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Huynen MA, Duarte I, Szklarczyk R. Loss, replacement and gain of proteins at the origin of the mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:224-31. [PMID: 22902511 DOI: 10.1016/j.bbabio.2012.08.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 07/19/2012] [Accepted: 08/05/2012] [Indexed: 01/28/2023]
Abstract
We review what has been inferred about the changes at the level of the proteome that accompanied the evolution of the mitochondrion from an alphaproteobacterium. We regard these changes from an alphaproteobacterial perspective: which proteins were lost during mitochondrial evolution? And, of the proteins that were lost, which ones have been replaced by other, non-orthologous proteins with a similar function? Combining literature-supported replacements with quantitative analyses of mitochondrial proteomics data we infer that most of the loss and replacements that separate current day mitochondria in mammals from alphaproteobacteria took place before the radiation of the eukaryotes. Recent analyses show that also the acquisition of new proteins to the large protein complexes of the oxidative phosphorylation and the mitochondrial ribosome occurred mainly before the divergence of the eukaryotes. These results indicate a significant number of pivotal evolutionary events between the acquisition of the endosymbiont and the radiation of the eukaryotes and therewith support an early acquisition of mitochondria in eukaryotic evolution. Technically, advancements in the reconstruction of the evolutionary trajectories of loss, replacement and gain of mitochondrial proteins depend on using profile-based homology detection methods for sequence analysis. We highlight the mitochondrial Holliday junction resolvase endonuclease, for which such methods have detected new "family members" and in which function differentiation is accompanied by the loss of catalytic residues for the original enzymatic function and the gain of a protein domain for the new function. This article is part of a Special Issue entitled: The evolutionary aspects of bioenergetic systems.
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Affiliation(s)
- Martijn A Huynen
- Centre for Molecular and Biomolecular Informatics, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6400 HB Nijmegen, The Netherlands.
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52
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Gawryluk RMR, Chisholm KA, Pinto DM, Gray MW. Composition of the mitochondrial electron transport chain in acanthamoeba castellanii: structural and evolutionary insights. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:2027-37. [PMID: 22709906 DOI: 10.1016/j.bbabio.2012.06.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Revised: 06/06/2012] [Accepted: 06/08/2012] [Indexed: 11/20/2022]
Abstract
The mitochondrion, derived in evolution from an α-proteobacterial progenitor, plays a key metabolic role in eukaryotes. Mitochondria house the electron transport chain (ETC) that couples oxidation of organic substrates and electron transfer to proton pumping and synthesis of ATP. The ETC comprises several multiprotein enzyme complexes, all of which have counterparts in bacteria. However, mitochondrial ETC assemblies from animals, plants and fungi are generally more complex than their bacterial counterparts, with a number of 'supernumerary' subunits appearing early in eukaryotic evolution. Little is known, however, about the ETC of unicellular eukaryotes (protists), which are key to understanding the evolution of mitochondria and the ETC. We present an analysis of the ETC proteome from Acanthamoeba castellanii, an ecologically, medically and evolutionarily important member of Amoebozoa (sister to Opisthokonta). Data obtained from tandem mass spectrometric (MS/MS) analyses of purified mitochondria as well as ETC complexes isolated via blue native polyacrylamide gel electrophoresis are combined with the results of bioinformatic queries of sequence databases. Our bioinformatic analyses have identified most of the ETC subunits found in other eukaryotes, confirming and extending previous observations. The assignment of proteins as ETC subunits by MS/MS provides important insights into the primary structures of ETC proteins and makes possible, through the use of sensitive profile-based similarity searches, the identification of novel constituents of the ETC along with the annotation of highly divergent but phylogenetically conserved ETC subunits.
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Affiliation(s)
- Ryan M R Gawryluk
- Centre for Comparative Genomics and Evolutionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
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53
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Luévano-Martínez LA. Uncoupling proteins (UCP) in unicellular eukaryotes: true UCPs or UCP1-like acting proteins? FEBS Lett 2012; 586:1073-8. [PMID: 22569266 DOI: 10.1016/j.febslet.2012.03.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Revised: 02/24/2012] [Accepted: 03/06/2012] [Indexed: 10/28/2022]
Abstract
Uncoupling proteins belong to the superfamily of mitochondrial anion carriers. They are apparently present throughout the Eukarya domain in which only some members have an established physiological function, i.e. UCP1 from brown adipose tissue is involved in non-shivering thermogenesis. However, the proteins responsible for the phenotype observed in unicellular organisms have not been characterized. In this report we analyzed functional evidence concerning unicellular UCPs and found that true UCPs are restricted to some taxonomical groups while proteins conferring a UCP1-like phenotype to fungi and most protists are the result of a promiscuous activity exerted by other mitochondrial anion carriers. We describe a possible evolutionary route followed by these proteins by which they acquire this promiscuous mechanism.
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Affiliation(s)
- Luis Alberto Luévano-Martínez
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Cidade Universitária, Av Prof Lineu Prestes 748, 05508-000 São Paulo, Brazil.
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Montagnes D, Roberts E, Lukeš J, Lowe C. The rise of model protozoa. Trends Microbiol 2012; 20:184-91. [PMID: 22342867 DOI: 10.1016/j.tim.2012.01.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Revised: 01/05/2012] [Accepted: 01/17/2012] [Indexed: 12/23/2022]
Abstract
It is timely to evaluate the role of protozoa as model organisms given their diversity, abundance and versatility as well as the economic and ethical pressures placed on animal-based experimentation. We first define the term model organism and then examine through examples why protozoa make good models. Our examples reflect major issues including evolution, ecology, population and community biology, disease, the role of organelles, ageing, space travel, toxicity and teaching. We conclude by recognising that although protozoa may in some cases not completely mimic tissue- or whole-animal-level processes, they are extremely flexible and their use should be embraced. Finally, we offer advice on obtaining emergent model protozoa.
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Affiliation(s)
- David Montagnes
- Institute of Integrative Biology, University of Liverpool, BioScience Building, Crown Street, Liverpool L69 7ZB, UK.
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55
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Wloga D, Frankel J. From Molecules to Morphology: Cellular Organization of Tetrahymena thermophila. Methods Cell Biol 2012; 109:83-140. [DOI: 10.1016/b978-0-12-385967-9.00005-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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56
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Abstract
Within the past decade, genomic studies have emerged as essential and highly productive tools to explore the biology of Tetrahymena thermophila. The current major resources, which have been extensively mined by the research community, are the annotated macronuclear genome assembly, transcriptomic data and the databases that house this information. Efforts in progress will soon improve these data sources and expand their scope, including providing annotated micronuclear and comparative genomic sequences. Future studies of Tetrahymena cell and molecular biology, development, physiology, evolution and ecology will benefit greatly from these resources and the advanced genomic technologies they enable.
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Conservation and innovation in Tetrahymena membrane traffic: proteins, lipids, and compartments. Methods Cell Biol 2012; 109:141-75. [PMID: 22444145 DOI: 10.1016/b978-0-12-385967-9.00006-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The past decade has seen a significant expansion in our understanding of membrane traffic in Tetrahymena thermophila, facilitated by the development of new experimental tools and by the availability of the macronuclear genome sequence. Here we review studies on multiple pathways of uptake and secretion, as well as work on metabolism of membrane lipids. We discuss evidence for conservation versus innovation in the mechanisms used in ciliates compared with those in other eukaryotic lineages, and raise the possibility that existing gene expression databases can be exploited to analyze specific pathways of membrane traffic in these cells.
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59
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Swart EC, Nowacki M, Shum J, Stiles H, Higgins BP, Doak TG, Schotanus K, Magrini VJ, Minx P, Mardis ER, Landweber LF. The Oxytricha trifallax mitochondrial genome. Genome Biol Evol 2011; 4:136-54. [PMID: 22179582 PMCID: PMC3318907 DOI: 10.1093/gbe/evr136] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Oxytricha trifallax mitochondrial genome contains the largest sequenced ciliate mitochondrial chromosome (~70 kb) plus a ~5-kb linear plasmid bearing mitochondrial telomeres. We identify two new ciliate split genes (rps3 and nad2) as well as four new mitochondrial genes (ribosomal small subunit protein genes: rps- 2, 7, 8, 10), previously undetected in ciliates due to their extreme divergence. The increased size of the Oxytricha mitochondrial genome relative to other ciliates is primarily a consequence of terminal expansions, rather than the retention of ancestral mitochondrial genes. Successive segmental duplications, visible in one of the two Oxytricha mitochondrial subterminal regions, appear to have contributed to the genome expansion. Consistent with pseudogene formation and decay, the subtermini possess shorter, more loosely packed open reading frames than the remainder of the genome. The mitochondrial plasmid shares a 251-bp region with 82% identity to the mitochondrial chromosome, suggesting that it most likely integrated into the chromosome at least once. This region on the chromosome is also close to the end of the most terminal member of a series of duplications, hinting at a possible association between the plasmid and the duplications. The presence of mitochondrial telomeres on the mitochondrial plasmid suggests that such plasmids may be a vehicle for lateral transfer of telomeric sequences between mitochondrial genomes. We conjecture that the extreme divergence observed in ciliate mitochondrial genomes may be due, in part, to repeated invasions by relatively error-prone DNA polymerase-bearing mobile elements.
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Affiliation(s)
- Estienne C Swart
- Department of Ecology and Evolutionary Biology, Princeton University, USA
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60
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Schneider RE, Brown MT, Shiflett AM, Dyall SD, Hayes RD, Xie Y, Loo JA, Johnson PJ. The Trichomonas vaginalis hydrogenosome proteome is highly reduced relative to mitochondria, yet complex compared with mitosomes. Int J Parasitol 2011; 41:1421-34. [PMID: 22079833 PMCID: PMC4437511 DOI: 10.1016/j.ijpara.2011.10.001] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 10/06/2011] [Accepted: 10/07/2011] [Indexed: 01/08/2023]
Abstract
The human pathogen Trichomonas vaginalis lacks conventional mitochondria and instead contains divergent mitochondrial-related organelles. These double-membrane bound organelles, called hydrogenosomes, produce molecular hydrogen. Phylogenetic and biochemical analyses of hydrogenosomes indicate a common origin with mitochondria; however identification of hydrogenosomal proteins and studies on its metabolism have been limited. Here we provide a detailed proteomic analysis of the T. vaginalis hydrogenosome. The proteome of purified hydrogenosomes consists of 569 proteins, a number substantially lower than the 1,000-1,500 proteins reported for fungal and animal mitochondrial proteomes, yet considerably higher than proteins assigned to mitosomes. Pathways common to and distinct from both mitochondria and mitosomes were revealed by the hydrogenosome proteome. Proteins known to function in amino acid and energy metabolism, Fe-S cluster assembly, flavin-mediated catalysis, oxygen stress response, membrane translocation, chaperonin functions, proteolytic processing and ATP hydrolysis account for ∼30% of the hydrogenosome proteome. Of the 569 proteins in the hydrogenosome proteome, many appear to be associated with the external surface of hydrogenosomes, including large numbers of GTPases and ribosomal proteins. Glycolytic proteins were also found to be associated with the hydrogenosome proteome, similar to that previously observed for mitochondrial proteomes. Approximately 18% of the hydrogenosomal proteome is composed of hypothetical proteins of unknown function, predictive of multiple activities and properties yet to be uncovered for these highly adapted organelles.
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Affiliation(s)
- Rachel E. Schneider
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Mark T. Brown
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - April M. Shiflett
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Sabrina D. Dyall
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Richard D. Hayes
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Yongming Xie
- Department of Chemistry and Biochemistry David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Joseph A. Loo
- Department of Chemistry and Biochemistry David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
- Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Patricia J. Johnson
- Department of Microbiology, Immunology & Molecular Genetics David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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61
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Orias E, Cervantes MD, Hamilton EP. Tetrahymena thermophila, a unicellular eukaryote with separate germline and somatic genomes. Res Microbiol 2011; 162:578-86. [PMID: 21624459 DOI: 10.1016/j.resmic.2011.05.001] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 04/14/2011] [Indexed: 12/11/2022]
Abstract
Tetrahymena thermophila is a ciliate--a unicellular eukaryote. Remarkably, every cell maintains differentiated germline and somatic genomes: one silent, the other expressed. Moreover, the two genomes undergo diverse processes, some as extreme as life and death, simultaneously in the same cytoplasm. Conserved eukaryotic mechanisms have been modified in ciliates to selectively deal with the two genomes. We describe research in several areas of Tetrahymena biology, including meiosis, amitosis, genetic assortment, selective nuclear pore transport, somatic RNAi-guided heterochromatin formation, DNA excision and programmed nuclear death by autophagy, which has enriched and broadened knowledge of those mechanisms.
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Affiliation(s)
- Eduardo Orias
- Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
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62
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Francis BR, Thorsness PE. Hsp90 and mitochondrial proteases Yme1 and Yta10/12 participate in ATP synthase assembly in Saccharomyces cerevisiae. Mitochondrion 2011; 11:587-600. [PMID: 21439406 DOI: 10.1016/j.mito.2011.03.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Revised: 02/22/2011] [Accepted: 03/15/2011] [Indexed: 10/18/2022]
Abstract
Hsc82 and Hsp82, the Hsp90 family proteins of yeast, are both required for fermentative growth at 37°C. Inactivation of either of the mitochondrial AAA proteases, Yme1 or Yta10/12, allows fermentative growth of hsc82∆ or hsp82∆ strains at 37°C. Genetic evidence indicates interaction of Hsc82/Hsp82 with the Yme1 and Yta10/Yta12 complexes in promoting F(1)F(o)-ATPase activity, with Hsc82 specifically required for F(1)-ATPase assembly. A previously reported mutation in Rpt3, one of the six ATPases of the proteasome, suppresses yme1∆ phenotypes and increases transcription of HSC82 but not HSP82. These genetic interactions describe a functional role for Hsp90 proteins in mitochondrial biogenesis.
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Affiliation(s)
- Brian R Francis
- Department of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
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63
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de Graaf RM, Ricard G, van Alen TA, Duarte I, Dutilh BE, Burgtorf C, Kuiper JWP, van der Staay GWM, Tielens AGM, Huynen MA, Hackstein JHP. The organellar genome and metabolic potential of the hydrogen-producing mitochondrion of Nyctotherus ovalis. Mol Biol Evol 2011; 28:2379-91. [PMID: 21378103 PMCID: PMC3144386 DOI: 10.1093/molbev/msr059] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
It is generally accepted that hydrogenosomes (hydrogen-producing organelles) evolved from a mitochondrial ancestor. However, until recently, only indirect evidence for this hypothesis was available. Here, we present the almost complete genome of the hydrogen-producing mitochondrion of the anaerobic ciliate Nyctotherus ovalis and show that, except for the notable absence of genes encoding electron transport chain components of Complexes III, IV, and V, it has a gene content similar to the mitochondrial genomes of aerobic ciliates. Analysis of the genome of the hydrogen-producing mitochondrion, in combination with that of more than 9,000 genomic DNA and cDNA sequences, allows a preliminary reconstruction of the organellar metabolism. The sequence data indicate that N. ovalis possesses hydrogen-producing mitochondria that have a truncated, two step (Complex I and II) electron transport chain that uses fumarate as electron acceptor. In addition, components of an extensive protein network for the metabolism of amino acids, defense against oxidative stress, mitochondrial protein synthesis, mitochondrial protein import and processing, and transport of metabolites across the mitochondrial membrane were identified. Genes for MPV17 and ACN9, two hypothetical proteins linked to mitochondrial disease in humans, were also found. The inferred metabolism is remarkably similar to the organellar metabolism of the phylogenetically distant anaerobic Stramenopile Blastocystis. Notably, the Blastocystis organelle and that of the related flagellate Proteromonas lacertae also lack genes encoding components of Complexes III, IV, and V. Thus, our data show that the hydrogenosomes of N. ovalis are highly specialized hydrogen-producing mitochondria.
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Affiliation(s)
- Rob M de Graaf
- Department of Evolutionary Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, The Netherlands
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64
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Rea SL, Graham BH, Nakamaru-Ogiso E, Kar A, Falk MJ. Bacteria, yeast, worms, and flies: exploiting simple model organisms to investigate human mitochondrial diseases. ACTA ACUST UNITED AC 2011; 16:200-18. [PMID: 20818735 DOI: 10.1002/ddrr.114] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The extensive conservation of mitochondrial structure, composition, and function across evolution offers a unique opportunity to expand our understanding of human mitochondrial biology and disease. By investigating the biology of much simpler model organisms, it is often possible to answer questions that are unreachable at the clinical level. Here, we review the relative utility of four different model organisms, namely the bacterium Escherichia coli, the yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster, in studying the role of mitochondrial proteins relevant to human disease. E. coli are single cell, prokaryotic bacteria that have proven to be a useful model system in which to investigate mitochondrial respiratory chain protein structure and function. S. cerevisiae is a single-celled eukaryote that can grow equally well by mitochondrial-dependent respiration or by ethanol fermentation, a property that has proven to be a veritable boon for investigating mitochondrial functionality. C. elegans is a multicellular, microscopic worm that is organized into five major tissues and has proven to be a robust model animal for in vitro and in vivo studies of primary respiratory chain dysfunction and its potential therapies in humans. Studied for over a century, D. melanogaster is a classic metazoan model system offering an abundance of genetic tools and reagents that facilitates investigations of mitochondrial biology using both forward and reverse genetics. The respective strengths and limitations of each species relative to mitochondrial studies are explored. In addition, an overview is provided of major discoveries made in mitochondrial biology in each of these four model systems.
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Affiliation(s)
- Shane L Rea
- Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, TX 78245-3207, USA.
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65
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Atkinson GC, Baldauf SL. Evolution of elongation factor G and the origins of mitochondrial and chloroplast forms. Mol Biol Evol 2010; 28:1281-92. [PMID: 21097998 DOI: 10.1093/molbev/msq316] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Protein synthesis elongation factor G (EF-G) is an essential protein with central roles in both the elongation and ribosome recycling phases of protein synthesis. Although EF-G evolution is predicted to be conservative, recent reports suggest otherwise. We have characterized EF-G in terms of its molecular phylogeny, genomic context, and patterns of amino acid substitution. We find that most bacteria carry a single "canonical" EF-G, which is phylogenetically conservative and encoded in an str operon. However, we also find a number of EF-G paralogs. These include a pair of EF-Gs that are mostly found together and in an eclectic subset of bacteria, specifically δ-proteobacteria, spirochaetes, and planctomycetes (the "spd" bacteria). These spdEFGs have also given rise to the mitochondrial factors mtEFG1 and mtEFG2, which probably arrived in eukaryotes before the eukaryotic last common ancestor. Meanwhile, chloroplasts apparently use an α-proteobacterial-derived EF-G rather than the expected cyanobacterial form. The long-term comaintenance of the spd/mtEFGs may be related to their subfunctionalization for translocation and ribosome recycling. Consistent with this, patterns of sequence conservation and site-specific evolutionary rate shifts suggest that the faster evolving spd/mtEFG2 has lost translocation function, but surprisingly, the protein also shows little conservation of sites related to recycling activity. On the other hand, spd/mtEFG1, although more slowly evolving, shows signs of substantial remodeling. This is particularly extensive in the GTPase domain, including a highly conserved three amino acid insertion in switch I. We suggest that subfunctionalization of the spd/mtEFGs is not a simple case of specialization for subsets of original activities. Rather, the duplication allows the release of one paralog from the selective constraints imposed by dual functionality, thus allowing it to become more highly specialized. Thus, the potential for fine tuning afforded by subfunctionalization may explain the maintenance of EF-G paralogs.
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Affiliation(s)
- Gemma C Atkinson
- Department of Systematic Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
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Tsaousis AD, Gaston D, Stechmann A, Walker PB, Lithgow T, Roger AJ. A functional Tom70 in the human parasite Blastocystis sp.: implications for the evolution of the mitochondrial import apparatus. Mol Biol Evol 2010; 28:781-91. [PMID: 20871025 DOI: 10.1093/molbev/msq252] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Core proteins of mitochondrial protein import are found in all mitochondria, suggesting a common origin of this import machinery. Despite the presence of a universal core import mechanism, there are specific proteins found only in a few groups of organisms. One of these proteins is the translocase of outer membrane 70 (Tom70), a protein that is essential for the import of preproteins with internal targeting sequences into the mitochondrion. Until now, Tom70 has only been found in animals and Fungi. We have identified a tom70 gene in the human parasitic anaerobic stramenopile Blastocystis sp. that is neither an animal nor a fungus. Using a combination of bioinformatics, genetic complementation, and immunofluorescence microscopy analyses, we demonstrate that this protein functions as a typical Tom70 in Blastocystis mitochondrion-related organelles. Additionally, we identified putative tom70 genes in the genomes of other stramenopiles and a haptophyte, that, in phylogenies, form a monophyletic group distinct from the animal and the fungal homologues. The presence of Tom70 in these lineages significantly expands the evolutionary spectrum of eukaryotes that contain this protein and suggests that it may have been part of the core mitochondrial protein import apparatus of the last common ancestral eukaryote.
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Affiliation(s)
- Anastasios D Tsaousis
- Department of Biochemistry and Molecular Biology, Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie University, Halifax, Canada.
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67
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Mitochondrial protein import: from proteomics to functional mechanisms. Nat Rev Mol Cell Biol 2010; 11:655-67. [PMID: 20729931 DOI: 10.1038/nrm2959] [Citation(s) in RCA: 500] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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68
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Balabaskaran Nina P, Dudkina NV, Kane LA, van Eyk JE, Boekema EJ, Mather MW, Vaidya AB. Highly divergent mitochondrial ATP synthase complexes in Tetrahymena thermophila. PLoS Biol 2010; 8:e1000418. [PMID: 20644710 PMCID: PMC2903591 DOI: 10.1371/journal.pbio.1000418] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Accepted: 06/01/2010] [Indexed: 12/28/2022] Open
Abstract
The F-type ATP synthase complex is a rotary nano-motor driven by proton motive force to synthesize ATP. Its F(1) sector catalyzes ATP synthesis, whereas the F(o) sector conducts the protons and provides a stator for the rotary action of the complex. Components of both F(1) and F(o) sectors are highly conserved across prokaryotes and eukaryotes. Therefore, it was a surprise that genes encoding the a and b subunits as well as other components of the F(o) sector were undetectable in the sequenced genomes of a variety of apicomplexan parasites. While the parasitic existence of these organisms could explain the apparent incomplete nature of ATP synthase in Apicomplexa, genes for these essential components were absent even in Tetrahymena thermophila, a free-living ciliate belonging to a sister clade of Apicomplexa, which demonstrates robust oxidative phosphorylation. This observation raises the possibility that the entire clade of Alveolata may have invented novel means to operate ATP synthase complexes. To assess this remarkable possibility, we have carried out an investigation of the ATP synthase from T. thermophila. Blue native polyacrylamide gel electrophoresis (BN-PAGE) revealed the ATP synthase to be present as a large complex. Structural study based on single particle electron microscopy analysis suggested the complex to be a dimer with several unique structures including an unusually large domain on the intermembrane side of the ATP synthase and novel domains flanking the c subunit rings. The two monomers were in a parallel configuration rather than the angled configuration previously observed in other organisms. Proteomic analyses of well-resolved ATP synthase complexes from 2-D BN/BN-PAGE identified orthologs of seven canonical ATP synthase subunits, and at least 13 novel proteins that constitute subunits apparently limited to the ciliate lineage. A mitochondrially encoded protein, Ymf66, with predicted eight transmembrane domains could be a substitute for the subunit a of the F(o) sector. The absence of genes encoding orthologs of the novel subunits even in apicomplexans suggests that the Tetrahymena ATP synthase, despite core similarities, is a unique enzyme exhibiting dramatic differences compared to the conventional complexes found in metazoan, fungal, and plant mitochondria, as well as in prokaryotes. These findings have significant implications for the origins and evolution of a central player in bioenergetics.
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Affiliation(s)
- Praveen Balabaskaran Nina
- Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Natalya V. Dudkina
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands
| | - Lesley A. Kane
- Department of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Biological Chemistry, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Jennifer E. van Eyk
- Department of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Biological Chemistry, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Egbert J. Boekema
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands
| | - Michael W. Mather
- Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Akhil B. Vaidya
- Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
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Gawryluk RMR, Gray MW. Evidence for an early evolutionary emergence of gamma-type carbonic anhydrases as components of mitochondrial respiratory complex I. BMC Evol Biol 2010; 10:176. [PMID: 20546574 PMCID: PMC2900272 DOI: 10.1186/1471-2148-10-176] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Accepted: 06/14/2010] [Indexed: 11/28/2022] Open
Abstract
Background The complexity of mitochondrial complex I (CI; NADH:ubiquinone oxidoreductase) has increased considerably relative to the homologous complex in bacteria. Comparative analyses of CI composition in animals, fungi and land plants/green algae suggest that novel components of mitochondrial CI include a set of 18 proteins common to all eukaryotes and a variable number of lineage-specific subunits. In plants and green algae, several purportedly plant-specific proteins homologous to γ-type carbonic anhydrases (γCA) have been identified as components of CI. However, relatively little is known about CI composition in the unicellular protists, the characterizations of which are essential to our understanding of CI evolution. Results We have performed a tandem mass spectrometric characterization of CI from the amoeboid protozoon Acanthamoeba castellanii. Among the proteins identified were two γCA homologs, AcCa1 and AcCa2, demonstrating that γCA proteins are not specific to plants/green algae. In fact, through bioinformatics searches we detected γCA homologs in diverse protist lineages, and several of these homologs are predicted to possess N-terminal mitochondrial targeting peptides. Conclusions The detection of γCAs in CI of Acanthamoeba, considered to be a closer relative of animals and fungi than plants, suggests that γCA proteins may have been an ancestral feature of mitochondrial CI, rather than a novel, plant-specific addition. This assertion is supported by the presence of genes encoding γCAs in the nuclear genomes of a wide variety of eukaryotes. Together, these findings emphasize the importance of a phylogenetically broad characterization of CI for elucidating CI evolution in eukaryotes.
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Affiliation(s)
- Ryan M R Gawryluk
- Centre for Comparative Genomics and Evolutionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada
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70
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Abstract
Many genes inherited from the alpha-proteobacterial ancestor of mitochondria have undergone evolutionary transfer to the nuclear genome in eukaryotes. In some rare cases, genes have been functionally transferred in pieces, resulting in split proteins that presumably interact in trans within mitochondria, fulfilling the same role as the ancestral, intact protein. We describe a nucleus-encoded mitochondrial protein (here named Cox1-c) in the amoeboid protist Acanthamoeba castellanii that is homologous to the C-terminal portion of conventional mitochondrial Cox1, whereas the corresponding portion of the mitochondrion-encoded A. castellanii Cox1 is absent. Bioinformatics searches retrieved nucleus-encoded Cox1-c homologs in most major eukaryotic supergroups; in these cases, also, the mitochondrion-encoded Cox1 lacks the corresponding C-terminal motif. These data constitute the first report of functional relocation of a portion of cox1 to the nucleus. This transfer event was likely ancient, with the resulting nuclear cox1-c being differentially activated across the eukaryotic domain.
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71
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Akematsu T, Endoh H. Role of apoptosis-inducing factor (AIF) in programmed nuclear death during conjugation in Tetrahymena thermophila. BMC Cell Biol 2010; 11:13. [PMID: 20146827 PMCID: PMC2829475 DOI: 10.1186/1471-2121-11-13] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Accepted: 02/11/2010] [Indexed: 01/08/2023] Open
Abstract
Background Programmed nuclear death (PND), which is also referred to as nuclear apoptosis, is a remarkable process that occurs in ciliates during sexual reproduction (conjugation). In Tetrahymena thermophila, when the new macronucleus differentiates, the parental macronucleus is selectively eliminated from the cytoplasm of the progeny, concomitant with apoptotic nuclear events. However, the molecular mechanisms underlying these events are not well understood. The parental macronucleus is engulfed by a large autophagosome, which contains numerous mitochondria that have lost their membrane potential. In animals, mitochondrial depolarization precedes apoptotic cell death, which involves DNA fragmentation and subsequent nuclear degradation. Results We focused on the role of mitochondrial apoptosis-inducing factor (AIF) during PND in Tetrahymena. The disruption of AIF delays the normal progression of PND, specifically, nuclear condensation and kilobase-size DNA fragmentation. AIF is localized in Tetrahymena mitochondria and is released into the macronucleus prior to nuclear condensation. In addition, AIF associates and co-operates with the mitochondrial DNase to facilitate the degradation of kilobase-size DNA, which is followed by oligonucleosome-size DNA laddering. Conclusions Our results suggest that Tetrahymena AIF plays an important role in the degradation of DNA at an early stage of PND, which supports the notion that the mitochondrion-initiated apoptotic DNA degradation pathway is widely conserved among eukaryotes.
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Affiliation(s)
- Takahiko Akematsu
- Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Shizenken, Kakuma-machi, Kanazawa, Ishikawa, Japan.
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72
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Huynen MA, de Hollander M, Szklarczyk R. Mitochondrial proteome evolution and genetic disease. Biochim Biophys Acta Mol Basis Dis 2009; 1792:1122-9. [DOI: 10.1016/j.bbadis.2009.03.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2008] [Revised: 03/04/2009] [Accepted: 03/20/2009] [Indexed: 11/16/2022]
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73
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Szklarczyk R, Huynen MA. Expansion of the human mitochondrial proteome by intra- and inter-compartmental protein duplication. Genome Biol 2009; 10:R135. [PMID: 19930686 PMCID: PMC3091328 DOI: 10.1186/gb-2009-10-11-r135] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2009] [Revised: 10/09/2009] [Accepted: 11/24/2009] [Indexed: 12/20/2022] Open
Abstract
The human mitochondrial proteome is shown to have expanded due to duplication of protein encoding genes and re-localization of these duplicated proteins. Background Mitochondria are highly complex, membrane-enclosed organelles that are essential to the eukaryotic cell. The experimental elucidation of organellar proteomes combined with the sequencing of complete genomes allows us to trace the evolution of the mitochondrial proteome. Results We present a systematic analysis of the evolution of mitochondria via gene duplication in the human lineage. The most common duplications are intra-mitochondrial, in which the ancestral gene and the daughter genes encode mitochondrial proteins. These duplications significantly expanded carbohydrate metabolism, the protein import machinery and the calcium regulation of mitochondrial activity. The second most prevalent duplication, inter-compartmental, extended the catalytic as well as the RNA processing repertoire by the novel mitochondrial localization of the protein encoded by one of the daughter genes. Evaluation of the phylogenetic distribution of N-terminal targeting signals suggests a prompt gain of the novel localization after inter-compartmental duplication. Relocalized duplicates are more often expressed in a tissue-specific manner relative to intra-mitochondrial duplicates and mitochondrial proteins in general. In a number of cases, inter-compartmental duplications can be observed in parallel in yeast and human lineages leading to the convergent evolution of subcellular compartments. Conclusions One-to-one human-yeast orthologs are typically restricted to their ancestral subcellular localization. Gene duplication relaxes this constraint on the cellular location, allowing nascent proteins to be relocalized to other compartments. We estimate that the mitochondrial proteome expanded at least 50% since the common ancestor of human and yeast.
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Affiliation(s)
- Radek Szklarczyk
- Centre for Molecular and Biomolecular Informatics, NCMLS, Radboud University Medical Centre, 6500 HB Nijmegen, The Netherlands.
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74
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Affiliation(s)
- Akhil B. Vaidya
- Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129;
| | - Michael W. Mather
- Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129;
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75
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Abstract
Respiratory complex I (NADH:ubiquinone oxidoreductase) is a large mitochondrial inner membrane enzyme consisting of 45 subunits and 8 iron-sulfur (Fe/S) clusters. While complex I dysfunction is the most common reason for mitochondrial diseases, the assembly of complex I and its Fe/S cofactors remains elusive. Here, we identify the human mitochondrial P-loop NTPase, designated huInd1, that is critically required for the assembly of complex I. huInd1 can bind an Fe/S cluster via a conserved CXXC motif in a labile fashion. Knockdown of huInd1 in HeLa cells by RNA interference technology led to strong decreases in complex I protein and activity levels, remodeling of respiratory supercomplexes, and alteration of mitochondrial morphology. In addition, huInd1 depletion resulted in massive decreases in several subunits (NDUFS1, NDUFV1, NDUFS3, and NDUFA13) of the peripheral arm of complex I, with the concomitant appearance of a 450-kDa subcomplex representing part of the membrane arm. By a novel radiolabeling technique, the amount of iron associated with complex I was also shown to reflect the dependence of this enzyme on huInd1 for assembly. Together, these data identify huInd1 as a new assembly factor for human respiratory complex I with a possible role in the delivery of one or more Fe/S clusters to complex I subunits.
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76
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Li J, Cai T, Wu P, Cui Z, Chen X, Hou J, Xie Z, Xue P, Shi L, Liu P, Yates JR, Yang F. Proteomic analysis of mitochondria from Caenorhabditis elegans. Proteomics 2009; 9:4539-53. [DOI: 10.1002/pmic.200900101] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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77
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Meng C, Jin X, Xia L, Shen SM, Wang XL, Cai J, Chen GQ, Wang LS, Fang NY. Alterations of mitochondrial enzymes contribute to cardiac hypertrophy before hypertension development in spontaneously hypertensive rats. J Proteome Res 2009; 8:2463-75. [PMID: 19265432 DOI: 10.1021/pr801059u] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Mitochondrial dysfunction is recently thought to be tightly associated with the development of cardiac hypertrophy as well as hypertension. However, the detailed molecular events in mitochondria at early stages of hypertrophic pathogenesis are still unclear. Applying two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) combined with MALDI-TOF/TOF tandem mass spectrometry, here we identified the changed mitochondrial proteins of left ventricular mitochondria in prehypertensive/hypertensive stages of cardiac hypertrophy through comparing spontaneously hypertensive rats (SHR) and the age-matched normotensive Wistar Kyoto (WKY) rats. The results revealed that in the hypertrophic left ventricle of SHR as early as 4 weeks old with normal blood pressure, 33 mitochondrial protein spots presented significant alterations, with 17 down-regulated and 16 up-regulated. Such alterations were much greater than those in 20-week-old SHR with elevated blood pressure. Of the total alterations, the expression of two mitochondrial enzymes, trifunctional enzyme alpha subunit (Hadha) and NADH dehydrogenase 1 alpha subcomplex 10 (Ndufa10), were found to have special expression modification patterns in SHR strain. These data would provide new clues to investigate the potential contribution of mitochondrial dysfunction to the development of cardiac hypertrophy.
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Affiliation(s)
- Chao Meng
- The Department of Geriatrics, Ren-Ji Hospital, Shanghai Jiao-Tong University School of Medicine (SJTU-SM), Shanghai 200001, China
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78
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Atteia A, Adrait A, Brugière S, Tardif M, van Lis R, Deusch O, Dagan T, Kuhn L, Gontero B, Martin W, Garin J, Joyard J, Rolland N. A proteomic survey of Chlamydomonas reinhardtii mitochondria sheds new light on the metabolic plasticity of the organelle and on the nature of the alpha-proteobacterial mitochondrial ancestor. Mol Biol Evol 2009; 26:1533-48. [PMID: 19349646 DOI: 10.1093/molbev/msp068] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Mitochondria play a key role in the life and death of eukaryotic cells, yet the full spectrum of mitochondrial functions is far from being fully understood, especially in photosynthetic organisms. To advance our understanding of mitochondrial functions in a photosynthetic cell, an extensive proteomic survey of Percoll-purified mitochondria from the metabolically versatile, hydrogen-producing green alga Chlamydomonas reinhardtii was performed. Different fractions of purified mitochondria from Chlamydomonas cells grown under aerobic conditions were analyzed by nano-liquid chromatography-electrospray ionization-mass spectrometry after protein separation on sodium dodecyl sulfate polyacrylamide gel electrophoresis or on blue-native polyacrylamide gel electrophoresis. Of the 496 nonredundant proteins identified, 149 are known or predicted to reside in other cellular compartments and were thus excluded from the molecular and evolutionary analyses of the Chlamydomonas proteome. The mitochondrial proteome of the photosynthetic alga reveals important lineage-specific differences with other mitochondrial proteomes, reflecting the high metabolic diversity of the organelle. Some mitochondrial metabolic pathways in Chlamydomonas appear to combine typical mitochondrial enzymes and bacterial-type ones, whereas others are unknown among mitochondriate eukaryotes. The comparison of the Chlamydomonas proteins to their identifiable homologs predicted from 354 sequenced genomes indicated that Arabidopsis is the most closely related nonalgal eukaryote. Furthermore, this phylogenomic analysis shows that free-living alpha-proteobacteria from the metabolically versatile orders Rhizobiales and Rhodobacterales better reflect the gene content of the ancestor of the chlorophyte mitochondria than parasitic alpha-proteobacteria with reduced and specialized genomes.
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Affiliation(s)
- Ariane Atteia
- Laboratoire de Physiologie Cellulaire Végétale, Centre Nationale la Recherche Scientifique, UMR 5168, Grenoble, France.
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79
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Gaston D, Tsaousis AD, Roger AJ. Predicting proteomes of mitochondria and related organelles from genomic and expressed sequence tag data. Methods Enzymol 2009; 457:21-47. [PMID: 19426860 DOI: 10.1016/s0076-6879(09)05002-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In eukaryotes, determination of the subcellular location of a novel protein encoded in genomic or transcriptomic data provides useful clues as to its possible function. However, experimental localization studies are expensive and time-consuming. As a result, accurate in silico prediction of subcellular localization from sequence data alone is an extremely important field of study in bioinformatics. This is especially so as genomic studies expand beyond model system organisms to encompass the full diversity of eukaryotes. Here we review some of the more commonly used programs for prediction of proteins that function in mitochondria, or mitochondrion-related organelles in diverse eukaryotic lineages and provide recommendations on how to apply these methods. Furthermore, we compare the predictive performance of these programs on a mixed set of mitochondrial and non-mitochondrial proteins. Although N-terminal targeting peptide prediction programs tend to have the highest accuracy, they cannot be effectively used for partial coding sequences derived from high-throughput expressed sequence tag surveys where data for the N-terminus of the encoded protein is often missing. Therefore methods that do not rely on the presence of an N-terminal targeting sequence alone are extremely useful, especially for expressed sequence tag data. The best strategy for classification of unknown proteins is to use multiple programs, incorporating a variety of prediction strategies, and closely examine the predictions with an understanding of how each of those programs will likely handle the data.
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Affiliation(s)
- Daniel Gaston
- Centre for Comparative Genomics and Evolutionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
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80
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Coyne RS, Thiagarajan M, Jones KM, Wortman JR, Tallon LJ, Haas BJ, Cassidy-Hanley DM, Wiley EA, Smith JJ, Collins K, Lee SR, Couvillion MT, Liu Y, Garg J, Pearlman RE, Hamilton EP, Orias E, Eisen JA, Methé BA. Refined annotation and assembly of the Tetrahymena thermophila genome sequence through EST analysis, comparative genomic hybridization, and targeted gap closure. BMC Genomics 2008; 9:562. [PMID: 19036158 PMCID: PMC2612030 DOI: 10.1186/1471-2164-9-562] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 11/26/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Tetrahymena thermophila, a widely studied model for cellular and molecular biology, is a binucleated single-celled organism with a germline micronucleus (MIC) and somatic macronucleus (MAC). The recent draft MAC genome assembly revealed low sequence repetitiveness, a result of the epigenetic removal of invasive DNA elements found only in the MIC genome. Such low repetitiveness makes complete closure of the MAC genome a feasible goal, which to achieve would require standard closure methods as well as removal of minor MIC contamination of the MAC genome assembly. Highly accurate preliminary annotation of Tetrahymena's coding potential was hindered by the lack of both comparative genomic sequence information from close relatives and significant amounts of cDNA evidence, thus limiting the value of the genomic information and also leaving unanswered certain questions, such as the frequency of alternative splicing. RESULTS We addressed the problem of MIC contamination using comparative genomic hybridization with purified MIC and MAC DNA probes against a whole genome oligonucleotide microarray, allowing the identification of 763 genome scaffolds likely to contain MIC-limited DNA sequences. We also employed standard genome closure methods to essentially finish over 60% of the MAC genome. For the improvement of annotation, we have sequenced and analyzed over 60,000 verified EST reads from a variety of cellular growth and development conditions. Using this EST evidence, a combination of automated and manual reannotation efforts led to updates that affect 16% of the current protein-coding gene models. By comparing EST abundance, many genes showing apparent differential expression between these conditions were identified. Rare instances of alternative splicing and uses of the non-standard amino acid selenocysteine were also identified. CONCLUSION We report here significant progress in genome closure and reannotation of Tetrahymena thermophila. Our experience to date suggests that complete closure of the MAC genome is attainable. Using the new EST evidence, automated and manual curation has resulted in substantial improvements to the over 24,000 gene models, which will be valuable to researchers studying this model organism as well as for comparative genomics purposes.
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Affiliation(s)
- Robert S Coyne
- J. Craig Venter Institute (formerly The Institute for Genomic Research), 9704 Medical Center Dr., Rockville, MD, USA.
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81
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Abstract
Mitochondria are central to cellular energetics, metabolism, and signaling. In this issue, Pagliarini et al. (2008) report the largest compendium of mammalian mitochondrial proteins to date. Together with proteomic studies in yeast, this study represents an important step toward the systematic characterization of the mitochondrial proteome and of mitochondrial diseases.
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Affiliation(s)
- Chris Meisinger
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany
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