51
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A trypanosomal pentatricopeptide repeat protein stabilizes the mitochondrial mRNAs of cytochrome oxidase subunits 1 and 2. EUKARYOTIC CELL 2011; 11:79-87. [PMID: 22058141 DOI: 10.1128/ec.05213-11] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The pentatricopeptide repeat (PPR) protein family consists of organellar proteins predicted to bind to specific RNA sequences. Plants have hundreds of distinct PPR proteins, whereas other eukaryotes generally have many fewer. The genome of the parasitic protozoon Trypanosoma brucei is predicted to encode more than 30 different PPR proteins, which is an extraordinarily high number for a nonplant organism. Here we report the characterization T. brucei PPR9 (TbPPR9). Epitope tagging shows that the protein is exclusively mitochondrially localized. Interestingly, while in induced RNA interference cell lines TbPPR9 is efficiently downregulated, the level of its mRNA is not affected. Ablation of TbPPR9 selectively abolishes oxidative but not mitochondrial substrate-level phosphorylation. The molecular basis of this phenotype is the fact that TbPPR9 is required for the stability of the cytochrome oxidase subunit 1 (COX1) and COX2 mRNAs. This is supported by the observation that ablation of TbPPR9 destabilizes the COX complex but not the cytochrome bc1 or the ATP synthase complex. Moreover, it was shown by blue native gel electrophoresis that TbPPR9 is present in a large complex of unknown composition.
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52
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Pusnik M, Schmidt O, Perry AJ, Oeljeklaus S, Niemann M, Warscheid B, Lithgow T, Meisinger C, Schneider A. Mitochondrial preprotein translocase of trypanosomatids has a bacterial origin. Curr Biol 2011; 21:1738-43. [PMID: 22000100 DOI: 10.1016/j.cub.2011.08.060] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Revised: 08/22/2011] [Accepted: 08/30/2011] [Indexed: 11/25/2022]
Abstract
Mitochondria are found in all eukaryotic cells and derive from a bacterial endosymbiont [1, 2]. The evolution of a protein import system was a prerequisite for the conversion of the endosymbiont into a true organelle. Tom40, the essential component of the protein translocase of the outer membrane, is conserved in mitochondria of almost all eukaryotes but lacks bacterial orthologs [3-6]. It serves as the gateway through which all mitochondrial proteins are imported. The parasitic protozoa Trypanosoma brucei and its relatives do not have a Tom40-like protein, which raises the question of how proteins are imported by their mitochondria [7, 8]. Using a combination of bioinformatics and in vivo and in vitro studies, we have discovered that T. brucei likely employs a different import channel, termed ATOM (archaic translocase of the outer mitochondrial membrane). ATOM mediates the import of nuclear-encoded proteins into mitochondria and is essential for viability of trypanosomes. It is not related to Tom40 but is instead an ortholog of a subgroup of the Omp85 protein superfamily that is involved in membrane translocation and insertion of bacterial outer membrane proteins [9]. This suggests that the protein import channel in trypanosomes is a relic of an archaic protein transport system that was operational in the ancestor of all eukaryotes.
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Affiliation(s)
- Mascha Pusnik
- Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland
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53
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Becker T, Wenz LS, Krüger V, Lehmann W, Müller JM, Goroncy L, Zufall N, Lithgow T, Guiard B, Chacinska A, Wagner R, Meisinger C, Pfanner N. The mitochondrial import protein Mim1 promotes biogenesis of multispanning outer membrane proteins. ACTA ACUST UNITED AC 2011; 194:387-95. [PMID: 21825073 PMCID: PMC3153637 DOI: 10.1083/jcb.201102044] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The Mim1 complex imports α-helical mitochondrial outer membrane proteins with multiple transmembrane segments. The mitochondrial outer membrane contains translocase complexes for the import of precursor proteins. The translocase of the outer membrane complex functions as a general preprotein entry gate, whereas the sorting and assembly machinery complex mediates membrane insertion of β-barrel proteins of the outer membrane. Several α-helical outer membrane proteins are known to carry multiple transmembrane segments; however, only limited information is available on the biogenesis of these proteins. We report that mitochondria lacking the mitochondrial import protein 1 (Mim1) are impaired in the biogenesis of multispanning outer membrane proteins, whereas overexpression of Mim1 stimulates their import. The Mim1 complex cooperates with the receptor Tom70 in binding of precursor proteins and promotes their insertion and assembly into the outer membrane. We conclude that the Mim1 complex plays a central role in the import of α-helical outer membrane proteins with multiple transmembrane segments.
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Affiliation(s)
- Thomas Becker
- Institute for Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research, Freiburg, Germany
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54
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Marom M, Dayan D, Demishtein-Zohary K, Mokranjac D, Neupert W, Azem A. Direct interaction of mitochondrial targeting presequences with purified components of the TIM23 protein complex. J Biol Chem 2011; 286:43809-43815. [PMID: 21969381 DOI: 10.1074/jbc.m111.261040] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Precursor proteins that are imported from the cytosol into the matrix of mitochondria carry positively charged amphipathic presequences and cross the inner membrane with the help of vital components of the TIM23 complex. It is currently unclear which subunits of the TIM23 complex recognize and directly bind to presequences. Here we analyzed the binding of presequence peptides to purified components of the TIM23 complex. The interaction of three different presequences with purified soluble domains of yeast Tim50 (Tim50IMS), Tim23 (Tim23IMS), and full-length Tim44 was examined. Using chemical cross-linking and surface plasmon resonance we demonstrate, for the first time, the ability of purified Tim50IMS and Tim44 to interact directly with the yeast Hsp60 presequence. We also analyzed their interaction with presequences derived from precursors of yeast mitochondrial 70-kDa heat shock protein (mHsp70) and of bovine cytochrome P450SCC. Moreover, we characterized the nature of the interactions and determined their KDs. On the basis of our results, we suggest a mechanism of translocation where stronger interactions of the presequences on the trans side of the channel support the import of precursor proteins through TIM23 into the matrix.
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Affiliation(s)
- Milit Marom
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Dana Dayan
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Keren Demishtein-Zohary
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Dejana Mokranjac
- Institute for Physiological Chemistry, University of Munich, Munich 81377, Germany
| | - Walter Neupert
- Max Planck Institute of Biochemistry, Martinsried 82152, Germany
| | - Abdussalam Azem
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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55
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von der Malsburg K, Müller J, Bohnert M, Oeljeklaus S, Kwiatkowska P, Becker T, Loniewska-Lwowska A, Wiese S, Rao S, Milenkovic D, Hutu D, Zerbes R, Schulze-Specking A, Meyer H, Martinou JC, Rospert S, Rehling P, Meisinger C, Veenhuis M, Warscheid B, van der Klei I, Pfanner N, Chacinska A, van der Laan M. Dual Role of Mitofilin in Mitochondrial Membrane Organization and Protein Biogenesis. Dev Cell 2011; 21:694-707. [DOI: 10.1016/j.devcel.2011.08.026] [Citation(s) in RCA: 316] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2011] [Revised: 08/25/2011] [Accepted: 08/29/2011] [Indexed: 11/28/2022]
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56
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Sharma NK, Reyes A, Green P, Caron MJ, Bonini MG, Gordon DM, Holt IJ, Santos JH. Human telomerase acts as a hTR-independent reverse transcriptase in mitochondria. Nucleic Acids Res 2011; 40:712-25. [PMID: 21937513 PMCID: PMC3258147 DOI: 10.1093/nar/gkr758] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is localized to mitochondria, as well as the nucleus, but details about its biology and function in the organelle remain largely unknown. Here we show, using multiple approaches, that mammalian TERT is mitochondrial, co-purifying with mitochondrial nucleoids and tRNAs. We demonstrate the canonical nuclear RNA [human telomerase RNA (hTR)] is not present in human mitochondria and not required for the mitochondrial effects of telomerase, which nevertheless rely on reverse transcriptase (RT) activity. Using RNA immunoprecipitations from whole cell and in organello, we show that hTERT binds various mitochondrial RNAs, suggesting that RT activity in the organelle is reconstituted with mitochondrial RNAs. In support of this conclusion, TERT drives first strand cDNA synthesis in vitro in the absence of hTR. Finally, we demonstrate that absence of hTERT specifically in mitochondria with maintenance of its nuclear function negatively impacts the organelle. Our data indicate that mitochondrial hTERT works as a hTR-independent reverse transcriptase, and highlight that nuclear and mitochondrial telomerases have different cellular functions. The implications of these findings to both the mitochondrial and telomerase fields are discussed.
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Affiliation(s)
- Nilesh K Sharma
- Department of Pharmacology and Physiology, New Jersey Medical School of UMDNJ, 185 South Orange Avenue, Medical Sciences Building, Newark, NJ 07103, USA
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57
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Stroud DA, Oeljeklaus S, Wiese S, Bohnert M, Lewandrowski U, Sickmann A, Guiard B, van der Laan M, Warscheid B, Wiedemann N. Composition and topology of the endoplasmic reticulum-mitochondria encounter structure. J Mol Biol 2011; 413:743-50. [PMID: 21945531 DOI: 10.1016/j.jmb.2011.09.012] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 09/05/2011] [Accepted: 09/07/2011] [Indexed: 11/17/2022]
Abstract
Eukaryotic cells contain multiple organelles, which are functionally and structurally interconnected. The endoplasmic reticulum-mitochondria encounter structure (ERMES) forms a junction between mitochondria and the endoplasmic reticulum (ER). Four ERMES proteins are known in yeast, the ER-anchored protein Mmm1 and three mitochondria-associated proteins, Mdm10, Mdm12 and Mdm34, with functions related to mitochondrial morphology and protein biogenesis. We mapped the glycosylation sites of ERMES and demonstrate that three asparagine residues in the N‑terminal domain of Mmm1 are glycosylated. While the glycosylation is dispensable, the cytosolic C‑terminal domain of Mmm1 that connects to the Mdm proteins is required for Mmm1 function. To analyze the composition of ERMES, we determined the subunits by quantitative mass spectrometry. We identified the calcium-binding GTPase Gem1 as a new ERMES subunit, revealing that ERMES is composed of five genuine subunits. Taken together, ERMES represents a platform that integrates components with functions in formation of ER-mitochondria junctions, maintenance of mitochondrial morphology, protein biogenesis and calcium binding.
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Affiliation(s)
- David A Stroud
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany
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58
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Stroud DA, Becker T, Qiu J, Stojanovski D, Pfannschmidt S, Wirth C, Hunte C, Guiard B, Meisinger C, Pfanner N, Wiedemann N. Biogenesis of mitochondrial β-barrel proteins: the POTRA domain is involved in precursor release from the SAM complex. Mol Biol Cell 2011; 22:2823-33. [PMID: 21680715 PMCID: PMC3154879 DOI: 10.1091/mbc.e11-02-0148] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The mitochondrial outer membrane contains proteinaceous machineries for the translocation of precursor proteins. The sorting and assembly machinery (SAM) is required for the insertion of β-barrel proteins into the outer membrane. Sam50 is the channel-forming core subunit of the SAM complex and belongs to the BamA/Sam50/Toc75 family of proteins that have been conserved from Gram-negative bacteria to mitochondria and chloroplasts. These proteins contain one or more N-terminal polypeptide transport-associated (POTRA) domains. POTRA domains can bind precursor proteins, however, different views exist on the role of POTRA domains in the biogenesis of β-barrel proteins. It has been suggested that the single POTRA domain of mitochondrial Sam50 plays a receptor-like function at the SAM complex. We established a system to monitor the interaction of chemical amounts of β-barrel precursor proteins with the SAM complex of wild-type and mutant yeast in organello. We report that the SAM complex lacking the POTRA domain of Sam50 efficiently binds β-barrel precursors, but is impaired in the release of the precursors. These results indicate the POTRA domain of Sam50 is not essential for recognition of β-barrel precursors but functions in a subsequent step to promote the release of precursor proteins from the SAM complex.
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Affiliation(s)
- David A Stroud
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany
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59
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Biogenesis of Mitochondria: Dual Role of Tom7 in Modulating Assembly of the Preprotein Translocase of the Outer Membrane. J Mol Biol 2011; 405:113-24. [DOI: 10.1016/j.jmb.2010.11.002] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2010] [Revised: 10/25/2010] [Accepted: 11/02/2010] [Indexed: 11/21/2022]
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60
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Regulation of Mitochondrial Protein Import by Cytosolic Kinases. Cell 2011; 144:227-39. [DOI: 10.1016/j.cell.2010.12.015] [Citation(s) in RCA: 189] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Revised: 09/04/2010] [Accepted: 12/07/2010] [Indexed: 12/27/2022]
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61
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Baseler WA, Dabkowski ER, Williamson CL, Croston TL, Thapa D, Powell MJ, Razunguzwa TT, Hollander JM. Proteomic alterations of distinct mitochondrial subpopulations in the type 1 diabetic heart: contribution of protein import dysfunction. Am J Physiol Regul Integr Comp Physiol 2010; 300:R186-200. [PMID: 21048079 DOI: 10.1152/ajpregu.00423.2010] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Diabetic cardiomyopathy is associated with increased risk of heart failure in type 1 diabetic patients. Mitochondrial dysfunction is suggested as an underlying contributor to diabetic cardiomyopathy. Cardiac mitochondria are characterized by subcellular spatial locale, including mitochondria located beneath the sarcolemma, subsarcolemmal mitochondria (SSM), and mitochondria situated between the myofibrils, interfibrillar mitochondria (IFM). The goal of this study was to determine whether type 1 diabetic insult in the heart influences proteomic make-up of spatially distinct mitochondrial subpopulations and to evaluate the role of nuclear encoded mitochondrial protein import. Utilizing multiple proteomic approaches (iTRAQ and two-dimensional-differential in-gel electrophoresis), IFM proteomic make-up was impacted by type 1 diabetes mellitus to a greater extent than SSM, as evidenced by decreased abundance of fatty acid oxidation and electron transport chain proteins. Mitochondrial phosphate carrier and adenine nucleotide translocator, as well as inner membrane translocases, were decreased in the diabetic IFM (P < 0.05 for both). Mitofilin, a protein involved in cristae morphology, was diminished in the diabetic IFM (P < 0.05). Posttranslational modifications, including oxidations and deamidations, were most prevalent in the diabetic IFM. Mitochondrial heat shock protein 70 (mtHsp70) was significantly decreased in diabetic IFM (P < 0.05). Mitochondrial protein import was decreased in the diabetic IFM with no change in the diabetic SSM (P < 0.05). Taken together, these results indicate that mitochondrial proteomic alterations in the type 1 diabetic heart are more pronounced in the IFM. Further, proteomic alterations are associated with nuclear encoded mitochondrial protein import dysfunction and loss of an essential mitochondrial protein import constituent, mtHsp70, implicating this process in the pathogenesis of the diabetic heart.
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Affiliation(s)
- Walter A Baseler
- West Virginia University School of Medicine, Division of Exercise Physiology, Center for Cardiovascular and Respiratory Sciences, 1 Medical Center Dr., Morgantown, WV 26506, USA
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62
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Lazarou M, Stojanovski D, Frazier AE, Kotevski A, Dewson G, Craigen WJ, Kluck RM, Vaux DL, Ryan MT. Inhibition of Bak activation by VDAC2 is dependent on the Bak transmembrane anchor. J Biol Chem 2010; 285:36876-83. [PMID: 20851889 DOI: 10.1074/jbc.m110.159301] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bax and Bak are pro-apoptotic factors that are required for cell death by the mitochondrial or intrinsic pathway. Bax is found in an inactive state in the cytosol and upon activation is targeted to the mitochondrial outer membrane where it releases cytochrome c and other factors that cause caspase activation. Although Bak functions in the same way as Bax, it is constitutively localized to the mitochondrial outer membrane. In the membrane, Bak activation is inhibited by the voltage-dependent anion channel isoform 2 (VDAC2) by an unknown mechanism. Using blue native gel electrophoresis, we show that in healthy cells endogenous inactive Bak exists in a 400-kDa complex that is dependent on the presence of VDAC2. Activation of Bak is concomitant with its release from the 400-kDa complex and the formation of lower molecular weight species. Furthermore, substitution of the Bak transmembrane anchor with that of the mitochondrial outer membrane tail-anchored protein hFis1 prevents association of Bak with the VDAC2 complex and increases the sensitivity of cells to an apoptotic stimulus. Our results suggest that VDAC2 interacts with the hydrophobic tail of Bak to sequester it in an inactive state in the mitochondrial outer membrane, thereby raising the stimulation threshold necessary for permeabilization of the mitochondrial outer membrane and cell death.
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Affiliation(s)
- Michael Lazarou
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia
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63
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Becker T, Guiard B, Thornton N, Zufall N, Stroud DA, Wiedemann N, Pfanner N. Assembly of the mitochondrial protein import channel: role of Tom5 in two-stage interaction of Tom40 with the SAM complex. Mol Biol Cell 2010; 21:3106-13. [PMID: 20668160 PMCID: PMC2938377 DOI: 10.1091/mbc.e10-06-0518] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Tom40 forms the channel of the mitochondrial preprotein translocase. This beta-barrel protein assembles with alpha-helical proteins, however little is known about the mechanism of assembly. Becker et al identified a new intermediate in Tom40 assembly and show that small alpha-helical Tom proteins associate with Tom40 directly at the SAM complex. The preprotein translocase of the outer mitochondrial membrane (TOM) consists of a central β-barrel channel, Tom40, and six proteins with α-helical transmembrane segments. The precursor of Tom40 is imported from the cytosol by a pre-existing TOM complex and inserted into the outer membrane by the sorting and assembly machinery (SAM). Tom40 then assembles with α-helical Tom proteins to the mature TOM complex. The outer membrane protein Mim1 promotes membrane insertion of several α-helical Tom proteins but also affects the biogenesis of Tom40 by an unknown mechanism. We have identified a novel intermediate in the assembly pathway of Tom40, revealing a two-stage interaction of the precursor with the SAM complex. The second SAM stage represents assembly of Tom5 with the precursor of Tom40. Mim1-deficient mitochondria accumulate Tom40 at the first SAM stage like Tom5-deficient mitochondria. Tom5 promotes formation of the second SAM stage and thus suppresses the Tom40 assembly defect of mim1Δ mitochondria. We conclude that the assembly of newly imported Tom40 is directly initiated at the SAM complex by its association with Tom5. The involvement of Mim1 in Tom40 biogenesis can be largely attributed to its role in import of Tom5.
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Affiliation(s)
- Thomas Becker
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, Freiburg, Germany
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64
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Nautiyal M, Sweatt AJ, MacKenzie JA, Mark Payne R, Szucs S, Matalon R, Wallin R, Hutson SM. Neuronal localization of the mitochondrial protein NIPSNAP1 in rat nervous system. Eur J Neurosci 2010; 32:560-9. [DOI: 10.1111/j.1460-9568.2010.07326.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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65
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Wagner K, Perschil I, Fichter CD, van der Laan M. Stepwise assembly of dimeric F(1)F(o)-ATP synthase in mitochondria involves the small F(o)-subunits k and i. Mol Biol Cell 2010; 21:1494-504. [PMID: 20219971 PMCID: PMC2861609 DOI: 10.1091/mbc.e09-12-1023] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Oligomerization of F1Fo-ATP synthase in the inner mitochondrial membrane governs the formation of cristae membrane domains. We show that the F1Fo-subunits Su i and Su k are crucial for the formation and maturation of ATP synthase dimers and oligomers. Su i additionally facilitates the incorporation of new subunits into ATP synthase monomers. F1Fo-ATP synthase is a key enzyme of oxidative phosphorylation that is localized in the inner membrane of mitochondria. It uses the energy stored in the proton gradient across the inner mitochondrial membrane to catalyze the synthesis of ATP from ADP and phosphate. Dimeric and higher oligomeric forms of ATP synthase have been observed in mitochondria from various organisms. Oligomerization of ATP synthase is critical for the morphology of the inner mitochondrial membrane because it supports the generation of tubular cristae membrane domains. Association of individual F1Fo-ATP synthase complexes is mediated by the membrane-embedded Fo-part. Several subunits were mapped to monomer-monomer-interfaces of yeast ATP synthase complexes, but only Su e (Atp21) and Su g (Atp20) have so far been identified as crucial for the formation of stable dimers. We show that two other small Fo-components, Su k (Atp19) and Su i (Atp18) are involved in the stepwise assembly of F1Fo-ATP synthase dimers and oligomers. We have identified an intermediate form of the ATP synthase dimer, which accumulates in the absence of Su i. Moreover, our data indicate that Su i facilitates the incorporation of newly synthesized subunits into ATP synthase complexes.
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Affiliation(s)
- Karina Wagner
- Institut für Biochemie und Molekularbiologie, Freiburg, Germany
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66
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Two Modular Forms of the Mitochondrial Sorting and Assembly Machinery Are Involved in Biogenesis of α-Helical Outer Membrane Proteins. J Mol Biol 2010; 396:540-9. [DOI: 10.1016/j.jmb.2009.12.026] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Revised: 12/11/2009] [Accepted: 12/13/2009] [Indexed: 11/19/2022]
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67
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Kamenisch Y, Fousteri M, Knoch J, von Thaler AK, Fehrenbacher B, Kato H, Becker T, Dollé MET, Kuiper R, Majora M, Schaller M, van der Horst GTJ, van Steeg H, Röcken M, Rapaport D, Krutmann J, Mullenders LH, Berneburg M. Proteins of nucleotide and base excision repair pathways interact in mitochondria to protect from loss of subcutaneous fat, a hallmark of aging. ACTA ACUST UNITED AC 2010; 207:379-90. [PMID: 20100872 PMCID: PMC2822596 DOI: 10.1084/jem.20091834] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Defects in the DNA repair mechanism nucleotide excision repair (NER) may lead to tumors in xeroderma pigmentosum (XP) or to premature aging with loss of subcutaneous fat in Cockayne syndrome (CS). Mutations of mitochondrial (mt)DNA play a role in aging, but a link between the NER-associated CS proteins and base excision repair (BER)-associated proteins in mitochondrial aging remains enigmatic. We show functional increase of CSA and CSB inside mt and complex formation with mtDNA, mt human 8-oxoguanine glycosylase (mtOGG)-1, and mt single-stranded DNA binding protein (mtSSBP)-1 upon oxidative stress. MtDNA mutations are highly increased in cells from CS patients and in subcutaneous fat of aged Csb(m/m) and Csa(-/-) mice. Thus, the NER-proteins CSA and CSB localize to mt and directly interact with BER-associated human mitochondrial 8-oxoguanine glycosylase-1 to protect from aging- and stress-induced mtDNA mutations and apoptosis-mediated loss of subcutaneous fat, a hallmark of aging found in animal models, human progeroid syndromes like CS and in normal human aging.
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Affiliation(s)
- York Kamenisch
- Department of Dermatology, Eberhard Karls University, D-72076 Tuebingen, Germany
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68
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Abstract
The rubella virus (RV) capsid is an RNA-binding protein that functions in nucleocapsid assembly at the Golgi complex, the site of virus budding. In addition to its role in virus assembly, pools of capsid associate with mitochondria, a localization that is not consistent with virus assembly. Here we examined the interaction of capsid with mitochondria and showed that this viral protein inhibits the import and processing of mitochondrial precursor proteins in vitro. Moreover, RV-infected cells were found to contain lower intramitochondrial levels of matrix protein p32. In addition to inhibiting the translocation of substrates into mammalian mitochondria, capsid efficiently blocked import into yeast mitochondria, thereby suggesting that it acts by targeting a highly conserved component of the translocation apparatus. Finally, mutation of a cluster of five arginine residues in the amino terminus of capsid, though not interfering with its binding to mitochondria, abrogated its ability to block protein import into mitochondria. This is the first report of a viral protein that affects the import of proteins into mitochondria.
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69
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Distinct forms of mitochondrial TOM-TIM supercomplexes define signal-dependent states of preprotein sorting. Mol Cell Biol 2010; 30:307-18. [PMID: 19884344 DOI: 10.1128/mcb.00749-09] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial import of cleavable preproteins occurs at translocation contact sites, where the translocase of the outer membrane (TOM) associates with the presequence translocase of the inner membrane (TIM23) in a supercomplex. Different views exist on the mechanism of how TIM23 mediates preprotein sorting to either the matrix or inner membrane. On the one hand, two TIM23 forms were proposed, a matrix transport form containing the presequence translocase-associated motor (PAM; TIM23-PAM) and a sorting form containing Tim21 (TIM23(SORT)). On the other hand, it was reported that TIM23 and PAM are permanently associated in a single-entity translocase. We have accumulated distinct transport intermediates of preproteins to analyze the translocases in their active, preprotein-carrying state. We identified two different forms of active TOM-TIM23 supercomplexes, TOM-TIM23(SORT) and TOM-TIM23-PAM. These two supercomplexes do not represent separate pathways but are in dynamic exchange during preprotein translocation and sorting. Depending on the signals of the preproteins, switches between the different forms of supercomplex and TIM23 are required for the completion of preprotein import.
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70
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Wagner K, Rehling P, Sanjuán Szklarz LK, Taylor RD, Pfanner N, van der Laan M. Mitochondrial F1Fo-ATP Synthase: The Small Subunits e and g Associate with Monomeric Complexes to Trigger Dimerization. J Mol Biol 2009; 392:855-61. [DOI: 10.1016/j.jmb.2009.07.059] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2009] [Revised: 07/18/2009] [Accepted: 07/21/2009] [Indexed: 10/20/2022]
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71
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Baker MJ, Webb CT, Stroud DA, Palmer CS, Frazier AE, Guiard B, Chacinska A, Gulbis JM, Ryan MT. Structural and functional requirements for activity of the Tim9-Tim10 complex in mitochondrial protein import. Mol Biol Cell 2008; 20:769-79. [PMID: 19037098 DOI: 10.1091/mbc.e08-09-0903] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Tim9-Tim10 complex plays an essential role in mitochondrial protein import by chaperoning select hydrophobic precursor proteins across the intermembrane space. How the complex interacts with precursors is not clear, although it has been proposed that Tim10 acts in substrate recognition, whereas Tim9 acts in complex stabilization. In this study, we report the structure of the yeast Tim9-Tim10 hexameric assembly determined to 2.5 A and have performed mutational analysis in yeast to evaluate the specific roles of Tim9 and Tim10. Like the human counterparts, each Tim9 and Tim10 subunit contains a central loop flanked by disulfide bonds that separate two extended N- and C-terminal tentacle-like helices. Buried salt-bridges between highly conserved lysine and glutamate residues connect alternating subunits. Mutation of these residues destabilizes the complex, causes defective import of precursor substrates, and results in yeast growth defects. Truncation analysis revealed that in the absence of the N-terminal region of Tim9, the hexameric complex is no longer able to efficiently trap incoming substrates even though contacts with Tim10 are still made. We conclude that Tim9 plays an important functional role that includes facilitating the initial steps in translocating precursor substrates into the intermembrane space.
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Affiliation(s)
- Michael J Baker
- Department of Biochemistry, La Trobe University, Melbourne 3086, Victoria, Australia
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72
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Reddehase S, Grumbt B, Neupert W, Hell K. The disulfide relay system of mitochondria is required for the biogenesis of mitochondrial Ccs1 and Sod1. J Mol Biol 2008; 385:331-8. [PMID: 19010334 DOI: 10.1016/j.jmb.2008.10.088] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 10/23/2008] [Accepted: 10/28/2008] [Indexed: 11/24/2022]
Abstract
Cells protect themselves against oxygen stress and reactive oxygen species. An important enzyme in this process is superoxide dismutase, Sod1, which converts superoxide radicals into water and hydrogen peroxide. The biogenesis of functional Sod1 is dependent on its copper chaperone, Ccs1, which introduces a disulfide bond and a copper ion into Sod1. Ccs1 and Sod1 are present in the cytosol but are also found in the mitochondrial intermembrane space (IMS), the compartment between the outer and the inner membrane of mitochondria. Ccs1 mediates mitochondrial localization of Sod1. Here, we report on the biogenesis of the fractions of Ccs1 and Sod1 present in mitochondria of Saccharomyces cerevisiae. The IMS of mitochondria harbors a disulfide relay system consisting of the import receptor Mia40 and the thiol oxidase Erv1, which drives the import of substrates with conserved cysteine residues arranged in typical twin Cx(3)C and twin Cx(9)C motifs. We show that depletion of Mia40 results in decreased levels of Ccs1 and Sod1. On the other hand, overexpression of Mia40 increased the mitochondrial fraction of both proteins. In addition, the import rates of Ccs1 were enhanced by increased levels of Mia40 and reduced upon depletion of Mia40. Mia40 forms mixed disulfides with Ccs1, suggesting a role of Mia40 for the generation of disulfide bonds in Ccs1. We suggest that the disulfide relay system transfers disulfide bonds via Mia40 to Ccs1, which then shuttles disulfide bonds to Sod1. In conclusion, the disulfide relay system is crucial for the import of Ccs1, thereby affecting the transport of Sod1, and it can control the distribution of Ccs1 and Sod1 between the IMS of mitochondria and the cytosol.
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Affiliation(s)
- Silvia Reddehase
- Adolf-Butenandt-Institut für Physiologische Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5, 81377 München, Germany
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73
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Stojanovski D, Milenkovic D, Müller JM, Gabriel K, Schulze-Specking A, Baker MJ, Ryan MT, Guiard B, Pfanner N, Chacinska A. Mitochondrial protein import: precursor oxidation in a ternary complex with disulfide carrier and sulfhydryl oxidase. ACTA ACUST UNITED AC 2008; 183:195-202. [PMID: 18852299 PMCID: PMC2568017 DOI: 10.1083/jcb.200804095] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The biogenesis of mitochondrial intermembrane space proteins depends on specific machinery that transfers disulfide bonds to precursor proteins. The machinery shares features with protein relays for disulfide bond formation in the bacterial periplasm and endoplasmic reticulum. A disulfide-generating enzyme/sulfhydryl oxidase oxidizes a disulfide carrier protein, which in turn transfers a disulfide to the substrate protein. Current views suggest that the disulfide carrier alternates between binding to the oxidase and the substrate. We have analyzed the cooperation of the disulfide relay components during import of precursors into mitochondria and identified a ternary complex of all three components. The ternary complex represents a transient and intermediate step in the oxidation of intermembrane space precursors, where the oxidase Erv1 promotes disulfide transfer to the precursor while both oxidase and precursor are associated with the disulfide carrier Mia40.
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Affiliation(s)
- Diana Stojanovski
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, 79104 Freiburg, Germany
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74
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Becker T, Pfannschmidt S, Guiard B, Stojanovski D, Milenkovic D, Kutik S, Pfanner N, Meisinger C, Wiedemann N. Biogenesis of the Mitochondrial TOM Complex. J Biol Chem 2008; 283:120-127. [DOI: 10.1074/jbc.m706997200] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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75
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Wiedemann N, van der Laan M, Hutu DP, Rehling P, Pfanner N. Sorting switch of mitochondrial presequence translocase involves coupling of motor module to respiratory chain. ACTA ACUST UNITED AC 2007; 179:1115-22. [PMID: 18070913 PMCID: PMC2140023 DOI: 10.1083/jcb.200709087] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The mitochondrial presequence translocase transports preproteins to either matrix or inner membrane. Two different translocase forms have been identified: the matrix transport form, which binds the heat-shock protein 70 (Hsp70) motor, and the inner membrane–sorting form, which lacks the motor but contains translocase of inner mitochondrial membrane 21 (Tim21). The sorting form interacts with the respiratory chain in a Tim21-dependent manner. It is unknown whether the respiratory chain–bound translocase transports preproteins and how the switch between sorting form and motor form occurs. We report that the respiratory chain–bound translocase contains preproteins in transit and, surprisingly, not only sorted but also matrix-targeted preproteins. Presequence translocase-associated motor (Pam) 16 and 18, two regulatory components of the six-subunit motor, interact with the respiratory chain independently of Tim21. Thus, the respiratory chain–bound presequence translocase is not only active in preprotein sorting to the inner membrane but also in an early stage of matrix translocation. The motor does not assemble en bloc with the translocase but apparently in a step-wise manner with the Pam16/18 module before the Hsp70 core.
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Affiliation(s)
- Nils Wiedemann
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Freiburg, Germany
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76
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Stojanovski D, Guiard B, Kozjak-Pavlovic V, Pfanner N, Meisinger C. Alternative function for the mitochondrial SAM complex in biogenesis of alpha-helical TOM proteins. ACTA ACUST UNITED AC 2007; 179:881-93. [PMID: 18039934 PMCID: PMC2099199 DOI: 10.1083/jcb.200706043] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The mitochondrial outer membrane contains two preprotein translocases: the general translocase of outer membrane (TOM) and the β-barrel–specific sorting and assembly machinery (SAM). TOM functions as the central entry gate for nuclear-encoded proteins. The channel-forming Tom40 is a β-barrel protein, whereas all Tom receptors and small Tom proteins are membrane anchored by a transmembrane α-helical segment in their N- or C-terminal portion. Synthesis of Tom precursors takes place in the cytosol, and their import occurs via preexisting TOM complexes. The precursor of Tom40 is then transferred to SAM for membrane insertion and assembly. Unexpectedly, we find that the biogenesis of α-helical Tom proteins with a membrane anchor in the C-terminal portion is SAM dependent. Each SAM protein is necessary for efficient membrane integration of the receptor Tom22, whereas assembly of the small Tom proteins depends on Sam37. Thus, the substrate specificity of SAM is not restricted to β-barrel proteins but also includes the majority of α-helical Tom proteins.
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Affiliation(s)
- Diana Stojanovski
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, D-79104 Freiburg, Germany
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77
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Grumbt B, Stroobant V, Terziyska N, Israel L, Hell K. Functional characterization of Mia40p, the central component of the disulfide relay system of the mitochondrial intermembrane space. J Biol Chem 2007; 282:37461-70. [PMID: 17959605 DOI: 10.1074/jbc.m707439200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mia40p and Erv1p are components of a translocation pathway for the import of cysteine-rich proteins into the intermembrane space of mitochondria. We have characterized the redox behavior of Mia40p and reconstituted the disulfide transfer system of Mia40p by using recombinant functional C-terminal fragment of Mia40p, Mia40C, and Erv1p. Oxidized Mia40p contains three intramolecular disulfide bonds. One disulfide bond connects the first two cysteine residues in the CPC motif. The second and the third bonds belong to the twin CX(9)C motif and bridge the cysteine residues of two CX(9)C segments. In contrast to the stabilizing disulfide bonds of the twin CX(9)C motif, the first disulfide bond was easily accessible to reducing agents. Partially reduced Mia40C generated by opening of this bond as well as fully reduced Mia40C were oxidized by Erv1p in vitro. In the course of this reaction, mixed disulfides of Mia40C and Erv1p were formed. Reoxidation of fully reduced Mia40C required the presence of the first two cysteine residues in Mia40C. However, efficient reoxidation of a Mia40C variant containing only the cysteine residues of the twin CX(9)C motif was observed when in addition to Erv1p low amounts of wild type Mia40C were present. In the reconstituted system the thiol oxidase Erv1p was sufficient to transfer disulfide bonds to Mia40C, which then could oxidize the variant of Mia40C. In summary, we reconstituted a disulfide relay system consisting of Mia40C and Erv1p.
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Affiliation(s)
- Barbara Grumbt
- Adolf-Butenandt-Institut für Physiologische Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5, 81377, München, Germany
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78
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Baker MJ, Frazier AE, Gulbis JM, Ryan MT. Mitochondrial protein-import machinery: correlating structure with function. Trends Cell Biol 2007; 17:456-64. [PMID: 17825565 DOI: 10.1016/j.tcb.2007.07.010] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 07/03/2007] [Accepted: 07/03/2007] [Indexed: 11/16/2022]
Abstract
Most mitochondrial proteins are synthesized in the cytosol, translocated into the organelle and directed along specific sorting pathways. Over the past 20 years, >30 proteins have been identified as having key roles in mitochondrial protein import. Recently, the elucidation of the structures of several import components has provided fresh insight into the import process. Here, we review the different pathways involved in sorting proteins into mitochondrial subcompartments. Along the way, we highlight the available structural information about the protein-import machinery and discuss how these structures correlate with previously ascribed functions. Future challenges for the cell biologists will be to use this structural information to test specific hypotheses addressing the molecular mechanisms of mitochondrial protein import.
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Affiliation(s)
- Michael J Baker
- Department of Biochemistry, La Trobe University, Melbourne 3086, Australia
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