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Open accessJournal ArticleDOI: 10.7554/ELIFE.65587

Archaeal chromatin ‘slinkies’ are inherently dynamic complexes with deflected DNA wrapping pathways

02 Mar 2021-eLife (eLife Sciences Publications Limited)-Vol. 10
Abstract: All animals, plants and fungi belong to a group of living organisms called eukaryotes. The two other groups are bacteria and archaea, which include unicellular, microscopic organisms. All three groups have genes, which are typically stored on long strands of DNA. Eukaryotes have so much DNA that they use proteins called histones to help package and organize it inside each cell. Archaea also have simplified histones that help store their DNA, and studying these proteins could reveal how eukaryotic histones first evolved. In eukaryotes, groups of eight histones form a short cylinder that organizes a small section of DNA into a structure called a nucleosome. Each cell needs hundreds of thousands of nucleosomes to arrange its DNA. Eukaryotic cells also contain other proteins that release pieces of DNA from histones so that their genetic information can be used. The histones in Archaea don’t form discrete nucleosomes, instead, they coil DNA into ‘slinky-like’ shapes. It’s still unclear how DNA packing in archaea works and how it differs from eukaryotes. Bowerman, Wereszczynski and Luger used computer simulations, biochemistry and cryo-electron microscopy to study the histones from archaea. The archaeal ‘slinky-like’ histone structures are more flexible than nucleosomes, and can open and close like clamshells. This flexibility allows the information in the genomes of Archaea to be easily accessed, so, unlike in eukaryotes, archaeal cells may not need other proteins to release the DNA from the histones. The ability to package DNA allows cells to contain many more genes, so evolving histones was a vital step in the evolution of eukaryotic life, including the appearance of animals. Archaeal histones may reflect early versions of histones in eukaryotes, and can be used to understand how DNA packing has evolved. Furthermore, a greater understanding of Archaea may help better explain their role in health and global ecosystems, and allow their use in industrial applications.

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Topics: Histone (60%), Chromatin (57%), Nucleosome (56%) ... show more
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8 results found


Journal ArticleDOI: 10.1038/S41594-021-00585-7
Abstract: Certain large DNA viruses, including those in the Marseilleviridae family, encode histones. Here we show that fused histone pairs Hβ-Hα and Hδ-Hγ from Marseillevirus are structurally analogous to the eukaryotic histone pairs H2B-H2A and H4-H3. These viral histones form 'forced' heterodimers, and a heterotetramer of four such heterodimers assembles DNA to form structures virtually identical to canonical eukaryotic nucleosomes.

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Topics: Marseillevirus (63%), Histone (61%), Nucleosome (61%) ... show more

10 Citations


Open accessJournal ArticleDOI: 10.1016/J.CELL.2021.06.032
Yang Liu1, Yang Liu2, Hugo Bisio3, Chelsea Marie Toner2  +9 moreInstitutions (3)
05 Aug 2021-Cell
Abstract: The organization of genomic DNA into defined nucleosomes has long been viewed as a hallmark of eukaryotes. This paradigm has been challenged by the identification of "minimalist" histones in archaea and more recently by the discovery of genes that encode fused remote homologs of the four eukaryotic histones in Marseilleviridae, a subfamily of giant viruses that infect amoebae. We demonstrate that viral doublet histones are essential for viral infectivity, localize to cytoplasmic viral factories after virus infection, and ultimately are found in the mature virions. Cryogenic electron microscopy (cryo-EM) structures of viral nucleosome-like particles show strong similarities to eukaryotic nucleosomes despite the limited sequence identify. The unique connectors that link the histone chains contribute to the observed instability of viral nucleosomes, and some histone tails assume structural roles. Our results further expand the range of "organisms" that require nucleosomes and suggest a specialized function of histones in the biology of these unusual viruses.

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Topics: Histone (61%), Viral factory (60%), Nucleosome (56%) ... show more

4 Citations


Journal ArticleDOI: 10.1016/J.JMB.2020.166791
Abstract: The three domains of life employ various strategies to organize their genomes. Archaea utilize features similar to those found in both eukaryotic and bacterial chromatin to organize their DNA. In this review, we discuss the current state of research regarding the structure-function relationships of several archaeal chromatin proteins (histones, Alba, Cren7, and Sul7d). We address individual structures as well as inferred models for higher-order chromatin formation. Each protein introduces a unique phenotype to chromatin organization, and these structures are put into the context of in vivo and in vitro data. We close by discussing the present gaps in knowledge that are preventing further studies of the organization of archaeal chromatin, on both the organismal and domain level.

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Topics: Chromatin (64%), Histone (52%)

4 Citations


Open accessJournal ArticleDOI: 10.3389/FMICB.2021.681150
Abstract: Histone proteins compact and organize DNA resulting in a dynamic chromatin architecture impacting DNA accessibility and ultimately gene expression. Eukaryotic chromatin landscapes are structured through histone protein variants, epigenetic marks, the activities of chromatin-remodeling complexes, and post-translational modification of histone proteins. In most Archaea, histone-based chromatin structure is dominated by the helical polymerization of histone proteins wrapping DNA into a repetitive and closely gyred configuration. The formation of the archaeal-histone chromatin-superhelix is a regulatory force of adaptive gene expression and is likely critical for regulation of gene expression in all histone-encoding Archaea. Single amino acid substitutions in archaeal histones that block formation of tightly packed chromatin structures have profound effects on cellular fitness, but the underlying gene expression changes resultant from an altered chromatin landscape have not been resolved. Using the model organism Thermococcus kodakarensis, we genetically alter the chromatin landscape and quantify the resultant changes in gene expression, including unanticipated and significant impacts on provirus transcription. Global transcriptome changes resultant from varying chromatin landscapes reveal the regulatory importance of higher-order histone-based chromatin architectures in regulating archaeal gene expression.

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Topics: Chromatin (71%), Histone (63%), Regulation of gene expression (61%) ... show more

2 Citations


Open accessPosted ContentDOI: 10.1101/2021.10.08.463051
John W. Sedat1, Angus McDonald2, Hu Cang3, Joseph S. Lucas4  +4 moreInstitutions (6)
09 Oct 2021-bioRxiv
Abstract: Cellular cryo-electron tomography (CET) of the cell nucleus using Scanning Transmission Electron Microscopy (STEM) and the use of deconvolution (DC) processing technology has highlighted a large-scale, 100-300 nm interphase chromosome structure (LSS), that is present throughout the nucleus. This chromosome structure appears to coil the nucleosome 11-nm fiber into a defined hollow structure, analogous to a Slinky (S) (1, motif used in 2) helical spring. This S architecture can be used to build chromosome territories, extended to polytene chromosome structure, as well as to the structure of Lampbrush chromosomes. Significance StatementCryo-preservation of the nuclear interior allows a large scale interphase chromosome structure--present throughout the nucleus--to be seen for the first time. This structure can be proposed to be a defined coiled entity, a Slinky. This structure can be further used to explain polytene chromosome structure, an unknown chromosome architecture as well as for lampbrush chromosomes. In addition, this new structure can be further organized as chromosome territories, using all 46 human interphase chromosomes as an example, easily into a 10 micron diameter nucleus. Thus, interphase chromosomes can be unified into a flexible defined structure.

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Topics: Interphase Chromosome (72%), Lampbrush chromosome (63%), Polytene chromosome (60%) ... show more

1 Citations


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55 results found


Journal ArticleDOI: 10.1016/0263-7855(96)00018-5
Abstract: VMD is a molecular graphics program designed for the display and analysis of molecular assemblies, in particular biopolymers such as proteins and nucleic acids. VMD can simultaneously display any number of structures using a wide variety of rendering styles and coloring methods. Molecules are displayed as one or more "representations," in which each representation embodies a particular rendering method and coloring scheme for a selected subset of atoms. The atoms displayed in each representation are chosen using an extensive atom selection syntax, which includes Boolean operators and regular expressions. VMD provides a complete graphical user interface for program control, as well as a text interface using the Tcl embeddable parser to allow for complex scripts with variable substitution, control loops, and function calls. Full session logging is supported, which produces a VMD command script for later playback. High-resolution raster images of displayed molecules may be produced by generating input scripts for use by a number of photorealistic image-rendering applications. VMD has also been expressly designed with the ability to animate molecular dynamics (MD) simulation trajectories, imported either from files or from a direct connection to a running MD simulation. VMD is the visualization component of MDScope, a set of tools for interactive problem solving in structural biology, which also includes the parallel MD program NAMD, and the MDCOMM software used to connect the visualization and simulation programs. VMD is written in C++, using an object-oriented design; the program, including source code and extensive documentation, is freely available via anonymous ftp and through the World Wide Web.

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Topics: Rendering (computer graphics) (52%), Molecular graphics (52%), Visualization (51%) ... show more

36,939 Citations


Journal ArticleDOI: 10.1063/1.445869
Abstract: Classical Monte Carlo simulations have been carried out for liquid water in the NPT ensemble at 25 °C and 1 atm using six of the simpler intermolecular potential functions for the water dimer: Bernal–Fowler (BF), SPC, ST2, TIPS2, TIP3P, and TIP4P. Comparisons are made with experimental thermodynamic and structural data including the recent neutron diffraction results of Thiessen and Narten. The computed densities and potential energies are in reasonable accord with experiment except for the original BF model, which yields an 18% overestimate of the density and poor structural results. The TIPS2 and TIP4P potentials yield oxygen–oxygen partial structure functions in good agreement with the neutron diffraction results. The accord with the experimental OH and HH partial structure functions is poorer; however, the computed results for these functions are similar for all the potential functions. Consequently, the discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons are also made for self‐diffusion coefficients obtained from molecular dynamics simulations. Overall, the SPC, ST2, TIPS2, and TIP4P models give reasonable structural and thermodynamic descriptions of liquid water and they should be useful in simulations of aqueous solutions. The simplicity of the SPC, TIPS2, and TIP4P functions is also attractive from a computational standpoint.

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Topics: Water model (53%), Solvent models (52%), Water dimer (51%) ... show more

29,424 Citations


Journal ArticleDOI: 10.1038/38444
18 Sep 1997-Nature
Abstract: The X-ray crystal structure of the nucleosome core particle of chromatin shows in atomic detail how the histone protein octamer is assembled and how 146 base pairs of DNA are organized into a superhelix around it. Both histone/histone and histone/DNA interactions depend on the histone fold domains and additional, well ordered structure elements extending from this motif. Histone amino-terminal tails pass over and between the gyres of the DNA superhelix to contact neighbouring particles. The lack of uniformity between multiple histone/DNA-binding sites causes the DNA to deviate from ideal superhelix geometry.

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Topics: Histone octamer (75%), Histone fold (74%), Histone binding (71%) ... show more

7,215 Citations


Open accessJournal ArticleDOI: 10.1021/ACS.JCTC.5B00255
Abstract: Molecular mechanics is powerful for its speed in atomistic simulations, but an accurate force field is required. The Amber ff99SB force field improved protein secondary structure balance and dynamics from earlier force fields like ff99, but weaknesses in side chain rotamer and backbone secondary structure preferences have been identified. Here, we performed a complete refit of all amino acid side chain dihedral parameters, which had been carried over from ff94. The training set of conformations included multidimensional dihedral scans designed to improve transferability of the parameters. Improvement in all amino acids was obtained as compared to ff99SB. Parameters were also generated for alternate protonation states of ionizable side chains. Average errors in relative energies of pairs of conformations were under 1.0 kcal/mol as compared to QM, reduced 35% from ff99SB. We also took the opportunity to make empirical adjustments to the protein backbone dihedral parameters as compared to ff99SB. Multiple sm...

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Topics: Side chain (56%), Dihedral angle (53%), Protein secondary structure (52%)

4,140 Citations


Open accessJournal ArticleDOI: 10.1038/NMETH.4193
01 Apr 2017-Nature Methods
Abstract: MotionCor2 software corrects for beam-induced sample motion, improving the resolution of cryo-EM reconstructions.

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3,454 Citations


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