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Liu Y, Wan L, Ngai CK, Wang Y, Lam SL, Guo P. Structures and conformational dynamics of DNA minidumbbells in pyrimidine-rich repeats associated with neurodegenerative diseases. Comput Struct Biotechnol J 2023; 21:1584-1592. [PMID: 36874156 PMCID: PMC9975016 DOI: 10.1016/j.csbj.2023.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 02/05/2023] [Accepted: 02/05/2023] [Indexed: 02/10/2023] Open
Abstract
Expansions of short tandem repeats (STRs) are associated with approximately 50 human neurodegenerative diseases. These pathogenic STRs are prone to form non-B DNA structure, which has been considered as one of the causative factors for repeat expansions. Minidumbbell (MDB) is a relatively new type of non-B DNA structure formed by pyrimidine-rich STRs. An MDB is composed of two tetraloops or pentaloops, exhibiting a highly compact conformation with extensive loop-loop interactions. The MDB structures have been found to form in CCTG tetranucleotide repeats associated with myotonic dystrophy type 2, ATTCT pentanucleotide repeats associated with spinocerebellar ataxia type 10, and the recently discovered ATTTT/ATTTC repeats associated with spinocerebellar ataxia type 37 and familial adult myoclonic epilepsy. In this review, we first introduce the structures and conformational dynamics of MDBs with a focus on the high-resolution structural information determined by nuclear magnetic resonance spectroscopy. Then we discuss the effects of sequence context, chemical environment, and nucleobase modification on the structure and thermostability of MDBs. Finally, we provide perspectives on further explorations of sequence criteria and biological functions of MDBs.
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Affiliation(s)
- Yuan Liu
- South China Advanced Institute for Soft Matter Science and Technology, School of Emergent Soft Matter, South China University of Technology, Guangzhou, Guangdong 510640, China
| | - Liqi Wan
- School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Cheuk Kit Ngai
- Department of Chemistry, The Chinese University of Hong Kong, Shatin N.T., Hong Kong, China
| | - Yang Wang
- Zhejiang Cancer Hospital, Institute of Basic Medicine and Cancer (IBMC) Chinese Academy of Sciences, Hangzhou, Zhejiang 310022, China
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin N.T., Hong Kong, China
| | - Pei Guo
- Zhejiang Cancer Hospital, Institute of Basic Medicine and Cancer (IBMC) Chinese Academy of Sciences, Hangzhou, Zhejiang 310022, China
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Ngai CK, Lam SL, Lee HK, Guo P. A purine and a backbone discontinuous site alter the structure and thermal stability of DNA minidumbbells containing two pentaloops. FEBS Lett 2022; 596:826-840. [DOI: 10.1002/1873-3468.14293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 01/13/2022] [Accepted: 01/13/2022] [Indexed: 11/11/2022]
Affiliation(s)
- Cheuk Kit Ngai
- Department of Chemistry The Chinese University of Hong Kong Shatin New Territories Hong Kong SAR China
| | - Sik Lok Lam
- Department of Chemistry The Chinese University of Hong Kong Shatin New Territories Hong Kong SAR China
| | - Hung Kay Lee
- Department of Chemistry The Chinese University of Hong Kong Shatin New Territories Hong Kong SAR China
| | - Pei Guo
- School of Biology and Biological Engineering South China University of Technology Guangzhou Guangdong 51006 China
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Wan L, Lam SL, Lee HK, Guo P. Effects of Adenine Methylation on the Structure and Thermodynamic Stability of a DNA Minidumbbell. Int J Mol Sci 2021; 22:3633. [PMID: 33807305 PMCID: PMC8037738 DOI: 10.3390/ijms22073633] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 03/24/2021] [Accepted: 03/25/2021] [Indexed: 11/17/2022] Open
Abstract
DNA methylation is a prevalent regulatory modification in prokaryotes and eukaryotes. N1-methyladenine (m1A) and N6-methyladenine (m6A) have been found to be capable of altering DNA structures via disturbing Watson-Crick base pairing. However, little has been known about their influences on non-B DNA structures, which are associated with genetic instabilities. In this work, we investigated the effects of m1A and m6A on both the structure and thermodynamic stability of a newly reported DNA minidumbbell formed by two TTTA tetranucleotide repeats. As revealed by the results of nuclear magnetic resonance spectroscopic studies, both m1A and m6A favored the formation of a T·m1A and T·m6A Hoogsteen base pair, respectively. More intriguingly, the m1A and m6A modifications brought about stabilization and destabilization effects on the DNA minidumbbell, respectively. This work provides new biophysical insights into the effects of adenine methylation on the structure and thermodynamic stability of DNA.
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Affiliation(s)
- Liqi Wan
- MOE International Joint Research Laboratory on Synthetic Biology and Medicines, School of Biology and Biological Engineering, South China University of Technology, Guangzhou 510006, China;
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR 999077, China;
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR 999077, China;
| | - Hung Kay Lee
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR 999077, China;
| | - Pei Guo
- MOE International Joint Research Laboratory on Synthetic Biology and Medicines, School of Biology and Biological Engineering, South China University of Technology, Guangzhou 510006, China;
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Guo P, Lam SL. Minidumbbell structures formed by ATTCT pentanucleotide repeats in spinocerebellar ataxia type 10. Nucleic Acids Res 2020; 48:7557-7568. [PMID: 32520333 PMCID: PMC7367182 DOI: 10.1093/nar/gkaa495] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 05/26/2020] [Accepted: 05/30/2020] [Indexed: 01/02/2023] Open
Abstract
Spinocerebellar ataxia type 10 (SCA10) is a progressive genetic disorder caused by ATTCT pentanucleotide repeat expansions in intron 9 of the ATXN10 gene. ATTCT repeats have been reported to form unwound secondary structures which are likely linked to large-scale repeat expansions. In this study, we performed high-resolution nuclear magnetic resonance spectroscopic investigations on DNA sequences containing two to five ATTCT repeats. Strikingly, we found the first two repeats of all these sequences well folded into highly compact minidumbbell (MDB) structures. The 3D solution structure of the sequence containing two ATTCT repeats was successfully determined, revealing the MDB comprises a regular TTCTA and a quasi TTCT/A pentaloops with extensive stabilizing loop-loop interactions. We further carried out in vitro primer extension assays to examine if the MDB formed in the primer could escape from the proofreading function of DNA polymerase. Results showed that when the MDB was formed at 5-bp or farther away from the priming site, it was able to escape from the proofreading by Klenow fragment of DNA polymerase I and thus retained in the primer. The intriguing structural findings bring about new insights into the origin of genetic instability in SCA10.
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Affiliation(s)
- Pei Guo
- School of Biology and Biological Engineering, South China University of Technology, Guangzhou, Guangdong 510006, China
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China
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Ngai CK, Lam SL, Lee HK, Guo P. High-Resolution Structures of DNA Minidumbbells Comprising Type II Tetraloops with a Purine Minor Groove Residue. J Phys Chem B 2020; 124:5131-5138. [PMID: 32484672 DOI: 10.1021/acs.jpcb.0c03163] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Minidumbbell (MDB) is a newly discovered DNA structure formed by native sequences, which serves as a possible structural intermediate causing repeat expansion mutations in the genome and also a functional structural motif in constructing DNA-based molecular switches. Until now, all the reported MDBs containing two adjacent type II tetraloops were formed by pyrimidine-rich sequences 5'-YYYR YYYR-3' (Y and R represent pyrimidine and purine, respectively), wherein the second and sixth residues folded into the minor groove and interacted with each other. In this study, we have conducted a high-resolution nuclear magnetic resonance (NMR) spectroscopic investigation on alternative MDB-forming sequences and discovered that an MDB could also be formed stably with a purine in the minor groove, which has never been observed in any previously reported DNA type II tetraloops. Our refined NMR solution structures of the two MDBs formed by 5'-CTTG CATG-3' and 5'-CTTG CGTG-3' reveal that the sixth purine residue was driven into the minor groove via base-base stacking with the second thymine residue and adenine stacked better than guanine. The results of our present research work expand the sequence criteria for the formation of MDBs and shed light to explore the significance of MDBs.
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Affiliation(s)
- Cheuk Kit Ngai
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China
| | - Hung Kay Lee
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China
| | - Pei Guo
- School of Biology and Biological Engineering, South China University of Technology, Guangzhou, Guangdong 510006, China
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Guo P, Lam SL. Unprecedented hydrophobic stabilizations from a reverse wobble T·T mispair in DNA minidumbbell. J Biomol Struct Dyn 2019; 38:1946-1953. [DOI: 10.1080/07391102.2019.1621211] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
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Abstract
The DNA minidumbbell (MDB) is a recently identified non-B structure. The reported MDBs contain two TTTA, CCTG, or CTTG type II loops. At present, the knowledge and understanding of the sequence criteria for MDB formation are still limited. In this study, we performed a systematic high-resolution nuclear magnetic resonance (NMR) and native gel study to investigate the effect of sequence variations in tandem repeats on the formation of MDBs. Our NMR results reveal the importance of hydrogen bonds, base-base stacking, and hydrophobic interactions from each of the participating residues. We conclude that in the MDBs formed by tandem repeats, C-G loop-closing base pairs are more stabilizing than T-A loop-closing base pairs, and thymine residues in both the second and third loop positions are more stabilizing than cytosine residues. The results from this study enrich our knowledge on the sequence criteria for the formation of MDBs, paving a path for better exploring their potential roles in biological systems and DNA nanotechnology.
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Affiliation(s)
- Yuan Liu
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories Hong Kong
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Abstract
The minidumbbell (MDB) is a new type of native DNA structure. At neutral pH, two TTTA or CCTG repeats can fold into the highly compact MDB with a melting temperature of ∼22 °C. Owing to the relatively low thermodynamic stability, MDBs have been proposed to be the structural intermediates that lead to efficient DNA repair escape and thus repeat expansions. In this study, we reveal that two CCTG repeats can also form an extraordinarily stable MDB with a melting temperature of ∼46 °C at pH 5.0. This unusual stability predominantly results from the formation of a three hydrogen bond C+·C mispair between the two minor groove cytosine residues. Due to the drastic stability change, the CCTG MDB, when combined with its complementary sequence, shows instant and complete structural conversions when the pH switches between 5.0 and 7.0, making the system serve as a simple and efficient pH-controlled molecular switch.
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Affiliation(s)
- Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong
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Mukherjee S, Dohno C, Nakatani K. Design and Synthesis of Cyclic Mismatch-Binding Ligands (CMBLs) with Variable Linkers by Ring-Closing Metathesis and their Photophysical and DNA Repeat Binding Properties. Chemistry 2017; 23:11385-11396. [DOI: 10.1002/chem.201702064] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Indexed: 02/06/2023]
Affiliation(s)
- Sanjukta Mukherjee
- Department of Regulatory Bioorganic Chemistry; The Institute of Scientific and Industrial Research; Osaka University; 8-1 Mihogaoka Ibaraki 567-0047 Japan
- National Centre for Biological Sciences (NCBS); Tata Institute of Fundamental Research (TIFR); Bellary Road Bangalore 560065 India
| | - Chikara Dohno
- Department of Regulatory Bioorganic Chemistry; The Institute of Scientific and Industrial Research; Osaka University; 8-1 Mihogaoka Ibaraki 567-0047 Japan
| | - Kazuhiko Nakatani
- Department of Regulatory Bioorganic Chemistry; The Institute of Scientific and Industrial Research; Osaka University; 8-1 Mihogaoka Ibaraki 567-0047 Japan
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Biomolecular diagnosis of myotonic dystrophy type 2: a challenging approach. J Neurol 2017; 264:1705-1714. [PMID: 28550479 DOI: 10.1007/s00415-017-8504-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 05/02/2017] [Indexed: 01/23/2023]
Abstract
Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are the most common adult form of muscular dystrophy, characterized by autosomal dominant progressive myopathy, myotonia, and multiorgan involvement. The onset and symptoms of the myotonic dystrophies are diverse, complicating their diagnoses and limiting a comprehensive approach to their clinical care. Diagnostic delay in DM2 is due not only to the heterogeneous phenotype and the aspecific onset but also to the unfamiliarity with the disorder by most clinicians. Moreover, the DM2 diagnostic odyssey is complicated by the difficulties to develop an accurate, robust, and cost-effective method for a routine molecular assay. The aim of this review is to underline by challenging approach the diagnostic limits and pitfalls that could results in failure to recognize the presence of DM2 disease. Understanding and preventing delays in DM2 diagnosis may facilitate family planning, improve symptom management in the short term, and facilitate more specific treatment in the long term.
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Finsterer J, Safoschnik G, Witsch-Baumgartner M. Marathoning with myotonic dystrophy type 2 (proximal myotonic myopathy) and leukopenia. SAGE Open Med Case Rep 2017; 5:2050313X17703021. [PMID: 28491317 PMCID: PMC5406121 DOI: 10.1177/2050313x17703021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 03/14/2017] [Indexed: 11/29/2022] Open
Abstract
Objectives: A mild, slowly progressive course of proximal myotonic myopathy, also known as myotonic dystrophy type 2, over years allowing the patient to continue with extreme sport activity, has been only rarely reported. Methods: Case report. Results: The patient is a 54-year-old female sport teacher who developed myotonia of the distal upper limbs at the age of 32 years. Over the following 22 years, myotonia spreaded to the entire musculature. Myotonia did not prevent her from doing her job and from marathoning and improved with continuous exercise. Additionally, she had developed hypothyroidism, ovarial cysts, incipient cataract, motor neuropathy, hepatopathy, leukopenia, and mild hyper-CK-emia. A heterozygous CCTG-repeat expansion of 500–9500 was found in the CNBP/ZNF9 gene. At the age of 54 years, she was still performing sport, without presenting with myotonia on clinical examination or having developed other typical manifestations of proximal myotonic myopathy. Conclusions: This case shows that proximal myotonic myopathy may take a mild course over at least 22 years, that proximal myotonic myopathy with mild myotonia may allow a patient to continue strenuous sport activity, and that continuous physical activity may contribute to the mild course of the disease.
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Affiliation(s)
| | - Georg Safoschnik
- First Neurological Department, Hospital Hietzing, Vienna, Austria
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Liu Y, Guo P, Lam SL. Formation of a DNA Mini-Dumbbell with a Quasi-Type II Loop. J Phys Chem B 2017; 121:2554-2560. [DOI: 10.1021/acs.jpcb.7b00556] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yuan Liu
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
| | - Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
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Meola G, Cardani R. Myotonic dystrophy type 2 and modifier genes: an update on clinical and pathomolecular aspects. Neurol Sci 2017; 38:535-546. [PMID: 28078562 DOI: 10.1007/s10072-016-2805-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Accepted: 12/22/2016] [Indexed: 12/20/2022]
Abstract
Myotonic dystrophy (DM) is the most common adult muscular dystrophy, characterized by autosomal dominant progressive myopathy, myotonia, and multiorgan involvement. To date, two distinct forms caused by similar mutations in two different genes have been identified: myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2). Aberrant transcription and mRNA processing of multiple genes due to RNA-mediated toxic gain-of function has been suggested to cause the complex phenotype in DM1 and DM2. However, despite clinical and genetic similarities, DM1 and DM2 may be considered as distinct disorders. This review is an update on the latest findings specific to DM2, including explanations for the differences in clinical manifestations and pathophysiology between the two forms of myotonic dystrophies.
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Affiliation(s)
- Giovanni Meola
- Department of Biomedical Sciences for Health, University of Milan, IRCCS Policlinico San Donato, Piazza E. Malan, 1, San Donato Mil., 20097, Milan, Italy. .,Department of Neurology, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy.
| | - Rosanna Cardani
- Laboratory of Muscle Histopathology and Molecular Biology, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy
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Guo P, Lam SL. The competing mini-dumbbell mechanism: new insights into CCTG repeat expansion. Signal Transduct Target Ther 2016; 1:16028. [PMID: 29263904 PMCID: PMC5661647 DOI: 10.1038/sigtrans.2016.28] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Revised: 11/04/2016] [Accepted: 11/08/2016] [Indexed: 12/20/2022] Open
Abstract
CCTG repeat expansions in intron 1 of the cellular nucleic acid-binding protein gene are associated with myotonic dystrophy type 2. Recently, we have reported a novel mini-dumbbell (MDB) structure formed by two CCTG or TTTA repeats, which potentially has a critical role in repeat expansions. Here we present a mechanism, called the competing MDB mechanism, to explain how the formation of MDB can lead to efficient mismatch repair (MMR) escape and thus CCTG repeat expansions during DNA replication. In a long tract of CCTG repeats, two competing MDBs can be formed in any segment of three repeats. Fast exchange between these MDBs will make the commonly occupied repeat behave like a mini-loop. Further participations of the 5'- or 3'-flanking repeat in forming competing MDBs will make the mini-loop shift in the 5'- or 3'-direction, thereby providing a pathway for the mini-loop to escape from MMR. To avoid the complications due to the formation of hairpin conformers in longer CCTG repeats, we made use of TTTA repeats as model sequences to demonstrate the formation of competing MDBs and shifting of mini-loop in a long tract of repeating sequence.
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Affiliation(s)
- Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong
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Guo P, Lam SL. Unusual structures of CCTG repeats and their participation in repeat expansion. Biomol Concepts 2016; 7:331-340. [DOI: 10.1515/bmc-2016-0024] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 11/01/2016] [Indexed: 11/15/2022] Open
Abstract
AbstractCCTG repeat expansion in intron 1 of the cellular nucleic acid-binding protein (CNBP) gene has been identified to be the genetic cause of myotonic dystrophy type 2 (DM2). Yet the underlying reasons for the genetic instability in CCTG repeats remain elusive. In recent years, CCTG repeats have been found to form various types of unusual secondary structures including mini-dumbbell (MDB), hairpin and dumbbell, revealing that there is a high structural diversity in CCTG repeats intrinsically. Upon strand slippage, the formation of unusual structures in the nascent strand during DNA replication has been proposed to be the culprit of CCTG repeat expansions. On the one hand, the thermodynamic stability, size, and conformational dynamics of these unusual structures affect the propensity of strand slippage. On the other hand, these structural properties determine whether the unusual structure can successfully escape from DNA repair. In this short overview, we first summarize the recent advances in elucidating the solution structures of CCTG repeats. We then discuss the potential pathways by which these unusual structures bring about variable sizes of repeat expansion, high strand slippage propensity and efficient repair escape.
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Affiliation(s)
- Pei Guo
- 1Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
| | - Sik Lok Lam
- 1Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
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Abstract
The non-B DNA structures formed by short tandem repeats on the nascent strand during DNA replication have been proposed to be the structural intermediates that lead to repeat expansion mutations. Tetranucleotide TTTA and CCTG repeat expansions have been known to cause reduction in biofilm formation in Staphylococcus aureus and myotonic dystrophy type 2 in human, respectively. In this study, we report the first three-dimensional minidumbbell (MDB) structure formed by natural DNA sequences containing two TTTA or CCTG repeats. The formation of MDB provides possible pathways for strand slippage to occur, which ultimately leads to repair escape and thus expansion mutations. Our result here shows that MDB is a highly compact structure composed of two type II loops. In addition to the typical stabilizing interactions in type II loops, MDB shows extensive stabilizing forces between the two loops, including two distinctive modes of interactions between the minor groove residues. The formation of MDB enriches the structural diversity of natural DNA sequences, reveals the importance of loop-loop interactions in unusual DNA structures, and provides insights into novel mechanistic pathways of DNA repeat expansion mutations.
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Affiliation(s)
- Pei Guo
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong
| | - Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong
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