1
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Hughes LA, Rackham O, Filipovska A. Illuminating mitochondrial translation through mouse models. Hum Mol Genet 2024; 33:R61-R79. [PMID: 38779771 PMCID: PMC11112386 DOI: 10.1093/hmg/ddae020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Revised: 01/22/2024] [Accepted: 01/31/2024] [Indexed: 05/25/2024] Open
Abstract
Mitochondria are hubs of metabolic activity with a major role in ATP conversion by oxidative phosphorylation (OXPHOS). The mammalian mitochondrial genome encodes 11 mRNAs encoding 13 OXPHOS proteins along with 2 rRNAs and 22 tRNAs, that facilitate their translation on mitoribosomes. Maintaining the internal production of core OXPHOS subunits requires modulation of the mitochondrial capacity to match the cellular requirements and correct insertion of particularly hydrophobic proteins into the inner mitochondrial membrane. The mitochondrial translation system is essential for energy production and defects result in severe, phenotypically diverse diseases, including mitochondrial diseases that typically affect postmitotic tissues with high metabolic demands. Understanding the complex mechanisms that underlie the pathologies of diseases involving impaired mitochondrial translation is key to tailoring specific treatments and effectively targeting the affected organs. Disease mutations have provided a fundamental, yet limited, understanding of mitochondrial protein synthesis, since effective modification of the mitochondrial genome has proven challenging. However, advances in next generation sequencing, cryoelectron microscopy, and multi-omic technologies have revealed unexpected and unusual features of the mitochondrial protein synthesis machinery in the last decade. Genome editing tools have generated unique models that have accelerated our mechanistic understanding of mitochondrial translation and its physiological importance. Here we review the most recent mouse models of disease pathogenesis caused by defects in mitochondrial protein synthesis and discuss their value for preclinical research and therapeutic development.
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Affiliation(s)
- Laetitia A Hughes
- Telethon Kids Institute, Northern Entrance, Perth Children’s Hospital, 15 Hospital Avenue, Nedlands, WA 6009, Australia
- Harry Perkins Institute of Medical Research, 6 Verdun Street, Nedlands, WA 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, 35 Stirling Highway, Crawley, WA 6009, The University of Western Australia, Crawley, WA 6009, Australia
| | - Oliver Rackham
- Telethon Kids Institute, Northern Entrance, Perth Children’s Hospital, 15 Hospital Avenue, Nedlands, WA 6009, Australia
- Harry Perkins Institute of Medical Research, 6 Verdun Street, Nedlands, WA 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, 35 Stirling Highway, Crawley, WA 6009, The University of Western Australia, Crawley, WA 6009, Australia
- Curtin Medical School, Curtin University, Kent Street, Bentley, WA 6102, Australia
- Curtin Health Innovation Research Institute, Curtin University, Kent Street, Bentley, WA 6102, Australia
| | - Aleksandra Filipovska
- Telethon Kids Institute, Northern Entrance, Perth Children’s Hospital, 15 Hospital Avenue, Nedlands, WA 6009, Australia
- ARC Centre of Excellence in Synthetic Biology, 35 Stirling Highway, Crawley, WA 6009, The University of Western Australia, Crawley, WA 6009, Australia
- Department of Biochemistry and Molecular Biology, Monash Biomedicine Discovery Institute, Monash University, 19 Innovation Walk, Clayton, Clayton, VIC 3168, Australia
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2
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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.
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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
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3
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Ayyub SA, Varshney U. Translation initiation in mammalian mitochondria- a prokaryotic perspective. RNA Biol 2019; 17:165-175. [PMID: 31696767 DOI: 10.1080/15476286.2019.1690099] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
ATP is generated in mitochondria of eukaryotic cells by oxidative phosphorylation (OXPHOS). The OXPHOS complex, which is crucial for cellular metabolism, comprises of both nuclear and mitochondrially encoded subunits. Also, the occurrence of several pathologies because of mutations in the mitochondrial translation apparatus indicates the importance of mitochondrial translation and its regulation. The mitochondrial translation apparatus is similar to its prokaryotic counterpart due to a common origin of evolution. However, mitochondrial translation has diverged from prokaryotic translation in many ways by reductive evolution. In this review, we focus on mammalian mitochondrial translation initiation, a highly regulated step of translation, and present a comparison with prokaryotic translation.
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Affiliation(s)
- Shreya Ahana Ayyub
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.,Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
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4
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Mitochondrial transcription and translation: overview. Essays Biochem 2018; 62:309-320. [PMID: 30030363 PMCID: PMC6056719 DOI: 10.1042/ebc20170102] [Citation(s) in RCA: 165] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 05/14/2018] [Accepted: 05/14/2018] [Indexed: 12/13/2022]
Abstract
Mitochondria are the major source of ATP in the cell. Five multi-subunit complexes in the inner membrane of the organelle are involved in the oxidative phosphorylation required for ATP production. Thirteen subunits of these complexes are encoded by the mitochondrial genome often referred to as mtDNA. For this reason, the expression of mtDNA is vital for the assembly and functioning of the oxidative phosphorylation complexes. Defects of the mechanisms regulating mtDNA gene expression have been associated with deficiencies in assembly of these complexes, resulting in mitochondrial diseases. Recently, numerous factors involved in these processes have been identified and characterized leading to a deeper understanding of the mechanisms that underlie mitochondrial diseases.
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5
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Lightowlers RN, Rozanska A, Chrzanowska-Lightowlers ZM. Mitochondrial protein synthesis: figuring the fundamentals, complexities and complications, of mammalian mitochondrial translation. FEBS Lett 2014; 588:2496-503. [PMID: 24911204 PMCID: PMC4099522 DOI: 10.1016/j.febslet.2014.05.054] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 05/28/2014] [Accepted: 05/29/2014] [Indexed: 12/28/2022]
Abstract
Mitochondrial protein synthesis is essential for all mammals, being responsible for providing key components of the oxidative phosphorylation complexes. Although only thirteen different polypeptides are made, the molecular details of this deceptively simple process remain incomplete. Central to this process is a non-canonical ribosome, the mitoribosome, which has evolved to address its unique mandate. In this review, we integrate the current understanding of the molecular aspects of mitochondrial translation with recent advances in structural biology. We identify numerous key questions that we will need to answer if we are to increase our knowledge of the molecular mechanisms underlying mitochondrial protein synthesis.
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Affiliation(s)
- Robert N Lightowlers
- The Wellcome Trust Centre for Mitochondrial Research, Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
| | - Agata Rozanska
- The Wellcome Trust Centre for Mitochondrial Research, Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Zofia M Chrzanowska-Lightowlers
- The Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
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6
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Ezelle HJ, Hassel BA. Pathologic effects of RNase-L dysregulation in immunity and proliferative control. Front Biosci (Schol Ed) 2012; 4:767-86. [PMID: 22202089 DOI: 10.2741/s298] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The endoribonuclease RNase-L is the terminal component of an RNA cleavage pathway that mediates antiviral, antiproliferative and immunomodulatory activities. Inactivation or dysregulation of RNase-L is associated with a compromised immune response and increased risk of cancer, accordingly its activity is tightly controlled and requires an allosteric activator, 2',5'-linked oligoadenylates, for enzymatic activity. The biological activities of RNase-L are a result of direct and indirect effects of RNA cleavage and microarray analyses have revealed that RNase-L impacts the gene expression program at multiple levels. The identification of RNase-L-regulated RNAs has provided insights into potential mechanisms by which it exerts antiproliferative, proapoptotic, senescence-inducing and innate immune activities. RNase-L protein interactors have been identified that serve regulatory functions and are implicated as alternate mechanisms of its biologic functions. Thus, while the molecular details are understood for only a subset of RNase-L activities, its regulation by small molecules and critical roles in host defense and as a candidate tumor suppressor make it a promising therapeutic target.
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Affiliation(s)
- Heather J Ezelle
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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7
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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.
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Affiliation(s)
- Brooke E Christian
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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8
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Haque ME, Koc H, Cimen H, Koc EC, Spremulli LL. Contacts between mammalian mitochondrial translational initiation factor 3 and ribosomal proteins in the small subunit. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1779-84. [PMID: 22015679 DOI: 10.1016/j.bbapap.2011.09.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 09/26/2011] [Accepted: 09/28/2011] [Indexed: 11/18/2022]
Abstract
Mammalian mitochondrial translational initiation factor 3 (IF3(mt)) binds to the small subunit of the ribosome displacing the large subunit during the initiation of protein biosynthesis. About half of the proteins in mitochondrial ribosomes have homologs in bacteria while the remainder are unique to the mitochondrion. To obtain information on the ribosomal proteins located near the IF3(mt) binding site, cross-linking studies were carried out followed by identification of the cross-linked proteins by mass spectrometry. IF3(mt) cross-links to mammalian mitochondrial homologs of the bacterial ribosomal proteins S5, S9, S10, and S18-2 and to unique mitochondrial ribosomal proteins MRPS29, MRPS32, MRPS36 and PTCD3 (Pet309) which has now been identified as a small subunit ribosomal protein. IF3(mt) has extensions on both the N- and C-termini compared to the bacterial factors. Cross-linking of a truncated derivative lacking these extensions gives the same hits as the full length IF3(mt) except that no cross-links were observed to MRPS36. IF3 consists of two domains separated by a flexible linker. Cross-linking of the isolated N- and C-domains was observed to a range of ribosomal proteins particularly with the C-domain carrying the linker which showed significant cross-linking to several ribosomal proteins not found in prokaryotes.
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MESH Headings
- Animals
- Cattle
- Eukaryotic Initiation Factor-3/chemistry
- Eukaryotic Initiation Factor-3/genetics
- Eukaryotic Initiation Factor-3/metabolism
- Humans
- Mammals/genetics
- Mammals/metabolism
- Mitochondrial Proteins/chemistry
- Mitochondrial Proteins/genetics
- Mitochondrial Proteins/metabolism
- Models, Biological
- Models, Molecular
- Peptide Chain Initiation, Translational/genetics
- Protein Binding
- Protein Interaction Mapping
- Protein Structure, Secondary
- Ribosomal Proteins/chemistry
- Ribosomal Proteins/genetics
- Ribosomal Proteins/metabolism
- Ribosome Subunits, Small, Eukaryotic/chemistry
- Ribosome Subunits, Small, Eukaryotic/genetics
- Ribosome Subunits, Small, Eukaryotic/metabolism
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Affiliation(s)
- Md Emdadul Haque
- Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA
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9
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Rasheedi S, Suragani M, Haq SK, Sachchidanand, Bhardwaj R, Hasnain SE, Ehtesham NZ. Expression, purification and ligand binding properties of the recombinant translation initiation factor (PeIF5B) from Pisum sativum. Mol Cell Biochem 2010; 344:33-41. [PMID: 20890638 DOI: 10.1007/s11010-010-0526-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Accepted: 06/22/2010] [Indexed: 10/19/2022]
Abstract
Gene encoding a novel translation initiation factor PeIF5B from Pisum sativum with sequence similarity to eIF5B from H. sapiens, D. melanogaster, S. cerevisiae as well as archaeal aIF5B from M. thermoautotrophicum was earlier reported by us. We now describe the expression and purification of 96 kDa recombinant PeIF5B (rPeIF5B) protein. Using fluorescence and circular dichroism spectra analyses, we show that Mg(2+) binding does not lead to any change in PeIF5B aromatic amino acid micro-environment, whereas GTP binding induces significant changes in the local environment of the aromatic amino acids. However, the protein undergoes changes in secondary structure upon metal ion and nucleotide binding. Charged initiator tRNA binding to PeIF5B is found to be cofactor dependent. PeIF5B binds to GTP in vitro as evident from autoradiography. Based on homology modeling of the catalytic domain of PeIF5B, we could confirm the conformational changes in PeIF5B following ligand binding.
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Affiliation(s)
- Sheeba Rasheedi
- Department of Biochemistry, University of Hyderabad, Hyderabad, India
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10
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Christian BE, Spremulli LL. Preferential selection of the 5'-terminal start codon on leaderless mRNAs by mammalian mitochondrial ribosomes. J Biol Chem 2010; 285:28379-86. [PMID: 20610392 DOI: 10.1074/jbc.m110.149054] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian mitochondrial mRNAs are basically leaderless, having few or no untranslated nucleotides prior to the 5'-start codon. We demonstrate here that mammalian mitochondrial 55 S ribosomes preferentially form initiation complexes at a 5'-terminal AUG codon over an internal AUG. The preferential use of the 5'-start codon is also seen on mitochondrial 28 S small subunits, which suggests that mitochondrial translation initiation on leaderless mRNAs does not require the large ribosomal subunit. The selection of the 5'-AUG is dependent on the presence of fMet-tRNA and is enhanced by the presence of the mitochondrial initiation factor IF2(mt). In prokaryotes, IF3 is believed to antagonize initiation on leaderless mRNAs. However, IF3(mt) stimulates initiation complex formation on leaderless mRNAs when tested with 55 S ribosomes. The addition of even a few nucleotides 5' to the AUG codon significantly reduces the efficiency of initiation, highlighting the importance of the leaderless or nearly leaderless nature of mitochondrial mRNAs. In addition, very few initiation complexes could form on a hybrid mRNA construct consisting of tRNA(Met) attached at the 5'-end of a mitochondrial protein-coding sequence. This observation demonstrates that post-transcriptional processing must occur prior to translation in mammalian mitochondria.
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Affiliation(s)
- Brooke E Christian
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA
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11
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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: 144] [Impact Index Per Article: 10.3] [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.
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12
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The effect of spermine on the initiation of mitochondrial protein synthesis. Biochem Biophys Res Commun 2009; 391:942-6. [PMID: 19962967 DOI: 10.1016/j.bbrc.2009.11.169] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Accepted: 11/27/2009] [Indexed: 11/23/2022]
Abstract
Polyamines are important in both prokaryotic and eukaryotic translational systems. Spermine is a quaternary aliphatic amine that is cationic under physiological conditions. In this paper, we demonstrate that spermine stimulates fMet-tRNA binding to mammalian mitochondrial 55S ribosomes. The stimulatory effect of spermine is independent of the identity of the mRNA. The degree of stimulation of spermine is the same at all concentrations of mitochondrial initiation factor 2 (IF2(mt)) and mitochondrial initiation factor 3 (IF3(mt)). This observation indicates that IF2(mt) and IF3(mt), while essential for initiation, are not the primary components of the translation initiation system affected by spermine. IF3(mt) dissociates 55S ribosomes detectably in the absence of spermine, but this effect is strongly inhibited in the presence of spermine. This observation indicates that the positive effect of spermine on initiation is not due to an increase in the availability of the small subunits for initiation. Spermine also promotes fMet-tRNA binding to small subunits of the mitochondrial ribosome in the presence of IF2(mt). The major effect of spermine in promoting initiation complex formation thus appears to be on the interaction of fMet-tRNA with the ribosome.
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Lee C, Tibbetts AS, Kramer G, Appling DR. Yeast AEP3p is an accessory factor in initiation of mitochondrial translation. J Biol Chem 2009; 284:34116-25. [PMID: 19843529 DOI: 10.1074/jbc.m109.055350] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Initiation of protein synthesis in mitochondria and chloroplasts normally uses a formylated initiator methionyl-tRNA (fMet-tRNA(f)(Met)). However, mitochondrial protein synthesis in Saccharomyces cerevisiae can initiate with nonformylated Met-tRNA(f)(Met), as demonstrated in yeast mutants in which the nuclear gene encoding mitochondrial methionyl-tRNA formyltransferase (FMT1) has been deleted. The role of formylation of the initiator tRNA is not known, but in vitro formylation increases binding of Met-tRNA(f)(Met) to translation initiation factor 2 (IF2). We hypothesize the existence of an accessory factor that assists mitochondrial IF2 (mIF2) in utilizing unformylated Met-tRNA(f)(Met). This accessory factor might be unnecessary when formylated Met-tRNA(f)(Met) is present but becomes essential when only the unformylated species are available. Using a synthetic petite genetic screen in yeast, we identified a mutation in the AEP3 gene that caused a synthetic respiratory-defective phenotype together with Delta fmt1. The same aep3 mutation also caused a synthetic respiratory defect in cells lacking formylated Met-tRNA(f)(Met) due to loss of the MIS1 gene that encodes the mitochondrial C(1)-tetrahydrofolate synthase. The AEP3 gene encodes a peripheral mitochondrial inner membrane protein that stabilizes mitochondrially encoded ATP6/8 mRNA. Here we show that the AEP3 protein (Aep3p) physically interacts with yeast mIF2 both in vitro and in vivo and promotes the binding of unformylated initiator tRNA to yeast mIF2. We propose that Aep3p functions as an accessory initiation factor in mitochondrial protein synthesis.
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Affiliation(s)
- Changkeun Lee
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA
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14
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Haque ME, Spremulli LL. Roles of the N- and C-terminal domains of mammalian mitochondrial initiation factor 3 in protein biosynthesis. J Mol Biol 2008; 384:929-40. [PMID: 18930736 DOI: 10.1016/j.jmb.2008.09.077] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 09/26/2008] [Accepted: 09/27/2008] [Indexed: 11/27/2022]
Abstract
Bacterial initiation factor 3 (IF3) is organized into N- and C-domains separated by a linker. Mitochondrial IF3 (IF3(mt)) has a similar domain organization, although both domains have extensions not found in the bacterial factors. Constructs of the N- and C-domains of IF3(mt) with and without the connecting linker were prepared. The K(d) values for the binding of full-length IF3(mt) and its C-domain with and without the linker to mitochondrial 28S subunits are 30, 60, and 95 nM, respectively, indicating that much of the ribosome binding interactions are mediated by the C-domain. However, the N-domain binds to 28S subunits with only a 10-fold lower affinity than full-length IF3(mt). This observation indicates that the N-domain of IF3(mt) has significant contacts with the protein-rich small subunit of mammalian mitochondrial ribosomes. The linker also plays a role in modulating the interactions between the 28S subunit and the factor; it is not just a physical connector between the two domains. The presence of the two domains and the linker may optimize the overall affinity of IF3(mt) for the ribosome. These results are in sharp contrast to observations with Escherichia coli IF3. Removal of the N-domain drastically reduces the activity of IF3(mt) in the dissociation of mitochondrial 55S ribosomes, although the C-domain itself retains some activity. This residual activity depends significantly on the linker region. The N-domain alone has no effect on the dissociation of ribosomes. Full-length IF3(mt) reduces the binding of fMet-tRNA to the 28S subunit in the absence of mRNA. Both the C-terminal extension and the linker are required for this effect. IF3(mt) promotes the formation of a binary complex between IF2(mt) and fMet-tRNA that may play an important role in mitochondrial protein synthesis. Both domains play a role promoting the formation of this complex.
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Affiliation(s)
- Md Emdadul Haque
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
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15
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Haque ME, Grasso D, Miller C, Spremulli LL, Saada A. The effect of mutated mitochondrial ribosomal proteins S16 and S22 on the assembly of the small and large ribosomal subunits in human mitochondria. Mitochondrion 2008; 8:254-61. [PMID: 18539099 PMCID: PMC2517634 DOI: 10.1016/j.mito.2008.04.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2008] [Revised: 04/17/2008] [Accepted: 04/23/2008] [Indexed: 10/22/2022]
Abstract
Mutations in mitochondrial small subunit ribosomal proteins MRPS16 or MRPS22 cause severe, fatal respiratory chain dysfunction due to impaired translation of mitochondrial mRNAs. The loss of either MRPS16 or MRPS22 was accompanied by the loss of most of another small subunit protein MRPS11. However, MRPS2 was reduced only about 2-fold in patient fibroblasts. This observation suggests that the small ribosomal subunit is only partially able to assemble in these patients. Two large subunit ribosomal proteins, MRPL13 and MRPL15, were present in substantial amounts suggesting that the large ribosomal subunit is still present despite a non-functional small subunit.
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Affiliation(s)
- Md. Emdadul Haque
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC-27599-3290
| | - Domenick Grasso
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC-27599-3290
| | - Chaya Miller
- Metabolic Disease Unit, Hadassah Medical Center, P.O.B. 12000, 91120 Jerusalem, Israel
| | - Linda L Spremulli
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC-27599-3290
| | - Ann Saada
- Metabolic Disease Unit, Hadassah Medical Center, P.O.B. 12000, 91120 Jerusalem, Israel
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16
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Sissler M, Lorber B, Messmer M, Schaller A, Pütz J, Florentz C. Handling mammalian mitochondrial tRNAs and aminoacyl-tRNA synthetases for functional and structural characterization. Methods 2008; 44:176-89. [PMID: 18241799 DOI: 10.1016/j.ymeth.2007.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 11/07/2007] [Accepted: 11/07/2007] [Indexed: 10/22/2022] Open
Abstract
The mammalian mitochondrial (mt) genome codes for only 13 proteins, which are essential components in the process of oxidative phosphorylation of ADP into ATP. Synthesis of these proteins relies on a proper mt translation machinery. While 22 tRNAs and 2 rRNAs are also coded by the mt genome, all other factors including the set of aminoacyl-tRNA synthetases (aaRSs) are encoded in the nucleus and imported. Investigation of mammalian mt aminoacylation systems (and mt translation in general) gains more and more interest not only in regard of evolutionary considerations but also with respect to the growing number of diseases linked to mutations in the genes of either mt-tRNAs, synthetases or other factors. Here we report on methodological approaches for biochemical, functional, and structural characterization of human/mammalian mt-tRNAs and aaRSs. Procedures for preparation of native and in vitro transcribed tRNAs are accompanied by recommendations for specific handling of tRNAs incline to structural instability and chemical fragility. Large-scale preparation of mg amounts of highly soluble recombinant synthetases is a prerequisite for structural investigations that requires particular optimizations. Successful examples leading to crystallization of four mt-aaRSs and high-resolution structures are recalled and limitations discussed. Finally, the need for and the state-of-the-art in setting up an in vitro mt translation system are emphasized. Biochemical characterization of a subset of mammalian aminoacylation systems has already revealed a number of unprecedented peculiarities of interest for the study of evolution and forensic research. Further efforts in this field will certainly be rewarded by many exciting discoveries.
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Affiliation(s)
- Marie Sissler
- Architecture et Réactivité de l'ARN, Université Louis Pasteur de Strasbourg, CNRS, IBMC, 15 rue René Descartes, 67084 Strasbourg, France.
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17
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Gaur R, Grasso D, Datta PP, Krishna PDV, Das G, Spencer A, Agrawal RK, Spremulli L, Varshney U. A single mammalian mitochondrial translation initiation factor functionally replaces two bacterial factors. Mol Cell 2008; 29:180-90. [PMID: 18243113 DOI: 10.1016/j.molcel.2007.11.021] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 08/30/2007] [Accepted: 11/05/2007] [Indexed: 11/19/2022]
Abstract
The mechanism of translation in eubacteria and organelles is thought to be similar. In eubacteria, the three initiation factors IF1, IF2, and IF3 are vital. Although the homologs of IF2 and IF3 are found in mammalian mitochondria, an IF1 homolog has never been detected. Here, we show that bovine mitochondrial IF2 (IF2(mt)) complements E. coli containing a deletion of the IF2 gene (E. coli DeltainfB). We find that IF1 is no longer essential in an IF2(mt)-supported E. coli DeltainfB strain. Furthermore, biochemical and molecular modeling data show that a conserved insertion of 37 amino acids in the IF2(mt) substitutes for the function of IF1. Deletion of this insertion from IF2(mt) supports E. coli for the essential function of IF2. However, in this background, IF1 remains essential. These observations provide strong evidence that a single factor (IF2(mt)) in mammalian mitochondria performs the functions of two eubacterial factors, IF1 and IF2.
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Affiliation(s)
- Rahul Gaur
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
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18
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Haque ME, Grasso D, Spremulli LL. The interaction of mammalian mitochondrial translational initiation factor 3 with ribosomes: evolution of terminal extensions in IF3mt. Nucleic Acids Res 2007; 36:589-97. [PMID: 18056078 PMCID: PMC2241858 DOI: 10.1093/nar/gkm1072] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mammalian mitochondrial initiation factor 3 (IF3mt) has a central region with homology to bacterial IF3. This homology region is preceded by an N-terminal extension and followed by a C-terminal extension. The role of these extensions on the binding of IF3mt to mitochondrial small ribosomal subunits (28S) was studied using derivatives in which the extensions had been deleted. The Kd for the binding of IF3mt to 28S subunits is ∼30 nM. Removal of either the N- or C-terminal extension has almost no effect on this value. IF3mt has very weak interactions with the large subunit of the mitochondrial ribosome (39S) (Kd = 1.5 μM). However, deletion of the extensions results in derivatives with significant affinity for 39S subunits (Kd = 0.12−0.25 μM). IF3mt does not bind 55S monosomes, while the deletion derivative binds slightly to these particles. IF3mt is very effective in dissociating 55S ribosomes. Removal of the N-terminal extension has little effect on this activity. However, removal of the C-terminal extension leads to a complex dissociation pattern due to the high affinity of this derivative for 39S subunits. These data suggest that the extensions have evolved to ensure the proper dissociation of IF3mt from the 28S subunits upon 39S subunit joining.
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Affiliation(s)
- Md Emdadul Haque
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC-27599-3290, USA
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19
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Le Roy F, Silhol M, Salehzada T, Bisbal C. Regulation of mitochondrial mRNA stability by RNase L is translation-dependent and controls IFNalpha-induced apoptosis. Cell Death Differ 2007; 14:1406-13. [PMID: 17431428 DOI: 10.1038/sj.cdd.4402130] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Interferons (IFNs) inhibit the growth of many different cell types by altering the expression of specific genes. IFNs activities are partly mediated by the 2'-5' oligoadenylates-RNase L RNA decay pathway. RNase L is an endoribonuclease requiring activation by 2'-5' oligoadenylates to cleave single-stranded RNA. Here, we present evidence that degradation of mitochondrial mRNA by RNase L leads to cytochrome c release and caspase 3 activation during IFNalpha-induced apoptosis. We identify and characterize the mitochondrial translation initiation factor (IF2mt) as a new partner of RNase L. Moreover, we show that specific inhibition of mitochondrial translation with chloramphenicol inhibits the IFNalpha-induced degradation of mitochondrial mRNA by RNase L. Finally, we demonstrate that overexpression of IF2mt in human H9 cells stabilizes mitochondrial mRNA, inhibits apoptosis induced by IFNalpha and partially reverses IFNalpha-cell growth inhibition. On the basis of our results, we propose a model describing how RNase L regulates mitochondrial mRNA stability through its interaction with IF2mt.
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Affiliation(s)
- F Le Roy
- UMR 5535, Institut de Génétique Moléculaire de Montpellier, 1919 route de Mende, 349293 Montpellier, France
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20
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Grasso DG, Christian BE, Spencer A, Spremulli LL. Overexpression and purification of mammalian mitochondrial translational initiation factor 2 and initiation factor 3. Methods Enzymol 2007; 430:59-78. [PMID: 17913635 DOI: 10.1016/s0076-6879(07)30004-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Two mammalian mitochondrial initiation factors have been identified. Initiation factor 2 (IF2(mt)) selects the initiator tRNA (fMet-tRNA) and promotes its binding to the ribosome. Initiation factor 3 (IF3(mt)) promotes the dissociation of the 55S mitochondrial ribosome into subunits and may play additional, less-well-understood, roles in initiation complex formation. Native bovine IF2(mt) was purified from liver a number of years ago. The yield of this factor is very low making biochemical studies difficult. The cDNA for bovine IF2(mt) was expressed in Escherichia coli under the control of the T7 polymerase promoter in a vector that provides a His(6)-tag at the C-terminus of the expressed protein. This factor was expressed in E. coli and purified by chromatography on Ni-NTA resins. The expressed protein has a number of degradation products in partially purified preparations and this factor is then further purified by high-performance liquid chromatography or gravity chromatography on anion exchange resins. IF3(mt) has never been purified from any mammalian system. However, the cDNA for this protein can be identified in the expressed sequence tag (EST) libraries. The portion of the sequence encoding the region of human IF3(mt) predicted to be present in the mitochondrially imported form of this factor was cloned and expressed in E. coli using a vector that provides a C-terminal His(6)-tag. The tagged factor is partially purified on Ni-NTA resins. However, a major proteolytic fragment arising from a defined cleavage of this protein is present in these preparations. This contaminant can be removed by a single step of high-performance liquid chromatography on a cation exchange resin. Alternatively, the mature form of IF3(mt) can be purified by two sequential passes through a gravity S-Sepharose column.
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Affiliation(s)
- Domenick G Grasso
- Department of Chemistry, University of North Carolina at Chapel Hill, USA
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21
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Bhargava K, Spremulli LL. Role of the N- and C-terminal extensions on the activity of mammalian mitochondrial translational initiation factor 3. Nucleic Acids Res 2005; 33:7011-8. [PMID: 16340009 PMCID: PMC1310894 DOI: 10.1093/nar/gki1007] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Mammalian mitochondrial translational initiation factor 3 (IF3mt) promotes initiation complex formation on mitochondrial 55S ribosomes in the presence of IF2mt, fMet-tRNA and poly(A,U,G). The mature form of IF3mt is predicted to be 247 residues. Alignment of IF3mt with bacterial IF3 indicates that it has a central region with 20–30% identity to the bacterial factors. Both the N- and C-termini of IF3mt have extensions of ∼30 residues compared with bacterial IF3. To examine the role of the extensions on IF3mt, deletion constructs were prepared in which the N-terminal extension, the C-terminal extension or both extensions were deleted. These truncated derivatives were slightly more active in promoting initiation complex formation than the mature form of IF3mt. Mitochondrial 28S subunits have the ability to bind fMet-tRNA in the absence of mRNA. IF3mt promotes the dissociation of the fMet-tRNA bound in the absence of mRNA. This activity of IF3mt requires the C-terminal extension of this factor. Mitochondrial 28S subunits also bind mRNA independently of fMet-tRNA or added initiation factors. IF3mt has no effect on the formation of these complexes and cannot dissociate them once formed. These observations have lead to a new model for the function of IF3mt in mitochondrial translational initiation.
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Affiliation(s)
| | - Linda L. Spremulli
- To whom correspondence should be addressed. Tel: +1 919 966 1567; Fax: +1 919 966 3675;
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22
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Jacobs LJAM, de Wert G, Geraedts JPM, de Coo IFM, Smeets HJM. The transmission of OXPHOS disease and methods to prevent this. Hum Reprod Update 2005; 12:119-36. [PMID: 16199488 DOI: 10.1093/humupd/dmi042] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Diseases owing to defects of oxidative phosphorylation (OXPHOS) affect approximately 1 in 8,000 individuals. Clinical manifestations can be extremely variable and range from single-affected tissues to multisystemic syndromes. In general, tissues with a high energy demand, like brain, heart and muscle, are affected. The OXPHOS system is under dual genetic control, and mutations in both nuclear and mitochondrial genes can cause OXPHOS diseases. The expression and segregation of mitochondrial DNA (mtDNA) mutations is different from nuclear gene defects. The mtDNA mutations can be either homoplasmic or heteroplasmic and in the latter case disease becomes manifest when the mutation exceeds a tissue-specific threshold. This mutation load can vary between tissues and often an exact correlation between mutation load and phenotypic expression is lacking. The transmission of mtDNA mutations is exclusively maternal, but the mutation load between embryos can vary tremendously because of a segregational bottleneck. Diseases by nuclear gene mutations show a normal Mendelian inheritance pattern and often have a more constant clinical manifestation. Given the prevalence and severity of OXPHOS disorders and the lack of adequate therapy, existing and new methods for the prevention of transmission of OXPHOS disorders, like prenatal diagnosis (PND), preimplantation genetic diagnosis (PGD), cytoplasmic transfer (CT) and nuclear transfer (NT), are technically and ethically evaluated.
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Affiliation(s)
- L J A M Jacobs
- Department of Genetics and Cell Biology, University of Maastricht, 6200 MD Maastricht, The Netherlands
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23
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Garofalo C, Kramer G, Appling DR. Characterization of the C2 subdomain of yeast mitochondrial initiation factor 2. Arch Biochem Biophys 2005; 439:113-20. [PMID: 15935987 DOI: 10.1016/j.abb.2005.05.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Revised: 04/26/2005] [Accepted: 05/02/2005] [Indexed: 11/20/2022]
Abstract
The COOH-terminal part of the yeast mitochondrial initiation factor 2 (ymIF2), containing the C2 subdomain, was expressed and purified as a histidine-tagged polypeptide of 137 amino acids. Like the recombinant full-length protein, the C2 subdomain binds both formyl-Met-tRNA(f)(Met) and unformylated Met-tRNA(f)(Met) with only a small preference for the former species. Formation of a binary complex between the C2 subdomain or the full-length ymIF2 and initiator tRNA was also assessed by fluorescence measurements. The binding of coumarin-Met-tRNA(f) to either protein caused a blue shift of the coumarin emission spectrum and an increase in anisotropy. Full-length ymIF2 is functionally competent in forming an initiation complex and supporting formation of the first peptide bond on Escherichia coli ribosomes. The results demonstrate that ymIF2 has the same domain structure and biochemical properties of a typical IF2 species as found in bacteria or mammalian mitochondria--but with enhanced ability to bind unformylated initiator Met-tRNA.
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Affiliation(s)
- Cristiana Garofalo
- Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas, Austin, TX 78712, USA
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24
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Taanman JW, Llewelyn Williams S. The Human Mitochondrial Genome. OXIDATIVE STRESS AND DISEASE 2005. [DOI: 10.1201/9781420028843.ch3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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25
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Spencer AC, Spremulli LL. The interaction of mitochondrial translational initiation factor 2 with the small ribosomal subunit. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2005; 1750:69-81. [PMID: 15935986 DOI: 10.1016/j.bbapap.2005.03.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/03/2005] [Accepted: 03/07/2005] [Indexed: 10/25/2022]
Abstract
Bovine mitochondrial translational initiation factor 2 (IF-2(mt)) is organized into four domains, an N-terminal domain, a central G-domain and two C-terminal domains. These domains correspond to domains III-VI in the six-domain model of Escherichia coli IF-2. Variants in IF-2(mt) were prepared and tested for their abilities to bind the small (28S) subunit of the mitochondrial ribosome. The binding of wild-type IF-2(mt) was strong (K(d) approximately 10-20 nM) and was not affected by fMet-tRNA. Deletion of the N-terminal domain substantially reduced the binding of IF-2(mt) to 28S subunits. However, the addition of fMet-tRNA stimulated the binding of this variant at least 2-fold demonstrating that contacts between fMet-tRNA and IF-2(mt) can stabilize the binding of this factor to 28S subunits. No binding was observed for IF-2(mt) variants lacking the G-domain which probably plays a critical role in organizing the structure of IF-2(mt). IF-2(mt) contains a 37-amino acid insertion region between domains V and VI that is not found in the prokaryotic factors. Mutations in this region caused a significant reduction in the ability of the factor to promote initiation complex formation and to bind 28S subunits.
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Affiliation(s)
- Angela C Spencer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
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26
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Coenen MJH, Antonicka H, Ugalde C, Sasarman F, Rossi R, Heister JGAMA, Newbold RF, Trijbels FJMF, van den Heuvel LP, Shoubridge EA, Smeitink JAM. Mutant mitochondrial elongation factor G1 and combined oxidative phosphorylation deficiency. N Engl J Med 2004; 351:2080-6. [PMID: 15537906 DOI: 10.1056/nejmoa041878] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Although most components of the mitochondrial translation apparatus are encoded by nuclear genes, all known molecular defects associated with impaired mitochondrial translation are due to mutations in mitochondrial DNA. We investigated two siblings with a severe defect in mitochondrial translation, reduced levels of oxidative phosphorylation complexes containing mitochondrial DNA (mtDNA)-encoded subunits, and progressive hepatoencephalopathy. We mapped the defective gene to a region on chromosome 3q containing elongation factor G1 (EFG1), which encodes a mitochondrial translation factor. Sequencing of EFG1 revealed a mutation affecting a conserved residue of the guanosine triphosphate (GTP)-binding domain. These results define a new class of gene defects underlying disorders of oxidative phosphorylation.
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Affiliation(s)
- Marieke J H Coenen
- Nijmegen Center for Mitochondrial Disorders, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands
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27
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Spremulli LL, Coursey A, Navratil T, Hunter SE. Initiation and elongation factors in mammalian mitochondrial protein biosynthesis. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2004; 77:211-61. [PMID: 15196894 DOI: 10.1016/s0079-6603(04)77006-3] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Linda L Spremulli
- Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA
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28
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Tibbetts AS, Oesterlin L, Chan SY, Kramer G, Hardesty B, Appling DR. Mammalian mitochondrial initiation factor 2 supports yeast mitochondrial translation without formylated initiator tRNA. J Biol Chem 2003; 278:31774-80. [PMID: 12799364 DOI: 10.1074/jbc.m304962200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Initiation of protein synthesis in mitochondria and chloroplasts is widely believed to require a formylated initiator methionyl-tRNA (fMet-tRNAfMet) in a process involving initiation factor 2 (IF2). However, yeast strains disrupted at the FMT1 locus, encoding mitochondrial methionyl-tRNA formyltransferase, lack detectable fMet-tRNAfMet but exhibit normal mitochondrial function as evidenced by normal growth on non-fermentable carbon sources. Here we show that mitochondrial translation products in Saccharomyces cerevisiae were synthesized in the absence of formylated initiator tRNA. ifm1 mutants, lacking the mitochondrial initiation factor 2 (mIF2), are unable to respire, indicative of defective mitochondrial protein synthesis, but their respiratory defect could be complemented by plasmid-borne copies of either the yeast IFM1 gene or a cDNA encoding bovine mIF2. Moreover, the bovine mIF2 sustained normal respiration in ifm1 fmt1 double mutants. Bovine mIF2 supported the same pattern of mitochondrial translation products as yeast mIF2, and the pattern did not change in cells lacking formylated Met-tRNAfMet. Mutant yeast lacking any mIF2 retained the ability to synthesize low levels of a subset of mitochondrially encoded proteins. The ifm1 null mutant was used to analyze the domain structure of yeast mIF2. Contrary to a previous report, the C terminus of yeast mIF2 is required for its function in vivo, whereas the N-terminal domain could be deleted. Our results indicate that formylation of initiator methionyl-tRNA is not required for mitochondrial protein synthesis. The ability of bovine mIF2 to support mitochondrial translation in the yeast fmt1 mutant suggests that this phenomenon may extend to mammalian mitochondria as well.
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Affiliation(s)
- Anne S Tibbetts
- Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA
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29
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Garofalo C, Trinko R, Kramer G, Appling DR, Hardesty B. Purification and characterization of yeast mitochondrial initiation factor 2. Arch Biochem Biophys 2003; 413:243-52. [PMID: 12729623 DOI: 10.1016/s0003-9861(03)00119-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Yeast mitochondrial initiation factor 2 (ymIF2) is encoded by the nuclear IFM1 gene. A His-tagged version of ymIF2, lacking its predicted mitochondrial presequence, was expressed in Escherichia coli and purified. Purified ymIF2 bound both E. coli fMet-tRNA(f)(Met) and Met-tRNA(f)(Met), but binding of formylated initiator tRNA was about four times higher than that of the unformylated species under the same conditions. In addition, the isolated ymIF2 was compared to E. coli IF2 in four other assays commonly used to characterize this initiation factor. Formylated and nonformylated Met-tRNA(f)(Met) were bound to E. coli 30S ribosomal subunits in the presence of ymIF2, GTP, and a short synthetic mRNA. The GTPase activity of ymIF2 was found to be dependent on the presence of E. coli ribosomes. The ymIF2 protected fMet-tRNA(f)(Met) to about the same extent as E. coli IF2 against nonenzymatic deaminoacylation. In contrast to E. coli IF2, the complex formed between ymIF2 and fMet-tRNA(f)(Met) was not stable enough to be analyzed in a gel shift assay. In similarity to other IF2 species isolated from bacteria or bovine mitochondria, the N-terminal domain could be eliminated without loss of initiator tRNA binding activity.
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Affiliation(s)
- Cristiana Garofalo
- Department of Chemistry & Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712, USA
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30
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Moraes CT, Srivastava S, Kirkinezos I, Oca-Cossio J, van Waveren C, Woischnick M, Diaz F. Mitochondrial DNA structure and function. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2003; 53:3-23. [PMID: 12512335 DOI: 10.1016/s0074-7742(02)53002-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Carlos T Moraes
- Department of Neurology, University of Miami School of Medicine, Miami, Florida 33136, USA
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31
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Koc EC, Spremulli LL. Identification of mammalian mitochondrial translational initiation factor 3 and examination of its role in initiation complex formation with natural mRNAs. J Biol Chem 2002; 277:35541-9. [PMID: 12095986 DOI: 10.1074/jbc.m202498200] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human mitochondrial translational initiation factor 3 (IF3(mt)) has been identified from the human expressed sequence tag data base. Using consensus sequences derived from conserved regions of the bacterial IF3, several partially sequenced cDNA clones were identified, and the complete sequence was assembled in silico from overlapping clones. IF3(mt) is 278 amino acid residues in length. MitoProt II predicts a 97% probability that this protein will be localized in mitochondria and further predicts that the mature protein will be 247 residues in length. The cDNA for the predicted mature form of IF3(mt) was cloned, and the protein was expressed in Escherichia coli in a His-tagged form. The mature form of IF3(mt) has short extensions on the N and C termini surrounding a region homologous to bacterial IF3. The region of IF3(mt) homologous to prokaryotic factors ranges between 21-26% identical to the bacterial proteins. Purified IF3(mt) promotes initiation complex formation on mitochondrial 55 S ribosomes in the presence of mitochondrial initiation factor 2 (IF2(mt)), [(35)S]fMet-tRNA, and either poly(A,U,G) or an in vitro transcript of the cytochrome oxidase subunit II gene as mRNA. IF3(mt) shifts the equilibrium between the 55 S mitochondrial ribosome and its subunits toward subunit dissociation. In addition, the ability of E. coli initiation factor 1 to stimulate initiation complex formation on E. coli 70 S and mitochondrial 55 S ribosomes was investigated in the presence of IF2(mt) and IF3(mt).
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Affiliation(s)
- Emine Cavdar Koc
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA
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32
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Clément K, Viguerie N, Diehn M, Alizadeh A, Barbe P, Thalamas C, Storey JD, Brown PO, Barsh GS, Langin D. In vivo regulation of human skeletal muscle gene expression by thyroid hormone. Genome Res 2002; 12:281-91. [PMID: 11827947 PMCID: PMC155277 DOI: 10.1101/gr.207702] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Thyroid hormones are key regulators of metabolism that modulate transcription via nuclear receptors. Hyperthyroidism is associated with increased metabolic rate, protein breakdown, and weight loss. Although the molecular actions of thyroid hormones have been studied thoroughly, their pleiotropic effects are mediated by complex changes in expression of an unknown number of target genes. Here, we measured patterns of skeletal muscle gene expression in five healthy men treated for 14 days with 75 microg of triiodothyronine, using 24,000 cDNA element microarrays. To analyze the data, we used a new statistical method that identifies significant changes in expression and estimates the false discovery rate. The 381 up-regulated genes were involved in a wide range of cellular functions including transcriptional control, mRNA maturation, protein turnover, signal transduction, cellular trafficking, and energy metabolism. Only two genes were down-regulated. Most of the genes are novel targets of thyroid hormone. Cluster analysis of triiodothyronine-regulated gene expression among 19 different human tissues or cell lines revealed sets of coregulated genes that serve similar biologic functions. These results define molecular signatures that help to understand the physiology and pathophysiology of thyroid hormone action.
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Affiliation(s)
- Karine Clément
- Department of Pediatrics and Genetics, Howard Hughes Medical Institute, Beckman Center, Stanford University School of Medicine, Stanford, California 94305, USA
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33
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Suzuki T, Terasaki M, Takemoto-Hori C, Hanada T, Ueda T, Wada A, Watanabe K. Proteomic analysis of the mammalian mitochondrial ribosome. Identification of protein components in the 28 S small subunit. J Biol Chem 2001; 276:33181-95. [PMID: 11402041 DOI: 10.1074/jbc.m103236200] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian mitochondrial ribosome (mitoribosome) has a highly protein-rich composition with a small sedimentation coefficient of 55 S, consisting of 39 S large and 28 S small subunits. In the previous study, we analyzed 39 S large subunit proteins from bovine mitoribosome (Suzuki, T., Terasaki, M., Takemoto-Hori, C., Hanada, T., Ueda, T., Wada, A., and Watanabe, K. (2001) J. Biol. Chem. 276, 21724-21736). The results suggested structural compensation for the rRNA deficit through proteins of increased molecular mass in the mitoribosome. We report here the identification of 28 S small subunit proteins. Each protein was separated by radical-free high-reducing two-dimensional polyacrylamide gel electrophoresis and analyzed by liquid chromatography/mass spectrometry/mass spectrometry using electrospray ionization/ion trap mass spectrometer to identify cDNA sequence by expressed sequence tag data base searches in silico. Twenty one proteins from the small subunit were identified, including 11 new proteins along with their complete cDNA sequences from human and mouse. In addition to these proteins, three new proteins were also identified in the 55 S mitoribosome. We have clearly identified a mitochondrial homologue of S12, which is a key regulatory protein of translation fidelity and a candidate for the autosomal dominant deafness gene, DFNA4. The apoptosis-related protein DAP3 was found to be a component of the small subunit, indicating a new function for the mitoribosome in programmed cell death. In summary, we have mapped a total of 55 proteins from the 55 S mitoribosome on the two-dimensional polyacrylamide gels.
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Affiliation(s)
- T Suzuki
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8562, Japan.
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Campos F, García-Gómez BI, Solórzano RM, Salazar E, Estevez J, León P, Alvarez-Buylla ER, Covarrubias AA. A cDNA for nuclear-encoded chloroplast translational initiation factor 2 from a higher plant is able to complement an infB Escherichia coli null mutant. J Biol Chem 2001; 276:28388-94. [PMID: 11356831 DOI: 10.1074/jbc.m100605200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Formation of the initiation translation complex containing the three initiation factors, IF1, IF2, and IF3, tRNA(fMet), and GTP constitutes the earliest event in the protein synthesis. IF2, a GTP-binding protein, is the principal factor involved in selecting and binding fMet-tRNA(fMet) to the 30 S ribosomal subunit. Although some chloroplast initiation translational factors have been identified and purified from algae, none of these factors have been characterized from plants. In this work, we report the molecular characterization of a nuclear-encoded chloroplastic IF2 gene from common bean (PvIF2cp). We show that the PvIF2cp gene encodes a protein containing a chloroplast translocation signal peptide, able to target a green fluorescent protein fusion protein to chloroplasts. A high accumulation of PvIF2cp transcript was found in photosynthetic tissues, whereas low mRNA levels were detected in etiolated plants and in nonphotosynthetic organs. Additional data indicate that the PvIF2cp transcript accumulation is modulated by light. The PvIF2cp gene encodes a functional factor, since the PvIF2cp conserved region, containing the G-domain and the C-terminal end, complements an Escherichia coli infB null mutation. Phylogenetic analysis using the PvIF2cp conserved region suggests that the PvIF2cp gene originated via endosymbiotic gene transfer to the nucleus and that it may be a useful marker for phylogeny reconstruction.
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MESH Headings
- Active Transport, Cell Nucleus
- Amino Acid Sequence
- Biological Transport
- Blotting, Northern
- Cell Nucleus/metabolism
- Chloroplasts/metabolism
- Cloning, Molecular
- DNA, Complementary/metabolism
- Escherichia coli/metabolism
- Gene Library
- Genes, Plant
- Genetic Complementation Test
- Genetic Markers
- Green Fluorescent Proteins
- Luminescent Proteins/metabolism
- Microscopy, Fluorescence
- Models, Genetic
- Molecular Sequence Data
- Mutation
- Peptide Initiation Factors/chemistry
- Peptide Initiation Factors/genetics
- Photosynthesis/genetics
- Phylogeny
- Plants, Toxic
- Prokaryotic Initiation Factor-2
- Protein Biosynthesis
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Recombinant Fusion Proteins/metabolism
- Sequence Analysis, DNA
- Time Factors
- Tissue Distribution
- Nicotiana/genetics
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Affiliation(s)
- F Campos
- Departamento de Biologia Molecular de Plantas del Instituto de Biotecnologia, Universidad Nacional Autónoma de México, A. P. 510-3, Cuernavaca, Morelos 62250, México
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35
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Suzuki T, Terasaki M, Takemoto-Hori C, Hanada T, Ueda T, Wada A, Watanabe K. Structural compensation for the deficit of rRNA with proteins in the mammalian mitochondrial ribosome. Systematic analysis of protein components of the large ribosomal subunit from mammalian mitochondria. J Biol Chem 2001; 276:21724-36. [PMID: 11279069 DOI: 10.1074/jbc.m100432200] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian mitochondrial ribosome (mitoribosome) is a highly protein-rich particle in which almost half of the rRNA contained in the bacterial ribosome is replaced with proteins. It is known that mitochondrial translation factors can function on both mitochondrial and Escherichia coli ribosomes, indicating that protein components in the mitoribosome compensate the reduced rRNA chain to make a bacteria-type ribosome. To elucidate the molecular basis of this compensation, we analyzed bovine mitoribosomal large subunit proteins; 31 proteins were identified including 15 newly identified proteins with their cDNA sequences from human and mouse. The results showed that the proteins with binding sites on rRNA shortened or lost in the mitoribosome were enlarged when compared with the E. coli counterparts; this suggests the structural compensation of the rRNA deficit by the enlarged proteins in the mitoribosome.
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Affiliation(s)
- T Suzuki
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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Taanman JW. The mitochondrial genome: structure, transcription, translation and replication. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1410:103-23. [PMID: 10076021 DOI: 10.1016/s0005-2728(98)00161-3] [Citation(s) in RCA: 1004] [Impact Index Per Article: 40.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mitochondria play a central role in cellular energy provision. The organelles contain their own genome with a modified genetic code. The mammalian mitochondrial genome is transmitted exclusively through the female germ line. The human mitochondrial DNA (mtDNA) is a double-stranded, circular molecule of 16569 bp and contains 37 genes coding for two rRNAs, 22 tRNAs and 13 polypeptides. The mtDNA-encoded polypeptides are all subunits of enzyme complexes of the oxidative phosphorylation system. Mitochondria are not self-supporting entities but rely heavily for their functions on imported nuclear gene products. The basic mechanisms of mitochondrial gene expression have been solved. Cis-acting mtDNA sequences have been characterised by sequence comparisons, mapping studies and mutation analysis both in vitro and in patients harbouring mtDNA mutations. Characterisation of trans-acting factors has proven more difficult but several key enzymes involved in mtDNA replication, transcription and protein synthesis have now been biochemically identified and some have been cloned. These studies revealed that, although some factors may have an additional function elsewhere in the cell, most are unique to mitochondria. It is expected that cell cultures of patients with mitochondrial diseases will increasingly be used to address fundamental questions about mtDNA expression.
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Affiliation(s)
- J W Taanman
- Department of Clinical Neurosciences, Royal Free Hospital School of Medicine, University of London, Rowland Hill Street, London NW3 2PF,
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Au HC, Scheffler IE. A respiration-deficient Chinese hamster cell line with a defect in mitochondrial protein synthesis: rapid turnover of some mitochondrial transcripts. SOMATIC CELL AND MOLECULAR GENETICS 1997; 23:27-35. [PMID: 9217999 DOI: 10.1007/bf02679953] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Translational initiation and elongation in mammalian mitochondria is still poorly understood, and genetic approaches are expected to be helpful in the elucidation of the mechanism. This study describes a further characterization of a Chinese hamster mutant cell line which is severely defective in mitochondrial protein synthesis. Additional proof is provided that the mutation is nuclear. It is shown that there is no dramatic depletion of mitochondrial DNA in these cells, and the mtDNA appears to have neither significant deletions nor rearrangements. Transcription is not affected, and the polycistronic transcripts are processed normally. However, mt mRNAs are differentially quite unstable, and some are at very low steady state levels. Several nuclear transcripts encoding mitochondrial proteins were also investigated and found to be present at normal levels, and in particular, it was demonstrated that complex II (and succinate dehydrogenase activity), encoded entirely by nuclear genes, was only moderately affected by the absence of all the other complexes of the electron transport chain.
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Affiliation(s)
- H C Au
- Department of Biology, University of California, San Diego La Jolla 92093-0322, USA
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