1
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Zalar M, Wang B, Plavec J, Šket P. Insight into Tetramolecular DNA G-Quadruplexes Associated with ALS and FTLD: Cation Interactions and Formation of Higher-Ordered Structure. Int J Mol Sci 2023; 24:13437. [PMID: 37686239 PMCID: PMC10487854 DOI: 10.3390/ijms241713437] [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: 07/18/2023] [Revised: 08/24/2023] [Accepted: 08/28/2023] [Indexed: 09/10/2023] Open
Abstract
The G4C2 hexanucleotide repeat expansion in the c9orf72 gene is a major genetic cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), with the formation of G-quadruplexes directly linked to the development of these diseases. Cations play a crucial role in the formation and structure of G-quadruplexes. In this study, we investigated the impact of biologically relevant potassium ions on G-quadruplex structures and utilized 15N-labeled ammonium cations as a substitute for K+ ions to gain further insights into cation binding and exchange dynamics. Through nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we demonstrate that the single d(G4C2) repeat, in the presence of 15NH4+ ions, adopts a tetramolecular G-quadruplex with an all-syn quartet at the 5'-end. The movement of 15NH4+ ions through the central channel of the G-quadruplex, as well as to the bulk solution, is governed by the vacant cation binding site, in addition to the all-syn quartet at the 5'-end. Furthermore, the addition of K+ ions to G-quadruplexes folded in the presence of 15NH4+ ions induces stacking of G-quadruplexes via their 5'-end G-quartets, leading to the formation of stable higher-ordered species.
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Affiliation(s)
- Matja Zalar
- Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia; (M.Z.); (B.W.); (J.P.)
| | - Baifan Wang
- Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia; (M.Z.); (B.W.); (J.P.)
| | - Janez Plavec
- Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia; (M.Z.); (B.W.); (J.P.)
- EN-FIST Center of Excellence, Trg OF 13, SI-1000 Ljubljana, Slovenia
- Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia
| | - Primož Šket
- Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia; (M.Z.); (B.W.); (J.P.)
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2
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Wright SE, Todd PK. Native functions of short tandem repeats. eLife 2023; 12:e84043. [PMID: 36940239 PMCID: PMC10027321 DOI: 10.7554/elife.84043] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Accepted: 03/08/2023] [Indexed: 03/21/2023] Open
Abstract
Over a third of the human genome is comprised of repetitive sequences, including more than a million short tandem repeats (STRs). While studies of the pathologic consequences of repeat expansions that cause syndromic human diseases are extensive, the potential native functions of STRs are often ignored. Here, we summarize a growing body of research into the normal biological functions for repetitive elements across the genome, with a particular focus on the roles of STRs in regulating gene expression. We propose reconceptualizing the pathogenic consequences of repeat expansions as aberrancies in normal gene regulation. From this altered viewpoint, we predict that future work will reveal broader roles for STRs in neuronal function and as risk alleles for more common human neurological diseases.
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Affiliation(s)
- Shannon E Wright
- Department of Neurology, University of Michigan–Ann ArborAnn ArborUnited States
- Neuroscience Graduate Program, University of Michigan–Ann ArborAnn ArborUnited States
- Department of Neuroscience, Picower InstituteCambridgeUnited States
| | - Peter K Todd
- Department of Neurology, University of Michigan–Ann ArborAnn ArborUnited States
- VA Ann Arbor Healthcare SystemAnn ArborUnited States
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3
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Hayward BE, Usdin K. Mechanisms of Genome Instability in the Fragile X-Related Disorders. Genes (Basel) 2021; 12:genes12101633. [PMID: 34681027 PMCID: PMC8536109 DOI: 10.3390/genes12101633] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 10/12/2021] [Accepted: 10/14/2021] [Indexed: 12/17/2022] Open
Abstract
The Fragile X-related disorders (FXDs), which include the intellectual disability fragile X syndrome (FXS), are disorders caused by expansion of a CGG-repeat tract in the 5′ UTR of the X-linked FMR1 gene. These disorders are named for FRAXA, the folate-sensitive fragile site that localizes with the CGG-repeat in individuals with FXS. Two pathological FMR1 allele size classes are distinguished. Premutation (PM) alleles have 54–200 repeats and confer the risk of fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated primary ovarian insufficiency (FXPOI). PM alleles are prone to both somatic and germline expansion, with female PM carriers being at risk of having a child with >200+ repeats. Inheritance of such full mutation (FM) alleles causes FXS. Contractions of PM and FM alleles can also occur. As a result, many carriers are mosaic for different sized alleles, with the clinical presentation depending on the proportions of these alleles in affected tissues. Furthermore, it has become apparent that the chromosomal fragility of FXS individuals reflects an underlying problem that can lead to chromosomal numerical and structural abnormalities. Thus, large numbers of CGG-repeats in the FMR1 gene predisposes individuals to multiple forms of genome instability. This review will discuss our current understanding of these processes.
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4
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Geng Y, Liu C, Cai Q, Luo Z, Miao H, Shi X, Xu N, Fung CP, Choy TT, Yan B, Li N, Qian P, Zhou B, Zhu G. Crystal structure of parallel G-quadruplex formed by the two-repeat ALS- and FTD-related GGGGCC sequence. Nucleic Acids Res 2021; 49:5881-5890. [PMID: 34048588 PMCID: PMC8191786 DOI: 10.1093/nar/gkab302] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2020] [Revised: 03/23/2021] [Accepted: 05/26/2021] [Indexed: 01/05/2023] Open
Abstract
The hexanucleotide repeat expansion, GGGGCC (G4C2), within the first intron of the C9orf72 gene is known to be the most common genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The G4C2 repeat expansions, either DNA or RNA, are able to form G-quadruplexes which induce toxicity leading to ALS/FTD. Herein, we report a novel crystal structure of d(G4C2)2 that self-associates to form an eight-layer parallel tetrameric G-quadruplex. Two d(G4C2)2 associate together as a parallel dimeric G-quadruplex which folds into a tetramer via 5'-to-5' arrangements. Each dimer consists of four G-tetrads connected by two CC propeller loops. Especially, the 3'-end cytosines protrude out and form C·C+•C·C+/ C·C•C·C+ quadruple base pair or C•C·C+ triple base pair stacking on the dimeric block. Our work sheds light on the G-quadruplexes adopted by d(G4C2) and yields the invaluable structural details for the development of small molecules to tackle neurodegenerative diseases, ALS and FTD.
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Affiliation(s)
- Yanyan Geng
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Changdong Liu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Qixu Cai
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Zhipu Luo
- Institute of Molecular Enzymology, School of Biology and Basic Medical Sciences, Soochow University, Suzhou, Jiangsu, 215123, China
| | - Haitao Miao
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Xiao Shi
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Naining Xu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Chun Po Fung
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - To To Choy
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Bing Yan
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Ning Li
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Peiyuan Qian
- Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Bo Zhou
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
| | - Guang Zhu
- Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
- State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 00000, China
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5
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Brcic J, Plavec J. NMR structure of a G-quadruplex formed by four d(G4C2) repeats: insights into structural polymorphism. Nucleic Acids Res 2019; 46:11605-11617. [PMID: 30277522 PMCID: PMC6265483 DOI: 10.1093/nar/gky886] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 09/19/2018] [Indexed: 12/13/2022] Open
Abstract
Most frequent genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), is a largely increased number of d(G4C2)n•(G2C4)n repeats located in the non-coding region of C9orf72 gene. Non-canonical structures, including G-quadruplexes, formed within expanded repeats have been proposed to drive repeat expansion and pathogenesis of ALS and FTD. Oligonucleotide d[(G4C2)3G4], which represents the shortest oligonucleotide model of d(G4C2) repeats with the ability to form a unimolecular G-quadruplex, forms two major G-quadruplex structures in addition to several minor species which coexist in solution with K+ ions. Herein, we used solution-state NMR to determine the high-resolution structure of one of the major G-quadruplex species adopted by d[(G4C2)3G4]. Structural characterization of the G-quadruplex named AQU was facilitated by a single substitution of dG with 8Br-dG at position 21 and revealed an antiparallel fold composed of four G-quartets and three lateral C-C loops. The G-quadruplex exhibits high thermal stability and is favored kinetically and under slightly acidic conditions. An unusual structural element distinct from a C-quartet is observed in the structure. Two C•C base pairs are stacked on the nearby G-quartet and are involved in a dynamic equilibrium between symmetric N3-amino and carbonyl-amino geometries and protonated C+•C state.
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Affiliation(s)
- Jasna Brcic
- Slovenian NMR Center, National Institute of Chemistry, Ljubljana SI-1000, Slovenia
| | - Janez Plavec
- Slovenian NMR Center, National Institute of Chemistry, Ljubljana SI-1000, Slovenia.,Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana SI-1000, Slovenia.,EN-FIST Center of Excellence, Ljubljana SI-1000, Slovenia
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6
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Kumari D, Gazy I, Usdin K. Pharmacological Reactivation of the Silenced FMR1 Gene as a Targeted Therapeutic Approach for Fragile X Syndrome. Brain Sci 2019; 9:brainsci9020039. [PMID: 30759772 PMCID: PMC6406686 DOI: 10.3390/brainsci9020039] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2019] [Revised: 02/07/2019] [Accepted: 02/08/2019] [Indexed: 12/22/2022] Open
Abstract
More than ~200 CGG repeats in the 5′ untranslated region of the FMR1 gene results in transcriptional silencing and the absence of the FMR1 encoded protein, FMRP. FMRP is an RNA-binding protein that regulates the transport and translation of a variety of brain mRNAs in an activity-dependent manner. The loss of FMRP causes dysregulation of many neuronal pathways and results in an intellectual disability disorder, fragile X syndrome (FXS). Currently, there is no effective treatment for FXS. In this review, we discuss reactivation of the FMR1 gene as a potential approach for FXS treatment with an emphasis on the use of small molecules to inhibit the pathways important for gene silencing.
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Affiliation(s)
- Daman Kumari
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Inbal Gazy
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Karen Usdin
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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7
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Dahlhaus R. Of Men and Mice: Modeling the Fragile X Syndrome. Front Mol Neurosci 2018; 11:41. [PMID: 29599705 PMCID: PMC5862809 DOI: 10.3389/fnmol.2018.00041] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Accepted: 01/31/2018] [Indexed: 12/26/2022] Open
Abstract
The Fragile X Syndrome (FXS) is one of the most common forms of inherited intellectual disability in all human societies. Caused by the transcriptional silencing of a single gene, the fragile x mental retardation gene FMR1, FXS is characterized by a variety of symptoms, which range from mental disabilities to autism and epilepsy. More than 20 years ago, a first animal model was described, the Fmr1 knock-out mouse. Several other models have been developed since then, including conditional knock-out mice, knock-out rats, a zebrafish and a drosophila model. Using these model systems, various targets for potential pharmaceutical treatments have been identified and many treatments have been shown to be efficient in preclinical studies. However, all attempts to turn these findings into a therapy for patients have failed thus far. In this review, I will discuss underlying difficulties and address potential alternatives for our future research.
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Affiliation(s)
- Regina Dahlhaus
- Institute for Biochemistry, Emil-Fischer Centre, University of Erlangen-Nürnberg, Erlangen, Germany
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8
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Virgilio A, Russo A, Amato T, Russo G, Mayol L, Esposito V, Galeone A. Monomolecular G-quadruplex structures with inversion of polarity sites: new topologies and potentiality. Nucleic Acids Res 2017; 45:8156-8166. [PMID: 28666330 PMCID: PMC5737522 DOI: 10.1093/nar/gkx566] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 06/21/2017] [Indexed: 12/11/2022] Open
Abstract
In this paper, we report investigations, based on circular dichroism, nuclear magnetic resonance spectroscopy and electrophoresis methods, on three oligonucleotide sequences, each containing one 3′-3′ and two 5′-5′ inversion of polarity sites, and four G-runs with a variable number of residues, namely two, three and four (mTG2T, mTG3T and mTG4T with sequence 3′-TGnT-5′-5′-TGnT-3′-3′-TGnT-5′-5′-TGnT-3′ in which n = 2, 3 and 4, respectively), in comparison with their canonical counterparts (TGnT)4 (n = 2, 3 and 4). Oligonucleotides mTG3T and mTG4T have been proven to form very stable unprecedented monomolecular parallel G-quadruplex structures, characterized by three side loops containing the inversion of polarity sites. Both G-quadruplexes have shown an all-syn G-tetrad, while the other guanosines adopt anti glycosidic conformations. All oligonucleotides investigated have shown a noteworthy antiproliferative activity against lung cancer cell line Calu 6 and colorectal cancer cell line HCT-116 p53−/−. Interestingly, mTG3T and mTG4T have proven to be mostly resistant to nucleases in a fetal bovine serum assay. The whole of the data suggest the involvement of specific pathways and targets for the biological activity.
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Affiliation(s)
- Antonella Virgilio
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Annapina Russo
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Teresa Amato
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Giulia Russo
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Luciano Mayol
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Veronica Esposito
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
| | - Aldo Galeone
- Dipartimento di Farmacia, Università degli Studi di Napoli Federico II, Via D. Montesano 49, 80131 Napoli, Italy
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9
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Manukyan A, Tekin A. The intermolecular dimer potential for guanine. J Chem Phys 2017; 147:154311. [DOI: 10.1063/1.4998792] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Affiliation(s)
- Artür Manukyan
- Informatics Institute, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
| | - Adem Tekin
- Informatics Institute, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
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10
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Ups and Downs: Mechanisms of Repeat Instability in the Fragile X-Related Disorders. Genes (Basel) 2016; 7:genes7090070. [PMID: 27657135 PMCID: PMC5042400 DOI: 10.3390/genes7090070] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 08/30/2016] [Accepted: 09/13/2016] [Indexed: 02/06/2023] Open
Abstract
The Fragile X-related disorders (FXDs) are a group of clinical conditions resulting from the expansion of a CGG/CCG-repeat tract in exon 1 of the Fragile X mental retardation 1 (FMR1) gene. While expansions of the repeat tract predominate, contractions are also seen with the net result being that individuals can show extensive repeat length heterogeneity in different tissues. The mechanisms responsible for expansion and contraction are still not well understood. This review will discuss what is known about these processes and current evidence that supports a model in which expansion arises from the interaction of components of the base excision repair, mismatch repair and transcription coupled repair pathways.
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11
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Bhattacharyya D, Mirihana Arachchilage G, Basu S. Metal Cations in G-Quadruplex Folding and Stability. Front Chem 2016; 4:38. [PMID: 27668212 PMCID: PMC5016522 DOI: 10.3389/fchem.2016.00038] [Citation(s) in RCA: 362] [Impact Index Per Article: 45.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 08/25/2016] [Indexed: 12/23/2022] Open
Abstract
This review is focused on the structural and physicochemical aspects of metal cation coordination to G-Quadruplexes (GQ) and their effects on GQ stability and conformation. G-quadruplex structures are non-canonical secondary structures formed by both DNA and RNA. G-quadruplexes regulate a wide range of important biochemical processes. Besides the sequence requirements, the coordination of monovalent cations in the GQ is essential for its formation and determines the stability and polymorphism of GQ structures. The nature, location, and dynamics of the cation coordination and their impact on the overall GQ stability are dependent on several factors such as the ionic radii, hydration energy, and the bonding strength to the O6 of guanines. The intracellular monovalent cation concentration and the localized ion concentrations determine the formation of GQs and can potentially dictate their regulatory roles. A wide range of biochemical and biophysical studies on an array of GQ enabling sequences have generated at a minimum the knowledge base that allows us to often predict the stability of GQs in the presence of the physiologically relevant metal ions, however, prediction of conformation of such GQs is still out of the realm.
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Affiliation(s)
| | | | - Soumitra Basu
- Department of Chemistry and Biochemistry, Kent State UniversityKent, OH, USA
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12
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Usdin K, Kumari D. Repeat-mediated epigenetic dysregulation of the FMR1 gene in the fragile X-related disorders. Front Genet 2015; 6:192. [PMID: 26089834 PMCID: PMC4452891 DOI: 10.3389/fgene.2015.00192] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 05/13/2015] [Indexed: 12/13/2022] Open
Abstract
The fragile X-related disorders are members of the Repeat Expansion Diseases, a group of genetic conditions resulting from an expansion in the size of a tandem repeat tract at a specific genetic locus. The repeat responsible for disease pathology in the fragile X-related disorders is CGG/CCG and the repeat tract is located in the 5′ UTR of the FMR1 gene, whose protein product FMRP, is important for the proper translation of dendritic mRNAs in response to synaptic activation. There are two different pathological FMR1 allele classes that are distinguished only by the number of repeats. Premutation alleles have 55–200 repeats and confer risk of fragile X-associated tremor/ataxia syndrome and fragile X-associated primary ovarian insufficiency. Full mutation alleles on the other hand have >200 repeats and result in fragile X syndrome, a disorder that affects learning and behavior. Different symptoms are seen in carriers of premutation and full mutation alleles because the repeat number has paradoxical effects on gene expression: Epigenetic changes increase transcription from premutation alleles and decrease transcription from full mutation alleles. This review will cover what is currently known about the mechanisms responsible for these changes in FMR1 expression and how they may relate to other Repeat Expansion Diseases that also show repeat-mediated changes in gene expression.
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Affiliation(s)
- Karen Usdin
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health , Bethesda, MD, USA
| | - Daman Kumari
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health , Bethesda, MD, USA
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13
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Manukyan A, Tekin A. First principles potential for the cytosine dimer. Phys Chem Chem Phys 2015; 17:14685-701. [DOI: 10.1039/c5cp00553a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new first principles potential for the cytosine dimer.
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Affiliation(s)
- Artür Manukyan
- Informatics Institute
- Istanbul Technical University
- Istanbul
- Turkey
| | - Adem Tekin
- Informatics Institute
- Istanbul Technical University
- Istanbul
- Turkey
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14
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Zhang D, Huang T, Lukeman PS, Paukstelis PJ. Crystal structure of a DNA/Ba2+ G-quadruplex containing a water-mediated C-tetrad. Nucleic Acids Res 2014; 42:13422-9. [PMID: 25389267 PMCID: PMC4245957 DOI: 10.1093/nar/gku1122] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We have determined the 1.50 Å crystal structure of the DNA decamer, d(CCA(CNV)KGCGTGG) ((CNV)K, 3-cyanovinylcarbazole), which forms a G-quadruplex structure in the presence of Ba(2+). The structure contains several unique features including a bulged nucleotide and the first crystal structure observation of a C-tetrad. The structure reveals that water molecules mediate contacts between the divalent cations and the C-tetrad, allowing Ba(2+) ions to occupy adjacent steps in the central ion channel. One ordered Mg(2+) facilitates 3'-3' stacking of two quadruplexes in the asymmetric unit, while the bulged nucleotide mediates crystal contacts. Despite the high diffraction limit, the first four nucleotides including the (CNV)K nucleoside are disordered though they are still involved in crystal packing. This work suggests that the bulky hydrophobic groups may locally influence the formation of non-Watson-Crick structures from otherwise complementary sequences. These observations lead to the intriguing possibility that certain types of DNA damage may act as modulators of G-quadruplex formation.
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Affiliation(s)
- Diana Zhang
- Department of Chemistry & Biochemistry, Center for Biomolecular Structure and Organization, Maryland NanoCenter, University of Maryland, College Park, MD 20742, USA
| | - Terry Huang
- Chemistry and Biochemistry Department, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768, USA
| | - Philip S. Lukeman
- Chemistry Department, St. John's University, 8000 Utopia Parkway, Queens, NY 11439, USA
| | - Paul J. Paukstelis
- Department of Chemistry & Biochemistry, Center for Biomolecular Structure and Organization, Maryland NanoCenter, University of Maryland, College Park, MD 20742, USA,To whom correspondence should be addressed. Tel: 301.405.9933; Fax: 301.314.0386;
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15
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Agarwal T, Lalwani MK, Kumar S, Roy S, Chakraborty TK, Sivasubbu S, Maiti S. Morphological Effects of G-Quadruplex Stabilization Using a Small Molecule in Zebrafish. Biochemistry 2014; 53:1117-24. [DOI: 10.1021/bi4009352] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tani Agarwal
- CSIR-Institute of Genomics and Integrative
Biology, , Mall Road, New Delhi 110 007, India
| | - Mukesh Kumar Lalwani
- CSIR-Institute of Genomics and Integrative
Biology, , Mall Road, New Delhi 110 007, India
| | - Santosh Kumar
- CSIR-Institute of Genomics and Integrative
Biology, , Mall Road, New Delhi 110 007, India
| | - Saumya Roy
- CSIR-Indian Institute of Chemical
Technology, , Hyderabad 500 007, India
| | - Tushar Kanti Chakraborty
- CSIR-Indian Institute of Chemical
Technology, , Hyderabad 500 007, India
- Department
of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
| | - Sridhar Sivasubbu
- CSIR-Institute of Genomics and Integrative
Biology, , Mall Road, New Delhi 110 007, India
| | - Souvik Maiti
- CSIR-Institute of Genomics and Integrative
Biology, , Mall Road, New Delhi 110 007, India
- CSIR-National Chemical Laboratory, Pune 411008, India
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16
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Amrane S, Mergny JL. Length and pH-dependent energetics of (CCG)n and (CGG)n trinucleotide repeats. Biochimie 2006; 88:1125-34. [PMID: 16690198 DOI: 10.1016/j.biochi.2006.03.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Accepted: 03/09/2006] [Indexed: 11/30/2022]
Abstract
Trinucleotide repeats are involved in a number of debilitating diseases such as fragile-X syndrome and myotonic dystrophy. Eighteen to 75 base-long (CCG)(n) and (CGG)(n) oligodeoxynucleotides were analysed using a combination of biophysical (UV-absorbance, differential scanning calorimetry) and biochemical methods (non-denaturing gel electrophoresis, enzymatic footprinting). All oligomers formed stable intramolecular structures under near physiological conditions with a melting temperature which was only weakly dependent on oligomer length. Thermodynamic analysis of the denaturation process by UV-melting and calorimetric experiments revealed a length-dependent discrepancy between the enthalpy values deduced from model-dependent (UV-melting) and model-independent experiments (calorimetry), as recently shown for CTG and CAG trinucleotides (Nucleic Acids Res. 33 (2005) 4065). Evidence for non-zero molar heat capacity changes was also derived from the analysis of the Arrhenius plots. Such behaviour is analysed in the framework of an intramolecular "branched" or "broken" hairpin model, in which long oligomers do not fold into a simple long hairpin-stem intramolecular structure, but allow the formation of several independent folding units of unequal stability. These results suggest that this observation may be extended to various trinucleotide repeats-containing sequences.
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Affiliation(s)
- S Amrane
- Laboratoire de Biophysique, Muséum National d'Histoire Naturelle, USM 503 Inserm UR 565, CNRS UMR 5153, 43, rue Cuvier, 75231 Paris cedex 5, France
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17
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Virgilio A, Esposito V, Randazzo A, Mayol L, Galeone A. 8-methyl-2'-deoxyguanosine incorporation into parallel DNA quadruplex structures. Nucleic Acids Res 2005; 33:6188-95. [PMID: 16257981 PMCID: PMC1275585 DOI: 10.1093/nar/gki924] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
This paper concerns the Circular Dichroism (CD) and Nuclear Magnetic Resonance (NMR) structural studies of the quadruple helix arrangements adopted by three tailored oligodeoxyribonucleotide analogues, namely d(TGMeGGT), d(TGGMeGT) and d(TGGGMeT), where dGMe represents a 8-methyl-2′-deoxyguanosine residue. The results of this study clearly demonstrate that the effects of the incorporation of dGMe instead of a dG residue are strongly dependant upon the positioning of a single base replacement along the sequence. As such, d(TGMeGGT), d(TGGMeGT) have been found to form 4-fold symmetric quadruplexes with all strands parallel and equivalent to each other, each more stable than their natural counterpart. NMR experiments clearly indicate that [d(TGMeGGT)]4 possesses a GMe-tetrad with all dGMe residues in a syn-glycosidic conformation while an anti-arrangement is apparent for the four dGMe of [d(TGGMeGT)]4. As the two complexes show a quite different CD behaviour, a possible relationship between the presence of residues adopting syn-glycosidic conformations and CD profiles is briefly discussed. As far as d(TGGGMeT) is concerned, NMR data indicate that at 25°C it exists primarily as a single-strand conformation in equilibrium with minor amounts of a quadruplex structure.
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Affiliation(s)
| | | | | | | | - Aldo Galeone
- To whom correspondence should be addressed. Tel: +39 081 678508; Fax: +39 081 678552;
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18
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Amrane S, Saccà B, Mills M, Chauhan M, Klump HH, Mergny JL. Length-dependent energetics of (CTG)n and (CAG)n trinucleotide repeats. Nucleic Acids Res 2005; 33:4065-77. [PMID: 16040598 PMCID: PMC1179733 DOI: 10.1093/nar/gki716] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Trinucleotide repeats are involved in a number of debilitating diseases such as myotonic dystrophy. Twelve to seventy-five base-long (CTG)n oligodeoxynucleotides were analysed using a combination of biophysical [UV-absorbance, circular dichroism and differential scanning calorimetry (DSC)] and biochemical methods (non-denaturing gel electrophoresis and enzymatic footprinting). All oligomers formed stable intramolecular structures under near physiological conditions with a melting temperature that was only weakly dependent on oligomer length. Thermodynamic analysis of the denaturation process by UV-melting and calorimetric experiments revealed an unprecedented length-dependent discrepancy between the enthalpy values deduced from model-dependent (UV-melting) and model-independent (calorimetry) experiments. Evidence for non-zero molar heat capacity changes was also derived from the analysis of the Arrhenius plots and DSC profiles. Such behaviour is analysed in the framework of an intramolecular 'branched-hairpin' model, in which long CTG oligomers do not fold into a simple long hairpin-stem intramolecular structure, but allow the formation of several independent folding units of unequal stability. We demonstrate that, for sequences ranging from 12 to 25 CTG repeats, an intramolecular structure with two loops is formed which we will call 'bis-hairpin'. Similar results were also found for CAG oligomers, suggesting that this observation may be extended to various trinucleotide repeats-containing sequences.
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Affiliation(s)
| | | | - Martin Mills
- Department of Molecular and Cell Biology, University of Cape TownP.B. Rondebosh 7701, Republic of South Africa
| | - Madhu Chauhan
- Department of Molecular and Cell Biology, University of Cape TownP.B. Rondebosh 7701, Republic of South Africa
| | - Horst H. Klump
- Department of Molecular and Cell Biology, University of Cape TownP.B. Rondebosh 7701, Republic of South Africa
| | - Jean-Louis Mergny
- To whom correspondence should be addressed. Tel: +33 1 40 79 36 89; Fax: +33 1 40 79 37 05;
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19
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Gu J, Wang J, Leszczynski J. Hydrogen Bonding in 5-Bromouracil-Adenine-5-Bromouracil-Adenine (T+AT+A) Tetrads. J Phys Chem B 2004. [DOI: 10.1021/jp0376830] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jiande Gu
- Drug Design and Discovery Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China, and Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217
| | - Jing Wang
- Drug Design and Discovery Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China, and Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217
| | - Jerzy Leszczynski
- Drug Design and Discovery Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China, and Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217
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20
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Bhavesh NS, Patel PK, Karthikeyan S, Hosur RV. Distinctive features in the structure and dynamics of the DNA repeat sequence GGCGGG. Biochem Biophys Res Commun 2004; 317:625-33. [PMID: 15063804 DOI: 10.1016/j.bbrc.2004.03.095] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Indexed: 10/26/2022]
Abstract
G-rich DNA has been known to form a variety of folded and multistranded structures, with even single base modifications causing important structural changes. But, very little is known about the dynamic characteristics of the structures, which may play crucial roles in facilitating the structural transitions. In this background, we report here NMR investigations on the structure and dynamics of a DNA repeat sequence GGCGGG in aqueous solution containing Na+ ions at neutral pH. The chosen sequence d-TGGCGGGT forms a parallel quadruplex with a C-tetrad in the middle, formed by symmetrical pairing of four Cs in a plane via NH2-O2 H-bonds. 13C relaxation measurements at natural abundance for C' sugar carbons provided valuable insight into the sequence specific dynamism of G and C-tetrads in the quadruplex. The C4 tetrad seems to introduce high conformational dynamism at milli- to micro-second time scale in the quadruplex. Concomitantly, there is a decrease in the pico-second time scale dynamics. Interestingly, these effects are seen more prominently at the G-tetrads on the 3' end of C-tetrad than on its 5' end. These observations would have important implications for the roles the tetrads may play in many biological functions.
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Affiliation(s)
- Neel S Bhavesh
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
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21
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Fojtík P, Kejnovská I, Vorlícková M. The guanine-rich fragile X chromosome repeats are reluctant to form tetraplexes. Nucleic Acids Res 2004; 32:298-306. [PMID: 14718550 PMCID: PMC373289 DOI: 10.1093/nar/gkh179] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Using circular dichroism spectroscopy, UV absorption spectroscopy and polyacrylamide gel electrophoresis, we studied conformational properties of guanine-rich DNA strands of the fragile X chromosome repeats d(GGC)n, d(GCG)n and d(CGG)n, with n = 2, 4, 8 and 16. These strands are generally considered in the literature to form guanine tetraplexes responsible for the repeat expansion. However, we show in this paper that the repeats are reluctant to form tetraplexes. At physiological concentrations of either Na+ or K+ ions, the hexamers and dodecamers associate to form homoduplexes and the longer repeats generate homoduplexes and hairpins. The tetraplexes are rarely observed being relatively most stable with d(GGC)n and least stable with d(GCG)n. The tetraplexes are exclusively formed in the presence of K+ ions, at salt concentrations higher than physiological, more easily at higher than physiological temperatures, and they arise with extremely long kinetics (even days). Moreover, the capability to form tetraplexes sharply diminishes with the oligonucleotide length. These facts make the concept of the tetraplex appearance in this motif in vivo very improbable. Rather, a hairpin of the fragile X repeats, whose stability increases with the repeat length, is the probable structure responsible for the repeat expansion in genomes.
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Affiliation(s)
- Petr Fojtík
- Academy of Sciences of the Czech Republic, Institute of Biophysics, Královopolská 135, CZ-612 65 Brno, Czech Republic
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Handa V, Saha T, Usdin K. The fragile X syndrome repeats form RNA hairpins that do not activate the interferon-inducible protein kinase, PKR, but are cut by Dicer. Nucleic Acids Res 2003; 31:6243-8. [PMID: 14576312 PMCID: PMC275460 DOI: 10.1093/nar/gkg818] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We show here that under physiologically reasonable conditions, CGG repeats in RNA readily form hairpins. In contrast to its DNA counterpart that forms a complex mixture of hairpins and tetraplexes, r(CGG)22 forms a single stable hairpin with no evidence for any other folded structure even at low pH. RNA with the sequence (CGG)9AGG (CGG)12AGG(CGG)97, found in a fragile X syndrome pre-mutation allele, forms a number of different hairpins. The most prominent hairpin forms in the 3' part of the repeat and involves the 97 uninterrupted CGG repeats. In contrast to the CUG-RNA hairpins formed by myotonic dystrophy type 1 repeats, we found no evidence that CGG-RNA hairpins activate PKR, the interferon-inducible protein kinase that is activated by a wide range of double-stranded RNAs. However, we do show that the CGG-RNA is digested, albeit inefficiently, by the human Dicer enzyme, a step central to the RNA interference effect on gene expression. These data provide clues to the basis of the toxic effect of CGG-RNA that is thought to occur in fragile X pre-mutation carriers. In addition, RNA hairpins may also account for the stalling of the 40S ribosomal subunit that is thought to contribute to the translation deficit in fragile X pre-mutation and full mutation alleles.
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Affiliation(s)
- Vaishali Handa
- Section on Genomic Structure and Function, Laboratory of Molecular and Cellular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0830, USA
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Greene E, Handa V, Kumari D, Usdin K. Transcription defects induced by repeat expansion: fragile X syndrome, FRAXE mental retardation, progressive myoclonus epilepsy type 1, and Friedreich ataxia. Cytogenet Genome Res 2003; 100:65-76. [PMID: 14526165 DOI: 10.1159/000072839] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2002] [Accepted: 02/06/2003] [Indexed: 11/19/2022] Open
Abstract
Fragile X mental retardation syndrome, FRAXE mental retardation, Progressive myoclonus epilepsy Type I, and Friedreich ataxia are members of a larger group of genetic disorders known as the Repeat Expansion Diseases. Unlike other members of this group, these four disorders all result from a primary defect in the initiation or elongation of transcription. In this review, we discuss current models for the relationship between the expanded repeat and the disease symptoms.
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Affiliation(s)
- E Greene
- Section on Genomic Structure and Function, Laboratory of Molecular and Cellular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0830, USA
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Monleón D, Esteve V, Celda B. NMR study of hexanucleotide d(CCGCGG)2 containing two triplet repeats of fragile X syndrome. Biochem Biophys Res Commun 2003; 303:81-90. [PMID: 12646170 DOI: 10.1016/s0006-291x(03)00304-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Long repeated stretches of d(CCG) and tri-nucleotide are crucial mutations that cause hereditary forms of mental retardation (fragile X-syndrome). Moreover, the alternating (CG) di-nucleotide is one of the candidates for Z-DNA conformation. Solution NMR structure of d(CCGCGG)(2) has been solved and is discussed. The determined NMR solution structure is a distorted highly bent B-DNA conformation with increased flexibility in both terminal residues. This conformation differs significantly from the Z-DNA tetramer structure reported for the same hexamer in the crystal state at similar ionic strength by Malinina and co-workers. Crystal structure of d(CCGCGG)(2) at high salt concentration includes a central alternating tetramer in Z-DNA conformation, while the initial cytosine swings out and forms a Watson-Crick base-pair with the terminal guanine of a symmetry-related molecule. In solution, NMR data for sugar ring puckering combined with restrained molecular dynamics simulations starting from a Z-DNA form show that terminal furanose residues could adopt the conformation required for aromatic bases swinging out. Therefore, tetramer formation could be considered possible once the hexanucleotide had previously adopted the Z-DNA form. This work gives some insight into correlations between anomalous crystal structures and their accessibility in the solution state.
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Affiliation(s)
- Daniel Monleón
- Departamento de Química Física, Universitat de València, Edifici d'Investigació, Lab 3-054, C/ Dr. Moliner, 50, Burjassot, 46100 Valencia, Spain
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25
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Crnugelj M, Hud NV, Plavec J. The solution structure of d(G(4)T(4)G(3))(2): a bimolecular G-quadruplex with a novel fold. J Mol Biol 2002; 320:911-24. [PMID: 12126614 DOI: 10.1016/s0022-2836(02)00569-7] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The G-rich 11-mer oligonucleotide d(G(4)T(4)G(3)) forms a bimolecular G-quadruplex in the presence of sodium ions with a topology that is distinct from the folds of the closely related and well-characterized sequences d(G(4)T(4)G(4)) and d(G(3)T(4)G(3)). The solution structure of d(G(4)T(4)G(3))(2) has been determined using a combination of NMR spectroscopy and restrained molecular dynamics calculations. d(G(4)T(4)G(3))(2) forms an asymmetric dimeric fold-back structure consisting of three stacked G-quartets. The two T(4) loops that span diagonally across the outer faces of the G-quartets assume different conformations. The glycosidic torsion angle conformations of the guanine bases are 5'-syn-anti-syn-anti-(T(4) loop)-anti-syn-anti in one strand and 5'-syn-anti-syn-anti-(T(4) loop)-syn-anti-syn in the other strand. The guanine bases of the two outer G-quartets exhibit a clockwise donor-acceptor hydrogen-bonding directionality, while those of the middle G-quartet exhibit the anti-clockwise directionality. The topology of this G-quadruplex, like other bimolecular fold-back structures with diagonal loops, places each strand of the G-quartet region next to a neighboring parallel and an anti-parallel strand. The two guanine residues not involved in G-quartet formation, G4 and G12 (i.e. the fourth guanine base of one strand and the first guanine base of the other strand), adopt distinct conformations. G4 is stacked on top of an adjacent G-quartet, and this base-stacking continues along with the bases of the loop residues T5 and T6. G12 is orientated away from the core of G-quartets; stacked on the T7 base and apparently involved in hydrogen-bonding interactions with the phosphodiester group of this same residue. The cation-dependent folding of the d(G(4)T(4)G(3))(2) quadruplex structure is distinct from that observed for similar sequences. While both d(G(4)T(4)G(4)) and d(G(3)T(4)G(3)) form bimolecular, diagonally looped G-quadruplex structures in the presence of Na(+), K(+) and NH(4)(+), we have observed this folding to be favored for d(G(4)T(4)G(3)) in the presence of Na(+), but not in the presence of K(+) or NH(4)(+). The structure of d(G(4)T(4)G(3))(2) exhibits a "slipped-loop" element that is similar to what has been proposed for structural intermediates in the folding pathway of some G-quadruplexes, and therefore provides support for the feasibility of these proposed transient structures in G-quadruplex formation.
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Affiliation(s)
- Martin Crnugelj
- NMR center, National Institute of Chemistry, Hajdrihova 19, SI-1000, Ljubljana, Slovenia
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Abstract
DNA oligonucleotides that have repetitive tracts of guanine bases can form G-quadruplex structures that display an amazing polymorphism. Structures of several new G-quadruplexes have been solved recently that greatly expand the known structural motifs observed in nucleic acid quadruplexes. Base triads, base hexads, and quartets that contain cytosine have recently been identified stacked over the familiar G-quartets. The current status of the diverse array of structural features in quadruplexes is described and used to provide insight into the polymorphism and folding pathways. This review also summarizes recent progress in the techniques used to probe the structures of G-quadruplexes and discusses the role of ion binding in quadruplex formation. Several of the quadruplex structures featured in this review can be accessed in the online version of this review as CHIME representations.
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Affiliation(s)
- M A Keniry
- Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia.
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