1
|
Seifer S, Kirchweger P, Edel KM, Elbaum M. Optimizing Contrast in Automated 4D STEM Cryotomography. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2024; 30:476-488. [PMID: 38885145 DOI: 10.1093/mam/ozae050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/26/2024] [Accepted: 05/09/2024] [Indexed: 06/20/2024]
Abstract
4D STEM is an emerging approach to electron microscopy. While it was developed principally for high-resolution studies in materials science, the possibility to collect the entire transmitted flux makes it attractive for cryomicroscopy in application to life science and radiation-sensitive materials where dose efficiency is of utmost importance. We present a workflow to acquire tomographic tilt series of 4D STEM data sets using a segmented diode and an ultrafast pixelated detector, demonstrating the methods using a specimen of a T4 bacteriophage. Full integration with the SerialEM platform conveniently provides all the tools for grid navigation and automation of the data collection. Scripts are provided to convert the raw data to mrc format files and further to generate a variety of modes representing both scattering and phase contrasts, including incoherent and annular bright field, integrated center of mass, and parallax decomposition of a simulated integrated differential phase contrast. Principal component analysis of virtual annular detectors proves particularly useful, and axial contrast is improved by 3D deconvolution with an optimized point spread function. Contrast optimization enables visualization of irregular features such as DNA strands and thin filaments of the phage tails, which would be lost upon averaging or imposition of an inappropriate symmetry.
Collapse
Affiliation(s)
- Shahar Seifer
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl St, Rehovot 7610001, Israel
| | - Peter Kirchweger
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl St, Rehovot 7610001, Israel
| | - Karlina Maria Edel
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl St, Rehovot 7610001, Israel
| | - Michael Elbaum
- Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl St, Rehovot 7610001, Israel
| |
Collapse
|
2
|
Sun T, Korolev N, Minhas V, Mirzoev A, Lyubartsev AP, Nordenskiöld L. Multiscale modeling reveals the ion-mediated phase separation of nucleosome core particles. Biophys J 2024; 123:1414-1434. [PMID: 37915169 PMCID: PMC11163297 DOI: 10.1016/j.bpj.2023.10.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 10/05/2023] [Accepted: 10/27/2023] [Indexed: 11/03/2023] Open
Abstract
Due to the vast length scale inside the cell nucleus, multiscale models are required to understand chromatin folding, structure, and dynamics and how they regulate genomic activities such as DNA transcription, replication, and repair. We study the interactions and structure of condensed phases formed by the universal building block of chromatin, the nucleosome core particle (NCP), using bottom-up multiscale coarse-grained (CG) simulations with a model extracted from all-atom MD simulations. In the presence of the multivalent cations Mg(H2O)62+ or CoHex3+, we analyze the internal structures of the NCP aggregates and the contributions of histone tails and ions to the aggregation patterns. We then derive a "super" coarse-grained (SCG) NCP model to study the macroscopic scale phase separation of NCPs. The SCG simulations show the formation of NCP aggregates with Mg(H2O)62+ concentration-dependent densities and sizes. Variation of the CoHex3+ concentrations results in highly ordered lamellocolumnar and hexagonal columnar phases in agreement with experimental data. The results give detailed insights into nucleosome interactions and for understanding chromatin folding in the cell nucleus.
Collapse
Affiliation(s)
- Tiedong Sun
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Nikolay Korolev
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Vishal Minhas
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Alexander Mirzoev
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Alexander P Lyubartsev
- Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
| | - Lars Nordenskiöld
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
| |
Collapse
|
3
|
Palao L, Murakami K, Chang YW. Combining per-particle cryo-ET and cryo-EM single particle analysis to elucidate heterogeneous DNA-protein organization. Curr Opin Struct Biol 2024; 84:102765. [PMID: 38181688 PMCID: PMC10922635 DOI: 10.1016/j.sbi.2023.102765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2023] [Revised: 12/06/2023] [Accepted: 12/11/2023] [Indexed: 01/07/2024]
Abstract
Cryo-electron microscopy single particle analysis (cryo-EM SPA) and cryo-electron tomography (cryo-ET) have historically been employed as distinct approaches for investigating molecular structures of disparate sample types, focusing on highly purified biological macromolecules and in situ cellular contexts, respectively. However, these techniques offer inherently complementary structural insights that, when combined, provide a more comprehensive understanding of complex biological systems. For example, if both techniques are applied to the same purified biological macromolecules, cryo-ET has the ability to resolve highly flexible yet strong signal features on an individual target molecule which will not be preserved in the high-resolution cryo-EM SPA results. In this review, we highlight recent achievements utilizing such applications to unveil new insights into the chromatin assembly and activities of DNA-protein assemblies. This convergence of cryo-EM SPA and cryo-ET holds great promise for elucidating new structural aspects of these essential molecular processes.
Collapse
Affiliation(s)
- Leon Palao
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, PA, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, PA, USA
| | - Kenji Murakami
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, PA, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, PA, USA; Institute of Structural Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
| | - Yi-Wei Chang
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, PA, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, PA, USA; Institute of Structural Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
| |
Collapse
|
4
|
Jentink N, Purnell C, Kable B, Swulius MT, Grigoryev SA. Cryoelectron tomography reveals the multiplex anatomy of condensed native chromatin and its unfolding by histone citrullination. Mol Cell 2023; 83:3236-3252.e7. [PMID: 37683647 PMCID: PMC10566567 DOI: 10.1016/j.molcel.2023.08.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 05/31/2023] [Accepted: 08/16/2023] [Indexed: 09/10/2023]
Abstract
Nucleosome chains fold and self-associate to form higher-order structures whose internal organization is unknown. Here, cryoelectron tomography (cryo-ET) of native human chromatin reveals intrinsic folding motifs such as (1) non-uniform nucleosome stacking, (2) intermittent parallel and perpendicular orientations of adjacent nucleosome planes, and (3) a regressive nucleosome chain path, which deviates from the direct zigzag topology seen in reconstituted nucleosomal arrays. By examining the self-associated structures, we observed prominent nucleosome stacking in cis and anti-parallel nucleosome interactions, which are consistent with partial nucleosome interdigitation in trans. Histone citrullination strongly inhibits nucleosome stacking and self-association with a modest effect on chromatin folding, whereas the reconstituted arrays undergo a dramatic unfolding into open zigzag chains induced by histone citrullination. This study sheds light on the internal structure of compact chromatin nanoparticles and suggests a mechanism for how epigenetic changes in chromatin folding are retained across both open and condensed forms.
Collapse
Affiliation(s)
- Nathan Jentink
- Penn State University College of Medicine, Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, P.O. Box 850, 500 University Drive, Hershey, PA 17033, USA
| | - Carson Purnell
- Penn State University College of Medicine, Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, P.O. Box 850, 500 University Drive, Hershey, PA 17033, USA
| | - Brianna Kable
- Penn State University College of Medicine, Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, P.O. Box 850, 500 University Drive, Hershey, PA 17033, USA
| | - Matthew T Swulius
- Penn State University College of Medicine, Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, P.O. Box 850, 500 University Drive, Hershey, PA 17033, USA.
| | - Sergei A Grigoryev
- Penn State University College of Medicine, Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, P.O. Box 850, 500 University Drive, Hershey, PA 17033, USA.
| |
Collapse
|
5
|
Tan ZY, Cai S, Noble AJ, Chen JK, Shi J, Gan L. Heterogeneous non-canonical nucleosomes predominate in yeast cells in situ. eLife 2023; 12:RP87672. [PMID: 37503920 PMCID: PMC10382156 DOI: 10.7554/elife.87672] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/29/2023] Open
Abstract
Nuclear processes depend on the organization of chromatin, whose basic units are cylinder-shaped complexes called nucleosomes. A subset of mammalian nucleosomes in situ (inside cells) resembles the canonical structure determined in vitro 25 years ago. Nucleosome structure in situ is otherwise poorly understood. Using cryo-electron tomography (cryo-ET) and 3D classification analysis of budding yeast cells, here we find that canonical nucleosomes account for less than 10% of total nucleosomes expected in situ. In a strain in which H2A-GFP is the sole source of histone H2A, class averages that resemble canonical nucleosomes both with and without GFP densities are found ex vivo (in nuclear lysates), but not in situ. These data suggest that the budding yeast intranuclear environment favors multiple non-canonical nucleosome conformations. Using the structural observations here and the results of previous genomics and biochemical studies, we propose a model in which the average budding yeast nucleosome's DNA is partially detached in situ.
Collapse
Affiliation(s)
- Zhi Yang Tan
- Department of Biological Sciences and Center for BioImaging Sciences, National University of SingaporeSingaporeSingapore
| | - Shujun Cai
- Department of Biological Sciences and Center for BioImaging Sciences, National University of SingaporeSingaporeSingapore
| | - Alex J Noble
- National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology CenterNew YorkUnited States
| | - Jon K Chen
- Department of Biological Sciences and Center for BioImaging Sciences, National University of SingaporeSingaporeSingapore
| | - Jian Shi
- Department of Biological Sciences and Center for BioImaging Sciences, National University of SingaporeSingaporeSingapore
| | - Lu Gan
- Department of Biological Sciences and Center for BioImaging Sciences, National University of SingaporeSingaporeSingapore
| |
Collapse
|
6
|
Kadam S, Kumari K, Manivannan V, Dutta S, Mitra MK, Padinhateeri R. Predicting scale-dependent chromatin polymer properties from systematic coarse-graining. Nat Commun 2023; 14:4108. [PMID: 37433821 PMCID: PMC10336007 DOI: 10.1038/s41467-023-39907-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 06/30/2023] [Indexed: 07/13/2023] Open
Abstract
Simulating chromatin is crucial for predicting genome organization and dynamics. Although coarse-grained bead-spring polymer models are commonly used to describe chromatin, the relevant bead dimensions, elastic properties, and the nature of inter-bead potentials are unknown. Using nucleosome-resolution contact probability (Micro-C) data, we systematically coarse-grain chromatin and predict quantities essential for polymer representation of chromatin. We compute size distributions of chromatin beads for different coarse-graining scales, quantify fluctuations and distributions of bond lengths between neighboring regions, and derive effective spring constant values. Unlike the prevalent notion, our findings argue that coarse-grained chromatin beads must be considered as soft particles that can overlap, and we derive an effective inter-bead soft potential and quantify an overlap parameter. We also compute angle distributions giving insights into intrinsic folding and local bendability of chromatin. While the nucleosome-linker DNA bond angle naturally emerges from our work, we show two populations of local structural states. The bead sizes, bond lengths, and bond angles show different mean behavior at Topologically Associating Domain (TAD) boundaries and TAD interiors. We integrate our findings into a coarse-grained polymer model and provide quantitative estimates of all model parameters, which can serve as a foundational basis for all future coarse-grained chromatin simulations.
Collapse
Affiliation(s)
- Sangram Kadam
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, India.
| | - Kiran Kumari
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Vinoth Manivannan
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Shuvadip Dutta
- Department of Physics, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Mithun K Mitra
- Department of Physics, Indian Institute of Technology Bombay, Mumbai, 400076, India
| | - Ranjith Padinhateeri
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400076, India.
- Sunita Sanghi Centre of Aging and Neurodegenerative Diseases, Indian Institute of Technology Bombay, Mumbai, 400076, India.
| |
Collapse
|
7
|
Rioux KL, Delaney S. Ionic strength modulates excision of uracil by SMUG1 from nucleosome core particles. DNA Repair (Amst) 2023; 125:103482. [PMID: 36931160 PMCID: PMC10073303 DOI: 10.1016/j.dnarep.2023.103482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 03/04/2023] [Accepted: 03/07/2023] [Indexed: 03/14/2023]
Abstract
Ionic strength affects many cellular processes including the packaging of genetic material in eukaryotes. For example, chromatin fibers are compacted in high ionic strength environments as are the minimal unit of packaging in chromatin, nucleosome core particles (NCPs). Furthermore, ionic strength is known to modulate several aspects of NCP dynamics including transient unwrapping of DNA from the histone protein core, nucleosome gaping, and intra- and internucleosomal interactions of the N-terminal histone tails. Changes in NCP structure may also impact interactions of transcriptional, repair, and other cellular machinery with nucleosomal DNA. One repair process, base excision repair (BER), is impacted by NCP structure and may be further influenced by changes in ionic strength. Here we examine the effects of ionic strength on the initiation of BER using biochemical assays. Using a population of NCPs containing uracil (U) at dozens of geometric locations, excision of U by single-strand selective monofunctional uracil DNA glycosylase (SMUG1) is assessed at higher and lower ionic strengths. SMUG1 has increased excision activity in the lower ionic strength conditions. On duplex DNA, however, SMUG1 activity is largely unaffected by ionic strength except at short incubation times, suggesting that changes in SMUG1 activity are likely due to alterations in NCP structure and dynamics. These results allow us to further understand the cellular role of SMUG1 in a changing ionic environment and broadly contribute to the understanding of BER on chromatin and genomic stability.
Collapse
Affiliation(s)
- Katelyn L Rioux
- Department of Chemistry, Brown University, Providence, RI, USA
| | - Sarah Delaney
- Department of Chemistry, Brown University, Providence, RI, USA.
| |
Collapse
|
8
|
Zhang M, Díaz-Celis C, Onoa B, Cañari-Chumpitaz C, Requejo KI, Liu J, Vien M, Nogales E, Ren G, Bustamante C. Molecular organization of the early stages of nucleosome phase separation visualized by cryo-electron tomography. Mol Cell 2022; 82:3000-3014.e9. [PMID: 35907400 DOI: 10.1016/j.molcel.2022.06.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 05/09/2022] [Accepted: 06/28/2022] [Indexed: 12/16/2022]
Abstract
It has been proposed that the intrinsic property of nucleosome arrays to undergo liquid-liquid phase separation (LLPS) in vitro is responsible for chromatin domain organization in vivo. However, understanding nucleosomal LLPS has been hindered by the challenge to characterize the structure of the resulting heterogeneous condensates. We used cryo-electron tomography and deep-learning-based 3D reconstruction/segmentation to determine the molecular organization of condensates at various stages of LLPS. We show that nucleosomal LLPS involves a two-step process: a spinodal decomposition process yielding irregular condensates, followed by their unfavorable conversion into more compact, spherical nuclei that grow into larger spherical aggregates through accretion of spinodal materials or by fusion with other spherical condensates. Histone H1 catalyzes more than 10-fold the spinodal-to-spherical conversion. We propose that this transition involves exposure of nucleosome hydrophobic surfaces causing modified inter-nucleosome interactions. These results suggest a physical mechanism by which chromatin may transition from interphase to metaphase structures.
Collapse
Affiliation(s)
- Meng Zhang
- Applied Science and Technology Graduate Group, University of California, Berkeley, CA, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA; The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - César Díaz-Celis
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
| | - Bibiana Onoa
- Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
| | | | - Katherinne I Requejo
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
| | - Jianfang Liu
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Michael Vien
- Department of Physics, University of California, Berkeley, CA, USA
| | - Eva Nogales
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA, USA; Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Gang Ren
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| | - Carlos Bustamante
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA, USA; Department of Chemistry, University of California, Berkeley, CA, USA; Department of Physics, University of California, Berkeley, CA, USA; Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Kavli Energy Nanoscience Institute, University of California, Berkeley, CA, USA.
| |
Collapse
|
9
|
Sun T, Minhas V, Mirzoev A, Korolev N, Lyubartsev AP, Nordenskiöld L. A Bottom-Up Coarse-Grained Model for Nucleosome-Nucleosome Interactions with Explicit Ions. J Chem Theory Comput 2022; 18:3948-3960. [PMID: 35580041 PMCID: PMC9202350 DOI: 10.1021/acs.jctc.2c00083] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nucleosome core particle (NCP) is a large complex of 145-147 base pairs of DNA and eight histone proteins and is the basic building block of chromatin that forms the chromosomes. Here, we develop a coarse-grained (CG) model of the NCP derived through a systematic bottom-up approach based on underlying all-atom MD simulations to compute the necessary CG interactions. The model produces excellent agreement with known structural features of the NCP and gives a realistic description of the nucleosome-nucleosome attraction in the presence of multivalent cations (Mg(H2O)62+ or Co(NH3)63+) for systems comprising 20 NCPs. The results of the simulations reveal structural details of the NCP-NCP interactions unavailable from experimental approaches, and this model opens the prospect for the rigorous modeling of chromatin fibers.
Collapse
Affiliation(s)
- Tiedong Sun
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Vishal Minhas
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Alexander Mirzoev
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Nikolay Korolev
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Alexander P Lyubartsev
- Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden
| | - Lars Nordenskiöld
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| |
Collapse
|
10
|
Ma OX, Chong WG, Lee JKE, Cai S, Siebert CA, Howe A, Zhang P, Shi J, Surana U, Gan L. Cryo-ET detects bundled triple helices but not ladders in meiotic budding yeast. PLoS One 2022; 17:e0266035. [PMID: 35421110 PMCID: PMC9009673 DOI: 10.1371/journal.pone.0266035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 03/13/2022] [Indexed: 11/19/2022] Open
Abstract
In meiosis, cells undergo two sequential rounds of cell division, termed meiosis I and meiosis II. Textbook models of the meiosis I substage called pachytene show that nuclei have conspicuous 100-nm-wide, ladder-like synaptonemal complexes and ordered chromatin loops. It remains unknown if these cells have any other large, meiosis-related intranuclear structures. Here we present cryo-ET analysis of frozen-hydrated budding yeast cells before, during, and after pachytene. We found no cryo-ET densities that resemble dense ladder-like structures or ordered chromatin loops. Instead, we found large numbers of 12-nm-wide triple-helices that pack into ordered bundles. These structures, herein called meiotic triple helices (MTHs), are present in meiotic cells, but not in interphase cells. MTHs are enriched in the nucleus but not enriched in the cytoplasm. Bundles of MTHs form at the same timeframe as synaptonemal complexes (SCs) in wild-type cells and in mutant cells that are unable to form SCs. These results suggest that in yeast, SCs coexist with previously unreported large, ordered assemblies.
Collapse
Affiliation(s)
- Olivia X. Ma
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - Wen Guan Chong
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - Joy K. E. Lee
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - Shujun Cai
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - C. Alistair Siebert
- Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, Oxfordshire, United Kingdom
| | - Andrew Howe
- Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, Oxfordshire, United Kingdom
| | - Peijun Zhang
- Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, Oxfordshire, United Kingdom
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
| | - Jian Shi
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - Uttam Surana
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Proteos, Singapore
- Bioprocessing Technology Institute, A*STAR, Singapore, Singapore
- Biotransformation Innovation Platform, A*STAR, Singapore, Singapore
- Department of Pharmacology, National University of Singapore, Singapore, Singapore
| | - Lu Gan
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| |
Collapse
|
11
|
Zakirov AN, Sosnovskaya S, Ryumina ED, Kharybina E, Strelkova OS, Zhironkina OA, Golyshev SA, Moiseenko A, Kireev II. Fiber-Like Organization as a Basic Principle for Euchromatin Higher-Order Structure. Front Cell Dev Biol 2022; 9:784440. [PMID: 35174159 PMCID: PMC8841976 DOI: 10.3389/fcell.2021.784440] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 12/23/2021] [Indexed: 11/13/2022] Open
Abstract
A detailed understanding of the principles of the structural organization of genetic material is of great importance for elucidating the mechanisms of differential regulation of genes in development. Modern ideas about the spatial organization of the genome are based on a microscopic analysis of chromatin structure and molecular data on DNA–DNA contact analysis using Chromatin conformation capture (3C) technology, ranging from the “polymer melt” model to a hierarchical folding concept. Heterogeneity of chromatin structure depending on its functional state and cell cycle progression brings another layer of complexity to the interpretation of structural data and requires selective labeling of various transcriptional states under nondestructive conditions. Here, we use a modified approach for replication timing-based metabolic labeling of transcriptionally active chromatin for ultrastructural analysis. The method allows pre-embedding labeling of optimally structurally preserved chromatin, thus making it compatible with various 3D-TEM techniques including electron tomography. By using variable pulse duration, we demonstrate that euchromatic genomic regions adopt a fiber-like higher-order structure of about 200 nm in diameter (chromonema), thus providing support for a hierarchical folding model of chromatin organization as well as the idea of transcription and replication occurring on a highly structured chromatin template.
Collapse
Affiliation(s)
- Amir N Zakirov
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.,Chair of Cell Biology and Histology, Biology Faculty, Lomonosov Moscow State University, Moscow, Russia
| | - Sophie Sosnovskaya
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.,Chair of Cell Biology and Histology, Biology Faculty, Lomonosov Moscow State University, Moscow, Russia
| | - Ekaterina D Ryumina
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.,Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, Russia
| | - Ekaterina Kharybina
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.,Chair of Cell Biology and Histology, Biology Faculty, Lomonosov Moscow State University, Moscow, Russia
| | - Olga S Strelkova
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Oxana A Zhironkina
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Sergei A Golyshev
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Andrey Moiseenko
- Laboratory of Electron Microscopy, Biology Faculty, Lomonosov Moscow State University, Moscow, Russia
| | - Igor I Kireev
- Department of Electron Microscopy, AN. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia.,Chair of Cell Biology and Histology, Biology Faculty, Lomonosov Moscow State University, Moscow, Russia
| |
Collapse
|
12
|
Harastani M, Eltsov M, Leforestier A, Jonic S. TomoFlow: Analysis of Continuous Conformational Variability of Macromolecules in Cryogenic Subtomograms based on 3D Dense Optical Flow. J Mol Biol 2021; 434:167381. [PMID: 34848215 DOI: 10.1016/j.jmb.2021.167381] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/21/2021] [Accepted: 11/22/2021] [Indexed: 01/14/2023]
Abstract
Cryogenic Electron Tomography (cryo-ET) allows structural and dynamics studies of macromolecules in situ. Averaging different copies of imaged macromolecules is commonly used to obtain their structure at higher resolution and discrete classification to analyze their dynamics. Instrumental and data processing developments are progressively equipping cryo-ET studies with the ability to escape the trap of classification into a complete continuous conformational variability analysis. In this work, we propose TomoFlow, a method for analyzing macromolecular continuous conformational variability in cryo-ET subtomograms based on a three-dimensional dense optical flow (OF) approach. The resultant lower-dimensional conformational space allows generating movies of macromolecular motion and obtaining subtomogram averages by grouping conformationally similar subtomograms. The animations and the subtomogram group averages reveal accurate trajectories of macromolecular motion based on a novel mathematical model that makes use of OF properties. This paper describes TomoFlow with tests on simulated datasets generated using different techniques, namely Normal Mode Analysis and Molecular Dynamics Simulation. It also shows an application of TomoFlow on a dataset of nucleosomes in situ, which provided promising results coherent with previous findings using the same dataset but without imposing any prior knowledge on the analysis of the conformational variability. The method is discussed with its potential uses and limitations.
Collapse
Affiliation(s)
- Mohamad Harastani
- IMPMC - UMR 7590 CNRS, Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France; Laboratoire de Physique des Solides (LPS), UMR 8502 CNRS, Université Paris-Saclay, Orsay, France. https://twitter.com/moh_harastani
| | - Mikhail Eltsov
- Department of Integrated Structural Biology, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France. https://twitter.com/EltsovMikhail
| | - Amélie Leforestier
- Laboratoire de Physique des Solides (LPS), UMR 8502 CNRS, Université Paris-Saclay, Orsay, France
| | - Slavica Jonic
- IMPMC - UMR 7590 CNRS, Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France.
| |
Collapse
|
13
|
Arimura Y, Shih RM, Froom R, Funabiki H. Structural features of nucleosomes in interphase and metaphase chromosomes. Mol Cell 2021; 81:4377-4397.e12. [PMID: 34478647 PMCID: PMC8571072 DOI: 10.1016/j.molcel.2021.08.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 08/05/2021] [Accepted: 08/06/2021] [Indexed: 12/17/2022]
Abstract
Structural heterogeneity of nucleosomes in functional chromosomes is unknown. Here, we devise the template-, reference- and selection-free (TRSF) cryo-EM pipeline to simultaneously reconstruct cryo-EM structures of protein complexes from interphase or metaphase chromosomes. The reconstructed interphase and metaphase nucleosome structures are on average indistinguishable from canonical nucleosome structures, despite DNA sequence heterogeneity, cell-cycle-specific posttranslational modifications, and interacting proteins. Nucleosome structures determined by a decoy-classifying method and structure variability analyses reveal the nucleosome structural variations in linker DNA, histone tails, and nucleosome core particle configurations, suggesting that the opening of linker DNA, which is correlated with H2A C-terminal tail positioning, is suppressed in chromosomes. High-resolution (3.4-3.5 Å) nucleosome structures indicate DNA-sequence-independent stabilization of superhelical locations ±0-1 and ±3.5-4.5. The linker histone H1.8 preferentially binds to metaphase chromatin, from which chromatosome cryo-EM structures with H1.8 at the on-dyad position are reconstituted. This study presents the structural characteristics of nucleosomes in chromosomes.
Collapse
Affiliation(s)
- Yasuhiro Arimura
- Laboratory of Chromosome and Cell Biology, The Rockefeller University, New York, NY 10065, USA.
| | - Rochelle M Shih
- Laboratory of Chromosome and Cell Biology, The Rockefeller University, New York, NY 10065, USA
| | - Ruby Froom
- Laboratory of Molecular Biophysics, The Rockefeller University, New York, NY 10065, USA
| | - Hironori Funabiki
- Laboratory of Chromosome and Cell Biology, The Rockefeller University, New York, NY 10065, USA.
| |
Collapse
|
14
|
Alvarado W, Moller J, Ferguson AL, de Pablo JJ. Tetranucleosome Interactions Drive Chromatin Folding. ACS CENTRAL SCIENCE 2021; 7:1019-1027. [PMID: 34235262 PMCID: PMC8227587 DOI: 10.1021/acscentsci.1c00085] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Indexed: 06/10/2023]
Abstract
The multiscale organizational structure of chromatin in eukaryotic cells is instrumental to DNA transcription, replication, and repair. At mesoscopic length scales, nucleosomes pack in a manner that serves to regulate gene expression through condensation and expansion of the genome. The particular structures that arise and their respective thermodynamic stabilities, however, have yet to be fully resolved. In this study, we combine molecular modeling using the 1CPN mesoscale model of chromatin with nonlinear manifold learning to identify and characterize the structure and free energy of metastable states of short chromatin segments comprising between 4- and 16-nucleosomes. Our results reveal the formation of two previously characterized tetranucleosomal conformations, the "α-tetrahedron" and the "β-rhombus", which have been suggested to play an important role in the accessibility of DNA and, respectively, induce local chromatin compaction or elongation. The spontaneous formation of these motifs is potentially responsible for the slow nucleosome dynamics observed in experimental studies. Increases of the nucleosome repeat length are accompanied by more pronounced structural irregularity and flexibility and, ultimately, a dynamic liquid-like behavior that allows for frequent structural reorganization. Our findings indicate that tetranucleosome motifs are intrinsically stable structural states, driven by local internucleosomal interactions, and support a mechanistic picture of chromatin packing, dynamics, and accessibility that is strongly influenced by emergent local mesoscale structure.
Collapse
Affiliation(s)
- Walter Alvarado
- Biophysical
Sciences, University of Chicago, Chicago, Illinois 60637 United States
| | - Joshua Moller
- Pritzker
School of Molecular Engineering, University
of Chicago, Chicago, Illinois 60637 United States
| | - Andrew L. Ferguson
- Pritzker
School of Molecular Engineering, University
of Chicago, Chicago, Illinois 60637 United States
| | - Juan J. de Pablo
- Pritzker
School of Molecular Engineering, University
of Chicago, Chicago, Illinois 60637 United States
| |
Collapse
|
15
|
Harastani M, Eltsov M, Leforestier A, Jonic S. HEMNMA-3D: Cryo Electron Tomography Method Based on Normal Mode Analysis to Study Continuous Conformational Variability of Macromolecular Complexes. Front Mol Biosci 2021; 8:663121. [PMID: 34095222 PMCID: PMC8170028 DOI: 10.3389/fmolb.2021.663121] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Accepted: 04/09/2021] [Indexed: 12/28/2022] Open
Abstract
Cryogenic electron tomography (cryo-ET) allows structural determination of biomolecules in their native environment (in situ). Its potential of providing information on the dynamics of macromolecular complexes in cells is still largely unexploited, due to the challenges of the data analysis. The crowded cell environment and continuous conformational changes of complexes make difficult disentangling the data heterogeneity. We present HEMNMA-3D, which is, to the best of our knowledge, the first method for analyzing cryo electron subtomograms in terms of continuous conformational changes of complexes. HEMNMA-3D uses a combination of elastic and rigid-body 3D-to-3D iterative alignments of a flexible 3D reference (atomic structure or electron microscopy density map) to match the conformation, orientation, and position of the complex in each subtomogram. The elastic matching combines molecular mechanics simulation (Normal Mode Analysis of the 3D reference) and experimental, subtomogram data analysis. The rigid-body alignment includes compensation for the missing wedge, due to the limited tilt angle of cryo-ET. The conformational parameters (amplitudes of normal modes) of the complexes in subtomograms obtained through the alignment are processed to visualize the distribution of conformations in a space of lower dimension (typically, 2D or 3D) referred to as space of conformations. This allows a visually interpretable insight into the dynamics of the complexes, by calculating 3D averages of subtomograms with similar conformations from selected (densest) regions and by recording movies of the 3D reference's displacement along selected trajectories through the densest regions. We describe HEMNMA-3D and show its validation using synthetic datasets. We apply HEMNMA-3D to an experimental dataset describing in situ nucleosome conformational variability. HEMNMA-3D software is available freely (open-source) as part of ContinuousFlex plugin of Scipion V3.0 (http://scipion.i2pc.es).
Collapse
Affiliation(s)
- Mohamad Harastani
- IMPMC-UMR 7590 CNRS, Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France
| | - Mikhail Eltsov
- Department of Integrated Structural Biology, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
| | - Amélie Leforestier
- Laboratoire de Physique des Solides, UMR 8502 CNRS, Université Paris-Saclay, Paris, France
| | - Slavica Jonic
- IMPMC-UMR 7590 CNRS, Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France
| |
Collapse
|
16
|
Brouwer T, Pham C, Kaczmarczyk A, de Voogd WJ, Botto M, Vizjak P, Mueller-Planitz F, van Noort J. A critical role for linker DNA in higher-order folding of chromatin fibers. Nucleic Acids Res 2021; 49:2537-2551. [PMID: 33589918 PMCID: PMC7969035 DOI: 10.1093/nar/gkab058] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 12/04/2020] [Accepted: 01/25/2021] [Indexed: 12/12/2022] Open
Abstract
Nucleosome-nucleosome interactions drive the folding of nucleosomal arrays into dense chromatin fibers. A better physical account of the folding of chromatin fibers is necessary to understand the role of chromatin in regulating DNA transactions. Here, we studied the unfolding pathway of regular chromatin fibers as a function of single base pair increments in linker length, using both rigid base-pair Monte Carlo simulations and single-molecule force spectroscopy. Both computational and experimental results reveal a periodic variation of the folding energies due to the limited flexibility of the linker DNA. We show that twist is more restrictive for nucleosome stacking than bend, and find the most stable stacking interactions for linker lengths of multiples of 10 bp. We analyzed nucleosomes stacking in both 1- and 2-start topologies and show that stacking preferences are determined by the length of the linker DNA. Moreover, we present evidence that the sequence of the linker DNA also modulates nucleosome stacking and that the effect of the deletion of the H4 tail depends on the linker length. Importantly, these results imply that nucleosome positioning in vivo not only affects the phasing of nucleosomes relative to DNA but also directs the higher-order structure of chromatin.
Collapse
Affiliation(s)
- Thomas Brouwer
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - Chi Pham
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - Artur Kaczmarczyk
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - Willem-Jan de Voogd
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - Margherita Botto
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - Petra Vizjak
- Biomedical Center, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany
| | - Felix Mueller-Planitz
- Biomedical Center, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany.,Institute of Physiological Chemistry, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Fetscherstraße 74, 01307 Dresden, Germany
| | - John van Noort
- Biological and Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| |
Collapse
|
17
|
Zhou Z, Yan R, Jiang W, Irudayaraj JMK. Chromatin hierarchical branching visualized at the nanoscale by electron microscopy. NANOSCALE ADVANCES 2021; 3:1019-1028. [PMID: 34381959 PMCID: PMC8323808 DOI: 10.1039/d0na00359j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 11/12/2020] [Indexed: 06/13/2023]
Abstract
Chromatin is spatially organized in a hierarchical manner by virtue of single nucleosomes condensing into higher order chromatin structures, conferring various mechanical properties and biochemical signals. These higher order chromatin structures regulate genomic function by organization of the heterochromatin and euchromatin landscape. Less is known about its transition state from higher order heterochromatin to the lower order nucleosome form, and there is no information on its physical properties. We have developed a facile method of electron microscopy visualization to reveal the interphase chromatin in eukaryotic cells and its organization into hierarchical branching structures. We note that chromatin hierarchical branching can be distinguished at four levels, clearly indicating the stepwise transition from heterochromatin to euchromatin. The protein-DNA density across the chromatin fibers decreases during the transition from compacted heterochromatin to dispersed euchromatin. Moreover, the thickness of the chromatin ranges between 10 to 270 nm, and the controversial 30 nm chromatin fiber exists as a prominent intermediate structure. This study provides important insights into higher order chromatin organization which plays a key role in diseases such as cancer.
Collapse
Affiliation(s)
- Zhongwu Zhou
- Bindley Bioscience Center, Department of Agricultural and Biological Engineering, Purdue University West Lafayette IN 47907 USA
- The University of Texas at Austin NHB 4.120, 100 E. 24th St. Austin TX 78712 USA
| | - Rui Yan
- Markey Center for Structural Biology, Department of Biological Science, Purdue University West Lafayette IN 47907 USA
- Howard Hughes Medical Institute, Janelia Research Campus 19700 Helix Drive Asburn Virginia 20147 USA
| | - Wen Jiang
- Markey Center for Structural Biology, Department of Biological Science, Purdue University West Lafayette IN 47907 USA
| | - Joseph M K Irudayaraj
- Bindley Bioscience Center, Department of Agricultural and Biological Engineering, Purdue University West Lafayette IN 47907 USA
- Cancer Center at Illinois, Department of Bioengineering, College of Engineering, University of Illinois at Urbana-Champaign Urbana IL 61801 USA
| |
Collapse
|
18
|
le Paige UB, Xiang S, Hendrix MMRM, Zhang Y, Folkers GE, Weingarth M, Bonvin AMJJ, Kutateladze TG, Voets IK, Baldus M, van Ingen H. Characterization of nucleosome sediments for protein interaction studies by solid-state NMR spectroscopy. MAGNETIC RESONANCE (GOTTINGEN, GERMANY) 2021; 2:187-202. [PMID: 35647606 PMCID: PMC9135053 DOI: 10.5194/mr-2-187-2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Regulation of DNA-templated processes such as gene transcription and DNA repair depend on the interaction of a wide range of proteins with the nucleosome, the fundamental building block of chromatin. Both solution and solid-state NMR spectroscopy have become an attractive approach to study the dynamics and interactions of nucleosomes, despite their high molecular weight of ~ 200 kDa. For solid-state NMR (ssNMR) studies, dilute solutions of nucleosomes are converted to a dense phase by sedimentation or precipitation. Since nucleosomes are known to self-associate, these dense phases may induce extensive interactions between nucleosomes, which could interfere with protein-binding studies. Here, we characterized the packing of nucleosomes in the dense phase created by sedimentation using NMR and small-angle X-ray scattering (SAXS) experiments. We found that nucleosome sediments are gels with variable degrees of solidity, have nucleosome concentration close to that found in crystals, and are stable for weeks under high-speed magic angle spinning (MAS). Furthermore, SAXS data recorded on recovered sediments indicate that there is no pronounced long-range ordering of nucleosomes in the sediment. Finally, we show that the sedimentation approach can also be used to study low-affinity protein interactions with the nucleosome. Together, our results give new insights into the sample characteristics of nucleosome sediments for ssNMR studies and illustrate the broad applicability of sedimentation-based NMR studies.
Collapse
Affiliation(s)
- Ulric B. le Paige
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - ShengQi Xiang
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - Marco M. R. M. Hendrix
- Laboratory of Self-Organizing Soft Matter, Department of Chemical Engineering and Chemistry & Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands
| | - Yi Zhang
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Gert E. Folkers
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - Markus Weingarth
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - Alexandre M. J. J. Bonvin
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - Tatiana G. Kutateladze
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Ilja K. Voets
- Laboratory of Self-Organizing Soft Matter, Department of Chemical Engineering and Chemistry & Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands
| | - Marc Baldus
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| | - Hugo van Ingen
- Utrecht NMR Group, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, the Netherlands
| |
Collapse
|
19
|
Boopathi R, Dimitrov S, Hamiche A, Petosa C, Bednar J. Cryo-electron microscopy of the chromatin fiber. Curr Opin Struct Biol 2020; 64:97-103. [PMID: 32717688 DOI: 10.1016/j.sbi.2020.06.016] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2020] [Revised: 06/16/2020] [Accepted: 06/22/2020] [Indexed: 01/10/2023]
Abstract
The three-dimensional (3D) organization of chromatin plays a crucial role in the regulation of gene expression. Chromatin conformation is strongly affected by the composition, structural features and dynamic properties of the nucleosome, which in turn determine the nature and geometry of interactions that can occur between neighboring nucleosomes. Understanding how chromatin is spatially organized above the nucleosome level is thus essential for understanding how gene regulation is achieved. Towards this end, great effort has been made to understand how an array of nucleosomes folds into a regular chromatin fiber. This review summarizes new insights into the 3D structure of the chromatin fiber that were made possible by recent advances in cryo-electron microscopy.
Collapse
Affiliation(s)
- Ramachandran Boopathi
- Université Grenoble Alpes, CNRS UMR 5309, INSERM U1209, Institute for Advanced Biosciences (IAB), Site Sante´ - Allée des Alpes, 38700 La Tronche, France; Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France
| | - Stefan Dimitrov
- Université Grenoble Alpes, CNRS UMR 5309, INSERM U1209, Institute for Advanced Biosciences (IAB), Site Sante´ - Allée des Alpes, 38700 La Tronche, France; Izmir Biomedicine and Genome Center, Dokuz Eylul University Health Campus, Balcova, Izmir 35330, Turkey
| | - Ali Hamiche
- Département de Génomique Fonctionnelle et Cancer, Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC)/Université de Strasbourg/CNRS/INSERM, 67404 Illkirch Cedex, France
| | - Carlo Petosa
- Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 38000 Grenoble, France
| | - Jan Bednar
- Université Grenoble Alpes, CNRS UMR 5309, INSERM U1209, Institute for Advanced Biosciences (IAB), Site Sante´ - Allée des Alpes, 38700 La Tronche, France; Laboratory of the Biology and Pathology of the Eye, Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Albertov 4, 128 00 Prague 2, Czech Republic.
| |
Collapse
|
20
|
Ng CT, Gan L. Investigating eukaryotic cells with cryo-ET. Mol Biol Cell 2020; 31:87-100. [PMID: 31935172 PMCID: PMC6960407 DOI: 10.1091/mbc.e18-05-0329] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 11/25/2019] [Accepted: 11/29/2019] [Indexed: 01/06/2023] Open
Abstract
The interior of eukaryotic cells is mysterious. How do the large communities of macromolecular machines interact with each other? How do the structures and positions of these nanoscopic entities respond to new stimuli? Questions like these can now be answered with the help of a method called electron cryotomography (cryo-ET). Cryo-ET will ultimately reveal the inner workings of a cell at the protein, secondary structure, and perhaps even side-chain levels. Combined with genetic or pharmacological perturbation, cryo-ET will allow us to answer previously unimaginable questions, such as how structure, biochemistry, and forces are related in situ. Because it bridges structural biology and cell biology, cryo-ET is indispensable for structural cell biology-the study of the 3-D macromolecular structure of cells. Here we discuss some of the key ideas, strategies, auxiliary techniques, and innovations that an aspiring structural cell biologist will consider when planning to ask bold questions.
Collapse
Affiliation(s)
- Cai Tong Ng
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543
| | - Lu Gan
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543
| |
Collapse
|
21
|
Beltran B, Kannan D, MacPherson Q, Spakowitz AJ. Geometrical Heterogeneity Dominates Thermal Fluctuations in Facilitating Chromatin Contacts. PHYSICAL REVIEW LETTERS 2019; 123:208103. [PMID: 31809067 DOI: 10.1103/physrevlett.123.208103] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Indexed: 06/10/2023]
Abstract
Within a living cell, the myriad of proteins that bind DNA introduce heterogeneously spaced kinks into an otherwise semiflexible DNA double helix. To investigate the effects of heterogeneous nucleosome binding on chromatin organization, we extend the wormlike chain model to include statistically spaced, rigid kinks. On timescales where nucleosome positions are fixed, we find that the probability of chromatin loop formation can vary by up to six orders of magnitude between two sets of nucleosome positions drawn from the same distribution. On longer timescales, we show that continuous rerandomization due to nucleosome turnover results in chromatin tracing out an effective WLC with a dramatically smaller Kuhn length than bare DNA. Together, these observations demonstrate that nucleosome spacing acts as the primary source of the structural heterogeneity that dominates local and global chromatin organization.
Collapse
Affiliation(s)
- Bruno Beltran
- Biophysics Program, Stanford University, Stanford, California 94305, USA
| | - Deepti Kannan
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Quinn MacPherson
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Andrew J Spakowitz
- Chemical Engineering Department, Stanford University, Stanford, California 94305, USA
- Department of Materials Science and Engineering, Stanford University Stanford, California 94305, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| |
Collapse
|
22
|
Wu C, Travers A. Modelling and DNA topology of compact 2-start and 1-start chromatin fibres. Nucleic Acids Res 2019; 47:9902-9924. [PMID: 31219588 PMCID: PMC6765122 DOI: 10.1093/nar/gkz495] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/15/2019] [Accepted: 05/28/2019] [Indexed: 01/21/2023] Open
Abstract
We have investigated the structure of the most compact 30-nm chromatin fibres by modelling those with 2-start or 1-start crossed-linker organisations. Using an iterative procedure we obtained possible structural solutions for fibres of the highest possible compaction permitted by physical constraints, including the helical repeat of linker DNA. We find that this procedure predicts a quantized nucleosome repeat length (NRL) and that only fibres with longer NRLs (≥197 bp) can more likely adopt the 1-start organisation. The transition from 2-start to 1-start fibres is consistent with reported differing binding modes of the linker histone. We also calculate that in 1-start fibres the DNA constrains more torsion (as writhe) than 2-start fibres with the same NRL and that the maximum constraint obtained is in accord with previous experimental results. We posit that the coiling of the fibre is driven by overtwisting of linker DNA which, in the most compact forms - for example, in echinoderm sperm and avian erythrocytes - could adopt a helical repeat of ∼10 bp/turn. We argue that in vivo the total twist of linker DNA could be modulated by interaction with other abundant chromatin-associated proteins and by epigenetic modifications of the C-terminal tail of linker histones.
Collapse
Affiliation(s)
- Chenyi Wu
- Molecular Biophysics Laboratories, School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, UK
| | - Andrew Travers
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK
| |
Collapse
|
23
|
Chromatin fiber structural motifs as regulatory hubs of genome function? Essays Biochem 2019; 63:123-132. [PMID: 30967476 PMCID: PMC6484786 DOI: 10.1042/ebc20180065] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 03/13/2019] [Accepted: 03/13/2019] [Indexed: 02/07/2023]
Abstract
Nucleosomes cover eukaryotic genomes like beads on a string and play a central role in regulating genome function. Isolated strings of nucleosomes have the potential to compact and form higher order chromatin structures, such as the well-characterized 30-nm fiber. However, despite tremendous advances in observing chromatin fibers in situ it has not been possible to confirm that regularly ordered fibers represent a prevalent structural level in the folding of chromosomes. Instead, it appears that folding at a larger scale than the nucleosome involves a variety of random structures with fractal characteristics. Nevertheless, recent progress provides evidence for the existence of structural motifs in chromatin fibers, potentially localized to strategic sites in the genome. Here we review the current understanding of chromatin fiber folding and the emerging roles that oligonucleosomal motifs play in the regulation of genome function.
Collapse
|
24
|
Zhou K, Gaullier G, Luger K. Nucleosome structure and dynamics are coming of age. Nat Struct Mol Biol 2018; 26:3-13. [PMID: 30532059 DOI: 10.1038/s41594-018-0166-x] [Citation(s) in RCA: 180] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Accepted: 11/07/2018] [Indexed: 11/09/2022]
Abstract
Since the first high-resolution structure of the nucleosome was reported in 1997, the available information on chromatin structure has increased very rapidly. Here, we review insights derived from cutting-edge biophysical and structural approaches applied to the study of nucleosome dynamics and nucleosome-binding factors, with a focus on the experimental advances driving the research. In addition, we highlight emerging challenges in nucleosome structural biology.
Collapse
Affiliation(s)
- Keda Zhou
- Department of Biochemistry, University of Colorado Boulder, Boulder, CO, USA
| | - Guillaume Gaullier
- Department of Biochemistry, University of Colorado Boulder, Boulder, CO, USA.,Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, CO, USA
| | - Karolin Luger
- Department of Biochemistry, University of Colorado Boulder, Boulder, CO, USA. .,Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, CO, USA.
| |
Collapse
|
25
|
Cryo-ET reveals the macromolecular reorganization of S. pombe mitotic chromosomes in vivo. Proc Natl Acad Sci U S A 2018; 115:10977-10982. [PMID: 30297429 DOI: 10.1073/pnas.1720476115] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Chromosomes condense during mitosis in most eukaryotes. This transformation involves rearrangements at the nucleosome level and has consequences for transcription. Here, we use cryo-electron tomography (cryo-ET) to determine the 3D arrangement of nuclear macromolecular complexes, including nucleosomes, in frozen-hydrated Schizosaccharomyces pombe cells. Using 3D classification analysis, we did not find evidence that nucleosomes resembling the crystal structure are abundant. This observation and those from other groups support the notion that a subset of fission yeast nucleosomes may be partially unwrapped in vivo. In both interphase and mitotic cells, there is also no evidence of monolithic structures the size of Hi-C domains. The chromatin is mingled with two features: pockets, which are positions free of macromolecular complexes; and "megacomplexes," which are multimegadalton globular complexes like preribosomes. Mitotic chromatin is more crowded than interphase chromatin in subtle ways. Nearest-neighbor distance analyses show that mitotic chromatin is more compacted at the oligonucleosome than the dinucleosome level. Like interphase, mitotic chromosomes contain megacomplexes and pockets. This uneven chromosome condensation helps explain a longstanding enigma of mitosis: a subset of genes is up-regulated.
Collapse
|
26
|
Cai S, Böck D, Pilhofer M, Gan L. The in situ structures of mono-, di-, and trinucleosomes in human heterochromatin. Mol Biol Cell 2018; 29:2450-2457. [PMID: 30091658 PMCID: PMC6233054 DOI: 10.1091/mbc.e18-05-0331] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The in situ three-dimensional organization of chromatin at the nucleosome and oligonucleosome levels is unknown. Here we use cryo-electron tomography to determine the in situ structures of HeLa nucleosomes, which have canonical core structures and asymmetric, flexible linker DNA. Subtomogram remapping suggests that sequential nucleosomes in heterochromatin follow irregular paths at the oligonucleosome level. This basic principle of higher-order repressive chromatin folding is compatible with the conformational variability of the two linker DNAs at the single-nucleosome level.
Collapse
Affiliation(s)
- Shujun Cai
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543
| | - Désirée Böck
- Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - Martin Pilhofer
- Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - Lu Gan
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543
| |
Collapse
|