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So M, Stiban J, Ciesielski GL, Hovde SL, Kaguni LS. Implications of Membrane Binding by the Fe-S Cluster-Containing N-Terminal Domain in the Drosophila Mitochondrial Replicative DNA Helicase. Front Genet 2021; 12:790521. [PMID: 34950192 PMCID: PMC8688847 DOI: 10.3389/fgene.2021.790521] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 11/15/2021] [Indexed: 11/13/2022] Open
Abstract
Recent evidence suggests that iron-sulfur clusters (ISCs) in DNA replicative proteins sense DNA-mediated charge transfer to modulate nuclear DNA replication. In the mitochondrial DNA replisome, only the replicative DNA helicase (mtDNA helicase) from Drosophila melanogaster (Dm) has been shown to contain an ISC in its N-terminal, primase-like domain (NTD). In this report, we confirm the presence of the ISC and demonstrate the importance of a metal cofactor in the structural stability of the Dm mtDNA helicase. Further, we show that the NTD also serves a role in membrane binding. We demonstrate that the NTD binds to asolectin liposomes, which mimic phospholipid membranes, through electrostatic interactions. Notably, membrane binding is more specific with increasing cardiolipin content, which is characteristically high in the mitochondrial inner membrane (MIM). We suggest that the N-terminal domain of the mtDNA helicase interacts with the MIM to recruit mtDNA and initiate mtDNA replication. Furthermore, Dm NUBPL, the known ISC donor for respiratory complex I and a putative donor for Dm mtDNA helicase, was identified as a peripheral membrane protein that is likely to execute membrane-mediated ISC delivery to its target proteins.
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Affiliation(s)
- Minyoung So
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, United States
| | - Johnny Stiban
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, United States.,Department of Biology and Biochemistry, Birzeit University, Birzeit, Palestine
| | - Grzegorz L Ciesielski
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, United States.,Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland.,Department of Chemistry, Auburn University at Montgomery, Montgomery, AL, United States
| | - Stacy L Hovde
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, United States
| | - Laurie S Kaguni
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, United States.,Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland
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2
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Peter B, Falkenberg M. TWINKLE and Other Human Mitochondrial DNA Helicases: Structure, Function and Disease. Genes (Basel) 2020; 11:genes11040408. [PMID: 32283748 PMCID: PMC7231222 DOI: 10.3390/genes11040408] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 04/06/2020] [Accepted: 04/07/2020] [Indexed: 12/30/2022] Open
Abstract
Mammalian mitochondria contain a circular genome (mtDNA) which encodes subunits of the oxidative phosphorylation machinery. The replication and maintenance of mtDNA is carried out by a set of nuclear-encoded factors—of which, helicases form an important group. The TWINKLE helicase is the main helicase in mitochondria and is the only helicase required for mtDNA replication. Mutations in TWINKLE cause a number of human disorders associated with mitochondrial dysfunction, neurodegeneration and premature ageing. In addition, a number of other helicases with a putative role in mitochondria have been identified. In this review, we discuss our current knowledge of TWINKLE structure and function and its role in diseases of mtDNA maintenance. We also briefly discuss other potential mitochondrial helicases and postulate on their role(s) in mitochondria.
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Ciesielski GL, Nadalutti CA, Oliveira MT, Jacobs HT, Griffith JD, Kaguni LS. Structural rearrangements in the mitochondrial genome of Drosophila melanogaster induced by elevated levels of the replicative DNA helicase. Nucleic Acids Res 2019; 46:3034-3046. [PMID: 29432582 PMCID: PMC5887560 DOI: 10.1093/nar/gky094] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 02/02/2018] [Indexed: 01/10/2023] Open
Abstract
Pathological conditions impairing functions of mitochondria often lead to compensatory upregulation of the mitochondrial DNA (mtDNA) replisome machinery, and the replicative DNA helicase appears to be a key factor in regulating mtDNA copy number. Moreover, mtDNA helicase mutations have been associated with structural rearrangements of the mitochondrial genome. To evaluate the effects of elevated levels of the mtDNA helicase on the integrity and replication of the mitochondrial genome, we overexpressed the helicase in Drosophila melanogaster Schneider cells and analyzed the mtDNA by two-dimensional neutral agarose gel electrophoresis and electron microscopy. We found that elevation of mtDNA helicase levels increases the quantity of replication intermediates and alleviates pausing at the replication slow zones. Though we did not observe a concomitant alteration in mtDNA copy number, we observed deletions specific to the segment of repeated elements in the immediate vicinity of the origin of replication, and an accumulation of species characteristic of replication fork stalling. We also found elevated levels of RNA that are retained in the replication intermediates. Together, our results suggest that upregulation of mtDNA helicase promotes the process of mtDNA replication but also results in genome destabilization.
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Affiliation(s)
- Grzegorz L Ciesielski
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, USA.,Institute of Biosciences and Medical Technology, University of Tampere, FI-33014 Tampere, Finland
| | - Cristina A Nadalutti
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Marcos T Oliveira
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, USA
| | - Howard T Jacobs
- Institute of Biosciences and Medical Technology, University of Tampere, FI-33014 Tampere, Finland.,Institute of Biotechnology, University of Helsinki, FI-00014 Helsinki, Finland
| | - Jack D Griffith
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Laurie S Kaguni
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, USA.,Institute of Biosciences and Medical Technology, University of Tampere, FI-33014 Tampere, Finland
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4
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Abstract
Recent advances in the field of mitochondrial DNA (mtDNA) replication highlight the diversity of both the mechanisms utilized and the structural and functional organization of the proteins at mtDNA replication fork, despite the relative simplicity of the animal mtDNA genome. DNA polymerase γ, mtDNA helicase and mitochondrial single-stranded DNA-binding protein-the key replisome proteins, have evolved distinct structural features and biochemical properties. These appear to be correlated with mtDNA genomic features in different metazoan taxa and with their modes of DNA replication, although substantial integrative research is warranted to establish firmly these links. To date, several modes of mtDNA replication have been described for animals: rolling circle, theta, strand-displacement, and RITOLS/bootlace. Resolution of a continuing controversy relevant to mtDNA replication in mammals/vertebrates will have a direct impact on the mechanistic interpretation of mtDNA-related human diseases. Here we review these subjects, integrating earlier and recent data to provide a perspective on the major challenges for future research.
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Affiliation(s)
- G L Ciesielski
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland; Michigan State University, East Lansing, MI, United States
| | - M T Oliveira
- Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho", Jaboticabal, SP, Brazil
| | - L S Kaguni
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland; Michigan State University, East Lansing, MI, United States.
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Rosado-Ruiz FA, So M, Kaguni LS. Purification and Comparative Assay of the Human Mitochondrial Replicative DNA Helicase. Methods Mol Biol 2016; 1351:185-98. [PMID: 26530683 PMCID: PMC4703107 DOI: 10.1007/978-1-4939-3040-1_14] [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] [Indexed: 02/11/2023]
Abstract
The replicative mitochondrial DNA (mtDNA) helicase is essential for mtDNA replication and maintenance of the mitochondrial genome. Despite substantial advances that have been made in its characterization, there is still much to be understood about the functional roles of its domains and its interactions with the other components of the minimal mitochondrial DNA replisome. Critical to achieving this is the ability to isolate the enzyme in a stable, active form. In this chapter we describe a modified, streamlined purification strategy for recombinant forms of the enzyme. We also present assays to assess its helix unwinding activity and the stimulatory effects of the mitochondrial single-stranded DNA-binding protein (mtSSB). Finally, we describe a concentration/buffer exchange method that we have employed to achieve greater enzyme stability and appropriate conditions for biochemical and biophysical studies.
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Affiliation(s)
- Fernando A Rosado-Ruiz
- Department of Biochemistry and Molecular Biology, Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, 48824, USA
| | - Minyoung So
- Department of Biochemistry and Molecular Biology, Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, 48824, USA
| | - Laurie S Kaguni
- Department of Biochemistry and Molecular Biology, Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, 48824, USA.
- Institute of Biosciences of Medical Technology, University of Tempere, Tempere, 33014, Finland.
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6
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Kaguni LS, Oliveira MT. Structure, function and evolution of the animal mitochondrial replicative DNA helicase. Crit Rev Biochem Mol Biol 2015; 51:53-64. [PMID: 26615986 DOI: 10.3109/10409238.2015.1117056] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The mitochondrial replicative DNA helicase is essential for animal mitochondrial DNA (mtDNA) maintenance. Deleterious mutations in the gene that encodes it cause mitochondrial dysfunction manifested in developmental delays, defects and arrest, limited life span, and a number of human pathogenic phenotypes that are recapitulated in animals across taxa. In fact, the replicative mtDNA helicase was discovered with the identification of human disease mutations in its nuclear gene, and based upon its deduced amino acid sequence homology with bacteriophage T7 gene 4 protein (T7 gp4), a bi-functional primase-helicase. Since that time, numerous investigations of its structure, mechanism, and physiological relevance have been reported, and human disease alleles have been modeled in the human, mouse, and Drosophila systems. Here, we review this literature and draw evolutionary comparisons that serve to shed light on its divergent features.
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Affiliation(s)
- Laurie S Kaguni
- a Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine , Michigan State University , East Lansing , MI , USA .,b Institute of Biosciences and Medical Technology, University of Tampere , Tampere , Finland , and
| | - Marcos T Oliveira
- c Departamento de Tecnologia , Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho" , Jaboticabal , Brazil
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7
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Sanchez-Sandoval E, Diaz-Quezada C, Velazquez G, Arroyo-Navarro LF, Almanza-Martinez N, Trasviña-Arenas CH, Brieba LG. Yeast mitochondrial RNA polymerase primes mitochondrial DNA polymerase at origins of replication and promoter sequences. Mitochondrion 2015; 24:22-31. [PMID: 26184436 DOI: 10.1016/j.mito.2015.06.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 06/22/2015] [Accepted: 06/23/2015] [Indexed: 11/15/2022]
Abstract
Three proteins phylogenetically grouped with proteins from the T7 replisome localize to yeast mitochondria: DNA polymerase γ (Mip1), mitochondrial RNA polymerase (Rpo41), and a single-stranded binding protein (Rim1). Human and T7 bacteriophage RNA polymerases synthesize primers for their corresponding DNA polymerases. In contrast, DNA replication in yeast mitochondria is explained by two models: a transcription-dependent model in which Rpo41 primes Mip1 and a model in which double stranded breaks create free 3' OHs that are extended by Mip1. Herein we found that Rpo41 transcribes RNAs that can be extended by Mip1 on single and double-stranded DNA. In contrast to human mitochondrial RNA polymerase, which primes DNA polymerase γ using transcripts from the light-strand and heavy-strand origins of replication, Rpo41 primes Mip1 at replication origins and promoter sequences in vitro. Our results suggest that in ori1, short transcripts serve as primers, whereas in ori5 an RNA transcript longer than 29 nucleotides is used as primer.
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Affiliation(s)
- Eugenia Sanchez-Sandoval
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Corina Diaz-Quezada
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Gilberto Velazquez
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Luis F Arroyo-Navarro
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Norineli Almanza-Martinez
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Carlos H Trasviña-Arenas
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico
| | - Luis G Brieba
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 629, CP 36500 Irapuato, Guanajuato, Mexico.
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Stiban J, Farnum GA, Hovde SL, Kaguni LS. The N-terminal domain of the Drosophila mitochondrial replicative DNA helicase contains an iron-sulfur cluster and binds DNA. J Biol Chem 2014; 289:24032-42. [PMID: 25023283 DOI: 10.1074/jbc.m114.587774] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The metazoan mitochondrial DNA helicase is an integral part of the minimal mitochondrial replisome. It exhibits strong sequence homology with the bacteriophage T7 gene 4 protein primase-helicase (T7 gp4). Both proteins contain distinct N- and C-terminal domains separated by a flexible linker. The C-terminal domain catalyzes its characteristic DNA-dependent NTPase activity, and can unwind duplex DNA substrates independently of the N-terminal domain. Whereas the N-terminal domain in T7 gp4 contains a DNA primase activity, this function is lost in metazoan mtDNA helicase. Thus, although the functions of the C-terminal domain and the linker are partially understood, the role of the N-terminal region in the metazoan replicative mtDNA helicase remains elusive. Here, we show that the N-terminal domain of Drosophila melanogaster mtDNA helicase coordinates iron in a 2Fe-2S cluster that enhances protein stability in vitro. The N-terminal domain binds the cluster through conserved cysteine residues (Cys(68), Cys(71), Cys(102), and Cys(105)) that are responsible for coordinating zinc in T7 gp4. Moreover, we show that the N-terminal domain binds both single- and double-stranded DNA oligomers, with an apparent Kd of ∼120 nm. These findings suggest a possible role for the N-terminal domain of metazoan mtDNA helicase in recruiting and binding DNA at the replication fork.
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Affiliation(s)
- Johnny Stiban
- From the Department of Biochemistry and Molecular Biology, and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, Michigan 48824 and the Department of Biology and Biochemistry, Birzeit University, P. O. Box 14, West Bank 627, Palestine
| | - Gregory A Farnum
- From the Department of Biochemistry and Molecular Biology, and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, Michigan 48824 and
| | - Stacy L Hovde
- From the Department of Biochemistry and Molecular Biology, and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, Michigan 48824 and
| | - Laurie S Kaguni
- From the Department of Biochemistry and Molecular Biology, and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, Michigan 48824 and
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9
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McKinney EA, Oliveira MT. Replicating animal mitochondrial DNA. Genet Mol Biol 2013; 36:308-15. [PMID: 24130435 PMCID: PMC3795181 DOI: 10.1590/s1415-47572013000300002] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2013] [Accepted: 07/11/2013] [Indexed: 11/22/2022] Open
Abstract
The field of mitochondrial DNA (mtDNA) replication has been experiencing incredible progress in recent years, and yet little is certain about the mechanism(s) used by animal cells to replicate this plasmid-like genome. The long-standing strand-displacement model of mammalian mtDNA replication (for which single-stranded DNA intermediates are a hallmark) has been intensively challenged by a new set of data, which suggests that replication proceeds via coupled leading- and lagging-strand synthesis (resembling bacterial genome replication) and/or via long stretches of RNA intermediates laid on the mtDNA lagging-strand (the so called RITOLS). The set of proteins required for mtDNA replication is small and includes the catalytic and accessory subunits of DNA polymerase γ, the mtDNA helicase Twinkle, the mitochondrial single-stranded DNA-binding protein, and the mitochondrial RNA polymerase (which most likely functions as the mtDNA primase). Mutations in the genes coding for the first three proteins are associated with human diseases and premature aging, justifying the research interest in the genetic, biochemical and structural properties of the mtDNA replication machinery. Here we summarize these properties and discuss the current models of mtDNA replication in animal cells.
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Affiliation(s)
- Emily A McKinney
- Institute of Biomedical Technology, University of Tampere, Tampere, Finland
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Kasiviswanathan R, Collins TRL, Copeland WC. The interface of transcription and DNA replication in the mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:970-8. [PMID: 22207204 DOI: 10.1016/j.bbagrm.2011.12.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2011] [Revised: 12/09/2011] [Accepted: 12/12/2011] [Indexed: 11/30/2022]
Abstract
DNA replication of the mitochondrial genome is unique in that replication is not primed by RNA derived from dedicated primases, but instead by extension of processed RNA transcripts laid down by the mitochondrial RNA polymerase. Thus, the RNA polymerase serves not only to generate the transcripts but also the primers needed for mitochondrial DNA replication. The interface between this transcription and DNA replication is not well understood but must be highly regulated and coordinated to carry out both mitochondrial DNA replication and transcription. This review focuses on the extension of RNA primers for DNA replication by the replication machinery and summarizes the current models of DNA replication in mitochondria as well as the proteins involved in mitochondrial DNA replication, namely, the DNA polymerase γ and its accessory subunit, the mitochondrial DNA helicase, the single-stranded DNA binding protein, topoisomerase I and IIIα and RNaseH1. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.
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Affiliation(s)
- Rajesh Kasiviswanathan
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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Patel G, Johnson DS, Sun B, Pandey M, Yu X, Egelman EH, Wang MD, Patel SS. A257T linker region mutant of T7 helicase-primase protein is defective in DNA loading and rescued by T7 DNA polymerase. J Biol Chem 2011; 286:20490-9. [PMID: 21515672 DOI: 10.1074/jbc.m110.201657] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The helicase and primase activities of the hexameric ring-shaped T7 gp4 protein reside in two separate domains connected by a linker region. This linker region is part of the subunit interface between monomers, and point mutations in this region have deleterious effects on the helicase functions. One such linker region mutant, A257T, is analogous to the A359T mutant of the homologous human mitochondrial DNA helicase Twinkle, which is linked to diseases such as progressive external opthalmoplegia. Electron microscopy studies show that A257T gp4 is normal in forming rings with dTTP, but the rings do not assemble efficiently on the DNA. Therefore, A257T, unlike the WT gp4, does not preassemble on the unwinding DNA substrate with dTTP without Mg(II), and its DNA unwinding activity in ensemble assays is slow and limited by the DNA loading rate. Single molecule assays measured a 45 times slower rate of A257T loading on DNA compared with WT gp4. Interestingly, once loaded, A257T has almost WT-like translocation and DNA unwinding activities. Strikingly, A257T preassembles stably on the DNA in the presence of T7 DNA polymerase, which restores the ensemble unwinding activity of A257T to ∼75% of WT, and the rescue does not require DNA synthesis. The DNA loading rate of A257T, however, remains slow even in the presence of the polymerase, which explains why A257T does not support T7 phage growth. Similar types of defects in the related human mitochondrial DNA helicase may be responsible for inefficient DNA replication leading to the disease states.
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Affiliation(s)
- Gayatri Patel
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
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12
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Animal models of mitochondrial DNA transactions in disease and ageing. Exp Gerontol 2010; 45:489-502. [PMID: 20123011 DOI: 10.1016/j.exger.2010.01.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2009] [Revised: 01/11/2010] [Accepted: 01/26/2010] [Indexed: 11/21/2022]
Abstract
Mitochondrial DNA (mtDNA) transactions, processes that include mtDNA replication, repair, recombination and transcription constitute the initial stages of mitochondrial biogenesis, and are at the core of understanding mitochondrial biology and medicine. All of the protein players are encoded in nuclear genes: some are proteins with well-known functions in the nucleus, others are well-known mitochondrial proteins now ascribed new functions, and still others are newly discovered factors. In this article we review recent advances in the field of mtDNA transactions with a special focus on physiological studies. In particular, we consider the expression of variant proteins, or altered expression of factors involved in these processes in powerful model organisms, such as Drosophila melanogaster and the mouse, which have promoted recognition of the broad relevance of oxidative phosphorylation defects resulting from improper maintenance of mtDNA. Furthermore, the animal models recapitulate many phenotypes related to human ageing and a variety of different diseases, a feature that has enhanced our understanding of, and inspired theories about, the molecular mechanisms of such biological processes.
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