1
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Maruszczak KK, Draczkowski P, Wnorowski A, Chacinska A. Structure prediction analysis of human core TIM23 complex reveals conservation of the protein translocation mechanism. FEBS Open Bio 2024. [PMID: 38837610 DOI: 10.1002/2211-5463.13840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Revised: 05/21/2024] [Accepted: 05/27/2024] [Indexed: 06/07/2024] Open
Abstract
The majority of mitochondrial proteins are encoded in the nucleus, translated on cytosolic ribosomes, and subsequently targeted to the mitochondrial surface. Their further import into the organelle is facilitated by highly specialized protein translocases. Mitochondrial precursor proteins that are destined to the mitochondrial matrix and, to some extent, the inner membrane, utilize translocase of the inner membrane (TIM23). This indispensable import machinery has been extensively studied in yeast. The translocating unit of the TIM23 complex in yeast consists of two membrane proteins, Tim17 and Tim23. In contrast to previous findings, recent reports demonstrate the primary role of Tim17, rather than Tim23, in the translocation of newly synthesized proteins. Very little is known about human TIM23 translocase. Human cells have two orthologs of yeast Tim17, TIMM17A and TIMM17B. Here, using computational tools, we present the architecture of human core TIM23 variants with either TIMM17A or TIMM17B, forming two populations of highly similar complexes. The structures reveal high conservation of the core TIM23 complex between human and yeast. Interestingly, both TIMM17A and TIMM17B variants interact with TIMM23 and reactive oxygen species modulator 1 (ROMO1); a homolog of yeast Mgr2, a protein that can create a channel-like structure with Tim17. The high structural conservation of proteins that form the core TIM23 complex in yeast and humans raises an interesting question about mechanistic and functional differences that justify existence of the two variants of TIM23 in higher eukaryotes.
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Affiliation(s)
| | - Piotr Draczkowski
- National Bioinformatics Infrastructure Sweden, SciLifeLab, Solna, Sweden
- Department of Synthesis and Chemical Technology of Pharmaceutical Substances, Medical University of Lublin, Poland
| | - Artur Wnorowski
- Department of Biopharmacy, Medical University of Lublin, Poland
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2
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Genge MG, Roy Chowdhury S, Dohnálek V, Yunoki K, Hirashima T, Endo T, Doležal P, Mokranjac D. Two domains of Tim50 coordinate translocation of proteins across the two mitochondrial membranes. Life Sci Alliance 2023; 6:e202302122. [PMID: 37748811 PMCID: PMC10520260 DOI: 10.26508/lsa.202302122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 09/13/2023] [Accepted: 09/14/2023] [Indexed: 09/27/2023] Open
Abstract
Hundreds of mitochondrial proteins with N-terminal presequences are translocated across the outer and inner mitochondrial membranes via the TOM and TIM23 complexes, respectively. How translocation of proteins across two mitochondrial membranes is coordinated is largely unknown. Here, we show that the two domains of Tim50 in the intermembrane space, named core and PBD, both have essential roles in this process. Building upon the surprising observation that the two domains of Tim50 can complement each other in trans, we establish that the core domain contains the main presequence-binding site and serves as the main recruitment point to the TIM23 complex. On the other hand, the PBD plays, directly or indirectly, a critical role in cooperation of the TOM and TIM23 complexes and supports the receptor function of Tim50. Thus, the two domains of Tim50 both have essential but distinct roles and together coordinate translocation of proteins across two mitochondrial membranes.
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Affiliation(s)
- Marcel G Genge
- Biocenter-Department of Cell Biology, LMU Munich, Munich, Germany
| | | | - Vít Dohnálek
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, Vestec, Czech Republic
| | - Kaori Yunoki
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Takashi Hirashima
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Toshiya Endo
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Pavel Doležal
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, Vestec, Czech Republic
| | - Dejana Mokranjac
- Biocenter-Department of Cell Biology, LMU Munich, Munich, Germany
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3
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Fielden LF, Busch JD, Merkt SG, Ganesan I, Steiert C, Hasselblatt HB, Busto JV, Wirth C, Zufall N, Jungbluth S, Noll K, Dung JM, Butenko L, von der Malsburg K, Koch HG, Hunte C, van der Laan M, Wiedemann N. Central role of Tim17 in mitochondrial presequence protein translocation. Nature 2023; 621:627-634. [PMID: 37527780 PMCID: PMC10511324 DOI: 10.1038/s41586-023-06477-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 07/25/2023] [Indexed: 08/03/2023]
Abstract
The presequence translocase of the mitochondrial inner membrane (TIM23) represents the major route for the import of nuclear-encoded proteins into mitochondria1,2. About 60% of more than 1,000 different mitochondrial proteins are synthesized with amino-terminal targeting signals, termed presequences, which form positively charged amphiphilic α-helices3,4. TIM23 sorts the presequence proteins into the inner membrane or matrix. Various views, including regulatory and coupling functions, have been reported on the essential TIM23 subunit Tim17 (refs. 5-7). Here we mapped the interaction of Tim17 with matrix-targeted and inner membrane-sorted preproteins during translocation in the native membrane environment. We show that Tim17 contains conserved negative charges close to the intermembrane space side of the bilayer, which are essential to initiate presequence protein translocation along a distinct transmembrane cavity of Tim17 for both classes of preproteins. The amphiphilic character of mitochondrial presequences directly matches this Tim17-dependent translocation mechanism. This mechanism permits direct lateral release of transmembrane segments of inner membrane-sorted precursors into the inner membrane.
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Affiliation(s)
- Laura F Fielden
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Jakob D Busch
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Sandra G Merkt
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Iniyan Ganesan
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Conny Steiert
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Hanna B Hasselblatt
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Jon V Busto
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Christophe Wirth
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Nicole Zufall
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Sibylle Jungbluth
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling, PZMS, Saarland University, Homburg, Germany
| | - Katja Noll
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling, PZMS, Saarland University, Homburg, Germany
| | - Julia M Dung
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ludmila Butenko
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Karina von der Malsburg
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling, PZMS, Saarland University, Homburg, Germany
| | - Hans-Georg Koch
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Carola Hunte
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- CIBSS-Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany
- BIOSS-Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Martin van der Laan
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling, PZMS, Saarland University, Homburg, Germany.
| | - Nils Wiedemann
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
- CIBSS-Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
- BIOSS-Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
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4
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Siebert V, Silber M, Heuten E, Muhle-Goll C, Lemberg MK. Cleavage of mitochondrial homeostasis regulator PGAM5 by the intramembrane protease PARL is governed by transmembrane helix dynamics and oligomeric state. J Biol Chem 2022; 298:102321. [PMID: 35921890 PMCID: PMC9436811 DOI: 10.1016/j.jbc.2022.102321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 07/07/2022] [Accepted: 07/08/2022] [Indexed: 11/07/2022] Open
Abstract
The intramembrane protease PARL acts as a crucial mitochondrial safeguard by cleaving the mitophagy regulators PINK1 and PGAM5. Depending on the stress level, PGAM5 can either stimulate cell survival or cell death. In contrast to PINK1, which is constantly cleaved in healthy mitochondria and only active when the inner mitochondrial membrane is depolarized, PGAM5 processing is inversely regulated. However, determinants of PGAM5 that indicate it as a conditional substrate for PARL have not been rigorously investigated, and it is unclear how uncoupling the mitochondrial membrane potential affects its processing compared to that of PINK1. Here, we show that several polar transmembrane residues in PGAM5 distant from the cleavage site serve as determinants for its PARL-catalyzed cleavage. Our NMR analysis indicates that a short N-terminal amphipathic helix, followed by a kink and a C-terminal transmembrane helix harboring the scissile peptide bond are key for a productive interaction with PARL. Furthermore, we also show that PGAM5 is stably inserted into the inner mitochondrial membrane until uncoupling the membrane potential triggers its disassembly into monomers, which are then cleaved by PARL. In conclusion, we propose a model in which PGAM5 is slowly processed by PARL-catalyzed cleavage that is influenced by multiple hierarchical substrate features, including a membrane potential–dependent oligomeric switch.
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5
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Kumar A, Matta SK, Vigneshwaran R, D'Silva P. A journey through the gateway of polytopic inner membrane proteins: The carrier translocase machinery. CURRENT OPINION IN PHYSIOLOGY 2022. [DOI: 10.1016/j.cophys.2022.100533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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6
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Eaglesfield R, Tokatlidis K. Targeting and Insertion of Membrane Proteins in Mitochondria. Front Cell Dev Biol 2022; 9:803205. [PMID: 35004695 PMCID: PMC8740019 DOI: 10.3389/fcell.2021.803205] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 12/09/2021] [Indexed: 01/26/2023] Open
Abstract
Mitochondrial membrane proteins play an essential role in all major mitochondrial functions. The respiratory complexes of the inner membrane are key for the generation of energy. The carrier proteins for the influx/efflux of essential metabolites to/from the matrix. Many other inner membrane proteins play critical roles in the import and processing of nuclear encoded proteins (∼99% of all mitochondrial proteins). The outer membrane provides another lipidic barrier to nuclear-encoded protein translocation and is home to many proteins involved in the import process, maintenance of ionic balance, as well as the assembly of outer membrane components. While many aspects of the import and assembly pathways of mitochondrial membrane proteins have been elucidated, many open questions remain, especially surrounding the assembly of the respiratory complexes where certain highly hydrophobic subunits are encoded by the mitochondrial DNA and synthesised and inserted into the membrane from the matrix side. This review will examine the various assembly pathways for inner and outer mitochondrial membrane proteins while discussing the most recent structural and biochemical data examining the biogenesis process.
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Affiliation(s)
- Ross Eaglesfield
- Institute of Molecular Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, University Avenue, Scotland, United Kingdom
| | - Kostas Tokatlidis
- Institute of Molecular Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, University Avenue, Scotland, United Kingdom
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7
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Zhao F, Zou MH. Role of the Mitochondrial Protein Import Machinery and Protein Processing in Heart Disease. Front Cardiovasc Med 2021; 8:749756. [PMID: 34651031 PMCID: PMC8505727 DOI: 10.3389/fcvm.2021.749756] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 08/26/2021] [Indexed: 12/12/2022] Open
Abstract
Mitochondria are essential organelles for cellular energy production, metabolic homeostasis, calcium homeostasis, cell proliferation, and apoptosis. About 99% of mammalian mitochondrial proteins are encoded by the nuclear genome, synthesized as precursors in the cytosol, and imported into mitochondria by mitochondrial protein import machinery. Mitochondrial protein import systems function not only as independent units for protein translocation, but also are deeply integrated into a functional network of mitochondrial bioenergetics, protein quality control, mitochondrial dynamics and morphology, and interaction with other organelles. Mitochondrial protein import deficiency is linked to various diseases, including cardiovascular disease. In this review, we describe an emerging class of protein or genetic variations of components of the mitochondrial import machinery involved in heart disease. The major protein import pathways, including the presequence pathway (TIM23 pathway), the carrier pathway (TIM22 pathway), and the mitochondrial intermembrane space import and assembly machinery, related translocases, proteinases, and chaperones, are discussed here. This review highlights the importance of mitochondrial import machinery in heart disease, which deserves considerable attention, and further studies are urgently needed. Ultimately, this knowledge may be critical for the development of therapeutic strategies in heart disease.
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Affiliation(s)
- Fujie Zhao
- Center for Molecular and Translational Medicine, Georgia State University, Atlanta, GA, United States
| | - Ming-Hui Zou
- Center for Molecular and Translational Medicine, Georgia State University, Atlanta, GA, United States
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8
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Finger Y, Riemer J. Protein import by the mitochondrial disulfide relay in higher eukaryotes. Biol Chem 2021; 401:749-763. [PMID: 32142475 DOI: 10.1515/hsz-2020-0108] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Accepted: 02/24/2020] [Indexed: 12/19/2022]
Abstract
The proteome of the mitochondrial intermembrane space (IMS) contains more than 100 proteins, all of which are synthesized on cytosolic ribosomes and consequently need to be imported by dedicated machineries. The mitochondrial disulfide relay is the major import machinery for soluble proteins in the IMS. Its major component, the oxidoreductase MIA40, interacts with incoming substrates, retains them in the IMS, and oxidatively folds them. After this reaction, MIA40 is reoxidized by the sulfhydryl oxidase augmenter of liver regeneration, which couples disulfide formation by this machinery to the activity of the respiratory chain. In this review, we will discuss the import of IMS proteins with a focus on recent findings showing the diversity of disulfide relay substrates, describing the cytosolic control of this import system and highlighting the physiological relevance of the disulfide relay machinery in higher eukaryotes.
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Affiliation(s)
- Yannik Finger
- Institute for Biochemistry, Redox Biochemistry, University of Cologne, Zülpicher Str. 47a/R. 3.49, D-50674 Cologne, Germany
| | - Jan Riemer
- Department of Chemistry, Institute for Biochemistry, Redox Biochemistry, University of Cologne, and Cologne Excellence Cluster on Cellular Stress Response in Aging-Associated Diseases, Zülpicher Str. 47a/R. 3.49, D-50674 Cologne, Germany
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9
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Callegari S, Cruz-Zaragoza LD, Rehling P. From TOM to the TIM23 complex - handing over of a precursor. Biol Chem 2021; 401:709-721. [PMID: 32074073 DOI: 10.1515/hsz-2020-0101] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Accepted: 02/13/2020] [Indexed: 12/31/2022]
Abstract
Mitochondrial precursor proteins with amino-terminal presequences are imported via the presequence pathway, utilizing the TIM23 complex for inner membrane translocation. Initially, the precursors pass the outer membrane through the TOM complex and are handed over to the TIM23 complex where they are sorted into the inner membrane or translocated into the matrix. This handover process depends on the receptor proteins at the inner membrane, Tim50 and Tim23, which are critical for efficient import. In this review, we summarize key findings that shaped the current concepts of protein translocation along the presequence import pathway, with a particular focus on the precursor handover process from TOM to the TIM23 complex. In addition, we discuss functions of the human TIM23 pathway and the recently uncovered pathogenic mutations in TIM50.
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Affiliation(s)
- Sylvie Callegari
- Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany
| | - Luis Daniel Cruz-Zaragoza
- Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany.,Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
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10
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Transmembrane Coordination of Preprotein Recognition and Motor Coupling by the Mitochondrial Presequence Receptor Tim50. Cell Rep 2021; 30:3092-3104.e4. [PMID: 32130909 DOI: 10.1016/j.celrep.2020.02.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2019] [Revised: 12/13/2019] [Accepted: 02/07/2020] [Indexed: 01/05/2023] Open
Abstract
Mitochondrial preproteins contain amino-terminal presequences directing them to the presequence translocase of the mitochondrial inner membrane (TIM23 complex). Depending on additional downstream import signals, TIM23 either inserts preproteins into the inner membrane or translocates them into the matrix. Matrix import requires the coupling of the presequence translocase-associated motor (PAM) to TIM23. The molecular mechanisms coordinating preprotein recognition by TIM23 in the intermembrane space (IMS) with PAM activation in the matrix are unknown. Here we show that subsequent to presequence recognition in the IMS, the Tim50 matrix domain facilitates the recruitment of the coupling factor Pam17. Next, the IMS domain of Tim50 promotes PAM recruitment to TIM23. Finally, the Tim50 transmembrane segment stimulates the matrix-directed import-driving force exerted by PAM. We propose that recognition of preprotein segments in the IMS and transfer of signal information across the inner membrane by Tim50 determine import motor activation.
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11
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Zhang Y, Ou X, Wang X, Sun D, Zhou X, Wu X, Li Q, Li L. Structure of the mitochondrial TIM22 complex from yeast. Cell Res 2021; 31:366-368. [PMID: 32918038 PMCID: PMC8027178 DOI: 10.1038/s41422-020-00399-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Accepted: 07/24/2020] [Indexed: 01/30/2023] Open
Affiliation(s)
- Yutong Zhang
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiaomin Ou
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Xuezheng Wang
- grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319State Key Laboratory of Protein and Plant Gene Research, Peking University, Beijing, China
| | - Dongjie Sun
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Xueyin Zhou
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiaofei Wu
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Qing Li
- grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319State Key Laboratory of Protein and Plant Gene Research, Peking University, Beijing, China
| | - Long Li
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
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12
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CHCHD4 (MIA40) and the mitochondrial disulfide relay system. Biochem Soc Trans 2021; 49:17-27. [PMID: 33599699 PMCID: PMC7925007 DOI: 10.1042/bst20190232] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 12/19/2020] [Accepted: 01/06/2021] [Indexed: 12/13/2022]
Abstract
Mitochondria are pivotal for normal cellular physiology, as they perform a crucial role in diverse cellular functions and processes, including respiration and the regulation of bioenergetic and biosynthetic pathways, as well as regulating cellular signalling and transcriptional networks. In this way, mitochondria are central to the cell's homeostatic machinery, and as such mitochondrial dysfunction underlies the pathology of a diverse range of diseases including mitochondrial disease and cancer. Mitochondrial import pathways and targeting mechanisms provide the means to transport into mitochondria the hundreds of nuclear-encoded mitochondrial proteins that are critical for the organelle's many functions. One such import pathway is the highly evolutionarily conserved disulfide relay system (DRS) within the mitochondrial intermembrane space (IMS), whereby proteins undergo a form of oxidation-dependent protein import. A central component of the DRS is the oxidoreductase coiled-coil-helix-coiled-coil-helix (CHCH) domain-containing protein 4 (CHCHD4, also known as MIA40), the human homologue of yeast Mia40. Here, we summarise the recent advances made to our understanding of the role of CHCHD4 and the DRS in physiology and disease, with a specific focus on the emerging importance of CHCHD4 in regulating the cellular response to low oxygen (hypoxia) and metabolism in cancer.
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13
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Mitochondrial control of cellular protein homeostasis. Biochem J 2021; 477:3033-3054. [PMID: 32845275 DOI: 10.1042/bcj20190654] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/20/2020] [Accepted: 08/03/2020] [Indexed: 02/08/2023]
Abstract
Mitochondria are involved in several vital functions of the eukaryotic cell. The majority of mitochondrial proteins are coded by nuclear DNA. Constant import of proteins from the cytosol is a prerequisite for the efficient functioning of the organelle. The protein import into mitochondria is mediated by diverse import pathways and is continuously under watch by quality control systems. However, it is often challenged by both internal and external factors, such as oxidative stress or energy shortage. The impaired protein import and biogenesis leads to the accumulation of mitochondrial precursor proteins in the cytosol and activates several stress response pathways. These defense mechanisms engage a network of processes involving transcription, translation, and protein clearance to restore cellular protein homeostasis. In this review, we provide a comprehensive analysis of various factors and processes contributing to mitochondrial stress caused by protein biogenesis failure and summarize the recovery mechanisms employed by the cell.
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14
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Chaudhuri M, Darden C, Soto Gonzalez F, Singha UK, Quinones L, Tripathi A. Tim17 Updates: A Comprehensive Review of an Ancient Mitochondrial Protein Translocator. Biomolecules 2020; 10:E1643. [PMID: 33297490 PMCID: PMC7762337 DOI: 10.3390/biom10121643] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 12/02/2020] [Accepted: 12/03/2020] [Indexed: 02/06/2023] Open
Abstract
The translocases of the mitochondrial outer and inner membranes, the TOM and TIMs, import hundreds of nucleus-encoded proteins into mitochondria. TOM and TIMs are multi-subunit protein complexes that work in cooperation with other complexes to import proteins in different sub-mitochondrial destinations. The overall architecture of these protein complexes is conserved among yeast/fungi, animals, and plants. Recent studies have revealed unique characteristics of this machinery, particularly in the eukaryotic supergroup Excavata. Despite multiple differences, homologues of Tim17, an essential component of one of the TIM complexes and a member of the Tim17/Tim22/Tim23 family, have been found in all eukaryotes. Here, we review the structure and function of Tim17 and Tim17-containing protein complexes in different eukaryotes, and then compare them to the single homologue of this protein found in Trypanosoma brucei, a unicellular parasitic protozoan.
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Affiliation(s)
- Minu Chaudhuri
- Department of Microbiology, Immunology, and Physiology, Meharry Medical College, 1005 Dr. D.B. Todd, Jr., Blvd, Nashville, TN 37208, USA; (C.D.); (F.S.G.); (U.K.S.); (L.Q.); (A.T.)
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15
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Valpadashi A, Callegari S, Linden A, Neumann P, Ficner R, Urlaub H, Deckers M, Rehling P. Defining the architecture of the human TIM22 complex by chemical crosslinking. FEBS Lett 2020; 595:157-168. [PMID: 33125709 DOI: 10.1002/1873-3468.13978] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 10/19/2020] [Accepted: 10/25/2020] [Indexed: 12/22/2022]
Abstract
The majority of mitochondrial proteins are nuclear encoded and imported into mitochondria as precursor proteins via dedicated translocases. The translocase of the inner membrane 22 (TIM22) is a multisubunit molecular machine specialized for the translocation of hydrophobic, multi-transmembrane-spanning proteins with internal targeting signals into the inner mitochondrial membrane. Here, we undertook a crosslinking-mass spectrometry (XL-MS) approach to determine the molecular arrangement of subunits of the human TIM22 complex. Crosslinking of the isolated TIM22 complex using the BS3 crosslinker resulted in the broad generation of crosslinks across the majority of TIM22 components, including the small TIM chaperone complex. The crosslinking data uncovered several unexpected features, opening new avenues for a deeper investigation into the steps required for TIM22-mediated translocation in humans.
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Affiliation(s)
- Anusha Valpadashi
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | - Sylvie Callegari
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany.,Ubiquitin Signalling Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia.,Department of Medical Biology, University of Melbourne, Australia
| | - Andreas Linden
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Department of Clinical Chemistry, Bioanalytics, University Medical Center Göttingen, Germany
| | - Piotr Neumann
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, Göttingen Center for Molecular Biosciences, Georg-August-University Göttingen, Germany
| | - Ralf Ficner
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, Göttingen Center for Molecular Biosciences, Georg-August-University Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Goettingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Department of Clinical Chemistry, Bioanalytics, University Medical Center Göttingen, Germany
| | - Markus Deckers
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Goettingen, Germany.,Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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16
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Herrmann JM, Riemer J. Apoptosis inducing factor and mitochondrial NADH dehydrogenases: redox-controlled gear boxes to switch between mitochondrial biogenesis and cell death. Biol Chem 2020; 402:289-297. [PMID: 32769219 DOI: 10.1515/hsz-2020-0254] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 08/03/2020] [Indexed: 02/07/2023]
Abstract
The mitochondrial complex I serves as entry point for NADH into the electron transport chain. In animals, fungi and plants, additional NADH dehydrogenases carry out the same electron transfer reaction, however they do not pump protons. The apoptosis inducing factor (AIF, AIFM1 in humans) is a famous member of this group as it was the first pro-apoptotic protein identified that can induce caspase-independent cell death. Recent studies on AIFM1 and the NADH dehydrogenase Nde1 of baker's yeast revealed two independent and experimentally separable activities of this class of enzymes: On the one hand, these proteins promote the functionality of mitochondrial respiration in different ways: They channel electrons into the respiratory chain and, at least in animals, promote the import of Mia40 (named MIA40 or CHCHD4 in humans) and the assembly of complex I. On the other hand, they can give rise to pro-apoptotic fragments that are released from the mitochondria to trigger cell death. Here we propose that AIFM1 and Nde1 serve as conserved redox switches which measure metabolic conditions on the mitochondrial surface and translate it into a binary life/death decision. This function is conserved among eukaryotic cells and apparently used to purge metabolically compromised cells from populations.
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Affiliation(s)
- Johannes M Herrmann
- Department of Cell Biology, University of Kaiserslautern, Erwin-Schrödinger-Strasse 13, D-67663Kaiserslautern, Germany
| | - Jan Riemer
- Department of Biochemistry, University of Cologne, Zülpicher Str. 47A, D-50674Cologne, Germany
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17
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Günsel U, Paz E, Gupta R, Mathes I, Azem A, Mokranjac D. InVivo Dissection of the Intrinsically Disordered Receptor Domain of Tim23. J Mol Biol 2020; 432:3326-3337. [PMID: 32277989 DOI: 10.1016/j.jmb.2020.03.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 03/05/2020] [Accepted: 03/31/2020] [Indexed: 01/11/2023]
Abstract
In the intermembrane space (IMS) of mitochondria, the receptor domain of Tim23 has an essential role during translocation of hundreds of different proteins from the cytosol via the TOM and TIM23 complexes in the outer and inner membranes, respectively. This intrinsically disordered domain, which can even extend into the cytosol, was shown, mostly in vitro, to interact with several subunits of the TOM and TIM23 complexes. To obtain molecular understanding of this organizational hub in the IMS, we dissected the IMS domain of Tim23 in vivo. We show that the interaction surface of Tim23 with Tim50 is larger than previously thought and reveal an unexpected interaction of Tim23 with Pam17 in the IMS, impairment of which influences their interaction in the matrix. Furthermore, mutations of two conserved negatively charged residues of Tim23, close to the inner membrane, prevented dimerization of Tim23. The same mutations increased exposure of Tim23 on the mitochondrial surface, whereas dissipation of membrane potential decreased it. Our results reveal an intricate network of Tim23 interactions in the IMS, whose influence is transduced across two mitochondrial membranes, ensuring efficient translocation of proteins into mitochondria.
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Affiliation(s)
- Umut Günsel
- BMC-Physiological Chemistry, LMU Munich, 82152 Martinsried, Germany
| | - Eyal Paz
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Ruhita Gupta
- BMC-Physiological Chemistry, LMU Munich, 82152 Martinsried, Germany
| | | | - Abdussalam Azem
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Dejana Mokranjac
- BMC-Physiological Chemistry, LMU Munich, 82152 Martinsried, Germany.
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18
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Kumar A, Matta SK, D'Silva P. Role of conserved regions of Tim22 in the structural organization of the carrier translocase. J Cell Sci 2020; 133:jcs.244632. [DOI: 10.1242/jcs.244632] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 06/15/2020] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial biogenesis requires efficient sorting of various proteins into different mitochondrial sub-compartments mediated by dedicated protein machinery present in the outer and inner membrane. Among them, the TIM22 complex enables the integration of complex membrane proteins with internal targeting signals into the inner membrane. Although the Tim22 forms the core of the complex, the dynamic recruitment of subunits to the channel is still enigmatic. The present study first-time highlights that IMS and TM4 regions of Tim22 are critically required for the interaction of the membrane-embedded subunits including, Tim54, Tim18, and Sdh3, thereby maintain the functional architecture of TIM22 translocase. On the other hand, TM1 and TM2 regions of Tim22 are important for the Tim18 association, while TM3 is exclusively required for the Sdh3 interaction. Moreover, the impairment in TIM22 complex assembly influences its translocase activity, mitochondrial network, and the viability of cells lacking mitochondrial DNA. Overall our findings provide compelling evidence to highlight the significance of conserved regions of Tim22 that are important for the maintenance of the TIM22 complex and mitochondrial integrity.
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Affiliation(s)
- Abhishek Kumar
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
| | - Srujan Kumar Matta
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
| | - Patrick D'Silva
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
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19
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Backes S, Garg SG, Becker L, Peleh V, Glockshuber R, Gould SB, Herrmann JM. Development of the Mitochondrial Intermembrane Space Disulfide Relay Represents a Critical Step in Eukaryotic Evolution. Mol Biol Evol 2019; 36:742-756. [PMID: 30668797 DOI: 10.1093/molbev/msz011] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The mitochondrial intermembrane space evolved from the bacterial periplasm. Presumably as a consequence of their common origin, most proteins of these compartments are stabilized by structural disulfide bonds. The molecular machineries that mediate oxidative protein folding in bacteria and mitochondria, however, appear to share no common ancestry. Here we tested whether the enzymes Erv1 and Mia40 of the yeast mitochondrial disulfide relay could be functionally replaced by corresponding components of other compartments. We found that the sulfhydryl oxidase Erv1 could be replaced by the Ero1 oxidase or the protein disulfide isomerase from the endoplasmic reticulum, however at the cost of respiration deficiency. In contrast to Erv1, the mitochondrial oxidoreductase Mia40 proved to be indispensable and could not be replaced by thioredoxin-like enzymes, including the cytoplasmic reductase thioredoxin, the periplasmic dithiol oxidase DsbA, and Pdi1. From our studies we conclude that the profound inertness against glutathione, its slow oxidation kinetics and its high affinity to substrates renders Mia40 a unique and essential component of mitochondrial biogenesis. Evidently, the development of a specific mitochondrial disulfide relay system represented a crucial step in the evolution of the eukaryotic cell.
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Affiliation(s)
- Sandra Backes
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Sriram G Garg
- Molecular Evolution, Heinrich-Heine-University of Dusseldorf, Dusseldorf, Germany
| | - Laura Becker
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Valentina Peleh
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Rudi Glockshuber
- Molecular Biology and Biophysics, ETH Zürich, Zürich, Switzerland
| | - Sven B Gould
- Molecular Evolution, Heinrich-Heine-University of Dusseldorf, Dusseldorf, Germany
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20
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Mitochondrial presequence import: Multiple regulatory knobs fine-tune mitochondrial biogenesis and homeostasis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1866:930-944. [PMID: 30802482 DOI: 10.1016/j.bbamcr.2019.02.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2019] [Revised: 02/14/2019] [Accepted: 02/19/2019] [Indexed: 12/22/2022]
Abstract
Mitochondria are pivotal organelles for cellular signaling and metabolism, and their dysfunction leads to severe cellular stress. About 60-70% of the mitochondrial proteome consists of preproteins synthesized in the cytosol with an amino-terminal cleavable presequence targeting signal. The TIM23 complex transports presequence signals towards the mitochondrial matrix. Ultimately, the mature protein segments are either transported into the matrix or sorted to the inner membrane. To ensure accurate preprotein import into distinct mitochondrial sub-compartments, the TIM23 machinery adopts specific functional conformations and interacts with different partner complexes. Regulatory subunits modulate the translocase dynamics, tailoring the import reaction to the incoming preprotein. The mitochondrial membrane potential and the ATP generated via oxidative phosphorylation are key energy sources in driving the presequence import pathway. Thus, mitochondrial dysfunctions have rapid repercussions on biogenesis. Cellular mechanisms exploit the presequence import pathway to monitor mitochondrial dysfunctions and mount transcriptional and proteostatic responses to restore functionality.
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21
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Pacheu-Grau D, Callegari S, Emperador S, Thompson K, Aich A, Topol SE, Spencer EG, McFarland R, Ruiz-Pesini E, Torkamani A, Taylor RW, Montoya J, Rehling P. Mutations of the mitochondrial carrier translocase channel subunit TIM22 cause early-onset mitochondrial myopathy. Hum Mol Genet 2018; 27:4135-4144. [PMID: 30452684 PMCID: PMC6240735 DOI: 10.1093/hmg/ddy305] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 08/10/2018] [Accepted: 08/10/2018] [Indexed: 11/13/2022] Open
Abstract
Protein import into mitochondria is facilitated by translocases within the outer and the inner mitochondrial membranes that are dedicated to a highly specific subset of client proteins. The mitochondrial carrier translocase (TIM22 complex) inserts multispanning proteins, such as mitochondrial metabolite carriers and translocase subunits (TIM23, TIM17A/B and TIM22), into the inner mitochondrial membrane. Both types of substrates are essential for mitochondrial metabolic function and biogenesis. Here, we report on a subject, diagnosed at 1.5 years, with a neuromuscular presentation, comprising hypotonia, gastroesophageal reflux disease and persistently elevated serum and Cerebrospinal fluid lactate (CSF). Patient fibroblasts displayed reduced oxidative capacity and altered mitochondrial morphology. Using trans-mitochondrial cybrid cell lines, we excluded a candidate variant in mitochondrial DNA as causative of these effects. Whole-exome sequencing identified compound heterozygous variants in the TIM22 gene (NM_013337), resulting in premature truncation in one allele (p.Tyr25Ter) and a point mutation in a conserved residue (p.Val33Leu), within the intermembrane space region, of the TIM22 protein in the second allele. Although mRNA transcripts of TIM22 were elevated, biochemical analyses revealed lower levels of TIM22 protein and an even greater deficiency of TIM22 complex formation. In agreement with a defect in carrier translocase function, carrier protein amounts in the inner membrane were found to be reduced. This is the first report of pathogenic variants in the TIM22 pore-forming subunit of the carrier translocase affecting the biogenesis of inner mitochondrial membrane proteins critical for metabolite exchange.
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Affiliation(s)
- David Pacheu-Grau
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, D-37073, Germany
| | - Sylvie Callegari
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, D-37073, Germany
| | - Sonia Emperador
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza-CIBER de Enfermedades Raras (CIBERER)-Instituto de Investigación Sanitaria de Aragón (IIS Aragón), Zaragoza, 50013, Spain
| | - Kyle Thompson
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Abhishek Aich
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, D-37073, Germany
| | - Sarah E Topol
- The Scripps Translational Science Institute, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Emily G Spencer
- The Scripps Translational Science Institute, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Robert McFarland
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Eduardo Ruiz-Pesini
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza-CIBER de Enfermedades Raras (CIBERER)-Instituto de Investigación Sanitaria de Aragón (IIS Aragón), Zaragoza, 50013, Spain
| | - Ali Torkamani
- The Scripps Translational Science Institute, The Scripps Research Institute, La Jolla, CA 92037, United States
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Julio Montoya
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza-CIBER de Enfermedades Raras (CIBERER)-Instituto de Investigación Sanitaria de Aragón (IIS Aragón), Zaragoza, 50013, Spain
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, D-37073, Germany
- Max-Planck Institute for Biophysical Chemistry, D-37077, Göttingen, Germany
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22
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Habich M, Salscheider SL, Riemer J. Cysteine residues in mitochondrial intermembrane space proteins: more than just import. Br J Pharmacol 2018; 176:514-531. [PMID: 30129023 DOI: 10.1111/bph.14480] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 06/20/2018] [Accepted: 06/26/2018] [Indexed: 12/13/2022] Open
Abstract
The intermembrane space (IMS) is a very small mitochondrial sub-compartment with critical relevance for many cellular processes. IMS proteins fulfil important functions in transport of proteins, lipids, metabolites and metal ions, in signalling, in metabolism and in defining the mitochondrial ultrastructure. Our understanding of the IMS proteome has become increasingly refined although we still lack information on the identity and function of many of its proteins. One characteristic of many IMS proteins are conserved cysteines. Different post-translational modifications of these cysteine residues can have critical roles in protein function, localization and/or stability. The close localization to different ROS-producing enzyme systems, a dedicated machinery for oxidative protein folding, and a unique equipment with antioxidative systems, render the careful balancing of the redox and modification states of the cysteine residues, a major challenge in the IMS. In this review, we discuss different functions of human IMS proteins, the involvement of cysteine residues in these functions, the consequences of cysteine modifications and the consequences of cysteine mutations or defects in the machinery for disulfide bond formation in terms of human health. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.
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Affiliation(s)
- Markus Habich
- Department of Chemistry, Institute of Biochemistry, Redox Biochemistry, University of Cologne, Cologne, Germany
| | - Silja Lucia Salscheider
- Department of Chemistry, Institute of Biochemistry, Redox Biochemistry, University of Cologne, Cologne, Germany
| | - Jan Riemer
- Department of Chemistry, Institute of Biochemistry, Redox Biochemistry, University of Cologne, Cologne, Germany
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23
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Abstract
Efficient movement of proteins across membranes is required for cell health. The translocation process is particularly challenging when the channel in the membrane through which proteins must pass is narrow—such as those in the membranes of the endoplasmic reticulum and mitochondria. Hsp70 molecular chaperones play roles on both sides of these membranes, ensuring efficient translocation of proteins synthesized on cytosolic ribosomes into the interior of these organelles. The “import motor” in the mitochondrial matrix, which is essential for driving the movement of proteins across the mitochondrial inner membrane, is arguably the most complex Hsp70-based system in the cell.
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Affiliation(s)
- Elizabeth A Craig
- Department of Biochemistry, University of Wisconsin - Madison, 433 Babcock Drive, Madison, WI, 53706, USA.
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24
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Mattie S, Riemer J, Wideman JG, McBride HM. A new mitofusin topology places the redox-regulated C terminus in the mitochondrial intermembrane space. J Cell Biol 2017; 217:507-515. [PMID: 29212658 PMCID: PMC5800796 DOI: 10.1083/jcb.201611194] [Citation(s) in RCA: 110] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 07/12/2017] [Accepted: 11/14/2017] [Indexed: 12/20/2022] Open
Abstract
Mitochondrial fusion occurs in many eukaryotes, including animals, plants, and fungi. It is essential for cellular homeostasis, and yet the underlying mechanisms remain elusive. Comparative analyses and phylogenetic reconstructions revealed that fungal Fzo1 and animal Mitofusin proteins are highly diverged from one another and lack strong sequence similarity. Bioinformatic analysis showed that fungal Fzo1 proteins exhibit two predicted transmembrane domains, whereas metazoan Mitofusins contain only a single transmembrane domain. This prediction contradicts the current models, suggesting that both animal and fungal proteins share one topology. This newly predicted topology of Mfn1 and Mfn2 was demonstrated biochemically, confirming that the C-terminal, redox-sensitive cysteine residues reside within the intermembrane space (IMS). Functional experiments established that redox-mediated disulfide modifications within the IMS domain are key modulators of reversible Mfn oligomerization that drives fusion. Together, these results lead to a revised understanding of Mfns as single-spanning outer membrane proteins with an Nout-Cin orientation, providing functional insight into the IMS contribution to redox-regulated fusion events.
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Affiliation(s)
- Sevan Mattie
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - Jan Riemer
- Institut für Biochemie, University of Cologne, Köln, Germany
| | - Jeremy G Wideman
- Biosciences, University of Exeter, Exeter, England, UK .,Wissenschaftskolleg zu Berlin, Berlin, Germany
| | - Heidi M McBride
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
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25
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Weems E, Singha UK, Smith JT, Chaudhuri M. The divergent N-terminal domain of Tim17 is critical for its assembly in the TIM complex in Trypanosoma brucei. Mol Biochem Parasitol 2017; 218:4-15. [PMID: 28965880 DOI: 10.1016/j.molbiopara.2017.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Revised: 09/18/2017] [Accepted: 09/25/2017] [Indexed: 10/18/2022]
Abstract
Trypanosoma brucei Tim17(TbTim17), the single member of the Tim17/23/22 protein family, is an essential component of the translocase of the mitochondrial inner membrane (TIM). In spite of the conserved secondary structure, the primary sequence of TbTim17, particularly the N-terminal hydrophilic region, is significantly divergent. In order to understand the function of this region we expressed two N-terminal deletion mutants (Δ20 and Δ30) of TbTim17 in T. brucei. Both of these mutants of TbTim17 were targeted to mitochondria, however, they failed to complement the growth defect of TbTim17 RNAi cells. In addition, the import defect of other nuclear encoded proteins into TbTim17 knockdown mitochondria were not restored by expression of the N-terminal deletion mutants but complemented by knock-in of the full-length protein. Further analysis revealed that Δ20-TbTim17 and Δ30-TbTim17 mutants were not localized in the mitochondrial inner membrane. Analysis of the protein complexes in the wild type and mutant mitochondria by two-dimensional Blue-native/SDS-PAGE revealed that none of these mutants are assembled into the TbTim17 protein complex. However, FL-TbTim17 was integrated into the mitochondrial inner membrane and assembled into TbTim17 complex. Co-immunoprecipitation analysis showed that unlike the FL-TbTim17, mutant proteins are not associated with the endogenous TbTim17 as well as its interacting partner TbTim62, a novel trypanosome specific Tim. Together, these results show that the N-terminal domain of TbTim17 plays unique and essential roles for its sorting and assembly into the TbTim17 protein complex.
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Affiliation(s)
- Ebony Weems
- Department of Microbiology and Immunology, Meharry Medical College, Nashville, TN, 37209, United States
| | - Ujjal K Singha
- Department of Microbiology and Immunology, Meharry Medical College, Nashville, TN, 37209, United States
| | - Joseph T Smith
- Department of Microbiology and Immunology, Meharry Medical College, Nashville, TN, 37209, United States
| | - Minu Chaudhuri
- Department of Microbiology and Immunology, Meharry Medical College, Nashville, TN, 37209, United States.
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26
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Sengers Syndrome-Associated Mitochondrial Acylglycerol Kinase Is a Subunit of the Human TIM22 Protein Import Complex. Mol Cell 2017; 67:457-470.e5. [DOI: 10.1016/j.molcel.2017.06.014] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 05/28/2017] [Accepted: 06/13/2017] [Indexed: 11/19/2022]
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27
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Protein trafficking in the mitochondrial intermembrane space: mechanisms and links to human disease. Biochem J 2017; 474:2533-2545. [PMID: 28701417 PMCID: PMC5509380 DOI: 10.1042/bcj20160627] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 05/03/2017] [Accepted: 05/09/2017] [Indexed: 01/20/2023]
Abstract
Mitochondria fulfill a diverse range of functions in cells including oxygen metabolism, homeostasis of inorganic ions and execution of apoptosis. Biogenesis of mitochondria relies on protein import pathways that are ensured by dedicated multiprotein translocase complexes localized in all sub-compartments of these organelles. The key components and pathways involved in protein targeting and assembly have been characterized in great detail over the last three decades. This includes the oxidative folding machinery in the intermembrane space, which contributes to the redox-dependent control of proteostasis. Here, we focus on several components of this system and discuss recent evidence suggesting links to human proteopathy.
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28
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Abstract
Mitochondria are essential organelles with numerous functions in cellular metabolism and homeostasis. Most of the >1,000 different mitochondrial proteins are synthesized as precursors in the cytosol and are imported into mitochondria by five transport pathways. The protein import machineries of the mitochondrial membranes and aqueous compartments reveal a remarkable variability of mechanisms for protein recognition, translocation, and sorting. The protein translocases do not operate as separate entities but are connected to each other and to machineries with functions in energetics, membrane organization, and quality control. Here, we discuss the versatility and dynamic organization of the mitochondrial protein import machineries. Elucidating the molecular mechanisms of mitochondrial protein translocation is crucial for understanding the integration of protein translocases into a large network that controls organelle biogenesis, function, and dynamics.
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Affiliation(s)
- Nils Wiedemann
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, and BIOSS Centre for Biological Signaling Studies, University of Freiburg, 79104 Freiburg, Germany; ,
| | - Nikolaus Pfanner
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, and BIOSS Centre for Biological Signaling Studies, University of Freiburg, 79104 Freiburg, Germany; ,
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29
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Role of Tim17 Transmembrane Regions in Regulating the Architecture of Presequence Translocase and Mitochondrial DNA Stability. Mol Cell Biol 2017; 37:MCB.00491-16. [PMID: 27994013 DOI: 10.1128/mcb.00491-16] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 12/11/2016] [Indexed: 12/11/2022] Open
Abstract
Mitochondrial life cycle and protein import are intricate cellular processes, which require precise coordination between the transport machineries of outer and inner mitochondrial membranes. Presequence translocase performs the indispensable function of translocating preproteins having N-terminal targeting sequences across the inner membrane. Tim23 forms the core of the voltage-gated import channel, while Tim17 is presumed to maintain the stoichiometry of the translocase. However, mechanistic insights into how Tim17 coordinates these regulatory events within the complex remained elusive. We demonstrate that Tim17 harbors conserved G/AXXXG/A motifs within its transmembrane regions and plays an imperative role in the translocase assembly through interaction with Tim23. Tandem motifs are highly essential, as most of the amino acid substitutions lead to nonviability due to the complete destabilization of the TIM23 channel. Importantly, Tim17 transmembrane regions regulate the dynamic assembly of translocase to form either the TIM23 (PAM)-complex or TIM23 (SORT)-complex by recruiting the presequence translocase-associated motor (PAM) machinery or Tim21, respectively. To a greater significance, tim17 mutants displayed mitochondrial DNA (mtDNA) instability, membrane potential loss, and defective import, resulting in organellar dysfunction. We conclude that the integrity of Tim17 transmembrane regions is critical for mitochondrial function and protein turnover.
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30
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Demishtein-Zohary K, Günsel U, Marom M, Banerjee R, Neupert W, Azem A, Mokranjac D. Role of Tim17 in coupling the import motor to the translocation channel of the mitochondrial presequence translocase. eLife 2017; 6. [PMID: 28165323 PMCID: PMC5308891 DOI: 10.7554/elife.22696] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 02/06/2017] [Indexed: 12/24/2022] Open
Abstract
The majority of mitochondrial proteins use N-terminal presequences for targeting to mitochondria and are translocated by the presequence translocase. During translocation, proteins, threaded through the channel in the inner membrane, are handed over to the import motor at the matrix face. Tim17 is an essential, membrane-embedded subunit of the translocase; however, its function is only poorly understood. Here, we functionally dissected its four predicted transmembrane (TM) segments. Mutations in TM1 and TM2 impaired the interaction of Tim17 with Tim23, component of the translocation channel, whereas mutations in TM3 compromised binding of the import motor. We identified residues in the matrix-facing region of Tim17 involved in binding of the import motor. Our results reveal functionally distinct roles of different regions of Tim17 and suggest how they may be involved in handing over the proteins, during their translocation into mitochondria, from the channel to the import motor of the presequence translocase. DOI:http://dx.doi.org/10.7554/eLife.22696.001
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Affiliation(s)
- Keren Demishtein-Zohary
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Umut Günsel
- BMC-Physiological Chemistry, LMU Munich, Martinsried, Germany
| | - Milit Marom
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Rupa Banerjee
- BMC-Physiological Chemistry, LMU Munich, Martinsried, Germany
| | - Walter Neupert
- Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Abdussalam Azem
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
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31
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Wasilewski M, Chojnacka K, Chacinska A. Protein trafficking at the crossroads to mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1864:125-137. [PMID: 27810356 DOI: 10.1016/j.bbamcr.2016.10.019] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/25/2016] [Accepted: 10/27/2016] [Indexed: 12/14/2022]
Abstract
Mitochondria are central power stations in the cell, which additionally serve as metabolic hubs for a plethora of anabolic and catabolic processes. The sustained function of mitochondria requires the precisely controlled biogenesis and expression coordination of proteins that originate from the nuclear and mitochondrial genomes. Accuracy of targeting, transport and assembly of mitochondrial proteins is also needed to avoid deleterious effects on protein homeostasis in the cell. Checkpoints of mitochondrial protein transport can serve as signals that provide information about the functional status of the organelles. In this review, we summarize recent advances in our understanding of mitochondrial protein transport and discuss examples that involve communication with the nucleus and cytosol.
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Affiliation(s)
- Michal Wasilewski
- International Institute of Molecular and Cell Biology in Warsaw, Poland.
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32
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Callegari S, Richter F, Chojnacka K, Jans DC, Lorenzi I, Pacheu-Grau D, Jakobs S, Lenz C, Urlaub H, Dudek J, Chacinska A, Rehling P. TIM29 is a subunit of the human carrier translocase required for protein transport. FEBS Lett 2016; 590:4147-4158. [PMID: 27718247 PMCID: PMC5215392 DOI: 10.1002/1873-3468.12450] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 09/21/2016] [Accepted: 10/04/2016] [Indexed: 12/13/2022]
Abstract
Hydrophobic inner mitochondrial membrane proteins with internal targeting signals, such as the metabolite carriers, use the carrier translocase (TIM22 complex) for transport into the inner membrane. Defects in this transport pathway have been associated with neurodegenerative disorders. While the TIM22 complex is well studied in baker's yeast, very little is known about the mammalian TIM22 complex. Using immunoprecipitation, we purified the human carrier translocase and identified a mitochondrial inner membrane protein TIM29 as a novel component, specific to metazoa. We show that TIM29 is a constituent of the 440 kDa TIM22 complex and interacts with oxidized TIM22. Our analyses demonstrate that TIM29 is required for the structural integrity of the TIM22 complex and for import of substrate proteins by the carrier translocase.
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Affiliation(s)
- Sylvie Callegari
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | - Frank Richter
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | | | - Daniel C Jans
- Department of NanoBiophotonics, Mitochondrial Structure and Dynamics Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Department of Neurology, University Medical Center Göttingen, Germany
| | - Isotta Lorenzi
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | - David Pacheu-Grau
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | - Stefan Jakobs
- Department of NanoBiophotonics, Mitochondrial Structure and Dynamics Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Department of Neurology, University Medical Center Göttingen, Germany
| | - Christof Lenz
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Bioanalytics, Institute for Clinical Chemistry, University Medical Center Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Bioanalytics, Institute for Clinical Chemistry, University Medical Center Göttingen, Germany
| | - Jan Dudek
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany
| | | | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, Germany.,MaxPlanck Institute for Biophysical Chemistry, Göttingen, Germany
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33
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Mokranjac D. Mitochondrial protein import: An unexpected disulfide bond. J Cell Biol 2016; 214:363-5. [PMID: 27502488 PMCID: PMC4987298 DOI: 10.1083/jcb.201607117] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 07/28/2016] [Indexed: 01/22/2023] Open
Abstract
Most mitochondrial proteins are imported through the TIM23 translocation channel, the structure and molecular nature of which are still unclear. In this issue, Ramesh et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201602074) show that the TIM23 subunit Tim17 contains a disulfide bond that is crucial for protein translocation and channel gating.
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Affiliation(s)
- Dejana Mokranjac
- Biomedical Center Munich - Physiological Chemistry, LMU Munich, 82152 Martinsried, Germany
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34
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Ramesh A, Peleh V, Martinez-Caballero S, Wollweber F, Sommer F, van der Laan M, Schroda M, Alexander RT, Campo ML, Herrmann JM. A disulfide bond in the TIM23 complex is crucial for voltage gating and mitochondrial protein import. J Cell Biol 2016; 214:417-31. [PMID: 27502485 PMCID: PMC4987294 DOI: 10.1083/jcb.201602074] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Accepted: 07/05/2016] [Indexed: 11/25/2022] Open
Abstract
Here, Ramesh et al. show that import and oxidation of Tim17, a membrane-embedded subunit of the mitochondrial protein import machinery, are mediated by the mitochondrial disulfide relay, although its disulfide bond is formed differently than soluble intermembrane space proteins. Tim17 is a central, membrane-embedded subunit of the mitochondrial protein import machinery. In this study, we show that Tim17 contains a pair of highly conserved cysteine residues that form a structural disulfide bond exposed to the intermembrane space (IMS). This disulfide bond is critical for efficient protein translocation through the TIM23 complex and for dynamic gating of its preprotein-conducting channel. The disulfide bond in Tim17 is formed during insertion of the protein into the inner membrane. Whereas the import of Tim17 depends on the binding to the IMS protein Mia40, the oxidoreductase activity of Mia40 is surprisingly dispensable for Tim17 oxidation. Our observations suggest that Tim17 can be directly oxidized by the sulfhydryl oxidase Erv1. Thus, import and oxidation of Tim17 are mediated by the mitochondrial disulfide relay, though the mechanism by which the disulfide bond in Tim17 is formed differs considerably from that of soluble IMS proteins.
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Affiliation(s)
- Ajay Ramesh
- Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Valentina Peleh
- Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Sonia Martinez-Caballero
- Departamento de Bioquímica y Biología Molecular y Genética, Universidad de Extremadura, 10003 Cáceres, Spain
| | - Florian Wollweber
- Biochemistry, Saarland University, 66421 Homburg, Germany Faculty of Medicine, Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research, University of Freiburg, 79104 Freiburg, Germany
| | - Frederik Sommer
- Molecular Biotechnology and Systems Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | | | - Michael Schroda
- Molecular Biotechnology and Systems Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - R Todd Alexander
- Department of Pediatrics, University of Alberta, Edmonton, Alberta T6G 1C9, Canada
| | - María Luisa Campo
- Departamento de Bioquímica y Biología Molecular y Genética, Universidad de Extremadura, 10003 Cáceres, Spain
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35
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Peleh V, Cordat E, Herrmann JM. Mia40 is a trans-site receptor that drives protein import into the mitochondrial intermembrane space by hydrophobic substrate binding. eLife 2016; 5. [PMID: 27343349 PMCID: PMC4951193 DOI: 10.7554/elife.16177] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 06/24/2016] [Indexed: 11/13/2022] Open
Abstract
Many proteins of the mitochondrial IMS contain conserved cysteines that are oxidized to disulfide bonds during their import. The conserved IMS protein Mia40 is essential for the oxidation and import of these proteins. Mia40 consists of two functional elements: an N-terminal cysteine-proline-cysteine motif conferring substrate oxidation, and a C-terminal hydrophobic pocket for substrate binding. In this study, we generated yeast mutants to dissect both Mia40 activities genetically and biochemically. Thereby we show that the substrate-binding domain of Mia40 is both necessary and sufficient to promote protein import, indicating that trapping by Mia40 drives protein translocation. An oxidase-deficient Mia40 mutant is inviable, but can be partially rescued by the addition of the chemical oxidant diamide. Our results indicate that Mia40 predominantly serves as a trans-site receptor of mitochondria that binds incoming proteins via hydrophobic interactions thereby mediating protein translocation across the outer membrane by a ‘holding trap’ rather than a ‘folding trap’ mechanism. DOI:http://dx.doi.org/10.7554/eLife.16177.001 Human, yeast and other eukaryotic cells contain compartments called mitochondria that perform several vital tasks, including supplying the cell with energy. Each mitochondrion is surrounded by an inner and an outer membrane, which are separated by an intermembrane space that contains a host of molecules, including proteins. Intermembrane space proteins are made in the cytosol before being transported into the intermembrane space through pores in the mitochondrion’s outer membrane. Many of these proteins have the ability to form disulfide bonds within their structures, which help the proteins to fold and assemble correctly, but they only acquire these bonds once they have entered the intermembrane space. An enzyme called Mia40 sits inside the intermembrane space and helps other proteins to fold correctly. This Mia40-induced folding had been suggested to help proteins to move into the intermembrane space. Mia40 contains two important regions: one region acts as an enzyme and adds disulfide bonds to other proteins, and the other region binds to the intermembrane space proteins. Peleh et al. have now generated versions of Mia40 that lack one or the other of these regions in yeast cells, and then tested to see if these mutants could drive proteins across the outer membrane of mitochondria. The results show that it is the ability of Mia40 to bind proteins – and not its enzyme activity – that is essential for importing proteins into the intermembrane space. As disulfide bond formation is not critical for importing proteins into the intermembrane space, future studies could test whether Mia40 also helps to transport proteins that cannot form disulfide bonds. Presumably, Mia40 has a much broader relevance for importing mitochondrial proteins than was previously thought. DOI:http://dx.doi.org/10.7554/eLife.16177.002
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Affiliation(s)
- Valentina Peleh
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
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