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Das P, Hazra A, Saha S, Roy S, Mukherjee M, Hazra S, Majumdar HK, BoseDasgupta S. Resolving the polycistronic aftermath: Essential role of topoisomerase IA in preventing R-loops in Leishmania. J Biol Chem 2024; 300:107162. [PMID: 38484800 PMCID: PMC11021369 DOI: 10.1016/j.jbc.2024.107162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 02/10/2024] [Accepted: 02/26/2024] [Indexed: 04/14/2024] Open
Abstract
Kinetoplastid parasites are "living bridges" in the evolution from prokaryotes to higher eukaryotes. The near-intronless genome of the kinetoplastid Leishmania exhibits polycistronic transcription which can facilitate R-loop formation. Therefore, to prevent such DNA-RNA hybrids, Leishmania has retained prokaryotic-like DNA Topoisomerase IA (LdTOPIA) in the course of evolution. LdTOPIA is an essential enzyme that is expressed ubiquitously and is adapted for the compartmentalized eukaryotic form in harboring functional bipartite nuclear localization signals. Although exhibiting greater homology to mycobacterial TOPIA, LdTOPIA could functionally complement the growth lethality of Escherichia coli TOPIA null GyrB ts strain at non-permissive temperatures. Purified LdTOPIA exhibits Mg2+-dependent relaxation of only negatively supercoiled DNA and preference towards single-stranded DNA substrates. LdTOPIA prevents nuclear R-loops as conditional LdTOPIA downregulated parasites exhibit R-loop formation and thereby parasite killing. The clinically used tricyclic antidepressant, norclomipramine could specifically inhibit LdTOPIA and lead to R-loop formation and parasite elimination. This comprehensive study therefore paves an avenue for drug repurposing against Leishmania.
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Affiliation(s)
- Payel Das
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Arnab Hazra
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Saradindu Saha
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Sadhana Roy
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Mandrita Mukherjee
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Saugata Hazra
- Department of Biosciences and Bioengineering, Indian Institute of Technology Roorkee, Roorkee, India
| | - Hemanta K Majumdar
- Infectious Diseases and Immunology Division, CSIR- Indian Institute of Chemical Biology, Kolkata, India
| | - Somdeb BoseDasgupta
- Molecular Immunology and Cellular Microbiology Laboratory, Department of Bioscience and Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, India.
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2
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Amodeo S, Bregy I, Ochsenreiter T. Mitochondrial genome maintenance-the kinetoplast story. FEMS Microbiol Rev 2023; 47:fuac047. [PMID: 36449697 PMCID: PMC10719067 DOI: 10.1093/femsre/fuac047] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 08/13/2022] [Accepted: 11/24/2022] [Indexed: 12/17/2023] Open
Abstract
Mitochondrial DNA replication is an essential process in most eukaryotes. Similar to the diversity in mitochondrial genome size and organization in the different eukaryotic supergroups, there is considerable diversity in the replication process of the mitochondrial DNA. In this review, we summarize the current knowledge of mitochondrial DNA replication and the associated factors in trypanosomes with a focus on Trypanosoma brucei, and provide a new model of minicircle replication for this protozoan parasite. The model assumes the mitochondrial DNA (kinetoplast DNA, kDNA) of T. brucei to be loosely diploid in nature and the replication of the genome to occur at two replication centers at the opposing ends of the kDNA disc (also known as antipodal sites, APS). The new model is consistent with the localization of most replication factors and in contrast to the current model, it does not require the assumption of an unknown sorting and transport complex moving freshly replicated DNA to the APS. In combination with the previously proposed sexual stages of the parasite in the insect vector, the new model provides a mechanism for maintenance of the mitochondrial genetic diversity.
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Affiliation(s)
- Simona Amodeo
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Hochschulstrasse 6, 3012 Bern, Switzerland
| | - Irina Bregy
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Hochschulstrasse 6, 3012 Bern, Switzerland
| | - Torsten Ochsenreiter
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
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3
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Amodeo S, Bregy I, Hoffmann A, Fradera-Sola A, Kern M, Baudouin H, Zuber B, Butter F, Ochsenreiter T. Characterization of two novel proteins involved in mitochondrial DNA anchoring in Trypanosoma brucei. PLoS Pathog 2023; 19:e1011486. [PMID: 37459364 PMCID: PMC10374059 DOI: 10.1371/journal.ppat.1011486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 07/27/2023] [Accepted: 06/14/2023] [Indexed: 07/28/2023] Open
Abstract
Trypanosoma brucei is a single celled eukaryotic parasite in the group of the Kinetoplastea. The parasite harbors a single mitochondrion with a singular mitochondrial genome that is known as the kinetoplast DNA (kDNA). The kDNA consists of a unique network of thousands of interlocked circular DNA molecules. To ensure proper inheritance of the kDNA to the daughter cells, the genome is physically linked to the basal body, the master organizer of the cell cycle in trypanosomes. The connection that spans, cytoplasm, mitochondrial membranes and the mitochondrial matrix is mediated by the Tripartite Attachment Complex (TAC). Using a combination of proteomics and RNAi we test the current model of hierarchical TAC assembly and identify TbmtHMG44 and TbKAP68 as novel candidates of a complex that connects the TAC to the kDNA. Depletion of TbmtHMG44 or TbKAP68 each leads to a strong kDNA loss but not missegregation phenotype as previously defined for TAC components. We demonstrate that the proteins rely on both the TAC and the kDNA for stable localization to the interface between these two structures. In vitro experiments suggest a direct interaction between TbmtHMG44 and TbKAP68 and that recombinant TbKAP68 is a DNA binding protein. We thus propose that TbmtHMG44 and TbKAP68 are part of a distinct complex connecting the kDNA to the TAC.
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Affiliation(s)
- Simona Amodeo
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Irina Bregy
- Institute of Cell Biology, University of Bern, Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, Bern, Switzerland
- Institute for Anatomy, University of Bern, Bern, Switzerland
| | | | - Albert Fradera-Sola
- Quantitative Proteomics, Institute of Molecular Biology GmbH, Mainz, Germany
| | - Mara Kern
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Hélène Baudouin
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Benoît Zuber
- Institute for Anatomy, University of Bern, Bern, Switzerland
| | - Falk Butter
- Quantitative Proteomics, Institute of Molecular Biology GmbH, Mainz, Germany
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4
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Lamba S, Roy A. DNA Topoisomerases in the Unicellular Protozoan Parasites: Unwinding the Mystery. Biochem Pharmacol 2022; 203:115158. [PMID: 35780829 DOI: 10.1016/j.bcp.2022.115158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 06/17/2022] [Accepted: 06/27/2022] [Indexed: 11/28/2022]
Abstract
DNA topoisomerases are a group of enzymes present ubiquitously in all organisms from unicellular protozoan parasites to humans. These enzymes control the topological problems caused by DNA double helix in the cell during nucleic acid metabolism. Certain types of topoisomerases present in unicellular parasites are quite different from human topoisomerases (hTop) concerning structure, expression, and function. Many protozoan parasites causing fatal diseases have DNA topoisomerases, which play vital roles in their survival. Given the fact that the structures of the protozoan parasite topoisomerases are different from humans, DNA topoisomerase acts as an essential target for potent drug development for parasitic diseases. Moreover, various studies revealed the therapeutic potential of these drugs targeting the parasitic topoisomerases. Therefore, the characterization of parasitic topoisomerases is pivotal for the development of future potential drug targets. Considering the importance of this ubiquitous enzyme as a potential drug target, we describe in detail all the reported protozoan topoisomerases in an organized manner including Leishmania, Trypanosoma, Plasmodium, Giardia, Entamoeba, Babesia, Theileria, Crithidia, Cryptosporidium, Toxoplasma, etc. This review highlights the unique attributes associated with the structure and function of different types of DNA topoisomerases from the unicellular protozoan parasites. So, it would be beneficial for researchers to obtain awareness about the currently characterized topoisomerases and the ones that need better characterization, understand the structure-function relationship of parasitic topoisomerases, to develop the potent anti-parasitic drugs, and also provides a future platform for therapeutic development.
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Affiliation(s)
- Swati Lamba
- Department of Biotechnology, Savitribai Phule Pune University, Ganeshkhind Road, Pune-411007, India
| | - Amit Roy
- Department of Biotechnology, Savitribai Phule Pune University, Ganeshkhind Road, Pune-411007, India.
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5
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Maldonado E, Morales-Pison S, Urbina F, Solari A. Molecular and Functional Characteristics of DNA Polymerase Beta-Like Enzymes From Trypanosomatids. Front Cell Infect Microbiol 2021; 11:670564. [PMID: 34422676 PMCID: PMC8375306 DOI: 10.3389/fcimb.2021.670564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 06/08/2021] [Indexed: 11/16/2022] Open
Abstract
Trypanosomatids are a group of primitive unicellular eukaryotes that can cause diseases in plants, insects, animals, and humans. Kinetoplast genome integrity is key to trypanosomatid cell survival and viability. Kinetoplast DNA (kDNA) is usually under attack by reactive oxygen and nitric species (ROS and RNS), damaging the DNA, and the cells must remove and repair those oxidatively generated lesions in order to survive and proliferate. Base excision repair (BER) is a well-conserved pathway for DNA repair after base damage, single-base loss, and single-strand breaks, which can arise from ROS, RSN, environmental genotoxic agents, and UV irradiation. A powerful BER system has been described in the T. cruzi kinetoplast and it is mainly carried out by DNA polymerase β (pol β) and DNA polymerase β-PAK (pol β-PAK), which are kinetoplast-located in T. cruzi as well as in other trypanosomatids. Both pol β and pol β-PAK belong to the X-family of DNA polymerases (pol X family), perform BER in trypanosomatids, and display intrinsic 5-deoxyribose phosphate (dRP) lyase and DNA polymerase activities. However, only Pol β-PAK is able to carry out trans-lesion synthesis (TLS) across 8oxoG lesions. T. cruzi cells overexpressing pol β are more resistant to ROS and are also more efficient to repair 8oxoG compared to control cells. Pol β seems to play a role in kDNA replication, since it associates with kinetoplast antipodal sites in those development stages in trypanosomatids which are competent for cell replication. ROS treatment of cells induces the overexpression of pol β, indicating that plays a role in kDNA repair. In this review, we will summarize the main features of trypanosomatid minicircle kDNA replication and the biochemical characteristics of pol β-like enzymes and their involvement in BER and kDNA replication. We also summarize key structural features of trypanosomatid pol β compared to their mammalian (human) counterpart.
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Affiliation(s)
- Edio Maldonado
- Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Sebastian Morales-Pison
- Laboratorio de Genética Molecular Humana, Programa de Genética Humana, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Fabiola Urbina
- Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Aldo Solari
- Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
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6
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Zuma AA, Dos Santos Barrias E, de Souza W. Basic Biology of Trypanosoma cruzi. Curr Pharm Des 2021; 27:1671-1732. [PMID: 33272165 DOI: 10.2174/1381612826999201203213527] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 10/01/2020] [Accepted: 10/08/2020] [Indexed: 11/22/2022]
Abstract
The present review addresses basic aspects of the biology of the pathogenic protozoa Trypanosoma cruzi and some comparative information of Trypanosoma brucei. Like eukaryotic cells, their cellular organization is similar to that of mammalian hosts. However, these parasites present structural particularities. That is why the following topics are emphasized in this paper: developmental stages of the life cycle in the vertebrate and invertebrate hosts; the cytoskeleton of the protozoa, especially the sub-pellicular microtubules; the flagellum and its attachment to the protozoan body through specialized junctions; the kinetoplast-mitochondrion complex, including its structural organization and DNA replication; glycosome and its role in the metabolism of the cell; acidocalcisome, describing its morphology, biochemistry, and functional role; cytostome and the endocytic pathway; the organization of the endoplasmic reticulum and Golgi complex; the nucleus, describing its structural organization during interphase and division; and the process of interaction of the parasite with host cells. The unique characteristics of these structures also make them interesting chemotherapeutic targets. Therefore, further understanding of cell biology aspects contributes to the development of drugs for chemotherapy.
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Affiliation(s)
- Aline A Zuma
- Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho - Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Emile Dos Santos Barrias
- Laboratorio de Metrologia Aplicada a Ciencias da Vida, Diretoria de Metrologia Aplicada a Ciencias da Vida - Instituto Nacional de Metrologia, Qualidade e Tecnologia (Inmetro), Rio de Janeiro, Brazil
| | - Wanderley de Souza
- Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho - Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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7
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The ultimate fate determinants of drug induced cell-death mechanisms in Trypanosomatids. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2021; 15:81-91. [PMID: 33601284 PMCID: PMC7900639 DOI: 10.1016/j.ijpddr.2021.01.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 01/15/2021] [Accepted: 01/19/2021] [Indexed: 02/06/2023]
Abstract
Chemotherapy constitutes a major part of modern-day therapy for infectious and chronic diseases. A drug is said to be effective if it can inhibit its target, induce stress, and thereby trigger an array of cell death pathways in the form of programmed cell death, autophagy, necrosis, etc. Chemotherapy is the only treatment choice against trypanosomatid diseases like Leishmaniasis, Chagas disease, and sleeping sickness. Anti-trypanosomatid drugs can induce various cell death phenotypes depending upon the drug dose and growth stage of the parasites. The mechanisms and pathways triggering cell death in Trypanosomatids serve to help identify potential targets for the development of effective anti-trypanosomatids. Studies show that the key proteins involved in cell death of trypanosomatids are metacaspases, Endonuclease G, Apoptosis-Inducing Factor, cysteine proteases, serine proteases, antioxidant systems, etc. Unlike higher eukaryotes, these organisms either lack the complete set of effectors involved in cell death pathways, or are yet to be deciphered. A detailed summary of the existing knowledge of different drug-induced cell death pathways would help identify the lacuna in each of these pathways and therefore open new avenues for research and thereby new therapeutic targets to explore. The cell death pathway associated complexities in metazoans are absent in trypanosomatids; hence this summary can also help understand the trigger points as well as cross-talk between these pathways. Here we provide an in-depth overview of the existing knowledge of these drug-induced trypanosomatid cell death pathways, describe their associated physiological changes, and suggest potential interconnections amongst them.
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8
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Seddek A, Annamalai T, Tse-Dinh YC. Type IA Topoisomerases as Targets for Infectious Disease Treatments. Microorganisms 2021; 9:E86. [PMID: 33401386 PMCID: PMC7823277 DOI: 10.3390/microorganisms9010086] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 12/13/2020] [Accepted: 12/17/2020] [Indexed: 12/19/2022] Open
Abstract
Infectious diseases are one of the main causes of death all over the world, with antimicrobial resistance presenting a great challenge. New antibiotics need to be developed to provide therapeutic treatment options, requiring novel drug targets to be identified and pursued. DNA topoisomerases control the topology of DNA via DNA cleavage-rejoining coupled to DNA strand passage. The change in DNA topological features must be controlled in vital processes including DNA replication, transcription, and DNA repair. Type IIA topoisomerases are well established targets for antibiotics. In this review, type IA topoisomerases in bacteria are discussed as potential targets for new antibiotics. In certain bacterial pathogens, topoisomerase I is the only type IA topoisomerase present, which makes it a valuable antibiotic target. This review will summarize recent attempts that have been made to identify inhibitors of bacterial topoisomerase I as potential leads for antibiotics and use of these inhibitors as molecular probes in cellular studies. Crystal structures of inhibitor-enzyme complexes and more in-depth knowledge of their mechanisms of actions will help to establish the structure-activity relationship of potential drug leads and develop potent and selective therapeutics that can aid in combating the drug resistant bacterial infections that threaten public health.
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Affiliation(s)
- Ahmed Seddek
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA; (A.S.); (T.A.)
- Biomolecular Sciences Institute, Florida International University, Miami, FL 33199, USA
| | - Thirunavukkarasu Annamalai
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA; (A.S.); (T.A.)
| | - Yuk-Ching Tse-Dinh
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA; (A.S.); (T.A.)
- Biomolecular Sciences Institute, Florida International University, Miami, FL 33199, USA
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9
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Miller JC, Delzell SB, Concepción-Acevedo J, Boucher MJ, Klingbeil MM. A DNA polymerization-independent role for mitochondrial DNA polymerase I-like protein C in African trypanosomes. J Cell Sci 2020; 133:jcs.233072. [PMID: 32079654 DOI: 10.1242/jcs.233072] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Accepted: 02/10/2020] [Indexed: 01/01/2023] Open
Abstract
Mitochondrial DNA of Trypanosoma brucei and related parasites is a catenated network containing thousands of minicircles and tens of maxicircles, called kinetoplast DNA (kDNA). Replication of a single nucleoid requires at least three DNA polymerase I-like proteins (i.e. POLIB, POLIC and POLID), each showing discrete localizations near the kDNA during S phase. POLIB and POLID have roles in minicircle replication but the specific role of POLIC in kDNA maintenance is less clear. Here, we use an RNA interference (RNAi)-complementation system to dissect the functions of two distinct POLIC regions, i.e. the conserved family A DNA polymerase (POLA) domain and the uncharacterized N-terminal region (UCR). While RNAi complementation with wild-type POLIC restored kDNA content and cell cycle localization of kDNA, active site point mutations in the POLA domain impaired minicircle replication similar to that of POLIB and POLID depletions. Complementation with POLA domain alone abolished the formation of POLIC foci and partially rescued the RNAi phenotype. Furthermore, we provide evidence that the UCR is crucial in cell cycle-dependent protein localization and facilitates proper distribution of progeny networks. This is the first report of a DNA polymerase that impacts on mitochondrial nucleoid distribution.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Jonathan C Miller
- Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA
| | - Stephanie B Delzell
- Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA
| | - Jeniffer Concepción-Acevedo
- Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases, 1600 Clifton Road, Atlanta, GA 30329, USA
| | - Michael J Boucher
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, CA 94158, USA
| | - Michele M Klingbeil
- Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA .,Division of Foodborne,Waterborne, and Environmental Diseases, The Institute of Applied Life Sciences, University of Massachusetts, Amherst, MA 01003, USA
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10
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Reguera RM, Elmahallawy EK, García-Estrada C, Carbajo-Andrés R, Balaña-Fouce R. DNA Topoisomerases of Leishmania Parasites; Druggable Targets for Drug Discovery. Curr Med Chem 2019; 26:5900-5923. [DOI: 10.2174/0929867325666180518074959] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2017] [Revised: 03/15/2018] [Accepted: 05/14/2018] [Indexed: 12/13/2022]
Abstract
DNA topoisomerases (Top) are a group of isomerase enzymes responsible for controlling the topological problems caused by DNA double helix in the cell during the processes of replication, transcription and recombination. Interestingly, these enzymes have been known since long to be key molecular machines in several cellular processes through overwinding or underwinding of DNA in all living organisms. Leishmania, a trypanosomatid parasite responsible for causing fatal diseases mostly in impoverished populations of low-income countries, has a set of six classes of Top enzymes. These are placed in the nucleus and the single mitochondrion and can be deadly targets of suitable drugs. Given the fact that there are clear differences in structure and expression between parasite and host enzymes, numerous studies have reported the therapeutic potential of Top inhibitors as antileishmanial drugs. In this regard, numerous compounds have been described as Top type IB and Top type II inhibitors in Leishmania parasites, such as camptothecin derivatives, indenoisoquinolines, indeno-1,5- naphthyridines, fluoroquinolones, anthracyclines and podophyllotoxins. The aim of this review is to highlight several facts about Top and Top inhibitors as potential antileishmanial drugs, which may represent a promising strategy for the control of this disease of public health importance.
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Affiliation(s)
- Rosa M. Reguera
- Department of Biomedical Sciences, University of Leon (ULE), Leon, Spain
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11
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Chowdhury SR, Majumder HK. DNA Topoisomerases in Unicellular Pathogens: Structure, Function, and Druggability. Trends Biochem Sci 2019; 44:415-432. [PMID: 30609953 DOI: 10.1016/j.tibs.2018.12.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 11/20/2018] [Accepted: 12/03/2018] [Indexed: 02/06/2023]
Abstract
All organisms, including unicellular pathogens, compulsorily possess DNA topoisomerases for successful nucleic acid metabolism. But particular subtypes of topoisomerases exist, in all prokaryotes and in some unicellular eukaryotes, that are absent in higher eukaryotes. Moreover, topoisomerases from pathogenic members of a niche possess some unique molecular architecture and functionalities completely distinct from their nonpathogenic colleagues. This review will highlight the unique attributes associated with the structures and functions of topoisomerases from the unicellular pathogens, with special reference to bacteria and protozoan parasites. It will also summarise the progress made in the domain pertaining to the druggability of these topoisomerases, upon which a future platform for therapeutic development can be successfully constructed.
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Affiliation(s)
- Somenath Roy Chowdhury
- Laboratory of Molecular Parasitology, Infectious Diseases and Immunology Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India
| | - Hemanta K Majumder
- Laboratory of Molecular Parasitology, Infectious Diseases and Immunology Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India.
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12
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Krishnan A, Burroughs AM, Iyer LM, Aravind L. Unexpected Evolution of Lesion-Recognition Modules in Eukaryotic NER and Kinetoplast DNA Dynamics Proteins from Bacterial Mobile Elements. iScience 2018; 9:192-208. [PMID: 30396152 PMCID: PMC6222260 DOI: 10.1016/j.isci.2018.10.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 10/15/2018] [Accepted: 10/15/2018] [Indexed: 12/29/2022] Open
Abstract
The provenance of several components of major uniquely eukaryotic molecular machines are increasingly being traced back to prokaryotic biological conflict systems. Here, we demonstrate that the N-terminal single-stranded DNA-binding domain from the anti-restriction protein ArdC, deployed by bacterial mobile elements against their host, was independently acquired twice by eukaryotes, giving rise to the DNA-binding domains of XPC/Rad4 and the Tc-38-like proteins in the stem kinetoplastid. In both instances, the ArdC-N domain tandemly duplicated forming an extensive DNA-binding interface. In XPC/Rad4, the ArdC-N domains (BHDs) also fused to the inactive transglutaminase domain of a peptide-N-glycanase ultimately derived from an archaeal conflict system. Alongside, we delineate several parallel acquisitions from conjugative elements/bacteriophages that gave rise to key components of the kinetoplast DNA (kDNA) replication apparatus. These findings resolve two outstanding questions in eukaryote biology: (1) the origin of the unique DNA lesion-recognition component of NER and (2) origin of the unusual, plasmid-like features of kDNA.
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Affiliation(s)
- Arunkumar Krishnan
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
| | - A Maxwell Burroughs
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
| | - Lakshminarayan M Iyer
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
| | - L Aravind
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
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13
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Concepción-Acevedo J, Miller JC, Boucher MJ, Klingbeil MM. Cell cycle localization dynamics of mitochondrial DNA polymerase IC in African trypanosomes. Mol Biol Cell 2018; 29:2540-2552. [PMID: 30133333 PMCID: PMC6254582 DOI: 10.1091/mbc.e18-02-0127] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Trypanosoma brucei has a unique catenated mitochondrial DNA (mtDNA) network called kinetoplast DNA (kDNA). Replication of kDNA occurs once per cell cycle in near synchrony with nuclear S phase and requires the coordination of many proteins. Among these are three essential DNA polymerases (TbPOLIB, IC, and ID). Localization dynamics of these proteins with respect to kDNA replication stages and how they coordinate their functions during replication are not well understood. We previously demonstrated that TbPOLID undergoes dynamic localization changes that are coupled to kDNA replication events. Here, we report the localization of TbPOLIC, a second essential DNA polymerase, and demonstrate the accumulation of TbPOLIC foci at active kDNA replication sites (antipodal sites) during stage II of the kDNA duplication cycle. While TbPOLIC was undetectable by immunofluorescence during other cell cycle stages, steady-state protein levels measured by Western blot remained constant. TbPOLIC foci colocalized with the fraction of TbPOLID that localized to the antipodal sites. However, the partial colocalization of the two essential DNA polymerases suggests a highly dynamic environment at the antipodal sites to coordinate the trafficking of replication proteins during kDNA synthesis. These data indicate that cell cycle-dependent localization is a major regulatory mechanism for essential mtDNA polymerases during kDNA replication.
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Affiliation(s)
| | - Jonathan C Miller
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003
| | - Michael J Boucher
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003
| | - Michele M Klingbeil
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003
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Expanding the toolbox for Trypanosoma cruzi: A parasite line incorporating a bioluminescence-fluorescence dual reporter and streamlined CRISPR/Cas9 functionality for rapid in vivo localisation and phenotyping. PLoS Negl Trop Dis 2018; 12:e0006388. [PMID: 29608569 PMCID: PMC5897030 DOI: 10.1371/journal.pntd.0006388] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2018] [Revised: 04/12/2018] [Accepted: 03/14/2018] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Infection with Trypanosoma cruzi causes Chagas disease, a major public health problem throughout Latin America. There is no vaccine and the only drugs have severe side effects. Efforts to generate new therapies are hampered by limitations in our understanding of parasite biology and disease pathogenesis. Studies are compromised by the complexity of the disease, the long-term nature of the infection, and the fact that parasites are barely detectable during the chronic stage. In addition, functional dissection of T. cruzi biology has been restricted by the limited flexibility of the genetic manipulation technology applicable to this parasite. METHODOLOGY/PRINCIPAL FINDINGS Here, we describe two technical innovations, which will allow the role of the parasite in disease progression to be better assessed. First, we generated a T. cruzi reporter strain that expresses a fusion protein comprising red-shifted luciferase and green fluorescent protein domains. Bioluminescence allows the kinetics of infection to be followed within a single animal, and specific foci of infection to be pinpointed in excised tissues. Fluorescence can then be used to visualise individual parasites in tissue sections to study host-parasite interactions at a cellular level. Using this strategy, we have been routinely able to find individual parasites within chronically infected murine tissues for the first time. The second advance is the incorporation of a streamlined CRISPR/Cas9 functionality into this reporter strain that can facilitate genome editing using a PCR-based approach that does not require DNA cloning. This system allows the rapid generation of null mutants and fluorescently tagged parasites in a background where the in vivo phenotype can be rapidly assessed. CONCLUSIONS/SIGNIFICANCE The techniques described here will have multiple applications for studying aspects of T. cruzi biology and Chagas disease pathogenesis previously inaccessible to conventional approaches. The reagents and cell lines have been generated as a community resource and are freely available on request.
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Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication. mBio 2015; 6:mBio.02425-14. [PMID: 25670781 PMCID: PMC4337576 DOI: 10.1128/mbio.02425-14] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import. Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.
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Týč J, Klingbeil MM, Lukeš J. Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication. mBio 2015. [PMID: 25670781 DOI: 10.1128/mbio.02425-02414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2023] Open
Abstract
UNLABELLED Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import. IMPORTANCE Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.
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Affiliation(s)
- Jiří Týč
- Faculty of Sciences, University of South Bohemia and Biology Centre, Institute of Parasitology, Czech Academy of Sciences, České Budějovice (Budweis), Czech Republic
| | - Michele M Klingbeil
- Department of Microbiology, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts, USA
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Verner Z, Basu S, Benz C, Dixit S, Dobáková E, Faktorová D, Hashimi H, Horáková E, Huang Z, Paris Z, Peña-Diaz P, Ridlon L, Týč J, Wildridge D, Zíková A, Lukeš J. Malleable mitochondrion of Trypanosoma brucei. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 315:73-151. [PMID: 25708462 DOI: 10.1016/bs.ircmb.2014.11.001] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The importance of mitochondria for a typical aerobic eukaryotic cell is undeniable, as the list of necessary mitochondrial processes is steadily growing. Here, we summarize the current knowledge of mitochondrial biology of an early-branching parasitic protist, Trypanosoma brucei, a causative agent of serious human and cattle diseases. We present a comprehensive survey of its mitochondrial pathways including kinetoplast DNA replication and maintenance, gene expression, protein and metabolite import, major metabolic pathways, Fe-S cluster synthesis, ion homeostasis, organellar dynamics, and other processes. As we describe in this chapter, the single mitochondrion of T. brucei is everything but simple and as such rivals mitochondria of multicellular organisms.
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Affiliation(s)
- Zdeněk Verner
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Present address: Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia; Present address: Faculty of Sciences, Charles University, Prague, Czech Republic
| | - Somsuvro Basu
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic; Present address: Institut für Zytobiologie und Zytopathologie, Philipps-Universität Marburg, Germany
| | - Corinna Benz
- Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Sameer Dixit
- Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Eva Dobáková
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Present address: Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
| | - Drahomíra Faktorová
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Hassan Hashimi
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Eva Horáková
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic
| | - Zhenqiu Huang
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Zdeněk Paris
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic
| | - Priscila Peña-Diaz
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic
| | - Lucie Ridlon
- Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic; Present address: Salk Institute, La Jolla, San Diego, USA
| | - Jiří Týč
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - David Wildridge
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic
| | - Alena Zíková
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
| | - Julius Lukeš
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czech Republic; Faculty of Sciences, University of South Bohemia, České Budějovice (Budweis), Czech Republic
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Balaña-Fouce R, Alvarez-Velilla R, Fernández-Prada C, García-Estrada C, Reguera RM. Trypanosomatids topoisomerase re-visited. New structural findings and role in drug discovery. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2014; 4:326-37. [PMID: 25516844 PMCID: PMC4266802 DOI: 10.1016/j.ijpddr.2014.07.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
There is an urgent need of new treatments against trypanosomatids-borne diseases. DNA topoisomerases are pointed as potential drug targets against unicellular parasites. Trypanosomatids have a full set of DNA topoisomerases in both nucleus and kinetoplast. TopII and TopIII are located in the kinetoplast and fully involved in kDNA replication. Tritryps TopIB differ in structure from mammalian’s pointing to an attractive target.
The Trypanosomatidae family, composed of unicellular parasites, causes severe vector-borne diseases that afflict human populations worldwide. Chagas disease, sleeping sickness, as well as different sorts of leishmaniases are amongst the most important infectious diseases produced by Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp., respectively. All these infections are closely related to weak health care services in low-income populations of less developed and least economically developed countries. Search for new therapeutic targets in order to hit these pathogens is of paramount priority, as no effective vaccine is currently in use against any of these parasites. Furthermore, present-day chemotherapy comprises old-fashioned drugs full of important side effects. Besides, they are prone to produce tolerance and resistance as a consequence of their continuous use for decades. DNA topoisomerases (Top) are ubiquitous enzymes responsible for solving the torsional tensions caused during replication and transcription processes, as well as in maintaining genomic stability during DNA recombination. As the inhibition of these enzymes produces cell arrest and triggers cell death, Top inhibitors are among the most effective and most widely used drugs in both cancer and antibacterial therapies. Top relaxation and decatenation activities, which are based on a common nicking–closing cycle involving one or both DNA strands, have been pointed as a promising drug target. Specific inhibitors that bind to the interface of DNA-Top complexes can stabilize Top-mediated transient DNA breaks. In addition, important structural differences have been found between Tops from the Trypanosomatidae family members and Tops from the host. Such dissimilarities make these proteins very interesting for drug design and molecular intervention. The present review is a critical update of the last findings regarding trypanosomatid’s Tops, their new structural features, their involvement both in the physiology and virulence of these parasites, as well as their use as promising targets for drug discovery.
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Affiliation(s)
- Rafael Balaña-Fouce
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana s/n, 24071 León, Spain
| | - Raquel Alvarez-Velilla
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana s/n, 24071 León, Spain
| | | | - Carlos García-Estrada
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana s/n, 24071 León, Spain
| | - Rosa M Reguera
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana s/n, 24071 León, Spain
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19
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Prada CF, Álvarez-Velilla R, Díaz-Gozález R, Pérez-Pertejo Y, Balaña-Fouce R, Reguera RM. Identification and characterization of the regions involved in the nuclear translocation of the heterodimeric leishmanial DNA topoisomerase IB. PLoS One 2013; 8:e73565. [PMID: 24023887 PMCID: PMC3759442 DOI: 10.1371/journal.pone.0073565] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 07/16/2013] [Indexed: 01/09/2023] Open
Abstract
Leishmania donovani, the causative organism for visceral leishmaniasis, contains a unique heterodimeric DNA-topoisomerase IB (LdTopIB). LdTopIB is a heterodimer made up of a large subunit and a small subunit that must interact with each other to build an active enzyme able to solve the topological tensions on the DNA. As LdTopIB is located within the nucleus, one or more nuclear localization signals (NLS) should exist to ensure its nuclear translocation. In this report three novel NLS have been identified through a sequential deletion study of the genes encoding of both subunits fused to that encoding the green fluorescent protein (GFP). NLS1 is a highly basic sequence of 43 amino acids in the C-terminal extension of the large protomer. We found two well-defined sequences in the small protomer: NLS2 is a 10-amino acid motif located in the N-terminal extension of the protein; NLS3 consists of a complex region of 28 amino acids placed in the vicinity of the catalytic Tyr-222 included at the conserved SKINY signature within the C-terminal. Furthermore, by means of yeast cell viability assays, conducted with several LdTopIB chimeras lacking any of the NLS motives, we have revealed that both subunits are transported independently to the nucleus. There was no evidence of LdTopIB accumulation in mitochondria or association to the kinetoplast DNA network. The results rule out the former hypothesis, which attributes nucleocytoplasmic transport of LdTopIB entirely to the large subunit. The LdTopIB is localized to the nucleus only.
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Affiliation(s)
- Christopher F. Prada
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana, León, Spain
| | - Raquel Álvarez-Velilla
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana, León, Spain
| | - Rosario Díaz-Gozález
- Instituto de Parasitología y Biomedicina "López-Neyra", Parque Tecnológico de Ciencias de la Salud, Granada, Spain
| | - Yolanda Pérez-Pertejo
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana, León, Spain
| | - Rafael Balaña-Fouce
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana, León, Spain
- * E-mail:
| | - Rosa M. Reguera
- Departamento de Ciencias Biomédicas, Universidad de León, Campus de Vegazana, León, Spain
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Abstract
One of the most fascinating and unusual features of trypanosomatids, parasites that cause disease in many tropical countries, is their mitochondrial DNA. This genome, known as kinetoplast DNA (kDNA), is organized as a single, massive DNA network formed of interlocked DNA rings. In this review, we discuss recent studies on kDNA structure and replication, emphasizing recent developments on replication enzymes, how the timing of kDNA synthesis is controlled during the cell cycle, and the machinery for segregating daughter networks after replication.
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Affiliation(s)
- Robert E Jensen
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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Wang J, Englund PT, Jensen RE. TbPIF8, a Trypanosoma brucei protein related to the yeast Pif1 helicase, is essential for cell viability and mitochondrial genome maintenance. Mol Microbiol 2012; 83:471-85. [PMID: 22220754 DOI: 10.1111/j.1365-2958.2011.07938.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The trypanosome mitochondrial genome, kinetoplast DNA (kDNA), is a massive network of interlocked DNA rings, including several thousand minicircles and dozens of maxicircles. The unusual complexity of kDNA would indicate that numerous proteins must be involved in its condensation, replication, segregation and gene expression. During our investigation of trypanosome mitochondrial PIF1-like helicases, we found that TbPIF8 is the smallest and most divergent. It lacks some conserved helicase domains, thus implying that unlike other mitochondrial PIF1-like helicases, this protein may have no enzymatic activity. TbPIF8 is positioned on the distal face of kDNA disk and its localization patterns vary with different kDNA replication stages. Stem-loop RNAi of TbPIF8 arrests cell growth and causes defects in kDNA segregation. RNAi of TbPIF8 causes only limited kDNA shrinkage but the networks become disorganized. Electron microcopy of thin sections of TbPIF8-depleted cells shows heterogeneous electron densities in the kinetoplast disk. Although we do not yet know its exact function, we conclude that TbPIF8 is essential for cell viability and is important for maintenance of kDNA.
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Affiliation(s)
- Jianyang Wang
- Departments of Biological Chemistry Cell Biology, Johns Hopkins Medical School, Baltimore, MD 21205, USA
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22
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Forterre P. Introduction and Historical Perspective. CANCER DRUG DISCOVERY AND DEVELOPMENT 2012. [DOI: 10.1007/978-1-4614-0323-4_1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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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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Banerjee B, Sen N, Majumder HK. Identification of a Functional Type IA Topoisomerase, LdTopIIIβ, from Kinetoplastid Parasite Leishmania donovani. Enzyme Res 2011; 2011:230542. [PMID: 21637326 PMCID: PMC3102327 DOI: 10.4061/2011/230542] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2010] [Accepted: 02/25/2011] [Indexed: 11/20/2022] Open
Abstract
DNA topoisomerases of kinetoplastids represent a family of DNA processing enzymes that essentially solve the topological problems not only in nuclear DNA but also in kinetoplast DNA. We have, for the first time, identified a Leishmania donovani homologue of bacterial and eukaryotic IA type of topoisomerase III protein and termed as LdTopIIIβ. Complementation study of wild-type and mutant LdTopIIIβ with slow-growing topoisomerase III mutant yeast S. cerevisiae revealed the functional conservation of the leishmanial counterpart of topoisomerase IIIβ protein, the 327 tyrosine being the active site amino acid. A C-terminal deletion construct of LdTopIIIβ could not suppress the slow-growth phenotype of mutant yeast, indicating the requirement of C-terminal region for the enzyme function in vivo.LdTopIIIβ localized inside the nucleus and kinetoplast of the parasite. Taken together, our study indicates functional conservation and possible role of LdTopIIIβ in parasite DNA processing.
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Affiliation(s)
- Bijoylaxmi Banerjee
- Molecular Parasitology Laboratory, Infectious Disease and Immunology Division, Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Kolkata 700032, India
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Three mitochondrial DNA polymerases are essential for kinetoplast DNA replication and survival of bloodstream form Trypanosoma brucei. EUKARYOTIC CELL 2011; 10:734-43. [PMID: 21531873 DOI: 10.1128/ec.05008-11] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Trypanosoma brucei, the causative agent of human African trypanosomiasis, has a complex life cycle that includes multiple life cycle stages and metabolic changes as the parasite switches between insect vector and mammalian host. The parasite's single mitochondrion contains a unique catenated mitochondrial DNA network called kinetoplast DNA (kDNA) that is composed of minicircles and maxicircles. Long-standing uncertainty about the requirement of kDNA in bloodstream form (BF) T. brucei has recently eroded, with reports of posttranscriptional editing and subsequent translation of kDNA-encoded transcripts as essential processes for BF parasites. These studies suggest that kDNA and its faithful replication are indispensable for this life cycle stage. Here we demonstrate that three kDNA replication proteins (mitochondrial DNA polymerases IB, IC, and ID) are required for BF parasite viability. Silencing of each polymerase was lethal, resulting in kDNA loss, persistence of prereplication DNA monomers, and collapse of the mitochondrial membrane potential. These data demonstrate that kDNA replication is indeed crucial for BF T. brucei. The contributions of mitochondrial DNA polymerases IB, IC, and ID to BF parasite viability suggest that these and other kDNA replication proteins warrant further investigation as a new class of targets for the development of antitrypanosomal drugs.
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A second mitochondrial DNA primase is essential for cell growth and kinetoplast minicircle DNA replication in Trypanosoma brucei. EUKARYOTIC CELL 2011; 10:445-54. [PMID: 21257796 DOI: 10.1128/ec.00308-10] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The mitochondrial DNA of trypanosomes contains two types of circular DNAs, minicircles and maxicircles. Both minicircles and maxicircles replicate from specific replication origins by unidirectional theta-type intermediates. Initiation of the minicircle leading strand and also that of at least the first Okazaki fragment involve RNA priming. The Trypanosoma brucei genome encodes two mitochondrial DNA primases, PRI1 and PRI2, related to the primases of eukaryotic nucleocytoplasmic large DNA viruses. These primases are members of the archeoeukaryotic primase superfamily, and each of them contain an RNA recognition motif and a PriCT-2 motif. In Leishmania species, PRI2 proteins are approximately 61 to 66 kDa in size, whereas in Trypanosoma species, PRI2 proteins have additional long amino-terminal extensions. RNA interference (RNAi) of T. brucei PRI2 resulted in the loss of kinetoplast DNA and accumulation of covalently closed free minicircles. Recombinant PRI2 lacking this extension (PRI2ΔNT) primes poly(dA) synthesis on a poly(dT) template in an ATP-dependent manner. Mutation of two conserved aspartate residues (PRI2ΔNTCS) resulted in loss of enzymatic activity but not loss of DNA binding. We propose that PRI2 is directly involved in initiating kinetoplast minicircle replication.
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Depletion of mitochondrial acyl carrier protein in bloodstream-form Trypanosoma brucei causes a kinetoplast segregation defect. EUKARYOTIC CELL 2011; 10:286-92. [PMID: 21239625 DOI: 10.1128/ec.00290-10] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Like other eukaryotes, trypanosomes have an essential type II fatty acid synthase in their mitochondrion. We have investigated the function of this synthase in bloodstream-form parasites by studying the effect of a conditional knockout of acyl carrier protein (ACP), a key player in this fatty acid synthase pathway. We found that ACP depletion not only caused small changes in cellular phospholipids but also, surprisingly, caused changes in the kinetoplast. This structure, which contains the mitochondrial genome in the form of a giant network of several thousand interlocked DNA rings (kinetoplast DNA [kDNA]), became larger in some cells and smaller or absent in others. We observed the same pattern in isolated networks viewed by either fluorescence or electron microscopy. We found that the changes in kDNA size were not due to the disruption of replication but, instead, to a defect in segregation. kDNA segregation is mediated by the tripartite attachment complex (TAC), and we hypothesize that one of the TAC components, a differentiated region of the mitochondrial double membrane, has an altered phospholipid composition when ACP is depleted. We further speculate that this compositional change affects TAC function, and thus kDNA segregation.
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The killing of African trypanosomes by ethidium bromide. PLoS Pathog 2010; 6:e1001226. [PMID: 21187912 PMCID: PMC3002999 DOI: 10.1371/journal.ppat.1001226] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Accepted: 11/11/2010] [Indexed: 11/19/2022] Open
Abstract
Introduced in the 1950s, ethidium bromide (EB) is still used as an anti-trypanosomal drug for African cattle although its mechanism of killing has been unclear and controversial. EB has long been known to cause loss of the mitochondrial genome, named kinetoplast DNA (kDNA), a giant network of interlocked minicircles and maxicircles. However, the existence of viable parasites lacking kDNA (dyskinetoplastic) led many to think that kDNA loss could not be the mechanism of killing. When recent studies indicated that kDNA is indeed essential in bloodstream trypanosomes and that dyskinetoplastic cells survive only if they have a compensating mutation in the nuclear genome, we investigated the effect of EB on kDNA and its replication. We here report some remarkable effects of EB. Using EM and other techniques, we found that binding of EB to network minicircles is low, probably because of their association with proteins that prevent helix unwinding. In contrast, covalently-closed minicircles that had been released from the network for replication bind EB extensively, causing them, after isolation, to become highly supertwisted and to develop regions of left-handed Z-DNA (without EB, these circles are fully relaxed). In vivo, EB causes helix distortion of free minicircles, preventing replication initiation and resulting in kDNA loss and cell death. Unexpectedly, EB also kills dyskinetoplastic trypanosomes, lacking kDNA, by inhibiting nuclear replication. Since the effect on kDNA occurs at a >10-fold lower EB concentration than that on nuclear DNA, we conclude that minicircle replication initiation is likely EB's most vulnerable target, but the effect on nuclear replication may also contribute to cell killing.
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Worthen C, Jensen BC, Parsons M. Diverse effects on mitochondrial and nuclear functions elicited by drugs and genetic knockdowns in bloodstream stage Trypanosoma brucei. PLoS Negl Trop Dis 2010; 4:e678. [PMID: 20454560 PMCID: PMC2864271 DOI: 10.1371/journal.pntd.0000678] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 03/23/2010] [Indexed: 01/01/2023] Open
Abstract
Background The options for treating the fatal disease human African trypanosomiasis are limited to a few drugs that are toxic or facing increasing resistance. New drugs that kill the causative agents, subspecies of Trypanosoma brucei, are therefore urgently needed. Little is known about the cellular mechanisms that lead to death of the pathogenic bloodstream stage. Methodology/Principal Findings We therefore conducted the first side by side comparison of the cellular effects of multiple death inducers that target different systems in bloodstream form parasites, including six drugs (pentamidine, prostaglandin D2, quercetin, etoposide, camptothecin, and a tetrahydroquinoline) and six RNAi knockdowns that target distinct cellular functions. All compounds tested were static at low concentrations and killed at high concentrations. Dead parasites were rapidly quantified by forward and side scatter during flow cytometry, as confirmed by ethidium homodimer and esterase staining, making these assays convenient for quantitating parasite death. The various treatments yielded different combinations of defects in mitochondrial potential, reactive oxygen species, cell cycle, and genome segregation. No evidence was seen for phosphatidylserine exposure, a marker of apoptosis. Reduction in ATP levels lagged behind decreases in live cell number. Even when the impact on growth was similar at 24 hours, drug-treated cells showed dramatic differences in their ability to further proliferate, demonstrating differences in the reversibility of effects induced by the diverse compounds. Conclusions/Significance Parasites showed different phenotypes depending on the treatment, but none of them were clear predictors of whether apparently live cells could go on to proliferate after drugs were removed. We therefore suggest that clonal proliferation assays may be a useful step in selecting anti-trypanosomal compounds for further development. Elucidating the genetic or biochemical events initiated by the compounds with the most profound effects on subsequent proliferation may identify new means to activate death pathways. The parasite Trypanosoma brucei causes human African trypanosomiasis, which is fatal unless treated. Currently used drugs are toxic, difficult to administer, and often are no longer effective due to drug resistance. The search for new drugs is long and expensive, and determining which compounds are worth pursuing is a key challenge in that process. In this study we sought to determine whether different compounds elicited different responses in the mammalian-infective stage of the parasite. We also examined whether genetic knockdown of parasite molecules led to similar responses. Our results show that, depending on the treatment, the replication of the parasite genomes, proper division of the cell, and mitochondrial function can be affected. Surprisingly, these different responses were not able to predict which compounds affected the long term proliferative potential of T. brucei. We found that some of the compounds had irreversible effects on the parasites within one day, so that even cells that appeared healthy could not proliferate. We suggest that determining which compounds set the parasites on a one-way journey to death may provide a means of identifying those that could lead to drugs with high efficacy.
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Affiliation(s)
- Christal Worthen
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Bryan C. Jensen
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
| | - Marilyn Parsons
- Seattle Biomedical Research Institute, Seattle, Washington, United States of America
- Department of Global Health, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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Drosophila topo IIIalpha is required for the maintenance of mitochondrial genome and male germ-line stem cells. Proc Natl Acad Sci U S A 2010; 107:6228-33. [PMID: 20308575 DOI: 10.1073/pnas.1001855107] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Topoisomerase IIIalpha (topo IIIalpha), a member of the conserved Type IA subfamily of topoisomerases, is required for the cell proliferation in mitotic tissues, but has a lesser effect on DNA endoreplication. The top3alpha gene encodes two forms of protein by utilizing alternative translation initiation sites: one (short form) with the nuclear localization signal only, exclusively localized in the nuclei, and the other (long form), retaining a mitochondrial import sequence at the N-terminus and the nuclear localization sequence at the C-terminus, localized primarily in the mitochondria, though with a small portion in the nuclei. Both forms of topo IIIalpha can rescue the viability of null mutants of top3alpha. No apparent defect is associated with the flies rescued by the long form; short-form-rescued flies (referred to as M1L), however, exhibit defects in fertilities. M1L females are sterile. They can lay eggs but with mitochondrial DNA (mtDNA) copy number and ATP content decreased by 20- and 2- to 3-fold, respectively, and they fail to hatch. Of the newly eclosed M1L males, 33% are completely sterile, whereas the rest have residual fertilities that are quickly lost in 6 days. The fertility loss of M1L males is caused by the disruption of the individualization complex and a progressive loss of germ-line stem cells. This study implicates topo IIIalpha in the maintenance of mtDNA and male germ-line stem cells, and thus is a causative candidate for genetic disorders associated with mtDNA depletion.
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Liu B, Yildirir G, Wang J, Tolun G, Griffith JD, Englund PT. TbPIF1, a Trypanosoma brucei mitochondrial DNA helicase, is essential for kinetoplast minicircle replication. J Biol Chem 2010; 285:7056-7066. [PMID: 20042610 PMCID: PMC2844155 DOI: 10.1074/jbc.m109.084038] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 12/22/2009] [Indexed: 12/17/2023] Open
Abstract
Kinetoplast DNA, the trypanosome mitochondrial genome, is a network of interlocked DNA rings including several thousand minicircles and a few dozen maxicircles. Minicircles replicate after release from the network, and their progeny reattach. Remarkably, trypanosomes have six mitochondrial DNA helicases related to yeast PIF1 helicase. Here we report that one of the six, TbPIF1, functions in minicircle replication. RNA interference (RNAi) of TbPIF1 causes a growth defect and kinetoplast DNA loss. Minicircle replication intermediates decrease during RNAi, and there is an accumulation of multiply interlocked, covalently closed minicircle dimers (fraction U). In studying the significance of fraction U, we found that this species also accumulates during RNAi of mitochondrial topoisomerase II. These data indicate that one function of TbPIF1 is an involvement, together with topoisomerase II, in the segregation of minicircle progeny.
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Affiliation(s)
- Beiyu Liu
- From the Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, Maryland 21205 and
| | - Gokben Yildirir
- From the Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, Maryland 21205 and
| | - Jianyang Wang
- From the Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, Maryland 21205 and
| | - Gökhan Tolun
- the Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Jack D. Griffith
- the Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Paul T. Englund
- From the Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, Maryland 21205 and
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Tang SC, Shapiro TA. Newly identified antibacterial compounds are topoisomerase poisons in African trypanosomes. Antimicrob Agents Chemother 2010; 54:620-6. [PMID: 20008775 PMCID: PMC2812133 DOI: 10.1128/aac.01025-09] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 09/24/2009] [Accepted: 12/06/2009] [Indexed: 11/20/2022] Open
Abstract
Human African trypanosomiasis, caused by the Trypanosoma brucei protozoan parasite, is fatal when left untreated. Current therapies are antiquated, and there is a need for new pharmacologic agents against T. brucei targets that have no human ortholog. Trypanosomes have a single mitochondrion with a unique mitochondrial DNA, known as kinetoplast DNA (kDNA), a topologically complex network that contains thousands of interlocking circular DNAs, termed minicircles (approximately 1 kb) and maxicircles (approximately 23 kb). Replication of kDNA depends on topoisomerases, enzymes that catalyze reactions that change DNA topology. T. brucei has an unusual type IA topoisomerase that is dedicated to kDNA metabolism. This enzyme has no ortholog in humans, and RNA interference (RNAi) studies have shown that it is essential for parasite survival, making it an ideal drug target. In a large chemical library screen, two compounds were recently identified as poisons of bacterial topoisomerase IA. We found that these compounds are trypanocidal in the low micromolar range and that they promote the formation of linearized minicircles covalently bound to protein on the 5' end, consistent with the poisoning of mitochondrial topoisomerase IA. Surprisingly, however, band depletion studies showed that it is topoisomerase IImt, and not topoisomerase IAmt, that is trapped. Both compounds are planar aromatic polycyclic structures that intercalate into and unwind DNA. These findings reinforce the utility of topoisomerase IImt as a target for development of new drugs for African sleeping sickness.
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Affiliation(s)
- Sonya C. Tang
- Division of Clinical Pharmacology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Theresa A. Shapiro
- Division of Clinical Pharmacology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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A mitochondrial DNA primase is essential for cell growth and kinetoplast DNA replication in Trypanosoma brucei. Mol Cell Biol 2010; 30:1319-28. [PMID: 20065037 DOI: 10.1128/mcb.01231-09] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Kinetoplast DNA in African trypanosomes contains a novel form of mitochondrial DNA consisting of thousands of minicircles and dozens of maxicircles topologically interlocked to form a two-dimensional sheet. The replication of this unusual form of mitochondrial DNA has been studied for more than 30 years, and although a large number of kinetoplast replication genes and proteins have been identified, in vitro replication of these DNAs has not been possible since a kinetoplast DNA primase has not been available. We describe here a Trypanosoma brucei DNA primase gene, PRI1, that encodes a 70-kDa protein that localizes to the kinetoplast and is essential for both cell growth and kinetoplast DNA replication. The expression of PRI1 mRNA is cyclic and reaches maximum levels at a time corresponding to duplication of the kinetoplast DNA. A 3'-hydroxyl-terminated oligoriboadenylate is synthesized on a poly(dT) template by a recombinant form of the PRI1 protein and is subsequently elongated by DNA polymerase and added dATP. Poly(dA) synthesis is dependent on both PRI1 protein and ATP and is inhibited by RNase H treatment of the product of PRI1 synthesis.
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Trypanosomes have six mitochondrial DNA helicases with one controlling kinetoplast maxicircle replication. Mol Cell 2009; 35:490-501. [PMID: 19646907 DOI: 10.1016/j.molcel.2009.07.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2008] [Revised: 05/19/2009] [Accepted: 07/14/2009] [Indexed: 11/23/2022]
Abstract
Kinetoplast DNA (kDNA), the trypanosome mitochondrial DNA, contains thousands of minicircles and dozens of maxicircles interlocked in a giant network. Remarkably, Trypanosoma brucei's genome encodes 8 PIF1-like helicases, 6 of which are mitochondrial. We now show that TbPIF2 is essential for maxicircle replication. Maxicircle abundance is controlled by TbPIF2 level, as RNAi of this helicase caused maxicircle loss, and its overexpression caused a 3- to 6-fold increase in maxicircle abundance. This regulation of maxicircle level is mediated by the TbHslVU protease. Previous experiments demonstrated that RNAi knockdown of TbHslVU dramatically increased abundance of minicircles and maxicircles, presumably because a positive regulator of their synthesis escaped proteolysis and allowed synthesis to continue. Here, we found that TbPIF2 level increases following RNAi of the protease. Therefore, this helicase is a TbHslVU substrate and an example of a positive regulator, thus providing a molecular mechanism for controlling maxicircle replication.
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Bruhn DF, Mozeleski B, Falkin L, Klingbeil MM. Mitochondrial DNA polymerase POLIB is essential for minicircle DNA replication in African trypanosomes. Mol Microbiol 2009; 75:1414-25. [PMID: 20132449 DOI: 10.1111/j.1365-2958.2010.07061.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The unique mitochondrial DNA of trypanosomes is a catenated network of minicircles and maxicircles called kinetoplast DNA (kDNA). The network is essential for survival, and requires an elaborate topoisomerase-mediated release and reattachment mechanism for minicircle theta structure replication. At least seven DNA polymerases (pols) are involved in kDNA transactions, including three essential proteins related to bacterial DNA pol I (POLIB, POLIC and POLID). How Trypanosoma brucei utilizes multiple DNA pols to complete the topologically complex task of kDNA replication is unknown. To fill this gap in knowledge we investigated the cellular role of POLIB using RNA interference (RNAi). POLIB silencing resulted in growth inhibition and progressive loss of kDNA networks. Additionally, unreplicated covalently closed precursors become the most abundant minicircle replication intermediate as minicircle copy number declines. Leading and lagging strand minicircle progeny similarly declined during POLIB silencing, indicating POLIB had no apparent strand preference. Interestingly, POLIB RNAi led to the accumulation of a novel population of free minicircles that is composed mainly of covalently closed minicircle dimers. Based on these data, we propose that POLIB performs an essential role at the core of the minicircle replication machinery.
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Affiliation(s)
- David F Bruhn
- Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA
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Stem-loop silencing reveals that a third mitochondrial DNA polymerase, POLID, is required for kinetoplast DNA replication in trypanosomes. EUKARYOTIC CELL 2008; 7:2141-6. [PMID: 18849470 DOI: 10.1128/ec.00199-08] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Kinetoplast DNA (kDNA), the mitochondrial genome of trypanosomes, is a catenated network containing thousands of minicircles and tens of maxicircles. The topological complexity dictates some unusual features including a topoisomerase-mediated release-and-reattachment mechanism for minicircle replication and at least six mitochondrial DNA polymerases (Pols) for kDNA transactions. Previously, we identified four family A DNA Pols from Trypanosoma brucei with similarity to bacterial DNA Pol I and demonstrated that two (POLIB and POLIC) were essential for maintaining the kDNA network, while POLIA was not. Here, we used RNA interference to investigate the function of POLID in procyclic T. brucei. Stem-loop silencing of POLID resulted in growth arrest and the progressive loss of the kDNA network. Additional defects in kDNA replication included a rapid decline in minicircle and maxicircle abundance and a transient accumulation of minicircle replication intermediates before loss of the kDNA network. These results demonstrate that POLID is a third essential DNA Pol required for kDNA replication. While other eukaryotes utilize a single DNA Pol (Pol gamma) for replication of mitochondrial DNA, T. brucei requires at least three to maintain the complex kDNA network.
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