1
|
Antolínez-Fernández Á, Esteban-Ramos P, Fernández-Moreno MÁ, Clemente P. Molecular pathways in mitochondrial disorders due to a defective mitochondrial protein synthesis. Front Cell Dev Biol 2024; 12:1410245. [PMID: 38855161 PMCID: PMC11157125 DOI: 10.3389/fcell.2024.1410245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2024] [Accepted: 05/09/2024] [Indexed: 06/11/2024] Open
Abstract
Mitochondria play a central role in cellular metabolism producing the necessary ATP through oxidative phosphorylation. As a remnant of their prokaryotic past, mitochondria contain their own genome, which encodes 13 subunits of the oxidative phosphorylation system, as well as the tRNAs and rRNAs necessary for their translation in the organelle. Mitochondrial protein synthesis depends on the import of a vast array of nuclear-encoded proteins including the mitochondrial ribosome protein components, translation factors, aminoacyl-tRNA synthetases or assembly factors among others. Cryo-EM studies have improved our understanding of the composition of the mitochondrial ribosome and the factors required for mitochondrial protein synthesis and the advances in next-generation sequencing techniques have allowed for the identification of a growing number of genes involved in mitochondrial pathologies with a defective translation. These disorders are often multisystemic, affecting those tissues with a higher energy demand, and often present with neurodegenerative phenotypes. In this article, we review the known proteins required for mitochondrial translation, the disorders that derive from a defective mitochondrial protein synthesis and the animal models that have been established for their study.
Collapse
Affiliation(s)
- Álvaro Antolínez-Fernández
- Instituto de Investigaciones Biomédicas Sols-Morreale (IIBM), Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Departamento de Bioquímica, Universidad Autónoma de Madrid, Madrid, Spain
| | - Paula Esteban-Ramos
- Instituto de Investigaciones Biomédicas Sols-Morreale (IIBM), Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Departamento de Bioquímica, Universidad Autónoma de Madrid, Madrid, Spain
| | - Miguel Ángel Fernández-Moreno
- Instituto de Investigaciones Biomédicas Sols-Morreale (IIBM), Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Departamento de Bioquímica, Universidad Autónoma de Madrid, Madrid, Spain
| | - Paula Clemente
- Instituto de Investigaciones Biomédicas Sols-Morreale (IIBM), Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Departamento de Bioquímica, Universidad Autónoma de Madrid, Madrid, Spain
| |
Collapse
|
2
|
Homberg B, Rehling P, Cruz-Zaragoza LD. The multifaceted mitochondrial OXA insertase. Trends Cell Biol 2023; 33:765-772. [PMID: 36863885 DOI: 10.1016/j.tcb.2023.02.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 02/02/2023] [Accepted: 02/03/2023] [Indexed: 03/04/2023]
Abstract
Most mitochondrial proteins are synthesized in the cytosol and transported into mitochondria by protein translocases. Yet, mitochondria contain their own genome and gene expression system, which generates proteins that are inserted in the inner membrane by the oxidase assembly (OXA) insertase. OXA contributes to targeting proteins from both genetic origins. Recent data provides insights into how OXA cooperates with the mitochondrial ribosome during synthesis of mitochondrial-encoded proteins. A picture of OXA emerges in which it coordinates insertion of OXPHOS core subunits and their assembly into protein complexes but also participates in the biogenesis of select imported proteins. These functions position the OXA as a multifunctional protein insertase that facilitates protein transport, assembly, and stability at the inner membrane.
Collapse
Affiliation(s)
- Bettina Homberg
- Department of Cellular Biochemistry, University Medical Center Göttingen, 37073 Göttingen, Germany
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, 37073 Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), 37073 University of Göttingen, Germany; Fraunhofer Institute for Translational Medicine and Pharmacology ITMP, Translational Neuroinflammation and Automated Microscopy TNM, 37075 Göttingen, Germany; Max Planck Institute for Multidisciplinary Science, 37077 Göttingen, Germany.
| | | |
Collapse
|
3
|
Zhu G, Chen S, Zhang Y, Lu L. Mitochondrial Membrane-Associated Protein Mba1 Confers Antifungal Resistance by Affecting the Production of Reactive Oxygen Species in Aspergillus fumigatus. Antimicrob Agents Chemother 2023; 67:e0022523. [PMID: 37428039 PMCID: PMC10433838 DOI: 10.1128/aac.00225-23] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2023] [Accepted: 06/08/2023] [Indexed: 07/11/2023] Open
Abstract
Azole resistance in the human fungal pathogen Aspergillus fumigatus is becoming a major threat to global health. To date, mutations in the azole target-encoding cyp51A gene have been implicated in conferring azole resistance, but a steady increase in the number of A. fumigatus isolates with azole resistance resulting from non-cyp51A mutations has been recognized. Previous studies have revealed that some isolates with non-cyp51A mutation-induced azole resistance are related to mitochondrial dysfunction. However, knowledge of the molecular mechanism underlying the involvement of non-cyp51A mutations is limited. In this study, using next-generation sequencing, we found that nine independent azole-resistant isolates without cyp51A mutations had normal mitochondrial membrane potential. Among these isolates, a mutation in a mitochondrial ribosome-binding protein, Mba1, conferred multidrug resistance to azoles, terbinafine, and amphotericin B but not caspofungin. Molecular characterization verified that the TIM44 domain of Mba1 was crucial for drug resistance and that the N terminus of Mba1 played a major role in growth. Deletion of mba1 had no effect on Cyp51A expression but decreased the fungal cellular reactive oxygen species (ROS) content, which contributed to mba1-mediated drug resistance. The findings in this study suggest that some non-cyp51A proteins drive drug resistance mechanisms that result from reduced ROS production induced by antifungals.
Collapse
Affiliation(s)
- Guoxing Zhu
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Shu Chen
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Yuanwei Zhang
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Ling Lu
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| |
Collapse
|
4
|
Wenger C, Harsman A, Niemann M, Oeljeklaus S, von Känel C, Calderaro S, Warscheid B, Schneider A. The Mba1 homologue of Trypanosoma brucei is involved in the biogenesis of oxidative phosphorylation complexes. Mol Microbiol 2023; 119:537-550. [PMID: 36829306 DOI: 10.1111/mmi.15048] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Revised: 02/16/2023] [Accepted: 02/21/2023] [Indexed: 02/26/2023]
Abstract
Consistent with other eukaryotes, the Trypanosoma brucei mitochondrial genome encodes mainly hydrophobic core subunits of the oxidative phosphorylation system. These proteins must be co-translationally inserted into the inner mitochondrial membrane and are synthesized by the highly unique trypanosomal mitoribosomes, which have a much higher protein to RNA ratio than any other ribosome. Here, we show that the trypanosomal orthologue of the mitoribosome receptor Mba1 (TbMba1) is essential for normal growth of procyclic trypanosomes but redundant in the bloodstream form, which lacks an oxidative phosphorylation system. Proteomic analyses of TbMba1-depleted mitochondria from procyclic cells revealed reduced levels of many components of the oxidative phosphorylation system, most of which belong to the cytochrome c oxidase (Cox) complex, three subunits of which are mitochondrially encoded. However, the integrity of the mitoribosome and its interaction with the inner membrane were not affected. Pull-down experiments showed that TbMba1 forms a dynamic interaction network that includes the trypanosomal Mdm38/Letm1 orthologue and a trypanosome-specific factor that stabilizes the CoxI and CoxII mRNAs. In summary, our study suggests that the function of Mba1 in the biogenesis of membrane subunits of OXPHOS complexes is conserved among yeast, mammals and trypanosomes, which belong to two eukaryotic supergroups.
Collapse
Affiliation(s)
- Christoph Wenger
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland
| | - Anke Harsman
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland
| | - Moritz Niemann
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland
| | - Silke Oeljeklaus
- Faculty of Chemistry and Pharmacy, Biochemistry II, Theodor Boveri-Institute, University of Würzburg, Würzburg, Germany
| | - Corinne von Känel
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland
| | - Salvatore Calderaro
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland
| | - Bettina Warscheid
- Faculty of Chemistry and Pharmacy, Biochemistry II, Theodor Boveri-Institute, University of Würzburg, Würzburg, Germany.,CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - André Schneider
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland.,Institute for Advanced Study (Wissenschaftskolleg) Berlin, Berlin, Germany
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
Franco LVR, Su CH, Tzagoloff A. Modular assembly of yeast mitochondrial ATP synthase and cytochrome oxidase. Biol Chem 2021; 401:835-853. [PMID: 32142477 DOI: 10.1515/hsz-2020-0112] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 02/24/2020] [Indexed: 12/27/2022]
Abstract
The respiratory pathway of mitochondria is composed of four electron transfer complexes and the ATP synthase. In this article, we review evidence from studies of Saccharomyces cerevisiae that both ATP synthase and cytochrome oxidase (COX) are assembled from independent modules that correspond to structurally and functionally identifiable components of each complex. Biogenesis of the respiratory chain requires a coordinate and balanced expression of gene products that become partner subunits of the same complex, but are encoded in the two physically separated genomes. Current evidence indicates that synthesis of two key mitochondrial encoded subunits of ATP synthase is regulated by the F1 module. Expression of COX1 that codes for a subunit of the COX catalytic core is also regulated by a mechanism that restricts synthesis of this subunit to the availability of a nuclear-encoded translational activator. The respiratory chain must maintain a fixed stoichiometry of the component enzyme complexes during cell growth. We propose that high-molecular-weight complexes composed of Cox6, a subunit of COX, and of the Atp9 subunit of ATP synthase play a key role in establishing the ratio of the two complexes during their assembly.
Collapse
Affiliation(s)
- Leticia Veloso Ribeiro Franco
- Department of Biological Sciences, Columbia University, New York City, NY 10027, USA.,Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-000, Brasil
| | - Chen Hsien Su
- Department of Biological Sciences, Columbia University, New York City, NY 10027, USA
| | - Alexander Tzagoloff
- Department of Biological Sciences, Columbia University, New York City, NY 10027, USA
| |
Collapse
|
7
|
Rudler DL, Hughes LA, Viola HM, Hool LC, Rackham O, Filipovska A. Fidelity and coordination of mitochondrial protein synthesis in health and disease. J Physiol 2020; 599:3449-3462. [PMID: 32710561 DOI: 10.1113/jp280359] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 07/07/2020] [Indexed: 12/12/2022] Open
Abstract
The evolutionary acquisition of mitochondria has given rise to the diversity of eukaryotic life. Mitochondria have retained their ancestral α-proteobacterial traits through the maintenance of double membranes and their own circular genome. Their genome varies in size from very large in plants to the smallest in animals and their parasites. The mitochondrial genome encodes essential genes for protein synthesis and has to coordinate its expression with the nuclear genome from which it sources most of the proteins required for mitochondrial biogenesis and function. The mitochondrial protein synthesis machinery is unique because it is encoded by both the nuclear and mitochondrial genomes thereby requiring tight regulation to produce the respiratory complexes that drive oxidative phosphorylation for energy production. The fidelity and coordination of mitochondrial protein synthesis are essential for ATP production. Here we compare and contrast the mitochondrial translation mechanisms in mammals and fungi to bacteria and reveal that their diverse regulation can have unusual impacts on the health and disease of these organisms. We highlight that in mammals the rate of protein synthesis is more important than the fidelity of translation, enabling coordinated biogenesis of the mitochondrial respiratory chain with respiratory chain proteins synthesised by cytoplasmic ribosomes. Changes in mitochondrial protein fidelity can trigger the activation of the diverse cellular signalling networks in fungi and mammals to combat dysfunction in energy conservation. The physiological consequences of altered fidelity of protein synthesis can range from liver regeneration to the onset and development of cardiomyopathy.
Collapse
Affiliation(s)
- Danielle L Rudler
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
| | - Laetitia A Hughes
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
| | - Helena M Viola
- School of Human Sciences, University of Western Australia, 35 Stirling Highway, Nedlands, Western Australia, 6009, Australia
| | - Livia C Hool
- School of Human Sciences, University of Western Australia, 35 Stirling Highway, Nedlands, Western Australia, 6009, Australia.,Victor Chang Cardiac Research Institute, Sydney, NSW, Australia
| | - Oliver Rackham
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,School of Pharmacy and Biomedical Sciences, Curtin University, Bentley, Western Australia, 6102, Australia.,Curtin Health Innovation Research Institute, Curtin University, Bentley, Western Australia, 6102, Australia.,Telethon Kids Institute, Northern Entrance, Perth Children's Hospital, 15 Hospital Avenue, Nedlands, Western Australia, Australia
| | - Aleksandra Filipovska
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia.,Telethon Kids Institute, Northern Entrance, Perth Children's Hospital, 15 Hospital Avenue, Nedlands, Western Australia, Australia.,School of Molecular Sciences, University of Western Australia, Crawley, Western Australia, 6009, Australia
| |
Collapse
|
8
|
Lee RG, Gao J, Siira SJ, Shearwood AM, Ermer JA, Hofferek V, Mathews JC, Zheng M, Reid GE, Rackham O, Filipovska A. Cardiolipin is required for membrane docking of mitochondrial ribosomes and protein synthesis. J Cell Sci 2020; 133:jcs240374. [PMID: 32576663 DOI: 10.1242/jcs.240374] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 06/12/2020] [Indexed: 01/01/2023] Open
Abstract
The mitochondrial inner membrane contains a unique phospholipid known as cardiolipin (CL), which stabilises the protein complexes embedded in the membrane and supports its overall structure. Recent evidence indicates that the mitochondrial ribosome may associate with the inner membrane to facilitate co-translational insertion of the hydrophobic oxidative phosphorylation (OXPHOS) proteins into the inner membrane. We generated three mutant knockout cell lines for the CL biosynthesis gene Crls1 to investigate the effects of CL loss on mitochondrial protein synthesis. Reduced CL levels caused altered mitochondrial morphology and transcriptome-wide changes that were accompanied by uncoordinated mitochondrial translation rates and impaired respiratory chain supercomplex formation. Aberrant protein synthesis was caused by impaired formation and distribution of mitochondrial ribosomes. Reduction or loss of CL resulted in divergent mitochondrial and endoplasmic reticulum stress responses. We show that CL is required to stabilise the interaction of the mitochondrial ribosome with the membrane via its association with OXA1 (also known as OXA1L) during active translation. This interaction facilitates insertion of newly synthesised mitochondrial proteins into the inner membrane and stabilises the respiratory supercomplexes.
Collapse
Affiliation(s)
- Richard G Lee
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
| | - Junjie Gao
- School of Biomedical Sciences, University of Western Australia, Perth, Australia
| | - Stefan J Siira
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
| | - Anne-Marie Shearwood
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
| | - Judith A Ermer
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
| | - Vinzenz Hofferek
- School of Chemistry, The University of Melbourne, Parkville, Victoria, 3010, Australia
| | - James C Mathews
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
| | - Minghao Zheng
- School of Biomedical Sciences, University of Western Australia, Perth, Australia
| | - Gavin E Reid
- School of Chemistry, The University of Melbourne, Parkville, Victoria, 3010, Australia
- Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, 3010, Australia
- Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, Victoria, 3010, Australia
| | - Oliver Rackham
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- School of Pharmacy and Biomedical Sciences, Curtin University, Bentley, Western Australia 6102, Australia
- Curtin Health Innovation Research Institute, Curtin University, Bentley, Western Australia 6102, Australia
- Telethon Kids Institute, Northern Entrance, Perth Children's Hospital, 15 Hospital Avenue, Nedlands, Western Australia, Australia
| | - Aleksandra Filipovska
- Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Curtin Health Innovation Research Institute, Curtin University, Bentley, Western Australia 6102, Australia
- Telethon Kids Institute, Northern Entrance, Perth Children's Hospital, 15 Hospital Avenue, Nedlands, Western Australia, Australia
- School of Molecular Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia
| |
Collapse
|
9
|
Barros MH, McStay GP. Modular biogenesis of mitochondrial respiratory complexes. Mitochondrion 2019; 50:94-114. [PMID: 31669617 DOI: 10.1016/j.mito.2019.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/04/2019] [Accepted: 10/10/2019] [Indexed: 11/29/2022]
Abstract
Mitochondrial function relies on the activity of oxidative phosphorylation to synthesise ATP and generate an electrochemical gradient across the inner mitochondrial membrane. These coupled processes are mediated by five multi-subunit complexes that reside in this inner membrane. These complexes are the product of both nuclear and mitochondrial gene products. Defects in the function or assembly of these complexes can lead to mitochondrial diseases due to deficits in energy production and mitochondrial functions. Appropriate biogenesis and function are mediated by a complex number of assembly factors that promote maturation of specific complex subunits to form the active oxidative phosphorylation complex. The understanding of the biogenesis of each complex has been informed by studies in both simple eukaryotes such as Saccharomyces cerevisiae and human patients with mitochondrial diseases. These studies reveal each complex assembles through a pathway using specific subunits and assembly factors to form kinetically distinct but related assembly modules. The current understanding of these complexes has embraced the revolutions in genomics and proteomics to further our knowledge on the impact of mitochondrial biology in genetics, medicine, and evolution.
Collapse
Affiliation(s)
- Mario H Barros
- Departamento de Microbiologia - Instituto de Ciências Biomédicas, Universidade de São Paulo, Brazil.
| | - Gavin P McStay
- Department of Biological Sciences, Staffordshire University, Stoke-on-Trent, United Kingdom.
| |
Collapse
|
10
|
Cogliati S, Lorenzi I, Rigoni G, Caicci F, Soriano ME. Regulation of Mitochondrial Electron Transport Chain Assembly. J Mol Biol 2018; 430:4849-4873. [DOI: 10.1016/j.jmb.2018.09.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/20/2018] [Accepted: 09/25/2018] [Indexed: 12/26/2022]
|
11
|
Vargas Möller-Hergt B, Carlström A, Suhm T, Ott M. Insertion Defects of Mitochondrially Encoded Proteins Burden the Mitochondrial Quality Control System. Cells 2018; 7:cells7100172. [PMID: 30336542 PMCID: PMC6211022 DOI: 10.3390/cells7100172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 10/07/2018] [Accepted: 10/16/2018] [Indexed: 12/31/2022] Open
Abstract
The mitochondrial proteome contains proteins from two different genetic systems. Proteins are either synthesized in the cytosol and imported into the different compartments of the organelle or directly produced in the mitochondrial matrix. To ensure proteostasis, proteins are monitored by the mitochondrial quality control system, which will degrade non-native polypeptides. Defective mitochondrial membrane proteins are degraded by membrane-bound AAA-proteases. These proteases are regulated by factors promoting protein turnover or preventing their degradation. Here we determined genetic interactions between the mitoribosome receptors Mrx15 and Mba1 with the quality control system. We show that simultaneous absence of Mrx15 and the regulators of the i-AAA protease Mgr1 and Mgr3 provokes respiratory deficiency. Surprisingly, mutants lacking Mrx15 were more tolerant against proteotoxic stress. Furthermore, yeast cells became hypersensitive against proteotoxic stress upon deletion of MBA1. Contrary to Mrx15, Mba1 cooperates with the regulators of the m-AAA and i-AAA proteases. Taken together, these results suggest that membrane protein insertion and mitochondrial AAA-proteases are functionally coupled, possibly reflecting an early quality control step during mitochondrial protein synthesis.
Collapse
Affiliation(s)
| | - Andreas Carlström
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
| | - Tamara Suhm
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
| | - Martin Ott
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
| |
Collapse
|
12
|
Möller-Hergt BV, Carlström A, Stephan K, Imhof A, Ott M. The ribosome receptors Mrx15 and Mba1 jointly organize cotranslational insertion and protein biogenesis in mitochondria. Mol Biol Cell 2018; 29:2386-2396. [PMID: 30091672 PMCID: PMC6233058 DOI: 10.1091/mbc.e18-04-0227] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Mitochondrial gene expression in Saccharomyces cerevisiae is responsible for the production of highly hydrophobic subunits of the oxidative phosphorylation system. Membrane insertion occurs cotranslationally on membrane-bound mitochondrial ribosomes. Here, by employing a systematic mass spectrometry–based approach, we discovered the previously uncharacterized membrane protein Mrx15 that interacts via a soluble C-terminal domain with the large ribosomal subunit. Mrx15 contacts mitochondrial translation products during their synthesis and plays, together with the ribosome receptor Mba1, an overlapping role in cotranslational protein insertion. Taken together, our data reveal how these ribosome receptors organize membrane protein biogenesis in mitochondria.
Collapse
Affiliation(s)
| | - Andreas Carlström
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
| | - Katharina Stephan
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
| | - Axel Imhof
- Protein Analysis Unit, Biomedical Center, Faculty of Medicine, Ludwig Maximilian University of Munich, DE-82152 Planegg-Martinsried, Germany
| | - Martin Ott
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
| |
Collapse
|
13
|
Bieri P, Greber BJ, Ban N. High-resolution structures of mitochondrial ribosomes and their functional implications. Curr Opin Struct Biol 2018; 49:44-53. [DOI: 10.1016/j.sbi.2017.12.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 12/08/2017] [Accepted: 12/22/2017] [Indexed: 01/06/2023]
|
14
|
Englmeier R, Pfeffer S, Förster F. Structure of the Human Mitochondrial Ribosome Studied In Situ by Cryoelectron Tomography. Structure 2017; 25:1574-1581.e2. [PMID: 28867615 DOI: 10.1016/j.str.2017.07.011] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 06/12/2017] [Accepted: 07/26/2017] [Indexed: 01/26/2023]
Abstract
Mitochondria maintain their own genome and its corresponding protein synthesis machine, the mitochondrial ribosome (mitoribosome). Mitoribosomes primarily synthesize highly hydrophobic proteins of the inner mitochondrial membrane. Recent studies revealed the complete structure of the isolated mammalian mitoribosome, but its mode of membrane association remained hypothetical. In this study, we used cryoelectron tomography to visualize human mitoribosomes in isolated mitochondria. The subtomogram average of the membrane-associated human mitoribosome reveals a single major contact site with the inner membrane, mediated by the mitochondria-specific protein mL45. A second rRNA-mediated contact site that is present in yeast is absent in humans, resulting in a more variable association of the human mitoribosome with the inner membrane. Despite extensive structural differences of mammalian and fungal mitoribosomal structure, the principal organization of peptide exit tunnel and the mL45 homolog remains invariant, presumably to align the mitoribosome with the membrane-embedded insertion machinery.
Collapse
Affiliation(s)
- Robert Englmeier
- Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands
| | - Stefan Pfeffer
- Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, 82152 Martinsried, Germany
| | - Friedrich Förster
- Cryo-Electron Microscopy, Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands; Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, 82152 Martinsried, Germany.
| |
Collapse
|
15
|
Bae NS, Seberg AP, Carroll LP, Swanson MJ. Identification of Genes in Saccharomyces cerevisiae that Are Haploinsufficient for Overcoming Amino Acid Starvation. G3 (BETHESDA, MD.) 2017; 7:1061-1084. [PMID: 28209762 PMCID: PMC5386856 DOI: 10.1534/g3.116.037416] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 02/11/2017] [Indexed: 12/17/2022]
Abstract
The yeast Saccharomyces cerevisiae responds to amino acid deprivation by activating a pathway conserved in eukaryotes to overcome the starvation stress. We have screened the entire yeast heterozygous deletion collection to identify strains haploinsufficient for growth in the presence of sulfometuron methyl, which causes starvation for isoleucine and valine. We have discovered that cells devoid of MET15 are sensitive to sulfometuron methyl, and loss of heterozygosity at the MET15 locus can complicate screening the heterozygous deletion collection. We identified 138 cases of loss of heterozygosity in this screen. After eliminating the issues of the MET15 loss of heterozygosity, strains isolated from the collection were retested on sulfometuron methyl. To determine the general effect of the mutations for a starvation response, SMM-sensitive strains were tested for the ability to grow in the presence of canavanine, which induces arginine starvation, and strains that were MET15 were also tested for growth in the presence of ethionine, which causes methionine starvation. Many of the genes identified in our study were not previously identified as starvation-responsive genes, including a number of essential genes that are not easily screened in a systematic way. The genes identified span a broad range of biological functions, including many involved in some level of gene expression. Several unnamed proteins have also been identified, giving a clue as to possible functions of the encoded proteins.
Collapse
Affiliation(s)
- Nancy S Bae
- Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, Arizona 85308
| | - Andrew P Seberg
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295
| | - Leslie P Carroll
- Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, Georgia 31207
| | - Mark J Swanson
- Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, Arizona 85308
- Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, Georgia 31207
| |
Collapse
|
16
|
Ribosome-Associated Mba1 Escorts Cox2 from Insertion Machinery to Maturing Assembly Intermediates. Mol Cell Biol 2016; 36:2782-2793. [PMID: 27550809 PMCID: PMC5086520 DOI: 10.1128/mcb.00361-16] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 07/08/2016] [Accepted: 08/17/2016] [Indexed: 01/25/2023] Open
Abstract
The three conserved core subunits of the cytochrome c oxidase are encoded by mitochondria in close to all eukaryotes. The Cox2 subunit spans the inner membrane twice, exposing the N and C termini to the intermembrane space. For this, the N terminus is exported cotranslationally by Oxa1 and subsequently undergoes proteolytic maturation in Saccharomyces cerevisiae. Little is known about the translocation of the C terminus, but Cox18 has been identified to be a critical protein in this process. Here we find that the scaffold protein Cox20, which promotes processing of Cox2, is in complex with the ribosome receptor Mba1 and translating mitochondrial ribosomes in a Cox2-dependent manner. The Mba1-Cox20 complex accumulates when export of the C terminus of Cox2 is blocked by the loss of the Cox18 protein. While Cox20 engages with Cox18, Mba1 is no longer present at this stage. Our analyses indicate that Cox20 associates with nascent Cox2 and Mba1 to promote Cox2 maturation cotranslationally. We suggest that Mba1 stabilizes the Cox20-ribosome complex and supports the handover of Cox2 to the Cox18 tail export machinery.
Collapse
|
17
|
The m -AAA Protease Associated with Neurodegeneration Limits MCU Activity in Mitochondria. Mol Cell 2016; 64:148-162. [DOI: 10.1016/j.molcel.2016.08.020] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Revised: 06/16/2016] [Accepted: 08/12/2016] [Indexed: 11/23/2022]
|
18
|
Mitochondrial OXA Translocase Plays a Major Role in Biogenesis of Inner-Membrane Proteins. Cell Metab 2016; 23:901-8. [PMID: 27166948 PMCID: PMC4873616 DOI: 10.1016/j.cmet.2016.04.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Revised: 01/02/2016] [Accepted: 04/08/2016] [Indexed: 01/08/2023]
Abstract
The mitochondrial inner membrane harbors three protein translocases. Presequence translocase and carrier translocase are essential for importing nuclear-encoded proteins. The oxidase assembly (OXA) translocase is required for exporting mitochondrial-encoded proteins; however, different views exist about its relevance for nuclear-encoded proteins. We report that OXA plays a dual role in the biogenesis of nuclear-encoded mitochondrial proteins. First, a systematic analysis of OXA-deficient mitochondria led to an unexpected expansion of the spectrum of OXA substrates imported via the presequence pathway. Second, biogenesis of numerous metabolite carriers depends on OXA, although they are not imported by the presequence pathway. We show that OXA is crucial for the biogenesis of the Tim18-Sdh3 module of the carrier translocase. The export translocase OXA is thus required for the import of metabolite carriers by promoting assembly of the carrier translocase. We conclude that OXA is of central importance for the biogenesis of the mitochondrial inner membrane.
Collapse
|
19
|
Abstract
Mitochondrial ribosomes (mitoribosomes) perform protein synthesis inside mitochondria, the organelles responsible for energy conversion and adenosine triphosphate production in eukaryotic cells. Throughout evolution, mitoribosomes have become functionally specialized for synthesizing mitochondrial membrane proteins, and this has been accompanied by large changes to their structure and composition. We review recent high-resolution structural data that have provided unprecedented insight into the structure and function of mitoribosomes in mammals and fungi.
Collapse
Affiliation(s)
- Basil J Greber
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, CH-8093 Zurich, Switzerland; .,*Present address: California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California 94720-3220
| | - Nenad Ban
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, CH-8093 Zurich, Switzerland;
| |
Collapse
|
20
|
Turakhiya U, von der Malsburg K, Gold VAM, Guiard B, Chacinska A, van der Laan M, Ieva R. Protein Import by the Mitochondrial Presequence Translocase in the Absence of a Membrane Potential. J Mol Biol 2016; 428:1041-1052. [PMID: 26827728 DOI: 10.1016/j.jmb.2016.01.020] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 12/15/2015] [Accepted: 01/01/2016] [Indexed: 11/17/2022]
Abstract
The highly organized mitochondrial inner membrane harbors enzymes that produce the bulk of cellular ATP via oxidative phosphorylation. The majority of inner membrane protein precursors are synthesized in the cytosol. Precursors with a cleavable presequence are imported by the presequence translocase (TIM23 complex), while other precursors containing internal targeting signals are imported by the carrier translocase (TIM22 complex). Both TIM23 and TIM22 are activated by the transmembrane electrochemical potential. Many small inner membrane proteins, however, do not resemble canonical TIM23 or TIM22 substrates and their mechanism of import is unknown. We report that subunit e of the F1Fo-ATP synthase, a small single-spanning inner membrane protein that is critical for inner membrane organization, is imported by TIM23 in a process that does not require activation by the membrane potential. Absence of positively charged residues at the matrix-facing amino-terminus of subunit e facilitates membrane potential-independent import. Instead, engineered positive charges establish a dependence of the import reaction on the electrochemical potential. Our results have two major implications. First, they reveal an unprecedented pathway of protein import into the mitochondrial inner membrane, which is mediated by TIM23. Second, they directly demonstrate the role of the membrane potential in driving the electrophoretic transport of positively charged protein segments across the inner membrane.
Collapse
Affiliation(s)
- Uma Turakhiya
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Spemann Graduate School for Biology and Medicine, University of Freiburg, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
| | - Karina von der Malsburg
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Vicki A M Gold
- Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Bernard Guiard
- Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, 91190 Gif-sur-Yvette, France
| | - Agnieszka Chacinska
- International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
| | - Martin van der Laan
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany; Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Raffaele Ieva
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de la Recherche Scientifique, Université Paul Sabatier, 31077 Toulouse, France.
| |
Collapse
|
21
|
Breiman A, Fieulaine S, Meinnel T, Giglione C. The intriguing realm of protein biogenesis: Facing the green co-translational protein maturation networks. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1864:531-50. [PMID: 26555180 DOI: 10.1016/j.bbapap.2015.11.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 11/05/2015] [Indexed: 01/13/2023]
Abstract
The ribosome is the cell's protein-making factory, a huge protein-RNA complex, that is essential to life. Determining the high-resolution structures of the stable "core" of this factory was among the major breakthroughs of the past decades, and was awarded the Nobel Prize in 2009. Now that the mysteries of the ribosome appear to be more traceable, detailed understanding of the mechanisms that regulate protein synthesis includes not only the well-known steps of initiation, elongation, and termination but also the less comprehended features of the co-translational events associated with the maturation of the nascent chains. The ribosome is a platform for co-translational events affecting the nascent polypeptide, including protein modifications, folding, targeting to various cellular compartments for integration into membrane or translocation, and proteolysis. These events are orchestrated by ribosome-associated protein biogenesis factors (RPBs), a group of a dozen or more factors that act as the "welcoming committee" for the nascent chain as it emerges from the ribosome. In plants these factors have evolved to fit the specificity of different cellular compartments: cytoplasm, mitochondria and chloroplast. This review focuses on the current state of knowledge of these factors and their interaction around the exit tunnel of dedicated ribosomes. Particular attention has been accorded to the plant system, highlighting the similarities and differences with other organisms.
Collapse
Affiliation(s)
- Adina Breiman
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France; Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel
| | - Sonia Fieulaine
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France
| | - Thierry Meinnel
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France
| | - Carmela Giglione
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France.
| |
Collapse
|
22
|
Pfeffer S, Woellhaf MW, Herrmann JM, Förster F. Organization of the mitochondrial translation machinery studied in situ by cryoelectron tomography. Nat Commun 2015; 6:6019. [PMID: 25609543 DOI: 10.1038/ncomms7019] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 12/02/2014] [Indexed: 11/09/2022] Open
Abstract
Whereas the structure and function of cytosolic ribosomes have been studied in great detail, we know surprisingly little about the structural basis of mitochondrial protein synthesis. Here we used cryoelectron tomography and subtomogram analysis to visualize mitoribosomes in isolated yeast mitochondria, avoiding perturbations during ribosomal purification. Most mitoribosomes reside in immediate proximity to the inner mitochondrial membrane, in line with their specialization in the synthesis of hydrophobic membrane proteins. The subtomogram average of membrane-associated mitoribosomes reveals two distinct membrane contact sites, formed by the 21S rRNA expansion segment 96-ES1 and the inner membrane protein Mba1. On the basis of our data, we further hypothesize that Mba1 is not just a passive mitoribosome receptor on the inner membrane, but that it spatially aligns mitoribosomes with the membrane insertion machinery. This study reveals detailed insights into the supramolecular organization of the mitochondrial translation machinery and its association with the inner membrane in translation-competent mitochondria.
Collapse
Affiliation(s)
- Stefan Pfeffer
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| | - Michael W Woellhaf
- Cell Biology, University of Kaiserslautern, Erwin-Schrodinger-Strasse 13, 67663 Kaiserslautern, Germany
| | - Johannes M Herrmann
- Cell Biology, University of Kaiserslautern, Erwin-Schrodinger-Strasse 13, 67663 Kaiserslautern, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| |
Collapse
|
23
|
Park K, Jung SJ, Kim H, Kim H. Mode of membrane insertion of individual transmembrane segments in Mdl1 and Mdl2, multi-spanning mitochondrial ABC transporters. FEBS Lett 2014; 588:3445-53. [DOI: 10.1016/j.febslet.2014.08.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 07/25/2014] [Accepted: 08/03/2014] [Indexed: 10/24/2022]
|
24
|
Richman TR, Rackham O, Filipovska A. Mitochondria: Unusual features of the mammalian mitoribosome. Int J Biochem Cell Biol 2014; 53:115-20. [PMID: 24842111 DOI: 10.1016/j.biocel.2014.05.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Accepted: 05/11/2014] [Indexed: 11/28/2022]
Abstract
Mitochondria are responsible for generating most of the energy required by the cell. The oxidative phosphorylation (OXPHOS) system that produces the energy is composed of nuclear and mitochondrial encoded polypeptides. The 13 polypeptides encoded by the mitochondrial genome are synthesized by mitochondrial ribosomes (mitoribosomes). The evolutionary divergence of mitoribosomes has seen a reduction in their rRNA content and an increase in ribosomal proteins compared to their bacterial and cytoplasmic counterparts. Recent advances in cryo-electron microscopy (cryo-EM) mapping have revealed not all of these proteins simply replace the roles of the rRNA and that many have new roles. The mitoribosome has unique features that include a gatelike structure at the mRNA entrance that may facilitate recruitment of leaderless mitochondrial mRNAs and also a polypeptide exit tunnel that has an unusual nascent-polypeptide exit mechanism. Defects in the mitochondrial translation machinery are a common contributor to multi-system disorders known as mitochondrial diseases for which currently there are no cures or effective treatments.
Collapse
Affiliation(s)
- Tara R Richman
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, Nedlands, Western Australia 6009, Australia
| | - Oliver Rackham
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, Nedlands, Western Australia 6009, Australia; School of Chemistry and Biochemistry, The University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Aleksandra Filipovska
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, Nedlands, Western Australia 6009, Australia; School of Chemistry and Biochemistry, The University of Western Australia, Crawley, Western Australia 6009, Australia.
| |
Collapse
|
25
|
Weckbecker D, Herrmann JM. Methods to study the biogenesis of membrane proteins in yeast mitochondria. Methods Mol Biol 2014; 1033:307-22. [PMID: 23996186 DOI: 10.1007/978-1-62703-487-6_20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
The biogenesis of mitochondrial membrane proteins is an intricate process that relies on the import and submitochondrial sorting of nuclear-encoded preproteins and on the synthesis of mitochondrial translation products in the matrix. Subsequently, these polypeptides need to be inserted into the outer and the inner membranes of the organelle where many of them assemble into multisubunit complexes. In this chapter we provide established protocols to study these different processes experimentally using mitochondria of budding yeast. In particular, methods are described in detail to purify mitochondria, to study mitochondrial protein synthesis, to follow the import of radiolabeled preproteins into isolated mitochondria, and to assess membrane association and the aggregation of mitochondrial proteins by fractionation. These protocols and a list of dos and don'ts shall enable beginners and experienced scientists to address the targeting and assembly of mitochondrial membrane proteins.
Collapse
|
26
|
Architecture of the large subunit of the mammalian mitochondrial ribosome. Nature 2013; 505:515-9. [PMID: 24362565 DOI: 10.1038/nature12890] [Citation(s) in RCA: 174] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 11/15/2013] [Indexed: 01/30/2023]
Abstract
Mitochondrial ribosomes synthesize a number of highly hydrophobic proteins encoded on the genome of mitochondria, the organelles in eukaryotic cells that are responsible for energy conversion by oxidative phosphorylation. The ribosomes in mammalian mitochondria have undergone massive structural changes throughout their evolution, including ribosomal RNA shortening and acquisition of mitochondria-specific ribosomal proteins. Here we present the three-dimensional structure of the 39S large subunit of the porcine mitochondrial ribosome determined by cryo-electron microscopy at 4.9 Å resolution. The structure, combined with data from chemical crosslinking and mass spectrometry experiments, reveals the unique features of the 39S subunit at near-atomic resolution and provides detailed insight into the architecture of the polypeptide exit site. This region of the mitochondrial ribosome has been considerably remodelled compared to its bacterial counterpart, providing a specialized platform for the synthesis and membrane insertion of the highly hydrophobic protein components of the respiratory chain.
Collapse
|
27
|
Ostojić J, Glatigny A, Herbert CJ, Dujardin G, Bonnefoy N. Does the study of genetic interactions help predict the function of mitochondrial proteins in Saccharomyces cerevisiae? Biochimie 2013; 100:27-37. [PMID: 24262604 DOI: 10.1016/j.biochi.2013.11.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/06/2013] [Indexed: 10/26/2022]
Abstract
Mitochondria are complex organelles of eukaryotic cells that contain their own genome, encoding key subunits of the respiratory complexes. The successive steps of mitochondrial gene expression are intimately linked, and are under the control of a large number of nuclear genes encoding factors that are imported into mitochondria. Investigating the relationships between these genes and their interaction networks, and whether they reveal direct or indirect partners, can shed light on their role in mitochondrial biogenesis, as well as identify new actors in this process. These studies, mainly developed in yeasts, are significant because mammalian equivalents of such yeast genes are candidate genes in mitochondrial pathologies. In practice, studies of physical, chemical and genetic interactions can be undertaken. The search for genetic interactions, either aggravating or alleviating the phenotype of the starting mutants, has proved to be particularly powerful in yeast since even subtle changes in respiratory phenotypes can be screened in a very efficient way. In addition, several high throughput genetic approaches have recently been developed. In this review we analyze the genetic network of three genes involved in different steps of mitochondrial gene expression, from the transcription and translation of mitochondrial RNAs to the insertion of newly synthesized proteins into the inner mitochondrial membrane, and we examine their relevance to our understanding of mitochondrial biogenesis. We find that these genetic interactions are seldom redundant with physical interactions, and thus bring a considerable amount of original and significant information as well as open new areas of research.
Collapse
Affiliation(s)
- Jelena Ostojić
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Annie Glatigny
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Christopher J Herbert
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Geneviève Dujardin
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Nathalie Bonnefoy
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
| |
Collapse
|
28
|
Hewitt VL, Gabriel K, Traven A. The ins and outs of the intermembrane space: diverse mechanisms and evolutionary rewiring of mitochondrial protein import routes. Biochim Biophys Acta Gen Subj 2013; 1840:1246-53. [PMID: 23994494 DOI: 10.1016/j.bbagen.2013.08.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 08/09/2013] [Accepted: 08/20/2013] [Indexed: 11/24/2022]
Abstract
BACKGROUND Mitochondrial biogenesis is an essential process in all eukaryotes. Import of proteins from the cytosol into mitochondria is a key step in organelle biogenesis. Recent evidence suggests that a given mitochondrial protein does not take the same import route in all organisms, suggesting that pathways of mitochondrial protein import can be rewired through evolution. Examples of this process so far involve proteins destined to the mitochondrial intermembrane space (IMS). SCOPE OF REVIEW Here we review the components, substrates and energy sources of the known mechanisms of protein import into the IMS. We discuss evolutionary rewiring of the IMS import routes, focusing on the example of the lactate utilisation enzyme cytochrome b2 (Cyb2) in the model yeast Saccharomyces cerevisiae and the human fungal pathogen Candida albicans. MAJOR CONCLUSIONS There are multiple import pathways used for protein entry into the IMS and they form a network capable of importing a diverse range of substrates. These pathways have been rewired, possibly in response to environmental pressures, such as those found in the niches in the human body inhabited by C. albicans. GENERAL SIGNIFICANCE We propose that evolutionary rewiring of mitochondrial import pathways can adjust the metabolic fitness of a given species to their environmental niche. This article is part of a Special Issue entitled Frontiers of Mitochondrial.
Collapse
Affiliation(s)
- Victoria L Hewitt
- Department of Biochemistry and Molecular Biology, Building 77, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne 3800, Australia.
| | - Kipros Gabriel
- Department of Biochemistry and Molecular Biology, Building 77, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne 3800, Australia.
| | - Ana Traven
- Department of Biochemistry and Molecular Biology, Building 77, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne 3800, Australia.
| |
Collapse
|
29
|
Abstract
The mitochondrion is arguably the most complex organelle in the budding yeast cell cytoplasm. It is essential for viability as well as respiratory growth. Its innermost aqueous compartment, the matrix, is bounded by the highly structured inner membrane, which in turn is bounded by the intermembrane space and the outer membrane. Approximately 1000 proteins are present in these organelles, of which eight major constituents are coded and synthesized in the matrix. The import of mitochondrial proteins synthesized in the cytoplasm, and their direction to the correct soluble compartments, correct membranes, and correct membrane surfaces/topologies, involves multiple pathways and macromolecular machines. The targeting of some, but not all, cytoplasmically synthesized mitochondrial proteins begins with translation of messenger RNAs localized to the organelle. Most proteins then pass through the translocase of the outer membrane to the intermembrane space, where divergent pathways sort them to the outer membrane, inner membrane, and matrix or trap them in the intermembrane space. Roughly 25% of mitochondrial proteins participate in maintenance or expression of the organellar genome at the inner surface of the inner membrane, providing 7 membrane proteins whose synthesis nucleates the assembly of three respiratory complexes.
Collapse
|
30
|
Benz M, Soll J, Ankele E. Arabidopsis thaliana Oxa proteins locate to mitochondria and fulfill essential roles during embryo development. PLANTA 2013; 237:573-88. [PMID: 23179441 DOI: 10.1007/s00425-012-1793-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 10/19/2012] [Indexed: 05/12/2023]
Abstract
Members of the Alb3/Oxa1/YidC protein family function as insertases in chloroplasts, mitochondria, and bacteria. Due to independent gene duplications, all organisms possess two isoforms, Oxa1 and Oxa2 except gram-negative bacteria, which encode only for one YidC-like protein. The genome of Arabidopsis thaliana however, encodes for eight different isoforms. The localization of three of these isoforms has been identified earlier: Alb3 and Alb4 located in thylakoid membranes of chloroplasts while AtOxa1 was found in the inner membrane of mitochondria. Here, we show that the second Oxa1 protein, Oxa1b as well as two Oxa2 proteins are also localized in mitochondria. The last two isoforms most likely encode truncated versions of Oxa-like proteins, which might be inoperable pseudogenes. Homozygous mutant lines were only obtained for Oxa1b, which did not reveal any significant phenotypes, while T-DNA insertion lines of Oxa1a, Oxa2a and Oxa2b resulted only in heterozygous plants indicating that these genes are indispensable for plant development. Phenotyping heterozygous lines showed that embryos are either retarded in growth, display an albino phenotype or embryo formation was entirely abolished suggesting that Oxa1a and both Oxa2 proteins function in embryo formation although at different developmental stages as indicated by the various phenotypes observed.
Collapse
Affiliation(s)
- Monique Benz
- Energy Biosciences Institute, University of California, 2151 Berkeley Way, Berkeley, CA 94720-5230, USA.
| | | | | |
Collapse
|
31
|
Funes S, Westerburg H, Jaimes-Miranda F, Woellhaf MW, Aguilar-Lopez JL, Janßen L, Bonnefoy N, Kauff F, Herrmann JM. Partial suppression of Oxa1 mutants by mitochondria-targeted signal recognition particle provides insights into the evolution of the cotranslational insertion systems. FEBS J 2013. [PMID: 23198851 DOI: 10.1111/febs.12082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The biogenesis of hydrophobic membrane proteins involves their cotranslational membrane integration in order to prevent their unproductive aggregation. In the cytosol of bacteria and eukaryotes, membrane targeting of ribosomes that synthesize membrane proteins is achieved by signal recognition particles (SRPs) and their cognate membrane-bound receptors. As is evident from the genomes of fully sequenced eukaryotes, mitochondria generally lack an SRP system. Instead, mitochondrial ribosomes are physically associated with the protein insertion machinery in the inner membrane. Accordingly, deletion of ribosome-binding sites on the Oxa1 insertase and the Mba1 ribosome receptor in yeast leads to severe defects in cotranslational protein insertion and results in respiration-deficient mutants. In this study, we expressed mitochondria-targeted versions of the bacterial SRP protein Ffh and its receptor FtsY in these yeast mutants. Interestingly, Ffh was found to bind to the large subunit of mitochondrial ribosomes, and could relieve, to some degree, the defect of these insertion mutants. Although FtsY could also bind to mitochondrial membranes, it did not improve membrane protein biogenesis in this strain, presumably because of its inability to interact with Ffh. Hence, mitochondrial ribosomes are still able to interact physically and functionally with the bacterial SRP system. Our observations are consistent with a model according to which the protein insertion system in mitochondria evolved in three steps. The loss of genes for hydrophilic polypeptides (step 1) allowed the development of ribosome-binding sites on membrane proteins (step 2), which finally made the existence of an SRP-mediated system dispensable (step 3).
Collapse
Affiliation(s)
- Soledad Funes
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Ciudad Universitaria, Universidad Nacional Autónoma de México, Distrito Federal, Mexico.
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Park K, Botelho SC, Hong J, Österberg M, Kim H. Dissecting stop transfer versus conservative sorting pathways for mitochondrial inner membrane proteins in vivo. J Biol Chem 2012. [PMID: 23184936 DOI: 10.1074/jbc.m112.409748] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial inner membrane proteins that carry an N-terminal presequence are sorted by one of two pathways: stop transfer or conservative sorting. However, the sorting pathway is known for only a small number of proteins, in part due to the lack of robust experimental tools with which to study. Here we present an approach that facilitates determination of inner membrane protein sorting pathways in vivo by fusing a mitochondrial inner membrane protein to the C-terminal part of Mgm1p containing the rhomboid cleavage region. We validated the Mgm1 fusion approach using a set of proteins for which the sorting pathway is known, and determined sorting pathways of inner membrane proteins for which the sorting mode was previously uncharacterized. For Sdh4p, a multispanning membrane protein, our results suggest that both conservative sorting and stop transfer mechanisms are required for insertion. Furthermore, the sorting process of Mgm1 fusion proteins was analyzed under different growth conditions and yeast mutant strains that were defective in the import motor or the m-AAA protease function. Our results show that the sorting of mitochondrial proteins carrying moderately hydrophobic transmembrane segments is sensitive to cellular conditions, implying that mitochondrial import and membrane sorting in the physiological environment may be dynamically tuned.
Collapse
Affiliation(s)
- Kwangjin Park
- School of Biological Sciences, Seoul National University, Building 504-421, Seoul 151-747, South Korea
| | | | | | | | | |
Collapse
|
33
|
Szklarczyk R, Wanschers BFJ, Nijtmans LG, Rodenburg RJ, Zschocke J, Dikow N, van den Brand MAM, Hendriks-Franssen MGM, Gilissen C, Veltman JA, Nooteboom M, Koopman WJH, Willems PHGM, Smeitink JAM, Huynen MA, van den Heuvel LP. A mutation in the FAM36A gene, the human ortholog of COX20, impairs cytochrome c oxidase assembly and is associated with ataxia and muscle hypotonia. Hum Mol Genet 2012; 22:656-67. [PMID: 23125284 DOI: 10.1093/hmg/dds473] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The mitochondrial respiratory chain complex IV (cytochrome c oxidase) is a multi-subunit enzyme that transfers electrons from cytochrome c to molecular oxygen, yielding water. Its biogenesis requires concerted expression of mitochondria- and nuclear-encoded subunits and assembly factors. In this report, we describe a homozygous missense mutation in FAM36A from a patient who displays ataxia and muscle hypotonia. The FAM36A gene is a remote, putative ortholog of the fungal complex IV assembly factor COX20. Messenger RNA (mRNA) and protein co-expression analyses support the involvement of FAM36A in complex IV function in mammals. The c.154A>C mutation in the FAM36A gene, a mutation that is absent in sequenced exomes, leads to a reduced activity and lower levels of complex IV and its protein subunits. The FAM36A protein is nearly absent in patient's fibroblasts. Cells affected by the mutation accumulate subassemblies of complex IV that contain COX1 but are almost devoid of COX2 protein. We observe co-purification of FAM36A and COX2 proteins, supporting that the FAM36A defect hampers the early step of complex IV assembly at the incorporation of the COX2 subunit. Lentiviral complementation of patient's fibroblasts with wild-type FAM36A increases the complex IV activity as well as the amount of holocomplex IV and of individual subunits. These results establish the function of the human gene FAM36A/COX20 in complex IV assembly and support a causal role of the gene in complex IV deficiency.
Collapse
Affiliation(s)
- Radek Szklarczyk
- Centre for Molecular and Biomolecular Informatics, Nijmegen Centre for Molecular Life Sciences, Radboud University Medical Centre, Nijmegen 6500HB, The Netherlands
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Keil M, Bareth B, Woellhaf MW, Peleh V, Prestele M, Rehling P, Herrmann JM. Oxa1-ribosome complexes coordinate the assembly of cytochrome C oxidase in mitochondria. J Biol Chem 2012; 287:34484-93. [PMID: 22904327 DOI: 10.1074/jbc.m112.382630] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The terminal enzyme of the respiratory chain, cytochrome c oxidase, consists of a hydrophobic reaction center formed by three mitochondrially encoded subunits with which 9-10 nuclear encoded subunits are associated. The three core subunits are synthesized on mitochondrial ribosomes and inserted into the inner membrane in a co-translational reaction facilitated by the Oxa1 insertase. Oxa1 consists of an N-terminal insertase domain and a C-terminal ribosome-binding region. Mutants lacking the C-terminal region show specific defects in co-translational insertion, suggesting that the close contact of the ribosome with the insertase promotes co-translational insertion of nascent chains. In this study, we inserted flexible linkers of 100 or 200 amino acid residues between the insertase domain and ribosome-binding region of Oxa1 of Saccharomyces cerevisiae. In the absence of the ribosome receptor Mba1, these linkers caused a length-dependent decrease in mitochondrial respiratory activity caused by diminished levels of cytochrome c oxidase. Interestingly, considerable amounts of mitochondrial translation products were still integrated into the inner membrane in these linker mutants. However, they showed severe defects in later stages of the biogenesis process, presumably during assembly into functional complexes. Our observations suggest that the close proximity of Oxa1 to ribosomes is not only used to improve membrane insertion but is also critical for the productive assembly of the subunits of the cytochrome c oxidase. This points to a role for Oxa1 in the spatial coordination of the ribosome with assembly factors that are critical for enzyme biogenesis.
Collapse
Affiliation(s)
- Melanie Keil
- Department of Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | | | | | | | | | | | | |
Collapse
|
35
|
Herrmann JM, Woellhaf MW, Bonnefoy N. Control of protein synthesis in yeast mitochondria: the concept of translational activators. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:286-94. [PMID: 22450032 DOI: 10.1016/j.bbamcr.2012.03.007] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Revised: 03/01/2012] [Accepted: 03/08/2012] [Indexed: 12/18/2022]
Abstract
Mitochondria contain their own genome which codes for a small number of proteins. Most mitochondrial translation products are part of the membrane-embedded reaction centers of the respiratory chain complexes. In the yeast Saccharomyces cerevisiae, the expression of these proteins is regulated by translational activators that bind mitochondrial mRNAs, in most cases to their 5'-untranslated regions, and each mitochondrial mRNA appears to have its own translational activator(s). Recent studies showed that these translational activators can be part of feedback control loops which only permit translation if the downstream assembly of nascent translation products can occur. In several cases, the accumulation of a non-assembled protein prevents further synthesis of this protein but not translation in general. These control loops prevent the synthesis of potentially harmful assembly intermediates of the reaction centers of mitochondrial enzymes. Since such regulatory feedback loops only work if translation occurs in the compartment in which the complexes of the respiratory chain are assembled, these control mechanisms require the presence of a translation machinery in mitochondria. This might explain why eukaryotic cells maintained DNA in mitochondria during the last two billion years of evolution. This review gives an overview of the mitochondrial translation system and summarizes the current knowledge on translational activators and their role in the regulation of mitochondrial protein synthesis. This article is part of a Special Issue entitled: Protein import and quality control in mitochondria and plastids.
Collapse
Affiliation(s)
- Johannes M Herrmann
- Cell Biology, Erwin-Schrödinger-Strasse 13, University of Kaiserslautern, 67663 Kaiserslautern, Germany.
| | | | | |
Collapse
|
36
|
Abstract
Depending on the organism, mitochondria consist approximately of 500-1,400 different proteins. By far most of these proteins are encoded by nuclear genes and synthesized on cytosolic ribosomes. Targeting signals direct these proteins into mitochondria and there to their respective subcompartment: the outer membrane, the intermembrane space (IMS), the inner membrane, and the matrix. Membrane-embedded translocation complexes allow the translocation of proteins across and, in the case of membrane proteins, the insertion into mitochondrial membranes. A small number of proteins are encoded by the mitochondrial genome: Most mitochondrial translation products represent hydrophobic proteins of the inner membrane which-together with many nuclear-encoded proteins-form the respiratory chain complexes. This chapter gives an overview on the mitochondrial protein translocases and the mechanisms by which they drive the transport and assembly of mitochondrial proteins.
Collapse
|
37
|
Christian BE, Spremulli LL. Mechanism of protein biosynthesis in mammalian mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:1035-54. [PMID: 22172991 DOI: 10.1016/j.bbagrm.2011.11.009] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 11/03/2011] [Accepted: 11/08/2011] [Indexed: 01/25/2023]
Abstract
Protein synthesis in mammalian mitochondria produces 13 proteins that are essential subunits of the oxidative phosphorylation complexes. This review provides a detailed outline of each phase of mitochondrial translation including initiation, elongation, termination, and ribosome recycling. The roles of essential proteins involved in each phase are described. All of the products of mitochondrial protein synthesis in mammals are inserted into the inner membrane. Several proteins that may help bind ribosomes to the membrane during translation are described, although much remains to be learned about this process. Mutations in mitochondrial or nuclear genes encoding components of the translation system often lead to severe deficiencies in oxidative phosphorylation, and a summary of these mutations is provided. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.
Collapse
Affiliation(s)
- Brooke E Christian
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | | |
Collapse
|
38
|
Multiple roles of the Cox20 chaperone in assembly of Saccharomyces cerevisiae cytochrome c oxidase. Genetics 2011; 190:559-67. [PMID: 22095077 DOI: 10.1534/genetics.111.135665] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The Cox2 subunit of Saccharomyces cerevisiae cytochrome c oxidase is synthesized in the mitochondrial matrix as a precursor whose leader peptide is rapidly processed by the inner membrane protease following translocation to the intermembrane space. Processing is chaperoned by Cox20, an integral inner membrane protein whose hydrophilic domains are located in the intermembrane space, and Cox20 remains associated with mature, unassembled Cox2. The Cox2 C-tail domain is exported post-translationally by the highly conserved translocase Cox18 and associated proteins. We have found that Cox20 is required for efficient export of the Cox2 C-tail. Furthermore, Cox20 interacts by co-immune precipitation with Cox18, and this interaction requires the presence of Cox2. We therefore propose that Cox20 binding to Cox2 on the trans side of the inner membrane accelerates dissociation of newly exported Cox2 from the Cox18 translocase, promoting efficient cycling of the translocase. The requirement for Cox20 in cytochrome c oxidase assembly and respiratory growth is partially bypassed by yme1, mgr1 or mgr3 mutations, each of which reduce i-AAA protease activity in the intermembrane space. Thus, Cox20 also appears to stabilize unassembled Cox2 against degradation by the i-AAA protease. Pre-Cox2 leader peptide processing by Imp1 occurs in the absence of Cox20 and i-AAA protease activity, but is greatly reduced in efficiency. Under these conditions some mature Cox2 is assembled into cytochrome c oxidase allowing weak respiratory growth. Thus, the Cox20 chaperone has important roles in leader peptide processing, C-tail export, and stabilization of Cox2.
Collapse
|
39
|
Funes S, Kauff F, van der Sluis EO, Ott M, Herrmann JM. Evolution of YidC/Oxa1/Alb3 insertases: three independent gene duplications followed by functional specialization in bacteria, mitochondria and chloroplasts. Biol Chem 2011; 392:13-9. [PMID: 21194367 DOI: 10.1515/bc.2011.013] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Members of the YidC/Oxa1/Alb3 protein family facilitate the insertion, folding and assembly of proteins of the inner membranes of bacteria and mitochondria and the thylakoid membrane of plastids. All homologs share a conserved hydrophobic core region comprising five transmembrane domains. On the basis of phylogenetic analyses, six subgroups of the family can be distinguished which presumably arose from three independent gene duplications followed by functional specialization. During evolution of bacteria, mitochondria and chloroplasts, subgroup-specific regions were added to the core domain to facilitate the association with ribosomes or other components contributing to the substrate spectrum of YidC/Oxa1/Alb3 proteins.
Collapse
Affiliation(s)
- Soledad Funes
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Circuito Exterior s/n, Ciudad Universitaria, Universidad Nacional Autónoma de México, Mexico D.F. 04510, Mexico
| | | | | | | | | |
Collapse
|
40
|
Gruschke S, Ott M. The polypeptide tunnel exit of the mitochondrial ribosome is tailored to meet the specific requirements of the organelle. Bioessays 2010; 32:1050-7. [PMID: 20967780 DOI: 10.1002/bies.201000081] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The ribosomal polypeptide tunnel exit is the site where a variety of factors interact with newly synthesized proteins to guide them through the early steps of their biogenesis. In mitochondrial ribosomes, this site has been considerably modified in the course of evolution. In contrast to all other translation systems, mitochondrial ribosomes are responsible for the synthesis of only a few hydrophobic membrane proteins that are essential subunits of the mitochondrial respiratory chain. Membrane insertion of these proteins occurs co-translationally and is connected to a sophisticated assembly process that not only includes the assembly of the different subunits but also the acquisition of redox co-factors. Here, we describe how mitochondrial translation is organized in the context of respiratory chain assembly and speculate how alteration of the ribosomal tunnel exit might allow the establishment of a subset of specialized ribosomes that individually organize the early steps in the biogenesis of distinct mitochondrially-encoded proteins.
Collapse
Affiliation(s)
- Steffi Gruschke
- Research Group Membrane Biogenesis, University of Kaiserslautern, Kaiserslautern, Germany
| | | |
Collapse
|
41
|
Bauerschmitt H, Mick DU, Deckers M, Vollmer C, Funes S, Kehrein K, Ott M, Rehling P, Herrmann JM. Ribosome-binding proteins Mdm38 and Mba1 display overlapping functions for regulation of mitochondrial translation. Mol Biol Cell 2010; 21:1937-44. [PMID: 20427570 PMCID: PMC2883938 DOI: 10.1091/mbc.e10-02-0101] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Biogenesis of respiratory chain complexes depends on the expression of mitochondrial-encoded subunits. Their synthesis occurs on membrane-associated ribosomes and is probably coupled to their membrane insertion. Defects in expression of mitochondrial translation products are among the major causes of mitochondrial disorders. Mdm38 is related to Letm1, a protein affected in Wolf-Hirschhorn syndrome patients. Like Mba1 and Oxa1, Mdm38 is an inner membrane protein that interacts with ribosomes and is involved in respiratory chain biogenesis. We find that simultaneous loss of Mba1 and Mdm38 causes severe synthetic defects in the biogenesis of cytochrome reductase and cytochrome oxidase. These defects are not due to a compromised membrane binding of ribosomes but the consequence of a mis-regulation in the synthesis of Cox1 and cytochrome b. Cox1 expression is restored by replacing Cox1-specific regulatory regions in the mRNA. We conclude, that Mdm38 and Mba1 exhibit overlapping regulatory functions in translation of selected mitochondrial mRNAs.
Collapse
|
42
|
Gruschke S, Gröne K, Heublein M, Hölz S, Israel L, Imhof A, Herrmann JM, Ott M. Proteins at the polypeptide tunnel exit of the yeast mitochondrial ribosome. J Biol Chem 2010; 285:19022-8. [PMID: 20404317 DOI: 10.1074/jbc.m110.113837] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Oxidative phosphorylation in mitochondria requires the synthesis of proteins encoded in the mitochondrial DNA. The mitochondrial translation machinery differs significantly from that of the bacterial ancestor of the organelle. This is especially evident from many mitochondria-specific ribosomal proteins. An important site of the ribosome is the polypeptide tunnel exit. Here, nascent chains are exposed to an aqueous environment for the first time. Many biogenesis factors interact with the tunnel exit of pro- and eukaryotic ribosomes to help the newly synthesized proteins to mature. To date, nothing is known about the organization of the tunnel exit of mitochondrial ribosomes. We therefore undertook a comprehensive approach to determine the composition of the yeast mitochondrial ribosomal tunnel exit. Mitochondria contain homologues of the ribosomal proteins located at this site in bacterial ribosomes. Here, we identified proteins located in their proximity by chemical cross-linking and mass spectrometry. Our analysis revealed a complex network of interacting proteins including proteins and protein domains specific to mitochondrial ribosomes. This network includes Mba1, the membrane-bound ribosome receptor of the inner membrane, as well as Mrpl3, Mrpl13, and Mrpl27, which constitute ribosomal proteins exclusively found in mitochondria. This unique architecture of the tunnel exit is presumably an adaptation of the translation system to the specific requirements of the organelle.
Collapse
Affiliation(s)
- Steffi Gruschke
- Abteilung Zellbiologie, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | | | | | | | | | | | | | | |
Collapse
|
43
|
Mitochondrial translation and beyond: processes implicated in combined oxidative phosphorylation deficiencies. J Biomed Biotechnol 2010; 2010:737385. [PMID: 20396601 PMCID: PMC2854570 DOI: 10.1155/2010/737385] [Citation(s) in RCA: 142] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2009] [Accepted: 01/29/2010] [Indexed: 12/22/2022] Open
Abstract
Mitochondrial disorders are a heterogeneous group of often multisystemic and early fatal diseases, which are amongst the most common inherited human diseases. These disorders are caused by defects in the oxidative phosphorylation (OXPHOS) system, which comprises five multisubunit enzyme complexes encoded by both the nuclear and the mitochondrial genomes. Due to the multitude of proteins and intricacy of the processes required for a properly functioning OXPHOS system, identifying the genetic defect that underlies an OXPHOS deficiency is not an easy task, especially in the case of combined OXPHOS defects. In the present communication we give an extensive overview of the proteins and processes (in)directly involved in mitochondrial translation and the biogenesis of the OXPHOS system and their roles in combined OXPHOS deficiencies. This knowledge is important for further research into the genetic causes, with the ultimate goal to effectively prevent and cure these complex and often devastating disorders.
Collapse
|
44
|
The role of Coa2 in hemylation of yeast Cox1 revealed by its genetic interaction with Cox10. Mol Cell Biol 2010; 30:172-85. [PMID: 19841065 DOI: 10.1128/mcb.00869-09] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saccharomyces cerevisiae cells lacking the cytochrome c oxidase (CcO) assembly factor Coa2 are impaired in Cox1 maturation and exhibit a rapid degradation of newly synthesized Cox1. The respiratory deficiency of coa2 Delta cells is suppressed either by the presence of a mutant allele of the Cox10 farnesyl transferase involved in heme a biosynthesis or through impaired proteolysis by the disruption of the mitochondrial Oma1 protease. Cox10 with an N196K substitution functions as a robust gain-of-function suppressor of the respiratory deficiency of coa2 Delta cells but lacks suppressor activity for two other CcO assembly mutant strains, the coa1 Delta and shy1 Delta mutants. The suppressor activity of N196K mutant Cox10 is dependent on its catalytic function and the presence of Cox15, the second enzyme involved in heme a biosynthesis. Varying the substitution at Asn196 reveals a correlation between the suppressor activity and the stabilization of the high-mass homo-oligomeric Cox10 complex. We postulate that the mutant Cox10 complex has enhanced efficiency in the addition of heme a to Cox1. Coa2 appears to impart stability to the oligomeric wild-type Cox10 complex involved in Cox1 hemylation.
Collapse
|
45
|
Ott M, Herrmann JM. Co-translational membrane insertion of mitochondrially encoded proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1803:767-75. [PMID: 19962410 DOI: 10.1016/j.bbamcr.2009.11.010] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Revised: 11/18/2009] [Accepted: 11/25/2009] [Indexed: 11/29/2022]
Abstract
The components of the mitochondrial proteome represent a mosaic of dual genetic origin: while most mitochondrial proteins are encoded by nuclear genes and imported into the organelle following synthesis in the cytosol, a small number of proteins is encoded by the mitochondrial genome. Though small in number, mitochondrial translation products are vital for cellular functionality as these proteins represent the core subunits of the respiratory chain and the ATPase which produce the vast majority of the cellular ATP. Mitochondrial translation products are almost exclusively highly hydrophobic polypeptides which are inserted into the inner membrane in the course of their synthesis. The machinery that mediates membrane insertion in mitochondria is deduced from that of their bacterial ancestors and hence shows profound similarities to the insertion machinery of prokaryotes. However, the specialization on the production of a very small set of translation products drove a severe reduction in the complexity of this system. The insertase Oxa1 forms the central component of the insertion machinery. Oxa1 directly binds to mitochondrial ribosomes and, together with the inner membrane protein Mba1, aligns the polypeptide exit tunnel of the ribosome with the insertion site at the inner membrane. The specific hallmarks and the critical components of this machinery are discussed in this review article.
Collapse
Affiliation(s)
- Martin Ott
- Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | | |
Collapse
|
46
|
Zhang YJ, Tian HF, Wen JF. The evolution of YidC/Oxa/Alb3 family in the three domains of life: a phylogenomic analysis. BMC Evol Biol 2009; 9:137. [PMID: 19534824 PMCID: PMC2706819 DOI: 10.1186/1471-2148-9-137] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2008] [Accepted: 06/18/2009] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND YidC/Oxa/Alb3 family includes a group of conserved translocases that are essential for protein insertion into inner membranes of bacteria and mitochondria, and thylakoid membranes of chloroplasts. Because mitochondria and chloroplasts are of bacterial origin, Oxa and Alb3, like many other mitochondrial/chloroplastic proteins, are hypothetically derived from the pre-existing protein (YidC) of bacterial endosymbionts. Here, we test this hypothesis and investigate the evolutionary history of the whole YidC/Oxa/Alb3 family in the three domains of life. RESULTS Our comprehensive analyses of the phylogenetic distribution and phylogeny of the YidC/Oxa/Alb3 family lead to the following findings: 1) In archaea, YidC homologs are only sporadically distributed in Euryarchaeota; 2) Most bacteria contain only one YidC gene copy; some species in a few taxa (Bacillus, Lactobacillales, Actinobacteria and Clostridia) have two gene copies; 3) Eukaryotic Oxa and Alb3 have two separate prokaryotic origins, but they might not arise directly from the YidC of proteobacteria and cyanobacteria through the endosymbiosis origins of mitochondrium and chloroplast, respectively; 4) An ancient duplication occurred on both Oxa and Alb3 immediately after their origins, and thus most eukaryotes generally bear two Oxa and two Alb3. However, secondary loss, duplication or acquisition of new domain also occurred on the two genes in some lineages, especially in protists, resulting in a rich diversity or adaptive differentiation of the two translocases in these lineages. CONCLUSION YidC is distributed in bacteria and some Euryarchaeota. Although mitochondrial Oxa and chloroplastic Alb3 are derived from the prokaryotic YidC, their origin might be not related to the endosymbiosis events of the two organelles. In some eukaryotic lineages, especially in protists, Oxa and Alb3 have diverse evolutionary histories. Finally, a model for the evolutionary history of the entire YidC/Oxa/Alb3 family in the three domains of life is proposed.
Collapse
Affiliation(s)
- Yu-Juan Zhang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan Province 650223, PR China.
| | | | | |
Collapse
|
47
|
Pir P, Kirdar B, Hayes A, Onsan ZI, Ulgen KO, Oliver SG. Exometabolic and transcriptional response in relation to phenotype and gene copy number in respiration-related deletion mutants of S. cerevisiae. Yeast 2008; 25:661-72. [PMID: 18727146 DOI: 10.1002/yea.1612] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The transcriptional and metabolic impact of deleting one or both copies of a respiration-related gene has been studied in glucose-limited chemostats. Integration of literature information on phenotype with our exometabolome and transcriptome data enabled the identification of novel relationships between gene copy number, transcriptional regulation and phenotype. We found that the effect of complete respiratory deficiency on transcription was limited to downregulation of genes involved in oxidoreductase activity and iron assimilation. Partial respiratory deficiency had no significant impact on gene transcription. Changes in the copy number of two transcription-factor genes, HAP4 and MIG1, had a major impact on genes involved in mitochondrial function. Regulation of respiratory chain components encoded in the nucleus and mitochondria appears to be divided between Hap4p and Oxa1p, respectively. Similarly, repression of respiration may be imposed by the action of Mig1p and Mba1p on nuclear and mitochondrial gene expression, respectively. However, it is not clear whether Oxa1p and Mba1p regulate mitochondrial gene expression via their interaction with mitochondrial ribosomes or by some indirect means. The phenotype of nuclear petite mutants may not simply be due to the absence of respiration; e.g. Oxa1p or Bcs1p may play a role in the regulation of ribosome assembly in the nucleolus. Integration between respiration and cell growth may also result from the action of a single transcription factor. Thus, Hap4p targets genes that are required for respiration and for fitness in nutrient-limited conditions. This suggests that Hap4p may enable cells to adapt to nutrient limitation as well as diauxy.
Collapse
Affiliation(s)
- Pinar Pir
- Department of Chemical Engineering, Boğaziçi University, Bebek, 34342 Istanbul, Turkey
| | | | | | | | | | | |
Collapse
|
48
|
Abstract
In Chlamydomonas reinhardtii several nucleus-encoded proteins that participate in the mitochondrial oxidative phosphorylation are targeted to the organelle by unusually long mitochondrial targeting sequences. Here, we explored the components of the mitochondrial import machinery of the green alga. We mined the algal genome, searching for yeast and plant homologs, and reconstructed the mitochondrial import machinery. All the main translocation components were identified in Chlamydomonas as well as in Arabidopsis thaliana and in the recently sequenced moss Physcomitrella patens. Some of these components appear to be duplicated, as is the case of Tim22. In contrast, several yeast components that have relatively large hydrophilic regions exposed to the cytosol or to the intermembrane space seem to be absent in land plants and green algae. If present at all, these components of plants and algae may differ significantly from their yeast counterparts. We propose that long mitochondrial targeting sequences in some Chlamydomonas mitochondrial protein precursors are involved in preventing the aggregation of the hydrophobic proteins they carry.
Collapse
|
49
|
Mokranjac D, Neupert W. Thirty years of protein translocation into mitochondria: unexpectedly complex and still puzzling. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:33-41. [PMID: 18672008 DOI: 10.1016/j.bbamcr.2008.06.021] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 06/16/2008] [Accepted: 06/26/2008] [Indexed: 11/26/2022]
Abstract
Mitochondria are essential organelles of the eukaryotic cells that are made by expansion and division of pre-existing mitochondria. The majority of their protein constituents are synthesized in the cytosol. They are transported into and put together within the organelle. This complex process is facilitated by several protein translocases. Here we summarize current knowledge on these sophisticated molecular machines that mediate recognition, transport across membranes and intramitochondrial sorting of many hundreds of mitochondrial proteins.
Collapse
Affiliation(s)
- Dejana Mokranjac
- Institute for Physiological Chemistry, Ludwig-Maximilians University, Butenandtstr. 5, 81377 Munich, Germany
| | | |
Collapse
|
50
|
Bonnefoy N, Fiumera HL, Dujardin G, Fox TD. Roles of Oxa1-related inner-membrane translocases in assembly of respiratory chain complexes. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:60-70. [PMID: 18522806 DOI: 10.1016/j.bbamcr.2008.05.004] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 05/02/2008] [Accepted: 05/05/2008] [Indexed: 11/28/2022]
Abstract
Members of the family of the polytopic inner membrane proteins are related to Saccharomyces cerevisiae Oxa1 function in the assembly of energy transducing complexes of mitochondria and chloroplasts. Here we focus on the two mitochondrial members of this family, Oxa1 and Cox18, reviewing studies on their biogenesis as well as their functions, reflected in the phenotypic consequences of their absence in various organisms. In yeast, cytochrome c oxidase subunit II (Cox2) is a key substrate of these proteins. Oxa1 is required for co-translational translocation and insertion of Cox2, while Cox18 is necessary for the export of its C-terminal domain. Genetic and biochemical strategies have been used to investigate the functions of distinct domains of Oxa1 and to identify its partners in protein insertion/translocation. Recent work on the related bacterial protein YidC strongly indicates that it is capable of functioning alone as a translocase for hydrophilic domains and an insertase for TM domains. Thus, the Oxa1 and Cox18 probably catalyze these reactions directly in a co- and/or posttranslational way. In various species, Oxa1 appears to assist in the assembly of different substrate proteins, although it is still unclear how Oxa1 recognizes its substrates, and whether additional factors participate in this beyond its direct interaction with mitochondrial ribosomes, demonstrated in S. cerevisiae. Oxa1 is capable of assisting posttranslational insertion and translocation in isolated mitochondria, and Cox18 may posttranslationally translocate its only known substrate, the Cox2 C-terminal domain, in vivo. Detailed understanding of the mechanisms of action of these two proteins must await the resolution of their structure in the membrane and the development of a true in vitro mitochondrial translation system.
Collapse
Affiliation(s)
- Nathalie Bonnefoy
- Centre de Génétique Moléculaire, CNRS UPR 2167, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | | | | | | |
Collapse
|