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Žuna K, Tyschuk T, Beikbaghban T, Sternberg F, Kreiter J, Pohl EE. The 2-oxoglutarate/malate carrier extends the family of mitochondrial carriers capable of fatty acid and 2,4-dinitrophenol-activated proton transport. Acta Physiol (Oxf) 2024; 240:e14143. [PMID: 38577966 DOI: 10.1111/apha.14143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 03/06/2024] [Accepted: 03/11/2024] [Indexed: 04/06/2024]
Abstract
AIMS Metabolic reprogramming in cancer cells has been linked to mitochondrial dysfunction. The mitochondrial 2-oxoglutarate/malate carrier (OGC) has been suggested as a potential target for preventing cancer progression. Although OGC is involved in the malate/aspartate shuttle, its exact role in cancer metabolism remains unclear. We aimed to investigate whether OGC may contribute to the alteration of mitochondrial inner membrane potential by transporting protons. METHODS The expression of OGC in mouse tissues and cancer cells was investigated by PCR and Western blot analysis. The proton transport function of recombinant murine OGC was evaluated by measuring the membrane conductance (Gm) of planar lipid bilayers. OGC-mediated substrate transport was measured in proteoliposomes using 14C-malate. RESULTS OGC increases proton Gm only in the presence of natural (long-chain fatty acids, FA) or chemical (2,4-dinitrophenol) protonophores. The increase in OGC activity directly correlates with the increase in the number of unsaturated bonds of the FA. OGC substrates and inhibitors compete with FA for the same protein binding site. Arginine 90 was identified as a critical amino acid for the binding of FA, ATP, 2-oxoglutarate, and malate, which is a first step towards understanding the OGC-mediated proton transport mechanism. CONCLUSION OGC extends the family of mitochondrial transporters with dual function: (i) metabolite transport and (ii) proton transport facilitated in the presence of protonophores. Elucidating the contribution of OGC to uncoupling may be essential for the design of targeted drugs for the treatment of cancer and other metabolic diseases.
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Affiliation(s)
- Kristina Žuna
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
| | - Tatyana Tyschuk
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
| | - Taraneh Beikbaghban
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
| | - Felix Sternberg
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
| | - Jürgen Kreiter
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
| | - Elena E Pohl
- Physiology and Biophysics, Department of Biological Sciences and Pathobiology, University of Veterinary Medicine, Vienna, Austria
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2
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Kreiter J, Škulj S, Brkljača Z, Bardakji S, Vazdar M, Pohl EE. FA Sliding as the Mechanism for the ANT1-Mediated Fatty Acid Anion Transport in Lipid Bilayers. Int J Mol Sci 2023; 24:13701. [PMID: 37762012 PMCID: PMC10531397 DOI: 10.3390/ijms241813701] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 08/27/2023] [Accepted: 08/29/2023] [Indexed: 09/29/2023] Open
Abstract
Mitochondrial adenine nucleotide translocase (ANT) exchanges ADP for ATP to maintain energy production in the cell. Its protonophoric function in the presence of long-chain fatty acids (FA) is also recognized. Our previous results imply that proton/FA transport can be best described with the FA cycling model, in which protonated FA transports the proton to the mitochondrial matrix. The mechanism by which ANT1 transports FA anions back to the intermembrane space remains unclear. Using a combined approach involving measurements of the current through the planar lipid bilayers reconstituted with ANT1, site-directed mutagenesis and molecular dynamics simulations, we show that the FA anion is first attracted by positively charged arginines or lysines on the matrix side of ANT1 before moving along the positively charged protein-lipid interface and binding to R79, where it is protonated. We show that R79 is also critical for the competitive binding of ANT1 substrates (ADP and ATP) and inhibitors (carboxyatractyloside and bongkrekic acid). The binding sites are well conserved in mitochondrial SLC25 members, suggesting a general mechanism for transporting FA anions across the inner mitochondrial membrane.
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Affiliation(s)
- Jürgen Kreiter
- Institute of Physiology, Pathophysiology, and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (S.Š.); (S.B.)
| | - Sanja Škulj
- Institute of Physiology, Pathophysiology, and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (S.Š.); (S.B.)
| | - Zlatko Brkljača
- Division of Organic Chemistry and Biochemistry, Rudjer Bošković Institute, 10000 Zagreb, Croatia;
| | - Sarah Bardakji
- Institute of Physiology, Pathophysiology, and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (S.Š.); (S.B.)
| | - Mario Vazdar
- Department of Mathematics, Informatics, and Cybernetics, University of Chemistry and Technology, 166 28 Prague, Czech Republic
| | - Elena E. Pohl
- Institute of Physiology, Pathophysiology, and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria; (J.K.); (S.Š.); (S.B.)
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3
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Tavoulari S, Sichrovsky M, Kunji ERS. Fifty years of the mitochondrial pyruvate carrier: New insights into its structure, function, and inhibition. Acta Physiol (Oxf) 2023; 238:e14016. [PMID: 37366179 PMCID: PMC10909473 DOI: 10.1111/apha.14016] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 06/12/2023] [Accepted: 06/14/2023] [Indexed: 06/28/2023]
Abstract
The mitochondrial pyruvate carrier (MPC) resides in the mitochondrial inner membrane, where it links cytosolic and mitochondrial metabolism by transporting pyruvate produced in glycolysis into the mitochondrial matrix. Due to its central metabolic role, it has been proposed as a potential drug target for diabetes, non-alcoholic fatty liver disease, neurodegeneration, and cancers relying on mitochondrial metabolism. Little is known about the structure and mechanism of MPC, as the proteins involved were only identified a decade ago and technical difficulties concerning their purification and stability have hindered progress in functional and structural analyses. The functional unit of MPC is a hetero-dimer comprising two small homologous membrane proteins, MPC1/MPC2 in humans, with the alternative complex MPC1L/MPC2 forming in the testis, but MPC proteins are found throughout the tree of life. The predicted topology of each protomer consists of an amphipathic helix followed by three transmembrane helices. An increasing number of inhibitors are being identified, expanding MPC pharmacology and providing insights into the inhibitory mechanism. Here, we provide critical insights on the composition, structure, and function of the complex and we summarize the different classes of small molecule inhibitors and their potential in therapeutics.
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Affiliation(s)
- Sotiria Tavoulari
- Medical Research Council Mitochondrial Biology UnitUniversity of CambridgeCambridgeUK
| | - Maximilian Sichrovsky
- Medical Research Council Mitochondrial Biology UnitUniversity of CambridgeCambridgeUK
| | - Edmund R. S. Kunji
- Medical Research Council Mitochondrial Biology UnitUniversity of CambridgeCambridgeUK
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4
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Mavridou V, King MS, Tavoulari S, Ruprecht JJ, Palmer SM, Kunji ERS. Substrate binding in the mitochondrial ADP/ATP carrier is a step-wise process guiding the structural changes in the transport cycle. Nat Commun 2022; 13:3585. [PMID: 35739110 PMCID: PMC9226169 DOI: 10.1038/s41467-022-31366-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 06/14/2022] [Indexed: 02/02/2023] Open
Abstract
Mitochondrial ADP/ATP carriers import ADP into the mitochondrial matrix and export ATP to the cytosol to fuel cellular processes. Structures of the inhibited cytoplasmic- and matrix-open states have confirmed an alternating access transport mechanism, but the molecular details of substrate binding remain unresolved. Here, we evaluate the role of the solvent-exposed residues of the translocation pathway in the process of substrate binding. We identify the main binding site, comprising three positively charged and a set of aliphatic and aromatic residues, which bind ADP and ATP in both states. Additionally, there are two pairs of asparagine/arginine residues on opposite sides of this site that are involved in substrate binding in a state-dependent manner. Thus, the substrates are directed through a series of binding poses, inducing the conformational changes of the carrier that lead to their translocation. The properties of this site explain the electrogenic and reversible nature of adenine nucleotide transport.
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Affiliation(s)
- Vasiliki Mavridou
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
| | - Martin S. King
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
| | - Sotiria Tavoulari
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
| | - Jonathan J. Ruprecht
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
| | - Shane M. Palmer
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
| | - Edmund R. S. Kunji
- grid.5335.00000000121885934Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY UK
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5
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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: 9] [Impact Index Per Article: 4.5] [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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6
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Montalvo-Acosta JJ, Kunji ERS, Ruprecht JJ, Dehez F, Chipot C. Structure, substrate binding, and symmetry of the mitochondrial ADP/ATP carrier in its matrix-open state. Biophys J 2021; 120:5187-5195. [PMID: 34748764 DOI: 10.1016/j.bpj.2021.11.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 10/14/2021] [Accepted: 11/02/2021] [Indexed: 01/28/2023] Open
Abstract
The mitochondrial ADP/ATP carrier (AAC) performs the first and last step in oxidative phosphorylation by exchanging ADP and ATP across the mitochondrial inner membrane. Its optimal function has been shown to be dependent on cardiolipins (CLs), unique phospholipids located almost exclusively in the mitochondrial membrane. In addition, AAC exhibits an enthralling threefold pseudosymmetry, a unique feature of members of the SLC25 family. Recently, its conformation poised for binding of ATP was solved by x-ray crystallography referred to as the matrix state. Binding of the substrate leads to conformational changes that export of ATP to the mitochondrial intermembrane space. In this contribution, we investigate the influence of CLs on the structure, substrate-binding properties, and structural symmetry of the matrix state, employing microsecond-scale molecular dynamics simulations. Our findings demonstrate that CLs play a minor stabilizing role on the AAC structure. The interdomain salt bridges and hydrogen bonds forming the cytoplasmic network and tyrosine braces, which ensure the integrity of the global AAC scaffold, highly benefit from the presence of CLs. Under these conditions, the carrier is found to be organized in a more compact structure in its interior, as revealed by analyses of the electrostatic potential, measure of the AAC cavity aperture, and the substrate-binding assays. Introducing a convenient structure-based symmetry metric, we quantified the structural threefold pseudosymmetry of AAC, not only for the crystallographic structure, but also for conformational states of the carrier explored in the molecular dynamics simulations. Our results suggest that CLs moderately contribute to preserve the pseudosymmetric structure of AAC.
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Affiliation(s)
- Joel José Montalvo-Acosta
- Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Unité Mixte de Recherche no 7019, Université de Lorraine, Vandœuvre-lès-Nancy cedex, France
| | - Edmund R S Kunji
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge, United Kingdom
| | - Jonathan J Ruprecht
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge, United Kingdom
| | - François Dehez
- Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Unité Mixte de Recherche no 7019, Université de Lorraine, Vandœuvre-lès-Nancy cedex, France.
| | - Christophe Chipot
- Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Unité Mixte de Recherche no 7019, Université de Lorraine, Vandœuvre-lès-Nancy cedex, France; Theoretical and Computational Biophysics Group, Beckman Institute for Advanced Science and Technology, Urbana, Illinois; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois.
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7
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Kunji ERS, King MS, Ruprecht JJ, Thangaratnarajah C. The SLC25 Carrier Family: Important Transport Proteins in Mitochondrial Physiology and Pathology. Physiology (Bethesda) 2021; 35:302-327. [PMID: 32783608 PMCID: PMC7611780 DOI: 10.1152/physiol.00009.2020] [Citation(s) in RCA: 68] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Members of the mitochondrial carrier family (SLC25) transport a variety of compounds across the inner membrane of mitochondria. These transport steps provide building blocks for the cell and link the pathways of the mitochondrial matrix and cytosol. An increasing number of diseases and pathologies has been associated with their dysfunction. In this review, the molecular basis of these diseases is explained based on our current understanding of their transport mechanism.
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Affiliation(s)
- Edmund R S Kunji
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, United Kingdom
| | - Martin S King
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, United Kingdom
| | - Jonathan J Ruprecht
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, United Kingdom
| | - Chancievan Thangaratnarajah
- Groningen Biomolecular Sciences and Biotechnology Institute, Membrane Enzymology, University of Groningen, Groningen, The Netherlands
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8
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The mitochondrial ADP/ATP carrier exists and functions as a monomer. Biochem Soc Trans 2021; 48:1419-1432. [PMID: 32725219 PMCID: PMC7458400 DOI: 10.1042/bst20190933] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 06/26/2020] [Accepted: 07/06/2020] [Indexed: 12/15/2022]
Abstract
For more than 40 years, the oligomeric state of members of the mitochondrial carrier family (SLC25) has been the subject of debate. Initially, the consensus was that they were dimeric, based on the application of a large number of different techniques. However, the structures of the mitochondrial ADP/ATP carrier, a member of the family, clearly demonstrated that its structural fold is monomeric, lacking a conserved dimerisation interface. A re-evaluation of previously published data, with the advantage of hindsight, concluded that technical errors were at the basis of the earlier dimer claims. Here, we revisit this topic, as new claims for the existence of dimers of the bovine ADP/ATP carrier have emerged using native mass spectrometry of mitochondrial membrane vesicles. However, the measured mass does not agree with previously published values, and a large number of post-translational modifications are proposed to account for the difference. Contrarily, these modifications are not observed in electron density maps of the bovine carrier. If they were present, they would interfere with the structure and function of the carrier, including inhibitor and substrate binding. Furthermore, the reported mass does not account for three tightly bound cardiolipin molecules, which are consistently observed in other studies and are important stabilising factors for the transport mechanism. The monomeric carrier has all of the required properties for a functional transporter and undergoes large conformational changes that are incompatible with a stable dimerisation interface. Thus, our view that the native mitochondrial ADP/ATP carrier exists and functions as a monomer remains unaltered.
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9
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Willis W, Willis E, Kuzmiak-Glancy S, Kras K, Hudgens J, Barakati N, Stern J, Mandarino L. Oxidative phosphorylation K 0.5ADP in vitro depends on substrate oxidative capacity: Insights from a luciferase-based assay to evaluate ADP kinetic parameters. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148430. [PMID: 33887230 DOI: 10.1016/j.bbabio.2021.148430] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 03/30/2021] [Accepted: 04/07/2021] [Indexed: 12/21/2022]
Abstract
The K0.5ADP of oxidative phosphorylation (OxPhos) identifies the cytosolic ADP concentration which elicits one-half the maximum OxPhos rate. This kinetic parameter is commonly measured to assess mitochondrial metabolic control sensitivity. Here we describe a luciferase-based assay to evaluate the ADP kinetic parameters of mitochondrial ATP production from OxPhos, adenylate kinase (AK), and creatine kinase (CK). The high sensitivity, reproducibility, and throughput of the microplate-based assay enabled a comprehensive kinetic assessment of all three pathways in mitochondria isolated from mouse liver, kidney, heart, and skeletal muscle. Carboxyatractyloside titrations were also performed with the assay to estimate the flux control strength of the adenine nucleotide translocase (ANT) over OxPhos in human skeletal muscle mitochondria. ANT flux control coefficients were 0.91 ± 0.07, 0.83 ± 0.06, and 0.51 ± 0.07 at ADP concentrations of 6.25, 12.5, and 25 μM, respectively, an [ADP] range which spanned the K0.5ADP. The oxidative capacity of substrate combinations added to drive OxPhos was found to dramatically influence ADP kinetics in mitochondria from several tissues. In mouse skeletal muscle ten different substrate combinations elicited a 7-fold range of OxPhos Vmax, which correlated positively (R2 = 0.963) with K0.5ADP values ranging from 2.3 ± 0.2 μM to 11.9 ± 0.6 μM. We propose that substrate-enhanced capacity to generate the protonmotive force increases the OxPhos K0.5ADP because flux control at ANT increases, thus K0.5ADP rises toward the dissociation constant, KdADP, of ADP-ANT binding. The findings are discussed in the context of top-down metabolic control analysis.
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Affiliation(s)
- Wayne Willis
- Department of Medicine, Division of Endocrinology, University of Arizona, Tucson, AZ, United States; Center for Disparities in Diabetes, Obesity, and Metabolism, University of Arizona, Tucson, AZ, United States.
| | - Elizabeth Willis
- College of Medicine, University of Kentucky, Lexington, KY, United States
| | - Sarah Kuzmiak-Glancy
- Department of Kinesiology, University of Maryland, College Park, MD, United States
| | - Katon Kras
- Department of Medicine, Division of Endocrinology, University of Arizona, Tucson, AZ, United States
| | - Jamie Hudgens
- College of Pharmacy, Midwestern University, Glendale, AZ, United States
| | - Neusha Barakati
- Department of Medicine, Division of Endocrinology, University of Arizona, Tucson, AZ, United States
| | - Jennifer Stern
- Department of Medicine, Division of Endocrinology, University of Arizona, Tucson, AZ, United States; Center for Disparities in Diabetes, Obesity, and Metabolism, University of Arizona, Tucson, AZ, United States
| | - Lawrence Mandarino
- Department of Medicine, Division of Endocrinology, University of Arizona, Tucson, AZ, United States; Center for Disparities in Diabetes, Obesity, and Metabolism, University of Arizona, Tucson, AZ, United States
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10
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Jaiquel Baron S, King MS, Kunji ER, Schirris TJ. Characterization of drug-induced human mitochondrial ADP/ATP carrier inhibition. Am J Cancer Res 2021; 11:5077-5091. [PMID: 33859735 PMCID: PMC8039944 DOI: 10.7150/thno.54936] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 01/18/2021] [Indexed: 01/10/2023] Open
Abstract
An increasing number of commonly prescribed drugs are known to interfere with mitochondrial function, causing cellular toxicity, but the underlying mechanisms are largely unknown. Although often not considered, mitochondrial transport proteins form a significant class of potential mitochondrial off-targets. So far, most drug interactions have been reported for the mitochondrial ADP/ATP carrier (AAC), which exchanges cytosolic ADP for mitochondrial ATP. Here, we show inhibition of cellular respiratory capacity by only a subset of the 18 published AAC inhibitors, which questions whether all compound do indeed inhibit such a central metabolic process. This could be explained by the lack of a simple, direct model system to evaluate and compare drug-induced AAC inhibition. Methods: For its development, we have expressed and purified human AAC1 (hAAC1) and applied two approaches. In the first, thermostability shift assays were carried out to investigate the binding of these compounds to human AAC1. In the second, the effect of these compounds on transport was assessed in proteoliposomes with reconstituted human AAC1, enabling characterization of their inhibition kinetics. Results: Of the proposed inhibitors, chebulinic acid, CD-437 and suramin are the most potent with IC50-values in the low micromolar range, whereas another six are effective at a concentration of 100 μM. Remarkably, half of all previously published AAC inhibitors do not show significant inhibition in our assays, indicating that they are false positives. Finally, we show that inhibitor strength correlates with a negatively charged surface area of the inhibitor, matching the positively charged surface of the substrate binding site. Conclusion: Consequently, we have provided a straightforward model system to investigate AAC inhibition and have gained new insights into the chemical compound features important for inhibition. Better evaluation methods of drug-induced inhibition of mitochondrial transport proteins will contribute to the development of drugs with an enhanced safety profile.
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11
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Abstract
Members of the mitochondrial carrier family [solute carrier family 25 (SLC25)] transport nucleotides, amino acids, carboxylic acids, fatty acids, inorganic ions, and vitamins across the mitochondrial inner membrane. They are important for many cellular processes, such as oxidative phosphorylation of lipids and sugars, amino acid metabolism, macromolecular synthesis, ion homeostasis, cellular regulation, and differentiation. Here, we describe the functional elements of the transport mechanism of mitochondrial carriers, consisting of one central substrate-binding site and two gates with salt-bridge networks on either side of the carrier. Binding of the substrate during import causes three gate elements to rotate inward, forming the cytoplasmic network and closing access to the substrate-binding site from the intermembrane space. Simultaneously, three core elements rock outward, disrupting the matrix network and opening the substrate-binding site to the matrix side of the membrane. During export, substrate binding triggers conformational changes involving the same elements but operating in reverse.
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Affiliation(s)
- J J Ruprecht
- Medical Research Council Mitochondrial Biology Unit, Keith Peters Building, University of Cambridge, Cambridge CB2 0XY, United Kingdom; ,
| | - E R S Kunji
- Medical Research Council Mitochondrial Biology Unit, Keith Peters Building, University of Cambridge, Cambridge CB2 0XY, United Kingdom; ,
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12
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A Single Cysteine Residue in the Translocation Pathway of the Mitosomal ADP/ATP Carrier from Cryptosporidium parvum Confers a Broad Nucleotide Specificity. Int J Mol Sci 2020; 21:ijms21238971. [PMID: 33255957 PMCID: PMC7730227 DOI: 10.3390/ijms21238971] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 11/09/2020] [Accepted: 11/23/2020] [Indexed: 12/18/2022] Open
Abstract
Cryptosporidiumparvum is a clinically important eukaryotic parasite that causes the disease cryptosporidiosis, which manifests with gastroenteritis-like symptoms. The protist has mitosomes, which are organelles of mitochondrial origin that have only been partially characterized. The genome encodes a highly reduced set of transport proteins of the SLC25 mitochondrial carrier family of unknown function. Here, we have studied the transport properties of one member of the C. parvum carrier family, demonstrating that it resembles the mitochondrial ADP/ATP carrier of eukaryotes. However, this carrier has a broader substrate specificity for nucleotides, transporting adenosine, thymidine, and uridine di- and triphosphates in contrast to its mitochondrial orthologues, which have a strict substrate specificity for ADP and ATP. Inspection of the putative translocation pathway highlights a cysteine residue, which is a serine in mitochondrial ADP/ATP carriers. When the serine residue is replaced by cysteine or larger hydrophobic residues in the yeast mitochondrial ADP/ATP carrier, the substrate specificity becomes broad, showing that this residue is important for nucleotide base selectivity in ADP/ATP carriers.
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13
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Zhang Y, Fernie AR. On the Detection and Functional Significance of the Protein-Protein Interactions of Mitochondrial Transport Proteins. Biomolecules 2020; 10:E1107. [PMID: 32722450 PMCID: PMC7464641 DOI: 10.3390/biom10081107] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/21/2020] [Accepted: 07/23/2020] [Indexed: 12/23/2022] Open
Abstract
Protein-protein assemblies are highly prevalent in all living cells. Considerable evidence has recently accumulated suggesting that particularly transient association/dissociation of proteins represent an important means of regulation of metabolism. This is true not only in the cytosol and organelle matrices, but also at membrane surfaces where, for example, receptor complexes, as well as those of key metabolic pathways, are common. Transporters also frequently come up in lists of interacting proteins, for example, binding proteins that catalyze the production of their substrates or that act as relays within signal transduction cascades. In this review, we provide an update of technologies that are used in the study of such interactions with mitochondrial transport proteins, highlighting the difficulties that arise in their use for membrane proteins and discussing our current understanding of the biological function of such interactions.
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Affiliation(s)
- Youjun Zhang
- Center of Plant Systems Biology and Biotechnology, 4000 Plovdiv, Bulgaria
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Alisdair R. Fernie
- Center of Plant Systems Biology and Biotechnology, 4000 Plovdiv, Bulgaria
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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14
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The SLC25 Mitochondrial Carrier Family: Structure and Mechanism. Trends Biochem Sci 2019; 45:244-258. [PMID: 31787485 PMCID: PMC7611774 DOI: 10.1016/j.tibs.2019.11.001] [Citation(s) in RCA: 175] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/30/2019] [Accepted: 11/01/2019] [Indexed: 12/27/2022]
Abstract
Members of the mitochondrial carrier family (SLC25) provide the transport steps for amino acids, carboxylic acids, fatty acids, cofactors, inorganic ions, and nucleotides across the mitochondrial inner membrane and are crucial for many cellular processes. Here, we use new insights into the transport mechanism of the mitochondrial ADP/ATP carrier to examine the structure and function of other mitochondrial carriers. They all have a single substrate-binding site and two gates, which are present on either side of the membrane and involve salt-bridge networks. Transport is likely to occur by a common mechanism, in which the coordinated movement of six structural elements leads to the alternating opening and closing of the matrix or cytoplasmic side of the carriers.
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15
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Hirst J, Kunji ERS, Walker JE. Comment on "Protein assemblies ejected directly from native membranes yield complexes for mass spectrometry". Science 2019; 366:eaaw9830. [PMID: 31699909 DOI: 10.1126/science.aaw9830] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 10/09/2019] [Indexed: 02/02/2023]
Abstract
Chorev et al (Reports, 16 November 2018, p. 829) describe mass spectrometry on mitochondrial membrane proteins ionized directly from their native environment. However, the assignments made to measured masses are incorrect or inconclusive and lack experimental validation. The proteins are not in their "native" condition: They have been stripped of tightly bound lipids, and the complexes are fragmented or in physiologically irrelevant oligomeric states.
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Affiliation(s)
- Judy Hirst
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK.
| | - Edmund R S Kunji
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK.
| | - John E Walker
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK.
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16
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Gaudry MJ, Keuper M, Jastroch M. Molecular evolution of thermogenic uncoupling protein 1 and implications for medical intervention of human disease. Mol Aspects Med 2019; 68:6-17. [DOI: 10.1016/j.mam.2019.06.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Revised: 06/20/2019] [Accepted: 06/21/2019] [Indexed: 12/12/2022]
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17
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Coyne LP, Chen XJ. Consequences of inner mitochondrial membrane protein misfolding. Mitochondrion 2019; 49:46-55. [PMID: 31195097 DOI: 10.1016/j.mito.2019.06.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/07/2019] [Accepted: 06/06/2019] [Indexed: 02/04/2023]
Abstract
Proteins embedded in the inner mitochondrial membrane (IMM) perform essential cellular functions. Maintaining the folding state of these proteins is therefore of the utmost importance, and this is ensured by IMM chaperones and proteases that refold and degrade unassembled and misfolded proteins. However, the physiological consequences specific to IMM protein misfolding remain obscure because deletion of these chaperones/proteases (the typical experimental strategy) often affects many mitochondrial processes other than protein folding and turnover. Thus, novel experimental systems are needed to evaluate the direct effects of misfolded protein on the membrane. Such a system has been developed in recent years. Studies suggest that numerous pathogenic mutations in isoform 1 of adenine nucleotide translocase (Ant1) cause its misfolding on the IMM. In this review, we first discuss potential mechanisms by which dominant Ant1 mutations may cause disease, highlighting IMM protein misfolding, per se, as a likely pathological factor. Then we discuss the intramitochondrial effects of Ant1 misfolding such as IMM proteostatic stress, respiratory chain dysfunction, and mtDNA instability. Finally, we summarize the mounting evidence that IMM proteostatic stress can perturb mitochondrial protein import to cause the toxic accumulation of mitochondrial proteins in the cytosol: a cell stress mechanism termed mitochondrial Precursor Overaccumulation Stress (mPOS).
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Affiliation(s)
- Liam P Coyne
- Departments of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY, USA
| | - Xin Jie Chen
- Departments of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY, USA; Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY, USA.
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18
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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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19
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Ruprecht JJ, King MS, Zögg T, Aleksandrova AA, Pardon E, Crichton PG, Steyaert J, Kunji ERS. The Molecular Mechanism of Transport by the Mitochondrial ADP/ATP Carrier. Cell 2019; 176:435-447.e15. [PMID: 30611538 PMCID: PMC6349463 DOI: 10.1016/j.cell.2018.11.025] [Citation(s) in RCA: 185] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 09/25/2018] [Accepted: 11/16/2018] [Indexed: 11/30/2022]
Abstract
Mitochondrial ADP/ATP carriers transport ADP into the mitochondrial matrix for ATP synthesis, and ATP out to fuel the cell, by cycling between cytoplasmic-open and matrix-open states. The structure of the cytoplasmic-open state is known, but it has proved difficult to understand the transport mechanism in the absence of a structure in the matrix-open state. Here, we describe the structure of the matrix-open state locked by bongkrekic acid bound in the ADP/ATP-binding site at the bottom of the central cavity. The cytoplasmic side of the carrier is closed by conserved hydrophobic residues, and a salt bridge network, braced by tyrosines. Glycine and small amino acid residues allow close-packing of helices on the matrix side. Uniquely, the carrier switches between states by rotation of its three domains about a fulcrum provided by the substrate-binding site. Because these features are highly conserved, this mechanism is likely to apply to the whole mitochondrial carrier family. Video Abstract
Structure of the matrix-open state of the mitochondrial ADP/ATP carrier solved The inhibitor bongkrekic acid locks the state by occupying the substrate-binding site Conformational changes during transport are highly dynamic, using six mobile elements Roles of all conserved sequence features in mitochondrial carriers are now explained
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Affiliation(s)
- Jonathan J Ruprecht
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK.
| | - Martin S King
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Thomas Zögg
- VIB-VUB Center for Structural Biology, VIB, Pleinlaan 2, 1050 Brussels, Belgium; Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
| | - Antoniya A Aleksandrova
- Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, MD 20892, USA
| | - Els Pardon
- VIB-VUB Center for Structural Biology, VIB, Pleinlaan 2, 1050 Brussels, Belgium; Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
| | - Paul G Crichton
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Jan Steyaert
- VIB-VUB Center for Structural Biology, VIB, Pleinlaan 2, 1050 Brussels, Belgium; Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
| | - Edmund R S Kunji
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK.
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20
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Chorev DS, Baker LA, Wu D, Beilsten-Edmands V, Rouse SL, Zeev-Ben-Mordehai T, Jiko C, Samsudin F, Gerle C, Khalid S, Stewart AG, Matthews SJ, Grünewald K, Robinson CV. Protein assemblies ejected directly from native membranes yield complexes for mass spectrometry. Science 2018; 362:829-834. [PMID: 30442809 PMCID: PMC6522346 DOI: 10.1126/science.aau0976] [Citation(s) in RCA: 142] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2018] [Accepted: 10/08/2018] [Indexed: 12/25/2022]
Abstract
Membrane proteins reside in lipid bilayers and are typically extracted from this environment for study, which often compromises their integrity. In this work, we ejected intact assemblies from membranes, without chemical disruption, and used mass spectrometry to define their composition. From Escherichia coli outer membranes, we identified a chaperone-porin association and lipid interactions in the β-barrel assembly machinery. We observed efflux pumps bridging inner and outer membranes, and from inner membranes we identified a pentameric pore of TonB, as well as the protein-conducting channel SecYEG in association with F1FO adenosine triphosphate (ATP) synthase. Intact mitochondrial membranes from Bos taurus yielded respiratory complexes and fatty acid-bound dimers of the ADP (adenosine diphosphate)/ATP translocase (ANT-1). These results highlight the importance of native membrane environments for retaining small-molecule binding, subunit interactions, and associated chaperones of the membrane proteome.
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Affiliation(s)
- Dror S Chorev
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
| | - Lindsay A Baker
- Division of Structural Biology, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK
| | - Di Wu
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
| | - Victoria Beilsten-Edmands
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
| | - Sarah L Rouse
- Department of Life Sciences, Imperial College, London, South Kensington Campus, London SW7 2AZ, UK
| | | | - Chimari Jiko
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Japan
| | - Firdaus Samsudin
- School of Chemistry, University of Southampton, University Road, Southampton SO17 1BJ, UK
| | - Christoph Gerle
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
- Core Research for Evolutional Science and Technology, Japan and Science and Technology Agency, Kawaguchi, Japan
| | - Syma Khalid
- School of Chemistry, University of Southampton, University Road, Southampton SO17 1BJ, UK
| | - Alastair G Stewart
- Molecular, Structural and Computational Biology Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia
- Faculty of Medicine, The University of New South Wales, Sydney, NSW, Australia
| | - Stephen J Matthews
- Department of Life Sciences, Imperial College, London, South Kensington Campus, London SW7 2AZ, UK
| | - Kay Grünewald
- Division of Structural Biology, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK
- Centre of Structural Systems Biology (CSSB), Notkestr. 85, D-22607, Heinrich-Pette Institute/University of Hamburg, Hamburg, Germany
| | - Carol V Robinson
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK.
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21
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Woznicka-Misaila A, Juillan-Binard C, Baud D, Pebay-Peyroula E, Ravaud S. Cell-free production, purification and characterization of human mitochondrial ADP/ATP carriers. Protein Expr Purif 2017; 144:46-54. [PMID: 29217202 DOI: 10.1016/j.pep.2017.11.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 11/17/2017] [Accepted: 11/29/2017] [Indexed: 11/17/2022]
Abstract
Mitochondrial Carriers (MCs) are responsible for fluent traffic of a variety of compounds that need to be shuttled via mitochondrial inner membranes to maintain cell metabolism. The ADP/ATP Carriers (AACs) are responsible for the import of ADP inside the mitochondria and the export of newly synthesized ATP. In human, four different AACs isoforms are described which are expressed in tissue-specific manner. They are involved in different genetic diseases and play a role in cancerogenesis. Up to now only the structures of the bovine (isoform 1) and yeast (isoforms 2 and 3) AAC have been determined in one particular conformation, obtained in complex with the CATR inhibitor. Herein, we report that full-length human ADP/ATP Carriers isoform 1 and 3 were successfully expressed in cell-free system and purified in milligram amounts in detergent-solubilized state. The proteins exhibited the expected secondary structure content. Thermostability profiles showing stabilization by the CATR inhibitor suggest that the carriers are well folded.
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Affiliation(s)
| | - Céline Juillan-Binard
- Univ. Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France
| | - Delphine Baud
- Univ. Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France
| | - Eva Pebay-Peyroula
- Univ. Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France
| | - Stéphanie Ravaud
- Univ. Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France.
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22
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Writzl K, Maver A, Kovačič L, Martinez-Valero P, Contreras L, Satrustegui J, Castori M, Faivre L, Lapunzina P, van Kuilenburg ABP, Radović S, Thauvin-Robinet C, Peterlin B, Del Arco A, Hennekam RC. De Novo Mutations in SLC25A24 Cause a Disorder Characterized by Early Aging, Bone Dysplasia, Characteristic Face, and Early Demise. Am J Hum Genet 2017; 101:844-855. [PMID: 29100094 PMCID: PMC5673633 DOI: 10.1016/j.ajhg.2017.09.017] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 09/19/2017] [Indexed: 12/21/2022] Open
Abstract
A series of simplex cases have been reported under various diagnoses sharing early aging, especially evident in congenitally decreased subcutaneous fat tissue and sparse hair, bone dysplasia of the skull and fingers, a distinctive facial gestalt, and prenatal and postnatal growth retardation. For historical reasons, we suggest naming the entity Fontaine syndrome. Exome sequencing of four unrelated affected individuals showed that all carried the de novo missense variant c.649C>T (p.Arg217Cys) or c.650G>A (p.Arg217His) in SLC25A24, a solute carrier 25 family member coding for calcium-binding mitochondrial carrier protein (SCaMC-1, also known as SLC25A24). SLC25A24 allows an electro-neutral and reversible exchange of ATP-Mg and phosphate between the cytosol and mitochondria, which is required for maintaining optimal adenine nucleotide levels in the mitochondrial matrix. Molecular dynamic simulation studies predict that p.Arg217Cys and p.Arg217His narrow the substrate cavity of the protein and disrupt transporter dynamics. SLC25A24-mutant fibroblasts and cells expressing p.Arg217Cys or p.Arg217His variants showed altered mitochondrial morphology, a decreased proliferation rate, increased mitochondrial membrane potential, and decreased ATP-linked mitochondrial oxygen consumption. The results suggest that the SLC25A24 mutations lead to impaired mitochondrial ATP synthesis and cause hyperpolarization and increased proton leak in association with an impaired energy metabolism. Our findings identify SLC25A24 mutations affecting codon 217 as the underlying genetic cause of human progeroid Fontaine syndrome.
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Affiliation(s)
- Karin Writzl
- Clinical Institute of Medical Genetics, University Medical Centre, 1000 Ljubljana, Slovenia.
| | - Ales Maver
- Clinical Institute of Medical Genetics, University Medical Centre, 1000 Ljubljana, Slovenia
| | - Lidija Kovačič
- Novartis Ireland Ltd., Novartis, Vista Building, Elm Business Park, D04A9N6 Dublin 4, Ireland
| | - Paula Martinez-Valero
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid and Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; Instituto de Investigación Sanitaria Fundación Jiménez Diaz, 28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, 28049 Madrid, Spain
| | - Laura Contreras
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid and Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; Instituto de Investigación Sanitaria Fundación Jiménez Diaz, 28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, 28049 Madrid, Spain
| | - Jorgina Satrustegui
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid and Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; Instituto de Investigación Sanitaria Fundación Jiménez Diaz, 28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, 28049 Madrid, Spain
| | - Marco Castori
- Division of Medical Genetics, Casa Sollievo della Sofferenza, Istituto di Ricovero e Cura a Carattere Scientifico, 71013 San Giovanni Rotondo, Foggia, Italy
| | - Laurence Faivre
- Centre de Référence Maladies Rares "cAnomalies du Développement et Syndromes Malformatifsc," Centre de Génétique, FHU-TRANSLAD, Hôpital d'Enfants, Centre Hospitalier Universitaire Dijon Bourgogne, 21079 Dijon, France; UMR 1231, Génétique des Anomalies du Développement, INSERM, Université de Bourgogne Franche-Comté, 21079 Dijon, France
| | - Pablo Lapunzina
- Instituto de Genética Médica y Molecular-IdiPAZ, Hospital Universitario La Paz, Centro de Investigación Biomédica en Red de Enfermedades Raras, 261-28046 Madrid, Spain
| | - André B P van Kuilenburg
- Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands
| | | | - Christel Thauvin-Robinet
- Centre de Référence Maladies Rares "cAnomalies du Développement et Syndromes Malformatifsc," Centre de Génétique, FHU-TRANSLAD, Hôpital d'Enfants, Centre Hospitalier Universitaire Dijon Bourgogne, 21079 Dijon, France; UMR 1231, Génétique des Anomalies du Développement, INSERM, Université de Bourgogne Franche-Comté, 21079 Dijon, France
| | - Borut Peterlin
- Clinical Institute of Medical Genetics, University Medical Centre, 1000 Ljubljana, Slovenia
| | - Araceli Del Arco
- Instituto de Investigación Sanitaria Fundación Jiménez Diaz, 28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, 28049 Madrid, Spain; Facultad de Ciencias Ambientales y Bioquímica, Centro Regional de Investigaciones Biomédicas, Universidad de Castilla la Mancha, 45071-Toledo, Spain
| | - Raoul C Hennekam
- Department of Pediatrics, Academic Medical Center, University of Amsterdam, 1105AZ Amsterdam, the Netherlands
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23
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Dallabona C, Baruffini E, Goffrini P, Lodi T. Dominance of yeast aac2 R96H and aac2 R252G mutations, equivalent to pathological mutations in ant1, is due to gain of function. Biochem Biophys Res Commun 2017; 493:909-913. [PMID: 28947214 DOI: 10.1016/j.bbrc.2017.09.122] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 09/21/2017] [Indexed: 01/20/2023]
Abstract
The mitochondrial ADP/ATP carrier is a nuclear encoded protein, which catalyzes the exchange of ATP generated in mitochondria with ADP produced in the cytosol. In humans, mutations in the major ADP/ATP carrier gene, ANT1, are involved in several degenerative mitochondrial pathologies, leading to instability of mitochondrial DNA. Recessive mutations have been associated with mitochondrial myopathy and cardiomyopathy whereas dominant mutations have been associated with autosomal dominant Progressive External Ophtalmoplegia (adPEO). Recently, two de novo dominant mutations, R80H and R235G, leading to extremely severe symptoms, have been identified. In order to evaluate if the dominance is due to haploinsufficiency or to a gain of function, the two mutations have been introduced in the equivalent positions of the AAC2 gene, the yeast orthologue of human ANT1, and their dominant effect has been studied in heteroallelic strains, containing both one copy of wild type AAC2 and one copy of mutant aac2 allele. Through phenotypic characterization of these yeast models we showed that the OXPHOS phenotypes in the heteroallelic strains were more affected than in the hemiallelic strain indicating that the dominant trait of the two mutations is due to gain of function.
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Affiliation(s)
- Cristina Dallabona
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | - Enrico Baruffini
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | - Paola Goffrini
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
| | - Tiziana Lodi
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy.
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24
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Heiske M, Letellier T, Klipp E. Comprehensive mathematical model of oxidative phosphorylation valid for physiological and pathological conditions. FEBS J 2017. [PMID: 28646582 DOI: 10.1111/febs.14151] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We developed a mathematical model of oxidative phosphorylation (OXPHOS) that allows for a precise description of mitochondrial function with respect to the respiratory flux and the ATP production. The model reproduced flux-force relationships under various experimental conditions (state 3 and 4, uncoupling, and shortage of respiratory substrate) as well as time courses, exhibiting correct P/O ratios. The model was able to reproduce experimental threshold curves for perturbations of the respiratory chain complexes, the F1 F0 -ATP synthase, the ADP/ATP carrier, the phosphate/OH carrier, and the proton leak. Thus, the model is well suited to study complex interactions within the OXPHOS system, especially with respect to physiological adaptations or pathological modifications, influencing substrate and product affinities or maximal catalytic rates. Moreover, it could be a useful tool to study the role of OXPHOS and its capacity to compensate or enhance physiopathologies of the mitochondrial and cellular energy metabolism.
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Affiliation(s)
- Margit Heiske
- Laboratoire d'Anthropologie Moléculaire et Imaginérie de Synthèse, Médecine Evolutive, UMR 5288 CNRS, Faculté de Médecine, Université de Toulouse, France.,Theoretische Biophysik, Institut für Biologie, Humboldt-Universität zu Berlin, Germany
| | - Thierry Letellier
- Laboratoire d'Anthropologie Moléculaire et Imaginérie de Synthèse, Médecine Evolutive, UMR 5288 CNRS, Faculté de Médecine, Université de Toulouse, France
| | - Edda Klipp
- Theoretische Biophysik, Institut für Biologie, Humboldt-Universität zu Berlin, Germany
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25
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Crichton PG, Lee Y, Kunji ERS. The molecular features of uncoupling protein 1 support a conventional mitochondrial carrier-like mechanism. Biochimie 2017; 134:35-50. [PMID: 28057583 PMCID: PMC5395090 DOI: 10.1016/j.biochi.2016.12.016] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 12/24/2016] [Indexed: 12/14/2022]
Abstract
Uncoupling protein 1 (UCP1) is an integral membrane protein found in the mitochondrial inner membrane of brown adipose tissue, and facilitates the process of non-shivering thermogenesis in mammals. Its activation by fatty acids, which overcomes its inhibition by purine nucleotides, leads to an increase in the proton conductance of the inner mitochondrial membrane, short-circuiting the mitochondrion to produce heat rather than ATP. Despite 40 years of intense research, the underlying molecular mechanism of UCP1 is still under debate. The protein belongs to the mitochondrial carrier family of transporters, which have recently been shown to utilise a domain-based alternating-access mechanism, cycling between a cytoplasmic and matrix state to transport metabolites across the inner membrane. Here, we review the protein properties of UCP1 and compare them to those of mitochondrial carriers. UCP1 has the same structural fold as other mitochondrial carriers and, in contrast to past claims, is a monomer, binding one purine nucleotide and three cardiolipin molecules tightly. The protein has a single substrate binding site, which is similar to those of the dicarboxylate and oxoglutarate carriers, but also contains a proton binding site and several hydrophobic residues. As found in other mitochondrial carriers, UCP1 has two conserved salt bridge networks on either side of the central cavity, which regulate access to the substrate binding site in an alternating way. The conserved domain structures and mobile inter-domain interfaces are consistent with an alternating access mechanism too. In conclusion, UCP1 has retained all of the key features of mitochondrial carriers, indicating that it operates by a conventional carrier-like mechanism.
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Affiliation(s)
- Paul G Crichton
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
| | - Yang Lee
- Laboratory of Molecular Biology, Medical Research Council, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Edmund R S Kunji
- Mitochondrial Biology Unit, Medical Research Council, Cambridge Biomedical Campus, Wellcome Trust, MRC Building, Hills Road, Cambridge CB2 0XY, United Kingdom.
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26
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Hedger G, Rouse SL, Domański J, Chavent M, Koldsø H, Sansom MSP. Lipid-Loving ANTs: Molecular Simulations of Cardiolipin Interactions and the Organization of the Adenine Nucleotide Translocase in Model Mitochondrial Membranes. Biochemistry 2016; 55:6238-6249. [PMID: 27786441 PMCID: PMC5120876 DOI: 10.1021/acs.biochem.6b00751] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
![]()
The exchange of ADP
and ATP across the inner mitochondrial membrane
is a fundamental cellular process. This exchange is facilitated by
the adenine nucleotide translocase, the structure and function of
which are critically dependent on the signature phospholipid of mitochondria,
cardiolipin (CL). Here we employ multiscale molecular dynamics simulations
to investigate CL interactions within a membrane environment. Using
simulations at both coarse-grained and atomistic resolutions, we identify
three CL binding sites on the translocase, in agreement with those
seen in crystal structures and inferred from nuclear magnetic resonance
measurements. Characterization of the free energy landscape for lateral
lipid interaction via potential of mean force calculations demonstrates
the strength of interaction compared to those of binding sites on
other mitochondrial membrane proteins, as well as their selectivity
for CL over other phospholipids. Extending the analysis to other members
of the family, yeast Aac2p and mouse uncoupling protein 2, suggests
a degree of conservation. Simulation of large patches of a model mitochondrial
membrane containing multiple copies of the translocase shows that
CL interactions persist in the presence of protein–protein
interactions and suggests CL may mediate interactions between translocases.
This study provides a key example of how computational microscopy
may be used to shed light on regulatory lipid–protein interactions.
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Affiliation(s)
- George Hedger
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K
| | - Sarah L Rouse
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K.,Department of Life Sciences, Imperial College London , London SW7 2AZ, U.K
| | - Jan Domański
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K
| | - Matthieu Chavent
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K
| | - Heidi Koldsø
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K.,D. E. Shaw Research , 120 West 45th Street, 39th Floor, New York, New York 10036, United States
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, U.K
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27
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Thompson K, Majd H, Dallabona C, Reinson K, King MS, Alston CL, He L, Lodi T, Jones SA, Fattal-Valevski A, Fraenkel ND, Saada A, Haham A, Isohanni P, Vara R, Barbosa IA, Simpson MA, Deshpande C, Puusepp S, Bonnen PE, Rodenburg RJ, Suomalainen A, Õunap K, Elpeleg O, Ferrero I, McFarland R, Kunji ERS, Taylor RW. Recurrent De Novo Dominant Mutations in SLC25A4 Cause Severe Early-Onset Mitochondrial Disease and Loss of Mitochondrial DNA Copy Number. Am J Hum Genet 2016; 99:860-876. [PMID: 27693233 PMCID: PMC5065686 DOI: 10.1016/j.ajhg.2016.08.014] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 08/18/2016] [Indexed: 11/26/2022] Open
Abstract
Mutations in SLC25A4 encoding the mitochondrial ADP/ATP carrier AAC1 are well-recognized causes of mitochondrial disease. Several heterozygous SLC25A4 mutations cause adult-onset autosomal-dominant progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions, whereas recessive SLC25A4 mutations cause childhood-onset mitochondrial myopathy and cardiomyopathy. Here, we describe the identification by whole-exome sequencing of seven probands harboring dominant, de novo SLC25A4 mutations. All affected individuals presented at birth, were ventilator dependent and, where tested, revealed severe combined mitochondrial respiratory chain deficiencies associated with a marked loss of mitochondrial DNA copy number in skeletal muscle. Strikingly, an identical c.239G>A (p.Arg80His) mutation was present in four of the seven subjects, and the other three case subjects harbored the same c.703C>G (p.Arg235Gly) mutation. Analysis of skeletal muscle revealed a marked decrease of AAC1 protein levels and loss of respiratory chain complexes containing mitochondrial DNA-encoded subunits. We show that both recombinant AAC1 mutant proteins are severely impaired in ADP/ATP transport, affecting most likely the substrate binding and mechanics of the carrier, respectively. This highly reduced capacity for transport probably affects mitochondrial DNA maintenance and in turn respiration, causing a severe energy crisis. The confirmation of the pathogenicity of these de novo SLC25A4 mutations highlights a third distinct clinical phenotype associated with mutation of this gene and demonstrates that early-onset mitochondrial disease can be caused by recurrent de novo mutations, which has significant implications for the application and analysis of whole-exome sequencing data in mitochondrial disease.
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Affiliation(s)
- Kyle Thompson
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Homa Majd
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Cristina Dallabona
- Department of Life Sciences, University of Parma, Parco Area delle Scienze 11A, Parma 43124, Italy
| | - Karit Reinson
- Department of Pediatrics, Institute of Clinical Medicine, University of Tartu, 51014 Tartu, Estonia; Department of Genetics, United Laboratories, Tartu University Hospital, 51014 Tartu, Estonia
| | - Martin S King
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Charlotte L Alston
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Langping He
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Tiziana Lodi
- Department of Life Sciences, University of Parma, Parco Area delle Scienze 11A, Parma 43124, Italy
| | - Simon A Jones
- Manchester Centre for Genomic Medicine, Central Manchester University Hospitals NHS Foundation Trust, St Marys Hospital, Oxford Road, Manchester M13 9WL, UK
| | - Aviva Fattal-Valevski
- Paediatric Neurology Unit, "Dana" Children Hospital, Tel Aviv Sourasky Medical Centre, Sackler Faculty of Medicine, Tel Aviv University, 64239 Tel Aviv, Israel
| | - Nitay D Fraenkel
- Department of Respiratory Rehabilitation, Alyn Hospital, Jerusalem 91090, Israel
| | - Ann Saada
- Metabolic Laboratory Department of Genetics and Metabolic Diseases, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel
| | - Alon Haham
- Neonatal Intensive Care Unit, "Lis" Maternity Hospital, Tel Aviv Sourasky Medical Centre, 64239 Tel Aviv, Israel
| | - Pirjo Isohanni
- Research Programs Unit, Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, 00290 Helsinki, Finland; Department of Pediatric Neurology, Children's Hospital, Helsinki University Hospital and University of Helsinki, 00290 Helsinki, Finland
| | - Roshni Vara
- Department of Paediatric Inherited Metabolic Diseases, Evelina Children's Hospital, London SE1 7EH, UK
| | - Inês A Barbosa
- Division of Genetics and Molecular Medicine, King's College London School of Medicine, London SE1 9RY, UK
| | - Michael A Simpson
- Division of Genetics and Molecular Medicine, King's College London School of Medicine, London SE1 9RY, UK
| | - Charu Deshpande
- Clinical Genetics Unit, Guys and St Thomas' NHS Foundation Trust, London SE1 9RT, UK
| | - Sanna Puusepp
- Department of Pediatrics, Institute of Clinical Medicine, University of Tartu, 51014 Tartu, Estonia; Department of Genetics, United Laboratories, Tartu University Hospital, 51014 Tartu, Estonia
| | - Penelope E Bonnen
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Richard J Rodenburg
- Radboud Center for Mitochondrial Medicine, Department of Paediatrics, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands
| | - Anu Suomalainen
- Research Programs Unit, Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, 00290 Helsinki, Finland; Department of Neurosciences, Helsinki University Hospital and University of Helsinki, 00290 Helsinki, Finland
| | - Katrin Õunap
- Department of Pediatrics, Institute of Clinical Medicine, University of Tartu, 51014 Tartu, Estonia; Department of Genetics, United Laboratories, Tartu University Hospital, 51014 Tartu, Estonia
| | - Orly Elpeleg
- The Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel
| | - Ileana Ferrero
- Department of Life Sciences, University of Parma, Parco Area delle Scienze 11A, Parma 43124, Italy
| | - Robert McFarland
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Edmund R S Kunji
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Robert W Taylor
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
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28
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An Evolutionary Framework for Understanding the Origin of Eukaryotes. BIOLOGY 2016; 5:biology5020018. [PMID: 27128953 PMCID: PMC4929532 DOI: 10.3390/biology5020018] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2016] [Revised: 04/15/2016] [Accepted: 04/25/2016] [Indexed: 12/12/2022]
Abstract
Two major obstacles hinder the application of evolutionary theory to the origin of eukaryotes. The first is more apparent than real-the endosymbiosis that led to the mitochondrion is often described as "non-Darwinian" because it deviates from the incremental evolution championed by the modern synthesis. Nevertheless, endosymbiosis can be accommodated by a multi-level generalization of evolutionary theory, which Darwin himself pioneered. The second obstacle is more serious-all of the major features of eukaryotes were likely present in the last eukaryotic common ancestor thus rendering comparative methods ineffective. In addition to a multi-level theory, the development of rigorous, sequence-based phylogenetic and comparative methods represents the greatest achievement of modern evolutionary theory. Nevertheless, the rapid evolution of major features in the eukaryotic stem group requires the consideration of an alternative framework. Such a framework, based on the contingent nature of these evolutionary events, is developed and illustrated with three examples: the putative intron proliferation leading to the nucleus and the cell cycle; conflict and cooperation in the origin of eukaryotic bioenergetics; and the inter-relationship between aerobic metabolism, sterol synthesis, membranes, and sex. The modern synthesis thus provides sufficient scope to develop an evolutionary framework to understand the origin of eukaryotes.
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29
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Del Arco A, Contreras L, Pardo B, Satrustegui J. Calcium regulation of mitochondrial carriers. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:2413-21. [PMID: 27033520 DOI: 10.1016/j.bbamcr.2016.03.024] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Revised: 03/23/2016] [Accepted: 03/23/2016] [Indexed: 11/16/2022]
Abstract
Mitochondrial function is regulated by calcium. In addition to the long known effects of matrix Ca(2+), regulation of metabolite transport by extramitochondrial Ca(2+) represents an alternative Ca(2+)-dependent mechanism to regulate mitochondrial function. The Ca(2+) regulated mitochondrial transporters (CaMCs) are well suited for that role, as they contain long N-terminal extensions harboring EF-hand Ca(2+) binding domains facing the intermembrane space. They fall in two groups, the aspartate/glutamate exchangers, AGCs, major components of the NADH malate aspartate shuttle (MAS) and urea cycle, and the ATP-Mg(2+)/Pi exchangers or short CaMCs (APCs or SCaMCs). The AGCs are activated by relatively low Ca(2+) levels only slightly higher than resting Ca(2+), whereas all SCaMCs studied so far require strong Ca(2+) signals, above micromolar, for activation. In addition, AGCs are not strictly Ca(2+) dependent, being active even in Ca(2+)-free conditions. Thus, AGCs are well suited to respond to small Ca(2+) signals and that do not reach mitochondria. In contrast, ATP-Mg(2+)/Pi carriers are inactive in Ca(2+) free conditions and activation requires Ca(2+) signals that will also activate the calcium uniporter (MCU). By changing the net content of adenine nucleotides of the matrix upon activation, SCaMCs regulate the activity of the permeability transition pore, and the Ca(2+) retention capacity of mitochondria (CRC), two functions synergizing with those of the MCU. The different Ca(2+) activation properties of the two CaMCs are discussed in relation to their newly obtained structures. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.
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Affiliation(s)
- Araceli Del Arco
- Facultad de Ciencias Ambientales y Bioquímica, Centro RegionaI de Investigaciones Biomédicas, Universidad de Castilla la Mancha, Toledo 45071, Spain; CIBER de Enfermedades Raras (CIBERER), ISCIII, Madrid, Spain; Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain
| | - Laura Contreras
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; CIBER de Enfermedades Raras (CIBERER), ISCIII, Madrid, Spain; Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain
| | - Beatriz Pardo
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; CIBER de Enfermedades Raras (CIBERER), ISCIII, Madrid, Spain; Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain
| | - Jorgina Satrustegui
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; CIBER de Enfermedades Raras (CIBERER), ISCIII, Madrid, Spain; Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain.
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30
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The transport mechanism of the mitochondrial ADP/ATP carrier. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:2379-93. [PMID: 27001633 DOI: 10.1016/j.bbamcr.2016.03.015] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 03/15/2016] [Accepted: 03/16/2016] [Indexed: 12/18/2022]
Abstract
The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix, which are key transport steps for oxidative phosphorylation in eukaryotic organisms. The transport protein belongs to the mitochondrial carrier family, a large transporter family in the inner membrane of mitochondria. It is one of the best studied members of the family and serves as a paradigm for the molecular mechanism of mitochondrial carriers. Structurally, the carrier consists of three homologous domains, each composed of two transmembrane α-helices linked with a loop and short α-helix on the matrix side. The transporter cycles between a cytoplasmic and matrix state in which a central substrate binding site is alternately accessible to these compartments for binding of ADP or ATP. On both the cytoplasmic and matrix side of the carrier are networks consisting of three salt bridges each. In the cytoplasmic state, the matrix salt bridge network is formed and the cytoplasmic network is disrupted, opening the central substrate binding site to the intermembrane space and cytosol, whereas the converse occurs in the matrix state. In the transport cycle, tighter substrate binding in the intermediate states allows the interconversion of conformations by lowering the energy barrier for disruption and formation of these networks, opening and closing the carrier to either side of the membrane in an alternating way. Conversion between cytoplasmic and matrix states might require the simultaneous rotation of three domains around a central translocation pathway, constituting a unique mechanism among transport proteins. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.
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31
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Liu QN, Chai XY, Tu J, Xin ZZ, Li CF, Jiang SH, Zhou CL, Tang BP. An adenine nucleotide translocase (ANT) gene from Apostichopus japonicus; molecular cloning and expression analysis in response to lipopolysaccharide (LPS) challenge and thermal stress. FISH & SHELLFISH IMMUNOLOGY 2016; 49:16-23. [PMID: 26706223 DOI: 10.1016/j.fsi.2015.12.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 12/12/2015] [Accepted: 12/14/2015] [Indexed: 06/05/2023]
Abstract
The adenine nucleotide translocases (ANTs) play a vital role in energy metabolism via ADP/ATP exchange in eukaryotic cells. Apostichopus japonicus (Echinodermata: Holothuroidea) is an important economic species in China. Here, a cDNA representing an ANT gene of A. japonicus was isolated and characterized from respiratory tree and named AjANT. The full-length AjANT cDNA is 1924 bp, including a 5'-untranslated region (UTR) of 38 bp, 3'-UTR of 980 bp and an open reading frame (ORF) of 906 bp encoding a polypeptide of 301 amino acids. The protein contains three homologous repeat Mito_carr domains (Pfam00153). The deduced AjANT protein sequence has 49-81% in comparison to ANT proteins from other individuals. The predicted tertiary structure of AjANT protein is highly similar to animal ANT proteins. Phylogenetic analysis showed that the AjANT is closely related to Holothuroidea ANT genes. Real-time quantitative reverse transcription-PCR (qPCR) analysis showed that AjANT expression is higher in the respiratory tree than in other examined tissues. After thermal stress or LPS challenge, expression of AjANT was significantly fluctuant compared to the control. These results suggested that changes in the expression of ANT gene might be involved in immune defense and in protecting A. japonicus against thermal stress.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Cloning, Molecular
- DNA, Complementary/genetics
- DNA, Complementary/metabolism
- Gene Expression Profiling
- Gene Expression Regulation/drug effects
- Hot Temperature
- Immunity, Innate/drug effects
- Lipopolysaccharides/pharmacology
- Mitochondrial ADP, ATP Translocases/chemistry
- Mitochondrial ADP, ATP Translocases/genetics
- Mitochondrial ADP, ATP Translocases/metabolism
- Molecular Sequence Data
- Phylogeny
- Protein Structure, Tertiary
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Alignment
- Stichopus/genetics
- Stichopus/immunology
- Stichopus/metabolism
- Tissue Distribution
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Affiliation(s)
- Qiu-Ning Liu
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Xin-Yue Chai
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Jie Tu
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Zhao-Zhe Xin
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Chao-Feng Li
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Sen-Hao Jiang
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China.
| | - Chun-Lin Zhou
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China
| | - Bo-Ping Tang
- Jiangsu Key Laboratory for Bioresources of Saline Soils, Jiangsu Synthetic Innovation Center for Coastal Bio-agriculture, Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources and Environmental Protection, School of Ocean and Biological Engineering, Yancheng Teachers University, Yancheng, 224051, PR China.
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32
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Complex formation and turnover of mitochondrial transporters and ion channels. J Bioenerg Biomembr 2016; 49:101-111. [DOI: 10.1007/s10863-016-9648-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 01/19/2016] [Indexed: 02/07/2023]
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33
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Seigneurin-Berny D, King MS, Sautron E, Moyet L, Catty P, André F, Rolland N, Kunji ERS, Frelet-Barrand A. Membrane Protein Production in Lactococcus lactis for Functional Studies. Methods Mol Biol 2016; 1432:79-101. [PMID: 27485331 DOI: 10.1007/978-1-4939-3637-3_6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Due to their unique properties, expression and study of membrane proteins in heterologous systems remains difficult. Among the bacterial systems available, the Gram-positive lactic bacterium, Lactococcus lactis, traditionally used in food fermentations, is nowadays widely used for large-scale production and functional characterization of bacterial and eukaryotic membrane proteins. The aim of this chapter is to describe the different possibilities for the functional characterization of peripheral or intrinsic membrane proteins expressed in Lactococcus lactis.
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Affiliation(s)
- Daphne Seigneurin-Berny
- Laboratoire de Physiologie Cellulaire et Végétale, CNRS (UMR-5168)/CEA/INRA (UMR1417)/Université Grenoble Alpes, BIG, CEA, Grenoble, France
| | - Martin S King
- Medical Research Council, Mitochondrial Biology Unit, Hills Road, Cambridge, CB2 2XY, UK
| | - Emiline Sautron
- Laboratoire de Physiologie Cellulaire et Végétale, CNRS (UMR-5168)/CEA/INRA (UMR1417)/Université Grenoble Alpes, BIG, CEA, Grenoble, France
| | - Lucas Moyet
- Laboratoire de Physiologie Cellulaire et Végétale, CNRS (UMR-5168)/CEA/INRA (UMR1417)/Université Grenoble Alpes, BIG, CEA, Grenoble, France
| | - Patrice Catty
- Laboratoire de Chimie et Biologie des Métaux, CNRS (UMR-5249)/CEA/Université Grenoble Alpes, BIG, CEA, Grenoble, France
| | - François André
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris Saclay, Gif-sur-Yvette, France
| | - Norbert Rolland
- Laboratoire de Physiologie Cellulaire et Végétale, CNRS (UMR-5168)/CEA/INRA (UMR1417)/Université Grenoble Alpes, BIG, CEA, Grenoble, France
| | - Edmund R S Kunji
- Medical Research Council, Mitochondrial Biology Unit, Hills Road, Cambridge, CB2 2XY, UK
| | - Annie Frelet-Barrand
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris Saclay, Gif-sur-Yvette, France. .,FEMTO-ST Institute, UMR CNRS 6174, University of Bourgogne Franche-Comte, Besançon, France.
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34
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King MS, Kerr M, Crichton PG, Springett R, Kunji ERS. Formation of a cytoplasmic salt bridge network in the matrix state is a fundamental step in the transport mechanism of the mitochondrial ADP/ATP carrier. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:14-22. [PMID: 26453935 PMCID: PMC4674015 DOI: 10.1016/j.bbabio.2015.09.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2015] [Revised: 09/15/2015] [Accepted: 09/30/2015] [Indexed: 02/02/2023]
Abstract
Mitochondrial ADP/ATP carriers catalyze the equimolar exchange of ADP and ATP across the mitochondrial inner membrane. Structurally, they consist of three homologous domains with a single substrate binding site. They alternate between a cytoplasmic and matrix state in which the binding site is accessible to these compartments for binding of ADP or ATP. It has been proposed that cycling between states occurs by disruption and formation of a matrix and cytoplasmic salt bridge network in an alternating way, but formation of the latter has not been shown experimentally. Here, we show that state-dependent formation of the cytoplasmic salt bridge network can be demonstrated by measuring the effect of mutations on the thermal stability of detergent-solubilized carriers locked in a specific state. For this purpose, mutations were made to increase or decrease the overall interaction energy of the cytoplasmic network. When locked in the cytoplasmic state by the inhibitor carboxyatractyloside, the thermostabilities of the mutant and wild-type carriers were similar, but when locked in the matrix state by the inhibitor bongkrekic acid, they correlated with the predicted interaction energy of the cytoplasmic network, demonstrating its formation. Changing the interaction energy of the cytoplasmic network also had a profound effect on the kinetics of transport, indicating that formation of the network is a key step in the transport cycle. These results are consistent with a unique alternating access mechanism that involves the simultaneous rotation of the three domains around a central translocation pathway. Mitochondrial ADP/ATP carriers alternate between the matrix and cytoplasmic state. Matrix and cytoplasmic salt bridge networks regulate access to central binding site. Thermostability assays are used to probe state-dependent interactions in carriers. Cytoplasmic salt bridge network mutations only affect matrix state thermostability. Formation of the cytoplasmic network is a fundamental step in the transport cycle.
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Affiliation(s)
- Martin S King
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
| | - Matthew Kerr
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
| | - Paul G Crichton
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
| | - Roger Springett
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
| | - Edmund R S Kunji
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
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35
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Harborne SPD, Ruprecht JJ, Kunji ERS. Calcium-induced conformational changes in the regulatory domain of the human mitochondrial ATP-Mg/Pi carrier. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1847:1245-53. [PMID: 26164100 PMCID: PMC4562336 DOI: 10.1016/j.bbabio.2015.07.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Revised: 06/15/2015] [Accepted: 07/06/2015] [Indexed: 12/21/2022]
Abstract
The mitochondrial ATP-Mg/Pi carrier imports adenine nucleotides from the cytosol into the mitochondrial matrix and exports phosphate. The carrier is regulated by the concentration of cytosolic calcium, altering the size of the adenine nucleotide pool in the mitochondrial matrix in response to energetic demands. The protein consists of three domains; (i) the N-terminal regulatory domain, which is formed of two pairs of fused calcium-binding EF-hands, (ii) the C-terminal mitochondrial carrier domain, which is involved in transport, and (iii) a linker region with an amphipathic α-helix of unknown function. The mechanism by which calcium binding to the regulatory domain modulates substrate transport in the carrier domain has not been resolved. Here, we present two new crystal structures of the regulatory domain of the human isoform 1. Careful analysis by SEC confirmed that although the regulatory domain crystallised as dimers, full-length ATP-Mg/Pi carrier is monomeric. Therefore, the ATP-Mg/Pi carrier must have a different mechanism of calcium regulation than the architecturally related aspartate/glutamate carrier, which is dimeric. The structure showed that an amphipathic α-helix is bound to the regulatory domain in a hydrophobic cleft of EF-hand 3/4. Detailed bioinformatics analyses of different EF-hand states indicate that upon release of calcium, EF-hands close, meaning that the regulatory domain would release the amphipathic α-helix. We propose a mechanism for ATP-Mg/Pi carriers in which the amphipathic α-helix becomes mobile upon release of calcium and could block the transport of substrates across the mitochondrial inner membrane.
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Affiliation(s)
- Steven P D Harborne
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Jonathan J Ruprecht
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Edmund R S Kunji
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK.
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36
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Uncoupling protein 1 binds one nucleotide per monomer and is stabilized by tightly bound cardiolipin. Proc Natl Acad Sci U S A 2015; 112:6973-8. [PMID: 26038550 DOI: 10.1073/pnas.1503833112] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Uncoupling protein 1 (UCP1) catalyzes fatty acid-activated, purine nucleotide-sensitive proton leak across the mitochondrial inner membrane of brown adipose tissue to produce heat, and could help combat obesity and metabolic disease in humans. Studies over the last 30 years conclude that the protein is a dimer, binding one nucleotide molecule per two proteins, and unlike the related mitochondrial ADP/ATP carrier, does not bind cardiolipin. Here, we have developed novel methods to purify milligram amounts of UCP1 from native sources by using covalent chromatography that, unlike past methods, allows the protein to be prepared in defined conditions, free of excess detergent and lipid. Assessment of purified preparations by TLC reveal that UCP1 retains tightly bound cardiolipin, with a lipid phosphorus content equating to three molecules per protein, like the ADP/ATP carrier. Cardiolipin stabilizes UCP1, as demonstrated by reconstitution experiments and thermostability assays, indicating that the lipid has an integral role in the functioning of the protein, similar to other mitochondrial carriers. Furthermore, we find that UCP1 is not dimeric but monomeric, as indicated by size exclusion analysis, and has a ligand titration profile in isothermal calorimetric measurements that clearly shows that one nucleotide binds per monomer. These findings reveal the fundamental composition of UCP1, which is essential for understanding the mechanism of the protein. Our assessment of the properties of UCP1 indicate that it is not unique among mitochondrial carriers and so is likely to use a common exchange mechanism in its primary function in brown adipose tissue mitochondria.
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Liu Y, Wang X, Chen XJ. Misfolding of mutant adenine nucleotide translocase in yeast supports a novel mechanism of Ant1-induced muscle diseases. Mol Biol Cell 2015; 26:1985-94. [PMID: 25833713 PMCID: PMC4472010 DOI: 10.1091/mbc.e15-01-0030] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 03/26/2015] [Indexed: 12/17/2022] Open
Abstract
Missense mutations in membrane proteins cause dominant diseases by unknown mechanisms. Pathogenic mutations in adenine nucleotide translocase 1 affect protein folding and the assembly of multiple protein complexes. The misfolding of one single protein is therefore sufficient to induce proteostatic stress on the membrane. Approximately one-third of proteins in the cell reside in the membrane. Mutations in membrane proteins can induce conformational changes and expose nonnative polar domains/residues to the lipid environment. The molecular effect of the resulting membrane stress is poorly defined. Adenine nucleotide translocase 1 (Ant1) is a mitochondrial inner membrane protein involved in ATP/ADP exchange. Missense mutations in the Ant1 isoform cause autosomal dominant progressive external ophthalmoplegia (adPEO), cardiomyopathy, and myopathy. The mechanism of the Ant1-induced pathologies is highly debated. Here we show that equivalent mutations in the yeast Aac2 protein cause protein misfolding. Misfolded Aac2 drastically affects the assembly and stability of multiple protein complexes in the membrane, which ultimately inhibits cell growth. Despite causing similar proteostatic damages, the adPEO- but not the cardiomyopathy/myopathy-type Aac2 proteins form large aggregates. The data suggest that the Ant1-induced diseases belong to protein misfolding disorders. Protein homeostasis is subtly maintained on the mitochondrial inner membrane and can be derailed by the misfolding of one single protein with or without aggregate formation. This finding could have broad implications for understanding other dominant diseases (e.g., retinitis pigmentosa) caused by missense mutations in membrane proteins.
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Affiliation(s)
- Yaxin Liu
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Xiaowen Wang
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Xin Jie Chen
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
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38
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The impact of mitochondrial endosymbiosis on the evolution of calcium signaling. Cell Calcium 2015; 57:133-9. [DOI: 10.1016/j.ceca.2014.11.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 11/06/2014] [Accepted: 11/17/2014] [Indexed: 11/18/2022]
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Crichton PG, Lee Y, Ruprecht JJ, Cerson E, Thangaratnarajah C, King MS, Kunji ERS. Trends in thermostability provide information on the nature of substrate, inhibitor, and lipid interactions with mitochondrial carriers. J Biol Chem 2015; 290:8206-17. [PMID: 25653283 PMCID: PMC4375477 DOI: 10.1074/jbc.m114.616607] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Mitochondrial carriers, including uncoupling proteins, are unstable in detergents, which hampers structural and mechanistic studies. To investigate carrier stability, we have purified ligand-free carriers and assessed their stability with a fluorescence-based thermostability assay that monitors protein unfolding with a thiol-reactive dye. We find that mitochondrial carriers from both mesophilic and thermophilic organisms exhibit poor stability in mild detergents, indicating that instability is inherent to the protein family. Trends in the thermostability of yeast ADP/ATP carrier AAC2 and ovine uncoupling protein UCP1 allow optimal conditions for stability in detergents to be established but also provide mechanistic insights into the interactions of lipids, substrates, and inhibitors with these proteins. Both proteins exhibit similar stability profiles across various detergents, where stability increases with the size of the associated detergent micelle. Detailed analysis shows that lipids stabilize carriers indirectly by increasing the associated detergent micelle size, but cardiolipin stabilizes by direct interactions as well. Cardiolipin reverses destabilizing effects of ADP and bongkrekic acid on AAC2 and enhances large stabilizing effects of carboxyatractyloside, revealing that this lipid interacts in the m-state and possibly other states of the transport cycle, despite being in a dynamic interface. Fatty acid activators destabilize UCP1 in a similar way, which can also be prevented by cardiolipin, indicating that they interact like transport substrates. Our controls show that carriers can be soluble but unfolded in some commonly used detergents, such as the zwitterionic Fos-choline-12, which emphasizes the need for simple validation assays like the one used here.
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Affiliation(s)
- Paul G Crichton
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Yang Lee
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Jonathan J Ruprecht
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Elizabeth Cerson
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Chancievan Thangaratnarajah
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Martin S King
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Edmund R S Kunji
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
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Monné M, Palmieri F. Antiporters of the mitochondrial carrier family. CURRENT TOPICS IN MEMBRANES 2014; 73:289-320. [PMID: 24745987 DOI: 10.1016/b978-0-12-800223-0.00008-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The eukaryotic transport protein family SLC25 consists of mitochondrial carriers (MCs) that are recognized on the sequence level by a threefold repeated and conserved signature motif. The majority of MCs characterized so far catalyzes strict exchanges of substrates across the mitochondrial inner membrane. The substrates are nucleotides, metabolic intermediates, and cofactors that are required in cytoplasmic and matrix metabolism. This review summarizes and discusses the current knowledge of the antiport mechanism(s) of MCs that has been deduced from determining transport characteristics and by analyzing structural, sequence, and mutagenesis data. The mode of transport varies among different MCs with respect to how the substrate translocation depends on the electrical and pH gradients across the mitochondrial inner membrane, for example, the ADP/ATP carrier is electrogenic (electrophoretic), the GTP/GDP carrier is dependent on the pH gradient, the aspartate/glutamate carrier is dependent on both, and the oxoglutarate/malate carrier is independent of them. The structure of the bovine ADP/ATP carrier consists of a six-transmembrane α-helix bundle with a pseudo-threefold symmetry and a closed matrix gate. By using this structure as a template in homology modeling, residues engaged in substrate binding and the formation of a cytoplasmic gate in MCs have been proposed. The functional importance of the residues of the binding site, the matrix, and the cytoplasmic gates is supported by transport activities of different MCs with single point mutations. Cumulative evidence has been used to postulate a general transport mechanism for MCs.
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Affiliation(s)
- Magnus Monné
- Department of Biosciences, Biotechnology and Biopharmaceutics, Laboratory of Biochemistry and Molecular Biology, University of Bari, Bari, Italy; Department of Sciences, University of Basilicata, Potenza, Italy
| | - Ferdinando Palmieri
- Department of Biosciences, Biotechnology and Biopharmaceutics, Laboratory of Biochemistry and Molecular Biology, University of Bari, Bari, Italy.
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Calcium-induced conformational changes of the regulatory domain of human mitochondrial aspartate/glutamate carriers. Nat Commun 2014; 5:5491. [PMID: 25410934 PMCID: PMC4250520 DOI: 10.1038/ncomms6491] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Accepted: 10/06/2014] [Indexed: 12/27/2022] Open
Abstract
The transport activity of human mitochondrial aspartate/glutamate carriers is central to the malate-aspartate shuttle, urea cycle, gluconeogenesis and myelin synthesis. They have a unique three-domain structure, comprising a calcium-regulated N-terminal domain with eight EF-hands, a mitochondrial carrier domain, and a C-terminal domain. Here we present the calcium-bound and calcium-free structures of the N- and C-terminal domains, elucidating the mechanism of calcium regulation. Unexpectedly, EF-hands 4-8 are involved in dimerization of the carrier and form a static unit, whereas EF-hands 1-3 form a calcium-responsive mobile unit. On calcium binding, an amphipathic helix of the C-terminal domain binds to the N-terminal domain, opening a vestibule. In the absence of calcium, the mobile unit closes the vestibule. Opening and closing of the vestibule might regulate access of substrates to the carrier domain, which is involved in their transport. These structures provide a framework for understanding cases of the mitochondrial disease citrin deficiency.
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Giangregorio N, Console L, Tonazzi A, Palmieri F, Indiveri C. Identification of amino acid residues underlying the antiport mechanism of the mitochondrial carnitine/acylcarnitine carrier by site-directed mutagenesis and chemical labeling. Biochemistry 2014; 53:6924-33. [PMID: 25325845 DOI: 10.1021/bi5009112] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The mitochondrial carnitine/acylcarnitine carrier catalyzes the transport of carnitine and acylcarnitines by antiport as well as by uniport with a rate slower than the rate of antiport. The mechanism of antiport resulting from coupling of two opposed uniport reactions was investigated by site-directed mutagenesis. The transport reaction was followed as [(3)H]carnitine uptake in or efflux from proteoliposomes reconstituted with the wild type or mutants, in the presence or absence of a countersubstrate. The ratio between the antiport and uniport rates for the wild type was 3.0 or 2.5, using the uptake or efflux procedure, respectively. This ratio did not vary substantially in mutants H29A, K35R, G121A, E132A, K135A, R178A, D179E, E191A, K194A, K234A, and E288A. A ratio of 1.0 was measured for mutant K35A, indicating a loss of antiport function by this mutant. Ratios of >1.0 but significantly lower than that of the wild type were measured for mutants D32A, K97A, and D231A, indicating the involvement of these residues in the antiport mechanism. To investigate the role of the countersubstrate in the conformational changes underlying the transport reaction, the m-state of the transporter (opened toward the matrix side) was specifically labeled with N-ethylmaleimide while the c-state of the carrier (opened toward the cytosolic side) was labeled with fluorescein maleimide. The labeling results indicated that the addition of an external substrate, on one hand, reduced the amount of protein in the m-state and, on the other, increased the protein fraction in the c-state. This substrate-induced conformational change was abolished in the protein lacking K35, pointing to the role of this residue as a sensor in the mechanism of the antiport reaction.
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Affiliation(s)
- Nicola Giangregorio
- CNR Institute of Biomembranes and Bioenergetics , via Amendola 165/A, 70126 Bari, Italy
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Mehnert CS, Rampelt H, Gebert M, Oeljeklaus S, Schrempp SG, Kochbeck L, Guiard B, Warscheid B, van der Laan M. The mitochondrial ADP/ATP carrier associates with the inner membrane presequence translocase in a stoichiometric manner. J Biol Chem 2014; 289:27352-27362. [PMID: 25124039 DOI: 10.1074/jbc.m114.556498] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The majority of mitochondrial proteins are synthesized with amino-terminal signal sequences. The presequence translocase of the inner membrane (TIM23 complex) mediates the import of these preproteins. The essential TIM23 core complex closely cooperates with partner protein complexes like the presequence translocase-associated import motor and the respiratory chain. The inner mitochondrial membrane also contains a large number of metabolite carriers, but their association with preprotein translocases has been controversial. We performed a comprehensive analysis of the TIM23 interactome based on stable isotope labeling with amino acids in cell culture. Subsequent biochemical studies on identified partner proteins showed that the mitochondrial ADP/ATP carrier associates with the membrane-embedded core of the TIM23 complex in a stoichiometric manner, revealing an unexpected connection of mitochondrial protein biogenesis to metabolite transport. Our data indicate that direct TIM23-AAC coupling may support preprotein import into mitochondria when respiratory activity is low.
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Affiliation(s)
- Carola S Mehnert
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany; Fakultät für Biologie, Universität Freiburg, 79104 Freiburg, Germany
| | - Heike Rampelt
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany
| | - Michael Gebert
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany; Fakultät für Biologie, Universität Freiburg, 79104 Freiburg, Germany
| | - Silke Oeljeklaus
- Institut für Biologie II, Fakultät für Biologie, Funktionelle Proteomik, and Universität Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signaling Studies, Universität Freiburg, 79104 Freiburg, Germany and
| | - Sandra G Schrempp
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany; Fakultät für Biologie, Universität Freiburg, 79104 Freiburg, Germany
| | - Lioba Kochbeck
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany
| | - Bernard Guiard
- Centre de Génétique Moléculaire, CNRS, 91190 Gif-sur-Yvette, France
| | - Bettina Warscheid
- Institut für Biologie II, Fakultät für Biologie, Funktionelle Proteomik, and Universität Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signaling Studies, Universität Freiburg, 79104 Freiburg, Germany and
| | - Martin van der Laan
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signaling Studies, Universität Freiburg, 79104 Freiburg, Germany and.
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Abstract
The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.
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Koshy C, Ziegler C. Structural insights into functional lipid-protein interactions in secondary transporters. Biochim Biophys Acta Gen Subj 2014; 1850:476-87. [PMID: 24859688 DOI: 10.1016/j.bbagen.2014.05.010] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 05/09/2014] [Accepted: 05/12/2014] [Indexed: 12/22/2022]
Abstract
BACKGROUND Structural evidences with functional corroborations have revealed distinct features of lipid-protein interactions especially in channels and receptors. Many membrane embedded transporters are also known to require specific lipids for their functions and for some of them cellular and biochemical data suggest tight regulation by the lipid bilayer. However, molecular details on lipid-protein interactions in transporters are sparse since lipids are either depleted from the detergent solubilized transporters in three-dimensional crystals or not readily resolved in crystal structures. Nevertheless the steady increase in the progress of transporter structure determination contributed more examples of structures with resolved lipids. SCOPE OF REVIEW This review gives an overview on transporter structures in complex with lipids reported to date and discusses commonly encountered difficulties in the identification of functionally significant lipid-protein interactions based on those structures and functional in vitro data. Recent structures provided molecular details into regulation mechanism of transporters by specific lipids. The review highlights common findings and conserved patterns for distantly related transporter families to draw a more general picture on the regulatory role of lipid-protein interactions. MAJOR CONCLUSIONS Several common themes of the manner in which lipids directly influence membrane-mediated folding, oligomerization and structure stability can be found. Especially for LeuT-like fold transporters similarities in structurally resolved lipid-protein interactions suggest a common way in which transporter conformations are affected by lipids even in evolutionarily distinct transporters. Lipids appear to play an additional role as joints mechanically reinforcing the inverted repeat topology, which is a major determinant in the alternating access mechanism of secondary transporters. GENERAL SIGNIFICANCE This review brings together and adds to the repertoire of knowledge on lipid-protein interactions of functional significance presented in structures of membrane transporters. Knowledge of specific lipid-binding sites and modes of lipid influence on these proteins not only accomplishes the molecular description of transport cycle further, but also sheds light into localization dependent differences of transporter function. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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Affiliation(s)
- Caroline Koshy
- Max Planck Institute of Biophysics, Structural Biology Department, Frankfurt am Main, Germany; Max-Planck Institute of Biophysics, Computational Structural Biology Group, Frankfurt am Main, Germany
| | - Christine Ziegler
- Max Planck Institute of Biophysics, Structural Biology Department, Frankfurt am Main, Germany; Institute of Biophysics and Physical Biochemistry, University of Regensburg, Regensburg, Germany.
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Ferramosca A, Zara V. Dietary fat and hepatic lipogenesis: mitochondrial citrate carrier as a sensor of metabolic changes. Adv Nutr 2014; 5:217-25. [PMID: 24829468 PMCID: PMC4013174 DOI: 10.3945/an.113.004762] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Citrate carrier (CIC) is an integral protein of the inner mitochondrial membrane that has a fundamental role in hepatic intermediary metabolism. Its primary function is to catalyze the transport of citrate from mitochondria, where this molecule is formed, to cytosol, where this molecule is used for fatty acid (FA) and cholesterol synthesis. Therefore, mitochondrial CIC acts upstream of cytosolic lipogenic reactions, and its regulation is particularly important in view of the modulation of hepatic lipogenesis. Although a great deal of data are currently available on the dietary modulation of cytosolic lipogenic enzymes, little is known about the nutritional regulation of CIC transport activity. In this review, we describe the differential effects of distinct FAs present in the diet on the activity of mitochondrial CIC. In particular, polyunsaturated FAs were powerful modulators of the activity of mitochondrial CIC by influencing its expression through transcriptional and posttranscriptional mechanisms. On the contrary, saturated and monounsaturated FAs did not influence mitochondrial CIC activity. Moreover, variations in CIC activity were connected to similar alterations in the metabolic pathways to which the transported citrate is channeled. Therefore, CIC may be considered as a sensor for changes occurring inside the hepatocyte and may represent an important target for the regulation of hepatic lipogenesis. The crucial role of this protein is reinforced by the recent discovery of its involvement in other cellular processes, such as glucose-stimulated insulin secretion, inflammation, tumorigenesis, genome stability, and sperm metabolism.
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Affiliation(s)
| | - Vincenzo Zara
- Department of Biological and Environmental Sciences and Technologies, University of Salento, Lecce, Italy
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47
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Structures of yeast mitochondrial ADP/ATP carriers support a domain-based alternating-access transport mechanism. Proc Natl Acad Sci U S A 2014; 111:E426-34. [PMID: 24474793 DOI: 10.1073/pnas.1320692111] [Citation(s) in RCA: 153] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix. The carrier cycles by an unresolved mechanism between the cytoplasmic state, in which the carrier accepts ADP from the cytoplasm, and the matrix state, in which it accepts ATP from the mitochondrial matrix. Here we present the structures of the yeast ADP/ATP carriers Aac2p and Aac3p in the cytoplasmic state. The carriers have three domains and are closed at the matrix side by three interdomain salt-bridge interactions, one of which is braced by a glutamine residue. Glutamine braces are conserved in mitochondrial carriers and contribute to an energy barrier, preventing the conversion to the matrix state unless substrate binding occurs. At the cytoplasmic side a second salt-bridge network forms during the transport cycle, as demonstrated by functional analysis of mutants with charge-reversed networks. Analyses of the domain structures and properties of the interdomain interfaces indicate that interconversion between states involves movement of the even-numbered α-helices across the surfaces of the odd-numbered α-helices by rotation of the domains. The odd-numbered α-helices have an L-shape, with proline or serine residues at the kinks, which functions as a lever-arm, coupling the substrate-induced disruption of the matrix network to the formation of the cytoplasmic network. The simultaneous movement of three domains around a central translocation pathway constitutes a unique mechanism among transport proteins. These findings provide a structural description of transport by mitochondrial carrier proteins, consistent with an alternating-access mechanism.
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Hoang T, Smith MD, Jelokhani-Niaraki M. Expression, folding, and proton transport activity of human uncoupling protein-1 (UCP1) in lipid membranes: evidence for associated functional forms. J Biol Chem 2013; 288:36244-58. [PMID: 24196960 DOI: 10.1074/jbc.m113.509935] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Uncoupling protein-1 (UCP1) is abundantly expressed in the mitochondrial inner membrane of brown adipose tissues and has an important role in heat generation, mediated by its proton transport function. The structure and function of UCP1 are not fully understood, partially due to the difficulty in obtaining native-like folded proteins in vitro. In this study, using the auto-induction method, we have successfully expressed UCP1 in Escherichia coli membranes in high yield. Overexpressed UCP1 in bacterial membranes was extracted using mild detergents and reconstituted into phospholipid bilayers for biochemical studies. UCP1 was folded in octyl glucoside, as indicated by its high helical content and binding to ATP, a known UCP1 proton transport inhibitor. Reconstituted UCP1 in phospholipid vesicles also exhibited highly helical structures and proton transport that is activated by fatty acids and inhibited by purine nucleotides. Self-associated functional forms of UCP1 in lipid membranes were observed for the first time. The self-assembly of UCP1 into tetramers was unambiguously characterized by circular dichroism and fluorescence spectroscopy, analytical ultracentrifugation, and semi-native gel electrophoresis. In addition, the mitochondrial lipid cardiolipin stabilized the structure of associated UCP1 and enhanced the proton transport activity of the protein. The existence of the functional oligomeric states of UCP1 in the lipid membranes has important implications for understanding the structure and proton transport mechanism of this protein in brown adipose tissues as well as structure-function relationships of other mammalian UCPs in other tissues.
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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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50
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Crichton PG, Harding M, Ruprecht JJ, Lee Y, Kunji ERS. Lipid, detergent, and Coomassie Blue G-250 affect the migration of small membrane proteins in blue native gels: mitochondrial carriers migrate as monomers not dimers. J Biol Chem 2013; 288:22163-73. [PMID: 23744064 PMCID: PMC3724668 DOI: 10.1074/jbc.m113.484329] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Blue native gel electrophoresis is a popular method for the determination of the oligomeric state of membrane proteins. Studies using this technique have reported that mitochondrial carriers are dimeric (composed of two ∼32-kDa monomers) and, in some cases, can form physiologically relevant associations with other proteins. Here, we have scrutinized the behavior of the yeast mitochondrial ADP/ATP carrier AAC3 in blue native gels. We find that the apparent mass of AAC3 varies in a detergent- and lipid-dependent manner (from ∼60 to ∼130 kDa) that is not related to changes in the oligomeric state of the protein, but reflects differences in the associated detergent-lipid micelle and Coomassie Blue G-250 used in this technique. Higher oligomeric state species are only observed under less favorable solubilization conditions, consistent with aggregation of the protein. Calibration with an artificial covalent AAC3 dimer indicates that the mass observed for solubilized AAC3 and other mitochondrial carriers corresponds to a monomer. Size exclusion chromatography of purified AAC3 in dodecyl maltoside under blue native gel-like conditions shows that the mass of the monomer is ∼120 kDa, but appears smaller on gels (∼60 kDa) due to the unusually high amount of bound negatively charged dye, which increases the electrophoretic mobility of the protein-detergent-dye micelle complex. Our results show that bound lipid, detergent, and Coomassie stain alter the behavior of mitochondrial carriers on gels, which is likely to be true for other small membrane proteins where the associated lipid-detergent micelle is large when compared with the mass of the protein.
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Affiliation(s)
- Paul G Crichton
- Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
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