1
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Hustmyer CM, Landick R. Bacterial chromatin proteins, transcription, and DNA topology: Inseparable partners in the control of gene expression. Mol Microbiol 2024; 122:81-112. [PMID: 38847475 PMCID: PMC11260248 DOI: 10.1111/mmi.15283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 05/10/2024] [Accepted: 05/13/2024] [Indexed: 06/15/2024]
Abstract
DNA in bacterial chromosomes is organized into higher-order structures by DNA-binding proteins called nucleoid-associated proteins (NAPs) or bacterial chromatin proteins (BCPs). BCPs often bind to or near DNA loci transcribed by RNA polymerase (RNAP) and can either increase or decrease gene expression. To understand the mechanisms by which BCPs alter transcription, one must consider both steric effects and the topological forces that arise when DNA deviates from its fully relaxed double-helical structure. Transcribing RNAP creates DNA negative (-) supercoils upstream and positive (+) supercoils downstream whenever RNAP and DNA are unable to rotate freely. This (-) and (+) supercoiling generates topological forces that resist forward translocation of DNA through RNAP unless the supercoiling is constrained by BCPs or relieved by topoisomerases. BCPs also may enhance topological stress and overall can either inhibit or aid transcription. Here, we review current understanding of how RNAP, BCPs, and DNA topology interplay to control gene expression.
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Affiliation(s)
| | - Robert Landick
- Department of Biochemistry, University of Wisconsin-Madison
- Department of Bacteriology, University of Wisconsin-Madison
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2
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Gil-Gomez A, Rest JS. Wiring Between Close Nodes in Molecular Networks Evolves More Quickly Than Between Distant Nodes. Mol Biol Evol 2024; 41:msae098. [PMID: 38768245 PMCID: PMC11136681 DOI: 10.1093/molbev/msae098] [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: 12/21/2023] [Revised: 04/14/2024] [Accepted: 05/15/2024] [Indexed: 05/22/2024] Open
Abstract
As species diverge, a wide range of evolutionary processes lead to changes in protein-protein interaction (PPI) networks and metabolic networks. The rate at which molecular networks evolve is an important question in evolutionary biology. Previous empirical work has focused on interactomes from model organisms to calculate rewiring rates, but this is limited by the relatively small number of species and sparse nature of network data across species. We present a proxy for variation in network topology: variation in drug-drug interactions (DDIs), obtained by studying drug combinations (DCs) across taxa. Here, we propose the rate at which DDIs change across species as an estimate of the rate at which the underlying molecular network changes as species diverge. We computed the evolutionary rates of DDIs using previously published data from a high-throughput study in gram-negative bacteria. Using phylogenetic comparative methods, we found that DDIs diverge rapidly over short evolutionary time periods, but that divergence saturates over longer time periods. In parallel, we mapped drugs with known targets in PPI and cofunctional networks. We found that the targets of synergistic DDIs are closer in these networks than other types of DCs and that synergistic interactions have a higher evolutionary rate, meaning that nodes that are closer evolve at a faster rate. Future studies of network evolution may use DC data to gain larger-scale perspectives on the details of network evolution within and between species.
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Affiliation(s)
- Alejandro Gil-Gomez
- Department of Ecology and Evolution, Laufer Center for Physical and Quantitative Biology, Stony Brook University, 650 Life Sciences, Stony Brook, NY 11794-4254, USA
| | - Joshua S Rest
- Department of Ecology and Evolution, Laufer Center for Physical and Quantitative Biology, Stony Brook University, 650 Life Sciences, Stony Brook, NY 11794-4254, USA
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3
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Liao Q, Ren Z, Wiesler EE, Fuqua C, Wang X. A dicentric bacterial chromosome requires XerC/D site-specific recombinases for resolution. Curr Biol 2022; 32:3609-3618.e7. [PMID: 35797999 PMCID: PMC9398967 DOI: 10.1016/j.cub.2022.06.050] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 05/24/2022] [Accepted: 06/15/2022] [Indexed: 12/18/2022]
Abstract
Unlike eukaryotes and archaea, which have multiple replication origins on their chromosomes, bacterial chromosomes usually contain a single replication origin.1 Here, we discovered a dicentric bacterial chromosome with two replication origins, which has resulted from the fusion of the circular and linear chromosomes in Agrobacterium tumefaciens. The fused chromosome is well tolerated, stably maintained, and retains similar subcellular organization and genome-wide DNA interactions found for the bipartite chromosomes. Strikingly, the two replication origins and their partitioning systems are both functional and necessary for cell survival. Finally, we discovered that the site-specific recombinases XerC and XerD2 are essential in cells harboring the fused chromosome but not in cells with bipartite chromosomes. Analysis of actively dividing cells suggests a model in which XerC/D are required to recombine the sister fusion chromosomes when the two centromeres on the same chromosome are segregated to opposite cell poles. Thus, faithful segregation of dicentric chromosomes in bacteria can occur because of site-specific recombination between the sister chromatids during chromosome partitioning. Our study provides a natural comparative platform to examine a bacterial chromosome with multiple origins and a possible explanation for the fundamental difference in bacterial genome architecture relative to eukaryotes and archaea.1.
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Affiliation(s)
- Qin Liao
- Department of Biology, Indiana University, 1001 E 3(rd) Street, Bloomington, IN 47405, USA
| | - Zhongqing Ren
- Department of Biology, Indiana University, 1001 E 3(rd) Street, Bloomington, IN 47405, USA
| | - Emma E Wiesler
- Department of Biology, Indiana University, 1001 E 3(rd) Street, Bloomington, IN 47405, USA
| | - Clay Fuqua
- Department of Biology, Indiana University, 1001 E 3(rd) Street, Bloomington, IN 47405, USA
| | - Xindan Wang
- Department of Biology, Indiana University, 1001 E 3(rd) Street, Bloomington, IN 47405, USA.
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4
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Colin A, Micali G, Faure L, Cosentino Lagomarsino M, van Teeffelen S. Two different cell-cycle processes determine the timing of cell division in Escherichia coli. eLife 2021; 10:67495. [PMID: 34612203 PMCID: PMC8555983 DOI: 10.7554/elife.67495] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 10/05/2021] [Indexed: 11/13/2022] Open
Abstract
Cells must control the cell cycle to ensure that key processes are brought to completion. In Escherichia coli, it is controversial whether cell division is tied to chromosome replication or to a replication-independent inter-division process. A recent model suggests instead that both processes may limit cell division with comparable odds in single cells. Here, we tested this possibility experimentally by monitoring single-cell division and replication over multiple generations at slow growth. We then perturbed cell width, causing an increase of the time between replication termination and division. As a consequence, replication became decreasingly limiting for cell division, while correlations between birth and division and between subsequent replication-initiation events were maintained. Our experiments support the hypothesis that both chromosome replication and a replication-independent inter-division process can limit cell division: the two processes have balanced contributions in non-perturbed cells, while our width perturbations increase the odds of the replication-independent process being limiting.
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Affiliation(s)
- Alexandra Colin
- Microbial Morphogenesis and Growth Laboratory, Institut Pasteur, Paris, France
| | - Gabriele Micali
- Department of Environmental Microbiology, Dübendorf, Switzerland.,Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland
| | - Louis Faure
- Microbial Morphogenesis and Growth Laboratory, Institut Pasteur, Paris, France
| | - Marco Cosentino Lagomarsino
- IFOM, FIRC Institute of Molecular Oncology, Milan, Italy.,Physics Department, University of Milan, and INFN, Milan, Italy
| | - Sven van Teeffelen
- Microbial Morphogenesis and Growth Laboratory, Institut Pasteur, Paris, France.,Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montréal, Canada
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5
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Zhang H, Venkatesan S, Nan B. Myxococcus xanthus as a Model Organism for Peptidoglycan Assembly and Bacterial Morphogenesis. Microorganisms 2021; 9:microorganisms9050916. [PMID: 33923279 PMCID: PMC8144978 DOI: 10.3390/microorganisms9050916] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 04/20/2021] [Accepted: 04/22/2021] [Indexed: 11/16/2022] Open
Abstract
A fundamental question in biology is how cell shapes are genetically encoded and enzymatically generated. Prevalent shapes among walled bacteria include spheres and rods. These shapes are chiefly determined by the peptidoglycan (PG) cell wall. Bacterial division results in two daughter cells, whose shapes are predetermined by the mother. This makes it difficult to explore the origin of cell shapes in healthy bacteria. In this review, we argue that the Gram-negative bacterium Myxococcus xanthus is an ideal model for understanding PG assembly and bacterial morphogenesis, because it forms rods and spheres at different life stages. Rod-shaped vegetative cells of M. xanthus can thoroughly degrade their PG and form spherical spores. As these spores germinate, cells rebuild their PG and reestablish rod shape without preexisting templates. Such a unique sphere-to-rod transition provides a rare opportunity to visualize de novo PG assembly and rod-like morphogenesis in a well-established model organism.
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6
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Martins-Duarte ÉS, Sheiner L, Reiff SB, de Souza W, Striepen B. Replication and partitioning of the apicoplast genome of Toxoplasma gondii is linked to the cell cycle and requires DNA polymerase and gyrase. Int J Parasitol 2021; 51:493-504. [PMID: 33581138 PMCID: PMC8113025 DOI: 10.1016/j.ijpara.2020.11.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 10/30/2020] [Accepted: 11/08/2020] [Indexed: 10/26/2022]
Abstract
Apicomplexans are the causative agents of numerous important infectious diseases including malaria and toxoplasmosis. Most of them harbour a chloroplast-like organelle called the apicoplast that is essential for the parasites' metabolism and survival. While most apicoplast proteins are nuclear encoded, the organelle also maintains its own genome, a 35 kb circle. In this study we used Toxoplasma gondii to identify and characterise essential proteins involved in apicoplast genome replication and to understand how apicoplast genome segregation unfolds over time. We demonstrated that the DNA replication enzymes Prex, DNA gyrase and DNA single stranded binding protein localise to the apicoplast. We show in knockdown experiments that apicoplast DNA Gyrase A and B, and Prex are required for apicoplast genome replication and growth of the parasite. Analysis of apicoplast genome replication by structured illumination microscopy in T. gondii tachyzoites showed that apicoplast nucleoid division and segregation initiate at the beginning of S phase and conclude during mitosis. Thus, the replication and division of the apicoplast nucleoid is highly coordinated with nuclear genome replication and mitosis. Our observations highlight essential components of apicoplast genome maintenance and shed light on the timing of this process in the context of the overall parasite cell cycle.
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Affiliation(s)
- Érica S Martins-Duarte
- Laboratório de Quimioterapia de Protozoários Egler Chiari, Departamento de Parasitologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil; Núcleo de Biologia Estrutural e Bioimagens (CENABIO) - Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Biomagens (INBEB), Rio de Janeiro, RJ, Brazil.
| | - Lilach Sheiner
- Wellcome Centre for Integrative Parasitology, University of Glasgow, 120 University Place Glasgow, United Kingdom
| | - Sarah B Reiff
- Department of Cellular Biology, University of Georgia, Athens, GA, USA
| | - Wanderley de Souza
- Núcleo de Biologia Estrutural e Bioimagens (CENABIO) - Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Biomagens (INBEB), Rio de Janeiro, RJ, Brazil; Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil
| | - Boris Striepen
- Department of Cellular Biology, University of Georgia, Athens, GA, USA; Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA. USA
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7
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Dersch S, Reimold C, Stoll J, Breddermann H, Heimerl T, Defeu Soufo HJ, Graumann PL. Polymerization of Bacillus subtilis MreB on a lipid membrane reveals lateral co-polymerization of MreB paralogs and strong effects of cations on filament formation. BMC Mol Cell Biol 2020; 21:76. [PMID: 33148162 PMCID: PMC7641798 DOI: 10.1186/s12860-020-00319-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 10/18/2020] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND MreB is a bacterial ortholog of actin and forms mobile filaments underneath the cell membrane, perpendicular to the long axis of the cell, which play a crucial role for cell shape maintenance. We wished to visualize Bacillus subtilis MreB in vitro and therefore established a protocol to obtain monomeric protein, which could be polymerized on a planar membrane system, or associated with large membrane vesicles. RESULTS Using a planar membrane system and electron microscopy, we show that Bacillus subtilis MreB forms bundles of filaments, which can branch and fuse, with an average width of 70 nm. Fluorescence microscopy of non-polymerized YFP-MreB, CFP-Mbl and mCherry-MreBH proteins showed uniform binding to the membrane, suggesting that 2D diffusion along the membrane could facilitate filament formation. After addition of divalent magnesium and calcium ions, all three proteins formed highly disordered sheets of filaments that could split up or merge, such that at high protein concentration, MreB and its paralogs generated a network of filaments extending away from the membrane. Filament formation was positively affected by divalent ions and negatively by monovalent ions. YFP-MreB or CFP-Mbl also formed filaments between two adjacent membranes, which frequently has a curved appearance. New MreB, Mbl or MreBH monomers could add to the lateral side of preexisting filaments, and MreB paralogs co-polymerized, indicating direct lateral interaction between MreB paralogs. CONCLUSIONS Our data show that B. subtilis MreB paralogs do not easily form ordered filaments in vitro, possibly due to extensive lateral contacts, but can co-polymerise. Monomeric MreB, Mbl and MreBH uniformly bind to a membrane, and form irregular and frequently split up filamentous structures, facilitated by the addition of divalent ions, and counteracted by monovalent ions, suggesting that intracellular potassium levels may be one important factor to counteract extensive filament formation and filament splitting in vivo.
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Affiliation(s)
- Simon Dersch
- Centre for Synthetic Microbiology (SYNMIKRO) Hans-Meerwein Strasse 6, Philipps-Universität Marburg, 35032, Marburg, Germany.,Fachbereich Chemie, Hans-Meerwein Strasse, Philipps-Universität Marburg, 35032, Marburg, Germany
| | - Christian Reimold
- Centre for Synthetic Microbiology (SYNMIKRO) Hans-Meerwein Strasse 6, Philipps-Universität Marburg, 35032, Marburg, Germany.,Fachbereich Chemie, Hans-Meerwein Strasse, Philipps-Universität Marburg, 35032, Marburg, Germany
| | - Joshua Stoll
- Centre for Synthetic Microbiology (SYNMIKRO) Hans-Meerwein Strasse 6, Philipps-Universität Marburg, 35032, Marburg, Germany.,Fachbereich Chemie, Hans-Meerwein Strasse, Philipps-Universität Marburg, 35032, Marburg, Germany
| | | | - Thomas Heimerl
- Centre for Synthetic Microbiology (SYNMIKRO) Hans-Meerwein Strasse 6, Philipps-Universität Marburg, 35032, Marburg, Germany.,Fachbereich Biologie, Karl-von-Frisch-Straße 10, Philipps-Universität Marburg, 35032, Marburg, Germany
| | - Hervé Joel Defeu Soufo
- Department of Microsystems Engineering - IMTEK, University of Freiburg, 79110, Freiburg, Germany
| | - Peter L Graumann
- Centre for Synthetic Microbiology (SYNMIKRO) Hans-Meerwein Strasse 6, Philipps-Universität Marburg, 35032, Marburg, Germany. .,Fachbereich Chemie, Hans-Meerwein Strasse, Philipps-Universität Marburg, 35032, Marburg, Germany.
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8
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Intracellular ion concentrations and cation-dependent remodelling of bacterial MreB assemblies. Sci Rep 2020; 10:12002. [PMID: 32686735 PMCID: PMC7371711 DOI: 10.1038/s41598-020-68960-w] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 06/08/2020] [Indexed: 12/20/2022] Open
Abstract
Here, we measured the concentrations of several ions in cultivated Gram-negative and Gram-positive bacteria, and analyzed their effects on polymer formation by the actin homologue MreB. We measured potassium, sodium, chloride, calcium and magnesium ion concentrations in Leptospira interrogans, Bacillus subtilis and Escherichia coli. Intracellular ionic strength contributed from these ions varied within the 130–273 mM range. The intracellular sodium ion concentration range was between 122 and 296 mM and the potassium ion concentration range was 5 and 38 mM. However, the levels were significantly influenced by extracellular ion levels. L. interrogans, Rickettsia rickettsii and E. coli MreBs were heterologously expressed and purified from E. coli using a novel filtration method to prepare MreB polymers. The structures and stability of Alexa-488 labeled MreB polymers, under varying ionic strength conditions, were investigated by confocal microscopy and MreB polymerization rates were assessed by measuring light scattering. MreB polymerization was fastest in the presence of monovalent cations in the 200–300 mM range. MreB filaments showed high stability in this concentration range and formed large assemblies of tape-like bundles that transformed to extensive sheets at higher ionic strengths. Changing the calcium concentration from 0.2 to 0 mM and then to 2 mM initialized rapid remodelling of MreB polymers.
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9
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Random Chromosome Partitioning in the Polyploid Bacterium Thermus thermophilus HB27. G3-GENES GENOMES GENETICS 2019; 9:1249-1261. [PMID: 30792193 PMCID: PMC6469415 DOI: 10.1534/g3.119.400086] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Little is known about chromosome segregation in polyploid prokaryotes. In this study, whether stringent or variable chromosome segregation occurs in polyploid thermophilic bacterium Thermus thermophilus was analyzed. A stable heterozygous strain (HL01) containing two antibiotic resistance markers at one gene locus was generated. The inheritance of the two alleles in the progeny of the heterozygous strain was then followed. During incubation without selection pressure, the fraction of heterozygous cells decreased and that of homozygous cells increased, while the relative abundance of each allele in the whole population remained constant, suggesting chromosome segregation had experienced random event. Consistently, in comparison with Bacillus subtilis in which the sister chromosomes were segregated equally, the ratios of DNA content in two daughter cells of T. thermophilus had a broader distribution and a larger standard deviation, indicating that the DNA content in the two daughter cells was not always identical. Further, the protein homologs (i.e., ParA and MreB) which have been suggested to be involved in bacterial chromosome partitioning did not actively participate in the chromosome segregation in T. thermophilus. Therefore, it seems that protein-based chromosome segregation machineries are less critical for the polyploid T. thermophilus, and chromosome segregation in this bacterium are not stringently controlled but tend to be variable, and random segregation can occur.
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10
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Zepeda Gurrola RC, Fu Y, Rodríguez Luna IC, Benítez Cardoza CG, López López MDJ, López Vidal Y, Gutíerrez GRA, Rodríguez Pérez MA, Guo X. Novel protein interactions with an actin homolog (MreB) of Helicobacter pylori determined by bacterial two-hybrid system. Microbiol Res 2017; 201:39-45. [PMID: 28602400 DOI: 10.1016/j.micres.2017.04.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 03/24/2017] [Accepted: 04/22/2017] [Indexed: 02/06/2023]
Abstract
The bacterium Helicobacter pylori infects more than 50% of the world population and causes several gastroduodenal diseases, including gastric cancer. Nevertheless, we still need to explore some protein interactions that may be involved in pathogenesis. MreB, an actin homolog, showed some special characteristics in previous studies, indicating that it could have different functions. Protein functions could be realized via protein-protein interactions. In the present study, the MreB protein from H. pylori 26695 fused with two tags 10×His and GST in tandem was overexpressed and purified from Escherchia coli. The purified recombinant protein was used to perform a pull-down assay with H. pylori 26695 cell lysate. The pulled-down proteins were identified by mass spectrometry (MALDI-TOF), in which the known important proteins related to morphogenesis were absent but several proteins related to pathogenesis process were observed. The bacterial two-hybrid system was further used to evaluate the protein interactions and showed that new interactions of MreB respectively with VacA, UreB, HydB, HylB and AddA were confirmed but the interaction MreB-MreC was not validated. These results indicated that the protein MreB in H. pylori has a distinct interactome, does not participate in cell morphogenesis via MreB-MreC but could be related to pathogenesis.
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Affiliation(s)
| | - Yajuan Fu
- Centro de Biotecnología Genómica, Instituto Politécnico Nacional, Cd. Reynosa Tamaulipas, Mexico
| | | | | | | | - Yolanda López Vidal
- Facultad de Medicina, División de Investigación, Universidad Nacional Autónoma de Mexico
| | - Germán Rubén Aguilar Gutíerrez
- Centro de Investigación sobre Enfermedades Infecciosas, Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico
| | - Mario A Rodríguez Pérez
- Centro de Biotecnología Genómica, Instituto Politécnico Nacional, Cd. Reynosa Tamaulipas, Mexico
| | - Xianwu Guo
- Centro de Biotecnología Genómica, Instituto Politécnico Nacional, Cd. Reynosa Tamaulipas, Mexico.
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11
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Phosphorylation of CMG helicase and Tof1 is required for programmed fork arrest. Proc Natl Acad Sci U S A 2016; 113:E3639-48. [PMID: 27298353 DOI: 10.1073/pnas.1607552113] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Several important physiological transactions, including control of replicative life span (RLS), prevention of collision between replication and transcription, and cellular differentiation, require programmed replication fork arrest (PFA). However, a general mechanism of PFA has remained elusive. We previously showed that the Tof1-Csm3 fork protection complex is essential for PFA by antagonizing the Rrm3 helicase that displaces nonhistone protein barriers that impede fork progression. Here we show that mutations of Dbf4-dependent kinase (DDK) of Saccharomyces cerevisiae, but not other DNA replication factors, greatly reduced PFA at replication fork barriers in the spacer regions of the ribosomal DNA array. A key target of DDK is the mini chromosome maintenance (Mcm) 2-7 complex, which is known to require phosphorylation by DDK to form an active CMG [Cdc45 (cell division cycle gene 45), Mcm2-7, GINS (Go, Ichi, Ni, and San)] helicase. In vivo experiments showed that mutational inactivation of DDK caused release of Tof1 from the chromatin fractions. In vitro binding experiments confirmed that CMG and/or Mcm2-7 had to be phosphorylated for binding to phospho-Tof1-Csm3 but not to its dephosphorylated form. Suppressor mutations that bypass the requirement for Mcm2-7 phosphorylation by DDK restored PFA in the absence of the kinase. Retention of Tof1 in the chromatin fraction and PFA in vivo was promoted by the suppressor mcm5-bob1, which bypassed DDK requirement, indicating that under this condition a kinase other than DDK catalyzed the phosphorylation of Tof1. We propose that phosphorylation regulates the recruitment and retention of Tof1-Csm3 by the replisome and that this complex antagonizes the Rrm3 helicase, thereby promoting PFA, by preserving the integrity of the Fob1-Ter complex.
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12
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PprA Protein Is Involved in Chromosome Segregation via Its Physical and Functional Interaction with DNA Gyrase in Irradiated Deinococcus radiodurans Bacteria. mSphere 2016; 1:mSphere00036-15. [PMID: 27303692 PMCID: PMC4863600 DOI: 10.1128/msphere.00036-15] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 12/09/2015] [Indexed: 11/30/2022] Open
Abstract
D. radiodurans is one of the most radiation-resistant organisms known. This bacterium is able to cope with high levels of DNA lesions generated by exposure to extreme doses of ionizing radiation and to reconstruct a functional genome from hundreds of radiation-induced chromosomal fragments. Here, we identified partners of PprA, a radiation-induced Deinococcus-specific protein, previously shown to be required for radioresistance. Our study leads to three main findings: (i) PprA interacts with DNA gyrase after irradiation, (ii) treatment of cells with novobiocin results in defects in chromosome segregation that are aggravated by the absence of PprA, and (iii) PprA stimulates the decatenation activity of DNA gyrase. Our results extend the knowledge of how D. radiodurans cells survive exposure to extreme doses of gamma irradiation and point out the link between DNA repair, chromosome segregation, and DNA gyrase activities in the radioresistant D. radiodurans bacterium. PprA, a radiation-induced Deinococcus-specific protein, was previously shown to be required for cell survival and accurate chromosome segregation after exposure to ionizing radiation. Here, we used an in vivo approach to determine, by shotgun proteomics, putative PprA partners coimmunoprecipitating with PprA when cells were exposed to gamma rays. Among them, we found the two subunits of DNA gyrase and, thus, chose to focus our work on characterizing the activities of the deinococcal DNA gyrase in the presence or absence of PprA. Loss of PprA rendered cells hypersensitive to novobiocin, an inhibitor of the B subunit of DNA gyrase. We showed that treatment of bacteria with novobiocin resulted in induction of the radiation desiccation response (RDR) regulon and in defects in chromosome segregation that were aggravated by the absence of PprA. In vitro, the deinococcal DNA gyrase, like other bacterial DNA gyrases, possesses DNA negative supercoiling and decatenation activities. These two activities are inhibited in vitro by novobiocin and nalidixic acid, whereas PprA specifically stimulates the decatenation activity of DNA gyrase. Together, these results suggest that PprA plays a major role in chromosome decatenation via its interaction with the deinococcal DNA gyrase when D. radiodurans cells are recovering from exposure to ionizing radiation. IMPORTANCED. radiodurans is one of the most radiation-resistant organisms known. This bacterium is able to cope with high levels of DNA lesions generated by exposure to extreme doses of ionizing radiation and to reconstruct a functional genome from hundreds of radiation-induced chromosomal fragments. Here, we identified partners of PprA, a radiation-induced Deinococcus-specific protein, previously shown to be required for radioresistance. Our study leads to three main findings: (i) PprA interacts with DNA gyrase after irradiation, (ii) treatment of cells with novobiocin results in defects in chromosome segregation that are aggravated by the absence of PprA, and (iii) PprA stimulates the decatenation activity of DNA gyrase. Our results extend the knowledge of how D. radiodurans cells survive exposure to extreme doses of gamma irradiation and point out the link between DNA repair, chromosome segregation, and DNA gyrase activities in the radioresistant D. radiodurans bacterium.
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13
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The actin-like MreB cytoskeleton organizes viral DNA replication in bacteria. Proc Natl Acad Sci U S A 2015; 106:13347-52. [PMID: 19654094 DOI: 10.1073/pnas.0906465106] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Little is known about the organization or proteins involved in membrane-associated replication of prokaryotic genomes. Here we show that the actin-like MreB cytoskeleton of the distantly related bacteria Escherichia coli and Bacillus subtilis is required for efficient viral DNA replication. Detailed analyses of B. subtilis phage ϕ29 showed that the MreB cytoskeleton plays a crucial role in organizing phage DNA replication at the membrane. Thus, phage double-stranded DNA and components of the ϕ29 replication machinery localize in peripheral helix-like structures in a cytoskeleton-dependent way. Importantly, we show that MreB interacts directly with the ϕ29 membrane-protein p16.7, responsible for attaching viral DNA at the cell membrane. Altogether, the results reveal another function for the MreB cytoskeleton and describe a mechanism by which viral DNA replication is organized at the bacterial membrane.
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14
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Wu H, Iwai N, Nakano T, Ooi Y, Ishihara S, Sano K. Route of intrabacterial nanotransportation system for CagA in Helicobacter pylori. Med Mol Morphol 2015; 48:191-203. [PMID: 25707504 DOI: 10.1007/s00795-015-0097-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2014] [Accepted: 02/05/2015] [Indexed: 12/11/2022]
Abstract
Helicobacter pylori (H. pylori) possesses an intrabacterial nanotransportation system (ibNoTS) for transporting CagA and urease within the bacterial cytoplasm; this system is controlled by the extrabacterial environment. The transportation routes of the system have not yet been studied in detail. In this study, we demonstrated by immunoelectron microscopy that CagA localizes closely with the MreB filament in the bacterium, and MreB polymerization inhibitor A22 obstructs ibNoTS for CagA. These findings indicate that the route of ibNoTS for CagA is closely associated with the MreB filament. Because these phenomena were not observed in ibNoTS for urease, the route of ibNoTS for CagA is different from that of ibNoTS for urease as previously suggested. We propose that the route of ibNoTS for CagA is associated with the MreB filament in H. pylori.
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Affiliation(s)
- Hong Wu
- Project Team for Study of Nanotransportation System, Central Research Center, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan. .,Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.
| | - Noritaka Iwai
- Project Team for Study of Nanotransportation System, Central Research Center, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.,Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa, 226-8501, Japan
| | - Takashi Nakano
- Project Team for Study of Nanotransportation System, Central Research Center, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.,Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan
| | - Yukimasa Ooi
- Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.,Infection Control Office, Osaka Medical College Hospital, Osaka, Japan
| | - Sonoko Ishihara
- Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan
| | - Kouichi Sano
- Project Team for Study of Nanotransportation System, Central Research Center, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.,Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan
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15
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Jin M, Chen Y, Xu C, Zhang X. The effect of inhibition of host MreB on the infection of thermophilic phage GVE2 in high temperature environment. Sci Rep 2014; 4:4823. [PMID: 24769758 PMCID: PMC4001104 DOI: 10.1038/srep04823] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Accepted: 04/03/2014] [Indexed: 11/09/2022] Open
Abstract
In eukaryotes, the manipulation of the host actin cytoskeleton is a necessary strategy for viral pathogens to invade host cells. Increasing evidence indicates that the actin homolog MreB of bacteria plays key roles in cell shape formation, cell polarity, cell wall biosynthesis, and chromosome segregation. However, the role of bacterial MreB in the bacteriophage infection is not extensively investigated. To address this issue, in this study, the MreB of thermophilic Geobacillus sp. E263 from a deep-sea hydrothermal field was characterized by inhibiting the MreB polymerization and subsequently evaluating the bacteriophage GVE2 infection. The results showed that the host MreB played important roles in the bacteriophage infection at high temperature. After the host cells were treated with small molecule drug A22 or MP265, the specific inhibitors of MreB polymerization, the adsorption of GVE2 and the replication of GVE2 genome were significantly repressed. The confocal microscopy data revealed that MreB facilitated the GVE2 infection by inducing the polar distribution of virions during the phage infection. Our study contributed novel information to understand the molecular events of the host in response to bacteriophage challenge and extended our knowledge about the host-virus interaction in deep-sea vent ecosystems.
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Affiliation(s)
- Min Jin
- 1] Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou 310058, The People's Republic of China [2]
| | - Yanjiang Chen
- 1] Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou 310058, The People's Republic of China [2]
| | - Chenxi Xu
- Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou 310058, The People's Republic of China
| | - Xiaobo Zhang
- Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou 310058, The People's Republic of China
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16
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Chromosome segregation by the Escherichia coli Min system. Mol Syst Biol 2014; 9:686. [PMID: 24022004 PMCID: PMC3792344 DOI: 10.1038/msb.2013.44] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Accepted: 08/07/2013] [Indexed: 12/26/2022] Open
Abstract
The mechanisms underlying chromosome segregation in prokaryotes remain a subject of debate and no unifying view has yet emerged. Given that the initial disentanglement of duplicated chromosomes could be achieved by purely entropic forces, even the requirement of an active prokaryotic segregation machinery has been questioned. Using computer simulations, we show that entropic forces alone are not sufficient to achieve and maintain full separation of chromosomes. This is, however, possible by assuming repeated binding of chromosomes along a gradient of membrane-associated tethering sites toward the poles. We propose that, in Escherichia coli, such a gradient of membrane tethering sites may be provided by the oscillatory Min system, otherwise known for its role in selecting the cell division site. Consistent with this hypothesis, we demonstrate that MinD binds to DNA and tethers it to the membrane in an ATP-dependent manner. Taken together, our combined theoretical and experimental results suggest the existence of a novel mechanism of chromosome segregation based on the Min system, further highlighting the importance of active segregation of chromosomes in prokaryotic cell biology.
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17
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Johnson MA, Sharma M, Mok MTS, Henderson BR. Stimulation of in vivo nuclear transport dynamics of actin and its co-factors IQGAP1 and Rac1 in response to DNA replication stress. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2334-47. [PMID: 23770048 DOI: 10.1016/j.bbamcr.2013.06.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Revised: 05/31/2013] [Accepted: 06/04/2013] [Indexed: 10/26/2022]
Abstract
Actin, a constituent of the cytoskeleton, is now recognized to function in the nucleus in gene transcription, chromatin remodeling and DNA replication/repair. Actin shuttles in and out of the nucleus through the action of transport receptors importin-9 and exportin-6. Here we have addressed the impact of cell cycle progression and DNA replication stress on actin nuclear localization, through study of actin dynamics in living cells. First, we showed that thymidine-induced G1/S phase cell cycle arrest increased the nuclear levels of actin and of two factors that stimulate actin polymerization: IQGAP1 and Rac1 GTPase. When cells were exposed to hydroxyurea to induce DNA replication stress, the nuclear localization of actin and its regulators was further enhanced. We employed live cell photobleaching assays and discovered that in response to DNA replication stress, GFP-actin nuclear import and export rates increased by up to 250%. The rate of import was twice as fast as export, accounting for actin nuclear accumulation. The faster shuttling dynamics correlated with reduced cellular retention of actin, and our data implicate actin polymerization in the stress-dependent uptake of nuclear actin. Furthermore, DNA replication stress induced a nuclear shift in IQGAP1 and Rac1 with enhanced import dynamics. Proximity ligation assays revealed that IQGAP1 associates in the nucleus with actin and Rac1, and formation of these complexes increased after hydroxyurea treatment. We propose that the replication stress checkpoint triggers co-ordinated nuclear entry and trafficking of actin, and of factors that regulate actin polymerization.
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Affiliation(s)
- Michael A Johnson
- Westmead Institute for Cancer Research, The University of Sydney, Westmead, Australia
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18
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Hayama R, Bahng S, Karasu ME, Marians KJ. The MukB-ParC interaction affects the intramolecular, not intermolecular, activities of topoisomerase IV. J Biol Chem 2013; 288:7653-7661. [PMID: 23349462 DOI: 10.1074/jbc.m112.418087] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proper chromosome organization is accomplished through binding of proteins such as condensins that shape the DNA and by modulation of chromosome topology by the action of topoisomerases. We found that the interaction between MukB, the bacterial condensin, and ParC, a subunit of topoisomerase IV, enhanced relaxation of negatively supercoiled DNA and knotting by topoisomerase IV, which are intramolecular DNA rearrangements but not decatenation of multiply linked DNA dimers, which is an intermolecular DNA rearrangement required for proper segregation of daughter chromosomes. MukB DNA binding and a specific chiral arrangement of the DNA was required for topoisomerase IV stimulation because relaxation of positively supercoiled DNA was unaffected. This effect could be attributed to a more effective topological reconfiguration of the negatively supercoiled compared with positively supercoiled DNA by MukB. These data suggest that the MukB-ParC interaction may play a role in chromosome organization rather than in separation of daughter chromosomes.
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Affiliation(s)
- Ryo Hayama
- Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School of Medical Sciences, New York, New York 10065
| | - Soon Bahng
- Molecular Biology Program, Jr. Graduate School of Biomedical Sciences, Memorial Sloan-Kettering Cancer Center, New York, New York 10065
| | - Mehmet E Karasu
- Louis V. Gerstner, Jr. Graduate School of Biomedical Sciences, Memorial Sloan-Kettering Cancer Center, New York, New York 10065
| | - Kenneth J Marians
- Molecular Biology Program, Jr. Graduate School of Biomedical Sciences, Memorial Sloan-Kettering Cancer Center, New York, New York 10065; Louis V. Gerstner, Jr. Graduate School of Biomedical Sciences, Memorial Sloan-Kettering Cancer Center, New York, New York 10065.
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19
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Nurse P, Marians KJ. Purification and characterization of Escherichia coli MreB protein. J Biol Chem 2012; 288:3469-75. [PMID: 23235161 DOI: 10.1074/jbc.m112.413708] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The actin homolog MreB is required in rod-shaped bacteria for maintenance of cell shape and is intimately connected to the holoenzyme that synthesizes the peptidoglycan layer. The protein has been reported variously to exist in helical loops under the cell surface, to rotate, and to move in patches in both directions around the cell surface. Studies of the Escherichia coli protein in vitro have been hampered by its tendency to aggregate. Here we report the purification and characterization of native E. coli MreB. The protein requires ATP hydrolysis for polymerization, forms bundles with a left-hand twist that can be as long as 4 μm, forms sheets in the presence of calcium, and has a critical concentration for polymerization of 1.5 μM.
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Affiliation(s)
- Pearl Nurse
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA
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20
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Masuda H, Tan Q, Awano N, Wu KP, Inouye M. YeeU enhances the bundling of cytoskeletal polymers of MreB and FtsZ, antagonizing the CbtA (YeeV) toxicity in Escherichia coli. Mol Microbiol 2012; 84:979-89. [DOI: 10.1111/j.1365-2958.2012.08068.x] [Citation(s) in RCA: 175] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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21
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Maeda YT, Nakadai T, Shin J, Uryu K, Noireaux V, Libchaber A. Assembly of MreB filaments on liposome membranes: a synthetic biology approach. ACS Synth Biol 2012; 1:53-9. [PMID: 23651045 DOI: 10.1021/sb200003v] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The physical interaction between the cytoskeleton and the cell membrane is essential in defining the morphology of living organisms. In this study, we use a synthetic approach to polymerize bacterial MreB filaments inside phospholipid vesicles. When the proteins MreB and MreC are expressed inside the liposomes, the MreB cytoskeleton structure develops at the inner membrane. Furthermore, when purified MreB is used inside the liposomes, MreB filaments form a 4-10 μm rigid bundle structure and deform the lipid vesicles in physical contact with the vesicle inner membrane. These results indicate that the fibrillation of MreB filaments can take place either in close proximity of deformable lipid membrane or in the presence of associated protein. Our finding might be relevant for the self-assembly of cytoskeleton filaments toward the construction of artificial cell systems.
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Affiliation(s)
| | | | - Jonghyeon Shin
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455,
United States
| | | | - Vincent Noireaux
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455,
United States
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22
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Masuda H, Tan Q, Awano N, Yamaguchi Y, Inouye M. A novel membrane-bound toxin for cell division, CptA (YgfX), inhibits polymerization of cytoskeleton proteins, FtsZ and MreB, in Escherichia coli. FEMS Microbiol Lett 2012; 328:174-81. [PMID: 22239607 DOI: 10.1111/j.1574-6968.2012.02496.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 01/03/2012] [Indexed: 01/16/2023] Open
Abstract
Nearly all free-living bacteria carry toxin-antitoxin (TA) systems on their genomes, through which cell growth and death are regulated. Toxins target a variety of essential cellular functions, including DNA replication, translation, and cell division. Here, we identified a novel toxin, YgfX, on the Escherichia coli genome. The toxin, consisting of 135 residues, is composed of the N-terminal membrane domain, which encompasses two transmembrane segments, and the C-terminal cytoplasmic domain. Upon YgfX expression, the cells were initially elongated and then the middle portion of the cells became inflated to form a lemon shape. YgfX was found to interact with MreB and FtsZ, two essential cytoskeletal proteins in E. coli. The cytoplasmic domain [YgfX(C)] was found to be responsible for the YgfX toxicity, as purified YgfX(C) was found to block the polymerization of FtsZ and MreB in vitro. YgfY, located immediately upstream of YgfX, was shown to be the cognate antitoxin; notably, YgfX is the first membrane-associating toxin in bacterial TA systems. We propose to rename the toxin and the antitoxin as CptA and CptB (for Cytoskeleton Polymerization inhibiting Toxin), respectively.
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Affiliation(s)
- Hisako Masuda
- Department of Biochemistry, Center for Advanced Biotechnology and Medicine, Robert Wood Johnson Medical School, Piscataway, NJ, USA
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23
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Bulmer DM, Kharraz L, Grant AJ, Dean P, Morgan FJE, Karavolos MH, Doble AC, McGhie EJ, Koronakis V, Daniel RA, Mastroeni P, Anjam Khan CM. The bacterial cytoskeleton modulates motility, type 3 secretion, and colonization in Salmonella. PLoS Pathog 2012; 8:e1002500. [PMID: 22291596 PMCID: PMC3266929 DOI: 10.1371/journal.ppat.1002500] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 12/07/2011] [Indexed: 11/26/2022] Open
Abstract
Although there have been great advances in our understanding of the bacterial cytoskeleton, major gaps remain in our knowledge of its importance to virulence. In this study we have explored the contribution of the bacterial cytoskeleton to the ability of Salmonella to express and assemble virulence factors and cause disease. The bacterial actin-like protein MreB polymerises into helical filaments and interacts with other cytoskeletal elements including MreC to control cell-shape. As mreB appears to be an essential gene, we have constructed a viable ΔmreC depletion mutant in Salmonella. Using a broad range of independent biochemical, fluorescence and phenotypic screens we provide evidence that the Salmonella pathogenicity island-1 type three secretion system (SPI1-T3SS) and flagella systems are down-regulated in the absence of MreC. In contrast the SPI-2 T3SS appears to remain functional. The phenotypes have been further validated using a chemical genetic approach to disrupt the functionality of MreB. Although the fitness of ΔmreC is reduced in vivo, we observed that this defect does not completely abrogate the ability of Salmonella to cause disease systemically. By forcing on expression of flagella and SPI-1 T3SS in trans with the master regulators FlhDC and HilA, it is clear that the cytoskeleton is dispensable for the assembly of these structures but essential for their expression. As two-component systems are involved in sensing and adapting to environmental and cell surface signals, we have constructed and screened a panel of such mutants and identified the sensor kinase RcsC as a key phenotypic regulator in ΔmreC. Further genetic analysis revealed the importance of the Rcs two-component system in modulating the expression of these virulence factors. Collectively, these results suggest that expression of virulence genes might be directly coordinated with cytoskeletal integrity, and this regulation is mediated by the two-component system sensor kinase RcsC. Salmonella are major global pathogens responsible for causing food-borne disease. In recent years the existence of a cytoskeleton in prokaryotes has received much attention. In this study the Salmonella cytoskeleton has been genetically disrupted, causing changes in morphology, motility and expression of key virulence factors. We provide evidence that the sensory protein RcsC detects changes at the cell surface caused by the disintegration of the bacterial cytoskeleton and modulates expression of key virulence factors. This study provides insights into the importance of the integrity of the bacterial cytoskeleton in the ability of Salmonella to cause disease, and thus may provide a novel target for antimicrobial drugs or vaccines.
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Affiliation(s)
- David M. Bulmer
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Lubna Kharraz
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Andrew J. Grant
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Paul Dean
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Fiona J. E. Morgan
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Michail H. Karavolos
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Anne C. Doble
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Emma J. McGhie
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Vassilis Koronakis
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Richard A. Daniel
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
| | - Pietro Mastroeni
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
| | - C. M. Anjam Khan
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle, United Kingdom
- * E-mail:
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24
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Vos SM, Tretter EM, Schmidt BH, Berger JM. All tangled up: how cells direct, manage and exploit topoisomerase function. Nat Rev Mol Cell Biol 2011; 12:827-41. [PMID: 22108601 DOI: 10.1038/nrm3228] [Citation(s) in RCA: 471] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Topoisomerases are complex molecular machines that modulate DNA topology to maintain chromosome superstructure and integrity. Although capable of stand-alone activity in vitro, topoisomerases are frequently linked to larger pathways and systems that resolve specific DNA superstructures and intermediates arising from cellular processes such as DNA repair, transcription, replication and chromosome compaction. Topoisomerase activity is indispensible to cells, but requires the transient breakage of DNA strands. This property has been exploited, often for significant clinical benefit, by various exogenous agents that interfere with cell proliferation. Despite decades of study, surprising findings involving topoisomerases continue to emerge with respect to their cellular function, regulation and utility as therapeutic targets.
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Affiliation(s)
- Seychelle M Vos
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA
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25
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Sliusarenko O, Heinritz J, Emonet T, Jacobs-Wagner C. High-throughput, subpixel precision analysis of bacterial morphogenesis and intracellular spatio-temporal dynamics. Mol Microbiol 2011; 80:612-27. [PMID: 21414037 DOI: 10.1111/j.1365-2958.2011.07579.x] [Citation(s) in RCA: 377] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Bacteria display various shapes and rely on complex spatial organization of their intracellular components for many cellular processes. This organization changes in response to internal and external cues. Quantitative, unbiased study of these spatio-temporal dynamics requires automated image analysis of large microscopy datasets. We have therefore developed MicrobeTracker, a versatile and high-throughput image analysis program that outlines and segments cells with subpixel precision, even in crowded images and mini-colonies, enabling cell lineage tracking. MicrobeTracker comes with an integrated accessory tool, SpotFinder, which precisely tracks foci of fluorescently labelled molecules inside cells. Using MicrobeTracker, we discover that the dynamics of the extensively studied Escherichia coli Min oscillator depends on Min protein concentration, unveiling critical limitations in robustness within the oscillator. We also find that the fraction of MinD proteins oscillating increases with cell length, indicating that the oscillator has evolved to be most effective when cells attain an appropriate length. MicrobeTracker was also used to uncover novel aspects of morphogenesis and cell cycle regulation in Caulobacter crescentus. By tracking filamentous cells, we show that the chromosomal origin at the old-pole is responsible for most replication/separation events while the others remain largely silent despite contiguous cytoplasm. This surprising position-dependent silencing is regulated by division.
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Affiliation(s)
- Oleksii Sliusarenko
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA
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26
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Wu X, Iwai N, Chen WL. Effects of S-(3,4-dichlorobenzyl) isothiourea on different cellular events in the cyanobacterium Anabaena sp. strain PCC 7120. Res Microbiol 2011; 162:375-81. [PMID: 21320591 DOI: 10.1016/j.resmic.2011.02.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Accepted: 01/14/2011] [Indexed: 01/01/2023]
Abstract
S-(3, 4-dichlorobenzyl) isothiourea (A22) has been reported to specifically inhibit the function of MreB, an actin-like protein in rod-shaped bacteria. This study investigated the role of A22 in cyanobacterium Anabaena sp. strain PCC 7120, which can form nitrogen-fixing heterocysts under combined-nitrogen deprivation. Results indicated that A22 could inhibit cell growth, cause abnormal cellular morphology and bring about asymmetric cell division and irregular DNA distribution. However, A22 has little effect on heterocyst formation. An A22-resistant mutant named C23 was isolated by growing cells on A22-containing plates. It had normal appearance of cell shape, division and DNA content when treated by A22. However, this mutant retained a wild-type allele of mreB.
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Affiliation(s)
- Xuan Wu
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China
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27
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Abstract
Bacteria, like eukaryotes, employ cytoskeletal elements to perform many functions, including cell morphogenesis, cell division, DNA partitioning, and cell motility. They not only possess counterparts of eukaryotic actin, tubulin, and intermediate filament proteins, but they also have cytoskeletal elements of their own. Unlike the rigid sequence and structural conservation often observed for eukaryotic cytoskeletal proteins, the bacterial counterparts can display considerable diversity in sequence and function across species. Their wide range of function highlights the flexibility of core cytoskeletal protein motifs, such that one type of cytoskeletal element can perform various functions, and one function can be performed by different types of cytoskeletal elements.
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Affiliation(s)
- Matthew T Cabeen
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
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28
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The Long Journey: Actin on the Road to Pro- and Eukaryotic Cells. Rev Physiol Biochem Pharmacol 2011; 161:67-85. [DOI: 10.1007/112_2011_1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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29
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Abstract
We present a cryo-electron tomographic analysis of the three-dimensional architecture of a strain of the Gram-negative bacterium Bdellovibrio bacteriovorus in which endogenous MreB2 was replaced with monomeric teal fluorescent protein (mTFP)-labeled MreB2. In contrast to wild-type Bdellovibrio cells that predominantly displayed a compact nucleoid region, cells expressing mTFP-labeled MreB2 displayed a twisted spiral organization of the nucleoid. The more open structure of the MreB2-mTFP nucleoids enabled clear in situ visualization of ribosomes decorating the periphery of the nucleoid. Ribosomes also bordered the edges of more compact nucleoids from both wild-type cells and mutant cells. Surprisingly, MreB2-mTFP localized to the interface between the spiral nucleoid and the cytoplasm, suggesting an intimate connection between nucleoid architecture and MreB arrangement. Further, in contrast to wild-type cells, where a single tight chemoreceptor cluster localizes close to the single polar flagellum, MreB2-mTFP cells often displayed extended chemoreceptor arrays present at one or both poles and displayed multiple or inaccurately positioned flagella. Our findings provide direct structural evidence for spiral organization of the bacterial nucleoid and suggest a possible role for MreB in regulation of nucleoid architecture and localization of the chemotaxis apparatus.
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30
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Skarp KP, Vartiainen MK. Actin on DNA-an ancient and dynamic relationship. Cytoskeleton (Hoboken) 2010; 67:487-95. [PMID: 20593452 DOI: 10.1002/cm.20464] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
In the cytoplasm of eukaryotic cells the coordinated assembly of actin filaments drives essential cell biological processes, such as cell migration. The discovery of prokaryotic actin homologues, as well as the appreciation of the existence of nuclear actin, have expanded the scope by which the actin family is utilized in different cell types. In bacteria, actin has been implicated in DNA movement tasks, while the connection with the RNA polymerase machinery appears to exist in both prokaryotes and eukaryotes. Within the nucleus, actin has further been shown to play a role in chromatin remodeling and RNA processing, possibly acting to link these to transcription, thereby facilitating the gene expression process. The molecular mechanism by which actin exerts these newly discovered functions is still unclear, because while polymer formation seems to be required in bacteria, these species lack conventional actin-binding proteins to regulate the process. Furthermore, although the nucleus contains a plethora of actin-regulating factors, the polymerization status of actin within this compartment still remains unclear. General theme, however, seems to be actin's ability to interact with numerous binding partners. A common feature to the novel modes of actin utilization is the connection between actin and DNA, and here we aim to review the recent literature to explore how this connection is exploited in different contexts.
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Affiliation(s)
- Kari-Pekka Skarp
- Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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31
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Escherichia coli condensin MukB stimulates topoisomerase IV activity by a direct physical interaction. Proc Natl Acad Sci U S A 2010; 107:18832-7. [PMID: 20921377 DOI: 10.1073/pnas.1008678107] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
In contrast to the current state of knowledge in the field of eukaryotic chromosome segregation, relatively little is known about the mechanisms coordinating the appropriate segregation of bacterial chromosomes. In Escherichia coli, the MukB/E/F complex and topoisomerase IV (Topo IV) are both crucial players in this process. Topo IV removes DNA entanglements following the replication of the chromosome, whereas MukB, a member of the structural maintenance of chromosomes protein family, serves as a bacterial condensin. We demonstrate here a direct physical interaction between the dimerization domain of MukB and the C-terminal domain of the ParC subunit of Topo IV. In addition, we find that MukB alters the activity of Topo IV in vitro. Finally, we isolate a MukB mutant, D692A, that is deficient in its interaction with ParC and show that this mutant fails to rescue the temperature-sensitive growth phenotype of a mukB(-) strain. These results show that MukB and Topo IV are linked physically and functionally and indicate that the activities of these proteins are not limited to chromosome segregation but likely also play a key role in the control of higher-order bacterial chromosome structure.
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Abstract
We present a new physical biology approach to understanding the relationship between the organization and segregation of bacterial chromosomes. We posit that replicated Escherichia coli daughter strands will spontaneously demix as a result of entropic forces, despite their strong confinement within the cell; in other words, we propose that entropy can act as a primordial physical force which drives chromosome segregation under the right physical conditions. Furthermore, proteins implicated in the regulation of chromosome structure and segregation may in fact function primarily in supporting such an entropy-driven segregation mechanism by regulating the physical state of chromosomes. We conclude that bacterial chromosome segregation is best understood in terms of spontaneous demixing of daughter strands. Our concept may also have important implications for chromosome segregation in eukaryotes, in which spindle-dependent chromosome movement follows an extended period of sister chromatid demixing and compaction.
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Physical and functional interaction between the condensin MukB and the decatenase topoisomerase IV in Escherichia coli. Proc Natl Acad Sci U S A 2010; 107:18826-31. [PMID: 20696938 DOI: 10.1073/pnas.1008140107] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proper geometric and topological organization of DNA is essential for all chromosomal processes. Two classes of proteins play major roles in organizing chromosomes: condensin complexes and type II topoisomerases. In Escherichia coli, MukB, a structural maintenance of chromosome-like component of the bacterial condensin, and topoisomerase IV (Topo IV), a type II topoisomerase that decatenates the newly replicated daughter chromosomes, are both essential for chromosome segregation in rapidly growing cells. However, little is known about the interplay between MukB and Topo IV. Here we demonstrate a physical and functional interaction between MukB and ParC, a subunit of Topo IV, in vitro. The site of MukB interaction was located on the C-terminal domain of ParC and a loss-of-interaction mutant, ParC R705E R729A, was isolated. This variant retained full activity as a topoisomerase when reconstituted with ParE to form Topo IV. We show that MukB stimulates the superhelical DNA relaxation activity of wild-type Topo IV, but not that of Topo IV reconstituted with ParC R705E R729A.
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Shaevitz JW, Gitai Z. The structure and function of bacterial actin homologs. Cold Spring Harb Perspect Biol 2010; 2:a000364. [PMID: 20630996 DOI: 10.1101/cshperspect.a000364] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
During the past decade, the appreciation and understanding of how bacterial cells can be organized in both space and time have been revolutionized by the identification and characterization of multiple bacterial homologs of the eukaryotic actin cytoskeleton. Some of these bacterial actins, such as the plasmid-borne ParM protein, have highly specialized functions, whereas other bacterial actins, such as the chromosomally encoded MreB protein, have been implicated in a wide array of cellular activities. In this review we cover our current understanding of the structure, assembly, function, and regulation of bacterial actins. We focus on ParM as a well-understood reductionist model and on MreB as a central organizer of multiple aspects of bacterial cell biology. We also discuss the outstanding puzzles in the field and possible directions where this fast-developing area may progress in the future.
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Affiliation(s)
- Joshua W Shaevitz
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
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Near-isotropic 3D optical nanoscopy with photon-limited chromophores. Proc Natl Acad Sci U S A 2010; 107:10068-73. [PMID: 20472826 DOI: 10.1073/pnas.1004899107] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Imaging approaches based on single molecule localization break the diffraction barrier of conventional fluorescence microscopy, allowing for bioimaging with nanometer resolution. It remains a challenge, however, to precisely localize photon-limited single molecules in 3D. We have developed a new localization-based imaging technique achieving almost isotropic subdiffraction resolution in 3D. A tilted mirror is used to generate a side view in addition to the front view of activated single emitters, allowing their 3D localization to be precisely determined for superresolution imaging. Because both front and side views are in focus, this method is able to efficiently collect emitted photons. The technique is simple to implement on a commercial fluorescence microscope, and especially suitable for biological samples with photon-limited chromophores such as endogenously expressed photoactivatable fluorescent proteins. Moreover, this method is relatively resistant to optical aberration, as it requires only centroid determination for localization analysis. Here we demonstrate the application of this method to 3D imaging of bacterial protein distribution and neuron dendritic morphology with subdiffraction resolution.
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Nan B, Mauriello EMF, Sun IH, Wong A, Zusman DR. A multi-protein complex from Myxococcus xanthus required for bacterial gliding motility. Mol Microbiol 2010; 76:1539-54. [PMID: 20487265 DOI: 10.1111/j.1365-2958.2010.07184.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Myxococcus xanthus moves by gliding motility powered by Type IV pili (S-motility) and a second motility system, A-motility, whose mechanism remains elusive despite the identification of approximately 40 A-motility genes. In this study, we used biochemistry and cell biology analyses to identify multi-protein complexes associated with A-motility. Previously, we showed that the N-terminal domain of FrzCD, the receptor for the frizzy chemosensory pathway, interacts with two A-motility proteins, AglZ and AgmU. Here we characterized AgmU, a protein that localized to both the periplasm and cytoplasm. On firm surfaces, AgmU-mCherry colocalized with AglZ as distributed clusters that remained fixed with respect to the substratum as cells moved forward. Cluster formation was favoured by hard surfaces where A-motility is favoured. In contrast, AgmU-mCherry clusters were not observed on soft agar surfaces or when cells were in large groups, conditions that favour S-motility. Using glutathione-S-transferase affinity chromatography, AgmU was found to interact either directly or indirectly with multiple A-motility proteins including AglZ, AglT, AgmK, AgmX, AglW and CglB. These proteins, important for the correct localization of AgmU and AglZ, appear to be organized as a motility complex, spanning the cytoplasm, inner membrane and the periplasm. Identification of this complex may be important for uncovering the mechanism of A-motility.
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Affiliation(s)
- Beiyan Nan
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3204, USA
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Kapoor P, Kumar A, Naik R, Ganguli M, Siddiqi MI, Sahasrabuddhe AA, Gupta CM. Leishmania actin binds and nicks kDNA as well as inhibits decatenation activity of type II topoisomerase. Nucleic Acids Res 2010; 38:3308-17. [PMID: 20147461 PMCID: PMC2879525 DOI: 10.1093/nar/gkq051] [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] [Indexed: 11/13/2022] Open
Abstract
Leishmania actin (LdACT) is an unconventional form of eukaryotic actin in that it markedly differs from other actins in terms of its filament forming as well as toxin and DNase-1-binding properties. Besides being present in the cytoplasm, cortical regions, flagellum and nucleus, it is also present in the kinetoplast where it appears to associate with the kinetoplast DNA (kDNA). However, nothing is known about its role in this organelle. Here, we show that LdACT is indeed associated with the kDNA disc in Leishmania kinetoplast, and under in vitro conditions, it specifically binds DNA primarily through electrostatic interactions involving its unique DNase-1-binding region and the DNA major groove. We further reveal that this protein exhibits DNA-nicking activity which requires its polymeric state as well as ATP hydrolysis and through this activity it converts catenated kDNA minicircles into open form. In addition, we show that LdACT specifically binds bacterial type II topoisomerase and inhibits its decatenation activity. Together, these results strongly indicate that LdACT could play a critical role in kDNA remodeling.
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Affiliation(s)
- Prabodh Kapoor
- Division of Molecular and Structural Biology, Central Drug Research Institute, Chattar Manzil Palace, CSIR, Lucknow 226001, India
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Bigot S, Marians KJ. DNA chirality-dependent stimulation of topoisomerase IV activity by the C-terminal AAA+ domain of FtsK. Nucleic Acids Res 2010; 38:3031-40. [PMID: 20081205 PMCID: PMC2875013 DOI: 10.1093/nar/gkp1243] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
We have studied the stimulation of topoisomerase IV (Topo IV) by the C-terminal AAA+ domain of FtsK. These two proteins combine to assure proper chromosome segregation in the cell. Stimulation of Topo IV activity was dependent on the chirality of the DNA substrate: FtsK stimulated decatenation of catenated DNA and relaxation of positively supercoiled [(+)ve sc] DNA, but inhibited relaxation of negatively supercoiled [(−)ve sc] DNA. The DNA translocation activity of FtsK was not required for stimulation, but was required for inhibition. DNA chirality did not affect any of the activities of FtsK, suggesting that FtsK possesses an inherent Topo IV stimulatory activity that is presumably mediated by protein–protein interactions, the stability of Topo IV on the DNA substrate dictated the effect observed. Inhibition occurs because FtsK can strip distributively acting topoisomerase off (−)ve scDNA, but not from either (+)ve scDNA or catenated DNA where the enzyme acts processively. Our analyses suggest that FtsK increases the efficiency of trapping of the transfer segment of DNA during the catalytic cycle of the topoisomerase.
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Affiliation(s)
- Sarah Bigot
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA
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Vats P, Yu J, Rothfield L. The dynamic nature of the bacterial cytoskeleton. Cell Mol Life Sci 2009; 66:3353-62. [PMID: 19641848 PMCID: PMC2810845 DOI: 10.1007/s00018-009-0092-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Revised: 05/27/2009] [Accepted: 07/03/2009] [Indexed: 10/20/2022]
Abstract
Three of the four well-established bacterial cytoskeletal systems-the MreB, MinCDE, and FtsZ systems-undergo a variety of short-range and long-range dynamic behaviors. These include the cellular reorganization of the cytoskeletal elements, in which the proteins redistribute from a predominantly helical pole-to-pole pattern into annular structures near midcell. Despite their apparent similarity, these dramatic redistributional events in the three systems are in large part independent of each other. In addition, some of the cytoskeletal structures undergo oscillatory behavior in which the helical elements move repetitively back-and-forth between the two ends of the cell. The details and mechanisms underlying these dynamic cellular events are just now being revealed by fluorescence microscopy of intact cells, fluorescence photobleaching recovery studies, single molecule tracking techniques, and in vitro studies of the purified proteins.
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Affiliation(s)
- Purva Vats
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
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Norris V, Root-Bernstein R. The eukaryotic cell originated in the integration and redistribution of hyperstructures from communities of prokaryotic cells based on molecular complementarity. Int J Mol Sci 2009; 10:2611-2632. [PMID: 19582221 PMCID: PMC2705508 DOI: 10.3390/ijms10062611] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2009] [Revised: 05/25/2009] [Accepted: 06/03/2009] [Indexed: 11/16/2022] Open
Abstract
In the "ecosystems-first" approach to the origins of life, networks of non-covalent assemblies of molecules (composomes), rather than individual protocells, evolved under the constraints of molecular complementarity. Composomes evolved into the hyperstructures of modern bacteria. We extend the ecosystems-first approach to explain the origin of eukaryotic cells through the integration of mixed populations of bacteria. We suggest that mutualism and symbiosis resulted in cellular mergers entailing the loss of redundant hyperstructures, the uncoupling of transcription and translation, and the emergence of introns and multiple chromosomes. Molecular complementarity also facilitated integration of bacterial hyperstructures to perform cytoskeletal and movement functions.
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Affiliation(s)
- Vic Norris
- AMMIS Laboratory, EA 3829, University of Rouen, Mont Saint Aignan, 76821 France; E-Mail:
(V.N.)
| | - Robert Root-Bernstein
- Department of Physiology, 2174 BPS, Michigan State University, East Lansing, MI 48824, USA
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