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Chang TR, Long X, Shastry S, Parks JW, Stone MD. Single-Molecule Mechanical Analysis of Strand Invasion in Human Telomere DNA. Biochemistry 2022; 61:1554-1560. [PMID: 35852986 PMCID: PMC9352315 DOI: 10.1021/acs.biochem.1c00448] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Telomeres are essential
chromosome end capping structures that
safeguard the genome from dangerous DNA processing events. DNA strand
invasion occurs during vital transactions at telomeres, including
telomere length maintenance by the alternative lengthening of telomeres
(ALT) pathway. During telomeric strand invasion, a single-stranded
guanine-rich (G-rich) DNA invades at a complementary duplex telomere
repeat sequence, forming a displacement loop (D-loop) in which the
displaced DNA consists of the same G-rich sequence as the invading
single-stranded DNA. Single-stranded G-rich telomeric DNA readily
folds into stable, compact, structures called G-quadruplexes (GQs)
in vitro and is anticipated to form within the context of a D-loop;
however, evidence supporting this hypothesis is lacking. Here, we
report a magnetic tweezers assay that permits the controlled formation
of telomeric D-loops (TDLs) within uninterrupted duplex human telomere
DNA molecules of physiologically relevant lengths. Our results are
consistent with a model wherein the displaced single-stranded DNA
of a TDL fold into a GQ. This study provides new insight into telomere
structure and establishes a framework for the development of novel
therapeutics designed to target GQs at telomeres in cancer cells.
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Affiliation(s)
- Terren R. Chang
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, United States
| | - Xi Long
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, United States
| | - Shankar Shastry
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, United States
- 10X Genomics, 6230 Stoneridge Mall Rd, Pleasanton, California 94588, United States
| | - Joseph W. Parks
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, United States
- Invitae, 1400 16th St, San Francisco, California 94103, United States
| | - Michael D. Stone
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, United States
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Zhang Y, Cheng Y, Chen J, Zheng K, You H. Mechanical diversity and folding intermediates of parallel-stranded G-quadruplexes with a bulge. Nucleic Acids Res 2021; 49:7179-7188. [PMID: 34139007 PMCID: PMC8266575 DOI: 10.1093/nar/gkab531] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/17/2021] [Accepted: 06/09/2021] [Indexed: 12/17/2022] Open
Abstract
A significant number of sequences in the human genome form noncanonical G-quadruplexes (G4s) with bulges or a guanine vacancy. Here, we systematically characterized the mechanical stability of parallel-stranded G4s with a one to seven nucleotides bulge at various positions. Our results show that G4-forming sequences with a bulge form multiple conformations, including fully-folded G4 with high mechanical stability (unfolding forces > 40 pN), partially-folded intermediates (unfolding forces < 40 pN). The folding probability and folded populations strongly depend on the positions and lengths of the bulge. By combining a single-molecule unfolding assay, dimethyl sulfate (DMS) footprinting, and a guanine-peptide conjugate that selectively stabilizes guanine-vacancy-bearing G-quadruplexes (GVBQs), we identified that GVBQs are the major intermediates of G4s with a bulge near the 5′ or 3′ ends. The existence of multiple structures may induce different regulatory functions in many biological processes. This study also demonstrates a new strategy for selectively stabilizing the intermediates of bulged G4s to modulate their functions.
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Affiliation(s)
- Yashuo Zhang
- Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Yuanlei Cheng
- Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Juannan Chen
- School of Pharmaceutical Sciences (Shenzhen), Sun Yat-Sen University, Guangzhou 510275, China
| | - Kewei Zheng
- School of Pharmaceutical Sciences (Shenzhen), Sun Yat-Sen University, Guangzhou 510275, China
| | - Huijuan You
- Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
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Cheng Y, Tang Q, Li Y, Zhang Y, Zhao C, Yan J, You H. Folding/unfolding kinetics of G-quadruplexes upstream of the P1 promoter of the human BCL-2 oncogene. J Biol Chem 2019; 294:5890-5895. [PMID: 30787104 DOI: 10.1074/jbc.ra119.007516] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 02/14/2019] [Indexed: 12/29/2022] Open
Abstract
The G-rich Pu39 region of the P1 promoter of the oncogene BCL-2, an apoptosis regulator, can fold into multiple G-quadruplex (G4) structures. Bcl2-2345 and Bcl2-1245 are two major G4 species forming with high thermal stability and distinct topologies in the Pu39 region, but their folding/unfolding kinetics have not yet been investigated. Here, we used magnetic tweezers to measure the mechanical stability and the folding/unfolding kinetics of the Bcl2-2345 and Bcl2-1245 G4 structures. We report that the hybrid-stranded Bcl2-2345 G4 had a lower mechanical stability than the parallel-stranded Bcl2-1245 G4. We observed that the Bcl2-2345 G4 is a kinetically favored structure, whereas the Bcl2-1245 G4, with a slow unfolding rate, may function as a kinetic barrier for transcription. We also determined that in addition to the Bcl2-2345 and Bcl2-1245 G4s, other stable DNA secondary structures, such as a hybrid-stranded Bcl2-1234 G4, can also form in the Pu39 sequence. The characterization of the folding/unfolding kinetics of specific G4s reported here sheds light on the participation of G4s during gene transcription and provides information for designing G4-targeting small molecules that could modulate BCL-2 gene expression.
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Affiliation(s)
- Yuanlei Cheng
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Qingnan Tang
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Yutong Li
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Yashuo Zhang
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Chuyuan Zhao
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Jie Yan
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore; the Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore
| | - Huijuan You
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China.
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