51
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Tangprasertchai NS, Zhang X, Ding Y, Tham K, Rohs R, Haworth IS, Qin PZ. An Integrated Spin-Labeling/Computational-Modeling Approach for Mapping Global Structures of Nucleic Acids. Methods Enzymol 2015; 564:427-53. [PMID: 26477260 PMCID: PMC4641853 DOI: 10.1016/bs.mie.2015.07.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The technique of site-directed spin labeling (SDSL) provides unique information on biomolecules by monitoring the behavior of a stable radical tag (i.e., spin label) using electron paramagnetic resonance (EPR) spectroscopy. In this chapter, we describe an approach in which SDSL is integrated with computational modeling to map conformations of nucleic acids. This approach builds upon a SDSL tool kit previously developed and validated, which includes three components: (i) a nucleotide-independent nitroxide probe, designated as R5, which can be efficiently attached at defined sites within arbitrary nucleic acid sequences; (ii) inter-R5 distances in the nanometer range, measured via pulsed EPR; and (iii) an efficient program, called NASNOX, that computes inter-R5 distances on given nucleic acid structures. Following a general framework of data mining, our approach uses multiple sets of measured inter-R5 distances to retrieve "correct" all-atom models from a large ensemble of models. The pool of models can be generated independently without relying on the inter-R5 distances, thus allowing a large degree of flexibility in integrating the SDSL-measured distances with a modeling approach best suited for the specific system under investigation. As such, the integrative experimental/computational approach described here represents a hybrid method for determining all-atom models based on experimentally-derived distance measurements.
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Affiliation(s)
| | - Xiaojun Zhang
- Department of Chemistry, University of Southern California, Los Angeles, California, USA
| | - Yuan Ding
- Department of Chemistry, University of Southern California, Los Angeles, California, USA
| | - Kenneth Tham
- Department of Chemistry, University of Southern California, Los Angeles, California, USA
| | - Remo Rohs
- Department of Chemistry, University of Southern California, Los Angeles, California, USA,Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California, USA
| | - Ian S. Haworth
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USA
| | - Peter Z. Qin
- Department of Chemistry, University of Southern California, Los Angeles, California, USA,Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California, USA,Corresponding author:
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52
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Bagryanskaya EG, Krumkacheva OA, Fedin MV, Marque SR. Development and Application of Spin Traps, Spin Probes, and Spin Labels. Methods Enzymol 2015; 563:365-96. [DOI: 10.1016/bs.mie.2015.06.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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53
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Kaminker I, Bye M, Mendelman N, Gislason K, Sigurdsson ST, Goldfarb D. Distance measurements between manganese(ii) and nitroxide spin-labels by DEER determine a binding site of Mn2+ in the HP92 loop of ribosomal RNA. Phys Chem Chem Phys 2015; 17:15098-102. [DOI: 10.1039/c5cp01624j] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
W-band (95 GHz) double electron–electron resonance (DEER) distance measurements between Mn2+ and nitroxide spin labels were used to determine the location of a Mn2+ binding site within an RNA molecule.
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Affiliation(s)
- Ilia Kaminker
- Department of Chemical Physics
- Weizmann Institute of Science
- Rehovot 76100
- Israel
| | - Morgan Bye
- Department of Chemical Physics
- Weizmann Institute of Science
- Rehovot 76100
- Israel
| | - Natanel Mendelman
- Department of Chemical Physics
- Weizmann Institute of Science
- Rehovot 76100
- Israel
| | - Kristmann Gislason
- Department of Chemical Physics
- Weizmann Institute of Science
- Rehovot 76100
- Israel
| | - Snorri Th. Sigurdsson
- University of Iceland
- Department of Chemistry
- Science Institute Dunhaga 3
- 107 Reykjavik
- Iceland
| | - Daniella Goldfarb
- University of Iceland
- Department of Chemistry
- Science Institute Dunhaga 3
- 107 Reykjavik
- Iceland
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54
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Saha S, Jagtap AP, Sigurdsson ST. Site-directed spin labeling of 2′-amino groups in RNA with isoindoline nitroxides that are resistant to reduction. Chem Commun (Camb) 2015; 51:13142-5. [DOI: 10.1039/c5cc05014f] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
2'-Amino groups in RNA were selectively spin labeled with reductively stable isoindoline nitroxides through a high-yielding reaction with aromatic isothiocyanates.
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Affiliation(s)
- Subham Saha
- University of Iceland
- Department of Chemistry
- Science Institute
- 107 Reykjavik
- Iceland
| | - Anil P. Jagtap
- University of Iceland
- Department of Chemistry
- Science Institute
- 107 Reykjavik
- Iceland
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55
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Chalmers BA, Saha S, Nguyen T, McMurtrie J, Sigurdsson ST, Bottle SE, Masters KS. TMIO-PyrImid Hybrids are Profluorescent, Site-Directed Spin Labels for Nucleic Acids. Org Lett 2014; 16:5528-31. [DOI: 10.1021/ol502003a] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Benjamin A. Chalmers
- Faculty
of Science and Engineering, Queensland University of Technology, P.O. Box 2434, 2 George Street, Brisbane, QLD 4001, Australia
| | - Subham Saha
- University of Iceland, Department of Chemistry, Science
Institute, Dunhaga 3, 107 Reykjavík, Iceland
| | | | | | - Snorri Th. Sigurdsson
- University of Iceland, Department of Chemistry, Science
Institute, Dunhaga 3, 107 Reykjavík, Iceland
| | - Steven E. Bottle
- Faculty
of Science and Engineering, Queensland University of Technology, P.O. Box 2434, 2 George Street, Brisbane, QLD 4001, Australia
| | - Kye-Simeon Masters
- Faculty
of Science and Engineering, Queensland University of Technology, P.O. Box 2434, 2 George Street, Brisbane, QLD 4001, Australia
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56
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Gophane DB, Endeward B, Prisner TF, Sigurdsson ST. Conformationally restricted isoindoline-derived spin labels in duplex DNA: distances and rotational flexibility by pulsed electron-electron double resonance spectroscopy. Chemistry 2014; 20:15913-9. [PMID: 25296640 DOI: 10.1002/chem.201403726] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 07/10/2014] [Indexed: 12/25/2022]
Abstract
Three structurally related isoindoline-derived spin labels that have different mobilities were incorporated into duplex DNA to systematically study the effect of motion on orientation-dependent pulsed electron-electron double resonance (PELDOR) measurements. To that end, a new nitroxide spin label, (ExIm)U, was synthesized and incorporated into DNA oligonucleotides. (ExIm)U is the first example of a conformationally unambiguous spin label for nucleic acids, in which the nitroxide N-O bond lies on the same axis as the three single bonds used to attach the otherwise rigid isoindoline-based spin label to a uridine base. Continuous-wave (CW) EPR measurements of (ExIm)U confirm a very high rotational mobility of the spin label in duplex DNA relative to the structurally related spin label (Im)U, which has restricted mobility due to an intramolecular hydrogen bond. The X-band CW-EPR spectra of (ExIm)U can be used to identify mismatches in duplex DNA. PELDOR distance measurements between pairs of the spin labels (Im)U, (Ox)U, and (ExIm)U in duplex DNA showed a strong angular dependence for (Im)U, a medium dependence for (Ox)U, and no orientation effect for (ExIm)U. Thus, precise distances can be extracted from (ExIm)U without having to take orientational effects into account.
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Affiliation(s)
- Dnyaneshwar B Gophane
- Department of Chemistry, Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik (Iceland), Fax: (+354)5528911
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57
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Ding Y, Zhang X, Tham KW, Qin PZ. Experimental mapping of DNA duplex shape enabled by global lineshape analyses of a nucleotide-independent nitroxide probe. Nucleic Acids Res 2014; 42:e140. [PMID: 25092920 PMCID: PMC4191381 DOI: 10.1093/nar/gku695] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Sequence-dependent variation in structure and dynamics of a DNA duplex, collectively referred to as ‘DNA shape’, critically impacts interactions between DNA and proteins. Here, a method based on the technique of site-directed spin labeling was developed to experimentally map shapes of two DNA duplexes that contain response elements of the p53 tumor suppressor. An R5a nitroxide spin label, which was covalently attached at a specific phosphate group, was scanned consecutively through the DNA duplex. X-band continuous-wave electron paramagnetic resonance spectroscopy was used to monitor rotational motions of R5a, which report on DNA structure and dynamics at the labeling site. An approach based on Pearson's coefficient analysis was developed to collectively examine the degree of similarity among the ensemble of R5a spectra. The resulting Pearson's coefficients were used to generate maps representing variation of R5a mobility along the DNA duplex. The R5a mobility maps were found to correlate with maps of certain DNA helical parameters, and were capable of revealing similarity and deviation in the shape of the two closely related DNA duplexes. Collectively, the R5a probe and the Pearson's coefficient-based lineshape analysis scheme yielded a generalizable method for examining sequence-dependent DNA shapes.
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Affiliation(s)
- Yuan Ding
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Xiaojun Zhang
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Kenneth W Tham
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Peter Z Qin
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
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58
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Helmling C, Bessi I, Wacker A, Schnorr KA, Jonker HRA, Richter C, Wagner D, Kreibich M, Schwalbe H. Noncovalent spin labeling of riboswitch RNAs to obtain long-range structural NMR restraints. ACS Chem Biol 2014; 9:1330-9. [PMID: 24673892 DOI: 10.1021/cb500050t] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Paramagnetic relaxation enhancement (PRE) NMR is a powerful method to study structure, dynamics and function of proteins. Up to now, the application of PRE NMR on RNAs is a significant challenge due to the limited size of chemically synthesized RNA. Here, we present a noncovalent spin labeling strategy to spin label RNAs in high yields required for NMR studies. The approach requires the presence of a helix segment composed of about 10 nucleotides (nt) but is not restricted by the size of the RNA. We show successful application of this strategy on the 2'dG sensing aptamer domain of Mesoplasma florum (78 nt). The aptamer domain was prepared in two fragments. A larger fragment was obtained by biochemical means, while a short spin labeled fragment was prepared by chemical solid-phase synthesis. The two fragments were annealed noncovalently by hybridization. We performed NMR, cw-EPR experiments and gel shift assays to investigate the stability of the two-fragment complex. NMR analysis in (15)N-TROSY and (1)H,(1)H-NOESY spectra of both unmodified and spin labeled aptamer domain show that the fragmented system forms a stable hybridization product, is in structural agreement with the full length aptamer domain and maintains its function. Together with structure modeling, experimentally determined (1)H-Γ2 rates are in agreement with reported crystal structure data and show that distance restraints up to 25 Å can be obtained from NMR PRE data of RNA.
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Affiliation(s)
- Christina Helmling
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Irene Bessi
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Anna Wacker
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Kai A. Schnorr
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Hendrik R. A. Jonker
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Christian Richter
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Dominic Wagner
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Michael Kreibich
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Harald Schwalbe
- Institute of Organic Chemistry
and Chemical Biology, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
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59
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Seven I, Weinrich T, Gränz M, Grünewald C, Brüß S, Krstić I, Prisner TF, Heckel A, Göbel MW. Photolabile Protecting Groups for Nitroxide Spin Labels. European J Org Chem 2014. [DOI: 10.1002/ejoc.201301692] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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60
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Deoxyribozyme-Mediated Ligation for Incorporating EPR Spin Labels and Reporter Groups into RNA. Methods Enzymol 2014; 549:85-104. [DOI: 10.1016/b978-0-12-801122-5.00004-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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61
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Esquiaqui JM, Sherman EM, Ye JD, Fanucci GE. Site-directed spin-labeling strategies and electron paramagnetic resonance spectroscopy for large riboswitches. Methods Enzymol 2014; 549:287-311. [PMID: 25432754 DOI: 10.1016/b978-0-12-801122-5.00013-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Genetic regulation effected by RNA riboswitches is governed by ligand-induced structural reorganization with modulation of RNA conformation and dynamics. Characterization of the conformational states of riboswitches in the presence or absence of salts and ligands is important for understanding how interconversion of riboswitch RNA folding states influences function. The methodology of site-directed spin labeling (SDSL) coupled with electron paramagnetic resonance (EPR) spectroscopy is suitable for such studies, wherein site-specific incorporation of a nitroxide radical spin probe allows for local dynamics and conformational changes to be investigated. This chapter reviews a strategy for SDSL-EPR studies of large riboswitches and uses the full length 232 nucleotide (nt) kink-turn motif-containing Vibrio cholerae (VC) glycine riboswitch as an example. Spin-labeling strategies and the challenges of incorporating spin labels into large riboswitches are reviewed and the approach to overcome these challenges is described. Results are subsequently presented illustrating changes in dynamics within the labeled region of the VC glycine riboswitch as observed using SDSL-EPR.
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Affiliation(s)
- Jackie M Esquiaqui
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Eileen M Sherman
- Department of Chemistry, University of Central Florida, Orlando, Florida, USA
| | - Jing-Dong Ye
- Department of Chemistry, University of Central Florida, Orlando, Florida, USA.
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, Gainesville, Florida, USA.
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62
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Nguyen P, Shi X, Sigurdsson ST, Herschlag D, Qin PZ. A single-stranded junction modulates nanosecond motional ordering of the substrate recognition duplex of a group I ribozyme. Chembiochem 2013; 14:1720-3. [PMID: 23900919 DOI: 10.1002/cbic.201300376] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Indexed: 12/26/2022]
Abstract
Rigid spinning: Site-directed spin-labeling studies using a rigid nitroxide spin label (Ç) reveal that both length and sequence of a single-stranded junction (J1/2) modulate nanosecond motional ordering of the substrate-recognition duplex (P1) of the 120 kD group I ribozyme. The studies demonstrate an approach for experimental measurements of nanosecond dynamics in high-molecular-weight RNA complexes.
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Affiliation(s)
- Phuong Nguyen
- Department of Chemistry, University of Southern California, LJS-251, 840 Downey Way, Los Angeles, CA 90089-0744 (USA) http://pzqin.usc.edu/pzqhome
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63
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Jeschke G. Conformational dynamics and distribution of nitroxide spin labels. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2013; 72:42-60. [PMID: 23731861 DOI: 10.1016/j.pnmrs.2013.03.001] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 03/26/2013] [Accepted: 03/27/2013] [Indexed: 06/02/2023]
Abstract
Long-range distance measurements based on paramagnetic relaxation enhancement (PRE) in NMR, quantification of surface water dynamics near biomacromolecules by Overhauser dynamic nuclear polarization (DNP) and sensitivity enhancement by solid-state DNP all depend on introducing paramagnetic species into an otherwise diamagnetic NMR sample. The species can be introduced by site-directed spin labeling, which offers precise control for positioning the label in the sequence of a biopolymer. However, internal flexibility of the spin label gives rise to dynamic processes that potentially influence PRE and DNP behavior and leads to a spatial distribution of the electron spin even in solid samples. Internal dynamics of spin labels and their static conformational distributions have been studied mainly by electron paramagnetic resonance spectroscopy and molecular dynamics simulations, with a large body of results for the most widely applied methanethiosulfonate spin label MTSL. These results are critically discussed in a unifying picture based on rotameric states of the group that carries the spin label. Deficiencies in our current understanding of dynamics and conformations of spin labeled groups and of their influence on NMR observables are highlighted and directions for further research suggested.
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Affiliation(s)
- Gunnar Jeschke
- ETH Zürich, Laboratory Physical Chemistry, Zürich, Switzerland.
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64
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Fairfull-Smith KE, Debele EA, Allen JP, Pfrunder MC, McMurtrie JC. Direct Iodination of Isoindolines and Isoindoline Nitroxides as Precursors to Functionalized Nitroxides. European J Org Chem 2013. [DOI: 10.1002/ejoc.201300313] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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65
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Synthesis of spin-labeled riboswitch RNAs using convertible nucleosides and DNA-catalyzed RNA ligation. Bioorg Med Chem 2013; 21:6171-80. [PMID: 23664496 DOI: 10.1016/j.bmc.2013.04.007] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 03/21/2013] [Accepted: 04/05/2013] [Indexed: 12/23/2022]
Abstract
Chemically stable nitroxide radicals that can be monitored by electron paramagnetic resonance (EPR) spectroscopy can provide information on structural and dynamic properties of functional RNA such as riboswitches. The convertible nucleoside approach is used to install 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,2,5,5-tetramethylpyrrolidin-1-oxyl (proxyl) labels at the exocyclic N(4)-amino group of cytidine and 2'-O-methylcytidine nucleotides in RNA. To obtain site-specifically labeled long riboswitch RNAs beyond the limit of solid-phase synthesis, we report the ligation of spin-labeled RNA using an in vitro selected deoxyribozyme as catalyst, and demonstrate the synthesis of TEMPO-labeled 53 nt SAM-III and 118 nt SAM-I riboswitch domains (SAM=S-adenosylmethionine).
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66
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Spindler PE, Glaser SJ, Skinner TE, Prisner TF. Broadband Inversion PELDOR Spectroscopy with Partially Adiabatic Shaped Pulses. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201207777] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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67
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Spindler PE, Glaser SJ, Skinner TE, Prisner TF. Broadband inversion PELDOR spectroscopy with partially adiabatic shaped pulses. Angew Chem Int Ed Engl 2013; 52:3425-9. [PMID: 23424088 DOI: 10.1002/anie.201207777] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Indexed: 12/14/2022]
Affiliation(s)
- Philipp E Spindler
- Institut für physikalische und theoretische Chemie und Biomolekulares Magnetresonanz Zentrum, Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany
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68
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Jayawardena VC, Fairfull-Smith KE, Bottle SE. Improving the Yield of the Exhaustive Grignard Alkylation of N-Benzylphthalimide. Aust J Chem 2013. [DOI: 10.1071/ch12528] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The tetraalkylation of N-benzylphthalimide is the major yield limiting step in the common synthetic route to isoindoline nitroxides. The progress of this reaction was found to be limited by the formation of previously unobserved mono- and dialkyl side products that do not lead to the desired product. The yield for the tetraalkylation of N-benzylphthalimide with ethylmagnesium iodide could be increased (60 % over two steps) when a stepwise addition sequence was employed. The new two-step synthesis offers a practical preparative scale alternative to the current approach.
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69
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Gophane DB, Sigurdsson ST. Hydrogen-bonding controlled rigidity of an isoindoline-derived nitroxide spin label for nucleic acids. Chem Commun (Camb) 2013; 49:999-1001. [DOI: 10.1039/c2cc36389e] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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70
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Reginsson GW, Kunjir NC, Sigurdsson ST, Schiemann O. Trityl radicals: spin labels for nanometer-distance measurements. Chemistry 2012; 18:13580-4. [PMID: 22996284 DOI: 10.1002/chem.201203014] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Indexed: 12/11/2022]
Abstract
Spin labelling with trityls: to gather information about the structure and dynamics of trityl radicals, spin-labelled polymers were measured with pulsed electron-electron double resonance (PELDOR) and double-quantum coherence (DQC). This study demonstrates that trityl radicals have great potential as spin labels that eliminate some limitations of nitroxide spin labels.
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Affiliation(s)
- Gunnar W Reginsson
- Biomedical Sciences Research Complex, Centre of Magnetic Resonance, St. Andrews, UK
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71
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Reginsson GW, Shelke SA, Rouillon C, White MF, Sigurdsson ST, Schiemann O. Protein-induced changes in DNA structure and dynamics observed with noncovalent site-directed spin labeling and PELDOR. Nucleic Acids Res 2012; 41:e11. [PMID: 22941643 PMCID: PMC3592447 DOI: 10.1093/nar/gks817] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Site-directed spin labeling and pulsed electron-electron double resonance (PELDOR or DEER) have previously been applied successfully to study the structure and dynamics of nucleic acids. Spin labeling nucleic acids at specific sites requires the covalent attachment of spin labels, which involves rather complicated and laborious chemical synthesis. Here, we use a noncovalent label strategy that bypasses the covalent labeling chemistry and show that the binding specificity and efficiency are large enough to enable PELDOR or DEER measurements in DNA duplexes and a DNA duplex bound to the Lac repressor protein. In addition, the rigidity of the label not only allows resolution of the structure and dynamics of oligonucleotides but also the determination of label orientation and protein-induced conformational changes. The results prove that this labeling strategy in combination with PELDOR has a great potential for studying both structure and dynamics of oligonucleotides and their complexes with various ligands.
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Affiliation(s)
- Gunnar W Reginsson
- Biomedical Sciences Research Complex, Centre of Magnetic Resonance, University of St Andrews, St Andrews KY16 9ST, UK
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72
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Höbartner C, Sicoli G, Wachowius F, Gophane DB, Sigurdsson ST. Synthesis and Characterization of RNA Containing a Rigid and Nonperturbing Cytidine-Derived Spin Label. J Org Chem 2012; 77:7749-54. [DOI: 10.1021/jo301227w] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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73
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Cekan P, Sigurdsson ST. Conformation and dynamics of nucleotides in bulges and symmetric internal loops in duplex DNA studied by EPR and fluorescence spectroscopies. Biochem Biophys Res Commun 2012; 420:656-61. [PMID: 22450317 DOI: 10.1016/j.bbrc.2012.03.059] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Accepted: 03/12/2012] [Indexed: 01/02/2023]
Abstract
The dynamics and conformation of base bulges and internal loops in duplex DNA were studied using the bifunctional spectroscopic probe Ç, which becomes fluorescent (Ç(f)) upon reduction of the nitroxide functional group, along with EPR and fluorescence spectroscopies. A one-base bulge was in a conformational equilibrium between looped-out and stacked states, the former favored at higher temperature and the latter at lower temperature. Stacking of bulge bases was favored in two- and three-base bulges, independent of temperature, resulting in DNA bending as evidenced by increased fluorescence of Ç(f). EPR spectra of Ç-labeled three-, four- and five-base symmetrical interior DNA bulges at 20 °C showed low mobility, indicating that the spin-label was stacked within the loop. The spin-label mobility at 37 °C increased as the loops became larger. A considerable variation in fluorescence between different loops was observed, as well as a temperature-dependence within constructs. Fluorescence unexpectedly increased as the size of the loop decreased at 2 °C. Fluorescence of the smallest loops, where a single T·T mismatch was located between the stem region and the probe, was even larger than for the single strand, indicating a considerable local structural deformation of these loops from regular B-DNA. These results show the value of combining EPR and fluorescence spectroscopy to study non-helical regions of nucleic acids.
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Affiliation(s)
- Pavol Cekan
- University of Iceland, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland
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Shelke SA, Sigurdsson ST. Structural changes of an abasic site in duplex DNA affect noncovalent binding of the spin label ç. Nucleic Acids Res 2011; 40:3732-40. [PMID: 22210856 PMCID: PMC3333849 DOI: 10.1093/nar/gkr1210] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The influence of structural changes of an abasic site in duplex DNA on noncovalent and site-directed spin labeling (NC-SDSL) of the spin label ç were examined with electron paramagnetic resonance (EPR) spectroscopy. The binding affinities of ç to sixteen different DNA duplexes containing all possible sequences immediately flanking the abasic site were determined and the results showed that the binding of ç is highly flanking-sequence dependent. In general, a 5′-dG nucleotide favors the binding of the spin label. In particular, 5′-d(G__T) was the best binding sequence whereas 5′-d(C__T) showed the lowest affinity. Changing the structure of the abasic site linker from a tetrahydrofuran analog (F) to the anucleosidic C3-spacer (C3) does not appreciably affect the binding of ç to the abasic site. For efficient binding of ç, the abasic site needs to be located at least four base pairs away from the duplex end. Introducing a methyl substituent at N3 of ç did not change the binding affinity, but a decreased binding was observed for both N3-ethyl and -propyl groups. These results will guide the design of abasic site receptors and spin label ligands for NC-SDSL of nucleic acids.
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Affiliation(s)
- Sandip A Shelke
- Department of Chemistry, University of Iceland, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland
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