenerative cell death (DCD) in yeast, which is sequentially manifested by inner membrane stress, mitochondrial DNA (mtDNA) loss, and progressive loss of cell viability. Ant is an abundant protein primarily involved in ADP/ATP exchange across the mitochondrial inner membrane. It also mediates basal proton leak and regulates the mitochondrial permeability transition pore. Missense mutations in the human Ant1 cause several degenerative diseases which are commonly manifested by fractional mtDNA deletions. Multiple models have been proposed to explain the Ant1-induced pathogenesis. Studies from yeast have suggested that in addition to altered nucleotide transport properties, the mutant proteins cause a global stress on the inner membrane. The mutant proteins likely interfere with general mitochondrial biogenesis in a dominant-negative manner, which secondarily destabilizes mtDNA. More recent work revealed that the Ant-induced DCD is suppressed by reduced cytosolic protein synthesis. This finding suggests a proteostatic crosstalk between mitochondria and the cytosol, which may play an important role for cell survival during aging.
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Barrera NP, Zhou M, Robinson CV. The role of lipids in defining membrane protein interactions: insights from mass spectrometry. Trends Cell Biol 2012; 23:1-8. [PMID: 22980035 DOI: 10.1016/j.tcb.2012.08.007] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 08/14/2012] [Accepted: 08/14/2012] [Indexed: 12/19/2022]
Abstract
Cellular membranes comprise hundreds of lipids in which protein complexes, such as ion channels, receptors, and scaffolding complexes, are embedded. These protein assemblies act as signalling and trafficking platforms for processes fundamental to life. Much effort in recent years has focused on identifying the protein components of these complexes after their extraction from the lipid membrane in detergent micelles. Spectacular advances have been made using X-ray crystallography, providing in some cases detailed information about the mechanism of pumping and channel gating. These structural studies are leading to a growing realisation that, to understand their function, it is not only the structures of the protein components that are important but also knowledge of the protein-lipid interactions. This review highlights recent insights gained from this knowledge, surveys methods being developed for probing these interactions, and focuses specifically on the potential of mass spectrometry in this growing area of research.
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Affiliation(s)
- Nelson P Barrera
- Department of Physiology, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, 8331150, Chile.
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Abstract
The mitochondrial ADP/ATP carrier (Ancp) has long been a paradigm for studies of the mitochondrial carrier family due to, among other properties, its natural abundance and the existence of specific inhibitors, namely, carboxyatractyloside (CATR) and bongkrekic acid (BA), which lock the carrier under distinct and stable conformations. Bovine Anc1p isolated in complex with CATR in the presence of an aminoxyde detergent (LAPAO) was crystallized and its 3D structure determined. It is the first mitochondrial carrier structure resolved at high resolution (2.2 A, as reported by Pebay-Peyroula et al. (Nature 426:39-44, 2003)). Analyses revealed a monomer while most of the biochemical studies led to hypothesize Ancp functions as a dimer. To address the structural organization issue, we engineered a mutant of the yeast Ancp that corresponds to a covalent homodimer in view of 3D structure determination. We compare in this chapter the purification yield and quality of the chimera tagged either with six histidines at its C-ter end or nine histidines at its N-ter. We show that, as expected, length and position of the tag are important criteria for qualitative purification. We also discuss the advantages and drawbacks of purifying Ancp either from a natural source or from engineered yeast cells.
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Kravenskaya EV, Kramar SB, Fedirko NV. Role of Carboxylic Groups in the Control of Nonspecific Permeability of Mitochondrial Membranes. NEUROPHYSIOLOGY+ 2010. [DOI: 10.1007/s11062-010-9125-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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9
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Kunji ERS, Crichton PG. Mitochondrial carriers function as monomers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:817-31. [PMID: 20362544 DOI: 10.1016/j.bbabio.2010.03.023] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2010] [Revised: 03/05/2010] [Accepted: 03/25/2010] [Indexed: 10/19/2022]
Abstract
Mitochondrial carriers link biochemical pathways in the mitochondrial matrix and cytosol by transporting metabolites, inorganic ions, nucleotides and cofactors across the mitochondrial inner membrane. Uncoupling proteins that dissipate the proton electrochemical gradient also belong to this protein family. For almost 35 years the general consensus has been that mitochondrial carriers are dimeric in structure and function. This view was based on data from inhibitor binding studies, small-angle neutron scattering, electron microscopy, differential tagging/affinity chromatography, size-exclusion chromatography, analytical ultracentrifugation, native gel electrophoresis, cross-linking experiments, tandem-fusions, negative dominance studies and mutagenesis. However, the structural folds of the ADP/ATP carriers were found to be monomeric, lacking obvious dimerisation interfaces. Subsequently, the yeast ADP/ATP carrier was demonstrated to function as a monomer. Here, we revisit the data that have been published in support of a dimeric state of mitochondrial carriers. Our analysis shows that when critical factors are taken into account, the monomer is the only plausible functional form of mitochondrial carriers. We propose a transport model based on the monomer, in which access to a single substrate binding site is controlled by two flanking salt bridge networks, explaining uniport and strict exchange of substrates.
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Affiliation(s)
- Edmund R S Kunji
- The Medical Research Council, Mitochondrial Biology Unit, Hills Road, Cambridge, CB2 0XY, UK.
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Nury H, Manon F, Arnou B, le Maire M, Pebay-Peyroula E, Ebel C. Mitochondrial Bovine ADP/ATP Carrier in Detergent Is Predominantly Monomeric but Also Forms Multimeric Species. Biochemistry 2008; 47:12319-31. [DOI: 10.1021/bi801053m] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hugues Nury
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
| | - Florence Manon
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
| | - Bertrand Arnou
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
| | - Marc le Maire
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
| | - Eva Pebay-Peyroula
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
| | - Christine Ebel
- CEA, DSV, and CNRS and Université Joseph Fourier, Institut de Biologie Structurale, 41 rue Jules Horowitz, F-38027, Grenoble, France, Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université Bordeaux 2, F-33077 Bordeaux Cedex, France, and CEA, Institut de Biologie et Technologies de Saclay, and CNRS URA 2096 and Université Paris-Sud 11, LRA 17V, F-91191 Gif-sur-Yvette, France
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Electrostatic funneling of substrate in mitochondrial inner membrane carriers. Proc Natl Acad Sci U S A 2008; 105:9598-603. [PMID: 18621725 DOI: 10.1073/pnas.0801786105] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Exchange of ATP and ADP across mitochondrial membrane replenishes the cytoplasm with newly synthesized ATP and provides the mitochondria with the substrate ADP for oxidative phosphorylation. The sole means of this exchange is the mitochondrial ADP/ATP carrier (AAC), a membrane protein that is suggested to cycle between two conformationally distinct states, cytosolic-open (c-state) and matrix-open (m-state), thereby shuttling nucleotides across the inner mitochondrial membrane. However, the c-state is the only structurally resolved state, and the binding site of ADP remains elusive. Here, we present approximately 0.3 mus of all-atom MD simulations of the c-state revealing rapid, spontaneous binding of ADP to deeply positioned binding sites within the AAC lumen. To our knowledge, a complete ligand-binding event has heretofore not been described in full atomic detail in unbiased simulations. The identified ADP-bound state and additional simulations shed light on key structural elements and the initial steps involved in conversion to the m-state. Electrostatic analysis of trajectories reveals the presence of an unusually strong positive electrostatic potential in the lumen of AAC that appears to be the main driving force for the observed spontaneous binding of ADP. We provide evidence that the positive electrostatic potential is likely a common attribute among the entire family of mitochondrial carriers. In addition to playing a key role in substrate recruitment and translocation, the electropositivity of mitochondrial carriers might also be critical for their binding to the negatively charged environment of the inner mitochondrial membrane.
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Klingenberg M. The ADP and ATP transport in mitochondria and its carrier. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1978-2021. [PMID: 18510943 DOI: 10.1016/j.bbamem.2008.04.011] [Citation(s) in RCA: 455] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 04/24/2008] [Accepted: 04/24/2008] [Indexed: 10/22/2022]
Abstract
Different from some more specialised short reviews, here a general although not encyclopaedic survey of the function, metabolic role, structure and mechanism of the ADP/ATP transport in mitochondria is presented. The obvious need for an "old fashioned" review comes from the gateway role in metabolism of the ATP transfer to the cytosol from mitochondria. Amidst the labours, 40 or more years ago, of unravelling the role of mitochondrial compartments and of the two membranes, the sequence of steps of how ATP arrives in the cytosol became a major issue. When the dust settled, a picture emerged where ATP is exported across the inner membrane in a 1:1 exchange against ADP and where the selection of ATP versus ADP is controlled by the high membrane potential at the inner membrane, thus uplifting the free energy of ATP in the cytosol over the mitochondrial matrix. Thus the disparate energy and redox states of the two major compartments are bridged by two membrane potential responsive carriers to enable their symbiosis in the eukaryotic cell. The advance to the molecular level by studying the binding of nucleotides and inhibitors was facilitated by the high level of carrier (AAC) binding sites in the mitochondrial membrane. A striking flexibility of nucleotide binding uncovered the reorientation of carrier sites between outer and inner face, assisted by the side specific high affinity inhibitors. The evidence of a single carrier site versus separate sites for substrate and inhibitors was expounded. In an ideal setting principles of transport catalysis were elucidated. The isolation of intact AAC as a first for any transporter enabled the reconstitution of transport for unravelling, independently of mitochondrial complications, the factors controlling the ADP/ATP exchange. Electrical currents measured with the reconstituted AAC demonstrated electrogenic translocation and charge shift of reorienting carrier sites. Aberrant or vital para-functions of AAC in basal uncoupling and in the mitochondrial pore transition were demonstrated in mitochondria and by patch clamp with reconstituted AAC. The first amino acid sequence of AAC and of any eukaryotic carrier furnished a 6-transmembrane helix folding model, and was the basis for mapping the structure by access studies with various probes, and for demonstrating the strong conformation changes demanded by the reorientation mechanism. Mutations served to elucidate the function of residues, including the particular sensitivity of ATP versus ADP transport to deletion of critical positive charge in AAC. After resisting for decades, at last the atomic crystal structure of the stabilised CAT-AAC complex emerged supporting the predicted principle fold of the AAC but showing unexpected features relevant to mechanism. Being a snapshot of an extreme abortive "c-state" the actual mechanism still remains a conjecture.
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Bamber L, Harding M, Monné M, Slotboom DJ, Kunji ERS. The yeast mitochondrial ADP/ATP carrier functions as a monomer in mitochondrial membranes. Proc Natl Acad Sci U S A 2007; 104:10830-4. [PMID: 17566106 PMCID: PMC1891095 DOI: 10.1073/pnas.0703969104] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial carriers are believed widely to be dimers both in structure and function. However, the structural fold is a barrel of six transmembrane alpha-helices without an obvious dimerisation interface. Here, we show by negative dominance studies that the yeast mitochondrial ADP/ATP carrier 2 from Saccharomyces cerevisiae (AAC2) is functional as a monomer in the mitochondrial membrane. Adenine nucleotide transport by wild-type AAC2 is inhibited by the sulfhydryl reagent 2-sulfonatoethyl-methanethiosulfonate (MTSES), whereas the activity of a mutant AAC2, devoid of cysteines, is unaffected. Wild-type and cysteine-less AAC2 were coexpressed in different molar ratios in yeast mitochondrial membranes. After addition of MTSES the residual transport activity correlated linearly with the fraction of cysteine-less carrier present in the membranes, and so the two versions functioned independently of each other. Also, the cysteine-less and wild-type carriers were purified separately, mixed in defined ratios and reconstituted into liposomes. Again, the residual transport activity in the presence of MTSES depended linearly on the amount of cysteine-less carrier. Thus, the entire transport cycle for ADP/ATP exchange is carried out by the monomer.
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Affiliation(s)
- Lisa Bamber
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom
| | - Marilyn Harding
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom
| | - Magnus Monné
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom
| | - Dirk-Jan Slotboom
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom
| | - Edmund R. S. Kunji
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom
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14
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Nury H, Dahout-Gonzalez C, Trézéguet V, Lauquin GJM, Brandolin G, Pebay-Peyroula E. Relations between structure and function of the mitochondrial ADP/ATP carrier. Annu Rev Biochem 2007; 75:713-41. [PMID: 16451122 DOI: 10.1146/annurev.biochem.75.103004.142747] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Import and export of metabolites through mitochondrial membranes are vital processes that are highly controlled and regulated at the level of the inner membrane. Proteins of the mitochondrial carrier family ( MCF ) are embedded in this membrane, and each member of the family achieves the selective transport of a specific metabolite. Among these, the ADP/ATP carrier transports ADP into the mitochondrial matrix and exports ATP toward the cytosol after its synthesis. Because of its natural abundance, the ADP/ATP carrier is the best characterized within MCF, and a high-resolution structure of one conformation is known. The overall structure is basket shaped and formed by six transmembrane helices that are not only tilted with respect to the membrane, but three of them are also kinked at the level of prolines. The functional mechanisms, nucleotide recognition, and conformational changes for the transport, suggested from the structure, are discussed along with the large body of biochemical and functional results.
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Affiliation(s)
- H Nury
- Institut de Biologie Structurale Jean-Pierre Ebel, UMR 5075 CEA-CNRS-Université Joseph Fourier, F-38027 Grenoble cedex 1, France.
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15
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Bamber L, Harding M, Butler PJG, Kunji ERS. Yeast mitochondrial ADP/ATP carriers are monomeric in detergents. Proc Natl Acad Sci U S A 2006; 103:16224-9. [PMID: 17056710 PMCID: PMC1618811 DOI: 10.1073/pnas.0607640103] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial carriers are believed widely to be homodimers both in the inner membrane of the organelle and in detergents. The dimensions and molecular masses of the detergent and protein-detergent micelles were measured for yeast ADP/ATP carriers in a range of different detergents. The radius of the carrier at the midpoint of the membrane, its average radius, its Stokes' radius, its molecular mass, and its excluded volume were determined. These parameters are consistent with the known structural model of the bovine ADP/ATP carrier and they demonstrate that the yeast mitochondrial ADP/ATP carriers are monomeric in detergents. Therefore, models of substrate transport have to be considered in which the carrier operates as a monomer rather than as a dimer.
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Affiliation(s)
| | | | - P. Jonathan G. Butler
- Laboratory of Molecular Biology, Medical Research Council, Hills Road, CB2 2XY Cambridge, United Kingdom
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16
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Dahout-Gonzalez C, Nury H, Trézéguet V, Lauquin GJM, Pebay-Peyroula E, Brandolin G. Molecular, functional, and pathological aspects of the mitochondrial ADP/ATP carrier. Physiology (Bethesda) 2006; 21:242-9. [PMID: 16868313 DOI: 10.1152/physiol.00005.2006] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In providing the cell with ATP generated by oxidative phosphorylation, the mitochondrial ADP/ATP carrier plays a central role in aerobic eukaryotic cells. Combining biochemical, genetic, and structural approaches contributes to understanding the molecular mechanism of this essential transport system, the dysfunction of which is implicated in neuromuscular diseases.
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Affiliation(s)
- C Dahout-Gonzalez
- Département de Réponse et Dynamique Cellulaires, CEA-Grenoble, Laboratoire de Biochimie et Biophysique des Systèmes Intégrés, UMR 5092 CEA-CNRS-Université Joseph Fourier, Grenoble, France
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17
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Nury H, Dahout-Gonzalez C, Trézéguet V, Lauquin G, Brandolin G, Pebay-Peyroula E. Structural basis for lipid-mediated interactions between mitochondrial ADP/ATP carrier monomers. FEBS Lett 2005; 579:6031-6. [PMID: 16226253 DOI: 10.1016/j.febslet.2005.09.061] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2005] [Revised: 09/13/2005] [Accepted: 09/26/2005] [Indexed: 10/25/2022]
Abstract
The oligomerization state of the ADP/ATP carrier is an important issue in understanding the mechanism underlying nucleotide exchange across the inner mitochondrial membrane. The first high resolution structure obtained in the presence of carboxyatractyloside revealed a large cavity formed within a monomer in which the inhibitor is strongly bound. Whereas the protein-protein interactions implicated in the first crystal form are not biologically relevant, the new crystal form described herein, highlights favorable protein-protein interactions. The interactions are mediated by endogenous cardiolipins, which are tightly bound to the protein, two cardiolipins being sandwiched between the monomers on the matrix side. The putative dimerization interface evidenced here is consistent with other structural, biochemical or functional data published so far.
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Affiliation(s)
- H Nury
- Institut de Biologie Structurale, UMR 5075 CEA-CNRS-Université Joseph Fourier, F-38027 Grenoble Cedex 1, France
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18
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Dassa EP, Dahout-Gonzalez C, Dianoux AC, Brandolin G. Functional characterization and purification of a Saccharomyces cerevisiae ADP/ATP carrier-iso 1 cytochrome c fusion protein. Protein Expr Purif 2005; 40:358-69. [PMID: 15766878 DOI: 10.1016/j.pep.2004.12.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Revised: 12/14/2004] [Indexed: 10/25/2022]
Abstract
A recombinant fusion protein combining the mitochondrial ADP/ATP carrier (Anc2p) and the iso-1-cytochrome c (Cyc1p), both from Saccharomyces cerevisiae, has been genetically elaborated with the aim of increasing the polar surface area of the carrier to facilitate its crystallization. The gene encoding the his-tagged fusion protein was expressed in yeast under the control of the regulatory sequences of ScANC2. The chimeric carrier, Anc2-Cyc1(His6)p, was able to restore growth on a non-fermentable carbon source of a yeast strain devoid of functional ADP/ATP carrier, which demonstrated its transport activity. The kinetic exchange properties of Anc2-Cyc1(His6)p and the wild type his-tagged carrier Anc2(His6)p were very similar. However, Anc2-Cyc1(His6)p restored cell growth less efficiently than Anc2(His6)p which correlates with the lower amount found in mitochondria. Purification of Anc2-Cyc1(His6)p in complex with carboxyatractyloside (CATR), a high affinity inhibitor of ADP/ATP transport, was achieved by combining ion-exchange chromatography and ion-metal affinity chromatography in the presence of LAPAO, an aminoxide detergent. As characterized by absorption in the visible range, heme was found to be present in isolated Anc2-Cyc1(His6)p, giving the protein a red color. Large-scale purification of Anc2-Cyc1(His6)p-CATR complex opens up novel possibilities for the use of crystallographic approaches to the yeast ADP/ATP carrier.
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Affiliation(s)
- Emmanuel Philippe Dassa
- Laboratoire de Biochimie et Biophysique des Systèmes Intégrés, Département de Réponse et Dynamique Cellulaires, UMR 5092 CNRS-CEA-Université Joseph Fourier, CEA-Grenoble, 17 Avenue des Martyrs, 38054 Grenoble Cedex 9, France
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19
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Pebay-Peyroula E, Brandolin G. Nucleotide exchange in mitochondria: insight at a molecular level. Curr Opin Struct Biol 2005; 14:420-5. [PMID: 15313235 DOI: 10.1016/j.sbi.2004.06.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Mitochondrial carrier proteins are embedded in the inner mitochondrial membrane and ensure the transport of many important metabolites. The ADP/ATP carrier imports ADP into the mitochondrial matrix in exchange for ATP after synthesis. It is the most studied mitochondrial carrier and its structure was the first to be unraveled at high resolution. The structure reveals six transmembrane helices forming a tightly closed bundle toward the matrix and a funnel-shaped cavity opening toward the intermembrane space. The cavity ends in a narrow pit 10A from the matrix. The analysis of residues located in the cavity hints at the mechanism of binding of adenine nucleotides. Additionally, the presence of conserved proline residues in three sharply kinked helices suggests a translocation mechanism.
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Affiliation(s)
- Eva Pebay-Peyroula
- Institut de Biologie Structurale, UMR 5075 CEA-CNRS-Université Joseph Fourier, 41 rue Jules Horowitz, F-38027 Grenoble cedex 1, France.
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20
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Trancíková A, Weisová P, Kissová I, Zeman I, Kolarov J. Production of reactive oxygen species and loss of viability in yeast mitochondrial mutants: protective effect of Bcl-xL. FEMS Yeast Res 2005; 5:149-56. [PMID: 15489198 DOI: 10.1016/j.femsyr.2004.06.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Revised: 05/31/2004] [Accepted: 06/22/2004] [Indexed: 10/26/2022] Open
Abstract
The capacity of yeast cells to produce reactive oxygen species (ROS), both as a response to manipulation of mitochondrial functions and to growth conditions, was estimated and compared with the viability of the cells. The chronological ageing of yeast cells (growth to late-stationary phase) was accompanied by increased ROS accumulation and a significantly higher loss of viability in the mutants with impaired mitochondrial functions than in the parental strain. Under these conditions, the ectopic expression of mammalian Bcl-x(L), which is an anti-apoptotic protein, allowed cells to survive longer in stationary phase. The protective effect of Bcl-x(L) was more prominent in respiratory-competent cells that contained defects in mitochondrial ADP/ATP translocation, suggesting a model for Bcl-x(L) regulation of chronological ageing at the mitochondria. Yeast can also be triggered into apoptosis-like cell death, at conditions leading to the depletion of the intramitochondrial ATP pool, as a consequence of the parallel inhibition of mitochondrial respiration and ADP/ATP translocation. If respiratory-deficient (rho(0)) cells were used, no correlation between the numbers of ROS-producing cells and the viability loss in the population was observed, indicating that ROS production may be an accompanying event. The protective effect of Bcl-x(L) against death of these cells suggests a mitochondrial mechanism which is different from the antioxidant activity of Bcl-x(L).
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Affiliation(s)
- Alzbeta Trancíková
- Department of Biochemistry, Faculty of Sciences, Comenius University, Mlynska Dolina CH-1, 842 15 Bratislava, Slovakia
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21
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Wohlrab H. Novel inter- and intrasubunit contacts between transport-relevant residues of the homodimeric mitochondrial phosphate transport protein. Biochem Biophys Res Commun 2004; 320:685-8. [PMID: 15240102 DOI: 10.1016/j.bbrc.2004.05.211] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Indexed: 10/26/2022]
Abstract
Ser158 is located near the middle of the matrix loop connecting transmembrane helices C and D of the mitochondrial phosphate transport protein (PTP). The mutant Ser158Thr PTP is transport-inactive. His32 is located near the middle of transmembrane helix A and Thr79 is located 5 residues away from transmembrane helix B and its N-terminal (matrix end). Single site mutant PTPs that have either residue replaced with Ala are transport-inactive. Based on the high resolution structure of a subunit of the bovine ADP/ATP translocase, on sequence similarities between members of the mitochondrial transport protein family, and on the PTP subunit/subunit contact site between transmembrane A helices, it is now suggested that the Ser158 site is at the PTP subunit/subunit contact site. This contact site is essential for keeping the transport cycles catalyzed by the two PTP subunits 180 degrees out of phase. The data also suggest that His32 and Thr79 of the same subunit interact and couple the phosphate and the proton transport paths.
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Affiliation(s)
- Hartmut Wohlrab
- Boston Biomedical Research Institute, Department of Biological Chemistry and Molecular Pharmacology, and Harvard Medical School, Watertown, MA 02472, USA.
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22
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Zeman I, Schwimmer C, Postis V, Brandolin G, David C, Trézéguet V, Lauquin GJM. Four mutations in transmembrane domains of the mitochondrial ADP/ATP carrier increase resistance to bongkrekic acid. J Bioenerg Biomembr 2004; 35:243-56. [PMID: 13678275 DOI: 10.1023/a:1024611731860] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Two distinct conformations of the mitochondrial ADP/ATP carrier involved in the adenine nucleotide transport are called BA and CATR conformations, as they were distinguished by binding of specific inhibitors bongkrekic acid (BA) and carboxyatractyloside (CATR), respectively. To find out which amino acids are implicated in the transition between these two conformations, which occurs during transport, mutants of the Saccharomyces cerevisiae ADP/ATP carrier Anc2p responsible for resistance of yeast cells to BA were identified and characterized after in vivo chemical or UV mutagenesis. Only four different mutations could be identified in spite of a large number of mutants analyzed. They are located in the Anc2p transmembrane segments I (G30S), II (Y97C), III (L142S), and VI (G298S), and are independently enabling growth of cells in the presence of BA. The variant and wild-type Anc2p were produced practically to the same level in mitochondria, as evidenced by immunochemical analysis and by atractyloside binding experiments. ADP/ATP exchange mediated by Anc2p variants in isolated mitochondria was more efficient than that of the wild-type Anc2p in the presence of BA, confirming that BA resistance of the mutant cells was linked to the functional properties of the modified ADP/ATP carrier. These results suggest that resistance to BA is caused by alternate conformation of Anc2p due to appearance of Ser or Cys at specific positions. Different interactions of these residues with other amino acids and/or BA could prevent formation of stable inactive Anc2p . BA complex.
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Affiliation(s)
- Igor Zeman
- Department of Biochemistry, Faculty of Sciences, Comenius University, Mlynská dolina CH-1, 842 15 Bratislava, Slovakia
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23
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Pebay-Peyroula E, Dahout-Gonzalez C, Kahn R, Trézéguet V, Lauquin GJM, Brandolin G. Structure of mitochondrial ADP/ATP carrier in complex with carboxyatractyloside. Nature 2003; 426:39-44. [PMID: 14603310 DOI: 10.1038/nature02056] [Citation(s) in RCA: 744] [Impact Index Per Article: 35.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2003] [Accepted: 09/15/2003] [Indexed: 02/04/2023]
Abstract
ATP, the principal energy currency of the cell, fuels most biosynthetic reactions in the cytoplasm by its hydrolysis into ADP and inorganic phosphate. Because resynthesis of ATP occurs in the mitochondrial matrix, ATP is exported into the cytoplasm while ADP is imported into the matrix. The exchange is accomplished by a single protein, the ADP/ATP carrier. Here we have solved the bovine carrier structure at a resolution of 2.2 A by X-ray crystallography in complex with an inhibitor, carboxyatractyloside. Six alpha-helices form a compact transmembrane domain, which, at the surface towards the space between inner and outer mitochondrial membranes, reveals a deep depression. At its bottom, a hexapeptide carrying the signature of nucleotide carriers (RRRMMM) is located. Our structure, together with earlier biochemical results, suggests that transport substrates bind to the bottom of the cavity and that translocation results from a transient transition from a 'pit' to a 'channel' conformation.
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Affiliation(s)
- Eva Pebay-Peyroula
- Institut de Biologie Structurale, UMR 5075 CEA-CNRS-Université Joseph Fourier, 41 rue Jules Horowitz, F-38027, Grenoble cedex 1, France.
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24
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Kunji ERS, Harding M. Projection structure of the atractyloside-inhibited mitochondrial ADP/ATP carrier of Saccharomyces cerevisiae. J Biol Chem 2003; 278:36985-8. [PMID: 12893834 DOI: 10.1074/jbc.c300304200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ADP/ATP carriers in the inner mitochondrial membrane catalyze the exchange of cytosolic ADP for ATP synthesized in the mitochondrial matrix by ATP synthase and thereby replenish the eukaryotic cell with metabolic energy. The yeast ADP/ATP carrier (AAC3) was overexpressed, inhibited by atractyloside, purified, and reconstituted into two-dimensional crystals. Images of frozen hydrated crystals were recorded by electron microscopy, and a projection structure was calculated to 8-A resolution. The AAC3 molecule has pseudo 3-fold symmetry in agreement with the 3-fold sequence repeats that are typical of members of the mitochondrial carrier family. The density distribution is consistent with a bundle of six transmembrane alpha-helices with two or three short alpha-helical extensions closing the central pore on the matrix side. The AAC3 molecules in the crystal are arranged in symmetrical homo-dimers, but the translocation pore for adenine nucleotides lies in the center of the molecule and not along the dyad axis of the dimer.
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Affiliation(s)
- Edmund R S Kunji
- Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom.
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25
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Dyall SD, Agius SC, De Marcos Lousa C, Trezeguet V, Tokatlidis K. The dynamic dimerization of the yeast ADP/ATP carrier in the inner mitochondrial membrane is affected by conserved cysteine residues. J Biol Chem 2003; 278:26757-64. [PMID: 12740376 DOI: 10.1074/jbc.m302700200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ADP/ATP carrier (AAC) that facilitates the translocation of ATP made in mitochondria is inserted at the inner mitochondrial membrane by the TIM10-TIM22 protein import system. Here we addressed the state of the AAC precursor during insertion (stage IV of import) and identified residues of the carrier important for dimerization. By a combination of (i) import of a mix of His-tagged and untagged versions of AAC either 35S-labeled or unlabeled, (ii) import of a tandem covalent dimer AAC into wild-type mitochondria, and (iii) import of monomeric AAC into mitochondria expressing only the tandem covalent dimer AAC, we found that the stage IV intermediate is a monomer, and this stage is probably the rate-limiting step of insertion in the membrane. Subsequent dimerization occurs extremely rapidly (within less than a minute). The incoming monomer dimerizes with monomeric endogenous AAC suggesting that the AAC dimer is very dynamic. Conserved Cys residues were found not to affect insertion significantly, but they are crucial for the dimerization process to obtain a functional carrier.
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Affiliation(s)
- Sabrina D Dyall
- School of Biological Sciences, 2.205 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom
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26
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Panneels V, Schüssler U, Costagliola S, Sinning I. Choline head groups stabilize the matrix loop regions of the ATP/ADP carrier ScAAC2. Biochem Biophys Res Commun 2003; 300:65-74. [PMID: 12480522 DOI: 10.1016/s0006-291x(02)02795-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ATP/ADP carriers (AACs) are essential to the cell as they exchange ATP produced in mitochondria for cytosolic ADP. Monoclonal antibodies against the isoform 2 of Saccharomyces cerevisiae AAC (ScAAC2) were used to probe the accessibility of the matrix loops 1 and 3 depending on the environment of the carrier. In mitochondrial membranes ScAAC2 was not recognized, whereas in dodecylmaltoside the antibodies bound to the carrier, suggesting that the epitopes are hidden in the native environment. Exposure of the epitopes by detergents was reversed by reconstitution of the carrier in phospholipids or by exchanging with detergents having a choline or a trimethylammonium head group. Circular dichroism spectroscopy on peptides representing the C-terminal regions of all three matrix loops showed that only phosphocholine detergents induced a structural reorganization. Since in addition phosphatidylcholine was found to be tightly associated with the purified carrier, the matrix loop regions are likely to be associated to the membrane by phosphatidylcholine.
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Affiliation(s)
- Valérie Panneels
- European Molecular Biology Laboratory, 1 MeyerhofStrasse, Heidelberg 69112, Germany
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27
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Ledesma A, de Lacoba MG, Arechaga I, Rial E. Modeling the transmembrane arrangement of the uncoupling protein UCP1 and topological considerations of the nucleotide-binding site. J Bioenerg Biomembr 2002; 34:473-86. [PMID: 12678439 DOI: 10.1023/a:1022522310279] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The uncoupling protein from brown adipose tissue (UCP1) is a mitochondrial proton transporter whose activity is inhibited by purine nucleotides. UCP1, like the other members of the mitochondrial transporter superfamily, is an homodimer and each subunit contains six transmembrane segments. In an attempt to understand the structural elements that are important for nucleotide binding, a model for the transmembrane arrangement of UCP1 has been built by computational methods. Biochemical and sequence analysis considerations are taken as constraints. The main features of the model include the following: (i) the six transmembrane alpha-helices (TMHs) associate to form an antiparallel helix bundle; (ii) TMHs have an amphiphilic nature and thus the hydrophobic and variable residues face the lipid bilayer; (iii) matrix loops do not penetrate in the core of the bundle; and (iv) the polar core constitutes the translocation pathway. Photoaffinity labeling and mutagenesis studies have identified several UCP1 regions that interact with the nucleotide. We present a model where the nucleotide binds deep inside the bundle core. The purine ring interacts with the matrix loops while the polyphosphate chain is stabilized through interactions with essential Arg residues in the TMH and whose side chains face the core of the helix bundle.
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Affiliation(s)
- Amalia Ledesma
- Centro de Investigaciones Biológicas, CSIC, Velázquez 144, 28006 Madrid, Spain
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28
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Abstract
The uncoupling proteins (UCPs) are transporters, present in the mitochondrial inner membrane, that mediate a regulated discharge of the proton gradient that is generated by the respiratory chain. This energy-dissipatory mechanism can serve functions such as thermogenesis, maintenance of the redox balance, or reduction in the production of reactive oxygen species. Some UCP homologs may not act as true uncouplers, however, and their activity has yet to be defined. The UCPs are integral membrane proteins, each with a molecular mass of 31-34 kDa and a tripartite structure in which a region of around 100 residues is repeated three times; each repeat codes for two transmembrane segments and a long hydrophilic loop. The functional carrier unit is a homodimer. So far, 45 genes encoding members of the UCP family have been described, and they can be grouped into six families. Most of the described genes are from mammals, but UCP genes have also been found in fish, birds and plants, and there is also functional evidence to suggest their presence in fungi and protozoa. UCPs are encoded in their mature form by nuclear genes and, unlike many nuclear-encoded mitochondrial proteins, they lack a cleavable mitochondrial import signal. The information for mitochondrial targeting resides in the first loop that protrudes into the mitochondrial matrix; the second matrix loop is essential for insertion of the protein into the inner mitochondrial membrane. UCPs are regulated at both the transcriptional level and by activation and inhibition in the mitochondrion.
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Affiliation(s)
- Amalia Ledesma
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas, Velázquez 144, 28006 Madrid, Spain
| | - Mario García de Lacoba
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas, Velázquez 144, 28006 Madrid, Spain
| | - Eduardo Rial
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas, Velázquez 144, 28006 Madrid, Spain
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29
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Manchado C, Orús J, Villarroya F, Roig E, Heras M, Giralt M, Iglesias R, Sanz G, Mampel T, Viñas O. Epitope mapping of mitochondrial adenine nucleotide translocase-1 in idiopathic dilated cardiomyopathy. J Mol Cell Cardiol 2002; 34:571-82. [PMID: 12056860 DOI: 10.1006/jmcc.2002.1538] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondrial adenine nucleotide translocase (ANT) is a specific target for the autoantibody response in idiopathic dilated cardiomyopathy (IDCM). We have undertaken an epitope analysis of ANT in IDCM by immunoblot with recombinant GST-ANT fusion proteins and with cellulose-bound decapeptides of human ANT1. Forty-five patients with IDCM, 17 patients with ischemic left ventricle dysfunction (LVD) and 20 controls were analyzed for circulating antibodies against ANT (AAb-ANT). Sixteen of the 45 (36%) IDCM patients showed AAb-ANT above controls. In immunoblots, AAb-ANT detected purified bovine heart ANT and GST-ANT1 and GST-ANT2 isoforms and, less frequently, the GST-ANT3 isoform. A construct lacking the last 146 amino acids did not react with AAb-ANT, indicating that the main epitopes are in the C-terminal 146 amino acids. Immunodetection of decapeptides covering this region shows that AAb-ANT detects at least three epitopes, demonstrating that ANT is the primary target of AAb-ANT. The most significant epitopes belong to the M2 and M3 hydrophilic loops of ANT suggesting that apart from being essential for its activity, these loops are highly immunogenic.
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Affiliation(s)
- Carlos Manchado
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Spain
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30
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Abstract
Alteration of mitochondrial membrane permeability is a central mechanism leading invariably to cell death, which results, at least in part, from the opening of the permeability transition pore complex (PTPC). Indeed, extended PTPC opening is sufficient to trigger an increase in mitochondrial membrane permeability and apoptosis. Among the various PTPC components, the adenine nucleotide translocator (ANT) appears to act as a bi-functional protein which, on the one hand, contributes to a crucial step of aerobic energy metabolism, the ADP/ATP translocation, and on the other hand, can be converted into a pro-apoptotic pore under the control of onco- and anti-oncoproteins from the Bax/Bcl-2 family. In this review, we will discuss recent advances in the cooperation between ANT and Bax/Bcl-2 family members, the multiplicity of agents affecting ANT pore function and the putative role of ANT isoforms in apoptosis control.
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Affiliation(s)
- Anne-Sophie Belzacq
- Centre national de la recherche scientifique, UMR 6022, université de technologie de Compiègne, Royallieu, BP20529, 60205 Compiègne, France
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31
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Huang SG, Odoy S, Klingenberg M. Chimers of two fused ADP/ATP carrier monomers indicate a single channel for ADP/ATP transport. Arch Biochem Biophys 2001; 394:67-75. [PMID: 11566029 DOI: 10.1006/abbi.2001.2520] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mitochondrial ADP/ATP carrier (AAC) is generally believed to function as a homodimer (Wt. Wt). It remains unknown whether the two monomers possess two independent but fully anticooperative channels or they form a single central channel for nucleotide transport. Here we generated fusion proteins consisting of two tandem covalent-linked AAC monomers and studied the kinetics of ADP/ATP transport in reconstituted proteoliposomes. Functional 64-kDa fusion proteins Wt-Wt and Wt-R294A (wild-type AAC linked to a mutant having low ATP transport activity) were expressed in mitochondria of yeast transformants. Compared to homodimer Wt. Wt, the fusion protein Wt-Wt retained the transport activity and selectivity of ADP versus ATP. The strongly divergent selectivities of Wt and R294A were partially propagated in the Wt-R294A fusion protein, suggesting a limited cooperativity during solute translocation. The rates of ADP or ATP transport were significantly higher than those predicted by the two-channel model. Fusion proteins for Wt-R204L (Wt linked to an inactive mutant) and R204L-Wt were not expressed in aerobically grown yeast cells, which contained plasmid rearrangements that regenerated the fully active 32-kDa homodimer Wt. Wt, suggesting that these fusion proteins are inactive in ADP/ATP transport. These results favor a single binding center gated pore model [Klingenberg, M. (1991) in A Study of Enzymes, Vol. 2: pp. 367-388] in which two AAC subunits cooperate for a coordinated ADP/ATP exchange through a single channel.
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Affiliation(s)
- S G Huang
- Institute of Physical Biochemistry, University of Munich, Schillerstrasse 44, Munich, D-80336, Germany.
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32
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Hatanaka T, Kihira Y, Shinohara Y, Majima E, Terada H. Characterization of loops of the yeast mitochondrial ADP/ATP carrier facing the cytosol by site-directed mutagenesis. Biochem Biophys Res Commun 2001; 286:936-42. [PMID: 11527389 DOI: 10.1006/bbrc.2001.5498] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To characterize structural features of the regions of the yeast type 2 ADP/ATP carrier (yAAC2) facing the cytosol, we prepared its Cys-less mutant, in which all four cysteine residues were replaced by alanine residues. The Cys-less mutant functioned like native yAAC2, showing that the cysteine residues are not essential. We then prepared cysteine mutants by substituting Ser(21) in the putative N-terminal region, Ala(124) and Ser(222) in the first and second loops facing cytosol, respectively, and Leu(312) in the C-terminal region of the Cys-less mutant for cysteine and examined the labeling of the substituted cysteine residues of the mutants with the membrane-impermeable SH reagent eosin-5-maleimide (EMA) from the cytosol. EMA labeled all the mutants, showing that all regions containing mutated residues faced the cytosolic side. The effects of transport inhibitors on EMA labeling were also examined. From the results, the location and conformation of the region around mutated residues were discussed.
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Affiliation(s)
- T Hatanaka
- Faculty of Pharmaceutical Sciences, University of Tokushima, Shomachi-1, Tokushima, 770-8505, Japan
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33
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Hatanaka T, Hashimoto M, Majima E, Shinohara Y, Terada H. Significant effect of the N-terminal region of the mitochondrial ADP/ATP carrier on its efficient expression in yeast mitochondria. J Biol Chem 2001; 276:28881-8. [PMID: 11384977 DOI: 10.1074/jbc.m102535200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low-level expression of the bovine heart mitochondrial ADP/ATP carrier (bovine type 1 ADP/ATP carrier (bAAC1)) in the yeast mitochondrial membrane is significantly improved by replacement of its N-terminal region with corresponding regions of the yeast type 1 and 2 carriers (yAAC1 and yAAC2) (Hashimoto, M., Shinohara, Y., Majima, E., Hatanaka, T., Yamazaki, N., and Terada, H. (1999) Biochim. Biophys. Acta 1409, 113--124). To understand why the bAAC1 chimeras were highly expressed in yeast mitochondria, we examined the effects of the length and sequence of the N-terminal region extending into the cytosol on the expression of bAAC1 and yAAC2 derivatives in yeast mitochondria. For this, their N-terminal regions were replaced with peptide fragments of various lengths and sequences derived from those of bAAC1, yAAC1, and yAAC2. We found that a specific amino acid sequence and a definite length of the N-terminal region of yAAC2 were required for high expression of bAAC1 and yAAC2 in yeast mitochondria. We also examined the steady-state transcript levels and expression of these derivatives in whole yeast cells. Based on our results, we discuss the role of the N-terminal region in efficient expression of bAAC1 and yAAC2 in yeast mitochondria.
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Affiliation(s)
- T Hatanaka
- Faculty of Pharmaceutical Sciences, University of Tokushima, Shomachi-1, Tokushima 770-8505, Japan
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