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Rudnizky S, Murray PJ, Wolfe CH, Ha T. Single-Macromolecule Studies of Eukaryotic Genomic Maintenance. Annu Rev Phys Chem 2024; 75:209-230. [PMID: 38382570 DOI: 10.1146/annurev-physchem-090722-010601] [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] [Indexed: 02/23/2024]
Abstract
Genomes are self-organized and self-maintained as long, complex macromolecules of chromatin. The inherent heterogeneity, stochasticity, phase separation, and chromatin dynamics of genome operation make it challenging to study genomes using ensemble methods. Various single-molecule force-, fluorescent-, and sequencing-based techniques rooted in different disciplines have been developed to fill critical gaps in the capabilities of bulk measurements, each providing unique, otherwise inaccessible, insights into the structure and maintenance of the genome. Capable of capturing molecular-level details about the organization, conformational changes, and packaging of genetic material, as well as processive and stochastic movements of maintenance factors, a single-molecule toolbox provides an excellent opportunity for collaborative research to understand how genetic material functions in health and malfunctions in disease. In this review, we discuss novel insights brought to genomic sciences by single-molecule techniques and their potential to continue to revolutionize the field-one molecule at a time.
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Affiliation(s)
- Sergei Rudnizky
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Peter J Murray
- Department of Biology, Johns Hopkins University, Baltimore, Maryland, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA;
| | - Clara H Wolfe
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Taekjip Ha
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA;
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
- Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts, USA
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Johnson S, Paul T, Sanford S, Schnable BL, Detwiler A, Thosar S, Van Houten B, Myong S, Opresko P. BG4 antibody can recognize telomeric G-quadruplexes harboring destabilizing base modifications and lesions. Nucleic Acids Res 2024; 52:1763-1778. [PMID: 38153143 PMCID: PMC10939409 DOI: 10.1093/nar/gkad1209] [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: 06/16/2023] [Revised: 11/30/2023] [Accepted: 12/11/2023] [Indexed: 12/29/2023] Open
Abstract
BG4 is a single-chain variable fragment antibody shown to bind various G-quadruplex (GQ) topologies with high affinity and specificity, and to detect GQ in cells, including GQ structures formed within telomeric TTAGGG repeats. Here, we used ELISA and single-molecule pull-down (SiMPull) detection to test how various lengths and GQ destabilizing base modifications in telomeric DNA constructs alter BG4 binding. We observed high-affinity BG4 binding to telomeric GQ independent of telomere length, although three telomeric repeat constructs that cannot form stable intramolecular GQ showed reduced affinity. A single guanine substitution with 8-aza-7-deaza-G, T, A, or C reduced affinity to varying degrees depending on the location and base type, whereas two G substitutions in the telomeric construct dramatically reduced or abolished binding. Substitution with damaged bases 8-oxoguanine and O6-methylguanine failed to prevent BG4 binding although affinity was reduced depending on lesion location. SiMPull combined with FRET revealed that BG4 binding promotes folding of telomeric GQ harboring a G to T substitution or 8-oxoguanine. Atomic force microscopy revealed that BG4 binds telomeric GQ with a 1:1 stoichiometry. Collectively, our data suggest that BG4 can recognize partially folded telomeric GQ structures and promote telomeric GQ stability.
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Affiliation(s)
- Samuel A Johnson
- Department of Environmental and Occupational Health, University of Pittsburgh School of Public Health, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
- Molecular Biophysics and Structural Biology Graduate Program, University of Pittsburgh, PA 15260, USA
| | - Tapas Paul
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115, USA
| | - Samantha L Sanford
- Department of Environmental and Occupational Health, University of Pittsburgh School of Public Health, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
| | - Brittani L Schnable
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
- Molecular Biophysics and Structural Biology Graduate Program, University of Pittsburgh, PA 15260, USA
| | - Ariana C Detwiler
- Department of Environmental and Occupational Health, University of Pittsburgh School of Public Health, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
| | - Sanjana A Thosar
- Department of Environmental and Occupational Health, University of Pittsburgh School of Public Health, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
| | - Bennett Van Houten
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
- Molecular Biophysics and Structural Biology Graduate Program, University of Pittsburgh, PA 15260, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, PA 15213, USA
| | - Sua Myong
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115, USA
| | - Patricia L Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh School of Public Health, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA
- Molecular Biophysics and Structural Biology Graduate Program, University of Pittsburgh, PA 15260, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, PA 15213, USA
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Tesmer VM, Brenner KA, Nandakumar J. Human POT1 protects the telomeric ds-ss DNA junction by capping the 5' end of the chromosome. Science 2023; 381:771-778. [PMID: 37590346 PMCID: PMC10666826 DOI: 10.1126/science.adi2436] [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: 04/19/2023] [Accepted: 07/19/2023] [Indexed: 08/19/2023]
Abstract
Protection of telomeres 1 (POT1) is the 3' single-stranded overhang-binding telomeric protein that prevents an ataxia telangiectasia and Rad3-related (ATR) DNA damage response (DDR) at chromosome ends. What precludes the DDR machinery from accessing the telomeric double-stranded-single-stranded junction is unknown. We demonstrate that human POT1 binds this junction by recognizing the phosphorylated 5' end of the chromosome. High-resolution crystallographic structures reveal that the junction is capped by POT1 through a "POT-hole" surface, the mutation of which compromises junction protection in vitro and telomeric 5'-end definition and DDR suppression in human cells. Whereas both mouse POT1 paralogs bind the single-stranded overhang, POT1a, not POT1b, contains a POT-hole and binds the junction, which explains POT1a's sufficiency for end protection. Our study shifts the paradigm for DDR suppression at telomeres by highlighting the importance of protecting the double-stranded-single-stranded junction.
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Affiliation(s)
- Valerie M. Tesmer
- Department of Molecular, Cellular and Developmental Biology, University of Michigan; Ann Arbor, 48109, USA
| | - Kirsten A. Brenner
- Department of Molecular, Cellular and Developmental Biology, University of Michigan; Ann Arbor, 48109, USA
| | - Jayakrishnan Nandakumar
- Department of Molecular, Cellular and Developmental Biology, University of Michigan; Ann Arbor, 48109, USA
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Abstract
We present single-molecule experimental and computational modeling studies investigating the accessibility of human telomeric overhangs of physiologically relevant lengths. We studied 25 different overhangs that contain 4-28 repeats of GGGTTA (G-Tract) sequence and accommodate one to seven tandem G-quadruplex (GQ) structures. Using the FRET-PAINT method, we probed the distribution of accessible sites via a short imager strand, which is complementary to a G-Tract and transiently binds to available sites. We report accessibility patterns that periodically change with overhang length and interpret these patterns in terms of the underlying folding landscape and folding frustration. Overhangs that have [4n]G-Tracts, (12, 16, 20…) demonstrate the broadest accessibility patterns where the peptide nucleic acid probe accesses G-Tracts throughout the overhang. On the other hand, constructs with [4n+2]G-Tracts, (14, 18, 22…) have narrower patterns where the neighborhood of the junction between single- and double-stranded telomeres is most accessible. We interpret these results as the folding frustration being higher in [4n]G-Tract constructs compared to [4n+2]G-Tract constructs. We also developed a computational model that tests the consistency of different folding stabilities and cooperativities between neighboring GQs with the observed accessibility patterns. Our experimental and computational studies suggest the neighborhood of the junction between single- and double-stranded telomeres is least stable and most accessible, which is significant as this is a potential site where the connection between POT1/TPP1 (bound to single-stranded telomere) and other shelterin proteins (localized on double-stranded telomere) is established.
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Paul T, Opresko PL, Ha T, Myong S. Vectorial folding of telomere overhang promotes higher accessibility. Nucleic Acids Res 2022; 50:6271-6283. [PMID: 35687089 PMCID: PMC9226509 DOI: 10.1093/nar/gkac401] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/20/2022] [Accepted: 06/08/2022] [Indexed: 11/13/2022] Open
Abstract
Human telomere overhang composed of tandem repeats of TTAGGG folds into G-quadruplex (G4). Unlike in an experimental setting in the test tube in which the entire length is allowed to fold at once, inside the cell, the overhang is expected to fold as it is synthesized directionally (5' to 3') and released segmentally by a specialized enzyme, the telomerase. To mimic such vectorial G4 folding process, we employed a superhelicase, Rep-X which can unwind DNA to release the TTAGGG repeats in 5' to 3' direction. We demonstrate that the folded conformation achieved by the refolding of full sequence is significantly different from that of the vectorial folding for two to eight TTAGGG repeats. Strikingly, the vectorially folded state leads to a remarkably higher accessibility to complementary C-rich strand and the telomere binding protein POT1, reflecting a less stably folded state resulting from the vectorial folding. Importantly, our study points to an inherent difference between the co-polymerizing and post-polymerized folding of telomere overhang that can impact telomere architecture and downstream processes.
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Affiliation(s)
- Tapas Paul
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA
| | - Patricia L Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, and UPMC Hillman Cancer Center, Pittsburgh, PA15213, USA
| | - Taekjip Ha
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA.,Physics Frontier Center (Center for Physics of Living Cells), University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA.,Howard Hughes Medical Institute, Johns Hopkins University, Baltimore, MD, USA
| | - Sua Myong
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA.,Physics Frontier Center (Center for Physics of Living Cells), University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA
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Paul T, Myong S. Protocol for generation and regeneration of PEG-passivated slides for single-molecule measurements. STAR Protoc 2022; 3:101152. [PMID: 35146451 PMCID: PMC8819390 DOI: 10.1016/j.xpro.2022.101152] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Single-molecule fluorescence detection by total internal reflection microscope requires surface passivation by polyethylene glycol (PEG) coating, which is labor intensive and is only good for one or two experiments. Here, we present an efficient and reliable protocol for generating and regenerating the PEG surface for multiple rounds of experiments (∼5–10 times) in the same channel. This protocol is very simple, robust, rapid, and versatile; i.e., multiple strategies can be implemented to regenerate different layers of surface. The regeneration strategy saves time, improves the cost effectiveness, and enhances the efficiency of single-molecule experiments. For complete details on the use and execution of this profile, please refer to Paul et al. (2021a). Regeneration of PEG-passivated slide is simple, quick, and cost effective Multiple experiments can be performed in a single channel Different strategies are implemented for different level of regeneration Regeneration leads to highly reproducible results
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Affiliation(s)
- Tapas Paul
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Sua Myong
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.,Physics Frontier Center, Center for the Physics of Living Cells, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
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Paul T, Myong S. Helicase mediated vectorial folding of telomere G-quadruplex. Methods Enzymol 2022; 672:283-297. [DOI: 10.1016/bs.mie.2022.03.065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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