1
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Chang MH, Lavrentovich MO, Männik J. Differentiating the roles of proteins and polysomes in nucleoid size homeostasis in Escherichia coli. Biophys J 2024; 123:1435-1448. [PMID: 37974398 PMCID: PMC11163298 DOI: 10.1016/j.bpj.2023.11.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 10/17/2023] [Accepted: 11/14/2023] [Indexed: 11/19/2023] Open
Abstract
A defining feature of the bacterial cytosolic interior is a distinct membrane-less organelle, the nucleoid, that contains the chromosomal DNA. Although increasing experimental evidence indicates that macromolecular crowding is the dominant mechanism for nucleoid formation, it has remained unclear which crowders control nucleoid volume. It is commonly assumed that polyribosomes play a dominant role, yet the volume fraction of soluble proteins in the cytosol is comparable with that of polyribosomes. Here, we develop a free energy-based model for the cytosolic interior of a bacterial cell to distinguish contributions arising from polyribosomes and cytosolic proteins in nucleoid volume control. The parameters of the model are determined from the existing experimental data. We show that, while the polysomes establish the existence of the nucleoid as a distinct phase, the proteins control the nucleoid volume in physiologically relevant conditions. Our model explains experimental findings in Escherichia coli that the nucleoid compaction curves in osmotic shock measurements do not depend on cell growth rate and that dissociation of polysomes in slow growth rates does not lead to significant nucleoid expansion, while the nucleoid phase disappears in fastest growth rates. Furthermore, the model predicts a cross-over in the exclusion of crowders by their linear dimensions from the nucleoid phase: below the cross-over of 30-50 nm, the concentration of crowders in the nucleoid phase decreases linearly as a function of the crowder diameter, while decreasing exponentially above the cross-over size. Our work points to the possibility that bacterial cells maintain nucleoid size and protein concentration homeostasis via feedback in which protein concentration controls nucleoid dimensions and the nucleoid dimensions control protein synthesis rate.
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Affiliation(s)
- Mu-Hung Chang
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee
| | - Maxim O Lavrentovich
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee; Department of Earth, Environment, and Physics, Worcester State University, Worcester, Massachusetts.
| | - Jaan Männik
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee.
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2
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Harju J, van Teeseling MCF, Broedersz CP. Loop-extruders alter bacterial chromosome topology to direct entropic forces for segregation. Nat Commun 2024; 15:4618. [PMID: 38816445 PMCID: PMC11139863 DOI: 10.1038/s41467-024-49039-w] [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: 11/28/2023] [Accepted: 05/21/2024] [Indexed: 06/01/2024] Open
Abstract
Entropic forces have been argued to drive bacterial chromosome segregation during replication. In many bacterial species, however, specifically evolved mechanisms, such as loop-extruding SMC complexes and the ParABS origin segregation system, contribute to or are even required for chromosome segregation, suggesting that entropic forces alone may be insufficient. The interplay between and the relative contributions of these segregation mechanisms remain unclear. Here, we develop a biophysical model showing that purely entropic forces actually inhibit bacterial chromosome segregation until late replication stages. By contrast, our model reveals that loop-extruders loaded at the origins of replication, as observed in many bacterial species, alter the effective topology of the chromosome, thereby redirecting and enhancing entropic forces to enable accurate chromosome segregation during replication. We confirm our model predictions with polymer simulations: purely entropic forces do not allow for concurrent replication and segregation, whereas entropic forces steered by specifically loaded loop-extruders lead to robust, global chromosome segregation during replication. Finally, we show how loop-extruders can complement locally acting origin separation mechanisms, such as the ParABS system. Together, our results illustrate how changes in the geometry and topology of the polymer, induced by DNA-replication and loop-extrusion, impact the organization and segregation of bacterial chromosomes.
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Affiliation(s)
- Janni Harju
- Department of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Muriel C F van Teeseling
- Junior research group Prokaryotic Cell Biology, Department for Microbial Interactions, Institute of Microbiology, Friedrich-Schiller-Universität, Jena, Germany
| | - Chase P Broedersz
- Department of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
- Arnold Sommerfeld Center for Theoretical Physics and Center for NanoScience, Department of Physics, Ludwig-Maximilian-University Munich, Munich, Germany.
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3
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Morini L, Sakai A, Vibhute MA, Koch Z, Voss M, Schoenmakers LLJ, Huck WTS. Leveraging Active Learning to Establish Efficient In Vitro Transcription and Translation from Bacterial Chromosomal DNA. ACS OMEGA 2024; 9:19227-19235. [PMID: 38708277 PMCID: PMC11064174 DOI: 10.1021/acsomega.4c00111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 03/29/2024] [Accepted: 04/03/2024] [Indexed: 05/07/2024]
Abstract
Gene expression is a fundamental aspect in the construction of a minimal synthetic cell, and the use of chromosomes will be crucial for the integration and regulation of complex modules. Expression from chromosomes in vitro transcription and translation (IVTT) systems presents limitations, as their large size and low concentration make them far less suitable for standard IVTT reactions. Here, we addressed these challenges by optimizing lysate-based IVTT systems at low template concentrations. We then applied an active learning tool to adapt IVTT to chromosomes as template DNA. Further insights into the dynamic data set led us to adjust the previous protocol for chromosome isolation and revealed unforeseen trends pointing at limiting transcription kinetics in our system. The resulting IVTT conditions allowed a high template DNA efficiency for the chromosomes. In conclusion, our system shows a protein-to-chromosome ratio that moves closer to in vivo biology and represents an advancement toward chromosome-based synthetic cells.
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Affiliation(s)
- Leonardo Morini
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
| | - Andrei Sakai
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
| | - Mahesh A. Vibhute
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
| | - Zef Koch
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
- HAN
University of Applied Sciences, Nijmegen 6503GL, The Netherlands
| | - Margo Voss
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
| | - Ludo L. J. Schoenmakers
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
- Konrad
Lorenz Institute for Evolution and Cognition Research, Klosterneuburg 3400, Austria
| | - Wilhelm T. S. Huck
- Institute
for Molecules and Materials, Radboud University, Nijmegen 6525 AJ, The Netherlands
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4
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Chaboche Q, Campos-Villalobos G, Giunta G, Dijkstra M, Cosentino Lagomarsino M, Scolari VF. A mean-field theory for predicting single polymer collapse induced by neutral crowders. SOFT MATTER 2024; 20:3271-3282. [PMID: 38456237 DOI: 10.1039/d3sm01522j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/09/2024]
Abstract
Macromolecular crowding can induce the collapse of a single long polymer into a globular form due to depletion forces of entropic nature. This phenomenon has been shown to play a significant role in compacting the genome within the bacterium Escherichia coli into a well-defined region of the cell known as the nucleoid. Motivated by the biological significance of this process, numerous theoretical and computational studies have searched for the primary determinants of the behavior of polymer-crowder phases. However, our understanding of this process remains incomplete and there is debate on a quantitatively unified description. In particular, different simulation studies with explicit crowders have proposed different order parameters as potential predictors for the collapse transition. In this work, we present a comprehensive analysis of published simulation data obtained from different sources. Based on the common behavior we find in this data, we develop a unified phenomenological model that we show to be predictive. Finally, to further validate the accuracy of the model, we conduct new simulations on polymers of various sizes, and investigate the role of jamming of the crowders.
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Affiliation(s)
- Quentin Chaboche
- Institut Curie, PSL Research University, Sorbonne Université, CNRS UMR168, Laboratoire Physique des Cellules et Cancer, 75005 Paris, France
- IFOM ETS, The AIRC Institute of Molecular Oncology, 20139, Milan, Italy.
| | - Gerardo Campos-Villalobos
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
| | - Giuliana Giunta
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
- BASF SE, Carl-Bosch-Strasse 38, 67056 Ludwigshafen am Rhein, Germany
| | - Marjolein Dijkstra
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
| | - Marco Cosentino Lagomarsino
- IFOM ETS, The AIRC Institute of Molecular Oncology, 20139, Milan, Italy.
- Physics Department, University of Milan, and INFN, Milan, Italy
| | - Vittore F Scolari
- Institut Curie, PSL Research University, Sorbonne Université, CNRS UMR168, Laboratoire Physique des Cellules et Cancer, 75005 Paris, France
- Institut Curie, PSL Research University, Sorbonne Université, CNRS UMR3664, Laboratoire Dynamique du Noyau, 75005 Paris, France.
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5
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Kuzminov A. Bacterial nucleoid is a riddle wrapped in a mystery inside an enigma. J Bacteriol 2024; 206:e0021123. [PMID: 38358278 PMCID: PMC10994824 DOI: 10.1128/jb.00211-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2024] Open
Abstract
Bacterial chromosome, the nucleoid, is traditionally modeled as a rosette of DNA mega-loops, organized around proteinaceous central scaffold by nucleoid-associated proteins (NAPs), and mixed with the cytoplasm by transcription and translation. Electron microscopy of fixed cells confirms dispersal of the cloud-like nucleoid within the ribosome-filled cytoplasm. Here, I discuss evidence that the nucleoid in live cells forms DNA phase separate from riboprotein phase, the "riboid." I argue that the nucleoid-riboid interphase, where DNA interacts with NAPs, transcribing RNA polymerases, nascent transcripts, and ssRNA chaperones, forms the transcription zone. An active part of phase separation, transcription zone enforces segregation of the centrally positioned information phase (the nucleoid) from the surrounding action phase (the riboid), where translation happens, protein accumulates, and metabolism occurs. I speculate that HU NAP mostly tiles up the nucleoid periphery-facilitating DNA mobility but also supporting transcription in the interphase. Besides extruding plectonemically supercoiled DNA mega-loops, condensins could compact them into solenoids of uniform rings, while HU could support rigidity and rotation of these DNA rings. The two-phase cytoplasm arrangement allows the bacterial cell to organize the central dogma activities, where (from the cell center to its periphery) DNA replicates and segregates, DNA is transcribed, nascent mRNA is handed over to ribosomes, mRNA is translated into proteins, and finally, the used mRNA is recycled into nucleotides at the inner membrane. The resulting information-action conveyor, with one activity naturally leading to the next one, explains the efficiency of prokaryotic cell design-even though its main intracellular transportation mode is free diffusion.
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Affiliation(s)
- Andrei Kuzminov
- Department of Microbiology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
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6
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Monterroso B, Margolin W, Boersma AJ, Rivas G, Poolman B, Zorrilla S. Macromolecular Crowding, Phase Separation, and Homeostasis in the Orchestration of Bacterial Cellular Functions. Chem Rev 2024; 124:1899-1949. [PMID: 38331392 PMCID: PMC10906006 DOI: 10.1021/acs.chemrev.3c00622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 12/01/2023] [Accepted: 01/10/2024] [Indexed: 02/10/2024]
Abstract
Macromolecular crowding affects the activity of proteins and functional macromolecular complexes in all cells, including bacteria. Crowding, together with physicochemical parameters such as pH, ionic strength, and the energy status, influences the structure of the cytoplasm and thereby indirectly macromolecular function. Notably, crowding also promotes the formation of biomolecular condensates by phase separation, initially identified in eukaryotic cells but more recently discovered to play key functions in bacteria. Bacterial cells require a variety of mechanisms to maintain physicochemical homeostasis, in particular in environments with fluctuating conditions, and the formation of biomolecular condensates is emerging as one such mechanism. In this work, we connect physicochemical homeostasis and macromolecular crowding with the formation and function of biomolecular condensates in the bacterial cell and compare the supramolecular structures found in bacteria with those of eukaryotic cells. We focus on the effects of crowding and phase separation on the control of bacterial chromosome replication, segregation, and cell division, and we discuss the contribution of biomolecular condensates to bacterial cell fitness and adaptation to environmental stress.
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Affiliation(s)
- Begoña Monterroso
- Department
of Structural and Chemical Biology, Centro de Investigaciones Biológicas
Margarita Salas, Consejo Superior de Investigaciones
Científicas (CSIC), 28040 Madrid, Spain
| | - William Margolin
- Department
of Microbiology and Molecular Genetics, McGovern Medical School, UTHealth-Houston, Houston, Texas 77030, United States
| | - Arnold J. Boersma
- Cellular
Protein Chemistry, Bijvoet Centre for Biomolecular Research, Faculty
of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Germán Rivas
- Department
of Structural and Chemical Biology, Centro de Investigaciones Biológicas
Margarita Salas, Consejo Superior de Investigaciones
Científicas (CSIC), 28040 Madrid, Spain
| | - Bert Poolman
- Department
of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Silvia Zorrilla
- Department
of Structural and Chemical Biology, Centro de Investigaciones Biológicas
Margarita Salas, Consejo Superior de Investigaciones
Científicas (CSIC), 28040 Madrid, Spain
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7
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Jung Y, Sadeghi A, Ha BY. Modeling the compaction of bacterial chromosomes by biomolecular crowding and the cross-linking protein H-NS. Sci Rep 2024; 14:139. [PMID: 38167921 PMCID: PMC10762067 DOI: 10.1038/s41598-023-50355-2] [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: 09/27/2023] [Accepted: 12/19/2023] [Indexed: 01/05/2024] Open
Abstract
Cells orchestrate the action of various molecules toward organizing their chromosomes. Using a coarse-grained computational model, we study the compaction of bacterial chromosomes by the cross-linking protein H-NS and cellular crowders. In this work, H-NS, modeled as a mobile "binder," can bind to a chromosome-like polymer with a characteristic binding energy. The simulation results reported here clarify the relative role of biomolecular crowding and H-NS in condensing a bacterial chromosome in a quantitative manner. In particular, they shed light on the nature and degree of crowder and H-NS synergetics: while the presence of crowders enhances H-NS binding to a chromosome-like polymer, the presence of H-NS makes crowding effects more efficient, suggesting two-way synergetics in chain compaction. Also, the results show how crowding effects promote clustering of bound H-NS. For a sufficiently large concentration of H-NS, the cluster size increases with the volume fraction of crowders.
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Affiliation(s)
- Youngkyun Jung
- Supercomputing Center, Korea Institute of Science and Technology Information, Daejeon, 34141, South Korea.
| | - Amir Sadeghi
- Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
| | - Bae-Yeun Ha
- Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
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8
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Collette D, Dunlap D, Finzi L. Macromolecular Crowding and DNA: Bridging the Gap between In Vitro and In Vivo. Int J Mol Sci 2023; 24:17502. [PMID: 38139331 PMCID: PMC10744201 DOI: 10.3390/ijms242417502] [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: 09/13/2023] [Revised: 11/29/2023] [Accepted: 12/05/2023] [Indexed: 12/24/2023] Open
Abstract
The cellular environment is highly crowded, with up to 40% of the volume fraction of the cell occupied by various macromolecules. Most laboratory experiments take place in dilute buffer solutions; by adding various synthetic or organic macromolecules, researchers have begun to bridge the gap between in vitro and in vivo measurements. This is a review of the reported effects of macromolecular crowding on the compaction and extension of DNA, the effect of macromolecular crowding on DNA kinetics, and protein-DNA interactions. Theoretical models related to macromolecular crowding and DNA are briefly reviewed. Gaps in the literature, including the use of biologically relevant crowders, simultaneous use of multi-sized crowders, empirical connections between macromolecular crowding and liquid-liquid phase separation of nucleic materials are discussed.
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Affiliation(s)
| | | | - Laura Finzi
- Department of Physics, College of Arts & Sciences, Emory University, Atlanta, GA 30322, USA; (D.C.); (D.D.)
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9
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Junier I, Ghobadpour E, Espeli O, Everaers R. DNA supercoiling in bacteria: state of play and challenges from a viewpoint of physics based modeling. Front Microbiol 2023; 14:1192831. [PMID: 37965550 PMCID: PMC10642903 DOI: 10.3389/fmicb.2023.1192831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 09/25/2023] [Indexed: 11/16/2023] Open
Abstract
DNA supercoiling is central to many fundamental processes of living organisms. Its average level along the chromosome and over time reflects the dynamic equilibrium of opposite activities of topoisomerases, which are required to relax mechanical stresses that are inevitably produced during DNA replication and gene transcription. Supercoiling affects all scales of the spatio-temporal organization of bacterial DNA, from the base pair to the large scale chromosome conformation. Highlighted in vitro and in vivo in the 1960s and 1970s, respectively, the first physical models were proposed concomitantly in order to predict the deformation properties of the double helix. About fifteen years later, polymer physics models demonstrated on larger scales the plectonemic nature and the tree-like organization of supercoiled DNA. Since then, many works have tried to establish a better understanding of the multiple structuring and physiological properties of bacterial DNA in thermodynamic equilibrium and far from equilibrium. The purpose of this essay is to address upcoming challenges by thoroughly exploring the relevance, predictive capacity, and limitations of current physical models, with a specific focus on structural properties beyond the scale of the double helix. We discuss more particularly the problem of DNA conformations, the interplay between DNA supercoiling with gene transcription and DNA replication, its role on nucleoid formation and, finally, the problem of scaling up models. Our primary objective is to foster increased collaboration between physicists and biologists. To achieve this, we have reduced the respective jargon to a minimum and we provide some explanatory background material for the two communities.
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Affiliation(s)
- Ivan Junier
- CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, Université Grenoble Alpes, Grenoble, France
| | - Elham Ghobadpour
- CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, Université Grenoble Alpes, Grenoble, France
- École Normale Supérieure (ENS) de Lyon, CNRS, Laboratoire de Physique and Centre Blaise Pascal de l'ENS de Lyon, Lyon, France
| | - Olivier Espeli
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France
| | - Ralf Everaers
- École Normale Supérieure (ENS) de Lyon, CNRS, Laboratoire de Physique and Centre Blaise Pascal de l'ENS de Lyon, Lyon, France
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10
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Yáñez-Cuna FO, Koszul R. Insights in bacterial genome folding. Curr Opin Struct Biol 2023; 82:102679. [PMID: 37604045 DOI: 10.1016/j.sbi.2023.102679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 07/18/2023] [Accepted: 07/19/2023] [Indexed: 08/23/2023]
Abstract
Chromosomes in all domains of life are well-defined structural entities with complex hierarchical organization. The regulation of this hierarchical organization and its functional interplay with gene expression or other chromosome metabolic processes such as repair, replication, or segregation is actively investigated in a variety of species, including prokaryotes. Bacterial chromosomes are typically gene-dense with few non-coding sequences and are organized into the nucleoid, a membrane-less compartment composed of DNA, RNA, and proteins (nucleoid-associated proteins or NAPs). The continuous improvement of imaging and genomic methods has put the organization of these Mb-long molecules at reach, allowing to disambiguate some of their highly dynamic properties and intertwined structural features. Here we review and discuss some of the recent advances in the field of bacterial chromosome organization.
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Affiliation(s)
- Fares Osam Yáñez-Cuna
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, 75015, Paris, France
| | - Romain Koszul
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, 75015, Paris, France.
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11
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Moazemi F, Ghanbari-Kashan S, Moharaminezhad F, Nikoofard N. Ejection dynamics of a semiflexible polymer from a nanosphere. Phys Rev E 2023; 108:044501. [PMID: 37978688 DOI: 10.1103/physreve.108.044501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 09/27/2023] [Indexed: 11/19/2023]
Abstract
Polymer ejection has been of interest due to its relation to the viral genome ejection. However, the ejection dynamics of a semiflexible polymer from a nanosphere is not yet understood. Here, a theory is developed for the ejection dynamics of a polymer with total length L_{0} and persistence length l from a sphere of diameter D. These length scales define different confinement regimes to study the polymer dynamics. The polymer sometimes undergoes between two to three regimes during its ejection. The rate of change of the free energy of confinement is balanced by the rate of energy dissipation, in each regime. The polymer experiences a final stage in which the free energy of polymer attachment to the sphere governs the ejection. The total ejection time τ depends on the polymer dynamics in the various regimes that it passes through in the phase space. Dependence of the ejection time on the polymer length, the persistence length, and the sphere diameter τ∝L_{0}^{α}D^{β}l^{γ} is obtained from the theory. It is shown that α changes between 1 and 1.7, β between 3 and 5, and γ takes a zero or positive value often smaller than 1. Agreement of these exponents with other theory and simulations are discussed.
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Affiliation(s)
- Farzaneh Moazemi
- Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan 87317-53153, Iran
| | | | - Fatemeh Moharaminezhad
- Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan 87317-53153, Iran
| | - Narges Nikoofard
- Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan 87317-53153, Iran
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12
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Gilbert BR, Thornburg ZR, Brier TA, Stevens JA, Grünewald F, Stone JE, Marrink SJ, Luthey-Schulten Z. Dynamics of chromosome organization in a minimal bacterial cell. Front Cell Dev Biol 2023; 11:1214962. [PMID: 37621774 PMCID: PMC10445541 DOI: 10.3389/fcell.2023.1214962] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Accepted: 07/10/2023] [Indexed: 08/26/2023] Open
Abstract
Computational models of cells cannot be considered complete unless they include the most fundamental process of life, the replication and inheritance of genetic material. By creating a computational framework to model systems of replicating bacterial chromosomes as polymers at 10 bp resolution with Brownian dynamics, we investigate changes in chromosome organization during replication and extend the applicability of an existing whole-cell model (WCM) for a genetically minimal bacterium, JCVI-syn3A, to the entire cell-cycle. To achieve cell-scale chromosome structures that are realistic, we model the chromosome as a self-avoiding homopolymer with bending and torsional stiffnesses that capture the essential mechanical properties of dsDNA in Syn3A. In addition, the conformations of the circular DNA must avoid overlapping with ribosomes identitied in cryo-electron tomograms. While Syn3A lacks the complex regulatory systems known to orchestrate chromosome segregation in other bacteria, its minimized genome retains essential loop-extruding structural maintenance of chromosomes (SMC) protein complexes (SMC-scpAB) and topoisomerases. Through implementing the effects of these proteins in our simulations of replicating chromosomes, we find that they alone are sufficient for simultaneous chromosome segregation across all generations within nested theta structures. This supports previous studies suggesting loop-extrusion serves as a near-universal mechanism for chromosome organization within bacterial and eukaryotic cells. Furthermore, we analyze ribosome diffusion under the influence of the chromosome and calculate in silico chromosome contact maps that capture inter-daughter interactions. Finally, we present a methodology to map the polymer model of the chromosome to a Martini coarse-grained representation to prepare molecular dynamics models of entire Syn3A cells, which serves as an ultimate means of validation for cell states predicted by the WCM.
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Affiliation(s)
- Benjamin R. Gilbert
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Zane R. Thornburg
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Troy A. Brier
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Jan A. Stevens
- Molecular Dynamics Group, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Fabian Grünewald
- Molecular Dynamics Group, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - John E. Stone
- NVIDIA Corporation, Santa Clara, CA, United States
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Siewert J. Marrink
- Molecular Dynamics Group, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Zaida Luthey-Schulten
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States
- NSF Center for the Physics of Living Cells, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, United States
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13
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Ho G, Kubušová V, Irabien C, Li V, Weinstein A, Chawla S, Yeung D, Mershin A, Zolotovsky K, Mogas-Soldevila L. Multiscale design of cell-free biologically active architectural structures. Front Bioeng Biotechnol 2023; 11:1125156. [PMID: 37064226 PMCID: PMC10100494 DOI: 10.3389/fbioe.2023.1125156] [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: 12/15/2022] [Accepted: 02/27/2023] [Indexed: 03/30/2023] Open
Abstract
Cell-free protein expression systems are here combined with 3D-printed structures to study the challenges and opportunities as biofabrication enters the spaces of architecture and design. Harnessing large-scale additive manufacturing of biological materials, we examined the addition of cell-free protein expression systems ("TXTL" i.e., biological transcription-translation machinery without the use of living cells) to printed structures. This allowed us to consider programmable, living-like, responsive systems for product design and indoor architectural applications. This emergent, pluripotent technology offers exciting potential in support of health, resource optimization, and reduction of energy use in the built environment, setting a new path to interactivity with mechanical, optical, and (bio) chemical properties throughout structures. We propose a roadmap towards creating healthier, functional and more durable systems by deploying a multiscale platform containing biologically-active components encapsulated within biopolymer lattices operating at three design scales: (i) supporting cell-free protein expression in a biopolymer matrix (microscale), (ii) varying material properties of porosity and strength within two-dimensional lattices to support biological and structural functions (mesoscale), and (iii) obtaining folded indoor surfaces that are structurally sound at the meter scale and biologically active (we label that regime macroscale). We embedded commercially available cell-free protein expression systems within silk fibroin and sodium alginate biopolymer matrices and used green fluorescent protein as the reporter to confirm their compatibility. We demonstrate mechanical attachment of freeze-dried bioactive pellets into printed foldable fibrous biopolymer lattices showing the first steps towards modular multiscale fabrication of large structures with biologically active zones. Our results discuss challenges to experimental setup affecting expression levels and show the potential of robust cell-free protein-expressing biosites within custom-printed structures at scales relevant to everyday consumer products and human habitats.
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Affiliation(s)
- G. Ho
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, United States
| | - V. Kubušová
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
- Department of Architecture and Design, Slovak University of Technology, Bratislava, Slovakia
| | - C. Irabien
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
| | - V. Li
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
| | - A. Weinstein
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
| | - Sh. Chawla
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
| | - D. Yeung
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
| | - A. Mershin
- Label Free Research Group, Center for Bits and Atoms, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - K. Zolotovsky
- Spatial Dynamics Program, Division of Experimental and Foundational Studies, Rhode Island School of Design, Providence, RI, United States
| | - L. Mogas-Soldevila
- Department of Graduate Architecture, DumoLab Research, Stuart Weitzman School of Design, University of Pennsylvania, Philadelphia, PA, United States
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14
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Woldringh CL. The Bacterial Nucleoid: From Electron Microscopy to Polymer Physics—A Personal Recollection. Life (Basel) 2023; 13:life13040895. [PMID: 37109423 PMCID: PMC10143432 DOI: 10.3390/life13040895] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 03/22/2023] [Accepted: 03/24/2023] [Indexed: 03/30/2023] Open
Abstract
In the 1960s, electron microscopy did not provide a clear answer regarding the compact or dispersed organization of the bacterial nucleoid. This was due to the necessary preparation steps of fixation and dehydration (for embedding) and freezing (for freeze-fracturing). Nevertheless, it was possible to measure the lengths of nucleoids in thin sections of slow-growing Escherichia coli cells, showing their gradual increase along with cell elongation. Later, through application of the so-called agar filtration method for electron microscopy, we were able to perform accurate measurements of cell size and shape. The introduction of confocal and fluorescence light microscopy enabled measurements of size and position of the bacterial nucleoid in living cells, inducing the concepts of “nucleoid occlusion” for localizing cell division and of “transertion” for the final step of nucleoid segregation. The question of why the DNA does not spread throughout the cytoplasm was approached by applying polymer-physical concepts of interactions between DNA and proteins. This gave a mechanistic insight in the depletion of proteins from the nucleoid, in accordance with its low refractive index observed by phase-contrast microscopy. Although in most bacterial species, the widely conserved proteins of the ParABS-system play a role in directing the segregation of newly replicated DNA strands, the basis for the separation and opposing movement of the chromosome arms was proposed to lie in preventing intermingling of nascent daughter strands already in the early replication bubble. E. coli, lacking the ParABS system, may be suitable for investigating this basic mechanism of DNA strand separation and segregation.
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Affiliation(s)
- Conrad L Woldringh
- Bacterial Cell Biology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, 1098 XH Amsterdam, The Netherlands
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15
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Gupta A, Joshi A, Arora K, Mukhopadhyay S, Guptasarma P. The bacterial nucleoid-associated proteins, HU, and Dps, condense DNA into context-dependent biphasic or multiphasic complex coacervates. J Biol Chem 2023; 299:104637. [PMID: 36963493 PMCID: PMC10141540 DOI: 10.1016/j.jbc.2023.104637] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 02/27/2023] [Accepted: 03/08/2023] [Indexed: 03/26/2023] Open
Abstract
The bacterial chromosome, known as its nucleoid, is an amorphous assemblage of globular nucleoprotein domains. It exists in a state of phase separation from the cell's cytoplasm, as an irregularly-shaped, membrane-less, intracellular compartment. This state (the nature of which remains largely unknown) is maintained through bacterial generations ad infinitum. Here, we show that HU, and Dps, two of the most abundant nucleoid-associated proteins (NAPs) of Escherichia coli, undergo spontaneous complex coacervation with different forms of DNA/RNA, both individually and in each other's presence, to cause accretion and compaction of DNA/RNA into liquid-liquid phase separated (LLPS) condensates in vitro. Upon mixing with nucleic acids, HU-A and HU-B form (a) bi-phasic heterotypic mixed condensates in which HU-B helps to lower the Csat of HU-A; and also (b) multi-phasic heterotypic condensates, with Dps, in which de-mixed domains display different contents of HU and Dps. We believe that these modes of complex coacervation that are seen in vitro can serve as models for the in vivo relationships amongst NAPs in nucleoids, involving local and global variations in the relative abundances of the different NAPs, especially in de-mixed sub-domains that are characterized by differing grades of phase separation. Our results clearly demonstrate some quantitative, and some qualitative, differences in the coacervating abilities of different NAPs with DNA, potentially explaining (i) why E. coli has two isoforms of HU, and (ii) why changes in the abundances of HU and Dps facilitate the lag, logarithmic and stationary phases of E. coli growth.
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Affiliation(s)
- Archit Gupta
- Centre for Protein Science, Design and Engineering, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India.
| | - Ashish Joshi
- Centre for Protein Science, Design and Engineering, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Kanika Arora
- Centre for Protein Science, Design and Engineering, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Samrat Mukhopadhyay
- Centre for Protein Science, Design and Engineering, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Chemical Sciences; Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
| | - Purnananda Guptasarma
- Centre for Protein Science, Design and Engineering, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India; Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India.
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16
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Roh S, Lee T, Cheong DY, Kim Y, Oh S, Lee G. Direct observation of surface charge and stiffness of human metaphase chromosomes. NANOSCALE ADVANCES 2023; 5:368-377. [PMID: 36756276 PMCID: PMC9846444 DOI: 10.1039/d2na00620k] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 12/17/2022] [Indexed: 06/18/2023]
Abstract
Metaphase chromosomes in which both polynucleotides and proteins are condensed with hierarchies are closely related to life phenomena such as cell division, cancer development, and cellular senescence. Nevertheless, their nature is rarely revealed, owing to their structural complexity and technical limitations in analytical methods. In this study, we used surface potential and nanomechanics mapping technology based on atomic force microscopy to measure the surface charge and intrinsic stiffness of metaphase chromosomes. We found that extra materials covering the chromosomes after the extraction process were positively charged. With the covering materials, the chromosomes were positively charged (ca. 44.9 ± 16.48 mV) and showed uniform stiffness (ca. 6.23 ± 1.98 MPa). In contrast, after getting rid of the extra materials through treatment with RNase and protease, the chromosomes were strongly negatively charged (ca. -197.4 ± 77.87 mV) and showed relatively non-uniform and augmented stiffness (ca. 36.87 ± 17.56 MPa). The results suggested undulating but compact coordination of condensed chromosomes. Additionally, excessive treatment with RNase and protease could destroy the chromosomal structure, providing an exceptional opportunity for multiscale stiffness mapping of polynucleotides, nucleosomes, chromatin fibers, and chromosomes in a single image. Our approach offers a new horizon in terms of an analytical technique for studying chromosome-related diseases.
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Affiliation(s)
- Seokbeom Roh
- Department of Biotechnology and Bioinformatics, Korea University Sejong 30019 Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University Sejong 30019 Korea
| | - Taeha Lee
- Department of Biotechnology and Bioinformatics, Korea University Sejong 30019 Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University Sejong 30019 Korea
| | - Da Yeon Cheong
- Department of Biotechnology and Bioinformatics, Korea University Sejong 30019 Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University Sejong 30019 Korea
| | - Yeonjin Kim
- Department of Biotechnology and Bioinformatics, Korea University Sejong 30019 Korea
| | - Soohwan Oh
- College of Pharmacy, Korea University Sejong 30019 Korea
| | - Gyudo Lee
- Department of Biotechnology and Bioinformatics, Korea University Sejong 30019 Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University Sejong 30019 Korea
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17
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Holub M, Birnie A, Japaridze A, van der Torre J, Ridder MD, de Ram C, Pabst M, Dekker C. Extracting and characterizing protein-free megabase-pair DNA for in vitro experiments. CELL REPORTS METHODS 2022; 2:100366. [PMID: 36590691 PMCID: PMC9795359 DOI: 10.1016/j.crmeth.2022.100366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 09/29/2022] [Accepted: 11/16/2022] [Indexed: 12/15/2022]
Abstract
Chromosome structure and function is studied using various cell-based methods as well as with a range of in vitro single-molecule techniques on short DNA substrates. Here, we present a method to obtain megabase-pair-length deproteinated DNA for in vitro studies. We isolated chromosomes from bacterial cells and enzymatically digested the native proteins. Mass spectrometry indicated that 97%-100% of DNA-binding proteins are removed from the sample. Fluorescence microscopy analysis showed an increase in the radius of gyration of the DNA polymers, while the DNA length remained megabase-pair sized. In proof-of-concept experiments using these deproteinated long DNA molecules, we observed DNA compaction upon adding the DNA-binding protein Fis or PEG crowding agents and showed that it is possible to track the motion of a fluorescently labeled DNA locus. These results indicate the practical feasibility of a "genome-in-a-box" approach to study chromosome organization from the bottom up.
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Affiliation(s)
- Martin Holub
- Department of Bionanoscience & Kavli Institute for Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Anthony Birnie
- Department of Bionanoscience & Kavli Institute for Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Aleksandre Japaridze
- Department of Bionanoscience & Kavli Institute for Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Jaco van der Torre
- Department of Bionanoscience & Kavli Institute for Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Maxime den Ridder
- Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Carol de Ram
- Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Martin Pabst
- Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
| | - Cees Dekker
- Department of Bionanoscience & Kavli Institute for Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, the Netherlands
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18
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Chauhan G, Norred SE, Dabbs RM, Caveney PM, George JKV, Collier CP, Simpson ML, Abel SM. Crowding-Induced Spatial Organization of Gene Expression in Cell-Sized Vesicles. ACS Synth Biol 2022; 11:3733-3742. [PMID: 36260840 DOI: 10.1021/acssynbio.2c00336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cell-free protein synthesis is an important tool for studying gene expression and harnessing it for applications. In cells, gene expression is regulated in part by the spatial organization of transcription and translation. Unfortunately, current cell-free approaches are unable to control the organization of molecular components needed for gene expression, which limits the ability to probe and utilize its effects. Here, we show, using complementary computational and experimental approaches, that macromolecular crowding can be used to control the spatial organization and translational efficiency of gene expression in cell-sized vesicles. Computer simulations and imaging experiments reveal that, as crowding is increased, DNA plasmids become localized at the inner surface of vesicles. Ribosomes, in contrast, remain uniformly distributed, demonstrating that crowding can be used to differentially organize components of gene expression. We further carried out cell-free protein synthesis reactions in cell-sized vesicles and quantified mRNA and protein abundance. At sufficiently high levels of crowding, we observed localization of mRNA near vesicle surfaces, a decrease in translational efficiency and protein abundance, and anomalous scaling of protein abundance as a function of vesicle size. These results are consistent with high levels of crowding causing altered spatial organization and slower diffusion. Our work demonstrates a straightforward way to control the organization of gene expression in cell-sized vesicles and provides insight into the spatial regulation of gene expression in cells.
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Affiliation(s)
- Gaurav Chauhan
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee37996, United States
| | - S Elizabeth Norred
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville and Oak Ridge National Laboratory, Knoxville, Tennessee37996, United States
| | - Rosemary M Dabbs
- Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville and Oak Ridge National Laboratory, Knoxville, Tennessee37996, United States
| | - Patrick M Caveney
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville and Oak Ridge National Laboratory, Knoxville, Tennessee37996, United States
| | - John K Vincent George
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville and Oak Ridge National Laboratory, Knoxville, Tennessee37996, United States
| | - C Patrick Collier
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Michael L Simpson
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville and Oak Ridge National Laboratory, Knoxville, Tennessee37996, United States
| | - Steven M Abel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee37996, United States
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19
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Mitra D, Pande S, Chatterji A. Topology-driven spatial organization of ring polymers under confinement. Phys Rev E 2022; 106:054502. [PMID: 36559479 DOI: 10.1103/physreve.106.054502] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 10/12/2022] [Indexed: 11/19/2022]
Abstract
Entropic repulsion between DNA ring polymers under confinement is a key mechanism governing the spatial segregation of bacterial DNA before cell division. Here we establish that "internal" loops within a modified-ring polymer architecture enhance entropic repulsion between two overlapping polymers confined in a cylinder. Interestingly, they also induce entropy-driven spatial organization of polymer segments as seen in vivo. Here we design polymers of different architectures in our simulations by introducing a minimal number of cross-links between specific monomers along the ring-polymer contour. The cross-links are likely induced by various bridging proteins inside living cells. We investigate the segregation of two polymers with modified topologies confined in a cylinder, which initially had spatially overlapping configurations. This helps us to identify the architectures that lead to higher success rates of segregation. We also establish the mechanism that leads to localization of specific polymer segments. We use the blob model to provide a theoretical understanding of why certain architectures lead to enhanced entropic repulsive forces between the polymers. Lastly, we establish a correspondence between the organizational patterns of the chromosome of the C.crescentus bacterium and our results for a specifically designed polymer architecture. However, the principles outlined here pertaining to the organization of polymeric segments are applicable to both synthetic and biological polymers.
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20
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Zhou M. DNA sliding and loop formation by E. coli SMC complex: MukBEF. Biochem Biophys Rep 2022; 31:101297. [PMID: 35770038 PMCID: PMC9234588 DOI: 10.1016/j.bbrep.2022.101297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 05/08/2022] [Accepted: 06/06/2022] [Indexed: 11/29/2022] Open
Abstract
SMC (structural maintenance of chromosomes) complexes share conserved architectures and function in chromosome maintenance via an unknown mechanism. Here we have used single-molecule techniques to study MukBEF, the SMC complex in Escherichia coli. Real-time movies show MukB alone can compact DNA and ATP inhibits DNA compaction by MukB. We observed that DNA unidirectionally slides through MukB, potentially by a ratchet mechanism, and the sliding speed depends on the elastic energy stored in the DNA. MukE, MukF and ATP binding stabilize MukB and DNA interaction, and ATP hydrolysis regulates the loading/unloading of MukBEF from DNA. Our data suggests a new model for how MukBEF organizes the bacterial chromosome in vivo; and this model will be relevant for other SMC proteins. ATP-independent DNA compaction by MukB. DNA unidirectionally slides through MukB, potentially by a ratchet mechanism. MukE, MukF and ATP binding stabilize MukB and DNA interaction. DNA sliding via ratchet driven by entropic force model for chromosome organization by SMC complex.
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Abstract
The next robotics frontier will be led by biohybrids. Capable biohybrid robots require microfluidics to sustain, improve, and scale the architectural complexity of their core ingredient: biological tissues. Advances in microfluidics have already revolutionized disease modeling and drug development, and are positioned to impact regenerative medicine but have yet to apply to biohybrids. Fusing microfluidics with living materials will improve tissue perfusion and maturation, and enable precise patterning of sensing, processing, and control elements. This perspective suggests future developments in advanced biohybrids.
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22
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Mitra D, Pande S, Chatterji A. Polymer architecture orchestrates the segregation and spatial organization of replicating E. coli chromosomes in slow growth. SOFT MATTER 2022; 18:5615-5631. [PMID: 35861071 DOI: 10.1039/d2sm00734g] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The mechanism of chromosome segregation and organization in the bacterial cell cycle of E. coli is one of the least understood aspects in its life cycle. The E. coli chromosome is often modelled as a bead spring ring polymer. We introduce cross-links in the DNA-ring polymer, resulting in the formation of loops within each replicating bacterial chromosome. We use simulations to show that the chosen polymer-topology ensures its self-organization along the cell long-axis, such that various chromosomal loci get spatially localized as seen in vivo. The localization of loci arises due to entropic repulsion between polymer loops within each daughter DNA confined in a cylinder. The cellular addresses of the loci in our model are in fair agreement with those seen in experiments as given in J. A. Cass et al., Biophys. J., 2016, 110, 2597-2609. We also show that the adoption of such modified polymer architectures by the daughter DNAs leads to an enhanced propensity of their spatial segregation. Secondly, we match other experimentally reported results, including observation of the cohesion time and the ter-transition. Additionally, the contact map generated from our simulations reproduces the macro-domain like organization as seen in the experimentally obtained Hi-C map. Lastly, we have also proposed a plausible reconciliation of the 'Train Track' and the 'Replication Factory' models which provide conflicting descriptions of the spatial organization of the replication forks. Thus, we reconcile observations from complementary experimental techniques probing bacterial chromosome organization.
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23
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Confinement anisotropy drives polar organization of two DNA molecules interacting in a nanoscale cavity. Nat Commun 2022; 13:4358. [PMID: 35902565 PMCID: PMC9334635 DOI: 10.1038/s41467-022-31398-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 06/15/2022] [Indexed: 11/08/2022] Open
Abstract
There is growing appreciation for the role phase transition based phenomena play in biological systems. In particular, self-avoiding polymer chains are predicted to undergo a unique confinement dependent demixing transition as the anisotropy of the confined space is increased. This phenomenon may be relevant for understanding how interactions between multiple dsDNA molecules can induce self-organized structure in prokaryotes. While recent in vivo experiments and Monte Carlo simulations have delivered essential insights into this phenomenon and its relation to bacteria, there are fundamental questions remaining concerning how segregated polymer states arise, the role of confinement anisotropy and the nature of the dynamics in the segregated states. To address these questions, we introduce an artificial nanofluidic model to quantify the interactions of multiple dsDNA molecules in cavities with controlled anisotropy. We find that two dsDNA molecules of equal size confined in an elliptical cavity will spontaneously demix and orient along the cavity poles as cavity eccentricity is increased; the two chains will then swap pole positions with a frequency that decreases with increasing cavity eccentricity. In addition, we explore a system consisting of a large dsDNA molecule and a plasmid molecule. We find that the plasmid is excluded from the larger molecule and will exhibit a preference for the ellipse poles, giving rise to a non-uniform spatial distribution in the cavity that may help explain the non-uniform plasmid distribution observed during in vivo imaging of high-copy number plasmids in bacteria.
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24
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Muskhelishvili G, Sobetzko P, Travers A. Spatiotemporal Coupling of DNA Supercoiling and Genomic Sequence Organization-A Timing Chain for the Bacterial Growth Cycle? Biomolecules 2022; 12:biom12060831. [PMID: 35740956 PMCID: PMC9221221 DOI: 10.3390/biom12060831] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 06/08/2022] [Accepted: 06/08/2022] [Indexed: 01/25/2023] Open
Abstract
In this article we describe the bacterial growth cycle as a closed, self-reproducing, or autopoietic circuit, reestablishing the physiological state of stationary cells initially inoculated in the growth medium. In batch culture, this process of self-reproduction is associated with the gradual decline in available metabolic energy and corresponding change in the physiological state of the population as a function of "travelled distance" along the autopoietic path. We argue that this directional alteration of cell physiology is both reflected in and supported by sequential gene expression along the chromosomal OriC-Ter axis. We propose that during the E. coli growth cycle, the spatiotemporal order of gene expression is established by coupling the temporal gradient of supercoiling energy to the spatial gradient of DNA thermodynamic stability along the chromosomal OriC-Ter axis.
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Affiliation(s)
- Georgi Muskhelishvili
- School of Natural Sciences, Biology Program, Agricultural University of Georgia, 0159 Tbilisi, Georgia
- Correspondence:
| | - Patrick Sobetzko
- Synmikro, Loewe Center for Synthetic Microbiology, Philipps-Universität Marburg, 35043 Marburg, Germany;
| | - Andrew Travers
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK;
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25
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Filippi M, Buchner T, Yasa O, Weirich S, Katzschmann RK. Microfluidic Tissue Engineering and Bio-Actuation. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2108427. [PMID: 35194852 DOI: 10.1002/adma.202108427] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 02/07/2022] [Indexed: 06/14/2023]
Abstract
Bio-hybrid technologies aim to replicate the unique capabilities of biological systems that could surpass advanced artificial technologies. Soft bio-hybrid robots consist of synthetic and living materials and have the potential to self-assemble, regenerate, work autonomously, and interact safely with other species and the environment. Cells require a sufficient exchange of nutrients and gases, which is guaranteed by convection and diffusive transport through liquid media. The functional development and long-term survival of biological tissues in vitro can be improved by dynamic flow culture, but only microfluidic flow control can develop tissue with fine structuring and regulation at the microscale. Full control of tissue growth at the microscale will eventually lead to functional macroscale constructs, which are needed as the biological component of soft bio-hybrid technologies. This review summarizes recent progress in microfluidic techniques to engineer biological tissues, focusing on the use of muscle cells for robotic bio-actuation. Moreover, the instances in which bio-actuation technologies greatly benefit from fusion with microfluidics are highlighted, which include: the microfabrication of matrices, biomimicry of cell microenvironments, tissue maturation, perfusion, and vascularization.
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Affiliation(s)
- Miriam Filippi
- Soft Robotics Laboratory, ETH Zurich, Tannenstrasse 3, Zurich, 8092, Switzerland
| | - Thomas Buchner
- Soft Robotics Laboratory, ETH Zurich, Tannenstrasse 3, Zurich, 8092, Switzerland
| | - Oncay Yasa
- Soft Robotics Laboratory, ETH Zurich, Tannenstrasse 3, Zurich, 8092, Switzerland
| | - Stefan Weirich
- Soft Robotics Laboratory, ETH Zurich, Tannenstrasse 3, Zurich, 8092, Switzerland
| | - Robert K Katzschmann
- Soft Robotics Laboratory, ETH Zurich, Tannenstrasse 3, Zurich, 8092, Switzerland
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26
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Geisel D, Lenz P. Machine learning classification of trajectories from molecular dynamics simulations of chromosome segregation. PLoS One 2022; 17:e0262177. [PMID: 35061790 PMCID: PMC8782305 DOI: 10.1371/journal.pone.0262177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/17/2021] [Indexed: 11/25/2022] Open
Abstract
In contrast to the well characterized mitotic machinery in eukaryotes it seems as if there is no universal mechanism organizing chromosome segregation in all bacteria. Apparently, some bacteria even use combinations of different segregation mechanisms such as protein machines or rely on physical forces. The identification of the relevant mechanisms is a difficult task. Here, we introduce a new machine learning approach to this problem. It is based on the analysis of trajectories of individual loci in the course of chromosomal segregation obtained by fluorescence microscopy. While machine learning approaches have already been applied successfully to trajectory classification in other areas, so far it has not been possible to use them to discriminate segregation mechanisms in bacteria. A main obstacle for this is the large number of trajectories required to train machine learning algorithms that we overcome here by using trajectories obtained from molecular dynamics simulations. We used these trajectories to train four different machine learning algorithms, two linear models and two tree-based classifiers, to discriminate segregation mechanisms and possible combinations of them. The classification was performed once using the complete trajectories as high-dimensional input vectors as well as on a set of features which were used to transform the trajectories into low-dimensional input vectors for the classifiers. Finally, we tested our classifiers on shorter trajectories with duration times comparable (or even shorter) than typical experimental trajectories and on trajectories measured with varying temporal resolutions. Our results demonstrate that machine learning algorithms are indeed capable of discriminating different segregation mechanisms in bacteria and to even resolve combinations of the mechanisms on rather short time scales.
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Affiliation(s)
- David Geisel
- Department of Physics, Philipps University Marburg, Marburg, Germany
| | - Peter Lenz
- Department of Physics, Philipps University Marburg, Marburg, Germany
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27
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Leroux M, Soubry N, Reyes-Lamothe R. Dynamics of Proteins and Macromolecular Machines in Escherichia coli. EcoSal Plus 2021; 9:eESP00112020. [PMID: 34060908 PMCID: PMC11163846 DOI: 10.1128/ecosalplus.esp-0011-2020] [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: 01/25/2021] [Accepted: 03/16/2021] [Indexed: 11/20/2022]
Abstract
Proteins are major contributors to the composition and the functions in the cell. They often assemble into larger structures, macromolecular machines, to carry out intricate essential functions. Although huge progress in understanding how macromolecular machines function has been made by reconstituting them in vitro, the role of the intracellular environment is still emerging. The development of fluorescence microscopy techniques in the last 2 decades has allowed us to obtain an increased understanding of proteins and macromolecular machines in cells. Here, we describe how proteins move by diffusion, how they search for their targets, and how they are affected by the intracellular environment. We also describe how proteins assemble into macromolecular machines and provide examples of how frequent subunit turnover is used for them to function and to respond to changes in the intracellular conditions. This review emphasizes the constant movement of molecules in cells, the stochastic nature of reactions, and the dynamic nature of macromolecular machines.
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Affiliation(s)
- Maxime Leroux
- Department of Biology, McGill University, Montreal, QC, Canada
| | - Nicolas Soubry
- Department of Biology, McGill University, Montreal, QC, Canada
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28
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Chen W, Wei S. Compressive deformations of ring polymers in a confining channel. POLYMER 2021. [DOI: 10.1016/j.polymer.2021.124340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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29
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Chen W, Kong X, Wei Q, Chen H, Liu J, Jiang D. Compression and Stretching of Confined Linear and Ring Polymers by Applying Force. Polymers (Basel) 2021; 13:polym13234193. [PMID: 34883696 PMCID: PMC8659573 DOI: 10.3390/polym13234193] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 11/17/2021] [Accepted: 11/19/2021] [Indexed: 11/16/2022] Open
Abstract
We use Langevin dynamics to study the deformations of linear and ring polymers in different confinements by applying compression and stretching forces on their two sides. Our results show that the compression deformations are the results of an interplay among of polymer rigidity, degree of confinement, and force applied. When the applied force is beyond the threshold required for the buckling transition, the semiflexible chain under the strong confinement firstly buckles; then comes helical deformation. However, under the same force loading, the semiflexible chain under the weaker confinement exhibits buckling instability and shrinks from the folded ends/sides until it becomes three-folded structures. This happens because the strong confinement not only strongly reduces the buckling wavelength, but also increases the critical buckling force threshold. For the weakly confined polymers, in compression process, the flexible linear polymer collapses into condensed states under a small external force, whereas the ring polymer only shows slight shrinkage, due to the excluded volume interactions of two strands in the crowded states. These results are essential for understanding the deformations of the ring biomacromolecules and polymer chains in mechanical compression or driven transport.
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Affiliation(s)
- Wenduo Chen
- School of Materials, Sun Yat-sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China; (Q.W.); (H.C.); (J.L.); (D.J.)
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen 518107, China
- Correspondence:
| | - Xiangxin Kong
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China;
| | - Qianqian Wei
- School of Materials, Sun Yat-sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China; (Q.W.); (H.C.); (J.L.); (D.J.)
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen 518107, China
| | - Huaiyu Chen
- School of Materials, Sun Yat-sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China; (Q.W.); (H.C.); (J.L.); (D.J.)
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen 518107, China
| | - Jiayin Liu
- School of Materials, Sun Yat-sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China; (Q.W.); (H.C.); (J.L.); (D.J.)
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen 518107, China
| | - Dazhi Jiang
- School of Materials, Sun Yat-sen University, No. 135, Xingang Xi Road, Guangzhou 510275, China; (Q.W.); (H.C.); (J.L.); (D.J.)
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen 518107, China
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30
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Steric interactions and out-of-equilibrium processes control the internal organization of bacteria. Proc Natl Acad Sci U S A 2021; 118:2106014118. [PMID: 34675077 DOI: 10.1073/pnas.2106014118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/13/2021] [Indexed: 11/18/2022] Open
Abstract
Despite the absence of a membrane-enclosed nucleus, the bacterial DNA is typically condensed into a compact body-the nucleoid. This compaction influences the localization and dynamics of many cellular processes including transcription, translation, and cell division. Here, we develop a model that takes into account steric interactions among the components of the Escherichia coli transcriptional-translational machinery (TTM) and out-of-equilibrium effects of messenger RNA (mRNA) transcription, translation, and degradation, to explain many observed features of the nucleoid. We show that steric effects, due to the different molecular shapes of the TTM components, are sufficient to drive equilibrium phase separation of the DNA, explaining the formation and size of the nucleoid. In addition, we show that the observed positioning of the nucleoid at midcell is due to the out-of-equilibrium process of mRNA synthesis and degradation: mRNAs apply a pressure on both sides of the nucleoid, localizing it to midcell. We demonstrate that, as the cell grows, the production of these mRNAs is responsible for the nucleoid splitting into two lobes and for their well-known positioning to 1/4 and 3/4 positions on the long cell axis. Finally, our model quantitatively accounts for the observed expansion of the nucleoid when the pool of cytoplasmic mRNAs is depleted. Overall, our study suggests that steric interactions and out-of-equilibrium effects of the TTM are key drivers of the internal spatial organization of bacterial cells.
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31
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Chauhan G, Simpson ML, Abel SM. Adsorption of semiflexible polymers in crowded environments. J Chem Phys 2021; 155:034904. [PMID: 34293868 DOI: 10.1063/5.0054797] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Macromolecular crowding is a feature of cellular and cell-free systems that, through depletion effects, can impact the interactions of semiflexible biopolymers with surfaces. In this work, we use computer simulations to study crowding-induced adsorption of semiflexible polymers on otherwise repulsive surfaces. Crowding particles are modeled explicitly, and we investigate the interplay between the bending stiffness of the polymer and the volume fraction and size of crowding particles. Adsorption to flat surfaces is promoted by stiffer polymers, smaller crowding particles, and larger volume fractions of crowders. We characterize transitions from non-adsorbed to partially and strongly adsorbed states as a function of bending stiffness. The crowding-induced transitions occur at smaller values of the bending stiffness as the volume fraction of crowders increases. Concomitant effects on the size and shape of the polymer are reflected by crowding- and stiffness-dependent changes to the radius of gyration. For various polymer lengths, we identify a critical crowding fraction for adsorption and analyze its scaling behavior in terms of polymer stiffness. We also consider crowding-induced adsorption in spherical confinement and identify a regime in which increasing the bending stiffness induces desorption. The results of our simulations shed light on the interplay of crowding and bending stiffness on the spatial organization of biopolymers in encapsulated cellular and cell-free systems.
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Affiliation(s)
- Gaurav Chauhan
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee 37996, USA
| | - Michael L Simpson
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee 37996, USA
| | - Steven M Abel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee 37996, USA
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32
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Jung Y, Ha BY. Collapse transition of a heterogeneous polymer in a crowded medium. J Chem Phys 2021; 155:054902. [PMID: 34364346 DOI: 10.1063/5.0056446] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Long chain molecules can be entropically compacted in a crowded medium. We study the compaction transition of a heterogeneous polymer with ring topology by crowding effects in a free or confined space. For this, we use molecular dynamics simulations in which the effects of crowders are taken into account through effective interactions between chain segments. Our parameter choices are inspired by the Escherichia coli chromosome. The polymer consists of small and big monomers; the big monomers dispersed along the backbone are to mimic the binding of RNA polymerases. Our results show that the compaction transition is a two-step process: initial compaction induced by the association (clustering) of big monomers followed by a gradual overall compaction. They also indicate that cylindrical confinement makes the initial transition more effective; for representative parameter choices, the initial compaction accounts for about 60% reduction in the chain size. Our simulation results support the view that crowding promotes clustering of active transcription units into transcription factories.
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Affiliation(s)
- Youngkyun Jung
- Supercomputing Center, Korea Institute of Science and Technology Information, Daejeon 34141, South Korea
| | - Bae-Yeun Ha
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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33
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Xiang Y, Surovtsev IV, Chang Y, Govers SK, Parry BR, Liu J, Jacobs-Wagner C. Interconnecting solvent quality, transcription, and chromosome folding in Escherichia coli. Cell 2021; 184:3626-3642.e14. [PMID: 34186018 DOI: 10.1016/j.cell.2021.05.037] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 12/09/2020] [Accepted: 05/25/2021] [Indexed: 12/12/2022]
Abstract
All cells fold their genomes, including bacterial cells, where the chromosome is compacted into a domain-organized meshwork called the nucleoid. How compaction and domain organization arise is not fully understood. Here, we describe a method to estimate the average mesh size of the nucleoid in Escherichia coli. Using nucleoid mesh size and DNA concentration estimates, we find that the cytoplasm behaves as a poor solvent for the chromosome when the cell is considered as a simple semidilute polymer solution. Monte Carlo simulations suggest that a poor solvent leads to chromosome compaction and DNA density heterogeneity (i.e., domain formation) at physiological DNA concentration. Fluorescence microscopy reveals that the heterogeneous DNA density negatively correlates with ribosome density within the nucleoid, consistent with cryoelectron tomography data. Drug experiments, together with past observations, suggest the hypothesis that RNAs contribute to the poor solvent effects, connecting chromosome compaction and domain formation to transcription and intracellular organization.
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Affiliation(s)
- Yingjie Xiang
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT 06520, USA; Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Ivan V Surovtsev
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Yunjie Chang
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510, USA
| | - Sander K Govers
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA; Department of Biology and Institute of Chemistry, Engineering and Medicine for Human Health, Stanford University, Palo Alto, CA 94305, USA
| | - Bradley R Parry
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Jun Liu
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510, USA
| | - Christine Jacobs-Wagner
- Microbial Sciences Institute, Yale University, West Haven, CT 06516, USA; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA; Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510, USA; Department of Biology and Institute of Chemistry, Engineering and Medicine for Human Health, Stanford University, Palo Alto, CA 94305, USA.
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34
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Gogou C, Japaridze A, Dekker C. Mechanisms for Chromosome Segregation in Bacteria. Front Microbiol 2021; 12:685687. [PMID: 34220773 PMCID: PMC8242196 DOI: 10.3389/fmicb.2021.685687] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 05/19/2021] [Indexed: 11/13/2022] Open
Abstract
The process of DNA segregation, the redistribution of newly replicated genomic material to daughter cells, is a crucial step in the life cycle of all living systems. Here, we review DNA segregation in bacteria which evolved a variety of mechanisms for partitioning newly replicated DNA. Bacterial species such as Caulobacter crescentus and Bacillus subtilis contain pushing and pulling mechanisms that exert forces and directionality to mediate the moving of newly synthesized chromosomes to the bacterial poles. Other bacteria such as Escherichia coli lack such active segregation systems, yet exhibit a spontaneous de-mixing of chromosomes due to entropic forces as DNA is being replicated under the confinement of the cell wall. Furthermore, we present a synopsis of the main players that contribute to prokaryotic genome segregation. We finish with emphasizing the importance of bottom-up approaches for the investigation of the various factors that contribute to genome segregation.
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Affiliation(s)
- Christos Gogou
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands
| | - Aleksandre Japaridze
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands
| | - Cees Dekker
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands
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35
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It is time to crowd your cell culture media - Physicochemical considerations with biological consequences. Biomaterials 2021; 275:120943. [PMID: 34139505 DOI: 10.1016/j.biomaterials.2021.120943] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 05/24/2021] [Accepted: 05/29/2021] [Indexed: 12/12/2022]
Abstract
In vivo, the interior and exterior of cells is populated by various macromolecules that create an extremely crowded milieu. Yet again, in vitro eukaryotic cell culture is conducted in dilute culture media that hardly imitate the native tissue density. Herein, the concept of macromolecular crowding is discussed in both intracellular and extracellular context. Particular emphasis is given on how the physicochemical properties of the crowding molecules govern and determine kinetics, equilibria and mechanism of action of biochemical and biological reactions, processes and functions. It is evidenced that we are still at the beginning of appreciating, let alone effectively implementing, the potential of macromolecular crowding in permanently differentiated and stem cell culture systems.
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36
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Mesoscale Simulation of Bacterial Chromosome and Cytoplasmic Nanoparticles in Confinement. ENTROPY 2021; 23:e23050542. [PMID: 33924872 PMCID: PMC8146307 DOI: 10.3390/e23050542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 04/22/2021] [Accepted: 04/26/2021] [Indexed: 11/18/2022]
Abstract
In this study we investigated, using a simple polymer model of bacterial chromosome, the subdiffusive behaviors of both cytoplasmic particles and various loci in different cell wall confinements. Non-Gaussian subdiffusion of cytoplasmic particles as well as loci were obtained in our Langevin dynamic simulations, which agrees with fluorescence microscope observations. The effects of cytoplasmic particle size, locus position, confinement geometry, and density on motions of particles and loci were examined systematically. It is demonstrated that the cytoplasmic subdiffusion can largely be attributed to the mechanical properties of bacterial chromosomes rather than the viscoelasticity of cytoplasm. Due to the randomly positioned bacterial chromosome segments, the surrounding environment for both particle and loci is heterogeneous. Therefore, the exponent characterizing the subdiffusion of cytoplasmic particle/loci as well as Laplace displacement distributions of particle/loci can be reproduced by this simple model. Nevertheless, this bacterial chromosome model cannot explain the different responses of cytoplasmic particles and loci to external compression exerted on the bacterial cell wall, which suggests that the nonequilibrium activity, e.g., metabolic reactions, play an important role in cytoplasmic subdiffusion.
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37
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Aghlmandi A, Nikshad A, Safaralizadeh R, Warkiani ME, Aghebati-Maleki L, Yousefi M. Microfluidics as efficient technology for the isolation and characterization of stem cells. EXCLI JOURNAL 2021; 20:426-443. [PMID: 33746671 PMCID: PMC7975637 DOI: 10.17179/excli2020-3028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 02/15/2021] [Indexed: 01/09/2023]
Abstract
The recent years have been passed with significant progressions in the utilization of microfluidic technologies for cellular investigations. The aim of microfluidics is to mimic small-scale body environment with features like optical transparency. Microfluidics can screen and monitor different cell types during culture and study cell function in response to stimuli in a fully controlled environment. No matter how the microfluidic environment is similar to in vivo environment, it is not possible to fully investigate stem cells behavior in response to stimuli during cell proliferation and differentiation. Researchers have used stem cells in different fields from fundamental researches to clinical applications. Many cells in the body possess particular functions, but stem cells do not have a specific task and can turn into almost any type of cells. Stem cells are undifferentiated cells with the ability of changing into specific cells that can be essential for the body. Researchers and physicians are interested in stem cells to use them in testing the function of the body's systems and solving their complications. This review discusses the recent advances in utilizing microfluidic techniques for the analysis of stem cells, and mentions the advantages and disadvantages of using microfluidic technology for stem cell research.
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Affiliation(s)
- Afsoon Aghlmandi
- Department of Animal Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran
| | - Aylin Nikshad
- Department of Animal Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran
| | - Reza Safaralizadeh
- Department of Animal Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran
| | - Majid Ebrahimi Warkiani
- The School of Biomedical Engineering, University of Technology Sydney, Sydney, NSW, Australia
| | | | - Mehdi Yousefi
- Stem Cell Research Center, Tabriz University of Medical Science, Tabriz, Iran
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38
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Birnie A, Dekker C. Genome-in-a-Box: Building a Chromosome from the Bottom Up. ACS NANO 2021; 15:111-124. [PMID: 33347266 PMCID: PMC7844827 DOI: 10.1021/acsnano.0c07397] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 12/16/2020] [Indexed: 05/24/2023]
Abstract
Chromosome structure and dynamics are essential for life, as the way that our genomes are spatially organized within cells is crucial for gene expression, differentiation, and genome transfer to daughter cells. There is a wide variety of methods available to study chromosomes, ranging from live-cell studies to single-molecule biophysics, which we briefly review. While these technologies have yielded a wealth of data, such studies still leave a significant gap between top-down experiments on live cells and bottom-up in vitro single-molecule studies of DNA-protein interactions. Here, we introduce "genome-in-a-box" (GenBox) as an alternative in vitro approach to build and study chromosomes, which bridges this gap. The concept is to assemble a chromosome from the bottom up by taking deproteinated genome-sized DNA isolated from live cells and subsequently add purified DNA-organizing elements, followed by encapsulation in cell-sized containers using microfluidics. Grounded in the rationale of synthetic cell research, the approach would enable to experimentally study emergent effects at the global genome level that arise from the collective action of local DNA-structuring elements. We review the various DNA-structuring elements present in nature, from nucleoid-associated proteins and SMC complexes to phase separation and macromolecular crowders. Finally, we discuss how GenBox can contribute to several open questions on chromosome structure and dynamics.
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Affiliation(s)
- Anthony Birnie
- Department of Bionanoscience, Kavli
Institute of Nanoscience Delft, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Cees Dekker
- Department of Bionanoscience, Kavli
Institute of Nanoscience Delft, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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39
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Chauhan G, Simpson ML, Abel SM. Crowding-induced interactions of ring polymers. SOFT MATTER 2021; 17:16-23. [PMID: 33155586 DOI: 10.1039/d0sm01847c] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Macromolecular crowding and the presence of surfaces can significantly impact the spatial organization of biopolymers. While the importance of crowding-induced depletion interactions in biology has been recognized, much remains to be understood about the effect of crowding on biopolymers such as DNA plasmids. A fundamental problem highlighted by recent experiments is to characterize the impact of crowding on polymer-polymer and polymer-surface interactions. Motivated by the need for quantitative insight, we studied flexible ring polymers in crowded environments using Langevin dynamics simulations. The simulations demonstrated that crowding can lead to compaction of isolated ring polymers and enhanced interactions between two otherwise repulsive polymers. Using umbrella sampling, we determined the potential of mean force (PMF) between two ring polymers as a function of their separation distance at different volume fractions of crowding particles, φ. An effective attraction emerged at φ≈ 0.4, which is similar to the degree of crowding in cells. Analogous simulations showed that crowding can lead to strong adsorption of a ring polymer to a wall, with an effective attraction to the wall emerging at a smaller volume fraction of crowders (φ≈ 0.2). Our results reveal the magnitude of depletion interactions in a biologically-inspired model and highlight how crowding can be used to tune interactions in both cellular and cell-free systems.
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Affiliation(s)
- Gaurav Chauhan
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
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40
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Wlodarski M, Mancini L, Raciti B, Sclavi B, Lagomarsino MC, Cicuta P. Cytosolic Crowding Drives the Dynamics of Both Genome and Cytosol in Escherichia coli Challenged with Sub-lethal Antibiotic Treatments. iScience 2020; 23:101560. [PMID: 33083729 PMCID: PMC7522891 DOI: 10.1016/j.isci.2020.101560] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 05/22/2020] [Accepted: 09/10/2020] [Indexed: 11/28/2022] Open
Abstract
In contrast to their molecular mode of action, the system-level effect of antibiotics on cells is only beginning to be quantified. Molecular crowding is expected to be a relevant global regulator, which we explore here through the dynamic response phenotypes in Escherichia coli, at single-cell resolution, under sub-lethal regimes of different classes of clinically relevant antibiotics, acting at very different levels in the cell. We measure chromosomal mobility through tracking of fast (<15 s timescale) fluctuations of fluorescently tagged chromosomal loci, and we probe the fluidity of the cytoplasm by tracking cytosolic aggregates. Measuring cellular density, we show how the overall levels of macromolecular crowding affect both quantities, regardless of antibiotic-specific effects. The dominant trend is a strong correlation between the effects in different parts of the chromosome and between the chromosome and cytosol, supporting the concept of an overall global role of molecular crowding in cellular physiology.
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Affiliation(s)
- Michal Wlodarski
- Biological and Soft Systems, Cavendish Laboratory, University of Cambridge, Cambridge, UK
- Dipartimento di Fisica and I.N.F.N., Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
| | - Leonardo Mancini
- Biological and Soft Systems, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Bianca Raciti
- Biological and Soft Systems, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Bianca Sclavi
- Laboratory of Biology and Applied Pharmacology (UMR 8113 CNRS), École Normale Supérieure, Paris-Saclay, France
| | | | - Pietro Cicuta
- IFOM Foundation FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy
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41
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Cristofalo M, Marrano CA, Salerno D, Corti R, Cassina V, Mammola A, Gherardi M, Sclavi B, Cosentino Lagomarsino M, Mantegazza F. Cooperative effects on the compaction of DNA fragments by the nucleoid protein H-NS and the crowding agent PEG probed by Magnetic Tweezers. Biochim Biophys Acta Gen Subj 2020; 1864:129725. [PMID: 32891648 DOI: 10.1016/j.bbagen.2020.129725] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 07/22/2020] [Accepted: 08/30/2020] [Indexed: 11/30/2022]
Abstract
BACKGROUND DNA bridging promoted by the H-NS protein, combined with the compaction induced by cellular crowding, plays a major role in the structuring of the E. coli genome. However, only few studies consider the effects of the physical interplay of these two factors in a controlled environment. METHODS We apply a single molecule technique (Magnetic Tweezers) to study the nanomechanics of compaction and folding kinetics of a 6 kb DNA fragment, induced by H-NS bridging and/or PEG crowding. RESULTS In the presence of H-NS alone, the DNA shows a step-wise collapse driven by the formation of multiple bridges, and little variations in the H-NS concentration-dependent unfolding force. Conversely, the DNA collapse force observed with PEG was highly dependent on the volume fraction of the crowding agent. The two limit cases were interpreted considering the models of loop formation in a pulled chain and pulling of an equilibrium globule respectively. CONCLUSIONS We observed an evident cooperative effect between H-NS activity and the depletion of forces induced by PEG. GENERAL SIGNIFICANCE Our data suggest a double role for H-NS in enhancing compaction while forming specific loops, which could be crucial in vivo for defining specific mesoscale domains in chromosomal regions in response to environmental changes.
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Affiliation(s)
- M Cristofalo
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy
| | - C A Marrano
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy
| | - D Salerno
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy
| | - R Corti
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy
| | - V Cassina
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy
| | - A Mammola
- Università degli Studi di Milano, Via Celoria 16, 20133 Milano (MI), Italy
| | - M Gherardi
- Università degli Studi di Milano, Via Celoria 16, 20133 Milano (MI), Italy; IFOM, FIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milano (MI), Italy; I.N.F.N. Sezione di Milano, Via Celoria 16, 20133 Milano (MI), Italy
| | - B Sclavi
- Université Pierre et Marie Curie, Institut de Biologie Paris Seine, 7-9 Quai Saint Bernard, 75005 Paris, France
| | - M Cosentino Lagomarsino
- Università degli Studi di Milano, Via Celoria 16, 20133 Milano (MI), Italy; IFOM, FIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milano (MI), Italy; I.N.F.N. Sezione di Milano, Via Celoria 16, 20133 Milano (MI), Italy
| | - F Mantegazza
- School of Medicine and Surgery, Nanomedicine Center NANOMIB, University of Milano-Bicocca, via Raoul Follereau 3, 20854, Vedano al Lambro (MB), Italy.
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42
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Michieletto D, Orlandini E, Turner MS, Micheletti C. Separation of Geometrical and Topological Entanglement in Confined Polymers Driven out of Equilibrium. ACS Macro Lett 2020; 9:1081-1085. [PMID: 35653213 DOI: 10.1021/acsmacrolett.0c00366] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We use Brownian dynamics simulations and advanced topological profiling methods to characterize the out-of-equilibrium evolution of self-entanglement in linear polymers confined into nanochannels and under periodic compression. By introducing suitable observables, we can distinguish two main forms of entanglement that we term geometrical and topological. The latter is measured by the number of (essential) crossings of the physical knot detected after a suitable bridging of the chain termini. The former is instead measured as the average number of times a linear chain appears to cross itself when viewed under all projections and is irrespective of the physical knotted state. The key discovery of our work is that these two forms of entanglement are uncoupled and evolve with distinct dynamics. While geometrical entanglement is typically in phase with the compression-elongation cycles and it is primarily sensitive to its force f, the topological measure is mildly sensitive to cyclic modulation but strongly depends on both compression force f and duration k. The findings could assist the interpretation of experiments using fluorescence molecular tracers to track physical knots in polymers. Furthermore, we identify optimal regions in the experimentally controllable parameter space in which to obtain more/less topological and geometrical entanglement; this may help designing polymers with targeted topology.
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Affiliation(s)
- Davide Michieletto
- School of Physics and Astronomy, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, United Kingdom.,MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, North Crewe Road, Edinburgh, EH4 2XU, United Kingdom
| | - Enzo Orlandini
- Dipartimento di Fisica e Astronomia and Sezione INFN, Universitá degli Studi di Padova, I-35131 Padova, Italy
| | - Matthew S Turner
- Department of Physics and Centre for Complexity Science, University of Warwick, Coventry, CV4 7AL, U.K.,Department of Chemical Engineering, Kyoto University, Kyoto, Japan
| | - Cristian Micheletti
- SISSA (Scuola Internazionale Superiore di Studi Avanzati), Via Bonomea 265, 34136 Trieste, Italy
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43
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Chromosome Segregation in Bacillus subtilis Follows an Overall Pattern of Linear Movement and Is Highly Robust against Cell Cycle Perturbations. mSphere 2020; 5:5/3/e00255-20. [PMID: 32554717 PMCID: PMC7300352 DOI: 10.1128/msphere.00255-20] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
We have followed the segregation of origin regions on the Bacillus subtilis chromosome in the fastest practically achievable temporal manner, for a large fraction of the cell cycle. We show that segregation occurred in highly variable patterns but overall in an almost linear manner throughout the cell cycle. Segregation was slowed down, but not arrested, by treatment of cells that led to transient blocks in DNA replication, showing that segregation is highly robust against cell cycle perturbation. Computer simulations based on entropy-driven separation of newly synthesized DNA polymers can recapitulate sudden bursts of movement and segregation patterns compatible with the observed in vivo patterns, indicating that for Bacillus, segregation patterns may include entropic forces helping to separate chromosomes during the cell cycle. Although several proteins have been identified that facilitate chromosome segregation in bacteria, no clear analogue of the mitotic machinery in eukaryotic cells has been identified. In order to investigate if recognizable patterns of segregation exist during the cell cycle, we tracked the segregation of duplicated origin regions in Bacillus subtilis for 60 min in the fastest practically achievable resolution, achieving 10-s intervals. We found that while separation occurred in random patterns, often including backwards movement, overall, segregation of loci near the origins of replication was linear for the entire cell cycle. Thus, the process of partitioning can be best described as directed motion. Simulations with entropy-driven separation of polymers synthesized by two polymerases show sudden bursts of movement and segregation patterns compatible with the observed in vivo patterns, showing that for Bacillus, segregation patterns can be modeled based on entropic forces. To test if obstacles for replication forks lead to an alteration of the partitioning pattern, we challenged cells with chemicals inducing DNA damage or blocking of topoisomerase activity. Both treatments led to a moderate slowing down of separation, but linear segregation was retained, showing that chromosome segregation is highly robust against cell cycle perturbation. IMPORTANCE We have followed the segregation of origin regions on the Bacillus subtilis chromosome in the fastest practically achievable temporal manner, for a large fraction of the cell cycle. We show that segregation occurred in highly variable patterns but overall in an almost linear manner throughout the cell cycle. Segregation was slowed down, but not arrested, by treatment of cells that led to transient blocks in DNA replication, showing that segregation is highly robust against cell cycle perturbation. Computer simulations based on entropy-driven separation of newly synthesized DNA polymers can recapitulate sudden bursts of movement and segregation patterns compatible with the observed in vivo patterns, indicating that for Bacillus, segregation patterns may include entropic forces helping to separate chromosomes during the cell cycle.
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Walker DM, Freddolino PL, Harshey RM. A Well-Mixed E. coli Genome: Widespread Contacts Revealed by Tracking Mu Transposition. Cell 2020; 180:703-716.e18. [PMID: 32059782 DOI: 10.1016/j.cell.2020.01.031] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 10/21/2019] [Accepted: 01/22/2020] [Indexed: 02/06/2023]
Abstract
The three-dimensional structures of chromosomes are increasingly being recognized as playing a major role in cellular regulatory states. The efficiency and promiscuity of phage Mu transposition was exploited to directly measure in vivo interactions between genomic loci in E. coli. Two global organizing principles have emerged: first, the chromosome is well-mixed and uncompartmentalized, with transpositions occurring freely between all measured loci; second, several gene families/regions show "clustering": strong three-dimensional co-localization regardless of linear genomic distance. The activities of the SMC/condensin protein MukB and nucleoid-compacting protein subunit HU-α are essential for the well-mixed state; HU-α is also needed for clustering of 6/7 ribosomal RNA-encoding loci. The data are explained by a model in which the chromosomal structure is driven by dynamic competition between DNA replication and chromosomal relaxation, providing a foundation for determining how region-specific properties contribute to both chromosomal structure and gene regulation.
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Affiliation(s)
- David M Walker
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA
| | - Peter L Freddolino
- Department of Biological Chemistry and Department of Computational Medicine & Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA.
| | - Rasika M Harshey
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA.
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45
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Yang D, Männik J, Retterer ST, Männik J. The effects of polydisperse crowders on the compaction of the Escherichia coli nucleoid. Mol Microbiol 2020; 113:1022-1037. [PMID: 31961016 DOI: 10.1111/mmi.14467] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 01/15/2020] [Accepted: 01/15/2020] [Indexed: 01/10/2023]
Abstract
DNA binding proteins, supercoiling, macromolecular crowders, and transient DNA attachments to the cell membrane have all been implicated in the organization of the bacterial chromosome. However, it is unclear what role these factors play in compacting the bacterial DNA into a distinct organelle-like entity, the nucleoid. By analyzing the effects of osmotic shock and mechanical squeezing on Escherichia coli, we show that macromolecular crowders play a dominant role in the compaction of the DNA into the nucleoid. We find that a 30% increase in the crowder concentration from physiological levels leads to a three-fold decrease in the nucleoid's volume. The compaction is anisotropic, being higher along the long axes of the cell at low crowding levels. At higher crowding levels, the nucleoid becomes spherical, and its compressibility decreases significantly. Furthermore, we find that the compressibility of the nucleoid is not significantly affected by cell growth rates and by prior treatment with rifampicin. The latter results point out that in addition to poly ribosomes, soluble cytoplasmic proteins have a significant contribution in determining the size of the nucleoid. The contribution of poly ribosomes dominates at faster and soluble proteins at slower growth rates.
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Affiliation(s)
- Da Yang
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN, USA
| | - Jaana Männik
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN, USA.,Department of Biochemistry, and Cellular and Molecular Biology, The University of Tennessee, Knoxville, TN, USA
| | - Scott T Retterer
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Jaan Männik
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN, USA
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Marko JF. Physics and Biology (of Chromosomes). J Mol Biol 2020; 432:621-631. [PMID: 31866291 PMCID: PMC6948178 DOI: 10.1016/j.jmb.2019.11.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 11/26/2019] [Accepted: 11/27/2019] [Indexed: 12/18/2022]
Abstract
Advances in molecular biology, optics, genetics, and bioinformatics have opened the door to mapping, in molecular detail, processes inside living cells. With the ability to observe the individual moving parts of cellular machinery, concepts formerly confined to physics are entering mainstream biology. This article discusses a few ideas of this sort related to chromosome biology, to illustrate what kinds of insights physics might yet bring to our understanding of living systems.
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Affiliation(s)
- John F Marko
- Department of Physics & Astronomy and Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA; CNRS, Laboratoire de Physique Théorique de la Matière Condensée (LPTMC), Sorbonne Université, Paris, 75005, France.
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47
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Rojas ER. The Mechanical Properties of Bacteria and Why they Matter. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1267:1-14. [PMID: 32894474 DOI: 10.1007/978-3-030-46886-6_1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
I review recent techniques to measure the mechanical properties of bacterial cells and their subcellular components, and then discuss what these techniques have revealed about the constitutive mechanical properties of whole bacterial cells and subcellular material, as well as the molecular basis for these properties.
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Affiliation(s)
- Enrique R Rojas
- Department of Biology, New York University, New York, NY, USA.
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48
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Chromosome disentanglement driven via optimal compaction of loop-extruded brush structures. Proc Natl Acad Sci U S A 2019; 116:24956-24965. [PMID: 31757850 DOI: 10.1073/pnas.1906355116] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Eukaryote cell division features a chromosome compaction-decompaction cycle that is synchronized with their physical and topological segregation. It has been proposed that lengthwise compaction of chromatin into mitotic chromosomes via loop extrusion underlies the compaction-segregation/resolution process. We analyze this disentanglement scheme via considering the chromosome to be a succession of DNA/chromatin loops-a polymer "brush"-where active extrusion of loops controls the brush structure. Given type-II DNA topoisomerase (Topo II)-catalyzed topology fluctuations, we find that interchromosome entanglements are minimized for a certain "optimal" loop that scales with the chromosome size. The optimal loop organization is in accord with experimental data across species, suggesting an important structural role of genomic loops in maintaining a less entangled genome. Application of the model to the interphase genome indicates that active loop extrusion can maintain a level of chromosome compaction with suppressed entanglements; the transition to the metaphase state requires higher lengthwise compaction and drives complete topological segregation. Optimized genomic loops may provide a means for evolutionary propagation of gene-expression patterns while simultaneously maintaining a disentangled genome. We also find that compact metaphase chromosomes have a densely packed core along their cylindrical axes that explains their observed mechanical stiffness. Our model connects chromosome structural reorganization to topological resolution through the cell cycle and highlights a mechanism of directing Topo II-mediated strand passage via loop extrusion-driven lengthwise compaction.
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49
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Liu X, Jiang H, Hou Z. Configuration dynamics of a flexible polymer chain in a bath of chiral active particles. J Chem Phys 2019; 151:174904. [DOI: 10.1063/1.5125607] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Xinshuang Liu
- Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at Microscales, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Huijun Jiang
- Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at Microscales, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhonghuai Hou
- Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at Microscales, University of Science and Technology of China, Hefei, Anhui 230026, China
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50
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Lu YC, Chang YR. Gene expression in E. coli influences the position and motion of the lac operon and vicinal loci. Biochem Biophys Res Commun 2019; 519:438-443. [PMID: 31522813 DOI: 10.1016/j.bbrc.2019.09.026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 09/08/2019] [Indexed: 10/26/2022]
Abstract
Transcription and translation of active genes play an important role in determining the global organization of the chromosome. To further elucidate this phenomenon, we examined how the expression of either the lacY or the cfp gene in the native lac operon influences adjacent chromosomal segments by fluorescently labeling loci upstream and downstream of the expressed gene. Based on the positions and motile behaviors of these loci, our results reveal that the local organization of the vicinal chromosomal segments and its position in the nucleoid are both influenced by gene expression. Furthermore, we found that the effects on local organization depend on whether the expressed gene encodes a membrane protein or a cytoplasmic protein. Our measurements showing the movement of loci toward the membrane and the correlation between the motions of the upstream and downstream loci support the conclusion that the expression of genes encoding membrane proteins greatly influences chromosome dynamics.
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Affiliation(s)
- Yuan-Chu Lu
- Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan, 88, Sec.4, Ting-Chou Rd., Taipei, 116, Taiwan
| | - Yi-Ren Chang
- Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan, 88, Sec.4, Ting-Chou Rd., Taipei, 116, Taiwan.
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