1
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Mir B, Serrano-Chacón I, Medina P, Macaluso V, Terrazas M, Gandioso A, Garavís M, Orozco M, Escaja N, González C. Site-specific incorporation of a fluorescent nucleobase analog enhances i-motif stability and allows monitoring of i-motif folding inside cells. Nucleic Acids Res 2024; 52:3375-3389. [PMID: 38366792 PMCID: PMC11014255 DOI: 10.1093/nar/gkae106] [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: 04/28/2023] [Revised: 01/17/2024] [Accepted: 02/09/2024] [Indexed: 02/18/2024] Open
Abstract
The i-motif is an intriguing non-canonical DNA structure, whose role in the cell is still controversial. Development of methods to study i-motif formation under physiological conditions in living cells is necessary to study its potential biological functions. The cytosine analog 1,3-diaza-2-oxophenoxazine (tCO) is a fluorescent nucleobase able to form either hemiprotonated base pairs with cytosine residues, or neutral base pairs with guanines. We show here that when tCO is incorporated in the proximity of a G:C:G:C minor groove tetrad, it induces a strong thermal and pH stabilization, resulting in i-motifs with Tm of 39ºC at neutral pH. The structural determination by NMR methods reveals that the enhanced stability is due to a large stacking interaction between the guanines of the tetrad with the tCO nucleobase, which forms a tCO:C+ in the folded structure at unusually-high pHs, leading to an increased quenching in its fluorescence at neutral conditions. This quenching is much lower when tCO is base-paired to guanines and totally disappears when the oligonucleotide is unfolded. By taking profit of this property, we have been able to monitor i-motif folding in cells.
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Affiliation(s)
- Bartomeu Mir
- Instituto de Química Física ‘Blas Cabrera’. CSIC. Serrano 119. 28006 Madrid. Spain
- Inorganic and Organic Chemistry Department. Organic Chemistry Section and IBUB. University of Barcelona, Martí i Franquès 1-11, 08028 Barcelona. Spain
| | - Israel Serrano-Chacón
- Instituto de Química Física ‘Blas Cabrera’. CSIC. Serrano 119. 28006 Madrid. Spain
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
| | - Pedro Medina
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
- Departament de Bioquímica i Biomedicina. Facultat de Biologia. Universitat de Barcelona. 08028 Barcelona. Spain
| | - Veronica Macaluso
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
| | - Montserrat Terrazas
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
- Inorganic and Organic Chemistry Department. Organic Chemistry Section and IBUB. University of Barcelona, Martí i Franquès 1-11, 08028 Barcelona. Spain
| | - Albert Gandioso
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
| | - Miguel Garavís
- Instituto de Química Física ‘Blas Cabrera’. CSIC. Serrano 119. 28006 Madrid. Spain
| | - Modesto Orozco
- Institute for Research in Biomedicine (IRB Barcelona). The Barcelona Institute of Science and Technology (BIST). 08028 Barcelona. Spain
- Departament de Bioquímica i Biomedicina. Facultat de Biologia. Universitat de Barcelona. 08028 Barcelona. Spain
| | - Núria Escaja
- Inorganic and Organic Chemistry Department. Organic Chemistry Section and IBUB. University of Barcelona, Martí i Franquès 1-11, 08028 Barcelona. Spain
| | - Carlos González
- Instituto de Química Física ‘Blas Cabrera’. CSIC. Serrano 119. 28006 Madrid. Spain
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2
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Ten TB, Zvoda V, Sarangi MK, Kuznetsov SV, Ansari A. "Flexible hinge" dynamics in mismatched DNA revealed by fluorescence correlation spectroscopy. J Biol Phys 2022; 48:253-272. [PMID: 35451661 PMCID: PMC9411374 DOI: 10.1007/s10867-022-09607-x] [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: 10/31/2021] [Accepted: 03/22/2022] [Indexed: 10/18/2022] Open
Abstract
Altered unwinding/bending fluctuations at DNA lesion sites are implicated as plausible mechanisms for damage sensing by DNA-repair proteins. These dynamics are expected to occur on similar timescales as one-dimensional (1D) diffusion of proteins on DNA if effective in stalling these proteins as they scan DNA. We examined the flexibility and dynamics of DNA oligomers containing 3 base pair (bp) mismatched sites specifically recognized in vitro by nucleotide excision repair protein Rad4 (yeast ortholog of mammalian XPC). A previous Forster resonance energy transfer (FRET) study mapped DNA conformational distributions with cytosine analog FRET pair primarily sensitive to DNA twisting/unwinding deformations (Chakraborty et al. Nucleic Acids Res. 46: 1240-1255 (2018)). These studies revealed B-DNA conformations for nonspecific (matched) constructs but significant unwinding for mismatched constructs specifically recognized by Rad4, even in the absence of Rad4. The timescales of these unwinding fluctuations, however, remained elusive. Here, we labeled DNA with Atto550/Atto647N FRET dyes suitable for fluorescence correlation spectroscopy (FCS). With these probes, we detected higher FRET in specific, mismatched DNA compared with matched DNA, reaffirming unwinding/bending deformations in mismatched DNA. FCS unveiled the dynamics of these spontaneous deformations at ~ 300 µs with no fluctuations detected for matched DNA within the ~ 600 ns-10 ms FCS time window. These studies are the first to visualize anomalous unwinding/bending fluctuations in mismatched DNA on timescales that overlap with the < 500 µs "stepping" times of repair proteins on DNA. Such "flexible hinge" dynamics at lesion sites could arrest a diffusing protein to facilitate damage interrogation and recognition.
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Affiliation(s)
- Timour B Ten
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Viktoriya Zvoda
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Manas K Sarangi
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
- Present Address: Department of Physics, Indian Institute of Technology, Patna, 801103, India
| | - Serguei V Kuznetsov
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Anjum Ansari
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA.
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3
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Tavakoli A, Paul D, Mu H, Kuchlyan J, Baral S, Ansari A, Broyde S, Min JH. Light-induced modulation of DNA recognition by the Rad4/XPC damage sensor protein. RSC Chem Biol 2021; 2:523-536. [PMID: 34041491 PMCID: PMC8142930 DOI: 10.1039/d0cb00192a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 12/18/2020] [Indexed: 12/20/2022] Open
Abstract
Biomolecular structural changes upon binding/unbinding are key to their functions. However, characterization of such dynamical processes is difficult as it requires ways to rapidly and specifically trigger the assembly/disassembly as well as ways to monitor the resulting changes over time. Recently, various chemical strategies have been developed to use light to trigger changes in oligonucleotide structures, and thereby their activities. Here we report that photocleavable DNA can be used to modulate the DNA binding of the Rad4/XPC DNA repair complex using light. Rad4/XPC specifically recognizes diverse helix-destabilizing/distorting lesions including bulky organic adduct lesions and functions as a key initiator for the eukaryotic nucleotide excision repair (NER) pathway. We show that the 6-nitropiperonyloxymethyl (NPOM)-modified DNA is recognized by the Rad4 protein as a specific substrate and that the specific binding can be abolished by light-induced cleavage of the NPOM group from DNA in a dose-dependent manner. Fluorescence lifetime-based analyses of the DNA conformations suggest that free NPOM-DNA retains B-DNA-like conformations despite its bulky NPOM adduct, but Rad4-binding causes it to be heterogeneously distorted. Subsequent extensive conformational searches and molecular dynamics simulations demonstrate that NPOM in DNA can be housed in the major groove of the DNA, with stacking interactions among the nucleotide pairs remaining largely unperturbed and thus retaining overall B-DNA conformation. Our work suggests that photoactivable DNA may be used as a DNA lesion surrogate to study DNA repair mechanisms such as nucleotide excision repair.
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Affiliation(s)
- Amirrasoul Tavakoli
- Department of Chemistry and Biochemistry, Baylor UniversityWacoTX 76798USA+1 254-710-2095
| | - Debamita Paul
- Department of Chemistry and Biochemistry, Baylor UniversityWacoTX 76798USA+1 254-710-2095
| | - Hong Mu
- Department of Biology, New York UniversityNew YorkNY 10003USA
| | - Jagannath Kuchlyan
- Department of Chemistry and Biochemistry, Baylor UniversityWacoTX 76798USA+1 254-710-2095
| | - Saroj Baral
- Department of Physics, University of Illinois at ChicagoChicagoIL 60607USA
| | - Anjum Ansari
- Department of Physics, University of Illinois at ChicagoChicagoIL 60607USA
| | - Suse Broyde
- Department of Biology, New York UniversityNew YorkNY 10003USA
| | - Jung-Hyun Min
- Department of Chemistry and Biochemistry, Baylor UniversityWacoTX 76798USA+1 254-710-2095
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4
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Paul D, Mu H, Tavakoli A, Dai Q, Chen X, Chakraborty S, He C, Ansari A, Broyde S, Min JH. Tethering-facilitated DNA 'opening' and complementary roles of β-hairpin motifs in the Rad4/XPC DNA damage sensor protein. Nucleic Acids Res 2020; 48:12348-12364. [PMID: 33119737 PMCID: PMC7708039 DOI: 10.1093/nar/gkaa909] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 08/28/2020] [Accepted: 10/02/2020] [Indexed: 01/01/2023] Open
Abstract
XPC/Rad4 initiates eukaryotic nucleotide excision repair on structurally diverse helix-destabilizing/distorting DNA lesions by selectively 'opening' these sites while rapidly diffusing along undamaged DNA. Previous structural studies showed that Rad4, when tethered to DNA, could also open undamaged DNA, suggesting a 'kinetic gating' mechanism whereby lesion discrimination relied on efficient opening versus diffusion. However, solution studies in support of such a mechanism were lacking and how 'opening' is brought about remained unclear. Here, we present crystal structures and fluorescence-based conformational analyses on tethered complexes, showing that Rad4 can indeed 'open' undamaged DNA in solution and that such 'opening' can largely occur without one or the other of the β-hairpin motifs in the BHD2 or BHD3 domains. Notably, the Rad4-bound 'open' DNA adopts multiple conformations in solution notwithstanding the DNA's original structure or the β-hairpins. Molecular dynamics simulations reveal compensatory roles of the β-hairpins, which may render robustness in dealing with and opening diverse lesions. Our study showcases how fluorescence-based studies can be used to obtain information complementary to ensemble structural studies. The tethering-facilitated DNA 'opening' of undamaged sites and the dynamic nature of 'open' DNA may shed light on how the protein functions within and beyond nucleotide excision repair in cells.
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Affiliation(s)
- Debamita Paul
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA
| | - Hong Mu
- Department of Biology, New York University, New York, NY 10003, USA
| | - Amirrasoul Tavakoli
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA
| | - Qing Dai
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
| | - Xuejing Chen
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Sagnik Chakraborty
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Chuan He
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Department of Biochemistry and Molecular Biology, Howard Hughes Medical Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Anjum Ansari
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Suse Broyde
- Department of Biology, New York University, New York, NY 10003, USA
| | - Jung-Hyun Min
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA
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5
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Füchtbauer AF, Wranne MS, Bood M, Weis E, Pfeiffer P, Nilsson JR, Dahlén A, Grøtli M, Wilhelmsson LM. Interbase FRET in RNA: from A to Z. Nucleic Acids Res 2019; 47:9990-9997. [PMID: 31544922 PMCID: PMC6821158 DOI: 10.1093/nar/gkz812] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 09/02/2019] [Accepted: 09/11/2019] [Indexed: 01/22/2023] Open
Abstract
Interbase FRET can reveal highly detailed information about distance, orientation and dynamics in nucleic acids, complementing the existing structure and dynamics techniques. We here report the first RNA base analogue FRET pair, consisting of the donor tCO and the non-emissive acceptor tCnitro. The acceptor ribonucleoside is here synthesised and incorporated into RNA for the first time. This FRET pair accurately reports the average structure of A-form RNA, and its utility for probing RNA structural changes is demonstrated by monitoring the transition from A- to Z-form RNA. Finally, the measured FRET data were compared with theoretical FRET patterns obtained from two previously reported Z-RNA PDB structures, to shed new light on this elusive RNA conformation.
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Affiliation(s)
- Anders F Füchtbauer
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg SE-412 96, Sweden
| | - Moa S Wranne
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg SE-412 96, Sweden
| | - Mattias Bood
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg SE-412 96, Sweden.,Medicinal Chemistry, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Erik Weis
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg SE-412 96, Sweden.,Medicinal Chemistry, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Pauline Pfeiffer
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg SE-412 96, Sweden
| | - Jesper R Nilsson
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg SE-412 96, Sweden
| | - Anders Dahlén
- Medicinal Chemistry, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Morten Grøtli
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg SE-412 96, Sweden
| | - L Marcus Wilhelmsson
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg SE-412 96, Sweden
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6
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Chakraborty S, Steinbach PJ, Paul D, Mu H, Broyde S, Min JH, Ansari A. Enhanced spontaneous DNA twisting/bending fluctuations unveiled by fluorescence lifetime distributions promote mismatch recognition by the Rad4 nucleotide excision repair complex. Nucleic Acids Res 2019; 46:1240-1255. [PMID: 29267981 PMCID: PMC5815138 DOI: 10.1093/nar/gkx1216] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 12/12/2017] [Indexed: 12/15/2022] Open
Abstract
Rad4/XPC recognizes diverse DNA lesions including ultraviolet-photolesions and carcinogen-DNA adducts, initiating nucleotide excision repair. Studies have suggested that Rad4/XPC senses lesion-induced helix-destabilization to flip out nucleotides from damaged DNA sites. However, characterizing how DNA deformability and/or distortions impact recognition has been challenging. Here, using fluorescence lifetime measurements empowered by a maximum entropy algorithm, we mapped the conformational heterogeneities of artificially destabilized mismatched DNA substrates of varying Rad4-binding specificities. The conformational distributions, as probed by FRET between a cytosine-analog pair exquisitely sensitive to DNA twisting/bending, reveal a direct connection between intrinsic DNA deformability and Rad4 recognition. High-specificity CCC/CCC mismatch, free in solution, sampled a strikingly broad range of conformations from B-DNA-like to highly distorted conformations that resembled those observed with Rad4 bound; the extent of these distortions increased with bound Rad4 and with temperature. Conversely, the non-specific TAT/TAT mismatch had a homogeneous, B-DNA-like conformation. Molecular dynamics simulations also revealed a wide distribution of conformations for CCC/CCC, complementing experimental findings. We propose that intrinsic deformability promotes Rad4 damage recognition, perhaps by stalling a diffusing protein and/or facilitating ‘conformational capture’ of pre-distorted damaged sites. Surprisingly, even mismatched DNA specifically bound to Rad4 remains highly dynamic, a feature that may reflect the versatility of Rad4/XPC to recognize many structurally dissimilar lesions.
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Affiliation(s)
- Sagnik Chakraborty
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Peter J Steinbach
- Center for Molecular Modeling, Center for Information Technology, National Institutes of Health, Bethesda, MD 20892, USA
| | - Debamita Paul
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Hong Mu
- Department of Biology, New York University, New York, NY 10003, USA
| | - Suse Broyde
- Department of Biology, New York University, New York, NY 10003, USA
| | - Jung-Hyun Min
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Anjum Ansari
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.,Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA
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7
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Bielecka P, Dembska A, Juskowiak B. Monitoring of pH Using an i-Motif-Forming Sequence Containing a Fluorescent Cytosine Analogue, tC. Molecules 2019; 24:molecules24050952. [PMID: 30857134 PMCID: PMC6429216 DOI: 10.3390/molecules24050952] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 02/26/2019] [Accepted: 03/05/2019] [Indexed: 01/31/2023] Open
Abstract
The i-motif is a four-stranded DNA structure formed from the cytosine (C)-rich ssDNA sequence, which is stabilized in slightly acidic pH. Additionally, labeling of a cytosine-rich sequence with a fluorescent molecule may constitute a way to construct a pH-sensitive biosensor. In this paper, we report tC-modified fluorescent probes that contain RET-related sequence C4GC4GC4GC4A. Results of the UV absorption melting experiments, circular dichroism (CD) spectra, and steady-state fluorescence measurements of tC-modified i-motifs are presented and discussed here. Efficient fluorescence quenching of tC fluorophore occurred upon lowering the pH from 8.0 to 5.5. Furthermore, we present and discuss fluorescence spectra of systems containing tC-modified i-motifs and complementary G-rich sequences in the ratios 1:1, 1:2, and 1:3 in response to pH changes. The fluorescence anisotropy was proposed for the study of conformational switching of the i-motif structure for tC-probes in the presence and absence of a complementary sequence. The possibility of using of the sensor for monitoring pH changes was demonstrated.
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Affiliation(s)
- Patrycja Bielecka
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland.
| | - Anna Dembska
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland.
| | - Bernard Juskowiak
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland.
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8
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Giassa IC, Rynes J, Fessl T, Foldynova-Trantirkova S, Trantirek L. Advances in the cellular structural biology of nucleic acids. FEBS Lett 2018; 592:1997-2011. [PMID: 29679394 DOI: 10.1002/1873-3468.13054] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 03/31/2018] [Accepted: 04/09/2018] [Indexed: 01/01/2023]
Abstract
Conventional biophysical and chemical biology approaches for delineating relationships between the structure and biological function of nucleic acids (NAs) abstract NAs from their native biological context. However, cumulative experimental observations have revealed that the structure, dynamics and interactions of NAs might be strongly influenced by a broad spectrum of specific and nonspecific physical-chemical environmental factors. This consideration has recently sparked interest in the development of novel tools for structural characterization of NAs in the native cellular context. Here, we review the individual methods currently being employed for structural characterization of NA structure in a native cellular environment with a focus on recent advances and developments in the emerging fields of in-cell NMR and electron paramagnetic resonance spectroscopy and in-cell single-molecule FRET of NAs.
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Affiliation(s)
- Ilektra-Chara Giassa
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Jan Rynes
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Tomas Fessl
- Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
| | - Silvie Foldynova-Trantirkova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic.,Institute of Biophysics, Academy of Science of the Czech Republic, Brno, Czech Republic
| | - Lukas Trantirek
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
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9
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Gustmann H, Lefrancois D, Reuss AJ, Gophane DB, Braun M, Dreuw A, Sigurdsson ST, Wachtveitl J. Spin the light off: rapid internal conversion into a dark doublet state quenches the fluorescence of an RNA spin label. Phys Chem Chem Phys 2018; 19:26255-26264. [PMID: 28933471 DOI: 10.1039/c7cp03975a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The spin label Çm and the fluorophore Çmf are close isosteric relatives: the secondary amine Çmf can be easily oxidized to a nitroxide group to form Çm. Thus, both compounds can serve as EPR and fluorescence labels, respectively, and their high structural similarity allows direct comparison of EPR and fluorescence data, e.g. in the context of investigations of RNA conformation and dynamics. Detailed UV/vis-spectroscopic studies demonstrate that the fluorescence lifetime and the quantum yield of Çmf are directly affected by intermolecular interactions, which makes it a sensitive probe of its microenvironment. On the other hand, Çm undergoes effective fluorescence quenching in the ps-time domain. The established quenching mechanisms that are usually operational for fluorophore-nitroxide compounds, do not explain the spectroscopic data for Çm. Quantum chemical calculations revealed that the lowest excited doublet state D1, which has no equivalent in Çmf, is a key state of the ultrafast quenching mechanism. This dark state is localized on the nitroxide group and is populated via rapid internal conversion.
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Affiliation(s)
- Henrik Gustmann
- Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt am Main, Max-von-Laue-Str. 7, 60438 Frankfurt, Germany.
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10
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Bood M, Sarangamath S, Wranne MS, Grøtli M, Wilhelmsson LM. Fluorescent nucleobase analogues for base-base FRET in nucleic acids: synthesis, photophysics and applications. Beilstein J Org Chem 2018; 14:114-129. [PMID: 29441135 PMCID: PMC5789401 DOI: 10.3762/bjoc.14.7] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 12/22/2017] [Indexed: 12/31/2022] Open
Abstract
Förster resonance energy transfer (FRET) between a donor nucleobase analogue and an acceptor nucleobase analogue, base–base FRET, works as a spectroscopic ruler and protractor. With their firm stacking and ability to replace the natural nucleic acid bases inside the base-stack, base analogue donor and acceptor molecules complement external fluorophores like the Cy-, Alexa- and ATTO-dyes and enable detailed investigations of structure and dynamics of nucleic acid containing systems. The first base–base FRET pair, tCO–tCnitro, has recently been complemented with among others the adenine analogue FRET pair, qAN1–qAnitro, increasing the flexibility of the methodology. Here we present the design, synthesis, photophysical characterization and use of such base analogues. They enable a higher control of the FRET orientation factor, κ2, have a different distance window of opportunity than external fluorophores, and, thus, have the potential to facilitate better structure resolution. Netropsin DNA binding and the B-to-Z-DNA transition are examples of structure investigations that recently have been performed using base–base FRET and that are described here. Base–base FRET has been around for less than a decade, only in 2017 expanded beyond one FRET pair, and represents a highly promising structure and dynamics methodology for the field of nucleic acids. Here we bring up its advantages as well as disadvantages and touch upon potential future applications.
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Affiliation(s)
- Mattias Bood
- Department of Chemistry and Molecular Biology, University of Gothenburg, SE-412 96 Gothenburg, Sweden
| | - Sangamesh Sarangamath
- Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
| | - Moa S Wranne
- Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
| | - Morten Grøtli
- Department of Chemistry and Molecular Biology, University of Gothenburg, SE-412 96 Gothenburg, Sweden
| | - L Marcus Wilhelmsson
- Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
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11
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Wranne MS, Füchtbauer AF, Dumat B, Bood M, El-Sagheer AH, Brown T, Gradén H, Grøtli M, Wilhelmsson LM. Toward Complete Sequence Flexibility of Nucleic Acid Base Analogue FRET. J Am Chem Soc 2017; 139:9271-9280. [PMID: 28613885 DOI: 10.1021/jacs.7b04517] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Förster resonance energy transfer (FRET) using fluorescent base analogues is a powerful means of obtaining high-resolution nucleic acid structure and dynamics information that favorably complements techniques such as NMR and X-ray crystallography. Here, we expand the base-base FRET repertoire with an adenine analogue FRET-pair. Phosphoramidite-protected quadracyclic 2'-deoxyadenosine analogues qAN1 (donor) and qAnitro (acceptor) were synthesized and incorporated into DNA by a generic, reliable, and high-yielding route, and both constitute excellent adenine analogues. The donor, qAN1, has quantum yields reaching 21% and 11% in single- and double-strands, respectively. To the best of our knowledge, this results in the highest average brightness of an adenine analogue inside DNA. Its potent emissive features overlap well with the absorption of qAnitro and thus enable accurate FRET-measurements over more than one turn of B-DNA. As we have shown previously for our cytosine analogue FRET-pair, FRET between qAN1 and qAnitro positioned at different base separations inside DNA results in efficiencies that are highly dependent on both distance and orientation. This facilitates significantly enhanced resolution in FRET structure determinations, demonstrated here in a study of conformational changes of DNA upon binding of the minor groove binder netropsin. Finally, we note that the donor and acceptor of our cytosine FRET-pair, tCO and tCnitro, can be conveniently combined with the acceptor and donor of our current adenine pair, respectively. Consequently, our base analogues can now measure base-base FRET between 3 of the 10 possible base combinations and, through base-complementarity, between all sequence positions in a duplex.
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Affiliation(s)
- Moa S Wranne
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology , Gothenburg S-41296, Sweden
| | - Anders Foller Füchtbauer
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology , Gothenburg S-41296, Sweden
| | - Blaise Dumat
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology , Gothenburg S-41296, Sweden
| | - Mattias Bood
- Department of Chemistry and Molecular Biology, University of Gothenburg , Gothenburg S-41296, Sweden.,Cardiovascular and Metabolic Diseases, Innovative Medicines and Early Development, AstraZeneca , Mölndal S-43183, Sweden
| | - Afaf H El-Sagheer
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford , Oxford OX1 3TA, United Kingdom.,Chemistry Branch, Faculty of Petroleum and Mining Engineering, Suez University , Suez 43721, Egypt
| | - Tom Brown
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford , Oxford OX1 3TA, United Kingdom
| | - Henrik Gradén
- Cardiovascular and Metabolic Diseases, Innovative Medicines and Early Development, AstraZeneca , Mölndal S-43183, Sweden
| | - Morten Grøtli
- Department of Chemistry and Molecular Biology, University of Gothenburg , Gothenburg S-41296, Sweden
| | - L Marcus Wilhelmsson
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology , Gothenburg S-41296, Sweden
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12
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Füchtbauer AF, Preus S, Börjesson K, McPhee SA, Lilley DMJ, Wilhelmsson LM. Fluorescent RNA cytosine analogue - an internal probe for detailed structure and dynamics investigations. Sci Rep 2017; 7:2393. [PMID: 28539582 PMCID: PMC5443824 DOI: 10.1038/s41598-017-02453-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 04/10/2017] [Indexed: 12/22/2022] Open
Abstract
The bright fluorescent cytosine analogue tCO stands out among fluorescent bases due to its virtually unquenched fluorescence emission in duplex DNA. However, like most reported base analogues, it has not been thoroughly characterized in RNA. We here report on the first synthesis and RNA-incorporation of tCO, and characterize its base-mimicking and fluorescence properties in RNA. As in DNA, we find a high quantum yield inside RNA duplexes (<ΦF> = 0.22) that is virtually unaffected by the neighbouring bases (ΦF = 0.20-0.25), resulting in an average brightness of 1900 M-1 cm-1. The average fluorescence lifetime in RNA duplexes is 4.3 ns and generally two lifetimes are required to fit the exponential decays. Fluorescence properties in ssRNA are defined by a small increase in average quantum yield (<ΦF > = 0.24) compared to dsRNA, with a broader distribution (ΦF = 0.17-0.34) and slightly shorter average lifetimes. Using circular dichroism, we find that the tCO-modified RNA duplexes form regular A-form helices and in UV-melting experiments the stability of the duplexes is only slightly higher than that of the corresponding natural RNA (<ΔT m> = + 2.3 °C). These properties make tCO a highly interesting fluorescent RNA base analogue for detailed FRET-based structural measurements, as a bright internal label in microscopy, and for fluorescence anisotropy measurements of RNA dynamics.
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Affiliation(s)
- Anders Foller Füchtbauer
- Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, Gothenburg, SE-41296, Sweden
| | - Søren Preus
- Department of Chemistry, University of Copenhagen, Copenhagen, DK-2100, Denmark
| | - Karl Börjesson
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, SE-41296, Sweden
| | - Scott A McPhee
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee, DD1 5EH, UK
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee, DD1 5EH, UK
| | - L Marcus Wilhelmsson
- Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, Gothenburg, SE-41296, Sweden.
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13
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Twist-open mechanism of DNA damage recognition by the Rad4/XPC nucleotide excision repair complex. Proc Natl Acad Sci U S A 2016; 113:E2296-305. [PMID: 27035942 DOI: 10.1073/pnas.1514666113] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
DNA damage repair starts with the recognition of damaged sites from predominantly normal DNA. In eukaryotes, diverse DNA lesions from environmental sources are recognized by the xeroderma pigmentosum C (XPC) nucleotide excision repair complex. Studies of Rad4 (radiation-sensitive 4; yeast XPC ortholog) showed that Rad4 "opens" up damaged DNA by inserting a β-hairpin into the duplex and flipping out two damage-containing nucleotide pairs. However, this DNA lesion "opening" is slow (˜5-10 ms) compared with typical submillisecond residence times per base pair site reported for various DNA-binding proteins during 1D diffusion on DNA. To address the mystery as to how Rad4 pauses to recognize lesions during diffusional search, we examine conformational dynamics along the lesion recognition trajectory using temperature-jump spectroscopy. Besides identifying the ˜10-ms step as the rate-limiting bottleneck towards opening specific DNA site, we uncover an earlier ˜100- to 500-μs step that we assign to nonspecific deformation (unwinding/"twisting") of DNA by Rad4. The β-hairpin is not required to unwind or to overcome the bottleneck but is essential for full nucleotide-flipping. We propose that Rad4 recognizes lesions in a step-wise "twist-open" mechanism, in which preliminary twisting represents Rad4 interconverting between search and interrogation modes. Through such conformational switches compatible with rapid diffusion on DNA, Rad4 may stall preferentially at a lesion site, offering time to open DNA. This study represents the first direct observation, to our knowledge, of dynamical DNA distortions during search/interrogation beyond base pair breathing. Submillisecond interrogation with preferential stalling at cognate sites may be common to various DNA-binding proteins.
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14
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Dumat B, Larsen AF, Wilhelmsson LM. Studying Z-DNA and B- to Z-DNA transitions using a cytosine analogue FRET-pair. Nucleic Acids Res 2016; 44:e101. [PMID: 26896804 PMCID: PMC4914084 DOI: 10.1093/nar/gkw114] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 02/16/2016] [Indexed: 11/28/2022] Open
Abstract
Herein, we report on the use of a tricyclic cytosine FRET pair, incorporated into DNA with different base pair separations, to study Z-DNA and B-Z DNA junctions. With its position inside the DNA structure, the FRET pair responds to a B- to Z-DNA transition with a distinct change in FRET efficiency for each donor/acceptor configuration allowing reliable structural probing. Moreover, we show how fluorescence spectroscopy and our cytosine analogues can be used to determine rate constants for the B- to Z-DNA transition mechanism. The modified cytosines have little influence on the transition and the FRET pair is thus an easily implemented and virtually non-perturbing fluorescence tool to study Z-DNA. This nucleobase analogue FRET pair represents a valuable addition to the limited number of fluorescence methods available to study Z-DNA and we suggest it will facilitate, for example, deciphering the B- to Z-DNA transition mechanism and investigating the interaction of DNA with Z-DNA binding proteins.
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Affiliation(s)
- Blaise Dumat
- Chalmers University of Technology, Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, SE-41296 Göteborg, Sweden
| | - Anders Foller Larsen
- Chalmers University of Technology, Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, SE-41296 Göteborg, Sweden
| | - L Marcus Wilhelmsson
- Chalmers University of Technology, Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, SE-41296 Göteborg, Sweden
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15
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Bielecka P, Juskowiak B. Fluorescent Sensor for PH Monitoring Based on an i-Motif---Switching Aptamer Containing a Tricyclic Cytosine Analogue (tC). Molecules 2015; 20:18511-25. [PMID: 26473815 PMCID: PMC6332284 DOI: 10.3390/molecules201018511] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 09/24/2015] [Accepted: 10/06/2015] [Indexed: 12/16/2022] Open
Abstract
There are cytosine-rich regions in the genome that bind protons with high specificity. Thus protonated C-rich sequence may undergo folding to tetraplex structures called i-motifs. Therefore, one can regard such specific C-rich oligonucleotides as aptamers that recognize protons and undergo conformational transitions. Proper labeling of the aptamer with a fluorescent tag constitutes a platform to construct a pH-sensitive aptasensor. Since the hemiprotonated C-C⁺ base pairs are responsible for the folded tetraplex structure of i-motif, we decided to substitute one of cytosines in an aptamer sequence with its fluorescent analogue, 1,3-diaza-2-oxophenothiazine (tC). In this paper we report on three tC-modified fluorescent probes that contain RET related sequences as a proton recognizing aptamer. Results of the circular dichroism (CD), UV absorption melting experiments, and steady-state fluorescence measurements of these tC-modified i-motif probes are presented and discussed. The pH-induced i-motif formation by the probes resulted in fluorescence quenching of tC fluorophore. Efficiency of quenching was related to the pH variations. Suitability of the sensor for monitoring pH changes was also demonstrated.
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Affiliation(s)
- Patrycja Bielecka
- Laboratory of Bioanalytical Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b 61-614 Poznan, Poland.
| | - Bernard Juskowiak
- Laboratory of Bioanalytical Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b 61-614 Poznan, Poland.
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16
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Foller Larsen A, Dumat B, Wranne MS, Lawson CP, Preus S, Bood M, Gradén H, Marcus Wilhelmsson L, Grøtli M. Development of bright fluorescent quadracyclic adenine analogues: TDDFT-calculation supported rational design. Sci Rep 2015; 5:12653. [PMID: 26227585 PMCID: PMC4530663 DOI: 10.1038/srep12653] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 07/06/2015] [Indexed: 02/01/2023] Open
Abstract
Fluorescent base analogues (FBAs) comprise a family of increasingly important molecules for the investigation of nucleic acid structure and dynamics. We recently reported the quantum chemical calculation supported development of four microenvironment sensitive analogues of the quadracyclic adenine (qA) scaffold, the qANs, with highly promising absorptive and fluorescence properties that were very well predicted by TDDFT calculations. Herein, we report on the efficient synthesis, experimental and theoretical characterization of nine novel quadracyclic adenine derivatives. The brightest derivative, 2-CNqA, displays a 13-fold increased brightness (εΦF = 4500) compared with the parent compound qA and has the additional benefit of being a virtually microenvironment-insensitive fluorophore, making it a suitable candidate for nucleic acid incorporation and use in quantitative FRET and anisotropy experiments. TDDFT calculations, conducted on the nine novel qAs a posteriori, successfully describe the relative fluorescence quantum yield and brightness of all qA derivatives. This observation suggests that the TDDFT-based rational design strategy may be employed for the development of bright fluorophores built up from a common scaffold to reduce the otherwise costly and time-consuming screening process usually required to obtain useful and bright FBAs.
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Affiliation(s)
- Anders Foller Larsen
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, S-41296 Gothenburg, Sweden
| | - Blaise Dumat
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, S-41296 Gothenburg, Sweden
| | - Moa S. Wranne
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, S-41296 Gothenburg, Sweden
| | - Christopher P. Lawson
- Department of Chemistry and Molecular Biology, University of Gothenburg, S-41296 Gothenburg, Sweden
| | - Søren Preus
- Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus C, DK-8000, Denmark
| | - Mattias Bood
- Department of Chemistry and Molecular Biology, University of Gothenburg, S-41296 Gothenburg, Sweden
| | | | - L. Marcus Wilhelmsson
- Department of Chemistry and Chemical Engineering/Chemistry and Biochemistry, Chalmers University of Technology, S-41296 Gothenburg, Sweden
| | - Morten Grøtli
- Department of Chemistry and Molecular Biology, University of Gothenburg, S-41296 Gothenburg, Sweden
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17
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Dumat B, Bood M, Wranne MS, Lawson CP, Larsen AF, Preus S, Streling J, Gradén H, Wellner E, Grøtli M, Wilhelmsson LM. Second-generation fluorescent quadracyclic adenine analogues: environment-responsive probes with enhanced brightness. Chemistry 2015; 21:4039-48. [PMID: 25641628 DOI: 10.1002/chem.201405759] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Indexed: 01/10/2023]
Abstract
Fluorescent base analogues comprise a group of increasingly important molecules for the investigation of nucleic acid structure, dynamics, and interactions with other molecules. Herein, we report on the quantum chemical calculation aided design, synthesis, and characterization of four new putative quadracyclic adenine analogues. The compounds were efficiently synthesized from a common intermediate through a two-step pathway with the Suzuki-Miyaura coupling as the key step. Two of the compounds, qAN1 and qAN4, display brightnesses (εΦF) of 1700 and 2300, respectively, in water and behave as wavelength-ratiometric pH probes under acidic conditions. The other two, qAN2 and qAN3, display lower brightnesses but exhibit polarity-sensitive dual-band emissions that could prove useful to investigate DNA structural changes induced by DNA-protein or -drug interactions. The four qANs are very promising microenvironment-sensitive fluorescent adenine analogues that display considerable brightness for such compounds.
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Affiliation(s)
- Blaise Dumat
- Department of Chemical and Chemical Engineering/, Chemistry and Biochemistry, Chalmers University of Technology, 41296 Gothenburg (Sweden)
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18
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Pan K, Boulais E, Yang L, Bathe M. Structure-based model for light-harvesting properties of nucleic acid nanostructures. Nucleic Acids Res 2014; 42:2159-70. [PMID: 24311563 PMCID: PMC3936709 DOI: 10.1093/nar/gkt1269] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 11/01/2013] [Accepted: 11/14/2013] [Indexed: 12/11/2022] Open
Abstract
Programmed self-assembly of DNA enables the rational design of megadalton-scale macromolecular assemblies with sub-nanometer scale precision. These assemblies can be programmed to serve as structural scaffolds for secondary chromophore molecules with light-harvesting properties. Like in natural systems, the local and global spatial organization of these synthetic scaffolded chromophore systems plays a crucial role in their emergent excitonic and optical properties. Previously, we introduced a computational model to predict the large-scale 3D solution structure and flexibility of nucleic acid nanostructures programmed using the principle of scaffolded DNA origami. Here, we use Förster resonance energy transfer theory to simulate the temporal dynamics of dye excitation and energy transfer accounting both for overall DNA nanostructure architecture as well as atomic-level DNA and dye chemical structure and composition. Results are used to calculate emergent optical properties including effective absorption cross-section, absorption and emission spectra and total power transferred to a biomimetic reaction center in an existing seven-helix double stranded DNA-based antenna. This structure-based computational framework enables the efficient in silico evaluation of nucleic acid nanostructures for diverse light-harvesting and photonic applications.
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Affiliation(s)
- Keyao Pan
- Department of Biological Engineering, Laboratory for Computational Biology & Biophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Etienne Boulais
- Department of Biological Engineering, Laboratory for Computational Biology & Biophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Lun Yang
- Department of Biological Engineering, Laboratory for Computational Biology & Biophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Mark Bathe
- Department of Biological Engineering, Laboratory for Computational Biology & Biophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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19
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20
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Xia S, Wood M, Bradley MJ, De La Cruz EM, Konigsberg WH. Alteration in the cavity size adjacent to the active site of RB69 DNA polymerase changes its conformational dynamics. Nucleic Acids Res 2013; 41:9077-89. [PMID: 23921641 PMCID: PMC3799440 DOI: 10.1093/nar/gkt674] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Internal cavities are a common feature of many proteins, often having profound effects on the dynamics of their interactions with substrate and binding partners. RB69 DNA polymerase (pol) has a hydrophobic cavity right below the nucleotide binding pocket at the tip of highly conserved L415 side chain. Replacement of this residue with Gly or Met in other B family pols resulted in higher mutation rates. When similar substitutions for L415 were introduced into RB69pol, only L415A and L415G had dramatic effects on pre-steady-state kinetic parameters, reducing base selectivity by several hundred fold. On the other hand, the L415M variant behaved like the wild-type. Using a novel tCo-tCnitro Förster Resonance Energy Transfer (FRET) assay, we were able to show that the partition of the primer terminus between pol and exonuclease (exo) domains was compromised with the L415A and L415G mutants, but not with the L415M variant. These results could be rationalized by changes in their structures as determined by high resolution X-ray crystallography.
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Affiliation(s)
- Shuangluo Xia
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
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21
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Preus S, Jønck S, Pittelkow M, Dierckx A, Karpkird T, Albinsson B, Wilhelmsson LM. The photoinduced transformation of fluorescent DNA base analogue tC triggers DNA melting. Photochem Photobiol Sci 2013; 12:1416-22. [PMID: 23689311 DOI: 10.1039/c3pp50057h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
While fluorescent analogues of the canonical nucleobases have proven to be highly valuable in a large number of applications, up until today, fluorescent DNA base analogues remain virtually inapplicable for single-molecule fluorescence experiments which require extremely bright and photostable dyes. Insight into the photodegradation processes of these fluorophores is thus a key step in the continuous development towards dyes with improved performances. Here, we show that the commercially available fluorescent nucleobase analogue tC under intense long-term illumination and in the presence of O2 is degraded to form a single photoreaction product which we suggest to be the sulfoxide form of tC. The photoproduct is characterized by a blue-shifted absorption and a less intense fluorescence compared to that of tC. Interestingly, when tC is positioned inside double-stranded DNA this photodriven conversion of tC to its photoproduct greatly reduces the duplex stability of the overall double helix in which the probe is positioned. Since tC can be excited selectively at 400 nm, well outside the absorption band of the natural DNA bases, this observation points towards the application of tC as a general light-triggered switch of DNA duplex stability.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, Copenhagen, DK-2100, Denmark
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22
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Mammalian transcription factor A is a core component of the mitochondrial transcription machinery. Proc Natl Acad Sci U S A 2012; 109:16510-5. [PMID: 23012404 DOI: 10.1073/pnas.1119738109] [Citation(s) in RCA: 133] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transcription factor A (TFAM) functions as a DNA packaging factor in mammalian mitochondria. TFAM also binds sequence-specifically to sites immediately upstream of mitochondrial promoters, but there are conflicting data regarding its role as a core component of the mitochondrial transcription machinery. We here demonstrate that TFAM is required for transcription in mitochondrial extracts as well as in a reconstituted in vitro transcription system. The absolute requirement of TFAM can be relaxed by conditions that allow DNA breathing, i.e., low salt concentrations or negatively supercoiled DNA templates. The situation is thus very similar to that described in nuclear RNA polymerase II-dependent transcription, in which the free energy of supercoiling can circumvent the need for a subset of basal transcription factors at specific promoters. In agreement with these observations, we demonstrate that TFAM has the capacity to induce negative supercoils in DNA, and, using the recently developed nucleobase analog FRET-pair tC(O)-tC(nitro), we find that TFAM distorts significantly the DNA structure. Our findings differ from recent observations reporting that TFAM is not a core component of the mitochondrial transcription machinery. Instead, our findings support a model in which TFAM is absolutely required to recruit the transcription machinery during initiation of transcription.
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23
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Preus S, Kilså K, Miannay FA, Albinsson B, Wilhelmsson LM. FRETmatrix: a general methodology for the simulation and analysis of FRET in nucleic acids. Nucleic Acids Res 2012; 41:e18. [PMID: 22977181 PMCID: PMC3592456 DOI: 10.1093/nar/gks856] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Förster resonance energy transfer (FRET) is a technique commonly used to unravel the structure and conformational changes of biomolecules being vital for all living organisms. Typically, FRET is performed using dyes attached externally to nucleic acids through a linker that complicates quantitative interpretation of experiments because of dye diffusion and reorientation. Here, we report a versatile, general methodology for the simulation and analysis of FRET in nucleic acids, and demonstrate its particular power for modelling FRET between probes possessing limited diffusional and rotational freedom, such as our recently developed nucleobase analogue FRET pairs (base–base FRET). These probes are positioned inside the DNA/RNA structures as a replacement for one of the natural bases, thus, providing unique control of their position and orientation and the advantage of reporting from inside sites of interest. In demonstration studies, not requiring molecular dynamics modelling, we obtain previously inaccessible insight into the orientation and nanosecond dynamics of the bases inside double-stranded DNA, and we reconstruct high resolution 3D structures of kinked DNA. The reported methodology is accompanied by a freely available software package, FRETmatrix, for the design and analysis of FRET in nucleic acid containing systems.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, Copenhagen DK-2100, Denmark
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24
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Preus S, Wilhelmsson LM. Advances in quantitative FRET-based methods for studying nucleic acids. Chembiochem 2012; 13:1990-2001. [PMID: 22936620 DOI: 10.1002/cbic.201200400] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Indexed: 01/02/2023]
Abstract
Förster resonance energy transfer (FRET) is a powerful tool for monitoring molecular distances and interactions at the nanoscale level. The strong dependence of transfer efficiency on probe separation makes FRET perfectly suited for "on/off" experiments. To use FRET to obtain quantitative distances and three-dimensional structures, however, is more challenging. This review summarises recent studies and technological advances that have improved FRET as a quantitative molecular ruler in nucleic acid systems, both at the ensemble and at the single-molecule levels.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
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25
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Xia S, Beckman J, Wang J, Konigsberg WH. Using a fluorescent cytosine analogue tC(o) to probe the effect of the Y567 to Ala substitution on the preinsertion steps of dNMP incorporation by RB69 DNA polymerase. Biochemistry 2012; 51:4609-17. [PMID: 22616982 PMCID: PMC3437246 DOI: 10.1021/bi300241m] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Residues in the nascent base pair binding pocket (NBP) of bacteriophage RB69 DNA polymerase (RB69pol) are responsible for base discrimination. Replacing Tyr567 with Ala leads to greater flexibility in the NBP, increasing the probability of misincorporation. We used the fluorescent cytosine analogue, 1,3-diaza-2-oxophenoxazine (tC(o)), to identify preinsertion step(s) altered by NBP flexibility. When tC(o) is the templating base in a wild-type (wt) RB69pol ternary complex, its fluorescence is quenched only in the presence of dGTP. However, with the RB69pol Y567A mutant, the fluorescence of tC(o) is also quenched in the presence of dATP. We determined the crystal structure of the dATP/tC(o)-containing ternary complex of the RB69pol Y567A mutant at 1.9 Å resolution and found that the incoming dATP formed two hydrogen bonds with an imino-tautomerized form of tC(o). Stabilization of the dATP/tC(o) base pair involved movement of the tC(o) backbone sugar into the DNA minor groove and required tilting of the tC(o) tricyclic ring to prevent a steric clash with L561. This structure, together with the pre-steady-state kinetic parameters and dNTP binding affinity, estimated from equilibrium fluorescence titrations, suggested that the flexibility of the NBP, provided by the Y567 to Ala substitution, led to a more favorable forward isomerization step resulting in an increase in dNTP binding affinity.
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Affiliation(s)
| | | | | | - William H. Konigsberg
- Corresponding author: Prof. William H. Konigsberg SHM CE-14 Department of Molecular Biophysics and Biochemistry Yale University New Haven, CT 06520-8114 Telephone: (203) 785-4599 Fax: (203) 785-7979
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26
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Xia S, Christian TD, Wang J, Konigsberg WH. Probing minor groove hydrogen bonding interactions between RB69 DNA polymerase and DNA. Biochemistry 2012; 51:4343-53. [PMID: 22571765 DOI: 10.1021/bi300416z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Minor groove hydrogen bonding (HB) interactions between DNA polymerases (pols) and N3 of purines or O2 of pyrimidines have been proposed to be essential for DNA synthesis from results obtained using various nucleoside analogues lacking the N3 or O2 contacts that interfered with primer extension. Because there has been no direct structural evidence to support this proposal, we decided to evaluate the contribution of minor groove HB interactions with family B pols. We have used RB69 DNA pol and 3-deaza-2'-deoxyadenosine (3DA), an analogue of 2-deoxyadenosine, which has the same HB pattern opposite T but with N3 replaced with a carbon atom. We then determined pre-steady-state kinetic parameters for the insertion of dAMP opposite dT using primer/templates (P/T)-containing 3DA. We also determined three structures of ternary complexes with 3DA at various positions in the duplex DNA substrate. We found that the incorporation efficiency of dAMP opposite dT decreased 10(2)-10(3)-fold even when only one minor groove HB interaction was missing. Our structures show that the HB pattern and base pair geometry of 3DA/dT is exactly the same as those of dA/dT, which makes 3DA an optimal analogue for probing minor groove HB interactions between a DNA polymerase and a nucleobase. In addition, our structures provide a rationale for the observed 10(2)-10(3)-fold decrease in the rate of nucleotide incorporation. The minor groove HB interactions between position n - 2 of the primer strand and RB69pol fix the rotomer conformations of the K706 and D621 side chains, as well as the position of metal ion A and its coordinating ligands, so that they are in the optinal orientation for DNA synthesis.
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Affiliation(s)
- Shuangluo Xia
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
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27
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Dierckx A, Miannay FA, Ben Gaied N, Preus S, Björck M, Brown T, Wilhelmsson LM. Quadracyclic adenine: a non-perturbing fluorescent adenine analogue. Chemistry 2012; 18:5987-97. [PMID: 22437923 DOI: 10.1002/chem.201103419] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Indexed: 12/26/2022]
Abstract
Fluorescent-base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base-pairing properties of a new environment-sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid-phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B-form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2-aminopurine, and the recently developed triazole adenine, qA shows highly specific base-pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8 % with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2-aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid-containing systems.
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Affiliation(s)
- Anke Dierckx
- Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology, 41296 Gothenburg, Sweden
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Sato K, Sasaki A, Matsuda A. Highly fluorescent 5-(5,6-dimethoxybenzothiazol-2-yl)-2'-deoxyuridine 5'-triphosphate as an efficient substrate for DNA polymerases. Chembiochem 2011; 12:2341-6. [PMID: 21887841 DOI: 10.1002/cbic.201100452] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Indexed: 11/08/2022]
Abstract
We herein describe the synthesis of fluorescent 5-(5,6-dimethoxybenzothiazol-2-yl)-2'-deoxyuridine 5'-triphosphate (d(bt)UTP) and primer extension reactions using d(bt)UTP. We also carried out primer extension reactions using the (bt)U template. B family DNA polymerases, such as KOD, Deep Vent (exo-), and 9°N(m) DNA polymerases, were effective for elongation with d(bt)UTP. Deep Vent (exo-) and KOD DNA polymerases have excellent fidelity for incorporating d(bt)UTP only at the site opposite the adenine template and only dATP when using the (bt)U template. Therefore, d(bt)UTP is an excellent fluorescent nucleotide that can be incorporated into DNA by DNA polymerases.
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Affiliation(s)
- Kousuke Sato
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Sapporo 060-0812, Japan
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Dierckx A, Dinér P, El-Sagheer AH, Kumar JD, Brown T, Grøtli M, Wilhelmsson LM. Characterization of photophysical and base-mimicking properties of a novel fluorescent adenine analogue in DNA. Nucleic Acids Res 2011; 39:4513-24. [PMID: 21278417 PMCID: PMC3105426 DOI: 10.1093/nar/gkr010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
To increase the diversity of fluorescent base analogues with improved properties, we here present the straightforward click-chemistry-based synthesis of a novel fluorescent adenine-analogue triazole adenine (AT) and its photophysical characterization inside DNA. AT shows promising properties compared to the widely used adenine analogue 2-aminopurine. Quantum yields reach >20% and >5% in single- and double-stranded DNA, respectively, and show dependence on neighbouring bases. Moreover, AT shows only a minor destabilization of DNA duplexes, comparable to 2-aminopurine, and circular dichroism investigations suggest that AT only causes minimal structural perturbations to normal B-DNA. Furthermore, we find that AT shows favourable base-pairing properties with thymine and more surprisingly also with normal adenine. In conclusion, AT shows strong potential as a new fluorescent adenine analogue for monitoring changes within its microenvironment in DNA.
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Affiliation(s)
- Anke Dierckx
- Department of Chemical and Biological Engineering/Physical Chemistry, Chalmers University of Technology, University of Gothenburg, S-41296 Gothenburg, Sweden
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Preus S, Kilså K, Wilhelmsson LM, Albinsson B. Photophysical and structural properties of the fluorescent nucleobase analogues of the tricyclic cytosine (tC) family. Phys Chem Chem Phys 2010; 12:8881-92. [PMID: 20532361 DOI: 10.1039/c000625d] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of the fluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour of these probes in nucleic acid environments, but will also be profitable in the development of new and improved fluorescent base analogues. Here, temperature-dependent fluorescence quantum yield measurements are used to successfully separate and quantify the temperature-dependent and temperature-independent non-radiative excited-state decay processes of the three nucleobase analogues tC, tC(O) and tC(nitro); all of which are derivatives of a phenothiazine or phenoxazine tricyclic framework. These results strongly suggest that the non-radiative decay process dominating the fast deactivation of tC(nitro) is an internal conversion of a different origin than the decay pathways of tC and tC(O). tC(nitro) is reported to be fluorescent only in less dipolar solvents at room temperature, which is explained by an increase in excited-state dipole moment along the main non-radiative decay pathway, a suggestion that applies in the photophysical discussion of large polycyclic nitroaromatics in general. New insight into the ground and excited-state potential energy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFT calculations. The S(0) potential energy surfaces of tC and tC(nitro) possess two global minima corresponding to geometries folded along the middle sulfur-nitrogen axis separated by an energy barrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potential energy surface of tC(O) is also predicted to be shallow along the bending coordinate but with an equilibrium geometry corresponding to the planar conformation of the tricyclic framework, which may explain some of the dissimilar properties of tC and tC(O) in various confined (biological) environments. The S(1) equilibrium geometries of all three base analogues are predicted to be planar. These results are discussed in the context of the tC bases positioned in double-stranded DNA scenarios.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, DK-2100 Copenhagen, Denmark.
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Abstract
The use of fluorescent nucleic acid base analogues is becoming increasingly important in the fields of biology, biochemistry and biophysical chemistry as well as in the field of DNA nanotechnology. The advantage of being able to incorporate a fluorescent probe molecule close to the site of examination in the nucleic acid-containing system of interest with merely a minimal perturbation to the natural structure makes fluorescent base analogues highly attractive. In recent years, there has been a growing interest in developing novel candidates in this group of fluorophores for utilization in various investigations. This review describes the different classes of fluorophores that can be used for studying nucleic acid-containing systems, with an emphasis on choosing the right kind of probe for the system under investigation. It describes the characteristics of the large group of base analogues that has an emission that is sensitive to the surrounding microenvironment and gives examples of investigations in which this group of molecules has been used so far. Furthermore, the characterization and use of fluorescent base analogues that are virtually insensitive to changes in their microenvironment are described in detail. This group of base analogues can be used in several fluorescence investigations of nucleic acids, especially in fluorescence anisotropy and fluorescence resonance energy transfer (FRET) measurements. Finally, the development and characterization of the first nucleic base analogue FRET pair, tC(O)-tC(nitro), and its possible future uses are discussed.
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