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Haldar S, Kührová P, Banáš P, Spiwok V, Šponer J, Hobza P, Otyepka M. Insights into Stability and Folding of GNRA and UNCG Tetraloops Revealed by Microsecond Molecular Dynamics and Well-Tempered Metadynamics. J Chem Theory Comput 2016; 11:3866-77. [PMID: 26574468 DOI: 10.1021/acs.jctc.5b00010] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
RNA hairpins capped by 5'-GNRA-3' or 5'-UNCG-3' tetraloops (TLs) are prominent RNA structural motifs. Despite their small size, a wealth of experimental data, and recent progress in theoretical simulations of their structural dynamics and folding, our understanding of the folding and unfolding processes of these small RNA elements is still limited. Theoretical description of the folding and unfolding processes requires robust sampling, which can be achieved by either an exhaustive time scale in standard molecular dynamics simulations or sophisticated enhanced sampling methods, using temperature acceleration or biasing potentials. Here, we study structural dynamics of 5'-GNRA-3' and 5'-UNCG-3' TLs by 15-μs-long standard simulations and a series of well-tempered metadynamics, attempting to accelerate sampling by bias in a few chosen collective variables (CVs). Both methods provide useful insights. The unfolding and refolding mechanisms of the GNRA TL observed by well-tempered metadynamics agree with the (reverse) folding mechanism suggested by recent replica exchange molecular dynamics simulations. The orientation of the glycosidic bond of the GL4 nucleobase is critical for the UUCG TL folding pathway, and our data strongly support the hypothesis that GL4-anti forms a kinetic trap along the folding pathway. Along with giving useful insight, our study also demonstrates that using only a few CVs apparently does not capture the full folding landscape of the RNA TLs. Despite using several sophisticated selections of the CVs, formation of the loop appears to remain a hidden variable, preventing a full convergence of the metadynamics. Finally, our data suggest that the unfolded state might be overstabilized by the force fields used.
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Affiliation(s)
- Susanta Haldar
- Institute of Organic Chemistry and Biochemistry and Gilead Science Research Center, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.,Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague , Albertov 6, 128 43 Prague 2, Czech Republic
| | - Petra Kührová
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc , tř. 17. Listopadu 12, 771 46 Olomouc, Czech Republic
| | - Pavel Banáš
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc , tř. 17. Listopadu 12, 771 46 Olomouc, Czech Republic
| | - Vojtěch Spiwok
- Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague , Technická 3, 166 28 Prague 6, Czech Republic
| | - Jiří Šponer
- Institute of Biophysics, Academy of Sciences of the Czech Republic , Královopolská 135, 612 65 Brno, Czech Republic
| | - Pavel Hobza
- Institute of Organic Chemistry and Biochemistry and Gilead Science Research Center, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.,Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc , tř. 17. Listopadu 12, 771 46 Olomouc, Czech Republic
| | - Michal Otyepka
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc , tř. 17. Listopadu 12, 771 46 Olomouc, Czech Republic
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52
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Imai S, Kumar P, Hellen CUT, D'Souza VM, Wagner G. An accurately preorganized IRES RNA structure enables eIF4G capture for initiation of viral translation. Nat Struct Mol Biol 2016; 23:859-64. [PMID: 27525590 DOI: 10.1038/nsmb.3280] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 07/21/2016] [Indexed: 02/06/2023]
Abstract
Many viruses bypass canonical cap-dependent translation in host cells by using internal ribosomal entry sites (IRESs) in their transcripts; IRESs hijack initiation factors for the assembly of initiation complexes. However, it is currently unknown how IRES RNAs recognize initiation factors that have no endogenous RNA binding partners; in a prominent example, the IRES of encephalomyocarditis virus (EMCV) interacts with the HEAT-1 domain of eukaryotic initiation factor 4G (eIF4G). Here we report the solution structure of the J-K region of this IRES and show that its stems are precisely organized to position protein-recognition bulges. This multisite interaction mechanism operates on an all-or-nothing principle in which all domains are required. This preorganization is accomplished by an 'adjuster module': a pentaloop motif that acts as a dual-sided docking station for base-pair receptors. Because subtle changes in the orientation abrogate protein capture, our study highlights how a viral RNA acquires affinity for a target protein.
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Affiliation(s)
- Shunsuke Imai
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Parimal Kumar
- Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York, USA
| | | | - Victoria M D'Souza
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
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53
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Asnani M, Pestova TV, Hellen CUT. PCBP2 enables the cadicivirus IRES to exploit the function of a conserved GRNA tetraloop to enhance ribosomal initiation complex formation. Nucleic Acids Res 2016; 44:9902-9917. [PMID: 27387282 PMCID: PMC5175331 DOI: 10.1093/nar/gkw609] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 06/24/2016] [Accepted: 06/24/2016] [Indexed: 12/22/2022] Open
Abstract
The cadicivirus IRES diverges structurally from canonical Type 1 IRESs (e.g. poliovirus) but nevertheless also contains an essential GNRA tetraloop in a subdomain (d10c) that is homologous to poliovirus dIVc. In addition to canonical initiation factors, the canonical Type 1 and divergent cadicivirus IRESs require the same IRES trans-acting factor, poly(C)-binding protein 2 (PCBP2). PCBP2 has three KH domains and binds poliovirus IRES domain dIV in the vicinity of the tetraloop. How PCBP2 binds the cadicivirus IRES, and the roles of PCBP2 and the tetraloop in Type 1 IRES function are unknown. Here, directed hydroxyl radical probing showed that KH1 also binds near the cadicivirus tetraloop. KH2 and KH3 bind adjacently to an IRES subdomain (d10b) that is unrelated to dIV, with KH3 in an inverted orientation. KH3 is critical for PCBP2's binding to this IRES whereas KH1 is essential for PCBP2's function in promoting initiation. PCBP2 enforced the wild-type structure of d10c when it contained minor destabilizing substitutions, exposing the tetraloop. Strikingly, PCBP2 enhanced initiation on mutant IRESs that retained consensus GNRA tetraloops, whereas mutants with divergent sequences did not respond to PCBP2. These studies show that PCBP2 enables the IRES to exploit the GNRA tetraloop to enhance initiation.
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Affiliation(s)
- Mukta Asnani
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC 44, Brooklyn, NY 11203, USA
| | - Tatyana V Pestova
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC 44, Brooklyn, NY 11203, USA
| | - Christopher U T Hellen
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC 44, Brooklyn, NY 11203, USA
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D'Ascenzo L, Leonarski F, Vicens Q, Auffinger P. 'Z-DNA like' fragments in RNA: a recurring structural motif with implications for folding, RNA/protein recognition and immune response. Nucleic Acids Res 2016; 44:5944-56. [PMID: 27151194 PMCID: PMC4937326 DOI: 10.1093/nar/gkw388] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 04/28/2016] [Indexed: 01/09/2023] Open
Abstract
Since the work of Alexander Rich, who solved the first Z-DNA crystal structure, we have known that d(CpG) steps can adopt a particular structure that leads to forming left-handed helices. However, it is still largely unrecognized that other sequences can adopt ‘left-handed’ conformations in DNA and RNA, in double as well as single stranded contexts. These ‘Z-like’ steps involve the coexistence of several rare structural features: a C2’-endo puckering, a syn nucleotide and a lone pair–π stacking between a ribose O4’ atom and a nucleobase. This particular arrangement induces a conformational stress in the RNA backbone, which limits the occurrence of Z-like steps to ≈0.1% of all dinucleotide steps in the PDB. Here, we report over 600 instances of Z-like steps, which are located within r(UNCG) tetraloops but also in small and large RNAs including riboswitches, ribozymes and ribosomes. Given their complexity, Z-like steps are probably associated with slow folding kinetics and once formed could lock a fold through the formation of unique long-range contacts. Proteins involved in immunologic response also specifically recognize/induce these peculiar folds. Thus, characterizing the conformational features of these motifs could be a key to understanding the immune response at a structural level.
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Affiliation(s)
- Luigi D'Ascenzo
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg 67084, France
| | - Filip Leonarski
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg 67084, France Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Quentin Vicens
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg 67084, France
| | - Pascal Auffinger
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg 67084, France
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Mustoe AM, Al-Hashimi HM, Brooks CL. Secondary structure encodes a cooperative tertiary folding funnel in the Azoarcus ribozyme. Nucleic Acids Res 2015; 44:402-12. [PMID: 26481360 PMCID: PMC4705646 DOI: 10.1093/nar/gkv1055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Accepted: 10/03/2015] [Indexed: 12/20/2022] Open
Abstract
A requirement for specific RNA folding is that the free-energy landscape discriminate against non-native folds. While tertiary interactions are critical for stabilizing the native fold, they are relatively non-specific, suggesting additional mechanisms contribute to tertiary folding specificity. In this study, we use coarse-grained molecular dynamics simulations to explore how secondary structure shapes the tertiary free-energy landscape of the Azoarcus ribozyme. We show that steric and connectivity constraints posed by secondary structure strongly limit the accessible conformational space of the ribozyme, and that these so-called topological constraints in turn pose strong free-energy penalties on forming different tertiary contacts. Notably, native A-minor and base-triple interactions form with low conformational free energy, while non-native tetraloop/tetraloop–receptor interactions are penalized by high conformational free energies. Topological constraints also give rise to strong cooperativity between distal tertiary interactions, quantitatively matching prior experimental measurements. The specificity of the folding landscape is further enhanced as tertiary contacts place additional constraints on the conformational space, progressively funneling the molecule to the native state. These results indicate that secondary structure assists the ribozyme in navigating the otherwise rugged tertiary folding landscape, and further emphasize topological constraints as a key force in RNA folding.
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Affiliation(s)
- Anthony M Mustoe
- Department of Biophysics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Hashim M Al-Hashimi
- Department of Biochemistry and Chemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Charles L Brooks
- Department of Biophysics, University of Michigan, Ann Arbor, MI 48109, USA Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
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56
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Salmon L, Giambaşu GM, Nikolova EN, Petzold K, Bhattacharya A, Case DA, Al-Hashimi HM. Modulating RNA Alignment Using Directional Dynamic Kinks: Application in Determining an Atomic-Resolution Ensemble for a Hairpin using NMR Residual Dipolar Couplings. J Am Chem Soc 2015; 137:12954-65. [PMID: 26306428 PMCID: PMC4748170 DOI: 10.1021/jacs.5b07229] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Approaches that combine experimental data and computational molecular dynamics (MD) to determine atomic resolution ensembles of biomolecules require the measurement of abundant experimental data. NMR residual dipolar couplings (RDCs) carry rich dynamics information, however, difficulties in modulating overall alignment of nucleic acids have limited the ability to fully extract this information. We present a strategy for modulating RNA alignment that is based on introducing variable dynamic kinks in terminal helices. With this strategy, we measured seven sets of RDCs in a cUUCGg apical loop and used this rich data set to test the accuracy of an 0.8 μs MD simulation computed using the Amber ff10 force field as well as to determine an atomic resolution ensemble. The MD-generated ensemble quantitatively reproduces the measured RDCs, but selection of a sub-ensemble was required to satisfy the RDCs within error. The largest discrepancies between the RDC-selected and MD-generated ensembles are observed for the most flexible loop residues and backbone angles connecting the loop to the helix, with the RDC-selected ensemble resulting in more uniform dynamics. Comparison of the RDC-selected ensemble with NMR spin relaxation data suggests that the dynamics occurs on the ps-ns time scales as verified by measurements of R(1ρ) relaxation-dispersion data. The RDC-satisfying ensemble samples many conformations adopted by the hairpin in crystal structures indicating that intrinsic plasticity may play important roles in conformational adaptation. The approach presented here can be applied to test nucleic acid force fields and to characterize dynamics in diverse RNA motifs at atomic resolution.
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Affiliation(s)
- Loïc Salmon
- Department of Molecular, Cellular, and Developmental Biology and Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan, USA
| | - George M. Giambaşu
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, USA
| | - Evgenia N. Nikolova
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Katja Petzold
- Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden
| | | | - David A. Case
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, USA
| | - Hashim M. Al-Hashimi
- Department of Biochemistry and Chemistry, Duke University School of Medicine, Durham, North Carolina, USA
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57
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Herschlag D, Allred BE, Gowrishankar S. From static to dynamic: the need for structural ensembles and a predictive model of RNA folding and function. Curr Opin Struct Biol 2015; 30:125-133. [PMID: 25744941 DOI: 10.1016/j.sbi.2015.02.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 02/11/2015] [Accepted: 02/11/2015] [Indexed: 12/18/2022]
Abstract
To understand RNA, it is necessary to move beyond a descriptive categorization towards quantitative predictions of its molecular conformations and functional behavior. An incisive approach to understanding the function and folding of biological RNA systems involves characterizing small, simple components that are largely responsible for the behavior of complex systems including helix-junction-helix elements and tertiary motifs. State-of-the-art methods have permitted unprecedented insight into the conformational ensembles of these elements revealing, for example, that conformations of helix-junction-helix elements are confined to a small region of the ensemble, that this region is highly dependent on the junction's topology, and that the correct alignment of tertiary motifs may be a rare conformation on the overall folding landscape. Further characterization of RNA components and continued development of experimental and computational methods with the goal of quantitatively predicting RNA folding and functional behavior will be critical to understanding biological RNA systems.
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Affiliation(s)
- Daniel Herschlag
- Department of Biochemistry, Beckman Center, B400, 279 W. Campus Dr. MC: 5307, Stanford University, Stanford, CA 94305, USA; Department of Chemistry, 333 Campus Drive, Mudd Building, Room 121, Stanford University, Stanford, CA 94305, USA; Department of Chemical Engineering, 443 Via Ortega, Room 129, Stanford University, Stanford, CA 94305, USA.
| | - Benjamin E Allred
- Department of Biochemistry, Beckman Center, B400, 279 W. Campus Dr. MC: 5307, Stanford University, Stanford, CA 94305, USA
| | - Seshadri Gowrishankar
- Department of Chemical Engineering, 443 Via Ortega, Room 129, Stanford University, Stanford, CA 94305, USA
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Holmstrom ED, Dupuis NF, Nesbitt DJ. Kinetic and thermodynamic origins of osmolyte-influenced nucleic acid folding. J Phys Chem B 2015; 119:3687-96. [PMID: 25621404 DOI: 10.1021/jp512491n] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The influential role of monovalent and divalent metal cations in facilitating conformational transitions in both RNA and DNA has been a target of intense biophysical research efforts. However, organic neutrally charged cosolutes can also significantly alter nucleic acid conformational transitions. For example, highly soluble small molecules such as trimethylamine N-oxide (TMAO) and urea are occasionally utilized by organisms to regulate cellular osmotic pressure. Ensemble studies have revealed that these so-called osmolytes can substantially influence the thermodynamics of nucleic acid conformational transitions. In the present work, we exploit single-molecule FRET (smFRET) techniques to measure, for first time, the kinetic origins of these osmolyte-induced changes to the folding free energy. In particular, we focus on smFRET RNA and DNA constructs designed as model systems for secondary and tertiary structure formation. These findings reveal that TMAO preferentially stabilizes both secondary and tertiary interactions by increasing kfold and decreasing kunfold, whereas urea destabilizes both conformational transitions, resulting in the exact opposite shift in kinetic rate constants (i.e., decreasing kfold and increasing kunfold). Complementary temperature-dependent smFRET experiments highlight a thermodynamic distinction between the two different mechanisms responsible for TMAO-facilitated conformational transitions, while only a single mechanism is seen for the destabilizing osmolyte urea. Finally, these results are interpreted in the context of preferential interactions between osmolytes, and the solvent accessible surface area (SASA) associated with the (i) nucleobase, (ii) sugar, and (iii) phosphate groups of nucleic acids in order to map out structural changes that occur during the conformational transitions.
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Affiliation(s)
- Erik D Holmstrom
- JILA, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0440, United States
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Devi G, Zhou Y, Zhong Z, Toh DFK, Chen G. RNA triplexes: from structural principles to biological and biotech applications. WILEY INTERDISCIPLINARY REVIEWS-RNA 2014; 6:111-28. [DOI: 10.1002/wrna.1261] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 06/30/2014] [Accepted: 07/14/2014] [Indexed: 12/29/2022]
Affiliation(s)
- Gitali Devi
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore Singapore
| | - Yuan Zhou
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore Singapore
| | - Zhensheng Zhong
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore Singapore
| | - Desiree-Faye Kaixin Toh
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore Singapore
| | - Gang Chen
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore Singapore
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