1
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Korolev N, Zinchenko A, Soman A, Chen Q, Wong SY, Berezhnoy NV, Basak R, van der Maarel JRC, van Noort J, Nordenskiöld L. Reconstituted TAD-size chromatin fibers feature heterogeneous nucleosome clusters. Sci Rep 2022; 12:15558. [PMID: 36114220 PMCID: PMC9481575 DOI: 10.1038/s41598-022-19471-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Accepted: 08/30/2022] [Indexed: 11/14/2022] Open
Abstract
Large topologically associated domains (TADs) contain irregularly spaced nucleosome clutches, and interactions between such clutches are thought to aid the compaction of these domains. Here, we reconstituted TAD-sized chromatin fibers containing hundreds of nucleosomes on native source human and lambda-phage DNA and compared their mechanical properties at the single-molecule level with shorter ‘601’ arrays with various nucleosome repeat lengths. Fluorescent imaging showed increased compaction upon saturation of the DNA with histones and increasing magnesium concentration. Nucleosome clusters and their structural fluctuations were visualized in confined nanochannels. Force spectroscopy revealed not only similar mechanical properties of the TAD-sized fibers as shorter fibers but also large rupture events, consistent with breaking the interactions between distant clutches of nucleosomes. Though the arrays of native human DNA, lambda-phage and ‘601’ DNA featured minor differences in reconstitution yield and nucleosome stability, the fibers’ global structural and mechanical properties were similar, including the interactions between nucleosome clutches. These single-molecule experiments quantify the mechanical forces that stabilize large TAD-sized chromatin domains consisting of disordered, dynamically interacting nucleosome clutches and their effect on the condensation of large chromatin domains.
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2
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A Horizontal Magnetic Tweezers for Studying Single DNA Molecules and DNA-Binding Proteins. Molecules 2021; 26:molecules26164781. [PMID: 34443369 PMCID: PMC8398817 DOI: 10.3390/molecules26164781] [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: 06/30/2021] [Revised: 07/30/2021] [Accepted: 08/03/2021] [Indexed: 11/17/2022] Open
Abstract
We report data from single molecule studies on the interaction between single DNA molecules and core histones using custom-designed horizontal magnetic tweezers. The DNA-core histone complexes were formed using λ-DNA tethers, core histones, and NAP1 and were exposed to forces ranging from ~2 pN to ~74 pN. During the assembly events, we observed the length of the DNA decrease in approximate integer multiples of ~50 nm, suggesting the binding of the histone octamers to the DNA tether. During the mechanically induced disassembly events, we observed disruption lengths in approximate integer multiples of ~50 nm, suggesting the unbinding of one or more octamers from the DNA tether. We also observed histone octamer unbinding events at forces as low as ~2 pN. Our horizontal magnetic tweezers yielded high-resolution, low-noise data on force-mediated DNA-core histone assembly and disassembly processes.
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3
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Reddy G, Thirumalai D. Asymmetry in histone rotation in forced unwrapping and force quench rewrapping in a nucleosome. Nucleic Acids Res 2021; 49:4907-4918. [PMID: 33877361 PMCID: PMC8136794 DOI: 10.1093/nar/gkab263] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 02/25/2021] [Accepted: 03/30/2021] [Indexed: 01/07/2023] Open
Abstract
Single molecule pulling experiments have shown that DNA in the nucleosomes unwraps in two stages from the histone protein core (HPC). The first stage, attributed to the rupture of the outer DNA turn, occurs between 3 and 5 pNs, and is reversible. The inner DNA turn ruptures irreversibly at forces between 9 and 15 pNs (or higher) in the second stage. Molecular simulations using the Self-Organized Polymer model capture the experimental findings. The unwrapping of the outer DNA turn is independent of the pulling direction. The rupture of the DNA inner turn depends on the pulling direction and involves overcoming substantial energetic (most likely electrostatic in origin) and kinetic barriers. They arise because the mechanical force has to generate sufficient torque to rotate the HPC by 180°. On the other hand, during the rewrapping process, HPC rotation is stochastic, with force playing no role. The assembly of the outer DNA wrap upon force quench nearly coincides with the unwrapping process, confirming the reversibility of the outer turn rupture. The asymmetry in HPC rotation during unwrapping and rewrapping explains the observed hysteresis in the stretch-release cycles in experiments. We propose experiments to test the prediction that HPC rotation produces kinetic barriers in the unwrapping process.
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Affiliation(s)
- Govardhan Reddy
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, Karnataka, India
| | - D Thirumalai
- Department of Chemistry, The University of Texas, Austin, TX 78712, USA
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4
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Timpano S, Picketts DJ. Neurodevelopmental Disorders Caused by Defective Chromatin Remodeling: Phenotypic Complexity Is Highlighted by a Review of ATRX Function. Front Genet 2020; 11:885. [PMID: 32849845 PMCID: PMC7432156 DOI: 10.3389/fgene.2020.00885] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Accepted: 07/20/2020] [Indexed: 12/15/2022] Open
Abstract
The ability to determine the genetic etiology of intellectual disability (ID) and neurodevelopmental disorders (NDD) has improved immensely over the last decade. One prevailing metric from these studies is the large percentage of genes encoding epigenetic regulators, including many members of the ATP-dependent chromatin remodeling enzyme family. Chromatin remodeling proteins can be subdivided into five classes that include SWI/SNF, ISWI, CHD, INO80, and ATRX. These proteins utilize the energy from ATP hydrolysis to alter nucleosome positioning and are implicated in many cellular processes. As such, defining their precise roles and contributions to brain development and disease pathogenesis has proven to be complex. In this review, we illustrate that complexity by reviewing the roles of ATRX on genome stability, replication, and transcriptional regulation and how these mechanisms provide key insight into the phenotype of ATR-X patients.
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Affiliation(s)
- Sara Timpano
- Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada
| | - David J. Picketts
- Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, ON, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON, Canada
- Department of Medicine, University of Ottawa, Ottawa, ON, Canada
- University of Ottawa Brain and Mind Research Institute, Ottawa, ON, Canada
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5
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Spakman D, King GA, Peterman EJG, Wuite GJL. Constructing arrays of nucleosome positioning sequences using Gibson Assembly for single-molecule studies. Sci Rep 2020; 10:9903. [PMID: 32555215 PMCID: PMC7303147 DOI: 10.1038/s41598-020-66259-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Accepted: 04/24/2020] [Indexed: 01/08/2023] Open
Abstract
As the basic building blocks of chromatin, nucleosomes play a key role in dictating the accessibility of the eukaryotic genome. Consequently, nucleosomes are involved in essential genomic transactions such as DNA transcription, replication and repair. In order to unravel the mechanisms by which nucleosomes can influence, or be altered by, DNA-binding proteins, single-molecule techniques are increasingly employed. To this end, DNA molecules containing a defined series of nucleosome positioning sequences are often used to reconstitute arrays of nucleosomes in vitro. Here, we describe a novel method to prepare DNA molecules containing defined arrays of the ‘601’ nucleosome positioning sequence by exploiting Gibson Assembly cloning. The approaches presented here provide a more accessible and efficient means to generate arrays of nucleosome positioning motifs, and facilitate a high degree of control over the linker sequences between these motifs. Nucleosomes reconstituted on such arrays are ideal for interrogation with single-molecule techniques. To demonstrate this, we use dual-trap optical tweezers, in combination with fluorescence microscopy, to monitor nucleosome unwrapping and histone localisation as a function of tension. We reveal that, although nucleosomes unwrap at ~20 pN, histones (at least histone H3) remain bound to the DNA, even at tensions beyond 60 pN.
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Affiliation(s)
- Dian Spakman
- Department of Physics and Astronomy, and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Graeme A King
- Department of Physics and Astronomy, and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands. .,Institute of Structural and Molecular Biology, University College London, Gower Street, London, WC1E 6BT, UK.
| | - Erwin J G Peterman
- Department of Physics and Astronomy, and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
| | - Gijs J L Wuite
- Department of Physics and Astronomy, and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
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6
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Le TT, Gao X, Park SH, Lee J, Inman JT, Lee JH, Killian JL, Badman RP, Berger JM, Wang MD. Synergistic Coordination of Chromatin Torsional Mechanics and Topoisomerase Activity. Cell 2020; 179:619-631.e15. [PMID: 31626768 PMCID: PMC6899335 DOI: 10.1016/j.cell.2019.09.034] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 06/16/2019] [Accepted: 09/24/2019] [Indexed: 12/23/2022]
Abstract
DNA replication in eukaryotes generates DNA supercoiling, which may intertwine (braid) daughter chromatin fibers to form precatenanes, posing topological challenges during chromosome segregation. The mechanisms that limit precatenane formation remain unclear. By making direct torque measurements, we demonstrate that the intrinsic mechanical properties of chromatin play a fundamental role in dictating precatenane formation and regulating chromatin topology. Whereas a single chromatin fiber is torsionally soft, a braided fiber is torsionally stiff, indicating that supercoiling on chromatin substrates is preferentially directed in front of the fork during replication. We further show that topoisomerase II relaxation displays a strong preference for a single chromatin fiber over a braided fiber. These results suggest a synergistic coordination-the mechanical properties of chromatin inherently suppress precatenane formation during replication elongation by driving DNA supercoiling ahead of the fork, where supercoiling is more efficiently removed by topoisomerase II. VIDEO ABSTRACT.
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Affiliation(s)
- Tung T Le
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA; Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - Xiang Gao
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA; Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - Seong Ha Park
- Biophysics Program, Cornell University, Ithaca, NY 14853, USA
| | - Jaeyoon Lee
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - James T Inman
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA; Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - Joyce H Lee
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jessica L Killian
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA; Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - Ryan P Badman
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Michelle D Wang
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA; Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA.
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7
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Huo XM, Meng LF, Jiang T, Li M, Sun FZ, Sun B, Li JK. Real-time observation of nucleoplasmin-mediated DNA decondensation and condensation reveals its specific functions as a chaperone. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2018; 1861:743-751. [PMID: 30012467 DOI: 10.1016/j.bbagrm.2018.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 07/09/2018] [Accepted: 07/09/2018] [Indexed: 11/24/2022]
Abstract
Fertilization requires decondensation of promatine-condensed sperm chromatin, a dynamic process serving as an attractive system for the study of chromatin reprogramming. Nucleoplasmin is a key factor in regulating nucleosome assembly as a chaperone during fertilization process. However, knowledge on nucleoplasmin in chromatin formation remains elusive. Herein, magnetic tweezers (MT) and a chromatin assembly system were used to study the nucleoplasmin-mediated DNA decondensation/condensation at the single-molecular level in vitro. We found that protamine induces DNA condensation in a stepwise manner. Once DNA was condensed, nucleoplasmin, polyglutamic acid, and RNA could remove protamine from the DNA at different rates. The affinity binding of the different polyanions with protamine suggests chaperone-mediated chromatin decondensation activity occurs through protein-protein interactions. After decondensation, both RNA and polyglutamic acid prevented the transfer of histones onto the naked DNA. In contrast, nucleoplasmin is able to assist the histone transfer process, even though it carries the same negative charge as RNA and polyglutamic acid. These observations imply that the chaperone effects of nucleoplasmin during the decondensation/condensation process may be driven by specific spatial configuration of its acidic pentamer structure, rather than by electrostatic interaction. Our findings offer a novel molecular understanding of nucleoplasmin in sperm chromatin decondensation and subsequent developmental chromatin reprogramming at individual molecular level.
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Affiliation(s)
- Xin-Mei Huo
- Institute of Apicultural Research/Key Laboratory of Pollinating Insect Biology, Ministry of Agriculture, Chinese Academy of Agricultural Science, Beijing 100081, China
| | - Li-Feng Meng
- Institute of Apicultural Research/Key Laboratory of Pollinating Insect Biology, Ministry of Agriculture, Chinese Academy of Agricultural Science, Beijing 100081, China
| | - Tao Jiang
- Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100080, China
| | - Ming Li
- Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Fang-Zhen Sun
- Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100080, China
| | - Bo Sun
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
| | - Jian-Ke Li
- Institute of Apicultural Research/Key Laboratory of Pollinating Insect Biology, Ministry of Agriculture, Chinese Academy of Agricultural Science, Beijing 100081, China.
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8
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Ordu O, Kremser L, Lusser A, Dekker NH. Modification of the histone tetramer at the H3-H3 interface impacts tetrasome conformations and dynamics. J Chem Phys 2018; 148:123323. [PMID: 29604863 DOI: 10.1063/1.5009100] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Nucleosomes consisting of a short piece of deoxyribonucleic acid (DNA) wrapped around an octamer of histone proteins form the fundamental unit of chromatin in eukaryotes. Their role in DNA compaction comes with regulatory functions that impact essential genomic processes such as replication, transcription, and repair. The assembly of nucleosomes obeys a precise pathway in which tetramers of histones H3 and H4 bind to the DNA first to form tetrasomes, and two dimers of histones H2A and H2B are subsequently incorporated to complete the complex. As viable intermediates, we previously showed that tetrasomes can spontaneously flip between a left-handed and right-handed conformation of DNA-wrapping. To pinpoint the underlying mechanism, here we investigated the role of the H3-H3 interface for tetramer flexibility in the flipping process at the single-molecule level. Using freely orbiting magnetic tweezers, we studied the assembly and structural dynamics of individual tetrasomes modified at the cysteines close to this interaction interface by iodoacetamide (IA) in real time. While such modification did not affect the structural properties of the tetrasomes, it caused a 3-fold change in their flipping kinetics. The results indicate that the IA-modification enhances the conformational plasticity of tetrasomes. Our findings suggest that subnucleosomal dynamics may be employed by chromatin as an intrinsic and adjustable mechanism to regulate DNA supercoiling.
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Affiliation(s)
- Orkide Ordu
- Bionanoscience Department, Kavli Institute of Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Leopold Kremser
- Division of Clinical Biochemistry, Biocenter, Medical University of Innsbruck, Innrain 80, 6020 Innsbruck, Austria
| | - Alexandra Lusser
- Division of Molecular Biology, Biocenter, Medical University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Nynke H Dekker
- Bionanoscience Department, Kavli Institute of Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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9
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Ordu O, Lusser A, Dekker NH. Recent insights from in vitro single-molecule studies into nucleosome structure and dynamics. Biophys Rev 2016; 8:33-49. [PMID: 28058066 PMCID: PMC5167136 DOI: 10.1007/s12551-016-0212-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 06/17/2016] [Indexed: 01/04/2023] Open
Abstract
Eukaryotic DNA is tightly packed into a hierarchically ordered structure called chromatin in order to fit into the micron-scaled nucleus. The basic unit of chromatin is the nucleosome, which consists of a short piece of DNA wrapped around a core of eight histone proteins. In addition to their role in packaging DNA, nucleosomes impact the regulation of essential nuclear processes such as replication, transcription, and repair by controlling the accessibility of DNA. Thus, knowledge of this fundamental DNA-protein complex is crucial for understanding the mechanisms of gene control. While structural and biochemical studies over the past few decades have provided key insights into both the molecular composition and functional aspects of nucleosomes, these approaches necessarily average over large populations and times. In contrast, single-molecule methods are capable of revealing features of subpopulations and dynamic changes in the structure or function of biomolecules, rendering them a powerful complementary tool for probing mechanistic aspects of DNA-protein interactions. In this review, we highlight how these single-molecule approaches have recently yielded new insights into nucleosomal and subnucleosomal structures and dynamics.
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Affiliation(s)
- Orkide Ordu
- Bionanoscience Department, Kavli Institute of Nanoscience,, Delft University of Technology, Van der Maasweg 9,, 2629 HZ Delft, The Netherlands
| | - Alexandra Lusser
- Division of Molecular Biology, Biocenter, Medical University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Nynke H. Dekker
- Bionanoscience Department, Kavli Institute of Nanoscience,, Delft University of Technology, Van der Maasweg 9,, 2629 HZ Delft, The Netherlands
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10
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Lequieu J, Córdoba A, Schwartz DC, de Pablo JJ. Tension-Dependent Free Energies of Nucleosome Unwrapping. ACS CENTRAL SCIENCE 2016; 2:660-666. [PMID: 27725965 PMCID: PMC5043429 DOI: 10.1021/acscentsci.6b00201] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Indexed: 05/20/2023]
Abstract
Nucleosomes form the basic unit of compaction within eukaryotic genomes, and their locations represent an important, yet poorly understood, mechanism of genetic regulation. Quantifying the strength of interactions within the nucleosome is a central problem in biophysics and is critical to understanding how nucleosome positions influence gene expression. By comparing to single-molecule experiments, we demonstrate that a coarse-grained molecular model of the nucleosome can reproduce key aspects of nucleosome unwrapping. Using detailed simulations of DNA and histone proteins, we calculate the tension-dependent free energy surface corresponding to the unwrapping process. The model reproduces quantitatively the forces required to unwrap the nucleosome and reveals the role played by electrostatic interactions during this process. We then demonstrate that histone modifications and DNA sequence can have significant effects on the energies of nucleosome formation. Most notably, we show that histone tails contribute asymmetrically to the stability of the outer and inner turn of nucleosomal DNA and that depending on which histone tails are modified, the tension-dependent response is modulated differently.
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Affiliation(s)
- Joshua Lequieu
- Institute
for Molecular Engineering, University of
Chicago, Chicago, Illinois 60637, United
States
| | - Andrés Córdoba
- Institute
for Molecular Engineering, University of
Chicago, Chicago, Illinois 60637, United
States
| | - David C. Schwartz
- Laboratory
for Molecular and Computational Genomics, Department of Chemistry,
Laboratory of Genetics, and UW-Biotechnology Center, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Juan J. de Pablo
- Institute
for Molecular Engineering, University of
Chicago, Chicago, Illinois 60637, United
States
- Materials
Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
- E-mail:
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11
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Le JV, Luo Y, Darcy MA, Lucas CR, Goodwin MF, Poirier MG, Castro CE. Probing Nucleosome Stability with a DNA Origami Nanocaliper. ACS NANO 2016; 10:7073-84. [PMID: 27362329 PMCID: PMC5460529 DOI: 10.1021/acsnano.6b03218] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The organization of eukaryotic DNA into nucleosomes and chromatin undergoes dynamic structural changes to regulate genome processing, including transcription and DNA repair. Critical chromatin rearrangements occur over a wide range of distances, including the mesoscopic length scale of tens of nanometers. However, there is a lack of methodologies that probe changes over this mesoscopic length scale within chromatin. We have designed, constructed, and implemented a DNA-based nanocaliper that probes this mesoscopic length scale. We developed an approach of integrating nucleosomes into our nanocaliper at two attachment points with over 50% efficiency. Here, we focused on attaching the two DNA ends of the nucleosome to the ends of the two nanocaliper arms, so the hinge angle is a readout of the nucleosome end-to-end distance. We demonstrate that nucleosomes integrated with 6, 26, and 51 bp linker DNA are partially unwrapped by the nanocaliper by an amount consistent with previously observed structural transitions. In contrast, the nucleosomes integrated with the longer 75 bp linker DNA remain fully wrapped. We found that the nanocaliper angle is a sensitive measure of nucleosome disassembly and can read out transcription factor (TF) binding to its target site within the nucleosome. Interestingly, the nanocaliper not only detects TF binding but also significantly increases the probability of TF occupancy at its site by partially unwrapping the nucleosome. These studies demonstrate the feasibility of using DNA nanotechnology to both detect and manipulate nucleosome structure, which provides a foundation of future mesoscale studies of nucleosome and chromatin structural dynamics.
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Affiliation(s)
- Jenny V. Le
- Biophysics Graduate Program, The Ohio State University, Columbus OH 43214
| | - Yi Luo
- Biophysics Graduate Program, The Ohio State University, Columbus OH 43214
| | - Michael A. Darcy
- Department of Physics, The Ohio State University, Columbus OH 43214
| | | | | | - Michael G. Poirier
- Biophysics Graduate Program, The Ohio State University, Columbus OH 43214
- Department of Physics, The Ohio State University, Columbus OH 43214
- Corresponding authors: ,
| | - Carlos E. Castro
- Biophysics Graduate Program, The Ohio State University, Columbus OH 43214
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus OH 43214
- Corresponding authors: ,
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12
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Abstract
Chromatin regulatory processes, like all biological reactions, are dynamic and stochastic in nature but can give rise to stable and inheritable changes in gene expression patterns. A molecular understanding of those processes is key for fundamental biological insight into gene regulation, epigenetic inheritance, lineage determination, and therapeutic intervention in the case of disease. In recent years, great progress has been made in identifying important molecular players involved in key chromatin regulatory pathways. Conversely, we are only beginning to understand the dynamic interplay between protein effectors, transcription factors, and the chromatin substrate itself. Single-molecule approaches employing both highly defined chromatin substrates in vitro, as well as direct observation of complex regulatory processes in vivo, open new avenues for a molecular view of chromatin regulation. This review highlights recent applications of single-molecule methods and related techniques to investigate fundamental chromatin regulatory processes.
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Affiliation(s)
- Beat Fierz
- Laboratory
of Biophysical
Chemistry of Macromolecules, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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13
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Schlingman DJ, Mack AH, Kamenetska M, Mochrie SGJ, Regan L. Routes to DNA accessibility: alternative pathways for nucleosome unwinding. Biophys J 2015; 107:384-392. [PMID: 25028880 DOI: 10.1016/j.bpj.2014.05.042] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 04/02/2014] [Accepted: 05/23/2014] [Indexed: 01/01/2023] Open
Abstract
The dynamic packaging of DNA into chromatin is a key determinant of eukaryotic gene regulation and epigenetic inheritance. Nucleosomes are the basic unit of chromatin, and therefore the accessible states of the nucleosome must be the starting point for mechanistic models regarding these essential processes. Although the existence of different unwound nucleosome states has been hypothesized, there have been few studies of these states. The consequences of multiple states are far reaching. These states will behave differently in all aspects, including their interactions with chromatin remodelers, histone variant exchange, and kinetic properties. Here, we demonstrate the existence of two distinct states of the unwound nucleosome, which are accessible at physiological forces and ionic strengths. Using optical tweezers, we measure the rates of unwinding and rewinding for these two states and show that the rewinding rates from each state are different. In addition, we show that the probability of unwinding into each state is dependent on the applied force and ionic strength. Our results demonstrate not only that multiple unwound states exist but that their accessibility can be differentially perturbed, suggesting possible roles for these states in gene regulation. For example, different histone variants or modifications may facilitate or suppress access to DNA by promoting unwinding into one state or the other. We anticipate that the two unwound states reported here will be the basis for future models of eukaryotic transcriptional control.
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Affiliation(s)
- Daniel J Schlingman
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut
| | - Andrew H Mack
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut; Department of Applied Physics, Yale University, New Haven, Connecticut
| | - Masha Kamenetska
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut; Department of Physics, Yale University, New Haven, Connecticut
| | - Simon G J Mochrie
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut; Department of Applied Physics, Yale University, New Haven, Connecticut; Department of Physics, Yale University, New Haven, Connecticut
| | - Lynne Regan
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut; Department of Chemistry, Yale University, New Haven, Connecticut.
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14
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Kenzaki H, Takada S. Partial Unwrapping and Histone Tail Dynamics in Nucleosome Revealed by Coarse-Grained Molecular Simulations. PLoS Comput Biol 2015; 11:e1004443. [PMID: 26262925 PMCID: PMC4532510 DOI: 10.1371/journal.pcbi.1004443] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2014] [Accepted: 06/01/2015] [Indexed: 01/18/2023] Open
Abstract
Nucleosomes, basic units of chromatin, are known to show spontaneous DNA unwrapping dynamics that are crucial for transcriptional activation, but its structural details are yet to be elucidated. Here, employing a coarse-grained molecular model that captures residue-level structural details up to histone tails, we simulated equilibrium fluctuations and forced unwrapping of single nucleosomes at various conditions. The equilibrium simulations showed spontaneous unwrapping from outer DNA and subsequent rewrapping dynamics, which are in good agreement with experiments. We found several distinct partially unwrapped states of nucleosomes, as well as reversible transitions among these states. At a low salt concentration, histone tails tend to sit in the concave cleft between the histone octamer and DNA, tightening the nucleosome. At a higher salt concentration, the tails tend to bound to the outer side of DNA or be expanded outwards, which led to higher degree of unwrapping. Of the four types of histone tails, H3 and H2B tail dynamics are markedly correlated with partial unwrapping of DNA, and, moreover, their contributions were distinct. Acetylation in histone tails was simply mimicked by changing their charges, which enhanced the unwrapping, especially markedly for H3 and H2B tails. Nucleosomes, folding units of chromatin, wrap DNA about 1.75 turns and provide bottlenecks for transcription. Recent experiments showed that nucleosomes are not rigid but dynamic, showing spontaneous and partial unwrapping which is thus important for transcriptional activation. Experimentally, however, one cannot directly watch DNA unwrapping at high resolution. On the other hand, molecular dynamics simulations have high spatio-temporal resolution and thus can be powerful and complementary to experiments. Here, we put forward coarse-grained modeling of protein-DNA interactions at residue-level resolution, which is rather generic and thus can be applied to any protein-DNA complexes. By this method, we could reveal spontaneous and salt-concentration dependent partial unwrapping of DNA from nucleosomes. In addition to consistency with single molecule experiments, the simulation showed multiple and distinct intermediate states of unwrapping. Interestingly, partial unwrapping of DNA is correlated with certain parts of histone tail dynamics. Deleting positive charges in histone tails that mimics histone acetylation facilitated partial unwrapping, most significantly for H3 and H2B.
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Affiliation(s)
- Hiroo Kenzaki
- Advanced Center for Computing and Communication, RIKEN, Hirosawa, Wako, Saitama, Japan
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Kitashirakawa Sakyo, Kyoto, Japan
| | - Shoji Takada
- Advanced Center for Computing and Communication, RIKEN, Hirosawa, Wako, Saitama, Japan
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Kitashirakawa Sakyo, Kyoto, Japan
- * E-mail:
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15
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Elbel T, Langowski J. The effect of DNA supercoiling on nucleosome structure and stability. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:064105. [PMID: 25563201 DOI: 10.1088/0953-8984/27/6/064105] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Nucleosomes have to open to allow access to DNA in transcription, replication, and DNA damage repair. Changes in DNA torsional strain (e.g. during transcription elongation) influence the accessibility of nucleosomal DNA. Here we investigated the effect of DNA supercoiling-induced torsional strain on nucleosome structure and stability by scanning force microscopy (SFM) and fluorescence correlation spectroscopy (FCS). Nucleosomes were reconstituted onto 2.7 kb DNA plasmids with varying superhelical densities. The SFM results show a clear dependence of the amount of DNA wrapped around the nucleosome core on the strength and type of supercoiling. Negative supercoiling led to smaller nucleosome opening angles as compared to relaxed or positively supercoiled DNA. FCS experiments show that nucleosomes reconstituted on negatively superhelical DNA are more resistant to salt-induced destabilization, as seen by reduced H2A-H2B dimer eviction from the nucleosome. Our results show that changes in DNA topology, e.g. during transcription elongation, affect the accessibility of nucleosomal DNA.
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Affiliation(s)
- Tabea Elbel
- German Cancer Research Center (DKFZ), Biophysics of Macromolecules (B040), Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany
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16
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Langecker M, Ivankin A, Carson S, Kinney SM, Simmel FC, Wanunu M. Nanopores suggest a negligible influence of CpG methylation on nucleosome packaging and stability. NANO LETTERS 2015; 15:783-90. [PMID: 25495735 PMCID: PMC4296928 DOI: 10.1021/nl504522n] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 12/09/2014] [Indexed: 05/21/2023]
Abstract
Nucleosomes are the fundamental repeating units of chromatin, and dynamic regulation of their positioning along DNA governs gene accessibility in eukaryotes. Although epigenetic factors have been shown to influence nucleosome structure and dynamics, the impact of DNA methylation on nucleosome packaging remains controversial. Further, all measurements to date have been carried out under zero-force conditions. In this paper, we present the first automated force measurements that probe the impact of CpG DNA methylation on nucleosome stability. In solid-state nanopore force spectroscopy, a nucleosomal DNA tail is captured into a pore and pulled on with a time-varying electrophoretic force until unraveling is detected. This is automatically repeated for hundreds of nucleosomes, yielding statistics of nucleosome lifetime vs electrophoretic force. The force geometry, which is similar to displacement forces exerted by DNA polymerases and helicases, reveals that nucleosome stability is sensitive to DNA sequence yet insensitive to CpG methylation. Our label-free method provides high-throughput data that favorably compares with other force spectroscopy experiments and is suitable for studying a variety of DNA-protein complexes.
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Affiliation(s)
- Martin Langecker
- Lehrstuhl für
Bioelektronik, Physics Department and ZNN/WSI, Technische Universität München, Am Coulombwall 4a, 85748 Garching, Germany
| | - Andrey Ivankin
- Departments of Physics and Chemistry/Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States
| | - Spencer Carson
- Departments of Physics and Chemistry/Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States
| | - Shannon
R. M. Kinney
- Department
of Pharmaceutical and Administrative Sciences, Western New England University, Springfield, Massachusetts 01119, United States
| | - Friedrich C. Simmel
- Lehrstuhl für
Bioelektronik, Physics Department and ZNN/WSI, Technische Universität München, Am Coulombwall 4a, 85748 Garching, Germany
- E-mail:
| | - Meni Wanunu
- Departments of Physics and Chemistry/Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States
- E-mail:
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17
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Inman J, Smith BY, Hall MA, Forties R, Jin J, Sethna JP, Wang MD. DNA Y structure: a versatile, multidimensional single molecule assay. NANO LETTERS 2014; 14:6475-80. [PMID: 25291441 PMCID: PMC4245981 DOI: 10.1021/nl503009d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Optical trapping is a powerful single molecule technique used to study dynamic biomolecular events, especially those involving DNA and DNA-binding proteins. Current implementations usually involve only one of stretching, unzipping, or twisting DNA along one dimension. To expand the capabilities of optical trapping for more complex measurements would require a multidimensional technique that combines all of these manipulations in a single experiment. Here, we report the development and utilization of such a novel optical trapping assay based on a three-branch DNA construct, termed a "Y structure". This multidimensional assay allows precise, real-time tracking of multiple configurational changes. When the Y structure template is unzipped under both force and torque, the force and extension of all three branches can be determined simultaneously. Moreover, the assay is readily compatible with fluorescence, as demonstrated by unzipping through a fluorescently labeled, paused transcription complex. This novel assay thus allows for the visualization and precision mapping of complex interactions of biomechanical events.
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Affiliation(s)
- James
T. Inman
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - Benjamin Y. Smith
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - Michael A. Hall
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - Robert
A. Forties
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - Jing Jin
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - James P. Sethna
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
| | - Michelle D. Wang
- Department of Physics, LASSP and Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States
- M.D.W. e-mail:
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18
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Torque modulates nucleosome stability and facilitates H2A/H2B dimer loss. Nat Commun 2014; 4:2579. [PMID: 24113677 PMCID: PMC3848035 DOI: 10.1038/ncomms3579] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2013] [Accepted: 09/10/2013] [Indexed: 12/27/2022] Open
Abstract
The nucleosome, the fundamental packing unit of chromatin, has a distinct chirality: 147 bp of DNA are wrapped around the core histones in a left-handed, negative superhelix. It has been suggested that this chirality has functional significance, particularly in the context of the cellular processes that generate DNA supercoiling, such as transcription and replication. However, the impact of torsion on nucleosome structure and stability is largely unknown. Here we perform a detailed investigation of single nucleosome behavior on the high affinity 601 positioning sequence under tension and torque using the angular optical trapping technique. We find that torque has only a moderate effect on nucleosome unwrapping. In contrast, we observe a dramatic loss of H2A/H2B dimers upon nucleosome disruption under positive torque, while (H3/H4)2 tetramers are efficiently retained irrespective of torsion. These data indicate that torque could regulate histone exchange during transcription and replication.
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Lavelle C. Pack, unpack, bend, twist, pull, push: the physical side of gene expression. Curr Opin Genet Dev 2014; 25:74-84. [PMID: 24576847 DOI: 10.1016/j.gde.2014.01.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 01/03/2014] [Indexed: 12/31/2022]
Abstract
Molecular motors such as polymerases produce physical constraints on DNA and chromatin. Recent techniques, in particular single-molecule micromanipulation, provide estimation of the forces and torques at stake. These biophysical approaches have improved our understanding of chromatin behaviour under physiological physical constraints and should, in conjunction with genome wide and in vivo studies, help to build more realistic mechanistic models of transcription in the context of chromatin. Here, we wish to provide a brief overview of our current knowledge in the field, and emphasize at the same time the importance of DNA supercoiling as a major parameter in gene regulation.
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Affiliation(s)
- Christophe Lavelle
- National Museum of Natural History, Paris, France; CNRS UMR7196, Paris, France; INSERM U1154, Paris, France; Nuclear Architecture and Dynamics, CNRS GDR3536, Paris, France.
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20
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Heller I, Hoekstra TP, King GA, Peterman EJG, Wuite GJL. Optical tweezers analysis of DNA-protein complexes. Chem Rev 2014; 114:3087-119. [PMID: 24443844 DOI: 10.1021/cr4003006] [Citation(s) in RCA: 113] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Iddo Heller
- Department of Physics and Astronomy and LaserLaB Amsterdam, VU University Amsterdam , De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
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21
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Ivankin A, Carson S, Kinney SRM, Wanunu M. Fast, label-free force spectroscopy of histone-DNA interactions in individual nucleosomes using nanopores. J Am Chem Soc 2013; 135:15350-2. [PMID: 24079416 DOI: 10.1021/ja408354s] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Herein we report a novel approach for fast, label-free probing of DNA-histone interactions in individual nucleosomes. We use solid-state nanopores to unravel individual DNA/histone complexes for the first time and find that the unraveling time depends on the applied electrophoretic force, and our results are in line with previous studies that employ optical tweezers. Our approach for studying nucleosomal interactions can greatly accelerate the understanding of fundamental mechanisms by which transcription, replication, and repair processes in a cell are modulated through DNA-histone interactions, as well as in diagnosis of diseases with abnormal patterns of DNA and histone modifications.
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Affiliation(s)
- Andrey Ivankin
- Departments of Physics and Chemistry/Chemical Biology, Northeastern University , Boston, Massachusetts 02115, United States
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22
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Mack AH, Schlingman DJ, Kamenetska M, Collins R, Regan L, Mochrie SGJ. The molecular yo-yo method: live jump detection improves throughput of single-molecule force spectroscopy for out-of-equilibrium transitions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:085119. [PMID: 24007119 DOI: 10.1063/1.4819026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
By monitoring multiple molecular transitions, force-clamp, and trap-position-clamp methods have led to precise determinations of the free energies and free energy landscapes for molecular states populated in equilibrium at the same or similar forces. Here, we present a powerful new elaboration of the force-clamp and force-jump methods, applicable to transitions far from equilibrium. Specifically, we have implemented a live jump detection and force-clamp algorithm that intelligently adjusts and maintains the force on a single molecule in response to the measured state of that molecule. We are able to collect hundreds of individual molecular transitions at different forces, many times faster than previously, permitting us to accurately determine force-dependent lifetime distributions and reaction rates. Application of our method to unwinding and rewinding the nucleosome inner turn, using optical tweezers reveals experimental lifetime distributions that comprise a statistically meaningful number of transitions, and that are accurately single exponential. These measurements significantly reduce the error in the previously measured rates, and demonstrate the existence of a single, dominant free energy barrier at each force studied. A key benefit of the molecular yo-yo method for nucleosomes is that it reduces as far as possible the time spent in the tangentially bound state, which minimizes the loss of nucleosomes by dissociation.
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Affiliation(s)
- A H Mack
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut 06511, USA
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23
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Dynamics of forced nucleosome unraveling and role of nonuniform histone-DNA interactions. Biophys J 2013; 103:989-98. [PMID: 23009848 DOI: 10.1016/j.bpj.2012.07.043] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Revised: 07/20/2012] [Accepted: 07/30/2012] [Indexed: 11/21/2022] Open
Abstract
A coarse-grained model of the nucleosome is introduced to investigate the dynamics of force-induced unwrapping of DNA from histone octamers. In this model, the DNA is treated as a charged, discrete worm-like chain, and the octamer is treated as a rigid cylinder carrying a positively charged superhelical groove that accommodates 1.7 turns of DNA. The groove charges are parameterized to reproduce the nonuniform histone/DNA interaction free energy profile and the loading rate-dependent unwrapping forces, both obtained from single-molecule experiments. Brownian dynamics simulations of the model under constant loading conditions reveal that nucleosome unraveling occurs in three distinct stages. At small extensions, the flanking DNA exhibits rapid unwrapping-rewrapping (breathing) dynamics and the octamer flips ∼180° and moves toward the pulling axis. At intermediate extensions, the outer turn of DNA unwraps gradually and the octamer swivels about the taut linkers and flips a further ∼90° to orient its superhelical axis almost parallel to the pulling axis. At large extensions, a portion of the inner turn unwraps abruptly with a notable rip in the force-extension plot and a >90° flip of the octamer. The remaining inner turn unwraps reversibly to leave a small portion of DNA attached to the octamer despite extended pulling. Our simulations further reveal that the nonuniform histone/DNA interactions in canonical nucleosomes serve to: stabilize the inner turn against unraveling while enhancing the breathing dynamics of the nucleosome and prevent dissociation of the octamer from the DNA while facilitating its mobility along the DNA. Thus, the modulation of the histone/DNA interactions could constitute one possible mechanism for regulating the accessibility of the nucleosome-wound DNA sequences.
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24
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Mochrie SGJ, Mack AH, Schlingman DJ, Collins R, Kamenetska M, Regan L. Unwinding and rewinding the nucleosome inner turn: force dependence of the kinetic rate constants. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:012710. [PMID: 23410362 PMCID: PMC3902847 DOI: 10.1103/physreve.87.012710] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 10/11/2012] [Indexed: 06/01/2023]
Abstract
A simple model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn is constructed and quantitatively compared to the results of recent measurements [A. H. Mack et al., J. Mol. Biol. 423, 687 (2012)]. First, a coarse-grained model for the histone-DNA free-energy landscape that incorporates both an elastic free-energy barrier and specific histone-DNA bonds is developed. Next, a theoretical expression for the rate of transitions across a piecewise linear free-energy landscape with multiple minima and maxima is presented. Then, the model free-energy landscape, approximated as a piecewise linear function, and the theoretical expression for the transition rates are combined to construct a model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn. Least-mean-squares fitting of the model rates to the rates observed in recent experiments rates demonstrates that this model is able to well describe the force-dependent unwinding and rewinding rates of the nucleosome inner turn, observed in the recent experiments, except at the highest forces studied, where an additional ad hoc term is required to describe the data, which may be interpreted as an indication of an alternate high-force nucleosome disassembly pathway, that bypasses simple unwinding. The good agreement between the measurements and the model at lower forces demonstrates that both specific histone-DNA contacts and an elastic free-energy barrier play essential roles for nucleosome winding and unwinding, and quantifies their relative contributions.
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Affiliation(s)
- S G J Mochrie
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut 06520, USA.
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25
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Victor JM, Zlatanova J, Barbi M, Mozziconacci J. Pulling chromatin apart: Unstacking or Unwrapping? BMC BIOPHYSICS 2012. [PMID: 23186373 PMCID: PMC3575279 DOI: 10.1186/2046-1682-5-21] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Background Understanding the mechanical properties of chromatin is an essential step towards deciphering the physical rules of gene regulation. In the past ten years, many single molecule experiments have been carried out, and high resolution measurements of the chromatin fiber stiffness are now available. Simulations have been used in order to link those measurements with structural cues, but so far no clear agreement among different groups has been reached. Results We revisit here some of the most precise experimental results obtained with carefully reconstituted fibers. Conclusions We show that the mechanical properties of the chromatin fiber can be quantitatively accounted for by the stiffness of the DNA molecule and the 3D structure of the chromatin fiber.
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Affiliation(s)
- Jean Marc Victor
- , Laboratory for Theoretical Physics of Condensed Matter, UPMC, 75005 Paris, France.
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26
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Vlijm R, Smitshuijzen JSJ, Lusser A, Dekker C. NAP1-assisted nucleosome assembly on DNA measured in real time by single-molecule magnetic tweezers. PLoS One 2012; 7:e46306. [PMID: 23050009 PMCID: PMC3457989 DOI: 10.1371/journal.pone.0046306] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 08/30/2012] [Indexed: 11/19/2022] Open
Abstract
While many proteins are involved in the assembly and (re)positioning of nucleosomes, the dynamics of protein-assisted nucleosome formation are not well understood. We study NAP1 (nucleosome assembly protein 1) assisted nucleosome formation at the single-molecule level using magnetic tweezers. This method allows to apply a well-defined stretching force and supercoiling density to a single DNA molecule, and to study in real time the change in linking number, stiffness and length of the DNA during nucleosome formation. We observe a decrease in end-to-end length when NAP1 and core histones (CH) are added to the dsDNA. We characterize the formation of complete nucleosomes by measuring the change in linking number of DNA, which is induced by the NAP1-assisted nucleosome assembly, and which does not occur for non-nucleosomal bound histones H3 and H4. By rotating the magnets, the supercoils formed upon nucleosome assembly are removed and the number of assembled nucleosomes can be counted. We find that the compaction of DNA at low force is about 56 nm per assembled nucleosome. The number of compaction steps and associated change in linking number indicate that NAP1-assisted nucleosome assembly is a two-step process.
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Affiliation(s)
- Rifka Vlijm
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
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27
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Kinetics and thermodynamics of phenotype: unwinding and rewinding the nucleosome. J Mol Biol 2012; 423:687-701. [PMID: 22944905 DOI: 10.1016/j.jmb.2012.08.021] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 08/23/2012] [Accepted: 08/24/2012] [Indexed: 02/01/2023]
Abstract
Chromatin "remodeling" is widely accepted as the mechanism that permits access to DNA by the transcription machinery. To date, however, there has been no experimental measurement of the changes in the kinetics and thermodynamics of the DNA-histone octamer association that are required to remodel chromatin so that transcription may occur. Here, we present the results of optical tweezer measurements that compare the kinetic and thermodynamic properties of nucleosomes composed of unmodified histones with those of nucleosomes that contain a mutant histone H4 (H4-R45H), which has been shown to allow SWI/SNF remodeling factor-independent transcription from the yeast HO promoter in vivo. Our measurements, carried out in a force-clamp mode, determine the force-dependent unwinding and rewinding rates of the nucleosome inner turn. At each force studied, nucleosomes containing H4-R45H unwind more rapidly and rewind more slowly than nucleosomes containing unmodified H4, indicating that the latter are the more stable. Extrapolation to forces at which the winding and unwinding rates are equal determines the absolute free energy of the nucleosome inner turn to be -32k(B)T for nucleosomes containing unmodified H4 and -27k(B)T for nucleosomes containing H4-R45H. Thus, the "loosening" or "remodeling" caused by this point mutation, which is demonstrated to be sufficient to allow transcriptional machinery access to the HO promoter (in the absence of other remodeling factors), is 5k(B)T. The correlation between the free energy of the nucleosome inner turn and the sin (SWI/SNF-independent) transcription suggests that, beyond partial unwinding, complete histone unwinding may play a role in transcriptional activation.
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28
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Choy JS, Lee TH. Structural dynamics of nucleosomes at single-molecule resolution. Trends Biochem Sci 2012; 37:425-35. [PMID: 22831768 DOI: 10.1016/j.tibs.2012.06.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Revised: 06/22/2012] [Accepted: 06/29/2012] [Indexed: 11/29/2022]
Abstract
The detailed mechanisms of how DNA that is assembled around a histone core can be accessed by DNA-binding proteins for transcription, replication, or repair, remain elusive nearly 40 years after Kornberg's nucleosome model was proposed. Uncovering the structural dynamics of nucleosomes is a crucial step in elucidating the mechanisms regulating genome accessibility. This requires the deconvolution of multiple structural states within an ensemble. Recent advances in single-molecule methods enable unprecedented efficiency in examining subpopulation dynamics. In this review, we summarize studies of nucleosome structure and dynamics from single-molecule approaches and how they advance our understanding of the mechanisms that govern DNA transactions.
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Affiliation(s)
- John S Choy
- Department of Physics, Bio-X Program, Stanford University, Stanford, CA 94305, USA.
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29
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Mollazadeh-Beidokhti L, Mohammad-Rafiee F, Schiessel H. Nucleosome dynamics between tension-induced states. Biophys J 2012; 102:2235-40. [PMID: 22677376 PMCID: PMC3353096 DOI: 10.1016/j.bpj.2012.04.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 03/13/2012] [Accepted: 04/10/2012] [Indexed: 10/28/2022] Open
Abstract
We studied the dynamical behavior of a mononucleosome under tension using a theoretical model that takes into account the nucleosomal geometry, DNA elasticity, nonspecific DNA-protein binding, and effective repulsion between the two DNA turns. Using a dynamical Monte-Carlo simulation algorithm, we demonstrate that this model shows a behavior that for an appropriate set of parameters is in quantitative agreement with data from micromanipulation experiments on individual nucleosomes. All of the parameters of the model follow from the data obtained from two types of pulling experiments, namely, constant force and constant loading rate ensembles.
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30
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Abstract
DNA unzipping is a powerful tool to study protein-DNA interactions at the single-molecule level. In this chapter, we provide a detailed and practical guide to performing this technique with an optical trap, using nucleosome studies as an example. We detail protocols for preparing an unzipping template, constructing and calibrating the instrument, and acquiring, processing, and analyzing unzipping data. We also summarize major results from utilization of this technique for the studies of nucleosome structure, dynamics, positioning, and remodeling.
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Affiliation(s)
- Ming Li
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, USA
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31
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Abstract
With nucleosomes being tightly associated with the majority of eukaryotic DNA, it is essential that mechanisms are in place that can move nucleosomes 'out of the way'. A focus of current research comprises chromatin remodeling complexes, which are ATP-consuming protein complexes that, for example, pull or push nucleosomes along DNA. The precise mechanisms used by those complexes are not yet understood. Hints for possible mechanisms might be found among the various spontaneous fluctuations that nucleosomes show in the absence of remodelers. Thermal fluctuations induce the partial unwrapping of DNA from the nucleosomes and introduce twist or loop defects in the wrapped DNA, leading to nucleosome sliding along DNA. In this minireview, we discuss nucleosome dynamics from two angles. First, we describe the dynamical modes of nucleosomes in the absence of remodelers that are experimentally fairly well characterized and theoretically understood. Then, we discuss remodelers and describe recent insights about the possible schemes that they might use.
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Affiliation(s)
- Ralf Blossey
- Université de Sciences et de Technologies de Lille, Interdisciplinary Research Institute, USR 3078 CNRS, Villeneuve d'Ascq, France.
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32
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Bednar J, Dimitrov S. Chromatin under mechanical stress: from single 30 nm fibers to single nucleosomes. FEBS J 2011; 278:2231-43. [PMID: 21535477 DOI: 10.1111/j.1742-4658.2011.08153.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
About a decade ago, the elastic properties of a single chromatin fiber and, subsequently, those of a single nucleosome started to be explored using optical and magnetic tweezers. These techniques have allowed direct measurements of several essential physical parameters of individual nucleosomes and nucleosomal arrays, including the forces responsible for the maintenance of the structure of both the chromatin fiber and the individual nucleosomes, as well as the mechanism of their unwinding under mechanical stress. Experiments on the assembly of individual chromatin fibers have illustrated the complexity of the process and the key role of certain specific components. Nevertheless a substantial disparity exists in the data reported from various experiments. Chromatin, unlike naked DNA, is a system which is extremely sensitive to environmental conditions, and studies carried out under even slightly different conditions are difficult to compare directly. In this review we summarize the available data and their impact on our knowledge of both nucleosomal structure and the dynamics of nucleosome and chromatin fiber assembly and organization.
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Affiliation(s)
- Jan Bednar
- CNRS, Laboratoire de Spectrometrie Physique, St Martin d'Heres, France.
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Chromatin fiber dynamics under tension and torsion. Int J Mol Sci 2010; 11:1557-79. [PMID: 20480035 PMCID: PMC2871131 DOI: 10.3390/ijms11041557] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 02/20/2010] [Accepted: 03/19/2010] [Indexed: 01/22/2023] Open
Abstract
Genetic and epigenetic information in eukaryotic cells is carried on chromosomes, basically consisting of large compact supercoiled chromatin fibers. Micromanipulations have recently led to great advances in the knowledge of the complex mechanisms underlying the regulation of DNA transaction events by nucleosome and chromatin structural changes. Indeed, magnetic and optical tweezers have allowed opportunities to handle single nucleosomal particles or nucleosomal arrays and measure their response to forces and torques, mimicking the molecular constraints imposed in vivo by various molecular motors acting on the DNA. These challenging technical approaches provide us with deeper understanding of the way chromatin dynamically packages our genome and participates in the regulation of cellular metabolism.
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Lavelle C. Forces and torques in the nucleus: chromatin under mechanical constraints. Biochem Cell Biol 2009; 87:307-22. [PMID: 19234543 DOI: 10.1139/o08-123] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Genomic DNA in eukaryotic cells is organized in discrete chromosome territories, each consisting of a single huge hierarchically supercoiled nucleosomal fiber. Through dynamic changes in structure, resulting from chemical modifications and mechanical constraints imposed by numerous factors in vivo, chromatin plays a critical role in the regulation of DNA metabolism processes, including replication and transcription. Indeed, DNA-translocating enzymes, such as polymerases, produce physical constraints that chromatin has to overcome. Recent techniques, in particular single-molecule micromanipulation, have allowed precise quantization of forces and torques at work in the nucleus and have greatly improved our understanding of chromatin behavior under physiological mechanical constraints. These new biophysical approaches should enable us to build realistic mechanistic models and progressively specify the ad hoc and hazy "because of chromatin structure" argument often used to interpret experimental studies of biological function in the context of chromatin.
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The ATTCT repeats of spinocerebellar ataxia type 10 display strong nucleosome assembly which is enhanced by repeat interruptions. Gene 2009; 434:29-34. [DOI: 10.1016/j.gene.2008.12.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 12/07/2008] [Accepted: 12/15/2008] [Indexed: 12/19/2022]
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Bussiek M, Hoischen C, Diekmann S, Bennink ML. Sequence-specific physical properties of African green monkey alpha-satellite DNA contribute to centromeric heterochromatin formation. J Struct Biol 2009; 167:36-46. [PMID: 19332128 DOI: 10.1016/j.jsb.2009.03.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 03/06/2009] [Accepted: 03/18/2009] [Indexed: 01/19/2023]
Abstract
Satellite DNA, a major component of eukaryotic centromeric heterochromatin, is potentially associated with the processes ensuring the faithful segregation of the genetic material during cell division. Structural properties of alpha-satellite DNA (AS) from African green monkey (AGM) were studied. Atomic force microscopy imaging showed smaller end-to-end distances of AS fragments than would be expected for the persistence length of random sequence DNA. The apparent persistence length of the AS was determined as 35nm. Gel-electrophoresis indicated only a weak contribution of intrinsic curvature to the DNA conformations suggesting an additional contribution of an elevated bending flexibility to the reduced end-to-end distances. Next, the force-extension behavior of the naked AS and in complex with nucleosomes was studied using optical tweezers. The naked AS showed a reduced overstretching transition force (-18% the value determined for random DNA) and higher forces required to straighten the DNA. Finally, reconstituted AS nucleosomes disrupted at significantly higher forces as compared with random DNA nucleosomes which is probably due to structural properties of the AS which stabilize the nucleosomes. The data support that the AS plays a role in the formation of centromeric heterochromatin due to specific structural properties and suggest that a relatively higher mechanical stability of nucleosomes is important in AGM-AS chromatin.
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Affiliation(s)
- Malte Bussiek
- Department Biophysical Engineering, Faculty of Science and Technology and Mesa+ Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. m.bussiek@utwente
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Kelbauskas L, Woodbury N, Lohr D. DNA sequence-dependent variation in nucleosome structure, stability, and dynamics detected by a FRET-based analysisThis paper is one of a selection of papers published in this Special Issue, entitled 29th Annual International Asilomar Chromatin and Chromosomes Conference, and has undergone the Journal’s usual peer review process. Biochem Cell Biol 2009; 87:323-35. [DOI: 10.1139/o08-126] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Förster resonance energy transfer (FRET) techniques provide powerful and sensitive methods for the study of conformational features in biomolecules. Here, we review FRET-based studies of nucleosomes, focusing particularly on our work comparing the widely used nucleosome standard, 5S rDNA, and 2 promoter-derived regulatory element-containing nucleosomes, mouse mammary tumor virus (MMTV)-B and GAL10. Using several FRET approaches, we detected significant DNA sequence-dependent structure, stability, and dynamics differences among the three. In particular, 5S nucleosomes and 5S H2A/H2B-depleted nucleosomal particles have enhanced stability and diminished DNA dynamics, compared with MMTV-B and GAL10 nucleosomes and particles. H2A/H2B-depleted nucleosomes are of interest because they are produced by the activities of many transcription-associated complexes. Significant location-dependent (intranucleosomal) stability and dynamics variations were also observed. These also vary among nucleosome types. Nucleosomes restrict regulatory factor access to DNA, thereby impeding genetic processes. Eukaryotic cells possess mechanisms to alter nucleosome structure, to generate DNA access, but alterations often must be targeted to specific nucleosomes on critical regulatory DNA elements. By endowing specific nucleosomes with intrinsically higher DNA accessibility and (or) enhanced facility for conformational transitions, DNA sequence-dependent nucleosome dynamics and stability variations have the potential to facilitate nucleosome recognition and, thus, aid in the crucial targeting process. This and other nucleosome structure and function conclusions from FRET analyses are discussed.
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Affiliation(s)
- L. Kelbauskas
- Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
| | - N. Woodbury
- Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
| | - D. Lohr
- Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
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Balaji S, Iyer LM, Aravind L. HPC2 and ubinuclein define a novel family of histone chaperones conserved throughout eukaryotes. MOLECULAR BIOSYSTEMS 2009; 5:269-75. [PMID: 19225618 PMCID: PMC2898643 DOI: 10.1039/b816424j] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Using sensitive protein sequence profile analyses we investigated the evolution of some histone chaperones and showed that Hir3p and Hpc2p have a much wider phyletic pattern than was previously known.
While histone chaperones have been intensely studied, the roles of components of the Hir–Asf1 histone chaperone complex such as Hir3p and Hpc2p are poorly understood. Using sensitive protein sequence profile analyses we investigated the evolution of these proteins and showed that Hir3p and Hpc2p have a much wider phyletic pattern than was previously known. We established the animal histone-deacetylase-complex-interacting proteins, CAIN/CABIN, to be orthologs of Hir3p. They contain a conserved core of around 30 TPR-like bi-helical repeats that are likely to form a super-helical scaffold. We identified a conserved domain, the HUN domain, in all Hpc2p homologs, including animal ubinuclein/yemanuclein and the recently discovered vertebrate cell-cycle regulator FLJ25778. The HUN domain has a characteristic pattern of conserved acidic residues based on which we predict that it is a previously unrecognized histone-tail-binding chaperone. By analyzing various high-throughput data sets, such as RNAi knock-downs, genetic and protein interaction maps and cell-cycle-specific gene expression data, we present evidence that Hpc2p homologs might be deployed in specific processes of chromatin dynamics relating to cell-cycle progression in vertebrates and schizogony in Plasmodium. Beyond the conserved HUN domain these proteins show extensive divergence patterns in different eukaryotic lineages. Hence, we propose that Hpc2p homologs are probably involved in recruitment of the ancient conserved histone-loading Hir–Asf1 complex to different lineage-specific chromatin reorganization processes.
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Affiliation(s)
- S Balaji
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
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High-resolution dynamic mapping of histone-DNA interactions in a nucleosome. Nat Struct Mol Biol 2009; 16:124-9. [PMID: 19136959 PMCID: PMC2635915 DOI: 10.1038/nsmb.1526] [Citation(s) in RCA: 305] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Accepted: 11/10/2008] [Indexed: 11/10/2022]
Abstract
The nature of the nucleosomal barrier which regulates access to the underlying DNA during many cellular processes is not fully understood. Here we present a detailed map of histone-DNA interactions along the DNA sequence to near basepair accuracy by mechanically unzipping single molecules of DNA, each containing a single nucleosome. This interaction map revealed a distinct ~5 bp periodicity that was enveloped by three broad regions of strong interactions, with the strongest at the dyad and the other two at ~ ±40 bp from the dyad. Unzipping up to the dyad allowed recovery of a canonical nucleosome upon relaxation of the DNA, but unzipping beyond the dyad resulted in removal of histone octamer from its initial DNA sequence. These findings have significant implications for how RNA polymerase and other DNA-based enzymes may gain access to DNA associated with a nucleosome.
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40
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Salomo M, Keyser UF, Struhalla M, Kremer F. Optical tweezers to study single Protein A/Immunoglobulin G interactions at varying conditions. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 37:927-34. [DOI: 10.1007/s00249-008-0310-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2007] [Revised: 03/05/2008] [Accepted: 03/10/2008] [Indexed: 10/22/2022]
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41
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Deniz AA, Mukhopadhyay S, Lemke EA. Single-molecule biophysics: at the interface of biology, physics and chemistry. J R Soc Interface 2008; 5:15-45. [PMID: 17519204 PMCID: PMC2094721 DOI: 10.1098/rsif.2007.1021] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Single-molecule methods have matured into powerful and popular tools to probe the complex behaviour of biological molecules, due to their unique abilities to probe molecular structure, dynamics and function, unhindered by the averaging inherent in ensemble experiments. This review presents an overview of the burgeoning field of single-molecule biophysics, discussing key highlights and selected examples from its genesis to our projections for its future. Following brief introductions to a few popular single-molecule fluorescence and manipulation methods, we discuss novel insights gained from single-molecule studies in key biological areas ranging from biological folding to experiments performed in vivo.
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Affiliation(s)
- Ashok A Deniz
- Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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42
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Kelbauskas L, Chan N, Bash R, DeBartolo P, Sun J, Woodbury N, Lohr D. Sequence-dependent variations associated with H2A/H2B depletion of nucleosomes. Biophys J 2008; 94:147-58. [PMID: 17933873 PMCID: PMC2134853 DOI: 10.1529/biophysj.107.111906] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Accepted: 08/06/2007] [Indexed: 02/05/2023] Open
Abstract
Mechanisms that can alter nucleosome structure to enhance DNA accessibility are of great interest because of their potential involvement in genomic processes. One such mechanism is H2A/H2B release from nucleosomes; it occurs in vivo and is involved in the in vitro activities of several transcription-associated complexes. Using fluorescence approaches based on Förster resonance energy transfer, we previously detected sequence-dependent structure/stability variations between 5S and two types of promoter nucleosomes (from yeast GAL10 or mouse mammary tumor virus promoters). Those variations included differing responses when nucleosomes were diluted to concentrations (sub-nM) known to produce H2A/H2B loss. Here, we show that treatment of these same three types of nucleosomes with the histone chaperone yNAP-1, which causes H2A/H2B release from nucleosomes in vitro, produces the same differential Förster resonance energy transfer responses, again demonstrating sequence-dependent variations associated with conditions that produce H2A/H2B loss. Single-molecule population data indicate that DNA dynamics on the particles produced by diluting nucleosomes to sub-nM concentrations follow two-state behavior. Rate information (determined by fluorescence correlation spectroscopy) suggests that these dynamics are enhanced in MMTV-B or GAL10 compared to 5S particles. Taken together, the results indicate that H2A/H2B loss has differing effects on 5S compared to these two promoter nucleosomes and the differences reflect sequence-dependent structure/stability variations in the depleted particles.
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Affiliation(s)
- L Kelbauskas
- Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA
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43
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Ranjith P, Yan J, Marko JF. Nucleosome hopping and sliding kinetics determined from dynamics of single chromatin fibers in Xenopus egg extracts. Proc Natl Acad Sci U S A 2007; 104:13649-54. [PMID: 17698962 PMCID: PMC1959436 DOI: 10.1073/pnas.0701459104] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Chromatin function in vivo is intimately connected with changes in its structure: a prime example is occlusion or exposure of regulatory sequences via repositioning of nucleosomes. Cell extracts used in concert with single-DNA micromanipulation can control and monitor these dynamics under in vivo-like conditions. We analyze a theory of the assembly-disassembly dynamics of chromatin fiber in such experiments, including effects of lateral nucleosome diffusion ("sliding") and sequence positioning. Experimental data determine the force-dependent on- and off-rates as well as the nucleosome sliding diffusion rate. The resulting theory simply explains the very different nucleosome displacement kinetics observed in constant-force and constant-pulling velocity experiments. We also show that few-piconewton tensions comparable to those generated by polymerases and helicases drastically affect nucleosome positions in a sequence-dependent manner and that there is a long-lived structural "memory" of force-driven nucleosome rearrangement events.
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Affiliation(s)
- Padinhateeri Ranjith
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.
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44
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Lin J, Gao H, Schallhorn KA, Harris RM, Cao W, Ke PC. Lesion recognition and cleavage by endonuclease V: a single-molecule study. Biochemistry 2007; 46:7132-7. [PMID: 17521169 PMCID: PMC2527690 DOI: 10.1021/bi6024534] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Endonuclease V (endo V) recognizes and cleaves deoxyinosine in deaminated DNA. These enzymatic activities are precursors of DNA repair and are fueled by metal ions such as Ca2+ and Mg2+, with the former being associated with protein binding and the latter with DNA cleavage. Using the technique of fluorescence resonance energy transfer (FRET), we determined the single-molecule kinetics of endo V in a catalytic cycle using a substrate of deoxyinosine-containing single-stranded DNA (ssDNA). The ssDNA was labeled with TAMRA, a fluorescence donor, while the endo V was labeled with Cy5, a fluorescence acceptor. The time lapses of FRET, resulting from the sequential association, recognition, and dissociation of the deoxyinosine by the endo V, were determined at 5.9, 14.5, and 9.1 s, respectively, in the presence of Mg2+. In contrast, the process of deoxyinosine recognition appeared little affected by the metal type. The prolonged association and dissociation events in the presence of the Ca2+-Mg2+ combination, as compared to that of Mg2+ alone, support the hypothesis that endo V has two metal binding sites to regulate its enzymatic activities.
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Affiliation(s)
- Jun Lin
- Department of Physics and Astronomy, South Carolina Experiment Station, Room 219 Biosystems Research Complex, 51 New Cherry Street, Clemson University, Clemson, South Carolina 29634, USA
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45
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Solis FJ, Bash R, Wang H, Yodh J, Lindsay SA, Lohr D. Properties of nucleosomes in acetylated mouse mammary tumor virus versus 5S arrays. Biochemistry 2007; 46:5623-34. [PMID: 17444617 DOI: 10.1021/bi062116z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Acetylation is one of the most abundant histone modifications found in nucleosomes. Although such modifications are thought to function mainly in recognition, acetylation is known to produce nucleosome structural alterations. These could be of functional significance in vivo. Here, the basic features of mouse mammary tumor virus (MMTV) promoter nucleosomal arrays reconstituted with highly acetylated histones prepared from butyrate-treated HeLa cells are characterized by atomic force microscopy. Results are compared to previous results obtained with hypoacetylated MMTV and hyper- or hypoacetylated 5S rDNA arrays. MMTV arrays containing highly acetylated histones show diminished intramolecular compaction compared to hypoacetylated MMTV arrays and no tendency for cooperativity in nucleosome occupation. Both features have been suggested to reflect histone tail-mediated internucleosomal interactions; these observations are consistent with that suggestion. 5S arrays show qualitatively similar behavior. Two other effects of acetylation show stronger DNA template dependence. Nucleosome salt stability is diminished in highly acetylated compared to hypoacetylated MMTV arrays, but nucleosome (histone) loading tendencies are unaffected by acetylation. However, highly acetylated histones show reduced loading tendencies on 5S templates (vs hypoacetylated), but 5S nucleosome salt stabilities are unaffected by acetylation. ATP-dependent nucleosome remodeling by human Swi-Snf is similar on hyper- and hypoacetylated MMTV arrays.
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Affiliation(s)
- F J Solis
- Department of Integrated Natural Life Sciences, Arizona State University West, Glendale, Arizona 85306, USA
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46
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Zheng H, Goldner LS, Leuba SH. Homebuilt single-molecule scanning confocal fluorescence microscope studies of single DNA/protein interactions. Methods 2007; 41:342-52. [PMID: 17309845 PMCID: PMC1853322 DOI: 10.1016/j.ymeth.2006.11.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 09/28/2006] [Accepted: 11/14/2006] [Indexed: 11/30/2022] Open
Abstract
Many technical improvements in fluorescence microscopy over the years have focused on decreasing background and increasing the signal to noise ratio (SNR). The scanning confocal fluorescence microscope (SCFM) represented a major improvement in these efforts. The SCFM acquires signal from a thin layer of a thick sample, rejecting light whose origin is not in the focal plane thereby dramatically decreasing the background signal. A second major innovation was the advent of high quantum-yield, low noise, single-photon counting detectors. The superior background rejection of SCFM combined with low-noise, high-yield detectors makes it possible to detect the fluorescence from single-dye molecules. By labeling a DNA molecule or a DNA/protein complex with a donor/acceptor dye pair, fluorescence resonance energy transfer (FRET) can be used to track conformational changes in the molecule/complex itself, on a single molecule/complex basis. In this methods paper, we describe the core concepts of SCFM in the context of a study that uses FRET to reveal conformational fluctuations in individual Holliday junction DNA molecules and nucleosomal particles. We also discuss data processing methods for SCFM.
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Affiliation(s)
- Haocheng Zheng
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
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47
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Zlatanova J, Seebart C, Tomschik M. Nap1: taking a closer look at a juggler protein of extraordinary skills. FASEB J 2007; 21:1294-310. [PMID: 17317729 DOI: 10.1096/fj.06-7199rev] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The nucleosome assembly protein Nap1 is used extensively in the chromatin field to reconstitute nucleosomal templates for structural and functional studies. Beyond its role in facilitating experimental investigation of nucleosomes, the highly conserved Nap1 is one of the best-studied members of the histone chaperone group. Here we review its numerous functions, focusing mainly on its roles in assembly and disassembly of the nucleosome particle, and its interactions with chromatin remodeling factors. Its presumed role in transcription through chromatin is also reviewed in detail. An attempt is made to clearly discriminate between fact and fiction, and to formulate the unresolved questions that need further attention. It is beyond doubt that the numerous, seemingly unrelated functions of this juggler protein have to be precisely channeled, coordinated, and regulated. Why nature endowed this specific protein with so many functions may remain a mystery. We are aware of the enormous challenge to the scientific community that understanding the mechanisms underlying these activities presents.
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Affiliation(s)
- Jordanka Zlatanova
- Department of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA.
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48
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Kelbauskas L, Chan N, Bash R, Yodh J, Woodbury N, Lohr D. Sequence-Dependent Nucleosome Structure and Stability Variations Detected by Förster Resonance Energy Transfer. Biochemistry 2007; 46:2239-48. [PMID: 17269656 DOI: 10.1021/bi061289l] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Nucleosomes, the basic unit of eukaryotic chromosome structure, cover most of the DNA in eukaryotes, including regulatory sequences. Here, a recently developed Förster resonance energy transfer approach is used to compare structure and stability features of sea urchin 5S nucleosomes and nucleosomes reconstituted on two promoter sequences that are nucleosomal in vivo, containing the yeast GAL10 TATA or the major transcription response elements from the mouse mammary tumor virus promoter. All three sequences form mononucleosomes with similar gel mobilities and similar stabilities at moderate salt concentrations. However, the two promoter nucleosomes differ from 5S nucleosomes in (1) diffusion coefficient values, which suggest differences in nucleosome compaction, (2) intrinsic FRET efficiencies (in solution or in gels), and (3) the response of FRET efficiency to high (>or=600 mM) NaCl concentrations, subnanomolar nucleosome concentrations, and elevated temperatures (to 42 degrees C). These results indicate that nucleosome features can vary depending on the DNA sequence they contain and show that this fluorescence approach is sufficiently sensitive to detect such differences. Sequence-dependent variations in nucleosome structure or stability could facilitate specific nucleosome recognition, working together with other known genomic regulatory mechanisms. The variations in salt-, concentration-, and temperature-dependent responses all occur under conditions that have been shown previously to produce release of H2A-H2B dimers or terminal DNA from nucleosomes and could thus involve differences in those processes, as well as in other features.
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Affiliation(s)
- L Kelbauskas
- Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA
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49
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Salomo M, Keyser UF, Kegler K, Gutsche C, Struhalla M, Immisch C, Hahn U, Kremer F. Kinetics of TmHU binding to DNA as observed by optical tweezers. Microsc Res Tech 2007; 70:938-43. [PMID: 17661366 DOI: 10.1002/jemt.20498] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The kinetics of binding for the histone-like protein TmHU (from Thermotoga maritima) to DNA is analyzed on a single molecule level by use of optical tweezers. For the reaction rate a pronounced concentration-dependence is found with an "all or nothing"-limit which suggests the cooperative nature of the binding-reaction. By analyzing the statistics of mechanically induced dissociation-events of TmHU from DNA multiple reaction sites are observed to become more likely with increasing TmHU concentration. This is interpreted as a hint for a secondary organizational level of the TmHU/DNA complex. The reaction rate of TmHU binding to DNA is remarkably higher than that of the HU protein from Escherichia coli which will be discussed.
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Affiliation(s)
- Mathias Salomo
- Faculty of Experimental Physics 1, University of Leipzig, Linnèstrasse 5, D-04103 Leipzig, Germany.
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50
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Korolev N, Vorontsova OV, Nordenskiöld L. Physicochemical analysis of electrostatic foundation for DNA-protein interactions in chromatin transformations. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2006; 95:23-49. [PMID: 17291569 DOI: 10.1016/j.pbiomolbio.2006.11.003] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 11/15/2006] [Indexed: 11/21/2022]
Abstract
Electrostatic interactions between DNA and DNA-packaging proteins, the histones, contribute substantially to stability of eukaryotic chromatin on all levels of its organization and are particularly important in formation of its elementary structural unit, the nucleosome. The release of DNA from the histones is an unavoidable stage in reading the DNA code. In the present review, we discuss the disassembly/assembly process of the nucleosome from a thermodynamic standpoint by considering it as a competition between an excess of polyanions (DNA and acidic/phosphorylated domains of the nuclear proteins) for binding to a limited pool of polycations (the histones). Results obtained in model systems are used to discuss conditions for the electrostatic component of DNA-protein interactions contributing to chromatin statics and dynamics. We propose a simple set of "electrostatic conditions" for the disassembly/assembly of nucleosome/chromatin and apply these to put forward a number of new interpretations for the observations reported in literature on chromatin. The approach sheds light on the functions of acidic domains in the nuclear proteins (nucleoplasmin and other histone chaperones, HMG proteins, the activation domains in transcriptional activators). It results in a putative explanation for the molecular mechanisms behind epigenetic regulation through histone acetylation, phosphorylation, and other alterations ("the language of covalent histone modification"). We also propose a new explanation for the role of phosphorylation of C-terminal domain of RNA polymerase II for regulation of the DNA transcription. Several other examples from literature on chromatin are discussed to support applicability of electrostatic rules for description of chromatin structure and dynamics.
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Affiliation(s)
- Nikolay Korolev
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore.
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