1
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Ruzycki CA, Montoya D, Irshad H, Cox J, Zhou Y, McDonald JD, Kuehl PJ. Inhalation delivery of nucleic acid gene therapies in preclinical drug development. Expert Opin Drug Deliv 2023; 20:1097-1113. [PMID: 37732957 DOI: 10.1080/17425247.2023.2261369] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Accepted: 09/18/2023] [Indexed: 09/22/2023]
Abstract
INTRODUCTION Inhaled gene therapy programs targeting diseases of the lung have seen increasing interest in recent years, though as of yet no product has successfully entered the market. Preclinical research to support such programs is critically important in maximizing the chances of developing successful candidates. AREAS COVERED Aspects of inhalation delivery of gene therapies are reviewed, with a focus on preclinical research in animal models. Various barriers to inhalation delivery of gene therapies are discussed, including aerosolization stresses, aerosol behavior in the respiratory tract, and disposition processes post-deposition. Important aspects of animal models are considered, including determinations of biologically relevant determinations of dose and issues related to translatability. EXPERT OPINION Development of clinically-efficacious inhaled gene therapies has proven difficult owing to numerous challenges. Fit-for-purpose experimental and analytical methods are necessary for determinations of biologically relevant doses in preclinical animal models. Further developments in disease-specific animal models may aid in improving the translatability of results in future work, and we expect to see accelerated interests in inhalation gene therapies for various diseases. Sponsors, researchers, and regulators are encouraged to engage in early and frequent discussion regarding candidate therapies, and additional dissemination of preclinical methodologies would be of immense value in avoiding common pitfalls.
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Affiliation(s)
- Conor A Ruzycki
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
| | - Derek Montoya
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
| | - Hammad Irshad
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
| | - Jason Cox
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
| | - Yue Zhou
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
| | | | - Philip J Kuehl
- Lovelace Biomedical Research Institute, Albuquerque, NM, USA
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2
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Rieu M, Valle-Orero J, Ducos B, Allemand JF, Croquette V. Single-molecule kinetic locking allows fluorescence-free quantification of protein/nucleic-acid binding. Commun Biol 2021; 4:1083. [PMID: 34526657 PMCID: PMC8443601 DOI: 10.1038/s42003-021-02606-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 08/25/2021] [Indexed: 11/09/2022] Open
Abstract
Fluorescence-free micro-manipulation of nucleic acids (NA) allows the functional characterization of DNA/RNA processing proteins, without the interference of labels, but currently fails to detect and quantify their binding. To overcome this limitation, we developed a method based on single-molecule force spectroscopy, called kinetic locking, that allows a direct in vitro visualization of protein binding while avoiding any kind of chemical disturbance of the protein’s natural function. We validate kinetic locking by measuring accurately the hybridization energy of ultrashort nucleotides (5, 6, 7 bases) and use it to measure the dynamical interactions of Escherichia coli/E. coli RecQ helicase with its DNA substrate. Rieu et al. present a magnetic tweezers based single-molecule manipulation method, called kinetic locking, for direct detection of biomolecular binding without use of fluorescent probes. By measuring dynamical interactions of E. coli RecQ helicase with its DNA substrate, authors show that this method holds promise for studying DNA-DNA and DNA-protein interactions while avoiding the need for labelling.
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Affiliation(s)
- Martin Rieu
- Laboratoire de physique de l'Ecole Normale Supérieure (LPENS), ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France. .,Institut de Biologie de l'Ecole Normale Supérieure (IBENS), ENS, Université PSL, CNRS, INSERM, Paris, France.
| | - Jessica Valle-Orero
- Laboratoire de physique de l'Ecole Normale Supérieure (LPENS), ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France.,Institut de Biologie de l'Ecole Normale Supérieure (IBENS), ENS, Université PSL, CNRS, INSERM, Paris, France
| | - Bertrand Ducos
- Laboratoire de physique de l'Ecole Normale Supérieure (LPENS), ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France.,Institut de Biologie de l'Ecole Normale Supérieure (IBENS), ENS, Université PSL, CNRS, INSERM, Paris, France
| | - Jean-François Allemand
- Laboratoire de physique de l'Ecole Normale Supérieure (LPENS), ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France.,Institut de Biologie de l'Ecole Normale Supérieure (IBENS), ENS, Université PSL, CNRS, INSERM, Paris, France
| | - Vincent Croquette
- Laboratoire de physique de l'Ecole Normale Supérieure (LPENS), ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France.,Institut de Biologie de l'Ecole Normale Supérieure (IBENS), ENS, Université PSL, CNRS, INSERM, Paris, France.,ESPCI Paris, Université PSL, 10 rue Vauquelin, 75005, Paris, France
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3
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Sundar Rajan V, Viader-Godoy X, Lin YL, Dutta U, Ritort F, Westerlund F, Wilhelmsson LM. Mechanical characterization of base analogue modified nucleic acids by force spectroscopy. Phys Chem Chem Phys 2021; 23:14151-14155. [PMID: 34180930 PMCID: PMC8261857 DOI: 10.1039/d1cp01985f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We use mechanical unfolding of single DNA hairpins with modified bases to accurately assess intra- and intermolecular forces in nucleic acids. As expected, the modification stabilizes the hybridized hairpin, but we also observe intriguing stacking interactions in the unfolded hairpin. Our study highlights the benefit of using base-modified nucleic acids in force-spectroscopy.
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Affiliation(s)
- Vinoth Sundar Rajan
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Sweden. and Department of Biology and Biological Engineering, Chalmers University of Technology, Sweden.
| | - Xavier Viader-Godoy
- Small Biosystems Lab, Condensed Matter Physics Department, Universitat de Barcelona, C/Marti i Franques 1, Barcelona 08028, Spain
| | - Yii-Lih Lin
- Department of Biology and Biological Engineering, Chalmers University of Technology, Sweden.
| | - Uttama Dutta
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Sweden. and Department of Biology and Biological Engineering, Chalmers University of Technology, Sweden.
| | - Felix Ritort
- Small Biosystems Lab, Condensed Matter Physics Department, Universitat de Barcelona, C/Marti i Franques 1, Barcelona 08028, Spain
| | - Fredrik Westerlund
- Department of Biology and Biological Engineering, Chalmers University of Technology, Sweden.
| | - L Marcus Wilhelmsson
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Sweden.
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4
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Zhuravlev PI, Hinczewski M, Thirumalai D. Low Force Unfolding of a Single-Domain Protein by Parallel Pathways. J Phys Chem B 2021; 125:1799-1805. [DOI: 10.1021/acs.jpcb.0c11308] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Pavel I. Zhuravlev
- Biophysics Program, Institute for Physical Science and Technology, Department of Chemistry & Biochemistry, University of Maryland, College Park, Maryland 20742, United States
| | - Michael Hinczewski
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - D. Thirumalai
- Department of Chemistry, The University of Texas, Austin, Texas 78712, United States
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5
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Kirmizialtin S, Pitici F, Cardenas AE, Elber R, Thirumalai D. Dramatic Shape Changes Occur as Cytochrome c Folds. J Phys Chem B 2020; 124:8240-8248. [PMID: 32840372 DOI: 10.1021/acs.jpcb.0c05802] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Extensive experimental studies on the folding of cytochrome c (Cyt c) make this small protein an ideal target for atomic detailed simulations for the purposes of quantitatively characterizing the structural transitions and the associated time scales for folding to the native state from an ensemble of unfolded states. We use previously generated atomically detailed folding trajectories by the stochastic difference equation in length to calculate the time-dependent changes in the small-angle X-ray scattering (SAXS) profiles. Excellent agreement is obtained between experiments and simulations for the time-dependent SAXS spectra, allowing us to identify the structures of the folding intermediates, which shows that Cyt c reaches the native state by a sequential folding mechanism. Using the ensembles of structures along the folding pathways, we show that compaction and the sphericity of Cyt c change dramatically from the prolate ellipsoid shape in the unfolded state to the spherical native state. Our data, which are in unprecedented quantitative agreement with all aspects of time-resolved SAXS experiments, show that hydrophobic collapse and amide group protection coincide on the 100 microseconds time scale, which is in accordance with ultrafast hydrogen/deuterium exchange studies. Based on these results, we propose that compaction of polypeptide chains, accompanied by dramatic shape changes, is a universal characteristic of globular proteins, regardless of the underlying folding mechanism.
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Affiliation(s)
- Serdal Kirmizialtin
- Chemistry Program, Math and Sciences, New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, UAE
| | | | - Alfredo E Cardenas
- Institute for Computational Science and Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Ron Elber
- Institute for Computational Science and Engineering, The University of Texas at Austin, Austin, Texas 78712, United States.,Department of Chemistry, University of Texas, Austin Texas, 78712, United States
| | - D Thirumalai
- Department of Chemistry, University of Texas, Austin Texas, 78712, United States
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6
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Qu H, Ma Q, Wang L, Mao Y, Eisenstein M, Soh HT, Zheng L. Measuring Aptamer Folding Energy Using a Molecular Clamp. J Am Chem Soc 2020; 142:11743-11749. [PMID: 32491843 DOI: 10.1021/jacs.0c01570] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Folding energy (ΔGfold) offers a useful metric for characterizing the stability and function of aptamers. However, experimentally measuring the folding energy is challenging, and there is currently no general technique to measure this parameter directly. In this work, we present a simple approach for measuring aptamer folding energy. First, the aptamer is stretched under equilibrium conditions with a double-stranded DNA "molecular clamp" that is coupled to the aptamer ends. We then measure the total internal energy of stressed DNA molecules using time-lapse gel electrophoresis and compare the folding and unfolding behavior of molecular clamp-stressed molecules that incorporate either the aptamer or unstructured random single-stranded DNA in order to derive the aptamer folding energy. Using this approach, we measured a folding energy of 10.40 kJ/mol for the HD22 thrombin aptamer, which is consistent with other predictions and estimates. We also analyzed a simple hairpin structure, generating a folding energy result of 9.05 kJ/mol, consistent with the value predicted by computational models (9.24 kJ/mol). We believe our strategy offers an accessible and generalizable approach for obtaining such measurements with virtually any aptamer.
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Affiliation(s)
- Hao Qu
- School of Food and Biological Engineering, Hefei University of Technology, Hefei 230009, China
| | - Qihui Ma
- School of Food and Biological Engineering, Hefei University of Technology, Hefei 230009, China
| | - Lu Wang
- School of Food and Biological Engineering, Hefei University of Technology, Hefei 230009, China
| | - Yu Mao
- School of Food and Biological Engineering, Hefei University of Technology, Hefei 230009, China
| | - Michael Eisenstein
- Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States.,Department of Radiology, Stanford University, Stanford, California 94305, United States
| | - Hyongsok Tom Soh
- Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States.,Department of Radiology, Stanford University, Stanford, California 94305, United States
| | - Lei Zheng
- School of Food and Biological Engineering, Hefei University of Technology, Hefei 230009, China
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7
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Bellino L, Florio G, Puglisi G. The influence of device handles in single-molecule experiments. SOFT MATTER 2019; 15:8680-8690. [PMID: 31621748 DOI: 10.1039/c9sm01376h] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We deduce a fully analytical model to predict the artifacts of the device handles in single molecule force spectroscopy experiments. As we show, neglecting the handle stiffness can lead to crucial overestimation or underestimation of the stability properties and unfolding thresholds of multistable molecules.
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Affiliation(s)
- Luca Bellino
- Politecnico di Bari, (DMMM) Dipartimento di Meccanica, Matematica e Management, Politecnico di Bari, Via Re David 200, 70125, Italy.
| | - Giuseppe Florio
- Politecnico di Bari, (DMMM) Dipartimento di Meccanica, Matematica e Management, Politecnico di Bari, Via Re David 200, 70125, Italy. and INFN, Sezione di Bari, I-70126, Italy
| | - Giuseppe Puglisi
- Politecnico di Bari, (DICAR) Dipartimento di Scienza dell'Ingegneria Civile e dell'Architettura, Politecnico di Bari, Via Re David 200, 70126, Italy.
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8
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Manca F, Pincet F, Truskinovsky L, Rothman JE, Foret L, Caruel M. SNARE machinery is optimized for ultrafast fusion. Proc Natl Acad Sci U S A 2019; 116:2435-2442. [PMID: 30700546 PMCID: PMC6377469 DOI: 10.1073/pnas.1820394116] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
SNARE proteins zipper to form complexes (SNAREpins) that power vesicle fusion with target membranes in a variety of biological processes. A single SNAREpin takes about 1 s to fuse two bilayers, yet a handful can ensure release of neurotransmitters from synaptic vesicles much faster: in a 10th of a millisecond. We propose that, similar to the case of muscle myosins, the ultrafast fusion results from cooperative action of many SNAREpins. The coupling originates from mechanical interactions induced by confining scaffolds. Each SNAREpin is known to have enough energy to overcome the fusion barrier of 25-[Formula: see text]; however, the fusion barrier only becomes relevant when the SNAREpins are nearly completely zippered, and from this state, each SNAREpin can deliver only a small fraction of this energy as mechanical work. Therefore, they have to act cooperatively, and we show that at least three of them are needed to ensure fusion in less than a millisecond. However, to reach the prefusion state collectively, starting from the experimentally observed half-zippered metastable state, the SNAREpins have to mechanically synchronize, which takes more time as the number of SNAREpins increases. Incorporating this somewhat counterintuitive idea in a simple coarse-grained model results in the prediction that there should be an optimum number of SNAREpins for submillisecond fusion: three to six over a wide range of parameters. Interestingly, in situ cryoelectron microscope tomography has very recently shown that exactly six SNAREpins participate in the fusion of each synaptic vesicle. This number is in the range predicted by our theory.
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Affiliation(s)
- Fabio Manca
- Laboratoire de Physique de l'Ecole Normale Supérieure (LPENS), CNRS, Ecole Normale Supérieure, 75005 Paris, France
- LPENS, Sorbonne Université, 75005 Paris, France
- LPENS, Université Paris-Diderot, 75005 Paris, France
- LPENS, Université PSL, 75005 Paris, France
| | - Frederic Pincet
- Laboratoire de Physique de l'Ecole Normale Supérieure (LPENS), CNRS, Ecole Normale Supérieure, 75005 Paris, France
- LPENS, Sorbonne Université, 75005 Paris, France
- LPENS, Université Paris-Diderot, 75005 Paris, France
- LPENS, Université PSL, 75005 Paris, France
| | - Lev Truskinovsky
- Physique et Mécanique des Milieux Hétérogènes, CNRS, Ecole Supérieure de Physique et de Chimie Industrielles, Université PSL, 75231 Paris Cedex 05, France
| | - James E Rothman
- Department of Cell Biology, Yale University, New Haven, CT 06520;
- Department of Experimental Epilepsy, Institute of Neurology, University College London, London WC1E 6BT, United Kingdom
| | - Lionel Foret
- Laboratoire de Physique de l'Ecole Normale Supérieure (LPENS), CNRS, Ecole Normale Supérieure, 75005 Paris, France
- LPENS, Sorbonne Université, 75005 Paris, France
- LPENS, Université Paris-Diderot, 75005 Paris, France
- LPENS, Université PSL, 75005 Paris, France
| | - Matthieu Caruel
- Modélisation et Simulation Multi-Echelle, CNRS, Université Paris-Est Créteil, 94010 Créteil Cedex, France
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9
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Yang L, Zhong Z, Tong C, Jia H, Liu Y, Chen G. Single-Molecule Mechanical Folding and Unfolding of RNA Hairpins: Effects of Single A-U to A·C Pair Substitutions and Single Proton Binding and Implications for mRNA Structure-Induced -1 Ribosomal Frameshifting. J Am Chem Soc 2018; 140:8172-8184. [PMID: 29884019 DOI: 10.1021/jacs.8b02970] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A wobble A·C pair can be protonated at near physiological pH to form a more stable wobble A+·C pair. Here, we constructed an RNA hairpin (rHP) and three mutants with one A-U base pair substituted with an A·C mismatch on the top (near the loop, U22C), middle (U25C), and bottom (U29C) positions of the stem, respectively. Our results on single-molecule mechanical (un)folding using optical tweezers reveal the destabilization effect of A-U to A·C pair substitution and protonation-dependent enhancement of mechanical stability facilitated through an increased folding rate, or decreased unfolding rate, or both. Our data show that protonation may occur rapidly upon the formation of an apparent mechanical folding transition state. Furthermore, we measured the bulk -1 ribosomal frameshifting efficiencies of the hairpins by a cell-free translation assay. For the mRNA hairpins studied, -1 frameshifting efficiency correlates with mechanical unfolding force at equilibrium and folding rate at around 15 pN. U29C has a frameshifting efficiency similar to that of rHP (∼2%). Accordingly, the bottom 2-4 base pairs of U29C may not form under a stretching force at pH 7.3, which is consistent with the fact that the bottom base pairs of the hairpins may be disrupted by ribosome at the slippery site. U22C and U25C have a similar frameshifting efficiency (∼1%), indicating that both unfolding and folding rates of an mRNA hairpin in a crowded environment may affect frameshifting. Our data indicate that mechanical (un)folding of RNA hairpins may mimic how mRNAs unfold and fold in the presence of translating ribosomes.
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Affiliation(s)
- Lixia Yang
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371
| | - Zhensheng Zhong
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371.,School of Physics, and State Key Laboratory of Optoelectronic Materials and Technologies , Sun Yat-sen University , Guangzhou 510275 , People's Republic of China
| | - Cailing Tong
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371
| | - Huan Jia
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371
| | - Yiran Liu
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371
| | - Gang Chen
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371
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10
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Weber JK, Kang SG, Zhou R. Rare Dissipative Transitions Punctuate the Initiation of Chemical Denaturation in Proteins. Biophys J 2018; 114:812-821. [PMID: 29490243 DOI: 10.1016/j.bpj.2017.12.038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 12/18/2017] [Accepted: 12/27/2017] [Indexed: 10/17/2022] Open
Abstract
Protein unfolding dynamics are bound by their degree of entropy production, a quantity that relates the amount of heat dissipated by a nonequilibrium process to a system's forward and time-reversed trajectories. We here explore the statistics of heat dissipation that emerge in protein molecules subjected to a chemical denaturant. Coupling large molecular dynamics datasets and Markov state models with the theory of entropy production, we demonstrate that dissipative processes can be rigorously characterized over the course of the urea-induced unfolding of the protein chymotrypsin inhibitor 2. By enumerating full entropy production probability distributions as a function of time, we first illustrate that distinct passive and dissipative regimes are present in the denaturation dynamics. Within the dissipative dynamical region, we next find that chymotrypsin inhibitor 2 is strongly driven into unfolded states in which the protein's hydrophobic core has been penetrated by urea molecules and disintegrated. Detailed analyses reveal that urea's interruption of key hydrophobic contacts between core residues causes many of the protein's native structural features to dissolve.
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Affiliation(s)
- Jeffrey K Weber
- IBM Thomas J. Watson Research Center, Yorktown Heights, New York
| | - Seung-Gu Kang
- IBM Thomas J. Watson Research Center, Yorktown Heights, New York
| | - Ruhong Zhou
- IBM Thomas J. Watson Research Center, Yorktown Heights, New York; Department of Chemistry, Columbia University, New York, New York.
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11
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Ritchie DB, Cappellano TR, Tittle C, Rezajooei N, Rouleau L, Sikkema WKA, Woodside MT. Conformational dynamics of the frameshift stimulatory structure in HIV-1. RNA (NEW YORK, N.Y.) 2017; 23:1376-1384. [PMID: 28522581 PMCID: PMC5558907 DOI: 10.1261/rna.061655.117] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/12/2017] [Indexed: 05/02/2023]
Abstract
Programmed ribosomal frameshifting (PRF) in HIV-1 is thought to be stimulated by a hairpin in the mRNA, although a pseudoknot-like triplex has also been proposed. Because the conformational dynamics of the stimulatory structure under tension applied by the ribosomal helicase during translation may play an important role in PRF, we used optical tweezers to apply tension to the HIV stimulatory structure and monitor its unfolding and refolding dynamics. The folding and unfolding kinetics and energy landscape of the hairpin were measured by ramping the force on the hairpin up and down, providing a detailed biophysical characterization. Unexpectedly, whereas unfolding reflected the simple two-state behavior typical of many hairpins, refolding was more complex, displaying significant heterogeneity. Evidence was found for multiple refolding pathways as well as previously unsuspected, partially folded intermediates. Measuring a variant mRNA containing only the sequence required to form the proposed triplex, it behaved largely in the same way. Nonetheless, very rarely, high-force unfolding events characteristic of pseudoknot-like structures were observed. The rare occurrence of the triplex suggests that the hairpin is the functional stimulatory structure. The unusual heterogeneity of the hairpin dynamics under tension suggests a possible functional role in PRF similar to the dynamics of other stimulatory structures.
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Affiliation(s)
- Dustin B Ritchie
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
| | - Tonia R Cappellano
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
| | - Collin Tittle
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
| | - Negar Rezajooei
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
| | - Logan Rouleau
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
| | | | - Michael T Woodside
- Department of Physics, University of Alberta, Edmonton AB T6G 2E1, Canada
- National Institute for Nanotechnology, National Research Council, Edmonton AB T6G 2M9, Canada
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12
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Xu H, Plaut B, Zhu X, Chen M, Mavinkurve U, Maiti A, Song G, Murari K, Mandal M. Direct Observation of Folding Energy Landscape of RNA Hairpin at Mechanical Loading Rates. J Phys Chem B 2017; 121:2220-2229. [PMID: 28248503 DOI: 10.1021/acs.jpcb.6b10362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
By applying a controlled mechanical load using optical tweezers, we measured the diffusive barrier crossing in a 49 nt long P5ab RNA hairpin. We find that in the free-energy landscape the barrier height (G‡) and transition distance (x‡) are dependent on the loading rate (r) along the pulling direction, x, as predicted by Bell. The barrier shifted toward the initial state, whereas ΔG‡ reduced significantly from 50 to 5 kT, as r increased from 0 to 32 pN/s. However, the equilibrium work (ΔG) during strand separation, as estimated by Crook's fluctuation theorem, remained unchanged at different rates. Previously, helix formation and denaturation have been described as two-state (F ↔ U) transitions for P5ab. Herein, we report three intermediate states I1, I, and I2 located at 4, 11, and 16 nm respectively, from the folded conformation. The intermediates were observed only when the hairpin was subjected to an optimal r, 7.6 pN/s. The results indicate that the complementary strands in P5ab can zip and unzip through complex routes, whereby mismatches act as checkpoints and often impose barriers. The study highlights the significance of loading rates in force-spectroscopy experiments that are increasingly being used to measure the folding properties of biomolecules.
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Affiliation(s)
- Huizhong Xu
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Benjamin Plaut
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Xiran Zhu
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Maverick Chen
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Udit Mavinkurve
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Anindita Maiti
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Guangtao Song
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Krishna Murari
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Maumita Mandal
- Department of Physics, ‡Department of Mathematical Sciences, §Department of Computer Science, and ∥Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
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13
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Vandebroek H, Vanderzande C. The effect of active fluctuations on the dynamics of particles, motors and DNA-hairpins. SOFT MATTER 2017; 13:2181-2191. [PMID: 28239703 DOI: 10.1039/c6sm02568d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Inspired by recent experiments on the dynamics of particles and polymers in artificial cytoskeletons and in cells, we introduce a modified Langevin equation for a particle in an environment that is a viscoelastic medium and that is brought out of equilibrium by the action of active fluctuations caused by molecular motors. We show that within such a model, the motion of a free particle crosses over from superdiffusive to subdiffusive as observed for tracer particles in an in vitro cytoskeleton or in a cell. We investigate the dynamics of a particle confined by a harmonic potential as a simple model for the motion of the tethered head of kinesin-1. We find that the probability that the head is close to its binding site on the microtubule can be enhanced by a factor of two due to active forces. Finally, we study the dynamics of a particle in a double well potential as a model for the dynamics of DNA-hairpins. We show that the active forces effectively lower the potential barrier between the two minima and study the impact of this phenomenon on the zipping/unzipping rate.
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Affiliation(s)
- Hans Vandebroek
- Faculty of Sciences, Hasselt University, 3590 Diepenbeek, Belgium.
| | - Carlo Vanderzande
- Faculty of Sciences, Hasselt University, 3590 Diepenbeek, Belgium. and Instituut Theoretische Fysica, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
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14
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Haider A, Potter D, Sulchek TA. Enhanced stochastic fluctuations to measure steep adhesive energy landscapes. Proc Natl Acad Sci U S A 2016; 113:14213-14218. [PMID: 27911778 PMCID: PMC5167171 DOI: 10.1073/pnas.1608792113] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Free-energy landscapes govern the behavior of all interactions in the presence of thermal fluctuations in the fields of physical chemistry, materials sciences, and the biological sciences. From the energy landscape, critical information about an interaction, such as the reaction kinetic rates, bond lifetimes, and the presence of intermediate states, can be determined. Despite the importance of energy landscapes to understanding reaction mechanisms, most experiments do not directly measure energy landscapes, particularly for interactions with steep force gradients that lead to premature jump to contact of the probe and insufficient sampling of transition regions. Here we present an atomic force microscopy (AFM) approach for measuring energy landscapes that increases sampling of strongly adhesive interactions by using white-noise excitation to enhance the cantilever's thermal fluctuations. The enhanced fluctuations enable the recording of subtle deviations from a harmonic potential to accurately reconstruct interfacial energy landscapes with steep gradients. Comparing the measured energy landscape with adhesive force measurements reveals the existence of an optimal excitation voltage that enables the cantilever fluctuations to fully sample the shape and depth of the energy surface.
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Affiliation(s)
- Ahmad Haider
- Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332
- Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
| | - Daniel Potter
- Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332
- Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
| | - Todd A Sulchek
- Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332;
- Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
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15
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Dulin D, Cui TJ, Cnossen J, Docter MW, Lipfert J, Dekker NH. High Spatiotemporal-Resolution Magnetic Tweezers: Calibration and Applications for DNA Dynamics. Biophys J 2016; 109:2113-25. [PMID: 26588570 DOI: 10.1016/j.bpj.2015.10.018] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Revised: 10/05/2015] [Accepted: 10/13/2015] [Indexed: 11/16/2022] Open
Abstract
The observation of biological processes at the molecular scale in real time requires high spatial and temporal resolution. Magnetic tweezers are straightforward to implement, free of radiation or photodamage, and provide ample multiplexing capability, but their spatiotemporal resolution has lagged behind that of other single-molecule manipulation techniques, notably optical tweezers and AFM. Here, we present, to our knowledge, a new high-resolution magnetic tweezers apparatus. We systematically characterize the achievable spatiotemporal resolution for both incoherent and coherent light sources, different types and sizes of beads, and different types and lengths of tethered molecules. Using a bright coherent laser source for illumination and tracking at 6 kHz, we resolve 3 Å steps with a 1 s period for surface-melted beads and 5 Å steps with a 0.5 s period for double-stranded-dsDNA-tethered beads, in good agreement with a model of stochastic bead motion in the magnetic tweezers. We demonstrate how this instrument can be used to monitor the opening and closing of a DNA hairpin on millisecond timescales in real time, together with attendant changes in the hairpin dynamics upon the addition of deoxythymidine triphosphate. Our approach opens up the possibility of observing biological events at submillisecond timescales with subnanometer resolution using camera-based detection.
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Affiliation(s)
- David Dulin
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
| | - Tao Ju Cui
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Jelmer Cnossen
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Margreet W Docter
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Jan Lipfert
- Department of Physics, Nanosystems Initiative Munich and Center for Nanoscience, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Nynke H Dekker
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
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16
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Caruel M, Truskinovsky L. Statistical mechanics of the Huxley-Simmons model. Phys Rev E 2016; 93:062407. [PMID: 27415298 DOI: 10.1103/physreve.93.062407] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Indexed: 06/06/2023]
Abstract
The chemomechanical model of Huxley and Simmons (HS) [A. F. Huxley and R. M. Simmons, Nature 233, 533 (1971)NATUAS0028-083610.1038/233533a0] provides a paradigmatic description of mechanically induced collective conformational changes relevant in a variety of biological contexts, from muscles power stroke and hair cell gating to integrin binding and hairpin unzipping. We develop a statistical mechanical perspective on the HS model by exploiting a formal analogy with a paramagnetic Ising model. We first study the equilibrium HS model with a finite number of elements and compute explicitly its mechanical and thermal properties. To model kinetics, we derive a master equation and solve it for several loading protocols. The developed formalism is applicable to a broad range of allosteric systems with mean-field interactions.
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Affiliation(s)
- M Caruel
- MSME, CNRS-UMR 8208, 61 Avenue du Général de Gaulle, 94010 Créteil, France
| | - L Truskinovsky
- LMS, CNRS-UMR 7649, Ecole Polytechnique, 91128 Palaiseau Cedex, France
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17
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Connecting thermal and mechanical protein (un)folding landscapes. Biophys J 2016; 107:2950-2961. [PMID: 25517160 DOI: 10.1016/j.bpj.2014.10.021] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Revised: 10/08/2014] [Accepted: 10/15/2014] [Indexed: 11/22/2022] Open
Abstract
Molecular dynamics simulations supplement single-molecule pulling experiments by providing the possibility of examining the full free energy landscape using many coordinates. Here, we use an all-atom structure-based model to study the force and temperature dependence of the unfolding of the protein filamin by applying force at both termini. The unfolding time-force relation τ(F) indicates that the force-induced unfolding behavior of filamin can be characterized into three regimes: barrier-limited low- and intermediate-force regimes, and a barrierless high-force regime. Slope changes of τ(F) separate the three regimes. We show that the behavior of τ(F) can be understood from a two-dimensional free energy landscape projected onto the extension X and the fraction of native contacts Q. In the low-force regime, the unfolding rate is roughly force-independent due to the small (even negative) separation in X between the native ensemble and transition state ensemble (TSE). In the intermediate-force regime, force sufficiently separates the TSE from the native ensemble such that τ(F) roughly follows an exponential relation. This regime is typically explored by pulling experiments. While X may fail to resolve the TSE due to overlap with the unfolded ensemble just below the folding temperature, the overlap is minimal at lower temperatures where experiments are likely to be conducted. The TSE becomes increasingly structured with force, whereas the average order of structural events during unfolding remains roughly unchanged. The high-force regime is characterized by barrierless unfolding, and the unfolding time approaches a limit of ∼10 μs for the highest forces we studied. Finally, a combination of X and Q is shown to be a good reaction coordinate for almost the entire force range.
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18
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Sheshka R, Recho P, Truskinovsky L. Rigidity generation by nonthermal fluctuations. Phys Rev E 2016; 93:052604. [PMID: 27300948 DOI: 10.1103/physreve.93.052604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Indexed: 06/06/2023]
Abstract
Active stabilization in systems with zero or negative stiffness is an essential element of a wide variety of biological processes. We study a prototypical example of this phenomenon and show how active rigidity, interpreted as a formation of a pseudowell in the effective energy landscape, can be generated in an overdamped stochastic system. We link the transition from negative to positive rigidity with time correlations in the additive noise, and we show that subtle differences in the out-of-equilibrium driving may compromise the emergence of a pseudowell.
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Affiliation(s)
- R Sheshka
- LITEN, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble, France
| | - P Recho
- Mathematical Institute, University of Oxford, Oxford OX26GG, United Kingdom
- Engineering Department, University of Cambridge, Cambridge CB2 1PZ, United Kingdom
| | - L Truskinovsky
- LMS, CNRS-UMR 7649, École Polytechnique, 91128 Palaiseau, France
- Physique et Mecanique des Milieux Heterogenes CNRS -- UMR 7636 ESPCI ParisTech 10 Rue Vauquelin, 75005 Paris, France
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19
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Stigler J, Rief M. Ligand-induced changes of the apparent transition-state position in mechanical protein unfolding. Biophys J 2016. [PMID: 26200872 DOI: 10.1016/j.bpj.2015.06.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Force-spectroscopic measurements of ligand-receptor systems and the unfolding/folding of nucleic acids or proteins reveal information on the underlying energy landscape along the pulling coordinate. The slope Δx(‡) of the force-dependent unfolding/unbinding rates is interpreted as the distance from the folded/bound state to the transition state for unfolding/unbinding and, hence, often related to the mechanical compliance of the sample molecule. Here we show that in ligand-binding proteins, the experimentally inferred Δx(‡) can depend on the ligand concentration, unrelated to changes in mechanical compliance. We describe the effect in single-molecule, force-spectroscopy experiments of the calcium-binding protein calmodulin and explain it in a simple model where mechanical unfolding and ligand binding occur on orthogonal reaction coordinates. This model predicts changes in the experimentally inferred Δx(‡), depending on ligand concentration and the associated shift of the dominant barrier between the two reaction coordinates. We demonstrate quantitative agreement between experiments and simulations using a realistic six-state kinetic scheme using literature values for calcium-binding kinetics and affinities. Our results have important consequences for the interpretation of force-spectroscopic data of ligand-binding proteins.
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Affiliation(s)
- Johannes Stigler
- Physik Department E22, Technische Universität München, Garching, Germany.
| | - Matthias Rief
- Physik Department E22, Technische Universität München, Garching, Germany; Munich Center for Integrated Protein Science, München, Germany
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20
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Ritchie DB, Woodside MT. Probing the structural dynamics of proteins and nucleic acids with optical tweezers. Curr Opin Struct Biol 2015; 34:43-51. [PMID: 26189090 PMCID: PMC7126019 DOI: 10.1016/j.sbi.2015.06.006] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 06/09/2015] [Accepted: 06/25/2015] [Indexed: 01/15/2023]
Abstract
Conformational changes are an essential feature of most molecular processes in biology. Optical tweezers have emerged as a powerful tool for probing conformational dynamics at the single-molecule level because of their high resolution and sensitivity, opening new windows on phenomena ranging from folding and ligand binding to enzyme function, molecular machines, and protein aggregation. By measuring conformational changes induced in a molecule by forces applied by optical tweezers, new insight has been gained into the relationship between dynamics and function. We discuss recent advances from studies of how structure forms in proteins and RNA, including non-native structures, fluctuations in disordered proteins, and interactions with chaperones assisting native folding. We also review the development of assays probing the dynamics of complex protein-nucleic acid and protein-protein assemblies that reveal the dynamic interactions between biomolecular machines and their substrates.
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Affiliation(s)
- Dustin B Ritchie
- Department of Physics, University of Alberta, Edmonton, AB T6G2E1 Canada
| | - Michael T Woodside
- Department of Physics, University of Alberta, Edmonton, AB T6G2E1 Canada; National Institute for Nanotechnology, National Research Council, Edmonton, AB T6G2M9, Canada.
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21
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Woodside MT, Lambert J, Beach KSD. Determining intrachain diffusion coefficients for biopolymer dynamics from single-molecule force spectroscopy measurements. Biophys J 2015; 107:1647-53. [PMID: 25296317 DOI: 10.1016/j.bpj.2014.08.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 07/07/2014] [Accepted: 08/07/2014] [Indexed: 12/23/2022] Open
Abstract
The conformational diffusion coefficient for intrachain motions in biopolymers, D, sets the timescale for structural dynamics. Recently, force spectroscopy has been applied to determine D both for unfolded proteins and for the folding transitions in proteins and nucleic acids. However, interpretation of the results remains unsettled. We investigated how instrumental effects arising from the force probes used in the measurement can affect the value of D recovered via force spectroscopy. We compared estimates of D for the folding of DNA hairpins found from measurements of rates and energy landscapes made using optical tweezers with estimates obtained from the same single-molecule trajectories via the transition path time. The apparent D obtained from the rates was much lower than the result found from the same data using transition time analysis, reflecting the effects of the mechanical properties of the force probe. Deconvolution of the finite compliance effects on the measurement allowed the intrinsic value to be recovered. These results were supported by Brownian dynamics simulations of the effects of force-probe compliance and bead size.
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Affiliation(s)
- Michael T Woodside
- Department of Physics, University of Alberta, Edmonton AB, T6G 2E1 Canada; National Institute for Nanotechnology, National Research Council, Edmonton AB, T6G 2M9 Canada.
| | - John Lambert
- Department of Physics, University of Alberta, Edmonton AB, T6G 2E1 Canada
| | - Kevin S D Beach
- Department of Physics, University of Alberta, Edmonton AB, T6G 2E1 Canada
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22
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Luo Z, Cheng B, Cui S. Effects of Water on the Single-Chain Elasticity of Poly(U) RNA. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6107-6113. [PMID: 25989243 DOI: 10.1021/acs.langmuir.5b01313] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Water, the dominant component under the physiological condition, is a complicated solvent which greatly affects the properties of solute molecules. Here, we utilize atomic force microscope-based single-molecule force spectroscopy to study the influence of water on the single-molecule elasticity of an unstructured single-stranded RNA (poly(U)). In nonpolar solvents, RNA presents its inherent elasticity, which is consistent with the theoretical single-chain elasticity calculated by quantum mechanics calculations. In aqueous buffers, however, an additional energy of 1.88 kJ/mol·base is needed for the stretching of the ssRNA chain. This energy is consumed by the bound water rearrangement (Ew) during chain elongation. Further experimental results indicate that the Ew value is uncorrelated to the salt concentrations and stretching velocity. The results obtained in an 8 M guanidine·HCl solution provide more evidence that the bound water molecules around RNA give rise to the observed deviation between aqueous and nonaqueous environments. Compared to synthetic water-soluble polymers, the value of Ew of RNA is much lower. The weak interference of water is supposed to be the precondition for the RNA secondary structure to exist in aqueous solution.
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Affiliation(s)
- Zhonglong Luo
- Key Lab of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China
| | - Bo Cheng
- Key Lab of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China
| | - Shuxun Cui
- Key Lab of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China
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23
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Reconstructing folding energy landscapes from splitting probability analysis of single-molecule trajectories. Proc Natl Acad Sci U S A 2015; 112:7183-8. [PMID: 26039984 DOI: 10.1073/pnas.1419490112] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Structural self-assembly in biopolymers, such as proteins and nucleic acids, involves a diffusive search for the minimum-energy state in a conformational free-energy landscape. The likelihood of folding proceeding to completion, as a function of the reaction coordinate used to monitor the transition, can be described by the splitting probability, p(fold)(x). P(fold) encodes information about the underlying energy landscape, and it is often used to judge the quality of the reaction coordinate. Here, we show how p(fold) can be used to reconstruct energy landscapes from single-molecule folding trajectories, using force spectroscopy measurements of single DNA hairpins. Calculating p(fold)(x) directly from trajectories of the molecular extension measured for hairpins fluctuating in equilibrium between folded and unfolded states, we inverted the result expected from diffusion over a 1D energy landscape to obtain the implied landscape profile. The results agreed well with the landscapes reconstructed by established methods, but, remarkably, without the need to deconvolve instrumental effects on the landscape, such as tether compliance. The same approach was also applied to hairpins with multistate folding pathways. The relative insensitivity of the method to the instrumental compliance was confirmed by simulations of folding measured with different tether stiffnesses. This work confirms that the molecular extension is a good reaction coordinate for these measurements, and validates a powerful yet simple method for reconstructing landscapes from single-molecule trajectories.
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24
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Zhong Z, Soh LH, Lim MH, Chen G. A U⋅U Pair-to-U⋅C Pair Mutation-Induced RNA Native Structure Destabilisation and Stretching-Force-Induced RNA Misfolding. Chempluschem 2015; 80:1267-1278. [PMID: 31973291 DOI: 10.1002/cplu.201500144] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 04/21/2015] [Indexed: 12/21/2022]
Abstract
Little is known about how a non-Watson-Crick pair affects the RNA folding dynamics. We studied the effects of a U⋅U-to-U⋅C pair mutation on the folding of a hairpin in human telomerase RNA. The ensemble thermal melting of the hairpins shows an on-pathway intermediate with the disruption of the internal loop structure containing the U⋅U/U⋅C pairs. By using optical tweezers, we applied a stretching force on the terminal ends of the hairpins to probe directly the non-nearest-neighbour effects upon the mutations. The single U⋅U to U⋅C mutations are observed to 1) lower the mechanical unfolding force by approximately 1 picoNewton (pN) per mutation without affecting the unfolding reaction transition-state position (thus suggesting that removing a single hydrogen bond affects the structural dynamics at least two base pairs away), 2) result in more frequent misfolding into a small hairpin at approximately 10 pN and 3) shift the folding reaction transition-state position towards the native hairpin structure and slightly increase the mechanical folding kinetics (thus suggesting that untrapping from the misfolded state is not the rate-limiting step).
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Affiliation(s)
- Zhensheng Zhong
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore), Fax: (+65) 6791-1961
| | - Lai Huat Soh
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore), Fax: (+65) 6791-1961
| | - Ming Hui Lim
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore), Fax: (+65) 6791-1961
| | - Gang Chen
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore), Fax: (+65) 6791-1961
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25
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Neupane K, Manuel AP, Lambert J, Woodside MT. Transition-Path Probability as a Test of Reaction-Coordinate Quality Reveals DNA Hairpin Folding Is a One-Dimensional Diffusive Process. J Phys Chem Lett 2015; 6:1005-10. [PMID: 26262860 DOI: 10.1021/acs.jpclett.5b00176] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Chemical reactions are typically described in terms of progress along a reaction coordinate. However, the quality of reaction coordinates for describing reaction dynamics is seldom tested experimentally. We applied a framework for gauging reaction-coordinate quality based on transition-path analysis to experimental data for the first time, looking at folding trajectories of single DNA hairpin molecules measured under tension applied by optical tweezers. The conditional probability for being on a reactive transition path was compared with the probability expected for ideal diffusion over a 1D energy landscape based on the committor function. Analyzing measurements and simulations of hairpin folding where end-to-end extension is the reaction coordinate, after accounting for instrumental effects on the analysis, we found good agreement between transition-path and committor analyses for model two-state hairpins, demonstrating that folding is well-described by 1D diffusion. This work establishes transition-path analysis as a powerful new tool for testing experimental reaction-coordinate quality.
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Affiliation(s)
- Krishna Neupane
- †Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, Alberta T6G 2E1, Canada
| | - Ajay P Manuel
- †Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, Alberta T6G 2E1, Canada
| | - John Lambert
- †Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, Alberta T6G 2E1, Canada
| | - Michael T Woodside
- †Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, Alberta T6G 2E1, Canada
- ‡National Institute for Nanotechnology, National Research Council Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
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26
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Alfaro K, Bustos P, O Sullivan C, Conejeros P. Facile and Cost-Effective Detection of Saxitoxin Exploiting Aptamer Structural Switching. Food Technol Biotechnol 2015; 53:337-341. [PMID: 27904366 DOI: 10.17113/ftb.53.03.15.3911] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A simple method to detect saxitoxin (STX), one of the main components of the paralytic shellfish poison from red tide, has been developed. By using a next generation dye for double-stranded DNA we were able to differentiate fluorescence from STX-binding aptamers when exposed to different concentrations of STX, suggesting a change in aptamer folding upon target binding. The developed method is extremely rapid, only requiring small sample volumes, with quantitative results in the concentration range of 15 ng/mL to 3 µg/mL of STX, with a detection limit of 7.5 ng/mL.
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Affiliation(s)
- Karol Alfaro
- Centro de Investigación y Gestión de Recursos Naturales, Facultad de Ciencias,
Universidad de Valparaíso, Gran Bretańa 1111, Valparaíso, Chile
| | - Paulina Bustos
- Centro de Investigación y Gestión de Recursos Naturales, Facultad de Ciencias,
Universidad de Valparaíso, Gran Bretańa 1111, Valparaíso, Chile
| | - Ciara O Sullivan
- Nanobiotechnology and Bioanalysis Group, Department of Chemical Engineering,
Universitat Rovira i Virgili, 43007 ES-Tarragona, Spain
| | - Pablo Conejeros
- Centro de Investigación y Gestión de Recursos Naturales, Facultad de Ciencias,
Universidad de Valparaíso, Gran Bretańa 1111, Valparaíso, Chile
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27
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Engel MC, Ritchie DB, Foster DAN, Beach KSD, Woodside MT. Reconstructing folding energy landscape profiles from nonequilibrium pulling curves with an inverse Weierstrass integral transform. PHYSICAL REVIEW LETTERS 2014; 113:238104. [PMID: 25526163 DOI: 10.1103/physrevlett.113.238104] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Indexed: 05/18/2023]
Abstract
The energy landscapes that drive structure formation in biopolymers are difficult to measure. Here we validate experimentally a novel method to reconstruct landscape profiles from single-molecule pulling curves using an inverse Weierstrass transform (IWT) of the Jarzysnki free-energy integral. The method was applied to unfolding measurements of a DNA hairpin, replicating the results found by the more-established weighted histogram (WHAM) and inverse Boltzmann methods. Applying both WHAM and IWT methods to reconstruct the folding landscape for a RNA pseudoknot having a stiff energy barrier, we found that landscape features with sharper curvature than the force probe stiffness could not be recovered with the IWT method. The IWT method is thus best for analyzing data from stiff force probes such as atomic force microscopes.
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Affiliation(s)
- Megan C Engel
- Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 Canada
| | - Dustin B Ritchie
- Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 Canada
| | - Daniel A N Foster
- Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 Canada
| | - Kevin S D Beach
- Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 Canada and Department of Physics and Astronomy, University of Mississippi, University, Mississippi 38677 USA
| | - Michael T Woodside
- Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 Canada and National Institute for Nanotechnology, National Research Council, Edmonton, Alberta, T6G 2M9 Canada
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28
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Porter EB, Marcano-Velázquez JG, Batey RT. The purine riboswitch as a model system for exploring RNA biology and chemistry. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1839:919-930. [PMID: 24590258 PMCID: PMC4148472 DOI: 10.1016/j.bbagrm.2014.02.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 02/17/2014] [Accepted: 02/20/2014] [Indexed: 12/11/2022]
Abstract
Over the past decade the purine riboswitch, and in particular its nucleobase-binding aptamer domain, has emerged as an important model system for exploring various aspects of RNA structure and function. Its relatively small size, structural simplicity and readily observable activity enable application of a wide variety of experimental approaches towards the study of this RNA. These analyses have yielded important insights into small molecule recognition, co-transcriptional folding and secondary structural switching, and conformational dynamics that serve as a paradigm for other RNAs. In this article, the current state of understanding of the purine riboswitch family and how this growing knowledge base is starting to be exploited in the creation of novel RNA devices are examined. This article is part of a Special Issue entitled: Riboswitches.
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Affiliation(s)
- Ely B Porter
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado, Boulder, CO 80309-0596, USA
| | - Joan G Marcano-Velázquez
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado, Boulder, CO 80309-0596, USA
| | - Robert T Batey
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado, Boulder, CO 80309-0596, USA.
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29
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Abstract
Folding may be described conceptually in terms of trajectories over a landscape of free energies corresponding to different molecular configurations. In practice, energy landscapes can be difficult to measure. Single-molecule force spectroscopy (SMFS), whereby structural changes are monitored in molecules subjected to controlled forces, has emerged as a powerful tool for probing energy landscapes. We summarize methods for reconstructing landscapes from force spectroscopy measurements under both equilibrium and nonequilibrium conditions. Other complementary, but technically less demanding, methods provide a model-dependent characterization of key features of the landscape. Once reconstructed, energy landscapes can be used to study critical folding parameters, such as the characteristic transition times required for structural changes and the effective diffusion coefficient setting the timescale for motions over the landscape. We also discuss issues that complicate measurement and interpretation, including the possibility of multiple states or pathways and the effects of projecting multiple dimensions onto a single coordinate.
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Affiliation(s)
- Michael T Woodside
- Department of Physics, University of Alberta, Edmonton, Alberta T6G2E1, Canada;
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30
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Stephenson W, Wan G, Tenenbaum SA, Li PTX. Nanomanipulation of single RNA molecules by optical tweezers. J Vis Exp 2014. [PMID: 25177917 DOI: 10.3791/51542] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
A large portion of the human genome is transcribed but not translated. In this post genomic era, regulatory functions of RNA have been shown to be increasingly important. As RNA function often depends on its ability to adopt alternative structures, it is difficult to predict RNA three-dimensional structures directly from sequence. Single-molecule approaches show potentials to solve the problem of RNA structural polymorphism by monitoring molecular structures one molecule at a time. This work presents a method to precisely manipulate the folding and structure of single RNA molecules using optical tweezers. First, methods to synthesize molecules suitable for single-molecule mechanical work are described. Next, various calibration procedures to ensure the proper operations of the optical tweezers are discussed. Next, various experiments are explained. To demonstrate the utility of the technique, results of mechanically unfolding RNA hairpins and a single RNA kissing complex are used as evidence. In these examples, the nanomanipulation technique was used to study folding of each structural domain, including secondary and tertiary, independently. Lastly, the limitations and future applications of the method are discussed.
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Affiliation(s)
- William Stephenson
- Nanoscale Engineering Graduate Program, College of Nanoscale Science and Engineering, University at Albany, State University of New York
| | - Gorby Wan
- Nanoscale Science Undergraduate Program, College of Nanoscale Science and Engineering, University at Albany, State University of New York
| | - Scott A Tenenbaum
- Nanobioscience Constellation, College of Nanoscale Science and Engineering, University at Albany, State University of New York; The RNA Institute, University at Albany, State University of New York
| | - Pan T X Li
- The RNA Institute, University at Albany, State University of New York; Department of Biological Sciences, University at Albany, State University of New York;
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31
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Savinov A, Perez CF, Block SM. Single-molecule studies of riboswitch folding. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1839:1030-1045. [PMID: 24727093 DOI: 10.1016/j.bbagrm.2014.04.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 03/27/2014] [Accepted: 04/03/2014] [Indexed: 10/25/2022]
Abstract
The folding dynamics of riboswitches are central to their ability to modulate gene expression in response to environmental cues. In most cases, a structural competition between the formation of a ligand-binding aptamer and an expression platform (or some other competing off-state) determines the regulatory outcome. Here, we review single-molecule studies of riboswitch folding and function, predominantly carried out using single-molecule FRET or optical trapping approaches. Recent results have supplied new insights into riboswitch folding energy landscapes, the mechanisms of ligand binding, the roles played by divalent ions, the applicability of hierarchical folding models, and kinetic vs. thermodynamic control schemes. We anticipate that future work, based on improved data sets and potentially combining multiple experimental techniques, will enable the development of more complete models for complex RNA folding processes. This article is part of a Special Issue entitled: Riboswitches.
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Affiliation(s)
- Andrew Savinov
- Biophysics Program, Stanford University, Stanford, CA 94305, USA
| | | | - Steven M Block
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA.
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32
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Senter E, Dotu I, Clote P. RNA folding pathways and kinetics using 2D energy landscapes. J Math Biol 2014; 70:173-96. [PMID: 24515409 DOI: 10.1007/s00285-014-0760-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Revised: 09/26/2013] [Indexed: 11/27/2022]
Abstract
RNA folding pathways play an important role in various biological processes, such as (i) the hok/sok (host-killing/suppression of killing) system in E. coli to check for sufficient plasmid copy number, (ii) the conformational switch in spliced leader (SL) RNA from Leptomonas collosoma, which controls trans splicing of a portion of the '5 exon, and (iii) riboswitches--portions of the 5' untranslated region of messenger RNA that regulate genes by allostery. Since RNA folding pathways are determined by the energy landscape, we describe a novel algorithm, FFTbor2D, which computes the 2D projection of the energy landscape for a given RNA sequence. Given two metastable secondary structures A, B for a given RNA sequence, FFTbor2D computes the Boltzmann probability p(x, y) = Z(x,y)/Z that a secondary structure has base pair distance x from A and distance y from B. Using polynomial interpolationwith the fast Fourier transform,we compute p(x, y) in O(n(5)) time and O(n(2)) space, which is an improvement over an earlier method, which runs in O(n(7)) time and O(n(4)) space. FFTbor2D has potential applications in synthetic biology, where one might wish to design bistable switches having target metastable structures A, B with favorable pathway kinetics. By inverting the transition probability matrix determined from FFTbor2D output, we show that L. collosoma spliced leader RNA has larger mean first passage time from A to B on the 2D energy landscape, than 97.145% of 20,000 sequences, each having metastable structures A, B. Source code and binaries are freely available for download at http://bioinformatics.bc.edu/clotelab/FFTbor2D. The program FFTbor2D is implemented in C++, with optional OpenMP parallelization primitives.
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Affiliation(s)
- Evan Senter
- Department of Biology, Boston College, Chestnut Hill, MA, 02467, USA
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33
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Anti-frameshifting ligand reduces the conformational plasticity of the SARS virus pseudoknot. J Am Chem Soc 2014; 136:2196-9. [PMID: 24446874 DOI: 10.1021/ja410344b] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Programmed -1 ribosomal frameshifting (-1 PRF) stimulated by mRNA pseudoknots regulates gene expression in many viruses, making pseudoknots potential targets for anti-viral drugs. The mechanism by which pseudoknots trigger -1 PRF, however, remains controversial, with several competing models. Recent work showed that high -1 PRF efficiency was linked to high pseudoknot conformational plasticity via the formation of alternate conformers. We tested whether pseudoknots bound with an anti-frameshifting ligand exhibited a similar correlation between conformational plasticity and -1 PRF efficiency by measuring the effects of a ligand that was found to inhibit -1 PRF in the SARS coronavirus on the conformational dynamics of the SARS pseudoknot. Using single-molecule force spectroscopy to unfold pseudoknots mechanically, we found that the ligand binding effectively abolished the formation of alternate conformers. This result extends the connection between -1 PRF and conformational dynamics and, moreover, suggests that targeting the conformational dynamics of pseudoknots may be an effective strategy for anti-viral drug design.
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34
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Stephenson W, Asare-Okai PN, Chen AA, Keller S, Santiago R, Tenenbaum SA, Garcia AE, Fabris D, Li PTX. The essential role of stacking adenines in a two-base-pair RNA kissing complex. J Am Chem Soc 2013; 135:5602-11. [PMID: 23517345 DOI: 10.1021/ja310820h] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In minimal RNA kissing complexes formed between hairpins with cognate GACG tetraloops, the two tertiary GC pairs are likely stabilized by the stacking of 5'-unpaired adenines at each end of the short helix. To test this hypothesis, we mutated the flanking adenines to various nucleosides and examined their effects on the kissing interaction. Electrospray ionization mass spectrometry was used to detect kissing dimers in a multiequilibria mixture, whereas optical tweezers were applied to monitor the (un)folding trajectories of single RNA molecules. The experimental findings were rationalized by molecular dynamics simulations. Together, the results showed that the stacked adenines are indispensable for the tertiary interaction. By shielding the tertiary base pairs from solvent and reducing their fraying, the stacked adenines made terminal pairs act more like interior base pairs. The purine double-ring of adenine was essential for effective stacking, whereas additional functional groups modulated the stabilizing effects through varying hydrophobic and electrostatic forces. Furthermore, formation of the kissing complex was dominated by base pairing, whereas its dissociation was significantly influenced by the flanking bases. Together, these findings indicate that unpaired flanking nucleotides play essential roles in the formation of otherwise unstable two-base-pair RNA tertiary interactions.
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Affiliation(s)
- William Stephenson
- Nanoscale Engineering Graduate Program, University at Albany, State University of New York, 1400 Washington Avenue, Albany, New York 12222, USA
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35
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Samanta HS, Thirumalai D. Exact solution of the Zwanzig-Lauritzen model of polymer crystallization under tension. J Chem Phys 2013; 138:104901. [DOI: 10.1063/1.4794154] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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36
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Lin JC, Hyeon C, Thirumalai D. RNA under tension: Folding Landscapes, Kinetic partitioning Mechanism, and Molecular Tensegrity. J Phys Chem Lett 2012; 3:3616-3625. [PMID: 23336034 PMCID: PMC3545440 DOI: 10.1021/jz301537t] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Non-coding RNA sequences play a great role in controlling a number of cellular functions, thus raising the need to understand their complex conformational dynamics in quantitative detail. In this perspective, we first show that single molecule pulling when combined with with theory and simulations can be used to quantitatively explore the folding landscape of nucleic acid hairpins, and riboswitches with tertiary interactions. Applications to riboswitches, which are non-coding RNA elements that control gene expression by undergoing dynamical conformational changes in response to binding of metabolites, lead to an organization principle that assembly of RNA is determined by the stability of isolated helices. We also point out the limitations of single molecule pulling experiments, with molecular extension as the only accessible parameter, in extracting key parameters of the folding landscapes of RNA molecules.
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Affiliation(s)
- Jong-Chin Lin
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
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37
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Manghi M, Destainville N, Palmeri J. Mesoscopic models for DNA stretching under force: New results and comparison with experiments. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2012; 35:110. [PMID: 23099534 DOI: 10.1140/epje/i2012-12110-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Revised: 09/21/2012] [Accepted: 09/26/2012] [Indexed: 06/01/2023]
Abstract
Single-molecule experiments on double-stranded B-DNA stretching have revealed one or two structural transitions, when increasing the external force. They are characterized by a sudden increase of DNA contour length and a decrease of the bending rigidity. The nature and the critical forces of these transitions depend on DNA base sequence, loading rate, salt conditions and temperature. It has been proposed that the first transition, at forces of 60-80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA, while the second one, at stronger forces, is a strand peeling resulting in single-stranded DNAs (ssDNA), similar to thermal denaturation. But due to experimental conditions these two transitions can overlap, for instance for poly(dA-dT). In an attempt to propose a coherent picture compatible with this variety of experimental observations, we derive an analytical formula using a coupled discrete worm-like chain-Ising model. Our model takes into account bending rigidity, discreteness of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit of zero force, this model simplifies into a coupled model already developed by us for studying thermal DNA melting, establishing a connection with previous fitting parameter values for denaturation profiles. Our results are summarized as follows: i) ssDNA is fitted, using an analytical formula, over a nano-Newton range with only three free parameters, the contour length, the bending modulus and the monomer size; ii) a surprisingly good fit on this force range is possible only by choosing a monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase length; iii) mesoscopic models are not able to fit B to ssDNA (or S to ss) transitions; iv) an analytical formula for fitting B to S transitions is derived in the strong force approximation and for long DNAs, which is in excellent agreement with exact transfer matrix calculations; v) this formula fits perfectly well poly(dG-dC) and λ-DNA force-extension curves with consistent parameter values; vi) a coherent picture, where S to ssDNA transitions are much more sensitive to base-pair sequence than the B to S one, emerges. This relatively simple model might allow one to further study quantitatively the influence of salt concentration and base-pairing interactions on DNA force-induced transitions.
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Affiliation(s)
- Manoel Manghi
- Laboratoire de Physique Théorique (IRSAMC), Université de Toulouse, UPS, F-31062, Toulouse, France.
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38
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Programmed -1 frameshifting efficiency correlates with RNA pseudoknot conformational plasticity, not resistance to mechanical unfolding. Proc Natl Acad Sci U S A 2012; 109:16167-72. [PMID: 22988073 DOI: 10.1073/pnas.1204114109] [Citation(s) in RCA: 100] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Programmed -1 frameshifting, whereby the reading frame of a ribosome on messenger RNA is shifted in order to generate an alternate gene product, is often triggered by a pseudoknot structure in the mRNA in combination with an upstream slippery sequence. The efficiency of frameshifting varies widely for different sites, but the factors that determine frameshifting efficiency are not yet fully understood. Previous work has suggested that frameshifting efficiency is related to the resistance of the pseudoknot against mechanical unfolding. We tested this hypothesis by studying the mechanical properties of a panel of pseudoknots with frameshifting efficiencies ranging from 2% to 30%: four pseudoknots from retroviruses, two from luteoviruses, one from a coronavirus, and a nonframeshifting bacteriophage pseudoknot. Using optical tweezers to apply tension across the RNA, we measured the distribution of forces required to unfold each pseudoknot. We found that neither the average unfolding force, nor the unfolding kinetics, nor the parameters describing the energy landscape for mechanical unfolding of the pseudoknot (energy barrier height and distance to the transition state) could be correlated to frameshifting efficiency. These results indicate that the resistance of pseudoknots to mechanical unfolding is not a primary determinant of frameshifting efficiency. However, increased frameshifting efficiency was correlated with an increased tendency to form alternate, incompletely folded structures, suggesting a more complex picture of the role of the pseudoknot involving the conformational dynamics.
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39
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Neupane K, Ritchie DB, Yu H, Foster DAN, Wang F, Woodside MT. Transition path times for nucleic Acid folding determined from energy-landscape analysis of single-molecule trajectories. PHYSICAL REVIEW LETTERS 2012; 109:068102. [PMID: 23006308 DOI: 10.1103/physrevlett.109.068102] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Indexed: 06/01/2023]
Abstract
The duration of structural transitions in biopolymers is only a fraction of the time spent searching diffusively over the configurational energy landscape. We found the transition time, τ(TP), and the diffusion constant, D, for DNA and RNA folding using energy landscapes obtained from single-molecule trajectories under tension in optical traps. DNA hairpins, RNA pseudoknots, and a riboswitch all had τ(TP)~10 μs and D~10(-13-14) m(2)/s, despite widely differing unfolding rates. These results show how energy-landscape analysis can be harnessed to characterize brief but critical events during folding reactions.
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Affiliation(s)
- Krishna Neupane
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada
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40
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Abstract
A riboswitch is a non-protein coding sequence capable of directly binding a small molecule effector without the assistance of accessory proteins to regulate expression of the mRNA in which it is embedded. Currently, over 20 different classes of riboswitches have been validated in bacteria with the promise of many more to come, making them an important means of regulating the genome in the bacterial kingdom. Strikingly, half of the known riboswitches recognize effector compounds that contain a purine or related moiety. In the last decade, significant progress has been made to determine how riboswitches specifically recognize these compounds against the background of many other similar cellular metabolites and transduce this signal into a regulatory response. Of the known riboswitches, the purine family containing guanine, adenine and 2'-deoxyguanosine-binding classes are the most extensively studied, serving as a simple and useful paradigm for understanding how these regulatory RNAs function. This review provides a comprehensive summary of the current state of knowledge regarding the structure and mechanism of these riboswitches, as well as insights into how they might be exploited as therapeutic targets and novel biosensors.
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41
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Swoboda M, Henig J, Cheng HM, Brugger D, Haltrich D, Plumeré N, Schlierf M. Enzymatic oxygen scavenging for photostability without pH drop in single-molecule experiments. ACS NANO 2012; 6:6364-9. [PMID: 22703450 PMCID: PMC3403312 DOI: 10.1021/nn301895c] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Accepted: 06/17/2012] [Indexed: 05/18/2023]
Abstract
Over the past years, bottom-up bionanotechnology has been developed as a promising tool for future technological applications. Many of these biomolecule-based assemblies are characterized using various single-molecule techniques that require strict anaerobic conditions. The most common oxygen scavengers for single-molecule experiments are glucose oxidase and catalase (GOC) or protocatechuate dioxygenase (PCD). One of the pitfalls of these systems, however, is the production of carboxylic acids. These acids can result in a significant pH drop over the course of experiments and must thus be compensated by an increased buffer strength. Here, we present pyranose oxidase and catalase (POC) as a novel enzymatic system to perform single-molecule experiments in pH-stable conditions at arbitrary buffer strength. We show that POC keeps the pH stable over hours, while GOC and PCD cause an increasing acidity of the buffer system. We further verify in single-molecule fluorescence experiments that POC performs as good as the common oxygen-scavenging systems, but offers long-term pH stability and more freedom in buffer conditions. This enhanced stability allows the observation of bionanotechnological assemblies in aqueous environments under well-defined conditions for an extended time.
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Affiliation(s)
- Marko Swoboda
- B CUBE, Center for Molecular Bioengineering, Technische Universität Dresden, Arnoldstraße 18, 01307 Dresden, Germany
| | - Jörg Henig
- Center for Electrochemical Sciences, CES, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Hsin-Mei Cheng
- B CUBE, Center for Molecular Bioengineering, Technische Universität Dresden, Arnoldstraße 18, 01307 Dresden, Germany
| | - Dagmar Brugger
- Food Biotechnology Laboratory, University of Natural Resources and Life Sciences Vienna, Muthgasse 18, 1190 Vienna, Austria
| | - Dietmar Haltrich
- Food Biotechnology Laboratory, University of Natural Resources and Life Sciences Vienna, Muthgasse 18, 1190 Vienna, Austria
| | - Nicolas Plumeré
- Center for Electrochemical Sciences, CES, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
- E-mail: ,
| | - Michael Schlierf
- B CUBE, Center for Molecular Bioengineering, Technische Universität Dresden, Arnoldstraße 18, 01307 Dresden, Germany
- E-mail: ,
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42
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Yangyuoru PM, Dhakal S, Yu Z, Koirala D, Mwongela SM, Mao H. Single-molecule measurements of the binding between small molecules and DNA aptamers. Anal Chem 2012; 84:5298-303. [PMID: 22702719 DOI: 10.1021/ac300427d] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Aptamers that bind small molecules can serve as basic biosensing platforms. Evaluation of the binding constant between an aptamer and a small molecule helps to determine the effectiveness of the aptamer-based sensors. Binding constants are often measured by a series of experiments with varying ligand or aptamer concentrations. Such experiments are time-consuming, material nonprudent, and prone to low reproducibility. Here, we use laser tweezers to determine the dissociation constant for aptamer-ligand interactions at the single-molecule level from only one ligand concentration. Using an adenosine 5'-triphosphate disodium salt (ATP) binding aptamer as an example, we have observed that the mechanical stabilities of aptamers bound with ATP are higher than those without a ligand. Comparison of the change in free energy of unfolding (ΔG(unfold)) between these two aptamers yields a ΔG of 33 ± 4 kJ/mol for the binding. By applying a Hess-like cycle at room temperature, we obtained a dissociation constant (K(d)) of 2.0 ± 0.2 μM, a value consistent with the K(d) obtained from our equilibrated capillary electrophoresis (CE) (2.4 ± 0.4 μM) and close to that determined by affinity chromatography in the literature (6 ± 3 μM). We anticipate that our laser tweezers and CE methodologies may be used to more conveniently evaluate the binding between receptors and ligands and also serve as analytical tools for force-based biosensing.
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Affiliation(s)
- Philip M Yangyuoru
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, USA
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43
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Hengesbach M, Akiyama BM, Stone MD. Single-molecule analysis of telomerase structure and function. Curr Opin Chem Biol 2011; 15:845-52. [PMID: 22057212 DOI: 10.1016/j.cbpa.2011.10.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 10/05/2011] [Accepted: 10/17/2011] [Indexed: 02/06/2023]
Abstract
The telomerase ribonucleoprotein is a specialized reverse transcriptase required to maintain protective chromosome end-capping structures called telomeres. In most cells, telomerase is not active and the natural shortening of telomeres with each round of DNA replication ultimately triggers cell growth arrest. In contrast, the presence of telomerase confers a high level of renewal capacity upon rapidly dividing cells. Telomerase is aberrantly activated in 90% of human cancers and thus represents an important target for anticancer therapeutics. However, the naturally low abundance of telomerase has hampered efforts to obtain high-resolution models for telomerase structure and function. To circumvent these challenges, single-molecule techniques have recently been employed to investigate telomerase assembly, structure, and catalysis.
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Affiliation(s)
- Martin Hengesbach
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA
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44
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Hoffmann A, Woodside MT. Signalpaar-Korrelationsanalyse von Einzelmolekültrajektorien. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201104033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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45
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Hoffmann A, Woodside MT. Signal-Pair Correlation Analysis of Single-Molecule Trajectories. Angew Chem Int Ed Engl 2011; 50:12643-6. [DOI: 10.1002/anie.201104033] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2011] [Revised: 09/20/2011] [Indexed: 11/05/2022]
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46
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McCauley MJ, Williams MC. Untying a nanoscale knot. Nat Chem 2011; 3:754-5. [DOI: 10.1038/nchem.1159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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47
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Heus HA, Puchner EM, van Vugt-Jonker AJ, Zimmermann JL, Gaub HE. Atomic force microscope-based single-molecule force spectroscopy of RNA unfolding. Anal Biochem 2011; 414:1-6. [DOI: 10.1016/j.ab.2011.03.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Revised: 03/07/2011] [Accepted: 03/08/2011] [Indexed: 01/28/2023]
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48
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Neupane K, Yu H, Foster DAN, Wang F, Woodside MT. Single-molecule force spectroscopy of the add adenine riboswitch relates folding to regulatory mechanism. Nucleic Acids Res 2011; 39:7677-87. [PMID: 21653559 PMCID: PMC3177178 DOI: 10.1093/nar/gkr305] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Riboswitches regulate gene expression via ligand binding to an aptamer domain which induces conformational changes in a regulatory expression platform. By unfolding and refolding single add adenine riboswitch molecules in an optical trap, an integrated picture of the folding was developed and related to the regulatory mechanism. Force-extension curves (FECs) and constant-force folding trajectories measured on the aptamer alone revealed multiple partially-folded states, including several misfolded states not on the native folding pathway. All states were correlated to key structural components and interactions within hierarchical folding pathways. FECs of the full-length riboswitch revealed that the thermodynamically stable conformation switches upon ligand binding from a structure repressing translation to one permitting it. Along with rapid equilibration of the two structures in the absence of adenine, these results support a thermodynamically-controlled regulatory mechanism, in contrast with the kinetic control of the closely-related pbuE adenine riboswitch. Comparison of the folding of these riboswitches revealed many similarities arising from shared structural features but also essential differences related to their different regulatory mechanisms.
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Affiliation(s)
- Krishna Neupane
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada
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49
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Chapagain PP, Gerstman BS, Bhandari YR, Rimal D. Free-energy landscapes and thermodynamic parameters of complex molecules from nonequilibrium simulation trajectories. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:061905. [PMID: 21797401 DOI: 10.1103/physreve.83.061905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Revised: 12/20/2010] [Indexed: 05/31/2023]
Abstract
Thermodynamic parameters such as free energies and heat capacities are important quantities for understanding processes involving structural transitions in complex molecules such as proteins. Computational investigations provide simulated data that can be used for calculating thermodynamic parameters. However, calculations give accurate results only if the simulations sample all of configuration space with the appropriate temperature-dependent Boltzmann equilibrium probabilities. For many systems, truly comprehensive sampling of configuration space is not computationally feasible. We present an approximation technique for the calculations that will give accurate values for thermodynamic parameters when the data is incomplete. Our work is applicable to systems in which there are two distinct, important regions of configuration space that must be sampled. Importantly, the results are also valid when the system is more complex than two-state systems. Transition pathways that involve intermediate configurations between two stable regions are allowed in this treatment, and therefore the results are valid for multistate systems.
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Affiliation(s)
- Prem P Chapagain
- Department of Physics, Florida International University, Miami, Florida 33199, USA.
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Nir G, Lindner M, Dietrich HRC, Girshevitz O, Vorgias CE, Garini Y. HU protein induces incoherent DNA persistence length. Biophys J 2011; 100:784-790. [PMID: 21281594 DOI: 10.1016/j.bpj.2010.12.3687] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 11/24/2010] [Accepted: 12/02/2010] [Indexed: 11/29/2022] Open
Abstract
HU is a highly conserved protein that is believed to play an important role in the architecture and dynamic compaction of bacterial DNA. Its ability to control DNA bending is crucial for functions such as transcription and replication. The effects of HU on the DNA structure have been studied so far mainly by single molecule methods that require us to apply stretching forces on the DNA and therefore may perturb the DNA-protein interaction. To overcome this hurdle, we study the effect of HU on the DNA structure without applying external forces by using an improved tethered particle motion method. By combining the results with DNA curvature analysis from atomic force microscopy measurements we find that the DNA consists of two different curvature distributions and the measured persistence length is determined by their interplay. As a result, the effective persistence length adopts a bimodal property that depends primarily on the HU concentration. The results can be explained according to a recently suggested model that distinguishes single protein binding from cooperative protein binding.
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Affiliation(s)
- Guy Nir
- Physics Department, Bar Ilan University, Ramat-Gan, Israel; Institute for Nanotechnology, Bar Ilan University, Ramat-Gan, Israel
| | - Moshe Lindner
- Physics Department, Bar Ilan University, Ramat-Gan, Israel; Institute for Nanotechnology, Bar Ilan University, Ramat-Gan, Israel
| | - Heidelinde R C Dietrich
- Department of Imaging Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Olga Girshevitz
- Institute for Nanotechnology, Bar Ilan University, Ramat-Gan, Israel
| | - Constantinos E Vorgias
- Department of Biochemistry and Molecular Biology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Yuval Garini
- Physics Department, Bar Ilan University, Ramat-Gan, Israel; Institute for Nanotechnology, Bar Ilan University, Ramat-Gan, Israel.
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