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He Z, Tu YC, Tsai CW, Mount J, Zhang J, Tsai MF, Yuan P. Structure and function of the human mitochondrial MRS2 channel. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.12.553106. [PMID: 37645897 PMCID: PMC10462007 DOI: 10.1101/2023.08.12.553106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
The human Mitochondrial RNA Splicing 2 protein (MRS2) has been implicated in Mg2+ transport across mitochondrial inner membranes, thus playing an important role in Mg2+ homeostasis critical for mitochondrial integrity and function. However, the molecular mechanisms underlying its fundamental channel properties such as ion selectivity and regulation remain unclear. Here, we present structural and functional investigation of MRS2. Cryo-electron microscopy structures in various ionic conditions reveal a pentameric channel architecture and the molecular basis of ion permeation and potential regulation mechanisms. Electrophysiological analyses demonstrate that MRS2 is a Ca2+-regulated, non-selective channel permeable to Mg2+, Ca2+, Na+ and K+, which contrasts with its prokaryotic ortholog, CorA, operating as a Mg2+-gated Mg2+ channel. Moreover, a conserved arginine ring within the pore of MRS2 functions to restrict cation movements, likely preventing the channel from collapsing the proton motive force that drives mitochondrial ATP synthesis. Together, our results provide a molecular framework for further understanding MRS2 in mitochondrial function and disease.
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Affiliation(s)
- Zhihui He
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- These authors contributed equally to this work
| | - Yung-Chi Tu
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
- These authors contributed equally to this work
| | - Chen-Wei Tsai
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Jonathan Mount
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Jingying Zhang
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Ming-Feng Tsai
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Peng Yuan
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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2
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Debar L, Ishak L, Moretton A, Anoosheh S, Morel F, Jenninger L, Balandier I, Vernet P, Hofer A, van den Wildenberg S, Farge G. NUDT6 and NUDT9, two mitochondrial members of the NUDIX family, have distinct hydrolysis activities. Mitochondrion 2023:S1567-7249(23)00054-5. [PMID: 37343711 DOI: 10.1016/j.mito.2023.06.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 06/16/2023] [Accepted: 06/17/2023] [Indexed: 06/23/2023]
Abstract
The 22 members of the NUDIX (NUcleoside DIphosphate linked to another moiety, X) hydrolase superfamily can hydrolyze a variety of phosphorylated molecules including (d)NTPs and their oxidized forms, nucleotide sugars, capped mRNAs and dinucleotide coenzymes such as NADH and FADH. Beside this broad range of enzymatic substrates, the NUDIX proteins can also be found in different cellular compartments, mainly in the nucleus and in the cytosol, but also in the peroxisome and in the mitochondria. Here we studied two members of the family, NUDT6 and NUDT9. We showed that NUDT6 is expressed in human cells and localizes exclusively to mitochondria and we confirmed that NUDT9 has a mitochondrial localization. To elucidate their potential role within this organelle, we investigated the functional consequences at the mitochondrial level of NUDT6- and NUDT9-deficiency and found that the depletion of either of the two proteins results in an increased activity of the respiratory chain and an alteration of the mitochondrial respiratory chain complexes expression. We demonstrated that NUDT6 and NUDT9 have distinct substrate specificity in vitro, which is dependent on the cofactor used. They can both hydrolyze a large range of low molecular weight compounds such as NAD+(H), FAD and ADPR, but NUDT6 is mainly active towards NADH, while NUDT9 displays a higher activity towards ADPR.
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Affiliation(s)
- Louis Debar
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France
| | - Layal Ishak
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, P.O. Box 440, SE-405 30 Gothenburg, Sweden
| | - Amandine Moretton
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France
| | - Saber Anoosheh
- Umeå University, Department of Medical Biochemistry and Biophysics, SE-90187 Umeå, Sweden
| | - Frederic Morel
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France
| | - Louise Jenninger
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, P.O. Box 440, SE-405 30 Gothenburg, Sweden
| | - Isabelle Balandier
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France
| | - Patrick Vernet
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France
| | - Anders Hofer
- Umeå University, Department of Medical Biochemistry and Biophysics, SE-90187 Umeå, Sweden
| | - Siet van den Wildenberg
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France; Université Clermont Auvergne, CNRS, IRD, Université Jean Monnet Saint Etienne, LMV, F-63000 Clermont-Ferrand, France
| | - Geraldine Farge
- Université Clermont Auvergne, CNRS, Laboratoire de Physique de Clermont, F-63000 CLERMONT-FERRAND, France.
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3
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Zhang YY, Li XS, Ren KD, Peng J, Luo XJ. Restoration of metal homeostasis: a potential strategy against neurodegenerative diseases. Ageing Res Rev 2023; 87:101931. [PMID: 37031723 DOI: 10.1016/j.arr.2023.101931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 04/04/2023] [Accepted: 04/06/2023] [Indexed: 04/11/2023]
Abstract
Metal homeostasis is critical to normal neurophysiological activity. Metal ions are involved in the development, metabolism, redox and neurotransmitter transmission of the central nervous system (CNS). Thus, disturbance of homeostasis (such as metal deficiency or excess) can result in serious consequences, including neurooxidative stress, excitotoxicity, neuroinflammation, and nerve cell death. The uptake, transport and metabolism of metal ions are highly regulated by ion channels. There is growing evidence that metal ion disorders and/or the dysfunction of ion channels contribute to the progression of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for diverse neurological diseases. This review summarizes recent advances in the studies regarding the physiological and pathophysiological functions of metal ions and their channels, as well as their role in neurodegenerative diseases. In addition, currently available metal ion modulators and in vivo quantitative metal ion imaging methods are also discussed. Current work provides certain recommendations based on literatures and in-depth reflections to improve neurodegenerative diseases. Future studies should turn to crosstalk and interactions between different metal ions and their channels. Concomitant pharmacological interventions for two or more metal signaling pathways may offer clinical advantages in treating the neurodegenerative diseases.
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Affiliation(s)
- Yi-Yue Zhang
- Department of Pharmacology, Xiangya School of Pharmaceutical Sciences, Central South University, Changsha 410078, China
| | - Xi-Sheng Li
- Department of Laboratory Medicine, The Third Xiangya Hospital of Central South University, Changsha 410013,China
| | - Kai-Di Ren
- Department of Pharmacy, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
| | - Jun Peng
- Department of Pharmacology, Xiangya School of Pharmaceutical Sciences, Central South University, Changsha 410078, China; Hunan Provincial Key Laboratory of Cardiovascular Research, Xiangya School of Pharmaceutical Sciences, Central South University, Changsha 410078, China.
| | - Xiu-Ju Luo
- Department of Laboratory Medicine, The Third Xiangya Hospital of Central South University, Changsha 410013,China.
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4
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Killilea DW, Killilea AN. Mineral requirements for mitochondrial function: A connection to redox balance and cellular differentiation. Free Radic Biol Med 2022; 182:182-191. [PMID: 35218912 DOI: 10.1016/j.freeradbiomed.2022.02.022] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 02/16/2022] [Accepted: 02/21/2022] [Indexed: 12/20/2022]
Abstract
Professor Bruce Ames demonstrated that nutritional recommendations should be adjusted in order to 'tune-up' metabolism and reduce mitochondria decay, a hallmark of aging and many disease processes. A major subset of tunable nutrients are the minerals, which despite being integral to every aspect of metabolism are often deficient in the typical Western diet. Mitochondria are particularly rich in minerals, where they function as essential cofactors for mitochondrial physiology and overall cellular health. Yet substantial knowledge gaps remain in our understanding of the form and function of these minerals needed for metabolic harmony. Some of the minerals have known activities in the mitochondria but with incomplete regulatory detail, whereas other minerals have no established mitochondrial function at all. A comprehensive metallome of the mitochondria is needed to fully understand the patterns and relationships of minerals within metabolic processes and cellular development. This brief overview serves to highlight the current progress towards understanding mineral homeostasis in the mitochondria and to encourage more research activity in key areas. Future work may likely reveal that adjusting the amounts of specific nutritional minerals has longevity benefits for human health.
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Affiliation(s)
- David W Killilea
- Office of Research, University of California, San Francisco, CA, USA.
| | - Alison N Killilea
- Department of Molecular & Cell Biology, University of California, Berkeley, CA, USA
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5
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Tatarkova Z, de Baaij JHF, Grendar M, Aschenbach JR, Racay P, Bos C, Sponder G, Hoenderop JGJ, Röntgen M, Turcanova Koprusakova M, Kolisek M. Dietary Mg 2+ Intake and the Na +/Mg 2+ Exchanger SLC41A1 Influence Components of Mitochondrial Energetics in Murine Cardiomyocytes. Int J Mol Sci 2020; 21:E8221. [PMID: 33153064 PMCID: PMC7663288 DOI: 10.3390/ijms21218221] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 10/27/2020] [Indexed: 01/02/2023] Open
Abstract
Cardiomyocytes are among the most energy-intensive cell types. Interplay between the components of cellular magnesium (Mg) homeostasis and energy metabolism in cardiomyocytes is poorly understood. We have investigated the effects of dietary Mg content and presence/functionality of the Na+/Mg2+ exchanger SLC41A1 on enzymatic functions of selected constituents of the Krebs cycle and complexes of the electron transport chain (ETC). The activities of aconitate hydratase (ACON), isocitrate dehydrogenase (ICDH), α-ketoglutarate dehydrogenase (KGDH), and ETC complexes CI-CV have been determined in vitro in mitochondria isolated from hearts of wild-type (WT) and Slc41a1-/- mice fed a diet with either normal or low Mg content. Our data demonstrate that both, the type of Mg diet and the Slc41a1 genotype largely impact on the activities of enzymes of the Krebs cycle and ETC. Moreover, a compensatory effect of Slc41a1-/- genotype on the effect of low Mg diet on activities of the tested Krebs cycle enzymes has been identified. A machine-learning analysis identified activities of ICDH, CI, CIV, and CV as common predictors of the type of Mg diet and of CII as suitable predictor of Slc41a1 genotype. Thus, our data delineate the effect of dietary Mg content and of SLC41A1 functionality on the energy-production in cardiac mitochondria.
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Affiliation(s)
- Zuzana Tatarkova
- Department of Medical Biochemistry, Jessenius Faculty of Medicine, Comenius University in Bratislava, Mala Hora 4D, 036 01 Martin, Slovakia; (Z.T.); (P.R.)
| | - Jeroen H. F. de Baaij
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, 6500HB Nijmegen, The Netherlands; (J.H.F.d.B.); (C.B.); (J.G.J.H.)
| | - Marian Grendar
- Biomedical Center Martin, Jessenius Faculty of Medicine, Comenius University in Bratislava, Mala Hora 4D, 036 01 Martin, Slovakia;
| | - Jörg R. Aschenbach
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163 Berlin, Germany; (J.R.A.); (G.S.)
| | - Peter Racay
- Department of Medical Biochemistry, Jessenius Faculty of Medicine, Comenius University in Bratislava, Mala Hora 4D, 036 01 Martin, Slovakia; (Z.T.); (P.R.)
- Biomedical Center Martin, Jessenius Faculty of Medicine, Comenius University in Bratislava, Mala Hora 4D, 036 01 Martin, Slovakia;
| | - Caro Bos
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, 6500HB Nijmegen, The Netherlands; (J.H.F.d.B.); (C.B.); (J.G.J.H.)
| | - Gerhard Sponder
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163 Berlin, Germany; (J.R.A.); (G.S.)
| | - Joost G. J. Hoenderop
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, 6500HB Nijmegen, The Netherlands; (J.H.F.d.B.); (C.B.); (J.G.J.H.)
| | - Monika Röntgen
- Leibniz Institute for Farm Animal Biology, Wilhelm-Stahl-Allee 2, 18196 Dummerstorf, Germany;
| | | | - Martin Kolisek
- Biomedical Center Martin, Jessenius Faculty of Medicine, Comenius University in Bratislava, Mala Hora 4D, 036 01 Martin, Slovakia;
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6
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Boreikaite V, Wicky BIM, Watt IN, Clarke J, Walker JE. Extrinsic conditions influence the self-association and structure of IF 1, the regulatory protein of mitochondrial ATP synthase. Proc Natl Acad Sci U S A 2019; 116:10354-10359. [PMID: 31064873 PMCID: PMC6535023 DOI: 10.1073/pnas.1903535116] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The endogenous inhibitor of ATP synthase in mitochondria, called IF1, conserves cellular energy when the proton-motive force collapses by inhibiting ATP hydrolysis. Around neutrality, the 84-amino-acid bovine IF1 is thought to self-assemble into active dimers and, under alkaline conditions, into inactive tetramers and higher oligomers. Dimerization is mediated by formation of an antiparallel α-helical coiled-coil involving residues 44-84. The inhibitory region of each monomer from residues 1-46 is largely α-helical in crystals, but disordered in solution. The formation of the inhibited enzyme complex requires the hydrolysis of two ATP molecules, and in the complex the disordered region from residues 8-13 is extended and is followed by an α-helix from residues 14-18 and a longer α-helix from residue 21, which continues unbroken into the coiled-coil region. From residues 21-46, the long α-helix binds to other α-helices in the C-terminal region of predominantly one of the β-subunits in the most closed of the three catalytic interfaces. The definition of the factors that influence the self-association of IF1 is a key to understanding the regulation of its inhibitory properties. Therefore, we investigated the influence of pH and salt-types on the self-association of bovine IF1 and the folding of its unfolded region. We identified the equilibrium between dimers and tetramers as a potential central factor in the in vivo modulation of the inhibitory activity and suggest that the intrinsically disordered region makes its inhibitory potency exquisitely sensitive and responsive to physiological changes that influence the capability of mitochondria to make ATP.
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Affiliation(s)
- Vytaute Boreikaite
- The Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, CB2 0XY Cambridge, United Kingdom
- The Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Basile I M Wicky
- The Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Ian N Watt
- The Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, CB2 0XY Cambridge, United Kingdom
| | - Jane Clarke
- The Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - John E Walker
- The Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, CB2 0XY Cambridge, United Kingdom;
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7
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Magnesium Extravaganza: A Critical Compendium of Current Research into Cellular Mg 2+ Transporters Other than TRPM6/7. Rev Physiol Biochem Pharmacol 2018; 176:65-105. [PMID: 30406297 DOI: 10.1007/112_2018_15] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Magnesium research has boomed within the last 20 years. The real breakthrough came at the start of the new millennium with the discovery of a plethora of possible Mg homeostatic factors that, in particular, included putative Mg2+ transporters. Until that point, Mg research was limited to biochemical and physiological work, as no target molecular entities were known that could be used to explore the molecular biology of Mg homeostasis at the level of the cell, tissue, organ, or organism and to translate such knowledge into the field of clinical medicine and pharmacology. Because of the aforementioned, Mg2+ and Mg homeostasis, both of which had been heavily marginalized within the biomedical field in the twentieth century, have become overnight a focal point of many studies ranging from primary biomedical research to translational medicine.The amount of literature concerning cellular Mg2+ transport and cellular Mg homeostasis is increasing, together with a certain amount of confusion, especially about the function(s) of the newly discovered and, in the majority of instances, still only putative Mg2+ transporters/Mg2+ homeostatic factors. Newcomers to the field of Mg research will thus find it particularly difficult to orient themselves.Here, we briefly but critically summarize the status quo of the current understanding of the molecular entities behind cellular Mg2+ homeostasis in mammalian/human cells other than TRPM6/7 chanzymes, which have been universally accepted as being unspecific cation channel kinases allowing the flux of Mg2+ while constituting the major gateway for Mg2+ to enter the cell.
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8
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Abdelraheim SR, Spiller DG, McLennan AG. Mouse Nudt13 is a Mitochondrial Nudix Hydrolase with NAD(P)H Pyrophosphohydrolase Activity. Protein J 2017; 36:425-432. [PMID: 28755312 PMCID: PMC5626787 DOI: 10.1007/s10930-017-9734-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The mammalian NUDT13 protein possesses a sequence motif characteristic of the NADH pyrophosphohydrolase subfamily of Nudix hydrolases. Due to the persistent insolubility of the recombinant product expressed in Escherichia coli, active mouse Nudt13 was expressed in insect cells from a baculovirus vector as a histidine-tagged recombinant protein. In vitro, it efficiently hydrolysed NADH to NMNH and AMP and NADPH to NMNH and 2',5'-ADP and had a marked preference for the reduced pyridine nucleotides. Much lower activity was obtained with other nucleotide substrates tested. K m and k cat values for NADH were 0.34 mM and 7 s-1 respectively. Expression of Nudt13 as an N-terminal fusion to green fluorescent protein revealed that it was targeted exclusively to mitochondria by the N-terminal targeting peptide, suggesting that Nudt13 may act to regulate the concentration of mitochondrial reduced pyridine nucleotide cofactors and the NAD(P)+/NAD(P)H ratio in this organelle and elsewhere. Future studies of the enzymology of pyridine nucleotide metabolism in relation to energy homeostasis, redox control, free radical production and cellular integrity should consider the possible regulatory role of Nudt13.
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Affiliation(s)
- Salama R Abdelraheim
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
- Department of Biochemistry, Faculty of Medicine, Minia University, Minia, 61519, Egypt
| | - David G Spiller
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
- Faculty of Biology, Medicine and Health, Systems Microscopy Centre, University of Manchester, Manchester, M13 9PT, UK
| | - Alexander G McLennan
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK.
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9
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Mitochondrial Mg(2+) homeostasis decides cellular energy metabolism and vulnerability to stress. Sci Rep 2016; 6:30027. [PMID: 27458051 PMCID: PMC4960558 DOI: 10.1038/srep30027] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 06/28/2016] [Indexed: 01/23/2023] Open
Abstract
Cellular energy production processes are composed of many Mg2+ dependent enzymatic reactions. In fact, dysregulation of Mg2+ homeostasis is involved in various cellular malfunctions and diseases. Recently, mitochondria, energy-producing organelles, have been known as major intracellular Mg2+ stores. Several biological stimuli alter mitochondrial Mg2+ concentration by intracellular redistribution. However, in living cells, whether mitochondrial Mg2+ alteration affect cellular energy metabolism remains unclear. Mg2+ transporter of mitochondrial inner membrane MRS2 is an essential component of mitochondrial Mg2+ uptake system. Here, we comprehensively analyzed intracellular Mg2+ levels and energy metabolism in Mrs2 knockdown (KD) cells using fluorescence imaging and metabolome analysis. Dysregulation of mitochondrial Mg2+ homeostasis disrupted ATP production via shift of mitochondrial energy metabolism and morphology. Moreover, Mrs2 KD sensitized cellular tolerance against cellular stress. These results indicate regulation of mitochondrial Mg2+via MRS2 critically decides cellular energy status and cell vulnerability via regulation of mitochondrial Mg2+ level in response to physiological stimuli.
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10
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Igamberdiev AU, Kleczkowski LA. Optimization of ATP synthase function in mitochondria and chloroplasts via the adenylate kinase equilibrium. FRONTIERS IN PLANT SCIENCE 2015; 6:10. [PMID: 25674099 PMCID: PMC4309032 DOI: 10.3389/fpls.2015.00010] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 01/06/2015] [Indexed: 05/09/2023]
Abstract
The bulk of ATP synthesis in plants is performed by ATP synthase, the main bioenergetics engine of cells, operating both in mitochondria and in chloroplasts. The reaction mechanism of ATP synthase has been studied in detail for over half a century; however, its optimal performance depends also on the steady delivery of ATP synthase substrates and the removal of its products. For mitochondrial ATP synthase, we analyze here the provision of stable conditions for (i) the supply of ADP and Mg(2+), supported by adenylate kinase (AK) equilibrium in the intermembrane space, (ii) the supply of phosphate via membrane transporter in symport with H(+), and (iii) the conditions of outflow of ATP by adenylate transporter carrying out the exchange of free adenylates. We also show that, in chloroplasts, AK equilibrates adenylates and governs Mg(2+) contents in the stroma, optimizing ATP synthase and Calvin cycle operation, and affecting the import of inorganic phosphate in exchange with triose phosphates. It is argued that chemiosmosis is not the sole component of ATP synthase performance, which also depends on AK-mediated equilibrium of adenylates and Mg(2+), adenylate transport, and phosphate release and supply.
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Affiliation(s)
- Abir U. Igamberdiev
- Department of Biology, Memorial University of Newfoundland, St. John’s, NL, Canada
- *Correspondence: Abir U. Igamberdiev, Department of Biology, Memorial University of Newfoundland, St. John’s, NL A1B3X9, Canada e-mail:
| | - Leszek A. Kleczkowski
- Department of Plant Physiology, Umeå Plant Science Centre, University of Umeå, Umeå, Sweden
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11
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Pradhan RK, Qi F, Beard DA, Dash RK. Characterization of Mg2+ inhibition of mitochondrial Ca2+ uptake by a mechanistic model of mitochondrial Ca2+ uniporter. Biophys J 2011; 101:2071-81. [PMID: 22067144 DOI: 10.1016/j.bpj.2011.09.029] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 09/15/2011] [Accepted: 09/19/2011] [Indexed: 01/13/2023] Open
Abstract
Ca(2+) is an important regulatory ion and alteration of mitochondrial Ca(2+) homeostasis can lead to cellular dysfunction and apoptosis. Ca(2+) is transported into respiring mitochondria via the Ca(2+) uniporter, which is known to be inhibited by Mg(2+). This uniporter-mediated mitochondrial Ca(2+) transport is also shown to be influenced by inorganic phosphate (Pi). Despite a large number of experimental studies, the kinetic mechanisms associated with the Mg(2+) inhibition and Pi regulation of the uniporter function are not well established. To gain a quantitative understanding of the effects of Mg(2+) and Pi on the uniporter function, we developed here a mathematical model based on known kinetic properties of the uniporter and presumed Mg(2+) inhibition and Pi regulation mechanisms. The model is extended from our previous model of the uniporter that is based on a multistate catalytic binding and interconversion mechanism and Eyring's free energy barrier theory for interconversion. The model satisfactorily describes a wide variety of experimental data sets on the kinetics of mitochondrial Ca(2+) uptake. The model also appropriately depicts the inhibitory effect of Mg(2+) on the uniporter function, in which Ca(2+) uptake is hyperbolic in the absence of Mg(2+) and sigmoid in the presence of Mg(2+). The model suggests a mixed-type inhibition mechanism for Mg(2+) inhibition of the uniporter function. This model is critical for building mechanistic models of mitochondrial bioenergetics and Ca(2+) handling to understand the mechanisms by which Ca(2+) mediates signaling pathways and modulates energy metabolism.
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Affiliation(s)
- Ranjan K Pradhan
- Biotechnology and Bioengineering Center and Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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12
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A novel kinetic assay of mitochondrial ATP-ADP exchange rate mediated by the ANT. Biophys J 2009; 96:2490-504. [PMID: 19289073 DOI: 10.1016/j.bpj.2008.12.3915] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 12/08/2008] [Accepted: 12/17/2008] [Indexed: 11/23/2022] Open
Abstract
A novel method exploiting the differential affinity of ADP and ATP to Mg(2+) was developed to measure mitochondrial ADP-ATP exchange rate. The rate of ATP appearing in the medium after addition of ADP to energized mitochondria, is calculated from the measured rate of change in free extramitochondrial [Mg(2+)] reported by the membrane-impermeable 5K(+) salt of the Mg(2+)-sensitive fluorescent indicator, Magnesium Green, using standard binding equations. The assay is designed such that the adenine nucleotide translocase (ANT) is the sole mediator of changes in [Mg(2+)] in the extramitochondrial volume, as a result of ADP-ATP exchange. We also provide data on the dependence of ATP efflux rate within the 6.8-7.8 matrix pH range as a function of membrane potential. Finally, by comparing the ATP-ADP steady-state exchange rate to the amount of the ANT in rat brain synaptic, brain nonsynaptic, heart and liver mitochondria, we provide molecular turnover numbers for the known ANT isotypes.
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13
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Firth AL, Yuill KH, Smirnov SV. Mitochondria-dependent regulation of Kv currents in rat pulmonary artery smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 2008; 295:L61-70. [PMID: 18469114 PMCID: PMC2494784 DOI: 10.1152/ajplung.90243.2008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Voltage-gated K+ (Kv) channels are important in the regulation of pulmonary vascular function having both physiological and pathophysiological implications. The pulmonary vasculature is essential for reoxygenation of the blood, supplying oxygen for cellular respiration. Mitochondria have been proposed as the major oxygen-sensing organelles in the pulmonary vasculature. Using electrophysiological techniques and immunofluorescence, an interaction of the mitochondria with Kv channels was investigated. Inhibitors, blocking the mitochondrial electron transport chain at different complexes, were shown to have a dual effect on Kv currents in freshly isolated rat pulmonary arterial smooth muscle cells (PASMCs). These dual effects comprised an enhancement of Kv current in a negative potential range (manifested as a 5- to 14-mV shift in the Kv activation to more negative membrane voltages) with a decrease in current amplitude at positive potentials. Such effects were most prominent as a result of inhibition of Complex III by antimycin A. Investigation of the mechanism of antimycin A-mediated effects on Kv channel currents (IKv) revealed the presence of a mitochondria-mediated Mg2+ and ATP-dependent regulation of Kv channels in PASMCs, which exists in addition to that currently proposed to be caused by changes in intracellular reactive oxygen species.
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Affiliation(s)
- Amy L Firth
- Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath, United Kingdom
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14
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Piskacek M, Zotova L, Zsurka G, Schweyen RJ. Conditional knockdown of hMRS2 results in loss of mitochondrial Mg(2+) uptake and cell death. J Cell Mol Med 2008; 13:693-700. [PMID: 18384665 PMCID: PMC3822876 DOI: 10.1111/j.1582-4934.2008.00328.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The human gene MRS2L encodes a mitochondrial protein distantly related to CorA Mg2+ transport proteins. Constitutive shRNA-mediated knockdown of hMRS2 in human HEK-293 cell line was found here to cause death. To further study its role in Mg2+ transport, we have established stable cell lines with conditionally expressing shRNAs directed against hMRS2L. The cells expressing shRNA for several generations exhibited lower steady-state levels of free mitochondrial Mg2+ ([Mg2+]m) and reduced capacity of mitochondrial Mg2+ uptake than control cells. Long-term expression of shRNAs resulted in loss of mitochondrial respiratory complex I, decreased mitochondrial membrane potential and cell death. We conclude that hMrs2 is the major transport protein for Mg + uptake into mitochondria and that expression of hMrs2 is essential for the maintenance of respiratory complex I and cell viability.
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15
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Goytain A, Quamme GA. Identification and characterization of a novel family of membrane magnesium transporters, MMgT1 and MMgT2. Am J Physiol Cell Physiol 2007; 294:C495-502. [PMID: 18057121 DOI: 10.1152/ajpcell.00238.2007] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Magnesium is an essential metal, but few selective transporters have been identified at the molecular level. Microarray analysis was used to identify two similar transcripts that are upregulated with low extracellular Mg(2+). The corresponding cDNAs encode proteins of 131 and 123 amino acids with two predicted transmembrane domains. The two separate gene products comprise the family that we have termed "membrane Mg(2+) transporters" (MMgTs), because the proteins reside in the membrane and mediate Mg(2+) transport. When expressed in Xenopus laevis oocytes, MMgT1 and MMgT2 mediate Mg(2+) transport as determined with two-electrode voltage-clamp analysis and fluorescence measurements. Transport is saturable Mg(2+) uptake with Michaelis constants of 1.47 +/- 0.17 and 0.58 +/- 0.07 mM, respectively. Real-time RT-PCR demonstrated that MMgT mRNAs are present in a wide variety of cells. Subcellular localization with immunohistochemistry determined that the MMgT1-hemagglutinin (HA) and MMgT2-V5 fusion proteins reside in the Golgi complex and post-Golgi vesicles, including the early endosomes in COS-7 cells transfected with the respective tagged constructs. Interestingly, MMgT1-HA and MMgT2-V5 were found in separate populations of post-Golgi vesicles. MMgT1 and MMgT2 mRNA increased by about threefold, respectively, in kidney epithelial cells cultured in low-magnesium media relative to normal media and in the kidney cortex of mice maintained on low-magnesium diets compared with those animals consuming normal diets. With the increase in transcripts, there was an apparent increase in MMgT1 and MMgT2 protein in the Golgi and post-Golgi vesicles. These experiments suggest that MMgT proteins may provide regulated pathways for Mg(2+) transport in the Golgi and post-Golgi organelles of epithelium-derived cells.
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Affiliation(s)
- Angela Goytain
- Department of Medicine, University of British Columbia, Vancouver, Canada
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16
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Nguyen MHT, Dudycha SJ, Jafri MS. Effect of Ca2+ on cardiac mitochondrial energy production is modulated by Na+ and H+ dynamics. Am J Physiol Cell Physiol 2007; 292:C2004-20. [PMID: 17344315 DOI: 10.1152/ajpcell.00271.2006] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The energy production of mitochondria in heart increases during exercise. Several works have suggested that calcium acts at multiple control points to activate net ATP production in what is termed "parallel activation". To study this, a computational model of mitochondrial energy metabolism in the heart has been developed that integrates the Dudycha-Jafri model for the tricarboxylic acid cycle with the Magnus-Keizer model for mitochondrial energy metabolism and calcium dynamics. The model improves upon the previous formulation by including an updated formulation for calcium dynamics, and new descriptions of sodium, hydrogen, phosphate, and ATP balance. To this end, it incorporates new formulations for the calcium uniporter, sodium-calcium exchange, sodium-hydrogen exchange, the F(1)F(0)-ATPase, and potassium-hydrogen exchange. The model simulates a wide range of experimental data, including steady-state and simulated pacing protocols. The model suggests that calcium is a potent activator of net ATP production and that as pacing increases energy production due to calcium goes up almost linearly. Furthermore, it suggests that during an extramitochondrial calcium transient, calcium entry and extrusion cause a transient depolarization that serve to increase NADH production by the tricarboxylic acid cycle and NADH consumption by the respiration driven proton pumps. The model suggests that activation of the F(1)F(0)-ATPase by calcium is essential to increase ATP production. In mitochondria very close to the release sites, the depolarization is more severe causing a temporary loss of ATP production. However, due to the short duration of the depolarization the net ATP production is also increased.
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Affiliation(s)
- My-Hanh T Nguyen
- Dept. of Bioinformatics and Computational Biology, George Mason University, Manassas, VA 20110, USA
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17
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Abstract
The mitochondrion represents a unique opportunity to apply mathematical modeling to a complex biological system. Understanding mitochondrial function and control is important since this organelle is critical in energy metabolism as well as playing key roles in biochemical synthesis, redox control/signaling, and apoptosis. A mathematical model, or hypothesis, provides several useful insights including a rigorous test of the consensus view of the operation of a biological process as well as providing methods of testing and creating new hypotheses. The advantages of the mitochondrial system for applying a mathematical model include the relative simplicity and understanding of the matrix reactions, the ability to study the mitochondria as a independent contained organelle, and, most importantly, one can dynamically measure many of the internal reaction intermediates, on line. The developing ability to internally monitor events within the metabolic network, rather than just the inflow and outflow, is extremely useful in creating critical bounds on complex mathematical models using the individual reaction mechanisms available. However, many serious problems remain in creating a working model of mitochondrial function including the incomplete definition of metabolic pathways, the uncertainty of using in vitro enzyme kinetics, as well as regulatory data in the intact system and the unknown chemical activities of relevant molecules in the matrix. Despite these formidable limitations, the advantages of the mitochondrial system make it one of the best defined mammalian metabolic networks that can be used as a model system for understanding the application and use of mathematical models to study biological systems.
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Affiliation(s)
- Robert S Balaban
- Laboratory of Cardiac Energetics, National Heart Lung and Blood Institute, Bethesda, MD 20892, USA.
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18
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Modeling the mechanism of metabolic oscillations in ischemic cardiac myocytes. J Theor Biol 2006; 242:801-17. [PMID: 16814324 DOI: 10.1016/j.jtbi.2006.05.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 04/10/2006] [Accepted: 05/10/2006] [Indexed: 10/24/2022]
Abstract
Oscillations in energy metabolism have been observed in a variety of cells under metabolically deprived conditions such as ischemia. In cardiac ventricular myocytes these metabolic oscillations may cause oscillations in the action potential duration, creating the potential for cardiac arrhythmias during ischemia (O'Rourke, 2000). A mathematical model of the mechanism behind metabolic oscillations is developed here. The model consists of descriptions of the mitochondrial components that regulate mitochondrial membrane potential (Psi), mitochondrial inorganic phosphate concentration, mitochondrial magnesium concentration, and cellular NADH and NAD(+) concentrations. Using parameters from the experimental literature, the model produces physiological values for these both under normoxic (steady state) and ischemic (oscillatory) conditions. The model includes the mitochondrial inner membrane anion channel (IMAC), the centum picosiemen channel (mCS), the phosphate carrier (PIC), and the respiration driven proton pumps. The model suggests that these are the essential components for producing oscillations with mCS essential for the rapid depolarization, PIC for the recovery from depolarization, and IMAC for the slow depolarization between depolarization peaks. A decrease of the inner membrane potential due to ischemia or experimental conditions seems to be a triggering factor for the oscillations. The model simulates the experimental observations that high levels of mitochondrial ADP and ATP abolish the oscillations, as does inhibition of electron transport. The model makes predictions on the influence of pH and magnesium levels on metabolic oscillations.
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19
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Weghuber J, Dieterich F, Froschauer EM, Svidovà S, Schweyen RJ. Mutational analysis of functional domains in Mrs2p, the mitochondrial Mg2+ channel protein of Saccharomyces cerevisiae. FEBS J 2006; 273:1198-209. [PMID: 16519685 DOI: 10.1111/j.1742-4658.2006.05157.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nuclear gene MRS2 in Saccharomyces cerevisiae encodes an integral protein (Mrs2p) of the inner mitochondrial membrane. It forms an ion channel mediating influx of Mg2+ into mitochondria. Orthologues of Mrs2p have been shown to exist in other lower eukaryotes, in vertebrates and in plants. Characteristic features of the Mrs2 protein family and the distantly related CorA proteins of bacteria are the presence of two adjacent transmembrane domains near the C terminus of Mrs2p one of which ends with a F/Y-G-M-N motif. Two coiled-coil domains and several conserved primary sequence blocks in the central part of Mrs2p are identified here as additional characteristics of the Mrs2p family. Gain-of-function mutations obtained upon random mutagenesis map to these conserved sequence blocks. They lead to moderate increases in mitochondrial Mg2+ concentrations and concomitant positive effects on splicing of mutant group II intron RNA. Site-directed mutations in several conserved sequences reduce Mrs2p-mediated Mg2+ uptake. Mutants with strong effects on mitochondrial Mg2+ concentrations also have decreased group II intron splicing. Deletion of a nonconserved basic region, previously invoked for interaction with mitochondrial introns, lowers intramitochondrial Mg2+ levels as well as group II intron splicing. Data presented support the notion that effects of mutations in Mrs2p on group II intron splicing are a consequence of changes in steady-state mitochondrial Mg2+ concentrations.
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Affiliation(s)
- Julian Weghuber
- Max F. Perutz Laboratories, Department of Genetics, University of Vienna, Austria
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20
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García N, Martínez-Abundis E, Pavón N, Chávez E. Sodium inhibits permeability transition by decreasing potassium matrix content in rat kidney mitochondria. Comp Biochem Physiol B Biochem Mol Biol 2006; 144:442-50. [PMID: 16762575 DOI: 10.1016/j.cbpb.2006.04.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2005] [Revised: 04/18/2006] [Accepted: 04/18/2006] [Indexed: 01/19/2023]
Abstract
Inner membrane mitochondria undergo a permeability increase elicited after the opening of a nonspecific pore due to supraphysiological matrix Ca2+ load, and the presence of an inducer. Multiple inducers have been used to promote the transition in permeability; among them are carboxyatractyloside (CAT) and reactive oxygen-derived species. In contrast, inhibitors such as ADP and cyclosporin A have been commonly used. In this work, we show that the opening or closure of the nonspecific pore depends on the cationic composition of the incubation medium. It was found that when mitochondria were incubated in either 125 mM KCl or 125 mM LiCl, ADP was essential to maintain selective membrane permeability. Interestingly, the nucleotide was not required when the medium contained 125 mM NaCl. Furthermore, it was established that CAT promotes membrane leakage in K(+)- or Li(+)-incubated mitochondria, while it failed to do so in Na(+)-incubated mitochondria. Evidence is also presented on the ability of Na+ to induce resistance in mitochondria against membrane damage by oxidative stress. Mitochondrial Ca2+ discharge, swelling, and transmembrane electric gradient were analyzed to establish permeability transition. It is concluded that the protection provided by Na+ was accomplished by inducing matrix K+ depletion, which, in turn, diminished the free fraction of matrix Ca2+.
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Affiliation(s)
- Noemí García
- Departamento de Bioquímica, Instituto Nacional de Cardiología, Ignacio Chávez, Juan Badiano No. 1, Col. Sección XVI, Tlalpan, DF, México, Mexico
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21
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Bradshaw PC, Pfeiffer DR. Release of Ca2+ and Mg2+ from yeast mitochondria is stimulated by increased ionic strength. BMC BIOCHEMISTRY 2006; 7:4. [PMID: 16460565 PMCID: PMC1386685 DOI: 10.1186/1471-2091-7-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Accepted: 02/06/2006] [Indexed: 11/10/2022]
Abstract
Background Divalent cations are required for many essential functions of mitochondrial metabolism. Yet the transporters that mediate the flux of these molecules into and out of the mitochondrion remain largely unknown. Previous studies in yeast have led to the molecular identification of a component of the major mitochondrial electrophoretic Mg2+ uptake system in this organism as well as a functional mammalian homolog. Other yeast mitochondrial studies have led to the characterization of an equilibrative fatty acid-stimulated Ca2+ transport activity. To gain a deeper understanding of the regulation of mitochondrial divalent cation levels we further characterized the efflux of Ca2+ and Mg2+ from yeast mitochondria. Results When isolated mitochondria from the yeast Saccharomyces cerevisiae were suspended in a salt-based suspension medium, Ca2+ and Mg2+ were released from the matrix space. Release did not spontaneously occur in a non-ionic mannitol media. When energized mitochondria were suspended in a mannitol medium in the presence of Ca2+ they were able to accumulate Ca2+ by the addition of the electrogenic Ca2+ ionophore ETH-129. However, in a KCl or choline Cl medium under the same conditions, they were unable to retain the Ca2+ that was taken up due to the activation of the Ca2+ efflux pathway, although a substantial membrane potential driving Ca2+ uptake was maintained. This Ca2+ efflux was independent of fatty acids, which have previously been shown to activate Ca2+ transport. Endogenous mitochondrial Mg2+ was also released when mitochondria were suspended in an ionic medium, but was retained in mitochondria upon fatty acid addition. When suspended in a mannitol medium, metal chelators released mitochondrial Mg2+, supporting the existence of an external divalent cation-binding site regulating release. Matrix space Mg2+ was also slowly released from mitochondria by the addition of Ca2+, respiratory substrates, increasing pH, or the nucleotides ATP, ADP, GTP, and ATP-gamma-S. Conclusion In isolated yeast mitochondria Ca2+ and Mg2+ release was activated by increased ionic strength. Free nucleotides, metal ion chelators, and increased pH also stimulated release. In yeast cells this release is likely an important mechanism in the regulation of mitochondrial matrix space divalent cation concentrations.
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Affiliation(s)
| | - Douglas R Pfeiffer
- Department of Molecular and Cellular Biochemistry, Department of Internal Medicine, Institute for Mitochondrial Biology, The Ohio State University, Columbus, OH, USA
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22
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Korge P, Honda HM, Weiss JN. K+-dependent regulation of matrix volume improves mitochondrial function under conditions mimicking ischemia-reperfusion. Am J Physiol Heart Circ Physiol 2005; 289:H66-77. [PMID: 15764674 DOI: 10.1152/ajpheart.01296.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
To delineate the role of mitochondrial K+ fluxes in cardioprotection, we investigated the effect of extramitochondrial K+ on the ability of mitochondria to support membrane potential (DeltaPsi), regulate matrix volume, consume oxygen, and phosphorylate ADP under conditions mimicking key elements of ischemia-reperfusion. Isolated energized mitochondria responded to ADP addition with depolarization, increased O2 consumption, and matrix shrinkage. The time required for full recovery of DeltaPsi, signaling the completion of ADP phosphorylation, was used to evaluate the rate of ATP synthesis during repeated ADP pulses. In mitochondria with a decreased ability to support DeltaPsi, the rate of ADP phosphorylation was significantly improved by extramitochondrial K+ > Na+ > Li+, especially at higher buffer osmolarity, which promotes matrix shrinkage. K+-induced improvement in DeltaPsi recovery after ADP pulses was accompanied by more rapid and complete matrix volume recovery and enhanced O2 consumption. Manipulations expected to affect matrix swelling by regulating K+ fluxes or water distribution indicate that matrix volume regulation by external factors becomes increasingly important in mitochondria with decreased ability to support DeltaPsi in the face of a high ADP load. Under these conditions, opening of K+ influx pathways improved mitochondrial function and delayed failure. This may be an important factor in the mechanism of diaxozide-induced cardioprotection.
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Affiliation(s)
- Paavo Korge
- Cardiovascular Research Laboratory, 3645 MRL Bldg., 675 Charles Young Dr. S., David Geffen School of Medicine, Univ. of California, Los Angeles, CA 90095, USA.
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23
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Vicente JAF, Madeira VMC, Vercesi AE. Regulation by Magnesium of Potato Tuber Mitochondrial Respiratory Activities. J Bioenerg Biomembr 2004; 36:525-31. [PMID: 15692731 DOI: 10.1007/s10863-004-8999-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Dehydrogenase activities of potato tuber mitochondria and corresponding phosphorylation rates were measured for the dependence on external and mitochondrial matrix Mg2+. Magnesium stimulated state 3 and state 4 respiration, with significantly different concentrations of matrix Mg2+ required for optimal activities of the several substrates. Maximal stimulation of respiration with all substrates was obtained at 2-mM external Mg2+. However, respiration of malate, citrate, and alpha-ketoglutarate requires at least 4-mM Mg2+ inside mitochondria for maximization of dehydrogenase activities. The phosphorylation system, requires a low level of internal Mg2+ (0.25 mM) to reach high activity, as judged by succinate-dependent respiration. However, mitochondria respiring on citrate or alpha-ketoglutarate only sustain high levels of phosphorylation with at least 4-mM matrix Mg2+. Respiration of succinate is active without external and matrix Mg2+, although stimulated by the cation. Respiration of alpha-ketoglutarate was strictly dependent on external Mg2+ required for substrate transport into mitochondria, and internal Mg2+ is required for dehydrogenase activity. Respiration of citrate and malate also depend on internal Mg2+ but, unlike alpha-ketoglutarate, some activity still remains without external Mg2+. All the substrates revealed insensitive to external and internal mitochondrial Ca2+, except the exogenous NADH dehydrogenase, which requires either external Ca2+ or Mg2+ for detectable activity. Calcium is more efficient than Mg2+, both having cumulative stimulation. Unlike Ca2+, Mn2+ could substitute for Mg2+, before and after addition of A23, showing its ability to regulate phosphorylation and succinate dehydrogenase activities, with almost the same efficiency as Mg2+.
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24
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Koslowsky DJ, Reifur L, Yu LE, Chen W. Evidence for U-tail stabilization of gRNA/mRNA interactions in kinetoplastid RNA editing. RNA Biol 2004; 1:28-34. [PMID: 17194935 PMCID: PMC2762388 DOI: 10.4161/rna.1.1.898] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The most dramatic example of RNA editing is found in the mitochondria of trypanosomes. In these organisms, U-insertions/deletions can create mRNAs that are twice as large as the gene that encodes them. Guide RNAs (gRNAs) that are complementary to short stretches of the mature message direct the precise placements of the U residues. The binding of gRNA to mRNA is a fundamental step in RNA editing and understanding the relative importance of the elements that confer affinity and specificity on this interaction is critical to our understanding of the editing process. In this study, we have analyzed the relative binding affinities of two different gRNA/mRNA pairs. The affinity of gA6-14 for its message (ATPase 6) is high, with an apparent K(D) in the 5-10 nM range. In contrast, gCYb-558 has a low affinity for its cognate mRNA. Deletion of the gRNA U-tail caused a significant reduction in the binding affinity for only the gCYb-558 pair, and was observed only under physiological magnesium conditions. These results indicate that the U-tail contribution can differ substantially between the different gRNA/mRNA pairs. In addition, our results suggest that the efficiency of gRNA/mRNA interaction is highly dependent on thermodynamic parameters determined by the local sequences and their adopted structures surrounding the anchor-binding site.
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Affiliation(s)
- Donna J Koslowsky
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824, USA.
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25
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Martínez F, Uribe A, Milán R, Teresa Espinosa-García M, Gracía-Pérez C, Flores-Herrera O. Differential effects of magnesium on the hydrolysis of ADP and ATP in human term placenta. Effect of substrates and potassium. Int J Biochem Cell Biol 2002; 34:1004-16. [PMID: 12007638 DOI: 10.1016/s1357-2725(02)00021-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
This study evaluates the effect of Mg2+ on the extramitochondrial hydrolysis of ATP and ADP by human term placental mitochondria (HPM) and submitochondrial particle (SMP). Extramitochondrial ATPase and ADPase activities were evaluated in the presence or absence of K+, and different oxidizable substrates. Mg2+ increased both ATP and ADP hydrolysis according to the experimental conditions, and this stimulation was related to the mitochondrial intactness. The ADPase activity in intact mitochondria is 100-fold higher in presence of K+, succinate and 1mM Mg2+ while this activity is only increased by two-fold on the SMP when compared to the sample without Mg2+. It is clearly demonstrated that up-regulation of these enzyme activities occur in intact mitochondria and not on the enzyme itself. The results suggest that the regulation of ATP and ADP hydrolysis is complex, and Mg2+ plays an important role in the modulation of the extramitochondrial ATPase and ADPase activities in HPM
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Affiliation(s)
- Federico Martínez
- Departamento de Bioquímica, Facultad de Medicina, UNAM Apdo, Postal 70-159, Mexico City, Mexico.
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26
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Schönfeld P, Schüttig R, Wojtczak L. Rapid release of Mg(2+) from liver mitochondria by nonesterified long-chain fatty acids in alkaline media. Arch Biochem Biophys 2002; 403:16-24. [PMID: 12061797 DOI: 10.1016/s0003-9861(02)00206-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Long-chain fatty acids induce a rapid release of Mg(2+) from both energized and nonenergized rat liver mitochondria suspended at pH 8 in isotonic saline but not sucrose media. The effect is observed only with fatty acids that possess protonophoric activity. The most active saturated fatty acids are myristic and palmitic, while the most active unsaturated acids are oleic, linolenic, and arachidonic. The rate of Mg(2+) release drastically decreases with decreasing medium pH to 7.2-7.6. However, at those pH values this rate is doubled by energization of mitochondria with respiratory substrates. Mg(2+) release is accompanied by cyclosporin A-insensitive large-amplitude swelling of mitochondria. This swelling is similar to that produced by the divalent metal ionophore A23187 and is interpreted as being due to activation of the inner membrane anion channel, the K(+) uniporter, and the K(+)/H(+) exchanger. In energized mitochondria, both swelling and Mg(2+) release are blocked by the exogenous K(+)/H(+) exchanger nigericin. It is proposed that fatty acids under conditions of alkaline mitochondrial matrix activate latent Mg(2+)-sensitive ion-conducting pathways in the inner mitochondrial membrane, which mediate swelling and Mg(2+) release. It is hypothesized that fatty acids activate an intrinsic Mg(2+)/H(+) exchanger that is related to, or identical with, the K(+)/H(+) exchanger.
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Affiliation(s)
- Peter Schönfeld
- Institute of Biochemistry, Otto-von-Guericke-University, Leipziger Strasse 44, D-39120 Magdeburg, Germany.
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27
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Korge P, Honda HM, Weiss JN. Protection of cardiac mitochondria by diazoxide and protein kinase C: implications for ischemic preconditioning. Proc Natl Acad Sci U S A 2002; 99:3312-7. [PMID: 11867760 PMCID: PMC122515 DOI: 10.1073/pnas.052713199] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial ATP-sensitive K (mitoK(ATP)) channels play a central role in protecting the heart from injury in ischemic preconditioning. In isolated mitochondria exposed to elevated extramitochondrial Ca, P(i), and anoxia to simulate ischemic conditions, the selective mitoK(ATP) channel agonist diazoxide (25-50 microM) potently reduced mitochondrial injury by preventing both the mitochondrial permeability transition (MPT) and cytochrome c loss from the intermembrane space. Both effects were blocked completely by the selective mitoK(ATP) antagonist 5-hydroxydecanoate. The protective effect against Ca-induced MPT was most evident under conditions in which the ability of electron transport to support membrane potential (Deltapsi(m)) was decreased and inner membrane leakiness was increased moderately. Under these conditions, mitoK(ATP) channel activity strongly regulated Deltapsi(m), and diazoxide prevented MPT by inhibiting the driving force for Ca uptake. Phorbol 12-myristate 13-acetate mimicked the protective effects of diazoxide, unless 5-hydroxydecanoate was present, indicating that protein kinase C activation also protects mitochondria by activating mitoK(ATP) channels. Because Deltapsi(m) recovery ultimately is required for heart functional recovery, these results may explain how mitoK(ATP) channel activation mimics ischemic preconditioning by protecting mitochondria as they pass through a critical vulnerability window during ischemia/reperfusion.
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Affiliation(s)
- Paavo Korge
- University of California Cardiovascular Research Laboratory and Department of Medicine (Cardiology), University of California School of Medicine, Los Angeles, CA 90095, USA
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28
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Grivennikova VG, Kapustin AN, Vinogradov AD. Catalytic activity of NADH-ubiquinone oxidoreductase (complex I) in intact mitochondria. evidence for the slow active/inactive transition. J Biol Chem 2001; 276:9038-44. [PMID: 11124957 DOI: 10.1074/jbc.m009661200] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian purified dispersed NADH-ubiquinone oxidoreductase (Complex I) and the enzyme in inside-out submitochondrial particles are known to be the slowly equilibrating mixture of the active and de-activated forms (Vinogradov, A. D. (1998) Biochim. Biophys. Acta 1364, 169-185). We report here the phenomenon of slow active/de-active transition in intact mitochondria where the enzyme is located within its natural environment being exposed to numerous mitochondrial matrix proteins. A simple procedure for permeabilization of intact mitochondria by channel-forming antibiotic alamethicin was worked out for the "in situ" assay of Complex I activity. Alamethicin-treated mitochondria catalyzed the rotenone-sensitive NADH-quinone reductase reaction with exogenousely added NADH and quinone-acceptor at the rates expected if the enzyme active sites would be freely accessible for the substrates. The matrix proteins were retained in alamethicin-treated mitochondria as judged by their high rotenone-sensitive malate-cytochrome c reductase activity in the presence of added NAD(+). The sensitivity of Complex I to N-ethylmaleimide and to the presence of Mg(2+) was used as the diagnostic tools to detect the presence of the de-activated enzyme. The NADH-quinone reductase activity of alamethicin-treated mitochondria was sensitive to neither N-ethylmaleimide nor Mg(2+). After exposure to elevated temperature (37 degrees C, the conditions known to induce de-activation of Complex I) the enzyme activity became sensitive to the sulfhydryl reagent and/or Mg(2+). The sensitivity to both inhibitors disappeared after brief exposure of the thermally de-activated mitochondria with malate/glutamate, NAD(+), and cytochrome c (the conditions known for the turnover-induced reactivation of the enzyme). We conclude that the slow active/de-active Complex I transition is a characteristic feature of the enzyme in intact mitochondria and discuss its possible physiological significance.
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Affiliation(s)
- V G Grivennikova
- Department of Biochemistry, School of Biology, Moscow State University, Moscow 119899, Russian Federation
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Zsurka G, Gregán J, Schweyen RJ. The human mitochondrial Mrs2 protein functionally substitutes for its yeast homologue, a candidate magnesium transporter. Genomics 2001; 72:158-68. [PMID: 11401429 DOI: 10.1006/geno.2000.6407] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We report here on the human MRS2 gene that encodes a protein, hsaMrs2p, the first molecularly characterized candidate for a magnesium transporter in metazoa. The protein, like the yeast mitochondrial Mrs2 and Lpe10 proteins, contains two predicted transmembrane domains in its carboxyl-terminus, the first of which terminates with the conserved motif F/Y-G-M-N. These are typical features of the CorA family of magnesium transporters. Expression of hsaMrs2p in mrs2-1 knock-out mutant yeast partly restores mitochondrial magnesium concentrations that are significantly reduced in this mutant. It also alleviates other defects of this mutant, which may be secondary to the reduction in magnesium concentrations. These findings suggest that hsaMrs2p and yMrs2p are functional homologues. Like its yeast homologues, hsaMrs2p has been localized in mitochondria. The hsaMRS2 gene is located on chromosome 6 (6p22.1-p22.3) and is composed of 11 exons. A low level of the transcript is detected in various mouse tissues.
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Affiliation(s)
- G Zsurka
- Vienna Biocenter, Department of Microbiology and Genetics, University of Vienna, Dr. Bohrgasse 9, Vienna, A-1030, Austria
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Jung DW, Brierley GP. Matrix free Mg(2+) and the regulation of mitochondrial volume. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:C1194-201. [PMID: 10600771 DOI: 10.1152/ajpcell.1999.277.6.c1194] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondria must maintain volume homeostasis in order to carry out oxidative phosphorylation. It has been postulated that the concentration of free Mg(2+) ([Mg(2+)]) serves as the sensor of matrix volume and regulates a K(+)-extruding K(+)/H(+) antiport (K. D. Garlid. J. Biol. Chem. 255: 11273-11279, 1980). To test this hypothesis, the fluorescent probe furaptra was used to monitor [Mg(2+)] and free Ca(2+) concentration ([Ca(2+)]) in the matrix of isolated beef heart mitochondria, and K(+)/H(+) antiport activity was measured by passive swelling in potassium acetate. Concentrations that result in 50% inhibition of maximum activity of 92 microM matrix [Mg(2+)] and 2.2 microM [Ca(2+)] were determined for the K(+)/H(+) antiport. Untreated mitochondria average 670 microM matrix [Mg(2+)], a value that would permit <1% of maximum K(+)/H(+) antiport activity. Hypotonic swelling results in large decreases in matrix [Mg(2+)], but swelling due to accumulation of acetate salts does not alter [Mg(2+)]. Swelling in phosphate salts decreases matrix [Mg(2+)], but not to levels that permit appreciable antiport activity. We conclude that 1) it is unlikely that matrix [Mg(2+)] serves as the mitochondrial volume sensor, 2) if K(+)/H(+) antiport functions as a volume control transporter, it is probably regulated by factors other than [Mg(2+)], and 3) alternative mechanisms for mitochondrial volume control should be considered.
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Affiliation(s)
- D W Jung
- Department of Medical Biochemistry, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
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