1
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Filliaux S, Sun Z, Lyubchenko YL. Nanoscale Structure, Interactions, and Dynamics of Centromere Nucleosomes. Biomacromolecules 2024; 25:4715-4727. [PMID: 38959412 DOI: 10.1021/acs.biomac.3c01440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Centromeres are specific segments of chromosomes comprising two types of nucleosomes: canonical nucleosomes containing an octamer of H2A, H2B, H3, and H4 histones and CENP-A nucleosomes in which H3 is replaced with its analogue CENP-A. This modification leads to a difference in DNA wrapping (∼121 bp), considerably less than 147 bp in canonical nucleosomes. We used atomic force microscopy (AFM) and high-speed AFM (HS-AFM) to characterize nanoscale features and dynamics for both types of nucleosomes. For both nucleosomes, spontaneous asymmetric unwrapping of DNA was observed, and this process occurs via a transient state with ∼100 bp DNA wrapped around the core, followed by a rapid dissociation of DNA. Additionally, HS-AFM revealed higher stability of CENP-A nucleosomes compared with H3 nucleosomes in which dissociation of the histone core occurs prior to the nucleosome dissociation. These results help elucidate the differences between these nucleosomes and the potential biological necessity for CENP-A nucleosomes.
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Affiliation(s)
- Shaun Filliaux
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025, United States
| | - Zhiqiang Sun
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025, United States
| | - Yuri L Lyubchenko
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025, United States
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2
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Lin X, Zhang B. Explicit ion modeling predicts physicochemical interactions for chromatin organization. eLife 2024; 12:RP90073. [PMID: 38289342 PMCID: PMC10945522 DOI: 10.7554/elife.90073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023] Open
Abstract
Molecular mechanisms that dictate chromatin organization in vivo are under active investigation, and the extent to which intrinsic interactions contribute to this process remains debatable. A central quantity for evaluating their contribution is the strength of nucleosome-nucleosome binding, which previous experiments have estimated to range from 2 to 14 kBT. We introduce an explicit ion model to dramatically enhance the accuracy of residue-level coarse-grained modeling approaches across a wide range of ionic concentrations. This model allows for de novo predictions of chromatin organization and remains computationally efficient, enabling large-scale conformational sampling for free energy calculations. It reproduces the energetics of protein-DNA binding and unwinding of single nucleosomal DNA, and resolves the differential impact of mono- and divalent ions on chromatin conformations. Moreover, we showed that the model can reconcile various experiments on quantifying nucleosomal interactions, providing an explanation for the large discrepancy between existing estimations. We predict the interaction strength at physiological conditions to be 9 kBT, a value that is nonetheless sensitive to DNA linker length and the presence of linker histones. Our study strongly supports the contribution of physicochemical interactions to the phase behavior of chromatin aggregates and chromatin organization inside the nucleus.
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Affiliation(s)
- Xingcheng Lin
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Bin Zhang
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
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3
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Mondal A, Kolomeisky AB. Why Are Nucleosome Breathing Dynamics Asymmetric? J Phys Chem Lett 2024; 15:422-431. [PMID: 38180351 DOI: 10.1021/acs.jpclett.3c03339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2024]
Abstract
In eukaryotic cells, DNA is bound to nucleosomes, but DNA segments occasionally unbind in the process known as nucleosome breathing. Although DNA can unwrap simultaneously from both ends of the nucleosome (symmetric breathing), experiments indicate that DNA prefers to dissociate from only one end (asymmetric breathing). However, the molecular origin of the asymmetry is not understood. We developed a new theoretical approach that gives microscopic explanations of asymmetric breathing. It is based on a stochastic description that leads to a comprehensive evaluation of dynamics by using effective free-energy landscapes. It is shown that asymmetric breathing follows the kinetically preferred pathways. In addition, it is also found that asymmetric breathing leads to a faster target search by transcription factors. Theoretical predictions, supported by computer simulations, agree with experiments. It is proposed that nature utilizes the symmetry of nucleosome breathing to achieve a better dynamic accessibility of chromatin for more efficient genetic regulation.
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Affiliation(s)
- Anupam Mondal
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, United States
- Department of Chemistry, Rice University, Houston, Texas 77005, United States
| | - Anatoly B Kolomeisky
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, United States
- Department of Chemistry, Rice University, Houston, Texas 77005, United States
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
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4
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Li X, Chou T. Stochastic nucleosome disassembly mediated by remodelers and histone fragmentation. J Chem Phys 2023; 159:204107. [PMID: 38010331 PMCID: PMC10684310 DOI: 10.1063/5.0165136] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 10/14/2023] [Indexed: 11/29/2023] Open
Abstract
We construct and analyze monomeric and multimeric models of the stochastic disassembly of a single nucleosome. Our monomeric model predicts the time needed for a number of histone-DNA contacts to spontaneously break, leading to dissociation of a non-fragmented histone from DNA. The dissociation process can be facilitated by DNA binding proteins or processing molecular motors that compete with histones for histone-DNA contact sites. Eigenvalue analysis of the corresponding master equation allows us to evaluate histone detachment times under both spontaneous detachment and protein-facilitated processes. We find that competitive DNA binding of remodeling proteins can significantly reduce the typical detachment time but only if these remodelers have DNA-binding affinities comparable to those of histone-DNA contact sites. In the presence of processive motors, the histone detachment rate is shown to be proportional to the product of the histone single-bond dissociation constant and the speed of motor protein procession. Our simple intact-histone model is then extended to allow for multimeric nucleosome kinetics that reveal additional pathways of disassembly. In addition to a dependence of complete disassembly times on subunit-DNA contact energies, we show how histone subunit concentrations in bulk solutions can mediate the disassembly process by rescuing partially disassembled nucleosomes. Moreover, our kinetic model predicts that remodeler binding can also bias certain pathways of nucleosome disassembly, with higher remodeler binding rates favoring intact-histone detachment.
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Affiliation(s)
- Xiangting Li
- Department of Computational Medicine, University of California, Los Angeles, California 90095-1766, USA
| | - Tom Chou
- Author to whom correspondence should be addressed:
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5
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Yang H, Shi X. The Free Energy of Nucleosomal DNA Based on the Landau Model and Topology. Biomolecules 2023; 13:1686. [PMID: 38136559 PMCID: PMC10741420 DOI: 10.3390/biom13121686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Revised: 10/30/2023] [Accepted: 11/09/2023] [Indexed: 12/24/2023] Open
Abstract
The free energy of nucleosomal DNA plays a key role in the formation of nucleosomes in eukaryotes. Some work on the free energy of nucleosomal DNA have been carried out in experiments. However, the relationships between the free energy of nucleosomal DNA and its conformation, especially its topology, remain unclear in theory. By combining the Landau theory, the Hopfion model and experimental data, we find that the free energy of nucleosomal DNA is at the lower level. With the help of the energy minimum principle, we conclude that nucleosomal DNA stays in a stable state. Moreover, we discover that small perturbations on nucleosomal DNA have little effect on its free energy. This implies that nucleosomal DNA has a certain redundancy in order to stay stable. This explains why nucleosomal DNA will not change significantly due to small perturbations.
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Affiliation(s)
| | - Xuguang Shi
- College of Science, Beijing Forestry University, Beijing 100083, China;
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6
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Lin X, Zhang B. Explicit Ion Modeling Predicts Physicochemical Interactions for Chromatin Organization. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.16.541030. [PMID: 37293007 PMCID: PMC10245791 DOI: 10.1101/2023.05.16.541030] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Molecular mechanisms that dictate chromatin organization in vivo are under active investigation, and the extent to which intrinsic interactions contribute to this process remains debatable. A central quantity for evaluating their contribution is the strength of nucleosome-nucleosome binding, which previous experiments have estimated to range from 2 to 14 kBT. We introduce an explicit ion model to dramatically enhance the accuracy of residue-level coarse-grained modeling approaches across a wide range of ionic concentrations. This model allows for de novo predictions of chromatin organization and remains computationally efficient, enabling large-scale conformational sampling for free energy calculations. It reproduces the energetics of protein-DNA binding and unwinding of single nucleosomal DNA, and resolves the differential impact of mono and divalent ions on chromatin conformations. Moreover, we showed that the model can reconcile various experiments on quantifying nucleosomal interactions, providing an explanation for the large discrepancy between existing estimations. We predict the interaction strength at physiological conditions to be 9 kBT, a value that is nonetheless sensitive to DNA linker length and the presence of linker histones. Our study strongly supports the contribution of physicochemical interactions to the phase behavior of chromatin aggregates and chromatin organization inside the nucleus.
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Affiliation(s)
- Xingcheng Lin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Bin Zhang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
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7
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Li X, Chou T. Stochastic nucleosome disassembly mediated by remodelers and histone fragmentation. ARXIV 2023:arXiv:2309.02736v1. [PMID: 37731652 PMCID: PMC10508821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
We construct and analyze monomeric and multimeric models of the stochastic disassembly of a single nucleosome. Our monomeric model predicts the time needed for a number of histone-DNA contacts to spontaneously break, leading to dissociation of a non-fragmented histone from DNA. The dissociation process can be facilitated by DNA binding proteins or processing molecular motors that compete with histones for histone-DNA contact sites. Eigenvalue analysis of the corresponding master equation allows us to evaluate histone detachment times under both spontaneous detachment and protein-facilitated processes. We find that competitive DNA binding of remodeling proteins can significantly reduce the typical detachment time but only if these remodelers have DNA-binding affinities comparable to those of histone-DNA contact sites. In the presence of processive motors, the histone detachment rate is shown to be proportional to the product of the histone single-bond dissociation constant and the speed of motor protein procession. Our simple intact-histone model is then extended to allow for multimeric nucleosome kinetics that reveal additional pathways of disassembly. In addition to a dependence of complete disassembly times on subunit-DNA contact energies, we show how histone subunit concentrations in bulk solution can mediate the disassembly process by rescuing partially disassembled nucleosomes. Moreover, our kinetic model predicts that remodeler binding can also bias certain pathways of nucleosome disassembly, with higher remodeler binding rates favoring intact-histone detachment.
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Affiliation(s)
- Xiangting Li
- Department of Computational Medicine, University of California, Los Angeles, CA 90095-1766 USA
| | - Tom Chou
- Department of Computational Medicine, University of California, Los Angeles, CA 90095-1766 USA
- Department of Mathematics, University of California, Los Angeles, CA 90095-1555 USA
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8
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Abstract
Nearly three-fourths of all eukaryotic DNA is occupied by nucleosomes, protein-DNA complexes comprising octameric histone core proteins and ∼150 base pairs of DNA. In addition to acting as a DNA compaction vehicle, the dynamics of nucleosomes regulate the DNA site accessibility for the nonhistone proteins, thereby controlling regulatory processes involved in determining the cell identity and cell fate. Here, we propose an analytical framework to analyze the role of nucleosome dynamics on the target search process of transcription factors through a simple discrete-state stochastic description of the search process. By considering the experimentally determined kinetic rates associated with protein and nucleosome dynamics as the only inputs, we estimate the target search time of a protein via first-passage probability calculations separately during nucleosome breathing and sliding dynamics. Although both the nucleosome dynamics permit transient access to the DNA sites that are otherwise occluded by the histone proteins, our result suggests substantial differences between the protein search mechanism on a nucleosome performing breathing and sliding dynamics. Furthermore, we identify the molecular factors that influence the search efficiency and demonstrate how these factors together portray a highly dynamic landscape of gene regulation. Our analytical results are validated using extensive Monte Carlo simulations.
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Affiliation(s)
- Sujeet Kumar Mishra
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Arnab Bhattacherjee
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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9
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Shi D, Huang Y, Bai C. Studies of the Mechanism of Nucleosome Dynamics: A Review on Multifactorial Regulation from Computational and Experimental Cases. Polymers (Basel) 2023; 15:polym15071763. [PMID: 37050377 PMCID: PMC10096840 DOI: 10.3390/polym15071763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 03/28/2023] [Accepted: 03/31/2023] [Indexed: 04/05/2023] Open
Abstract
The nucleosome, which organizes the long coil of genomic DNA in a highly condensed, polymeric way, is thought to be the basic unit of chromosomal structure. As the most important protein–DNA complex, its structural and dynamic features have been successively revealed in recent years. However, its regulatory mechanism, which is modulated by multiple factors, still requires systemic discussion. This study summarizes the regulatory factors of the nucleosome’s dynamic features from the perspective of histone modification, DNA methylation, and the nucleosome-interacting factors (transcription factors and nucleosome-remodeling proteins and cations) and focuses on the research exploring the molecular mechanism through both computational and experimental approaches. The regulatory factors that affect the dynamic features of nucleosomes are also discussed in detail, such as unwrapping, wrapping, sliding, and stacking. Due to the complexity of the high-order topological structures of nucleosomes and the comprehensive effects of regulatory factors, the research on the functional modulation mechanism of nucleosomes has encountered great challenges. The integration of computational and experimental approaches, the construction of physical modes for nucleosomes, and the application of deep learning techniques will provide promising opportunities for further exploration.
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Affiliation(s)
- Danfeng Shi
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
| | - Yuxin Huang
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China
| | - Chen Bai
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China
- Chenzhu (MoMeD) Biotechnology Co., Ltd., Hangzhou 310005, China
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10
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Donovan BT, Luo Y, Meng Z, Poirier MG. The nucleosome unwrapping free energy landscape defines distinct regions of transcription factor accessibility and kinetics. Nucleic Acids Res 2023; 51:1139-1153. [PMID: 36688297 PMCID: PMC9943653 DOI: 10.1093/nar/gkac1267] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 11/27/2022] [Accepted: 01/16/2023] [Indexed: 01/24/2023] Open
Abstract
Transcription factors (TF) require access to target sites within nucleosomes to initiate transcription. The target site position within the nucleosome significantly influences TF occupancy, but how is not quantitatively understood. Using ensemble and single-molecule fluorescence measurements, we investigated the targeting and occupancy of the transcription factor, Gal4, at different positions within the nucleosome. We observe a dramatic decrease in TF occupancy to sites extending past 30 base pairs (bp) into the nucleosome which cannot be explained by changes in the TF dissociation rate or binding site orientation. Instead, the nucleosome unwrapping free energy landscape is the primary determinant of Gal4 occupancy by reducing the Gal4 binding rate. The unwrapping free energy landscape defines two distinct regions of accessibility and kinetics with a boundary at 30 bp into the nucleosome where the inner region is over 100-fold less accessible. The Gal4 binding rate in the inner region no longer depends on its concentration because it is limited by the nucleosome unwrapping rate, while the frequency of nucleosome rewrapping decreases because Gal4 exchanges multiple times before the nucleosome rewraps. Our findings highlight the importance of the nucleosome unwrapping free energy landscape on TF occupancy and dynamics that ultimately influences transcription initiation.
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Affiliation(s)
- Benjamin T Donovan
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Yi Luo
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Zhiyuan Meng
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Michael G Poirier
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43214, USA
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11
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Wang Y, Le JV, Crocker K, Darcy MA, Halley PD, Zhao D, Andrioff N, Croy C, Poirier MG, Bundschuh R, Castro CE. A nanoscale DNA force spectrometer capable of applying tension and compression on biomolecules. Nucleic Acids Res 2021; 49:8987-8999. [PMID: 34358322 PMCID: PMC8421221 DOI: 10.1093/nar/gkab656] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 06/30/2021] [Accepted: 07/27/2021] [Indexed: 02/04/2023] Open
Abstract
Single molecule force spectroscopy is a powerful approach to probe the structure, conformational changes, and kinetic properties of biological and synthetic macromolecules. However, common approaches to apply forces to biomolecules require expensive and cumbersome equipment and relatively large probes such as beads or cantilevers, which limits their use for many environments and makes integrating with other methods challenging. Furthermore, existing methods have key limitations such as an inability to apply compressive forces on single molecules. We report a nanoscale DNA force spectrometer (nDFS), which is based on a DNA origami hinge with tunable mechanical and dynamic properties. The angular free energy landscape of the nDFS can be engineered across a wide range through substitution of less than 5% of the strand components. We further incorporate a removable strut that enables reversible toggling of the nDFS between open and closed states to allow for actuated application of tensile and compressive forces. We demonstrate the ability to apply compressive forces by inducing a large bend in a 249bp DNA molecule, and tensile forces by inducing DNA unwrapping of a nucleosome sample. These results establish a versatile tool for force spectroscopy and robust methods for designing nanoscale mechanical devices with tunable force application.
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Affiliation(s)
- Yuchen Wang
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Jenny V Le
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Kyle Crocker
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Michael A Darcy
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Patrick D Halley
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Dengke Zhao
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Nick Andrioff
- Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Cassie Croy
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Michael G Poirier
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Ralf Bundschuh
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
- Division of Hematology, Department of Internal Medicine, The Ohio State University, Columbus, OH 43210, USA
| | - Carlos E Castro
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
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12
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Farr SE, Woods EJ, Joseph JA, Garaizar A, Collepardo-Guevara R. Nucleosome plasticity is a critical element of chromatin liquid-liquid phase separation and multivalent nucleosome interactions. Nat Commun 2021; 12:2883. [PMID: 34001913 PMCID: PMC8129070 DOI: 10.1038/s41467-021-23090-3] [Citation(s) in RCA: 71] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 03/23/2021] [Indexed: 12/19/2022] Open
Abstract
Liquid-liquid phase separation (LLPS) is an important mechanism that helps explain the membraneless compartmentalization of the nucleus. Because chromatin compaction and LLPS are collective phenomena, linking their modulation to the physicochemical features of nucleosomes is challenging. Here, we develop an advanced multiscale chromatin model-integrating atomistic representations, a chemically-specific coarse-grained model, and a minimal model-to resolve individual nucleosomes within sub-Mb chromatin domains and phase-separated systems. To overcome the difficulty of sampling chromatin at high resolution, we devise a transferable enhanced-sampling Debye-length replica-exchange molecular dynamics approach. We find that nucleosome thermal fluctuations become significant at physiological salt concentrations and destabilize the 30-nm fiber. Our simulations show that nucleosome breathing favors stochastic folding of chromatin and promotes LLPS by simultaneously boosting the transient nature and heterogeneity of nucleosome-nucleosome contacts, and the effective nucleosome valency. Our work puts forward the intrinsic plasticity of nucleosomes as a key element in the liquid-like behavior of nucleosomes within chromatin, and the regulation of chromatin LLPS.
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Affiliation(s)
- Stephen E Farr
- Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Esmae J Woods
- Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Jerelle A Joseph
- Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
- Department of Genetics, University of Cambridge, Cambridge, UK
| | - Adiran Garaizar
- Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Rosana Collepardo-Guevara
- Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK.
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
- Department of Genetics, University of Cambridge, Cambridge, UK.
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13
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Brehove M, Shatoff E, Donovan BT, Jipa CM, Bundschuh R, Poirier MG. DNA sequence influences hexasome orientation to regulate DNA accessibility. Nucleic Acids Res 2019; 47:5617-5633. [PMID: 31216039 PMCID: PMC6582347 DOI: 10.1093/nar/gkz283] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2019] [Revised: 04/03/2019] [Accepted: 04/20/2019] [Indexed: 02/02/2023] Open
Abstract
Nucleosomes, the fundamental organizing units of eukaryotic genomes, contain ∼146 base pairs of DNA wrapped around a histone H3–H4 tetramer and two histone H2A–H2B dimers. Converting nucleosomes into hexasomes by removal of a H2A–H2B dimer is an important regulatory event, but its regulation and functional consequences are not well-understood. To investigate the influence of hexasomes on DNA accessibility, we used the property of the Widom-601 Nucleosome Positioning Sequence (NPS) to form homogeneously oriented hexasomes in vitro. We find that DNA accessibility to transcription factors (TF) on the hexasome H2A–H2B distal side is identical to naked DNA, while the accessibility on the H2A–H2B proximal side is reduced by 2-fold, which is due to a 2-fold reduction in hexasome unwrapping probability. We then determined that a 23 bp region of the Widom-601 NPS is responsible for forming homogeneously oriented hexasomes. Analysis of published ChIP-exo data of hexasome containing genes identified two DNA sequence motifs that correlate with hexasome orientation in vivo, while ExoIII mapping studies of these sequences revealed they generate homogeneously oriented hexasomes in vitro. These results indicate that hexasome orientation, which is influenced by the underlying DNA sequence in vivo, is important for modulating DNA accessibility to regulate transcription.
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Affiliation(s)
- Matthew Brehove
- Department of Physics, Ohio State University, Columbus, OH 43210, USA
| | - Elan Shatoff
- Department of Physics, Ohio State University, Columbus, OH 43210, USA
| | - Benjamin T Donovan
- Biophysics Graduate Program, Ohio State University, Columbus, OH 43210, USA
| | - Caroline M Jipa
- Department of Physics, Ohio State University, Columbus, OH 43210, USA
| | - Ralf Bundschuh
- Department of Physics, Ohio State University, Columbus, OH 43210, USA.,Biophysics Graduate Program, Ohio State University, Columbus, OH 43210, USA.,Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH 43210, USA.,Division of Hematology, Ohio State University, Columbus, OH 43210, USA.,Center for RNA Biology, Ohio State University, Columbus, OH 43210, USA
| | - Michael G Poirier
- Department of Physics, Ohio State University, Columbus, OH 43210, USA.,Biophysics Graduate Program, Ohio State University, Columbus, OH 43210, USA.,Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH 43210, USA.,Ohio State Biochemistry Program, Ohio State University, Columbus, OH 43210, USA
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14
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Zhao D, Le JV, Darcy MA, Crocker K, Poirier MG, Castro C, Bundschuh R. Quantitative Modeling of Nucleosome Unwrapping from Both Ends. Biophys J 2019; 117:2204-2216. [PMID: 31732143 DOI: 10.1016/j.bpj.2019.09.048] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 08/05/2019] [Accepted: 09/27/2019] [Indexed: 01/08/2023] Open
Abstract
In eukaryotic cells, DNA is packaged into chromatin where nucleosomes are the basic packaging unit. Important cellular processes including gene expression, DNA replication, and DNA repair require nucleosomal DNA to be unwrapped so that functional proteins can access their target sites, which otherwise are sterically occluded. A key question in this process is what the unwrapped conformations individual nucleosomes adopt within chromatin are. Here, we develop a concurrent nucleosome unwrapping model to address this question. We hypothesize that for a given end-to-end distance of the nucleosomal DNA, the nucleosomal DNA stochastically unwraps from the histone core from both ends independently and that this combination of unwrapping from both sides results in a significant increase in the average distance between the DNA extending from both sides of the nucleosomes. We test our model on recently published experiments using a DNA origami nanocaliper that quantifies nucleosome unwrapping and achieve good agreement between experiment and model prediction. We then investigate the DNA origami caliper distribution when attached to a hexasome (a nucleosome lacking an H2A/H2B dimer). A significant shift in the caliper angle distribution caused by the asymmetric structural features of the hexasome seen experimentally is consistent with the model. Our modeling approach may be more broadly useful to the interpretation of other studies of nucleosome dynamics, chromatin dynamics, and regulatory processes involving nucleosome unwrapping, as well as more generally to optimization of future DNA origami designs to probe mechanical properties of biomolecules.
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Affiliation(s)
- Dengke Zhao
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio
| | - Jenny V Le
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio
| | - Michael A Darcy
- Department of Physics, The Ohio State University, Columbus, Ohio
| | - Kyle Crocker
- Department of Physics, The Ohio State University, Columbus, Ohio
| | - Michael G Poirier
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio; Department of Physics, The Ohio State University, Columbus, Ohio; Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio
| | - Carlos Castro
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio; Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, Ohio
| | - Ralf Bundschuh
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio; Department of Physics, The Ohio State University, Columbus, Ohio; Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio; Division of Hematology, Department of Internal Medicine, The Ohio State University, Columbus, Ohio; Center for RNA Biology, The Ohio State University, Columbus, Ohio.
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15
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Parsons T, Zhang B. Critical role of histone tail entropy in nucleosome unwinding. J Chem Phys 2019; 150:185103. [PMID: 31091895 DOI: 10.1063/1.5085663] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The nucleosome is the fundamental packaging unit for the genome. It must remain tightly wound to ensure genome stability while simultaneously being flexible enough to keep the DNA molecule accessible for genome function. The set of physicochemical interactions responsible for the delicate balance between these naturally opposed processes have not been determined due to challenges in resolving partially unwound nucleosome configurations at atomic resolution. Using a near atomistic protein-DNA model and advanced sampling techniques, we calculate the free energy cost of nucleosome DNA unwinding. Our simulations identify a large energetic barrier that decouples the outer and the inner DNA unwinding into two separate processes, occurring on different time scales. This dynamical decoupling allows the exposure of outer DNA at a modest cost to ensure accessibility while keeping the inner DNA and the histone core intact to maintain stability. We also reveal that this energetic barrier arises from a delayed loss of contacts between disordered histone tails and the DNA and is, surprisingly, largely offset by an entropic contribution from these tails. Implications of this enthalpy entropy compensation for the regulation of nucleosome stability and genome function are discussed.
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Affiliation(s)
- Thomas Parsons
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
| | - Bin Zhang
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
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16
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Abstract
Nucleosomes and chromatin control eukaryotic genome accessibility and thereby regulate DNA processes, including transcription, replication, and repair. Conformational dynamics within the nucleosome and chromatin structure play a key role in this regulatory function. Structural fluctuations continuously expose internal DNA sequences and nucleosome surfaces, thereby providing transient access for the nuclear machinery. Progress in structural studies of nucleosomes and chromatin has provided detailed insight into local chromatin organization and has set the stage for recent in-depth investigations of the structural dynamics of nucleosomes and chromatin fibers. Here, we discuss the dynamic processes observed in chromatin over different length scales and timescales and review current knowledge about the biophysics of distinct structural transitions.
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Affiliation(s)
- Beat Fierz
- Laboratory of Biophysical Chemistry of Macromolecules, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Michael G. Poirier
- Department of Physics, Biophysics Graduate Program, Ohio State Biochemistry Graduate Program, and Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210-1117, USA
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17
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Donovan BT, Chen H, Jipa C, Bai L, Poirier MG. Dissociation rate compensation mechanism for budding yeast pioneer transcription factors. eLife 2019; 8:43008. [PMID: 30888317 PMCID: PMC6449090 DOI: 10.7554/elife.43008] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 03/14/2019] [Indexed: 01/06/2023] Open
Abstract
Nucleosomes restrict the occupancy of most transcription factors (TF) by reducing binding and accelerating dissociation, while a small group of TFs have high affinities to nucleosome-embedded sites and facilitate nucleosome displacement. To understand this process mechanistically, we investigated two Saccharomyces cerevisiae TFs, Reb1 and Cbf1. We show that these factors bind to their sites within nucleosomes with similar binding affinities as to naked DNA, trapping a partially unwrapped nucleosome without histone eviction. Both the binding and dissociation rates of Reb1 and Cbf1 are significantly slower at the nucleosomal sites relative to those for naked DNA, demonstrating that the high affinities are achieved by increasing the dwell time on nucleosomes in order to compensate for reduced binding. Reb1 also shows slow migration rate in the yeast nuclei. These properties are similar to those of human pioneer factors (PFs), suggesting that the mechanism of nucleosome targeting is conserved from yeast to humans.
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Affiliation(s)
- Benjamin T Donovan
- Biophysics Graduate Program, The Ohio State University, Columbus, United States
| | - Hengye Chen
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, State College, United States.,Center for Eukaryotic Gene Regulation, The Pennsylvania State University, State College, United States
| | - Caroline Jipa
- Department of Physics, The Ohio State University, Columbus, United States
| | - Lu Bai
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, State College, United States.,Department of Physics, The Pennsylvania State University, State College, United States
| | - Michael G Poirier
- Biophysics Graduate Program, The Ohio State University, Columbus, United States.,Department of Physics, The Ohio State University, Columbus, United States.,Ohio State Biochemistry Graduate Program, The Ohio State University, Columbus, United States.,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, United States
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18
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Nucleosome DNA unwrapping does not affect prototype foamy virus integration efficiency or site selection. PLoS One 2019; 14:e0212764. [PMID: 30865665 PMCID: PMC6415784 DOI: 10.1371/journal.pone.0212764] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 02/09/2019] [Indexed: 12/27/2022] Open
Abstract
Eukaryotic DNA binding proteins must access genomic DNA that is packaged into chromatin in vivo. During a productive infection, retroviral integrases (IN) must similarly interact with chromatin to integrate the viral cDNA genome. Here we examine the role of nucleosome DNA unwrapping in the retroviral integrase search for a target site. These studies utilized PFV intasomes that are comprised of a tetramer of PFV IN with two oligomers mimicking the viral cDNA ends. Modified recombinant human histones were used to generate nucleosomes with increased unwrapping rates at different DNA regions. These modifications included the acetylmimetic H3(K56Q) and the chemically engineered H4(K77ac, K79ac). While transcription factors and DNA damage sensors may search nucleosome bound DNA during transient unwrapping, PFV intasome mediated integration appears to be unaffected by increased nucleosome unwrapping. These studies suggest PFV intasomes do not utilize nucleosome unwrapping to search nucleosome targets.
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19
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Hanne J, Britton BM, Park J, Liu J, Martín-López J, Jones N, Schoffner M, Klajner P, Bundschuh R, Lee JB, Fishel R. MutS homolog sliding clamps shield the DNA from binding proteins. J Biol Chem 2018; 293:14285-14294. [PMID: 30072380 DOI: 10.1074/jbc.ra118.002264] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2018] [Revised: 07/31/2018] [Indexed: 11/06/2022] Open
Abstract
Sliding clamps on DNA consist of evolutionarily conserved enzymes that coordinate DNA replication, repair, and the cellular DNA damage response. MutS homolog (MSH) proteins initiate mismatch repair (MMR) by recognizing mispaired nucleotides and in the presence of ATP form stable sliding clamps that randomly diffuse along the DNA. The MSH sliding clamps subsequently load MutL homolog (MLH/PMS) proteins that form a second extremely stable sliding clamp, which together coordinate downstream MMR components with the excision-initiation site that may be hundreds to thousands of nucleotides distant from the mismatch. Specific or nonspecific binding of other proteins to the DNA between the mismatch and the distant excision-initiation site could conceivably obstruct the free diffusion of these MMR sliding clamps, inhibiting their ability to initiate repair. Here, we employed bulk biochemical analysis, single-molecule fluorescence imaging, and mathematical modeling to determine how sliding clamps might overcome such hindrances along the DNA. Using both bacterial and human MSH proteins, we found that increasing the number of MSH sliding clamps on a DNA decreased the association of the Escherichia coli transcriptional repressor LacI to its cognate promoter LacO. Our results suggest a simple mechanism whereby thermal diffusion of MSH sliding clamps along the DNA alters the association kinetics of other DNA-binding proteins over extended distances. These observations appear generally applicable to any stable sliding clamp that forms on DNA.
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Affiliation(s)
- Jeungphill Hanne
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Brooke M Britton
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Jonghyun Park
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 790-784 Korea
| | - Jiaquan Liu
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Juana Martín-López
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Nathan Jones
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210.,Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio 43210
| | - Matthew Schoffner
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Piotr Klajner
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Ralf Bundschuh
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio 43210, .,Department of Physics, The Ohio State University, Columbus, Ohio 43210.,Department of Chemistry and Biochemistry, Division of Hematology, Department of Internal Medicine, Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, and
| | - Jong-Bong Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 790-784 Korea, .,School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang 790-784 Korea
| | - Richard Fishel
- From the Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, .,Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio 43210
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20
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Kono H, Sakuraba S, Ishida H. Free energy profiles for unwrapping the outer superhelical turn of nucleosomal DNA. PLoS Comput Biol 2018; 14:e1006024. [PMID: 29505570 PMCID: PMC5854429 DOI: 10.1371/journal.pcbi.1006024] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 03/15/2018] [Accepted: 02/01/2018] [Indexed: 11/19/2022] Open
Abstract
The eukaryotic genome is packaged into a nucleus in the form of chromatin. The fundamental structural unit of chromatin is a protein-DNA complex, the nucleosome, where 146 or 147 base pairs of DNA wrap 1.75 times around a histone core. To function in cellular processes, however, nucleosomal DNA must be unwrapped. Although this unwrapping has been experimentally investigated, details of the process at an atomic level are not yet well understood. Here, we used molecular dynamics simulation with an enhanced sampling method to calculate the free energy profiles for unwrapping the outer superhelical turn of nucleosomal DNA. A free energy change of about 11.5 kcal/mol for the unwrapping agrees well with values obtained in single molecule experiments. This simulation revealed a variety of conformational states, indicating there are many potential paths to outer superhelicdal turn unwrapping, but the dominant path is likely asymmetric. At one end of the DNA, the first five bps unwrap, after which a second five bps unwrap at the same end with no increase in free energy. The unwrapping then starts at the other end of the DNA, where 10 bps are unwrapped. During further unwrapping of 15 bps, the unwrapping advances at one of the ends, after which the other end of the DNA unwraps to complete the unwrapping of the outer superhelical turn. These results provide insight into the construction, disruption, and repositioning of nucleosomes, which are continuously ongoing during cellular processes.
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Affiliation(s)
- Hidetoshi Kono
- Molecular Modeling and Simulation Group, Department of Quantum Beam Life Science, National Institutes for Quantum and Radiological Science and Technology, Umemidai, Kizugawa, Kyoto, Japan
- * E-mail:
| | - Shun Sakuraba
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba, Japan
| | - Hisashi Ishida
- Molecular Modeling and Simulation Group, Department of Quantum Beam Life Science, National Institutes for Quantum and Radiological Science and Technology, Umemidai, Kizugawa, Kyoto, Japan
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21
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Djordjevic M, Djordjevic M, Zdobnov E. Scoring Targets of Transcription in Bacteria Rather than Focusing on Individual Binding Sites. Front Microbiol 2017; 8:2314. [PMID: 29213263 PMCID: PMC5702782 DOI: 10.3389/fmicb.2017.02314] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 11/09/2017] [Indexed: 11/13/2022] Open
Abstract
Reliable identification of targets of bacterial regulators is necessary to understand bacterial gene expression regulation. These targets are commonly predicted by searching for high-scoring binding sites in the upstream genomic regions, which typically leads to a large number of false positives. In contrast to the common approach, here we propose a novel concept, where overrepresentation of the scoring distribution that corresponds to the entire searched region is assessed, as opposed to predicting individual binding sites. We explore two implementations of this concept, based on Kolmogorov-Smirnov (KS) and Anderson-Darling (AD) tests, which both provide straightforward P-value estimates for predicted targets. This approach is implemented for pleiotropic bacterial regulators, including σ70 (bacterial housekeeping σ factor) target predictions, which is a classical bioinformatics problem characterized by low specificity. We show that KS based approach is both faster and more accurate, departing from the current paradigm of AD being slower, but more accurate. Moreover, KS approach leads to a significant increase in the search accuracy compared to the standard approach, while at the same time straightforwardly assigning well established P-values to each potential target. Consequently, the new KS based method proposed here, which assigns P-values to fixed length upstream regions, provides a fast and accurate approach for predicting bacterial transcription targets.
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Affiliation(s)
- Marko Djordjevic
- Institute of Physiology and Biochemistry, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | | | - Evgeny Zdobnov
- Swiss Institute of Bioinformatics and Department of Genetic Medicine and Development, University of Geneva, Geneva, Switzerland
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22
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Rajagopalan M, Balasubramanian S, Ioshikhes I, Ramaswamy A. Structural dynamics of nucleosome mediated by acetylations at H3K56 and H3K115,122. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 46:471-484. [DOI: 10.1007/s00249-016-1191-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 11/03/2016] [Accepted: 11/28/2016] [Indexed: 12/15/2022]
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23
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Cheffings T, Burroughs N, Balasubramanian M. Actomyosin Ring Formation and Tension Generation in Eukaryotic Cytokinesis. Curr Biol 2016; 26:R719-R737. [DOI: 10.1016/j.cub.2016.06.071] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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24
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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: 73] [Impact Index Per Article: 9.1] [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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25
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Brown MW, Kim Y, Williams GM, Huck JD, Surtees JA, Finkelstein IJ. Dynamic DNA binding licenses a repair factor to bypass roadblocks in search of DNA lesions. Nat Commun 2016; 7:10607. [PMID: 26837705 PMCID: PMC4742970 DOI: 10.1038/ncomms10607] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 01/04/2016] [Indexed: 12/17/2022] Open
Abstract
DNA-binding proteins search for specific targets via facilitated diffusion along a crowded genome. However, little is known about how crowded DNA modulates facilitated diffusion and target recognition. Here we use DNA curtains and single-molecule fluorescence imaging to investigate how Msh2-Msh3, a eukaryotic mismatch repair complex, navigates on crowded DNA. Msh2-Msh3 hops over nucleosomes and other protein roadblocks, but maintains sufficient contact with DNA to recognize a single lesion. In contrast, Msh2-Msh6 slides without hopping and is largely blocked by protein roadblocks. Remarkably, the Msh3-specific mispair-binding domain (MBD) licences a chimeric Msh2-Msh6(3MBD) to bypass nucleosomes. Our studies contrast how Msh2-Msh3 and Msh2-Msh6 navigate on a crowded genome and suggest how Msh2-Msh3 locates DNA lesions outside of replication-coupled repair. These results also provide insights into how DNA repair factors search for DNA lesions in the context of chromatin.
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Affiliation(s)
- Maxwell W Brown
- Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Yoori Kim
- Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Gregory M Williams
- Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214, USA
| | - John D Huck
- Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214, USA
| | - Jennifer A Surtees
- Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214, USA
| | - Ilya J Finkelstein
- Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA.,Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, Texas 78712, USA
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26
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Abstract
Highly conserved MutS homologs (MSH) and MutL homologs (MLH/PMS) are the fundamental components of mismatch repair (MMR). After decades of debate, it appears clear that the MSH proteins initiate MMR by recognizing a mismatch and forming multiple extremely stable ATP-bound sliding clamps that diffuse without hydrolysis along the adjacent DNA. The function(s) of MLH/PMS proteins is less clear, although they too bind ATP and are targeted to MMR by MSH sliding clamps. Structural analysis combined with recent real-time single molecule and cellular imaging technologies are providing new and detailed insight into the thermal-driven motions that animate the complete MMR mechanism.
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Affiliation(s)
- Richard Fishel
- From the Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210 and the Department of Physics and the Biophysics Program, The Ohio State University, Columbus, Ohio 43210
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27
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Brehove M, Wang T, North J, Luo Y, Dreher SJ, Shimko JC, Ottesen JJ, Luger K, Poirier MG. Histone core phosphorylation regulates DNA accessibility. J Biol Chem 2015; 290:22612-21. [PMID: 26175159 PMCID: PMC4566235 DOI: 10.1074/jbc.m115.661363] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Revised: 07/13/2015] [Indexed: 01/02/2023] Open
Abstract
Nucleosome unwrapping dynamics provide transient access to the complexes involved in DNA transcription, repair, and replication, whereas regulation of nucleosome unwrapping modulates occupancy of these complexes. Histone H3 is phosphorylated at tyrosine 41 (H3Y41ph) and threonine 45 (H3T45ph). H3Y41ph is implicated in regulating transcription, whereas H3T45ph is involved in DNA replication and apoptosis. These modifications are located in the DNA-histone interface near where the DNA exits the nucleosome, and are thus poised to disrupt DNA-histone interactions. However, the impact of histone phosphorylation on nucleosome unwrapping and accessibility is unknown. We find that the phosphorylation mimics H3Y41E and H3T45E, and the chemically correct modification, H3Y41ph, significantly increase nucleosome unwrapping. This enhances DNA accessibility to protein binding by 3-fold. H3K56 acetylation (H3K56ac) is also located in the same DNA-histone interface and increases DNA unwrapping. H3K56ac is implicated in transcription regulation, suggesting that H3Y41ph and H3K56ac could function together. We find that the combination of H3Y41ph with H3K56ac increases DNA accessibility by over an order of magnitude. These results suggest that phosphorylation within the nucleosome DNA entry-exit region increases access to DNA binding complexes and that the combination of phosphorylation with acetylation has the potential to significantly influence DNA accessibility to transcription regulatory complexes.
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Affiliation(s)
| | - Tao Wang
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523
| | | | - Yi Luo
- Biophysics Graduate Program
| | | | - John C Shimko
- Ohio State Biochemistry Program, and Department of Chemistry and Biochemistry, The Ohio State University, Columbus Ohio 43210 and
| | - Jennifer J Ottesen
- Biophysics Graduate Program, Ohio State Biochemistry Program, and Department of Chemistry and Biochemistry, The Ohio State University, Columbus Ohio 43210 and
| | - Karolin Luger
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523 the Howard Hughes Medical Institute and
| | - Michael G Poirier
- From the Department of Physics, Biophysics Graduate Program, Ohio State Biochemistry Program, and Department of Chemistry and Biochemistry, The Ohio State University, Columbus Ohio 43210 and
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28
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Bowman GD, Poirier MG. Post-translational modifications of histones that influence nucleosome dynamics. Chem Rev 2015; 115:2274-95. [PMID: 25424540 PMCID: PMC4375056 DOI: 10.1021/cr500350x] [Citation(s) in RCA: 319] [Impact Index Per Article: 35.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Indexed: 12/12/2022]
Affiliation(s)
- Gregory D. Bowman
- T.
C. Jenkins Department of Biophysics, Johns
Hopkins University, Baltimore, Maryland 21218, United States
| | - Michael G. Poirier
- Department of Physics, and Department of
Chemistry and Biochemistry, The Ohio State
University, Columbus, Ohio 43210, United
States
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29
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Lansky Z, Braun M, Lüdecke A, Schlierf M, ten Wolde P, Janson M, Diez S. Diffusible Crosslinkers Generate Directed Forces in Microtubule Networks. Cell 2015; 160:1159-68. [DOI: 10.1016/j.cell.2015.01.051] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 11/11/2014] [Accepted: 01/06/2015] [Indexed: 10/23/2022]
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30
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Abstract
Nucleosome is a histone-DNA complex known as the fundamental repeating unit of chromatin. Up to 90% of eukaryotic DNA is wrapped around consecutive octamers made of the core histones H2A, H2B, H3 and H4. Nucleosome positioning affects numerous cellular processes that require robust and timely access to genomic DNA, which is packaged into the tight confines of the cell nucleus. In living cells, nucleosome positions are determined by intrinsic histone-DNA sequence preferences, competition between histones and other DNA-binding proteins for genomic sequence, and ATP-dependent chromatin remodelers. We discuss the major energetic contributions to nucleosome formation and remodeling, focusing especially on partial DNA unwrapping off the histone octamer surface. DNA unwrapping enables efficient access to nucleosome-buried binding sites and mediates rapid nucleosome removal through concerted action of two or more DNA-binding factors. High-resolution, genome-scale maps of distances between neighboring nucleosomes have shown that DNA unwrapping and nucleosome crowding (mutual invasion of nucleosome territories) are much more common than previously thought. Ultimately, constraints imposed by nucleosome energetics on the rates of ATP-dependent and spontaneous chromatin remodeling determine nucleosome occupancy genome-wide, and shape pathways of cellular response to environmental stresses.
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31
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Chen C, Bundschuh R. Quantitative models for accelerated protein dissociation from nucleosomal DNA. Nucleic Acids Res 2014; 42:9753-60. [PMID: 25114052 PMCID: PMC4150810 DOI: 10.1093/nar/gku719] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Binding of transcription factors to their binding sites in promoter regions is the fundamental event in transcriptional gene regulation. When a transcription factor binding site is located within a nucleosome, the DNA has to partially unwrap from the nucleosome to allow transcription factor binding. This reduces the rate of transcription factor binding and is a known mechanism for regulation of gene expression via chromatin structure. Recently a second mechanism has been reported where transcription factor off-rates are dramatically increased when binding to target sites within the nucleosome. There are two possible explanations for such an increase in off-rate short of an active role of the nucleosome in pushing the transcription factor off the DNA: (i) for dimeric transcription factors the nucleosome can change the equilibrium between monomeric and dimeric binding or (ii) the nucleosome can change the equilibrium between specific and non-specific binding to the DNA. We explicitly model both scenarios and find that dimeric binding can explain a large increase in off-rate while the non-specific binding model cannot be reconciled with the large, experimentally observed increase. Our results suggest a general mechanism how nucleosomes increase transcription factor dissociation to promote exchange of transcription factors and regulate gene expression.
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Affiliation(s)
- Cai Chen
- Biophysics Graduate Program, The Ohio State University, Columbus, OH, USA Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Ralf Bundschuh
- Biophysics Graduate Program, The Ohio State University, Columbus, OH, USA Departments of Physics and Chemistry & Biochemistry and Division of Hematology, The Ohio State University, Columbus, OH, USA Center for RNA Biology, The Ohio State University, Columbus, OH, USA
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32
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Lee JB, Cho WK, Park J, Jeon Y, Kim D, Lee SH, Fishel R. Single-molecule views of MutS on mismatched DNA. DNA Repair (Amst) 2014; 20:82-93. [PMID: 24629484 PMCID: PMC4245035 DOI: 10.1016/j.dnarep.2014.02.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 02/11/2014] [Accepted: 02/14/2014] [Indexed: 01/09/2023]
Abstract
Base-pair mismatches that occur during DNA replication or recombination can reduce genetic stability or conversely increase genetic diversity. The genetics and biophysical mechanism of mismatch repair (MMR) has been extensively studied since its discovery nearly 50 years ago. MMR is a strand-specific excision-resynthesis reaction that is initiated by MutS homolog (MSH) binding to the mismatched nucleotides. The MSH mismatch-binding signal is then transmitted to the immediate downstream MutL homolog (MLH/PMS) MMR components and ultimately to a distant strand scission site where excision begins. The mechanism of signal transmission has been controversial for decades. We have utilized single molecule Forster Resonance Energy Transfer (smFRET), Fluorescence Tracking (smFT) and Polarization Total Internal Reflection Fluorescence (smP-TIRF) to examine the interactions and dynamic behaviors of single Thermus aquaticus MutS (TaqMutS) particles on mismatched DNA. We determined that TaqMutS forms an incipient clamp to search for a mismatch in ~1 s intervals by 1-dimensional (1D) thermal fluctuation-driven rotational diffusion while in continuous contact with the helical duplex DNA. When MutS encounters a mismatch it lingers for ~3 s to exchange bound ADP for ATP (ADP→ATP exchange). ATP binding by TaqMutS induces an extremely stable clamp conformation (~10 min) that slides off the mismatch and moves along the adjacent duplex DNA driven simply by 1D thermal diffusion. The ATP-bound sliding clamps rotate freely while in discontinuous contact with the DNA. The visualization of a train of MSH proteins suggests that dissociation of ATP-bound sliding clamps from the mismatch permits multiple mismatch-dependent loading events. These direct observations have provided critical clues into understanding the molecular mechanism of MSH proteins during MMR.
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Affiliation(s)
- Jong-Bong Lee
- Department of Physics, POSTECH, Pohang 790-784, Republic of Korea; School of Interdisciplinary Bioscience & Bioengineering, POSTECH, Pohang 790-784, Republic of Korea.
| | - Won-Ki Cho
- Department of Physics, POSTECH, Pohang 790-784, Republic of Korea
| | - Jonghyun Park
- Department of Physics, POSTECH, Pohang 790-784, Republic of Korea
| | - Yongmoon Jeon
- Department of Physics, POSTECH, Pohang 790-784, Republic of Korea
| | - Daehyung Kim
- Department of Physics, POSTECH, Pohang 790-784, Republic of Korea
| | - Seung Hwan Lee
- School of Interdisciplinary Bioscience & Bioengineering, POSTECH, Pohang 790-784, Republic of Korea
| | - Richard Fishel
- Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, Columbus, OH 43210, United States; Physics Department, The Ohio State University, Columbus, OH 43210, United States.
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Wang S, Linde MH, Munde M, Carvalho VD, Wilson WD, Poon GMK. Mechanistic heterogeneity in site recognition by the structurally homologous DNA-binding domains of the ETS family transcription factors Ets-1 and PU.1. J Biol Chem 2014; 289:21605-16. [PMID: 24952944 DOI: 10.1074/jbc.m114.575340] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
ETS family transcription factors regulate diverse genes through binding at cognate DNA sites that overlap substantially in sequence. The DNA-binding domains of ETS proteins (ETS domains) are highly conserved structurally yet share limited amino acid homology. To define the mechanistic implications of sequence diversity within the ETS family, we characterized the thermodynamics and kinetics of DNA site recognition by the ETS domains of Ets-1 and PU.1, which represent the extremes in amino acid divergence among ETS proteins. Even though the two ETS domains bind their optimal sites with similar affinities under physiologic conditions, their nature of site recognition differs strikingly in terms of the role of hydration and counter ion release. The data suggest two distinct mechanisms wherein Ets-1 follows a "dry" mechanism that rapidly parses sites through electrostatic interactions and direct protein-DNA contacts, whereas PU.1 utilizes hydration to interrogate sequence-specific sites and form a long-lived complex relative to the Ets-1 counterpart. The kinetic persistence of the high affinity PU.1 · DNA complex may be relevant to an emerging role of PU.1, but not Ets-1, as a pioneer transcription factor in vivo. In addition, PU.1 activity is critical to the development and function of macrophages and lymphocytes, which present osmotically variable environments, and hydration-dependent specificity may represent an important regulatory mechanism in vivo, a hypothesis that finds support in gene expression profiles of primary murine macrophages.
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Affiliation(s)
- Shuo Wang
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303 and
| | - Miles H Linde
- the Department of Pharmaceutical Sciences, Washington State University, Spokane, Washington 99210-1495
| | - Manoj Munde
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303 and
| | - Victor D Carvalho
- the Department of Pharmaceutical Sciences, Washington State University, Spokane, Washington 99210-1495
| | - W David Wilson
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303 and
| | - Gregory M K Poon
- the Department of Pharmaceutical Sciences, Washington State University, Spokane, Washington 99210-1495
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Abstract
Nucleosomes may undergo a conformational change in which a stretch of DNA peels off the histone octamer surface as a result of thermal fluctuations or interactions with chromatin remodelers. Thus, neighboring nucleosomes may invade each other's territories by DNA unwrapping and translocation, or through initial assembly in partially wrapped states. A recent high-resolution map of distances between dyads of neighboring nucleosomes in Saccharomyces cerevisiae reveals that nucleosomes frequently overlap DNA territories of their neighbors. This conclusion is supported by lower-resolution maps of S. cerevisiae nucleosome lengths based on micrococcal nuclease digestion and paired-end sequencing. The average length of wrapped DNA follows a stereotypical pattern in genes and promoters, correlated with the well-known distribution of nucleosome occupancy: nucleosomal DNA tends to be shorter in promoters and longer in coding regions. To explain these observations, we have developed a biophysical model that uses a 10-11-bp periodic histone-DNA binding energy profile. The profile is based on the pattern of histone-DNA contacts in nucleosome crystal structures, as well as the idea of linker length discretization caused by higher-order chromatin structure. Our model is in agreement with the observed genome-wide distributions of interdyad distances, wrapped DNA lengths, and nucleosome occupancies. Furthermore, our approach explains in vitro measurements of the accessibility of nucleosome-covered target sites and nucleosome-induced cooperativity between DNA-binding factors. We rule out several alternative scenarios of histone-DNA interactions as inconsistent with the genomic data.
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Teif VB, Erdel F, Beshnova DA, Vainshtein Y, Mallm JP, Rippe K. Taking into account nucleosomes for predicting gene expression. Methods 2013; 62:26-38. [PMID: 23523656 DOI: 10.1016/j.ymeth.2013.03.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 03/10/2013] [Indexed: 01/10/2023] Open
Abstract
The eukaryotic genome is organized in a chain of nucleosomes that consist of 145-147 bp of DNA wrapped around a histone octamer protein core. Binding of transcription factors (TF) to nucleosomal DNA is frequently impeded, which makes it a challenging task to calculate TF occupancy at a given regulatory genomic site for predicting gene expression. Here, we review methods to calculate TF binding to DNA in the presence of nucleosomes. The main theoretical problems are (i) the computation speed that is becoming a bottleneck when partial unwrapping of DNA from the nucleosome is considered, (ii) the perturbation of the binding equilibrium by the activity of ATP-dependent chromatin remodelers, which translocate nucleosomes along the DNA, and (iii) the model parameterization from high-throughput sequencing data and fluorescence microscopy experiments in living cells. We discuss strategies that address these issues to efficiently compute transcription factor binding in chromatin.
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Affiliation(s)
- Vladimir B Teif
- Research Group Genome Organization & Function, Deutsches Krebsforschungszentrum-DKFZ & BioQuant, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
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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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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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38
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There and back again: new single-molecule insights in the motion of DNA repair proteins. Curr Opin Struct Biol 2012; 23:154-60. [PMID: 23260129 DOI: 10.1016/j.sbi.2012.11.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 11/26/2012] [Accepted: 11/27/2012] [Indexed: 11/24/2022]
Abstract
Cellular DNA repair machines are constantly at work supporting the integrity of our genomes. Numerous proteins cooperate to form a complex and adaptive system dedicated to detection and timely processing of DNA damage. The molecular underpinnings of how these proteins locate and discriminate DNA lesions, match homologous sequences, mend the DNA and attend to a replication in distress are of a paramount biomedical importance, but in many cases remain unclear. Combined with more conventional tools, single-molecule biochemistry has been stepping in to address the age-old problems in the DNA repair field. This review will address new insights into diffusive properties of three DNA repair systems: I will discuss the emerging model of how MutS homologues locate and respond to mismatches in the dsDNA; the mechanism by which RAD52 promotes annealing of complementary DNA strands coated with ssDNA binding protein RPA; and how the nucleoprotein filament formed by RecA recombinase on ssDNA searches for homology within duplex DNA. These three distinct DNA repair factors exemplify the dynamic nature of cellular DNA repair machines revealed by single-molecule studies.
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Florescu AM, Schiessel H, Blossey R. Kinetic control of nucleosome displacement by ISWI/ACF chromatin remodelers. PHYSICAL REVIEW LETTERS 2012; 109:118103. [PMID: 23005680 DOI: 10.1103/physrevlett.109.118103] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Indexed: 06/01/2023]
Abstract
Chromatin structure is dynamically organized by chromatin remodelers, motor protein complexes which move and remove nucleosomes. The regulation of remodeler action has recently been proposed to underlie a kinetic proofreading scheme which combines the recognition of histone-tail states and the ATP-dependent loosening of DNA around nucleosomes. Members of the ISWI-family of remodelers additionally recognize linker length between nucleosomes. Here, we show that the additional proofreading step involving linker length alone is sufficient to promote the formation of regular arrays of nucleosomes. ATP-dependent remodeling by bidirectional motors is shown to reinforce positioning as compared to statistical positioning.
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Affiliation(s)
- Ana-Maria Florescu
- Max-Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, D-01187 Dresden, Germany
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40
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North JA, Shimko JC, Javaid S, Mooney AM, Shoffner MA, Rose SD, Bundschuh R, Fishel R, Ottesen JJ, Poirier MG. Regulation of the nucleosome unwrapping rate controls DNA accessibility. Nucleic Acids Res 2012; 40:10215-27. [PMID: 22965129 PMCID: PMC3488218 DOI: 10.1093/nar/gks747] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Eukaryotic genomes are repetitively wrapped into nucleosomes that then regulate access of transcription and DNA repair complexes to DNA. The mechanisms that regulate extrinsic protein interactions within nucleosomes are unresolved. We demonstrate that modulation of the nucleosome unwrapping rate regulates protein binding within nucleosomes. Histone H3 acetyl-lysine 56 [H3(K56ac)] and DNA sequence within the nucleosome entry-exit region additively influence nucleosomal DNA accessibility by increasing the unwrapping rate without impacting rewrapping. These combined epigenetic and genetic factors influence transcription factor (TF) occupancy within the nucleosome by at least one order of magnitude and enhance nucleosome disassembly by the DNA mismatch repair complex, hMSH2-hMSH6. Our results combined with the observation that ∼30% of Saccharomyces cerevisiae TF-binding sites reside in the nucleosome entry-exit region suggest that modulation of nucleosome unwrapping is a mechanism for regulating transcription and DNA repair.
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Affiliation(s)
- Justin A North
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
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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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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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Histone fold modifications control nucleosome unwrapping and disassembly. Proc Natl Acad Sci U S A 2011; 108:12711-6. [PMID: 21768347 DOI: 10.1073/pnas.1106264108] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nucleosomes are stable DNA-histone protein complexes that must be unwrapped and disassembled for genome expression, replication, and repair. Histone posttranslational modifications (PTMs) are major regulatory factors of these nucleosome structural changes, but the molecular mechanisms associated with PTM function remains poorly understood. Here we demonstrate that histone PTMs within distinct structured regions of the nucleosome directly regulate the inherent dynamic properties of the nucleosome. Precise PTMs were introduced into nucleosomes by chemical ligation. Single molecule magnetic tweezers measurements determined that only PTMs near the nucleosome dyad increase the rate of histone release in unwrapped nucleosomes. In contrast, FRET and restriction enzyme analysis reveal that only PTMs throughout the DNA entry-exit region increase unwrapping and enhance transcription factor binding to nucleosomal DNA. These results demonstrate that PTMs in separate structural regions of the nucleosome control distinct dynamic events, where the dyad regulates disassembly while the DNA entry-exit region regulates unwrapping. These studies are consistent with the conclusion that histone PTMs may independently influence nucleosome dynamics and associated chromatin functions.
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