1
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Thienoguanosine, a unique non-perturbing reporter for investigating rotational dynamics of DNA duplexes and their complexes with proteins. Int J Biol Macromol 2022; 213:210-225. [DOI: 10.1016/j.ijbiomac.2022.05.162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 05/02/2022] [Accepted: 05/23/2022] [Indexed: 11/05/2022]
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2
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Dziuba D, Didier P, Ciaco S, Barth A, Seidel CAM, Mély Y. Fundamental photophysics of isomorphic and expanded fluorescent nucleoside analogues. Chem Soc Rev 2021; 50:7062-7107. [PMID: 33956014 DOI: 10.1039/d1cs00194a] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Fluorescent nucleoside analogues (FNAs) are structurally diverse mimics of the natural essentially non-fluorescent nucleosides which have found numerous applications in probing the structure and dynamics of nucleic acids as well as their interactions with various biomolecules. In order to minimize disturbance in the labelled nucleic acid sequences, the FNA chromophoric groups should resemble the natural nucleobases in size and hydrogen-bonding patterns. Isomorphic and expanded FNAs are the two groups that best meet the criteria of non-perturbing fluorescent labels for DNA and RNA. Significant progress has been made over the past decades in understanding the fundamental photophysics that governs the spectroscopic and environmentally sensitive properties of these FNAs. Herein, we review recent advances in the spectroscopic and computational studies of selected isomorphic and expanded FNAs. We also show how this information can be used as a rational basis to design new FNAs, select appropriate sequences for optimal spectroscopic response and interpret fluorescence data in FNA applications.
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Affiliation(s)
- Dmytro Dziuba
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
| | - Pascal Didier
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
| | - Stefano Ciaco
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France. and Department of Biotechnology, Chemistry and Pharmacy, University of Siena, via Aldo Moro 2, 53100 Siena, Italy
| | - Anders Barth
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany
| | - Claus A M Seidel
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany
| | - Yves Mély
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
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3
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Das A, Gupta A, Hong Y, Carver JA, Maiti S. A Spectroscopic Marker for Structural Transitions Associated with Amyloid-β Aggregation. Biochemistry 2020; 59:1813-1822. [PMID: 32329604 DOI: 10.1021/acs.biochem.0c00113] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
An amyloid aggregate evolves through a series of intermediates that have different secondary structures and intra- and intermolecular contacts. The structural parameters of these intermediates are important determinants of their toxicity. For example, the early oligomeric species of the amyloid-β (Aβ) peptide have been implicated as the most cytotoxic species in Alzheimer's disease but are difficult to identify because of their dynamic and transitory nature. Conventional aggregation monitors such as the fluorescent dye thioflavin T report on only the overall transition of the soluble species to the final amyloid fibrillar aggregated state. Here, we show that the fluorescent dye bis(triphenylphosphonium) tetraphenylethene (TPE-TPP) identifies at least three distinct aggregation intermediates of Aβ. Some atomic-level features of these intermediates are known from solid state nuclear magnetic resonance spectroscopy. Hence, the TPE-TPP fluorescence data may be interpreted in terms of these Aβ structural transitions. Steady state fluorescence and lifetime characteristics of TPE-TPP distinguish between the small oligomeric species (emission wavelength maximum, λmax = 465 nm; average fluorescence lifetime, τFl measured at 420 nm = 3.58 ± 0.04 ns), the intermediate species (λmax = 452 nm; τFl = 3.00 ± 0.03 ns), and the fibrils (λmax = 406 nm; τFl = 5.19 ± 0.08 ns). Thus, TPE-TPP provides a ready diagnostic for differentiating between the various, including the toxic, Aβ aggregates and potentially can be utilized to screen for amyloid aggregation inhibitors.
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Affiliation(s)
- Anirban Das
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Ankur Gupta
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Yuning Hong
- Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, VIC 3086, Australia
| | - John A Carver
- Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia
| | - Sudipta Maiti
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
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4
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Michel BY, Dziuba D, Benhida R, Demchenko AP, Burger A. Probing of Nucleic Acid Structures, Dynamics, and Interactions With Environment-Sensitive Fluorescent Labels. Front Chem 2020; 8:112. [PMID: 32181238 PMCID: PMC7059644 DOI: 10.3389/fchem.2020.00112] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2019] [Accepted: 02/06/2020] [Indexed: 12/13/2022] Open
Abstract
Fluorescence labeling and probing are fundamental techniques for nucleic acid analysis and quantification. However, new fluorescent probes and approaches are urgently needed in order to accurately determine structural and conformational dynamics of DNA and RNA at the level of single nucleobases/base pairs, and to probe the interactions between nucleic acids with proteins. This review describes the means by which to achieve these goals using nucleobase replacement or modification with advanced fluorescent dyes that respond by the changing of their fluorescence parameters to their local environment (altered polarity, hydration, flipping dynamics, and formation/breaking of hydrogen bonds).
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Affiliation(s)
- Benoît Y. Michel
- Université Côte d'Azur, CNRS, Institut de Chimie de Nice, UMR 7272 – Parc Valrose, Nice, France
| | - Dmytro Dziuba
- Université Côte d'Azur, CNRS, Institut de Chimie de Nice, UMR 7272 – Parc Valrose, Nice, France
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Faculté de Pharmacie, Université de Strasbourg, Illkirch, France
| | - Rachid Benhida
- Université Côte d'Azur, CNRS, Institut de Chimie de Nice, UMR 7272 – Parc Valrose, Nice, France
- Mohamed VI Polytechnic University, UM6P, Ben Guerir, Morocco
| | - Alexander P. Demchenko
- Laboratory of Nanobiotechnologies, Palladin Institute of Biochemistry, Kyiv, Ukraine
- Institute of Physical, Technical and Computer Science, Yuriy Fedkovych National University, Chernivtsi, Ukraine
| | - Alain Burger
- Université Côte d'Azur, CNRS, Institut de Chimie de Nice, UMR 7272 – Parc Valrose, Nice, France
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5
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Remington JM, McCullagh M, Kohler B. Molecular Dynamics Simulations of 2-Aminopurine-Labeled Dinucleoside Monophosphates Reveal Multiscale Stacking Kinetics. J Phys Chem B 2019; 123:2291-2304. [PMID: 30767498 DOI: 10.1021/acs.jpcb.8b12172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Molecular dynamics (MD) simulations of 2-aminopurine (2Ap)-labeled DNA dinucleoside monophosphates (DNMPs) were performed to investigate the hypothesis that base stacking dynamics occur on timescales sufficiently rapid to influence the emission signals measured in time-resolved fluorescence experiments. Analysis of multiple microsecond-length trajectories shows that the DNMPs sample all four coplanar stacking motifs. In addition, three metastable unstacked conformations are detected. A hidden Markov-state model (HMSM) was applied to the simulations to estimate transition rates between the stacked and unstacked states. Transitions between different stacked states generally occur at higher rates when the number of nucleobase faces requiring desolvation is minimized. Time constants for structural relaxation range between 1.6 and 25 ns, suggesting that emission from photoexcited 2Ap, which has an excited-state lifetime of 10 ns, is sensitive to base stacking kinetics. A master equation model for the excited-state population of 2Ap predicts multiexponential emission decays that reproduce the sub-10 ns emission decay lifetimes and amplitudes seen in experiments. Combining MD simulations with HMSM analysis is a powerful way to understand the dynamics that influence 2Ap excited-state relaxation and represents an important step toward using observed emission signals to validate MD simulations.
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Affiliation(s)
- Jacob M Remington
- Department of Chemistry and Biochemistry , Montana State University , Bozeman , Montana 59717 , United States
| | - Martin McCullagh
- Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523 , United States
| | - Bern Kohler
- Department of Chemistry and Biochemistry , The Ohio State University , 100 West 18th Avenue , Columbus , Ohio 43210 , United States
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6
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Smith DA, Holroyd LF, van Mourik T, Jones AC. A DFT study of 2-aminopurine-containing dinucleotides: prediction of stacked conformations with B-DNA structure. Phys Chem Chem Phys 2017; 18:14691-700. [PMID: 27186599 DOI: 10.1039/c5cp07816d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The fluorescence properties of dinucleotides incorporating 2-aminopurine (2AP) suggest that the simplest oligonucleotides adopt conformations similar to those found in duplex DNA. However, there is a lack of structural data for these systems. We report a density functional theory (DFT) study of the structures of 2AP-containing dinucleotides (deoxydinucleoside monophosphates), including full geometry optimisation of the sugar-phosphate backbone. Our DFT calculations employ the M06-2X functional for reliable treatment of dispersion interactions and include implicit aqueous solvation. Dinucleotides with 2AP in the 5'-position and each of the natural bases in the 3'-position are examined, together with the analogous 5'-adenine-containing systems. Computed structures are compared in detail with typical B-DNA base-step parameters, backbone torsional angles and sugar pucker, derived from crystallographic data. We find that 2AP-containing dinucleotides adopt structures that closely conform to B-DNA in all characteristic parameters. The structures of 2AP-containing dinucleotides closely resemble those of their adenine-containing counterparts, demonstrating the fidelity of 2AP as a mimic of the natural base. As a first step towards exploring the conformational heterogeneity of dinucleotides, we also characterise an imperfectly stacked conformation and one in which the bases are completely unstacked.
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Affiliation(s)
- Darren A Smith
- EaStCHEM School of Chemistry, The University of Edinburgh, David Brewster Road, Edinburgh, EH9 3FJ, UK.
| | - Leo F Holroyd
- EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | - Tanja van Mourik
- EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | - Anita C Jones
- EaStCHEM School of Chemistry, The University of Edinburgh, David Brewster Road, Edinburgh, EH9 3FJ, UK.
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7
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Biswas A, Mariam J, Kombrabail M, Narayan S, Krishnamoorthy G, Anand R. Site-Specific Fluorescence Dynamics To Probe Polar Arrest by Fob1 in Replication Fork Barrier Sequences. ACS OMEGA 2017; 2:7389-7399. [PMID: 30023550 PMCID: PMC6045349 DOI: 10.1021/acsomega.7b01117] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 10/12/2017] [Indexed: 06/08/2023]
Abstract
Fob1 protein plays an important role in aging and maintains genomic stability by avoiding clashes between the replication and transcription machinery. It facilitates polar arrest by binding to replication fork barrier (RFB) sites, present within the nontranscribed spacer region of the ribosomal DNA. Here, we investigate the mechanism of unidirectional arrest by creating multiple prosthetic forks within the RFB, with fluorescent adenine analogue 2-aminopurine incorporated site-specifically in both the "permissible" and "nonpermissible" directions. The motional dynamics of the RFB-Fob1 complexes analyzed by fluorescence lifetime and fluorescence anisotropy decay kinetics shows that Fob1 adopts a clamp-lock model of arrest and causes stronger perturbation with the bases in the double-stranded region of the nonpermissible-directed forks over those of the permissible directed ones, thereby creating a polar barrier. Corroborative thermal melting studies reveal a skewed distribution of GC content within the RFB sequence that potentially assists in Fob1-mediated arrest.
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Affiliation(s)
- Anwesha Biswas
- Department
of Chemistry, Indian Institute of Technology
Bombay, Mumbai, Maharashtra 400076, India
| | - Jessy Mariam
- Department
of Chemistry, Indian Institute of Technology
Bombay, Mumbai, Maharashtra 400076, India
| | - Mamta Kombrabail
- Department
of Chemical Sciences, Tata Institute of
Fundamental Research, Mumbai, Maharashtra 400005, India
| | - Satya Narayan
- Department
of Chemical Sciences, Tata Institute of
Fundamental Research, Mumbai, Maharashtra 400005, India
| | - G. Krishnamoorthy
- Department
of Chemistry, Indian Institute of Technology
Bombay, Mumbai, Maharashtra 400076, India
- Department
of Chemical Sciences, Tata Institute of
Fundamental Research, Mumbai, Maharashtra 400005, India
| | - Ruchi Anand
- Department
of Chemistry, Indian Institute of Technology
Bombay, Mumbai, Maharashtra 400076, India
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8
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Remington JM, Philip AM, Hariharan M, Kohler B. On the origin of multiexponential fluorescence decays from 2-aminopurine-labeled dinucleotides. J Chem Phys 2017; 145:155101. [PMID: 27782452 DOI: 10.1063/1.4964718] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The fluorescent probe 2-aminopurine (2Ap) has been used for decades to study local conformational fluctuations in DNA. Steady-state and time-resolved measurements of 2Ap fluorescence have been used to predict specific conformational states through suitable modeling of the quenching of the fluorescence of a 2Ap residue incorporated site-specifically into a DNA strand. The success of this approach has been limited by a lack of understanding of the precise factors responsible for the complex, multiexponential decays observed experimentally. In this study, dinucleotides composed of 2Ap and adenine were studied by the time-correlated single-photon counting technique to investigate the causes of heterogeneous emission kinetics. Contrary to previous reports, we argue that emission from 2Ap that is stacked with a neighboring base contributes negligibly to the emission signals recorded more than 50 ps after excitation, which are instead dominated by emission from unstacked 2Ap. We find that the decay kinetics can be modeled using a continuous lifetime distribution, which arises from the inherent distance dependence of electron transfer rates without the need to postulate a small number of discrete states with decay times derived from multiexponential fits. These results offer a new perspective on the quenching of 2Ap fluorescence and expand the information that can be obtained from experiments.
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Affiliation(s)
- Jacob M Remington
- Department of Chemistry, Montana State University, Bozeman, Montana 59715, USA
| | - Abbey M Philip
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, Sreekaryam, Thiruvananthapuram, Kerala 695016, India
| | - Mahesh Hariharan
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, Sreekaryam, Thiruvananthapuram, Kerala 695016, India
| | - Bern Kohler
- Department of Chemistry, Montana State University, Bozeman, Montana 59715, USA
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9
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Kundu N, Roy A, Banik D, Sarkar N. Unveiling the Mode of Interaction of Berberine Alkaloid in Different Supramolecular Confined Environments: Interplay of Surface Charge between Nano-Confined Charged Layer and DNA. J Phys Chem B 2016; 120:1106-20. [PMID: 26756221 DOI: 10.1021/acs.jpcb.5b10121] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
In this Article, we demonstrate a detailed characterization of binding interaction of berberine chloride (BBCl) with calf-thymus DNA (CT-DNA) in buffer solution as well as in two differently charged reverse micelles (RMs). The photophyscial properties of this alkaloid have been modulated within these microheterogeneous bioassemblies. The mode of binding of this alkaloid with DNA is of debate to date. However, fluorescence spectroscopic measurements, circular dichroism (CD) measurement, and temperature-dependent study unambiguously establish that BBCl partially intercalates into the DNA base pairs. The nonplanarity imposed by partial saturation in their structure causes the nonclassical types of intercalation into DNA. Besides the intercalation, electrostatic interactions also play a significant role in the binding between BBCl and DNA. DNA structure turns into a condensed form after encapsulation into RMs, which is followed by the CD spectra and microscopy study. The probe location and dynamics in the nanopool of the RMs depended on the electrostatic interaction between the charged surfactants and cationic berberine. The structural alteration of CT-DNA from B form to condensed form and the interplay of surface charge between RMs and DNA determine the interaction between the alkaloid and DNA in RMs. Time-resolved study and fluorescence anisotropy measurements successfully provide the binding interaction of BBCl in the nanopool of the RMs in the absence and in the presence of DNA. This study motivates us to judge further the potential applicability of this alkaloid in other biological systems or other biomimicking organized assemblies.
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Affiliation(s)
- Niloy Kundu
- Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB India
| | - Arpita Roy
- Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB India
| | - Debasis Banik
- Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB India
| | - Nilmoni Sarkar
- Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, WB India
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10
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Greiner VJ, Kovalenko L, Humbert N, Richert L, Birck C, Ruff M, Zaporozhets OA, Dhe-Paganon S, Bronner C, Mély Y. Site-Selective Monitoring of the Interaction of the SRA Domain of UHRF1 with Target DNA Sequences Labeled with 2-Aminopurine. Biochemistry 2015; 54:6012-20. [PMID: 26368281 DOI: 10.1021/acs.biochem.5b00419] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
UHRF1 plays a central role in the maintenance and transmission of epigenetic modifications by recruiting DNMT1 to hemimethylated CpG sites via its SET and RING-associated (SRA) domain, ensuring error-free duplication of methylation profiles. To characterize SRA-induced changes in the conformation and dynamics of a target 12 bp DNA duplex as a function of the methylation status, we labeled duplexes by the environment-sensitive probe 2-aminopurine (2-Ap) at various positions near or far from the central CpG recognition site containing either a nonmodified cytosine (NM duplex), a methylated cytosine (HM duplex), or methylated cytosines on both strands (BM duplex). Steady-state and time-resolved fluorescence indicated that binding of SRA induced modest conformational and dynamical changes in NM, HM, and BM duplexes, with only slight destabilization of base pairs, restriction of global duplex flexibility, and diminution of local nucleobase mobility. Moreover, significant restriction of the local motion of residues flanking the methylcytosine in the HM duplex suggested that these residues are more rigidly bound to SRA, in line with a slightly higher affinity of the HM duplex as compared to that of the NM or BM duplex. Our results are consistent with a "reader" role, in which the SRA domain scans DNA sequences for hemimethylated CpG sites without perturbation of the structure of contacted nucleotides.
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Affiliation(s)
- Vanille J Greiner
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France
| | - Lesia Kovalenko
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France.,Analytical Chemistry Department, Taras Shevchenko National University of Kyiv , 64 Volodymyrska Street, 01033 Kyiv, Ukraine
| | - Nicolas Humbert
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France
| | - Ludovic Richert
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France
| | - Catherine Birck
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964 CNRS UMR 7104, Université de Strasbourg , 1 rue Laurent Fries, Illkirch, France
| | - Marc Ruff
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964 CNRS UMR 7104, Université de Strasbourg , 1 rue Laurent Fries, Illkirch, France
| | - Olga A Zaporozhets
- Analytical Chemistry Department, Taras Shevchenko National University of Kyiv , 64 Volodymyrska Street, 01033 Kyiv, Ukraine
| | - Sirano Dhe-Paganon
- Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School , 360 Brookline Avenue, Boston, Massachusetts 02215, United States
| | - Christian Bronner
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France.,Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964 CNRS UMR 7104, Université de Strasbourg , 1 rue Laurent Fries, Illkirch, France
| | - Yves Mély
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de pharmacie , 74 route du Rhin, 67401 Illkirch, France
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11
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2-aminopurine as a fluorescent probe of DNA conformation and the DNA–enzyme interface. Q Rev Biophys 2015; 48:244-79. [DOI: 10.1017/s0033583514000158] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractNearly 50 years since its potential as a fluorescent base analogue was first recognized, 2-aminopurine (2AP) continues to be the most widely used fluorescent probe of DNA structure and the perturbation of that structure by interaction with enzymes and other molecules. In this review, we begin by considering the origin of the dramatic and intriguing difference in photophysical properties between 2AP and its structural isomer, adenine; although 2AP differs from the natural base only in the position of the exocyclic amine group, its fluorescence intensity is one thousand times greater. We then discuss the mechanism of interbase quenching of 2AP fluorescence in DNA, which is the basis of its use as a conformational probe but remains imperfectly understood. There are hundreds of examples in the literature of the use of changes in the fluorescence intensity of 2AP as the basis of assays of conformational change; however, in this review we will consider in detail only a few intensity-based studies. Our primary aim is to highlight the use of time-resolved fluorescence measurements, and the interpretation of fluorescence decay parameters, to explore the structure and dynamics of DNA. We discuss the salient features of the fluorescence decay of 2AP when incorporated in DNA and review the use of decay measurements in studying duplexes, single strands and other structures. We survey the use of 2AP as a probe of DNA-enzyme interaction and enzyme-induced distortion, focusing particularly on its use to study base flipping and the enhanced mechanistic insights that can be gained by a detailed analysis of the decay parameters, rather than merely monitoring changes in fluorescence intensity. Finally we reflect on the merits and shortcomings of 2AP and the prospects for its wider adoption as a fluorescence-decay-based probe.
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12
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Sholokh M, Sharma R, Shin D, Das R, Zaporozhets OA, Tor Y, Mély Y. Conquering 2-aminopurine's deficiencies: highly emissive isomorphic guanosine surrogate faithfully monitors guanosine conformation and dynamics in DNA. J Am Chem Soc 2015; 137:3185-8. [PMID: 25714036 DOI: 10.1021/ja513107r] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The archetypical fluorescent nucleoside analog, 2-aminopurine (2Ap), has been used in countless assays, though it suffers from very low quantum yield, especially when included in double strands, and from the fact that its residual emission frequently does not represent biologically relevant conformations. To conquer 2Ap's deficiencies, deoxythienoguanosine (d(th)G) was recently developed. Here, steady-state and time-resolved fluorescence spectroscopy was used to compare the ability of 2Ap and d(th)G, to substitute and provide relevant structural and dynamical information on a key G residue in the (-) DNA copy of the HIV-1 primer binding site, (-)PBS, both in its stem loop conformation and in the corresponding (-)/(+)PBS duplex. In contrast to 2Ap, this fluorescent nucleoside when included in (-)PBS or (-)/(+)PBS duplex fully preserves their stability and exhibits a respectable quantum yield and a simple fluorescence decay, with marginal amounts of dark species. In further contrast to 2Ap, the fluorescently detected d(th)G species reflect the predominantly populated G conformers, which allows exploring their relevant dynamics. Being able to perfectly substitute G residues, d(th)G will transform nucleic acid biophysics by allowing, for the first time, to selectively and faithfully monitor the conformations and dynamics of a given G residue in a DNA sequence.
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Affiliation(s)
- Marianna Sholokh
- Laboratoire de Biophotonique et Pharmacologie, Faculté de Pharmacie, UMR 7213 CNRS, Université de Strasbourg , 74 route du Rhin, 67401 Illkirch, France
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13
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Narayan S, Kombrabail MH, Das S, Singh H, Chary KVR, Rao BJ, Krishnamoorthy G. Site-specific fluorescence dynamics in an RNA 'thermometer' reveals the role of ribosome binding in its temperature-sensitive switch function. Nucleic Acids Res 2014; 43:493-503. [PMID: 25477380 PMCID: PMC4288164 DOI: 10.1093/nar/gku1264] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
RNA thermometers control the translation of several heat shock and virulence genes by their temperature-sensitive structural transitions. Changes in the structure and dynamics of MiniROSE RNA, which regulates translation in the temperature range of 20–45°C, were studied by site specifically replacing seven adenine residues with the fluorescent analog, 2-aminopurine (2-AP), one at a time. Dynamic fluorescence observables of 2-AP-labeled RNAs were compared in their free versus ribosome-bound states for the first time. Noticeably, position dependence of fluorescence observables, which was prominent at 20°C, was persistent even at 45ºC, suggesting the persistence of structural integrity up to 45ºC. Interestingly, position-dependent dispersion of fluorescence lifetime and quenching constant at 45°C was ablated in ribosome-bound state, when compared to those at 20°C, underscoring loss of structural integrity at 45°C, in ribosome-bound RNA. Significant increase in the value of mean lifetime for 2-AP corresponding to Shine–Dalgarno sequences, when the temperature was raised from 20 to 45°C, to values seen in the presence of urea at 45°C was a strong indicator of melting of the 3D structure of MiniROSE RNA at 45°C, only when it was ribosome bound. Taken all together, we propose a model where we invoke that ribosome binding of the RNA thermometer critically regulates temperature sensing functions in MiniROSE RNA.
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Affiliation(s)
- Satya Narayan
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Mamta H Kombrabail
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Sudipta Das
- Tata Institute of Fundamental Research, Center for Interdisciplinary Sciences, Hyderabad 500075, India
| | - Himanshu Singh
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Kandala V R Chary
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Basuthkar J Rao
- Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
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14
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Singh TS, Rao BJ, Krishnamoorthy G. GTP binding leads to narrowing of the conformer population while preserving the structure of the RNA aptamer: a site-specific time-resolved fluorescence dynamics study. Biochemistry 2012; 51:9260-9. [PMID: 23110669 DOI: 10.1021/bi301110u] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, we employed a combination of steady-state and time-resolved fluorescence spectroscopy and studied the site-specific dynamics in a GTP aptamer using 2-aminopurine as a fluorescent probe. We compared the dynamics of the GTP-bound aptamer with that of the free aptamer as well as when it is denatured. GTP binding leads to an overall compaction of structure in the aptamer. The general pattern of fluorescence lifetimes and correlation times scanned across several locations in the aptamer does not seem to change following GTP binding. However, a remarkable narrowing of the lifetime distribution of the aptamer ensues following its compaction by GTP binding. Interestingly, such a "conformational narrowing" is evident from the lifetime readouts of the nucleotide belonging to the stem as well as the "bulge" part of the aptamer, independent of whether it is directly interacting with GTP. Taken together, these results underscore the importance of an overall intrinsic structure associated with the free aptamer that is further modulated following GTP binding. This work provides strong support for the "conformational selection" hypothesis of ligand binding.
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Affiliation(s)
- T Sanjoy Singh
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400 005, India
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15
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Katz RA, Merkel G, Andrake MD, Roder H, Skalka AM. Retroviral integrases promote fraying of viral DNA ends. J Biol Chem 2011; 286:25710-8. [PMID: 21622554 DOI: 10.1074/jbc.m111.229179] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In the initial step of integration, retroviral integrase (IN) introduces precise nicks in the degenerate, short inverted repeats at the ends of linear viral DNA. The scissile phosphodiester bond is located immediately 3' of a highly conserved CA/GT dinucleotide, usually 2 bp from the ends. These nicks create new recessed 3'-OH viral DNA ends that are required for joining to host cell DNA. Previous studies have indicated that unpairing, "fraying," of the viral DNA ends by IN contributes to end recognition or catalysis. Here, we report that end fraying can be detected independently of catalysis with both avian sarcoma virus (ASV) and human immunodeficiency virus type 1 (HIV-1) IN proteins by use of fluorescence resonance energy transfer (FRET). The results were indicative of an IN-induced intramolecular conformational change in the viral DNA ends (cis FRET). Fraying activity is tightly coupled to the DNA binding capabilities of these enzymes, as follows: an inhibitor effective against both IN proteins was shown to block ASV IN DNA binding and end fraying, with similar dose responses; ASV IN substitutions that reduced DNA binding also reduced end fraying activity; and HIV-1 IN DNA binding and end fraying were both undetectable in the absence of a metal cofactor. Consistent with our previous results, end fraying is sequence-independent, suggesting that the DNA terminus per se is a major structural determinant for recognition. We conclude that frayed ends represent a functional intermediate in which DNA termini can be sampled for suitability for endonucleolytic processing.
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Affiliation(s)
- Richard A Katz
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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16
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Nag S, Sarkar B, Bandyopadhyay A, Sahoo B, Sreenivasan VKA, Kombrabail M, Muralidharan C, Maiti S. Nature of the amyloid-beta monomer and the monomer-oligomer equilibrium. J Biol Chem 2011; 286:13827-33. [PMID: 21349839 DOI: 10.1074/jbc.m110.199885] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The monomer to oligomer transition initiates the aggregation and pathogenic transformation of Alzheimer amyloid-β (Aβ) peptide. However, the monomeric state of this aggregation-prone peptide has remained beyond the reach of most experimental techniques, and a quantitative understanding of this transition is yet to emerge. Here, we employ single-molecule level fluorescence tools to characterize the monomeric state and the monomer-oligomer transition at physiological concentrations in buffers mimicking the cerebrospinal fluid (CSF). Our measurements show that the monomer has a hydrodynamic radius of 0.9 ± 0.1 nm, which confirms the prediction made by some of the in silico studies. Surprisingly, at equilibrium, both Aβ(40) and Aβ(42) remain predominantly monomeric up to 3 μm, above which it forms large aggregates. This concentration is much higher than the estimated concentrations in the CSF of either normal or diseased brains. If Aβ oligomers are present in the CSF and are the key agents in Alzheimer pathology, as is generally believed, then these must be released in the CSF as preformed entities. Although the oligomers are thermodynamically unstable, we find that a large kinetic barrier, which is mostly entropic in origin, strongly impedes their dissociation. Thermodynamic principles therefore allow the development of a pharmacological agent that can catalytically convert metastable oligomers into nontoxic monomers.
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Affiliation(s)
- Suman Nag
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India
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17
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Goel T, Mukherjee T, Rao BJ, Krishnamoorthy G. Fluorescence dynamics of double- and single-stranded DNA bound to histone and micellar surfaces. J Phys Chem B 2010; 114:8986-93. [PMID: 20568809 DOI: 10.1021/jp912029m] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The study of structure and dynamics of bound DNA has special implications in the context of its biological as well as material functions. It is of fundamental importance to understand how a binding surface affects different positions of DNA with respect to its open ends. Because double-stranded (ds) and single-stranded (ss) DNA are the predominant functional forms, we studied the site-specific dynamics of these DNA forms, bound to the oppositely charged surface of histones, and compared the effects with that of DNA bound to cetyltrimethyl ammonium bromide micelles. We utilized a time-resolved fluorescence technique using fluorescent base analogue 2-aminopurine located at specific positions of synthetic poly-A DNA strands to obtain fluorescence lifetime and anisotropy information. It is observed that the binding leads to overall rigidification of the DNA backbone, and the highly flexible ends show drastic dampening of their internal dynamics as well as the fraying motions. In the case of ds-DNA, we find that the binding not only decreases the flexibility but also leads to significant weakening of base-stacking interactions. An important revelation that strong binding between DNA and the binding agents (histones as well as micelles) does not dampen the internal dynamics of the bases completely suggests that the DNA in its bound form stays in some semiactive state, retaining its full biological activity. Considering that the two binding agents (histones and micelles) are chemically very different, an interesting comparison is made between DNA-histones and DNA-micelle interactions.
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Affiliation(s)
- Teena Goel
- Radiation and PhotoChemistry Divison, Chemistry Group, Bhabha Atomic Research Center, Mumbai 400 085, India
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18
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Nakano SI, Oka H, Uotani Y, Uenishi K, Fujii M, Sugimoto N. Stacking interaction in the middle and at the end of a DNA helix studied with non-natural nucleotides. MOLECULAR BIOSYSTEMS 2010; 6:2023-9. [PMID: 20694257 DOI: 10.1039/c0mb00002g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Base stacking is important for the base pair interaction of a DNA duplex, DNA replication by polymerases, and single-stranded nucleotide overhangs. To study the mechanisms responsible for DNA stacking interactions, we measured the thermal stability of DNA duplexes containing a non-natural nucleotide tethered to a simple aromatic hydrocarbon group devoid of dipole moments and hydrogen bonding sites. The duplexes containing tetrahydrofuran were paired with a deoxyadenosine derivative (A/T base pair analog) or a deoxycytidine derivative (C/G base pair analog) and showed a lower stability than Watson-Crick base pairing, partly due to the loss of interbase hydrogen bonds. Conversely, non-natural nucleotides present at a dangling end yielded an interaction energy as high as that observed with base pairing. Importantly, the non-natural nucleotides yielded an interaction energy with a linear correlation similar to that of the analogous Watson-Crick base pairs both in the middle and at the end of a DNA duplex, although a different stacking mechanism between the middle and the end was suggested. Moreover, a positive cooperativity was observed in dangling end stacking of the nucleotide base moiety and aromatic hydrocarbon group. These observations are useful to understand nucleic acid interactions and to design new non-natural nucleotides.
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Affiliation(s)
- Shu-ichi Nakano
- Faculty of Frontiers of Innovative Research in Science and Technology, Konan University, 7-1-20 Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan.
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19
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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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20
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Avilov SV, Godet J, Piémont E, Mély Y. Site-specific characterization of HIV-1 nucleocapsid protein binding to oligonucleotides with two binding sites. Biochemistry 2010; 48:2422-30. [PMID: 19186983 DOI: 10.1021/bi8022366] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nucleocapsid protein (NC) of HIV-1 is a highly conserved protein essential for the virus life cycle that constitutes an attractive target for new antiviral agents. Most NC functions rely on its binding to the HIV-1 genomic RNA and its DNA copies that contain multiple and possibly interdependent binding sites. Therefore, a detailed understanding of NC binding requires a site-specific experimental approach. We have recently shown that 2-aminopurine (2Ap), a fluorescent adenine analogue, can site-selectively probe the binding of NC. Here, we introduced 2Ap at various positions of model single-stranded dodecanucleotides containing two TG motifs which constitute putative specific binding sites. Steady-state and time-resolved fluorescence experiments indicated that NC binding strongly increased the fluorescence quantum yield of 2AP by reducing the dynamic quenching of 2Ap by its close neighbors and slowing the picosecond to nanosecond conformational fluctuations of the oligonucleotides. The dodecanucleotides were found to bind two NC molecules at physiological salt concentrations, confirming the preferential binding of NC to TG motifs and an occluded binding site size for NC of five to six bases. Using the NC-induced changes in 2Ap fluorescence, we determined the microscopic affinity constants of the individual binding sites and showed that affinities can significantly differ from one site to another within the same dodecanucleotide, depending on the position of the TG dinucleotide and the nature of its close neighbors. Moreover, our data suggest that binding of NC even to close binding sites shows no strong cooperativity.
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Affiliation(s)
- Sergiy V Avilov
- Laboratoire Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74 route du Rhin, 67401 Illkirch, France
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21
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Preus S, Börjesson K, Kilså K, Albinsson B, Wilhelmsson LM. Characterization of nucleobase analogue FRET acceptor tCnitro. J Phys Chem B 2010; 114:1050-6. [PMID: 20039634 DOI: 10.1021/jp909471b] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The fluorescent nucleobase analogues of the tricyclic cytosine (tC) family, tC and tC(O), possess high fluorescence quantum yields and single fluorescence lifetimes, even after incorporation into double-stranded DNA, which make these base analogues particularly useful as fluorescence resonance energy transfer (FRET) probes. Recently, we reported the first all-nucleobase FRET pair consisting of tC(O) as the donor and the novel tC(nitro) as the acceptor. The rigid and well-defined position of this FRET pair inside the DNA double helix, and consequently excellent control of the orientation factor in the FRET efficiency, are very promising features for future studies of nucleic acid structures. Here, we provide the necessary spectroscopic and photophysical characterization of tC(nitro) needed in order to utilize this probe as a FRET acceptor in nucleic acids. The lowest energy absorption band from 375 to 525 nm is shown to be the result of a single in-plane polarized electronic transition oriented approximately 27 degrees from the molecular long axis. This band overlaps the emission bands of both tC and tC(O), and the Forster characteristics of these donor-acceptor pairs are calculated for double-stranded DNA scenarios. In addition, the UV-vis absorption of tC(nitro) is monitored in a broad pH range and the neutral form is found to be totally predominant under physiological conditions with a pK(a) of 11.1. The structure and electronic spectrum of tC(nitro) is further characterized by density functional theory calculations.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
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22
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Spadafora M, Postupalenko VY, Shvadchak VV, Klymchenko AS, Mély Y, Burger A, Benhida R. Efficient Synthesis of Ratiometric Fluorescent Nucleosides Featuring 3-Hydroxychromone Nucleobases. Tetrahedron 2009. [DOI: 10.1016/j.tet.2009.07.021] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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23
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Noothi SK, Minda R, Rao BJ. MutS and UvrD Proteins Stimulate Exonuclease Action: Insights into Exonuclease-Mediated Strand Repair. Biochemistry 2009; 48:7787-93. [DOI: 10.1021/bi8020313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sunil K. Noothi
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - Renu Minda
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - Basuthkar J. Rao
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
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24
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Ramreddy T, Kombrabail M, Krishnamoorthy G, Rao BJ. Site-Specific Dynamics in TAT Triplex DNA As Revealed by Time-Domain Fluorescence of 2-Aminopurine. J Phys Chem B 2009; 113:6840-6. [DOI: 10.1021/jp901216h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- T. Ramreddy
- Department of Chemical Science and Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - Mamata Kombrabail
- Department of Chemical Science and Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - G. Krishnamoorthy
- Department of Chemical Science and Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - B. J. Rao
- Department of Chemical Science and Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
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25
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Ranjit S, Gurunathan K, Levitus M. Photophysics of Backbone Fluorescent DNA Modifications: Reducing Uncertainties in FRET. J Phys Chem B 2009; 113:7861-6. [DOI: 10.1021/jp810842u] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Suman Ranjit
- Department of Chemistry and Biochemistry, Department of Physics and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287-5601
| | - Kaushik Gurunathan
- Department of Chemistry and Biochemistry, Department of Physics and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287-5601
| | - Marcia Levitus
- Department of Chemistry and Biochemistry, Department of Physics and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287-5601
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26
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Intermolecular association provides specific optical and NMR signatures for serotonin at intravesicular concentrations. Biophys J 2008; 94:4145-53. [PMID: 18234835 DOI: 10.1529/biophysj.107.121384] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurotransmitter vesicles contain biomolecules at extraordinarily high concentrations (hundreds of millimoles/liter). Such concentrations can drive intermolecular associations, which may affect vesicular osmolarity and neuronal signaling. Here we investigate whether aqueous serotonin (a monoamine neurotransmitter) forms oligomers at intravesicular concentrations and whether these oligomers have specific spectroscopic signatures that can potentially be used for monitoring neuronal storage and release. We report that, as serotonin concentration is increased from 60 microM to 600 mM, the normalized fluorescence spectrum of serotonin displays a growing long-wavelength tail, with an isoemissive point at 376 nm. The fluorescence decay is monoexponential with a lifetime of 4 ns at low concentrations but is multiexponential with an average lifetime of 0.41 ns at 600 mM. A 600 mM serotonin solution has 30% less osmolarity than expected for monomeric serotonin, indicating oligomer formation. The proton NMR chemical shifts move upfield by as much as 0.3 ppm at 600 mM compared to those at 10 mM, indicating a stacking of the serotonin indole moieties. However, no intermolecular crosspeak is evident in the two-dimensional NMR rotating frame Overhauser effect spectroscopy spectrum even at 600 mM, suggesting that oligomeric structures are possibly weakly coupled. The appearance of a single peak for each proton suggests that the rate of interconversion between the monomeric and the oligomeric structures is faster than 240 Hz. A stopped-flow kinetic experiment also confirms that the rate of dissociation is faster than 100 ms. We conclude that serotonin forms oligomers at intravesicular concentrations but becomes monomeric quickly on dilution. NMR signatures of the oligomers provide potential contrast agents for monitoring the activity of serotonergic neurons in vivo.
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27
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Abstract
This chapter is focused on the fluorescent pteridine guanine analogs, 3MI and 6MI and on the pteridine adenine analog, 6MAP. A brief overview of commonly used methods to fluorescently label oligonucleotides reveals the role the pteridines play in the extensive variety of available probes. We describe the fluorescence characteristics of the pteridine probes as monomers and incorporated into DNA and review a variety of applications including changes in fluorescence intensity, anisotropies, time resolved studies, two photon excitation and single molecule detection.
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28
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Avilov SV, Piemont E, Shvadchak V, de Rocquigny H, Mély Y. Probing dynamics of HIV-1 nucleocapsid protein/target hexanucleotide complexes by 2-aminopurine. Nucleic Acids Res 2007; 36:885-96. [PMID: 18086707 PMCID: PMC2241888 DOI: 10.1093/nar/gkm1109] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The nucleocapsid protein (NC) plays an important role in HIV-1, mainly through interactions with the genomic RNA and its DNA copies. Though the structures of several complexes of NC with oligonucleotides (ODNs) are known, detailed information on the ODN dynamics in the complexes is missing. To address this, we investigated the steady state and time-resolved fluorescence properties of 2-aminopurine (2Ap), a fluorescent adenine analog introduced at positions 2 and 5 of AACGCC and AATGCC sequences. In the absence of NC, 2Ap fluorescence was strongly quenched in the flexible ODNs, mainly through picosecond to nanosecond dynamic quenching by its neighboring bases. NC strongly restricted the ODN flexibility and 2Ap local mobility, impeding the collisions of 2Ap with its neighbors and thus, reducing its dynamic quenching. Phe16→Ala and Trp37→Leu mutations largely decreased the ability of NC to affect the local dynamics of 2Ap at positions 2 and 5, respectively, while a fingerless NC was totally ineffective. The restriction of 2Ap local mobility was thus associated with the NC hydrophobic platform at the top of the folded fingers. Since this platform supports the NC chaperone properties, the restriction of the local mobility of the bases is likely a mechanistic component of these properties.
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Affiliation(s)
- S V Avilov
- Institut Gilbert-Laustriat, UMR 7175 CNRS/Université Louis Pasteur (Strasbourg I), Dépt. Pharmacologie et Physicochimie, Faculté de Pharmacie, 74 route du Rhin, 67401 Illkirch, France
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29
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Ivanova A, Jezierski G, Rösch N. Electronic coupling between base pair dimers of LNA:DNA oligomers. Phys Chem Chem Phys 2007; 10:414-21. [PMID: 18174983 DOI: 10.1039/b712506b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We calculated ab initio electronic coupling elements between neighboring base-pair dimers in a set of LNA:DNA oligomers with different numbers of locked nucleotides and compared them by averaging the values over ensembles of snapshots from molecular dynamics trajectories. Averaging was based on coupling elements for various ensembles comprising of 33,000 structures. The known pronounced variations of coupling elements on the nanosecond timescale due to thermal fluctuations of the DNA structure were confirmed. We found significant differences in electronic coupling at the dimer level between a non-modified DNA:DNA duplex and the corresponding duplex containing one fully LNA-substituted strand. We rationalized these differences by very dissimilar overlap in the pi-stack as a consequence of the LNA-modified system approximating an A-DNA-type helix. The calculated coupling elements for the non-modified reference duplex were similar to those of standard B-DNA and those for the fully modified oligomer resembled the matrix elements estimated for standard A-DNA.
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Affiliation(s)
- Anela Ivanova
- Department Chemie, Theoretische Chemie, Technische Universität München, 85747, Garching, Germany
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30
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Nag N, Rao BJ, Krishnamoorthy G. Altered dynamics of DNA bases adjacent to a mismatch: a cue for mismatch recognition by MutS. J Mol Biol 2007; 374:39-53. [PMID: 17919654 DOI: 10.1016/j.jmb.2007.08.065] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Revised: 08/27/2007] [Accepted: 08/27/2007] [Indexed: 10/22/2022]
Abstract
The structural deviations as well as the alteration in the dynamics of DNA at mismatch sites are considered to have a crucial role in mismatch recognition followed by its repair utilizing mismatch repair family proteins. To compare the dynamics at a mismatch and a non-mismatch site, we incorporated 2-aminopurine, a fluorescent analogue of adenine next to a G.T mismatch, a C.C mismatch, or an unpaired T, and at several other non-mismatch positions. Rotational diffusion of 2-aminopurine at these locations, monitored by time-resolved fluorescence anisotropy, showed distinct differences in the dynamics. This alteration in the motional dynamics is largely confined to the normally matched base-pairs that are immediately adjacent to a mismatch/ unpaired base and could be used by MutS as a cue for mismatch-specific recognition. Interestingly, the enhanced dynamics associated with base-pairs adjacent to a mismatch are significantly restricted upon MutS binding, perhaps "resetting" the cues for downstream events that follow MutS binding. Recognition of such details of motional dynamics of DNA for the first time in the current study enabled us to propose a model that integrates the details of mismatch recognition by MutS as revealed by the high-resolution crystal structure with that of observed base dynamics, and unveils a minimal composite read-out involving the base mismatch and its adjacent normal base-pairs.
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Affiliation(s)
- Nabanita Nag
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
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