51
|
Choi YJ, Gibala KS, Ayele T, Deventer KV, Resendiz MJE. Biophysical properties, thermal stability and functional impact of 8-oxo-7,8-dihydroguanine on oligonucleotides of RNA-a study of duplex, hairpins and the aptamer for preQ1 as models. Nucleic Acids Res 2017; 45:2099-2111. [PMID: 28426093 PMCID: PMC5389535 DOI: 10.1093/nar/gkw885] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 09/22/2016] [Indexed: 01/12/2023] Open
Abstract
A better understanding of the effects that oxidative lesions have on RNA is of importance to understand their role in the development/progression of disease. 8-oxo-7,8-dihydroguanine was incorporated into RNA to understand its structural and functional impact on RNA:RNA and RNA:DNA duplexes, hairpins and pseudoknots. One to three modifications were incorporated into dodecamers of RNA [AAGAGGGAUGAC] resulting in thermal destabilization (ΔTm – 10°C per lesion). Hairpins with tetraloops c-UUCG*-g* (8-10), a-ACCG-g* (11-12), c-UUG*G*-g* (13-16) and c-ACG*G*-g* (17-20) were modified and used to determine thermal stabilities, concluding that: (i) modifying the stem leads to destabilization unless adenosine is the opposing basepair of 8-oxoGua; (ii) modification at the loop is position- and sequence-dependent and varies from slight stabilization to large destabilization, in some cases leading to formation of other secondary structures (hairpin→duplex). Functional effects were established using the aptamer for preQ1 as model. Modification at G5 disrupted the stem P1 and inhibited recognition of the target molecule 7-methylamino-7-deazaguanine (preQ1). Modifying G11 results in increased thermal stability, albeit with a Kd 4-fold larger than its canonical analog. These studies show the capability of 8-oxoG to affect structure and function of RNA, resulting in distinct outcomes as a function of number and position of the lesion.
Collapse
Affiliation(s)
- Yu J Choi
- Department of Chemistry, University of Colorado Denver, Science Building 1151 Arapahoe St, Denver, CO 80204, USA
| | - Krzysztof S Gibala
- Department of Chemistry, University of Colorado Denver, Science Building 1151 Arapahoe St, Denver, CO 80204, USA
| | - Tewoderos Ayele
- Department of Chemistry, University of Colorado Denver, Science Building 1151 Arapahoe St, Denver, CO 80204, USA
| | - Katherine V Deventer
- Department of Chemistry, University of Colorado Denver, Science Building 1151 Arapahoe St, Denver, CO 80204, USA
| | - Marino J E Resendiz
- Department of Chemistry, University of Colorado Denver, Science Building 1151 Arapahoe St, Denver, CO 80204, USA
| |
Collapse
|
52
|
Stagno JR, Bhandari YR, Conrad CE, Liu Y, Wang YX. Real-time crystallographic studies of the adenine riboswitch using an X-ray free-electron laser. FEBS J 2017; 284:3374-3380. [PMID: 28504865 DOI: 10.1111/febs.14110] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 04/27/2017] [Accepted: 05/12/2017] [Indexed: 11/26/2022]
Abstract
Structures of the four reaction states of the adenine riboswitch aptamer domain, including a transient intermediate state were solved by serial femtosecond crystallography. The structures not only demonstrate the use of X-ray free-electron lasers for RNA crystallography but have also proven that transient states can be determined in real time by mix-and-inject crystallography. These results illustrate the structural basis for the ligand-induced conformational changes associated with the molecular 'switch'.
Collapse
Affiliation(s)
- Jason R Stagno
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD, USA
| | - Yuba R Bhandari
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD, USA
| | - Chelsie E Conrad
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD, USA
| | - Yu Liu
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD, USA
| | - Yun-Xing Wang
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD, USA
| |
Collapse
|
53
|
An excited state underlies gene regulation of a transcriptional riboswitch. Nat Chem Biol 2017; 13:968-974. [PMID: 28719589 PMCID: PMC5562522 DOI: 10.1038/nchembio.2427] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 05/22/2017] [Indexed: 11/08/2022]
Abstract
Riboswitches control gene expression through ligand-dependent structural rearrangements of the sensing aptamer domain. However, we found that the Bacillus cereus fluoride riboswitch aptamer adopts identical tertiary structures in solution with and without ligand. Using chemical-exchange saturation transfer (CEST) NMR spectroscopy, we revealed that the structured ligand-free aptamer transiently accesses a low-populated (∼1%) and short-lived (∼3 ms) excited conformational state that unravels a conserved 'linchpin' base pair to signal transcription termination. Upon fluoride binding, this highly localized, fleeting process is allosterically suppressed, which activates transcription. We demonstrated that this mechanism confers effective fluoride-dependent gene activation over a wide range of transcription rates, which is essential for robust toxicity responses across diverse cellular conditions. These results unveil a novel switching mechanism that employs ligand-dependent suppression of an aptamer excited state to coordinate regulatory conformational transitions rather than adopting distinct aptamer ground-state tertiary architectures, exemplifying a new mode of ligand-dependent RNA regulation.
Collapse
|
54
|
Jones CP, Ferré-D'Amaré AR. Long-Range Interactions in Riboswitch Control of Gene Expression. Annu Rev Biophys 2017; 46:455-481. [PMID: 28375729 DOI: 10.1146/annurev-biophys-070816-034042] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Riboswitches are widespread RNA motifs that regulate gene expression in response to fluctuating metabolite concentrations. Known primarily from bacteria, riboswitches couple specific ligand binding and changes in RNA structure to mRNA expression in cis. Crystal structures of the ligand binding domains of most of the phylogenetically widespread classes of riboswitches, each specific to a particular metabolite or ion, are now available. Thus, the bound states-one end point-have been thoroughly characterized, but the unbound states have been more elusive. Consequently, it is less clear how the unbound, sensing riboswitch refolds into the ligand binding-induced output state. The ligand recognition mechanisms of riboswitches are diverse, but we find that they share a common structural strategy in positioning their binding sites at the point of the RNA three-dimensional fold where the residues farthest from one another in sequence meet. We review how riboswitch folds adhere to this fundamental strategy and propose future research directions for understanding and harnessing their ability to specifically control gene expression.
Collapse
Affiliation(s)
- Christopher P Jones
- Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20824;
| | - Adrian R Ferré-D'Amaré
- Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20824;
| |
Collapse
|
55
|
Characterization of Engineered PreQ1 Riboswitches for Inducible Gene Regulation in Mycobacteria. J Bacteriol 2017; 199:JB.00656-16. [PMID: 28069821 DOI: 10.1128/jb.00656-16] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 01/03/2017] [Indexed: 11/20/2022] Open
Abstract
We report here the behavior of naturally occurring and rationally engineered preQ1 riboswitches and their application to inducible gene regulation in mycobacteria. Because mycobacteria lack preQ1 biosynthetic genes, we hypothesized that preQ1 could be used as an exogenous nonmetabolite ligand to control riboswitches in mycobacteria. Selected naturally occurring preQ1 riboswitches were assayed and successfully drove preQ1-dependent repression of a green fluorescent protein reporter in Mycobacterium smegmatis Using structure-based design, we engineered three preQ1 riboswitches from Thermoanaerobacter tencongensis, Bacillus subtilis, and Lactobacillus rhamnosus toward achieving higher response ratios and increased repression. Assuming a steady-state model, variants of the T. tencongensis riboswitch most closely followed the predicted trends. Unexpectedly, the preQ1 dose response was best described by a model with a second, independent preQ1 binding site. This behavior was general to the preQ1 riboswitch family, since the wild type and rationally designed mutants of riboswitches from all three bacteria behaved analogously. Across all variants, the response ratios, which describe expression in the absence versus the presence of preQ1, ranged from <2 to ∼10, but repression in all cases was incomplete up to 1 mM preQ1. By reducing the transcript expression level, we obtained a preQ1 riboswitch variant appropriate for inducible knockdown applications. We further showed that the preQ1 response is reversible, is titratable, and can be used to control protein expression in mycobacteria within infected macrophages. By engineering naturally occurring preQ1 riboswitches, we have not only extended the tools available for inducible gene regulation in mycobacteria but also uncovered new behavior of these riboswitches.IMPORTANCE Riboswitches are elements found in noncoding regions of mRNA that regulate gene expression, typically in response to an endogenous metabolite. Riboswitches have emerged as important tools for inducible gene expression in diverse organisms. We noted that mycobacteria lack the biosynthesis genes for preQ1, a ligand for riboswitches from diverse bacteria. Predicting that preQ1 is not present in mycobacteria, we showed that it controls optimized riboswitches appropriate for gene knockdown applications. Further, the riboswitch response is subject to a second independent preQ1 binding event that has not been previously documented. By engineering naturally occurring riboswitches, we have uncovered a new behavior, with implications for riboswitch function in its native context, and extended the tools available for inducible gene regulation in mycobacteria.
Collapse
|
56
|
Structure-Based Discovery of Small Molecules Binding to RNA. TOPICS IN MEDICINAL CHEMISTRY 2017. [DOI: 10.1007/7355_2016_29] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
|
57
|
Moschen T, Grutsch S, Juen MA, Wunderlich CH, Kreutz C, Tollinger M. Measurement of Ligand-Target Residence Times by 1H Relaxation Dispersion NMR Spectroscopy. J Med Chem 2016; 59:10788-10793. [PMID: 27933946 PMCID: PMC5150660 DOI: 10.1021/acs.jmedchem.6b01110] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
![]()
A ligand-observed 1H NMR
relaxation experiment is introduced
for measuring the binding kinetics of low-molecular-weight compounds
to their biomolecular targets. We show that this approach, which does
not require any isotope labeling, is applicable to ligand–target
systems involving proteins and nucleic acids of variable molecular
size. The experiment is particularly useful for the systematic investigation
of low affinity molecules with residence times in the micro- to millisecond
time regime.
Collapse
Affiliation(s)
- Thomas Moschen
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| | - Sarina Grutsch
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| | - Michael A Juen
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| | - Christoph H Wunderlich
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| | - Christoph Kreutz
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| | - Martin Tollinger
- Institute of Organic Chemistry and Centre for Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck 6020, Austria
| |
Collapse
|
58
|
Structures of riboswitch RNA reaction states by mix-and-inject XFEL serial crystallography. Nature 2016; 541:242-246. [PMID: 27841871 DOI: 10.1038/nature20599] [Citation(s) in RCA: 196] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Accepted: 11/04/2016] [Indexed: 12/27/2022]
Abstract
Riboswitches are structural RNA elements that are generally located in the 5' untranslated region of messenger RNA. During regulation of gene expression, ligand binding to the aptamer domain of a riboswitch triggers a signal to the downstream expression platform. A complete understanding of the structural basis of this mechanism requires the ability to study structural changes over time. Here we use femtosecond X-ray free electron laser (XFEL) pulses to obtain structural measurements from crystals so small that diffusion of a ligand can be timed to initiate a reaction before diffraction. We demonstrate this approach by determining four structures of the adenine riboswitch aptamer domain during the course of a reaction, involving two unbound apo structures, one ligand-bound intermediate, and the final ligand-bound conformation. These structures support a reaction mechanism model with at least four states and illustrate the structural basis of signal transmission. The three-way junction and the P1 switch helix of the two apo conformers are notably different from those in the ligand-bound conformation. Our time-resolved crystallographic measurements with a 10-second delay captured the structure of an intermediate with changes in the binding pocket that accommodate the ligand. With at least a 10-minute delay, the RNA molecules were fully converted to the ligand-bound state, in which the substantial conformational changes resulted in conversion of the space group. Such notable changes in crystallo highlight the important opportunities that micro- and nanocrystals may offer in these and similar time-resolved diffraction studies. Together, these results demonstrate the potential of 'mix-and-inject' time-resolved serial crystallography to study biochemically important interactions between biomacromolecules and ligands, including those that involve large conformational changes.
Collapse
|
59
|
Perez-Gonzalez C, Lafontaine DA, Penedo JC. Fluorescence-Based Strategies to Investigate the Structure and Dynamics of Aptamer-Ligand Complexes. Front Chem 2016; 4:33. [PMID: 27536656 PMCID: PMC4971091 DOI: 10.3389/fchem.2016.00033] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 07/11/2016] [Indexed: 12/11/2022] Open
Abstract
In addition to the helical nature of double-stranded DNA and RNA, single-stranded oligonucleotides can arrange themselves into tridimensional structures containing loops, bulges, internal hairpins and many other motifs. This ability has been used for more than two decades to generate oligonucleotide sequences, so-called aptamers, that can recognize certain metabolites with high affinity and specificity. More recently, this library of artificially-generated nucleic acid aptamers has been expanded by the discovery that naturally occurring RNA sequences control bacterial gene expression in response to cellular concentration of a given metabolite. The application of fluorescence methods has been pivotal to characterize in detail the structure and dynamics of these aptamer-ligand complexes in solution. This is mostly due to the intrinsic high sensitivity of fluorescence methods and also to significant improvements in solid-phase synthesis, post-synthetic labeling strategies and optical instrumentation that took place during the last decade. In this work, we provide an overview of the most widely employed fluorescence methods to investigate aptamer structure and function by describing the use of aptamers labeled with a single dye in fluorescence quenching and anisotropy assays. The use of 2-aminopurine as a fluorescent analog of adenine to monitor local changes in structure and fluorescence resonance energy transfer (FRET) to follow long-range conformational changes is also covered in detail. The last part of the review is dedicated to the application of fluorescence techniques based on single-molecule microscopy, a technique that has revolutionized our understanding of nucleic acid structure and dynamics. We finally describe the advantages of monitoring ligand-binding and conformational changes, one molecule at a time, to decipher the complexity of regulatory aptamers and summarize the emerging folding and ligand-binding models arising from the application of these single-molecule FRET microscopy techniques.
Collapse
Affiliation(s)
- Cibran Perez-Gonzalez
- Laboratory for Biophysics and Biomolecular Dynamics, SUPA School of Physics and Astronomy, University of St. AndrewsSt Andrews, UK
| | - Daniel A. Lafontaine
- RNA Group, Department of Biology, Faculty of Science, Université de SherbrookeSherbrooke, QC, Canada
| | - J. Carlos Penedo
- Laboratory for Biophysics and Biomolecular Dynamics, SUPA School of Physics and Astronomy, University of St. AndrewsSt Andrews, UK
- Laboratory for Biophysics and Biomolecular Dynamics, Biomedical Sciences Research Complex, School of Biology, University of St. AndrewsSt. Andrews, UK
| |
Collapse
|
60
|
Mehdizadeh Aghdam E, Hejazi MS, Barzegar A. Riboswitches: From living biosensors to novel targets of antibiotics. Gene 2016; 592:244-59. [PMID: 27432066 DOI: 10.1016/j.gene.2016.07.035] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2016] [Revised: 07/11/2016] [Accepted: 07/14/2016] [Indexed: 12/24/2022]
Abstract
Riboswitches are generally located in 5'-UTR region of mRNAs and specifically bind small ligands. Following ligand binding, gene expression is controlled mostly by transcription termination, translation inhibition or mRNA degradation processes. More than 30 classes of known riboswitches have been identified by now. Most riboswitches consist of an aptamer domain and an expression platform. The aptamer domain of each class of riboswitch is a conserved structure and stabilizes specific structures of the expression platforms through binding to specific compounds. In this review, we are highlighting most aspects of riboswitch research including the novel riboswitch discoveries, routine methods for discovering and investigating riboswitches along with newly discovered classes and mechanistic principles of riboswitch-mediated gene expression control. Moreover, we will give an overview about the potential of riboswitches as therapeutic targets for antibiotic design and also their utilization as biosensors for molecular detection.
Collapse
Affiliation(s)
- Elnaz Mehdizadeh Aghdam
- Department of Pharmaceutical Biotechnology, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran; Molecular Medicine Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran.
| | - Mohammad Saeid Hejazi
- Department of Pharmaceutical Biotechnology, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran; Molecular Medicine Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Abolfazl Barzegar
- Research Institute for Fundamental Sciences (RIFS), University of Tabriz, Tabriz, Iran; The School of Advanced Biomedical Sciences (SABS), Tabriz University of Medical Sciences, Tabriz, Iran
| |
Collapse
|
61
|
Frener M, Micura R. Conformational Rearrangements of Individual Nucleotides during RNA-Ligand Binding Are Rate-Differentiated. J Am Chem Soc 2016; 138:3627-30. [PMID: 26974261 PMCID: PMC4959565 DOI: 10.1021/jacs.5b11876] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A pronounced rate differentiation has been found for conformational rearrangements of individual nucleobases that occur during ligand recognition of the preQ1 class-I riboswitch aptamer from Thermoanaerobacter tengcongensis. Rate measurements rely on the 2ApFold approach by analyzing the fluorescence response of riboswitch variants, each with a single, strategically positioned 2-aminopurine nucleobase substitution. Observed rate discrimination between the fastest and the slowest conformational adaption is 22-fold, with the largest rate observed for the rearrangement of a nucleoside directly at the binding site and the smallest rate observed for the 3'-unpaired nucleoside that stacks onto the pseudo-knot-closing Watson-Crick base pair. Our findings provide novel insights into how compact, prefolded RNAs that follow the induced-fit recognition mechanism adapt local structural elements in response to ligand binding on a rather broad time scale and how this process culminates in a structural signal that is responsible for efficient downregulation of ribosomal translation.
Collapse
Affiliation(s)
- Marina Frener
- Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck, Austria
| | - Ronald Micura
- Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck, Austria
| |
Collapse
|
62
|
Rinaldi AJ, Lund PE, Blanco MR, Walter NG. The Shine-Dalgarno sequence of riboswitch-regulated single mRNAs shows ligand-dependent accessibility bursts. Nat Commun 2016; 7:8976. [PMID: 26781350 PMCID: PMC4735710 DOI: 10.1038/ncomms9976] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 10/21/2015] [Indexed: 01/20/2023] Open
Abstract
In response to intracellular signals in Gram-negative bacteria, translational riboswitches—commonly embedded in messenger RNAs (mRNAs)—regulate gene expression through inhibition of translation initiation. It is generally thought that this regulation originates from occlusion of the Shine-Dalgarno (SD) sequence upon ligand binding; however, little direct evidence exists. Here we develop Single Molecule Kinetic Analysis of RNA Transient Structure (SiM-KARTS) to investigate the ligand-dependent accessibility of the SD sequence of an mRNA hosting the 7-aminomethyl-7-deazaguanine (preQ1)-sensing riboswitch. Spike train analysis reveals that individual mRNA molecules alternate between two conformational states, distinguished by ‘bursts' of probe binding associated with increased SD sequence accessibility. Addition of preQ1 decreases the lifetime of the SD's high-accessibility (bursting) state and prolongs the time between bursts. In addition, ligand-jump experiments reveal imperfect riboswitching of single mRNA molecules. Such complex ligand sensing by individual mRNA molecules rationalizes the nuanced ligand response observed during bulk mRNA translation. In response to intracellular signals, bacterial translational riboswitches embedded in mRNAs can regulate gene expression through inhibition of translation initiation. Here, the authors describe SiM-KARTS, a novel approach for detecting changes in the structure of single RNA molecules in response to a ligand.
Collapse
Affiliation(s)
- Arlie J Rinaldi
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Paul E Lund
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.,Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Mario R Blanco
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Nils G Walter
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
| |
Collapse
|
63
|
Ren A, Xue Y, Peselis A, Serganov A, Al-Hashimi HM, Patel DJ. Structural and Dynamic Basis for Low-Affinity, High-Selectivity Binding of L-Glutamine by the Glutamine Riboswitch. Cell Rep 2015; 13:1800-13. [PMID: 26655897 DOI: 10.1016/j.celrep.2015.10.062] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Revised: 08/17/2015] [Accepted: 10/20/2015] [Indexed: 12/24/2022] Open
Abstract
Naturally occurring L-glutamine riboswitches occur in cyanobacteria and marine metagenomes, where they reside upstream of genes involved in nitrogen metabolism. By combining X-ray, NMR, and MD, we characterized an L-glutamine-dependent conformational transition in the Synechococcus elongatus glutamine riboswitch from tuning fork to L-shaped alignment of stem segments. This transition generates an open ligand-binding pocket with L-glutamine selectivity enforced by Mg(2+)-mediated intermolecular interactions. The transition also stabilizes the P1 helix through a long-range "linchpin" Watson-Crick G-C pair-capping interaction, while melting a short helix below P1 potentially capable of modulating downstream readout. NMR data establish that the ligand-free glutamine riboswitch in Mg(2+) solution exists in a slow equilibrium between flexible tuning fork and a minor conformation, similar, but not identical, to the L-shaped bound conformation. We propose that an open ligand-binding pocket combined with a high conformational penalty for forming the ligand-bound state provide mechanisms for reducing binding affinity while retaining high selectivity.
Collapse
Affiliation(s)
- Aiming Ren
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA
| | - Yi Xue
- Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Alla Peselis
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
| | - Alexander Serganov
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
| | - Hashim M Al-Hashimi
- Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA.
| | - Dinshaw J Patel
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
| |
Collapse
|
64
|
Aytenfisu AH, Liberman JA, Wedekind JE, Mathews DH. Molecular mechanism for preQ1-II riboswitch function revealed by molecular dynamics. RNA (NEW YORK, N.Y.) 2015; 21:1898-907. [PMID: 26370581 PMCID: PMC4604430 DOI: 10.1261/rna.051367.115] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Accepted: 07/02/2015] [Indexed: 05/06/2023]
Abstract
Riboswitches are RNA molecules that regulate gene expression using conformational change, affected by binding of small molecule ligands. A crystal structure of a ligand-bound class II preQ1 riboswitch has been determined in a previous structural study. To gain insight into the dynamics of this riboswitch in solution, eight total molecular dynamic simulations, four with and four without ligand, were performed using the Amber force field. In the presence of ligand, all four of the simulations demonstrated rearranged base pairs at the 3' end, consistent with expected base-pairing from comparative sequence analysis in a prior bioinformatic analysis; this suggests the pairing in this region was altered by crystallization. Additionally, in the absence of ligand, three of the simulations demonstrated similar changes in base-pairing at the ligand binding site. Significantly, although most of the riboswitch architecture remained intact in the respective trajectories, the P3 stem was destabilized in the ligand-free simulations in a way that exposed the Shine-Dalgarno sequence. This work illustrates how destabilization of two major groove base triples can influence a nearby H-type pseudoknot and provides a mechanism for control of gene expression by a fold that is frequently found in bacterial riboswitches.
Collapse
Affiliation(s)
- Asaminew H Aytenfisu
- Department of Biochemistry & Biophysics and Center for RNA Biology, University of Rochester Medical Center, Rochester, New York 14642, USA
| | - Joseph A Liberman
- Department of Biochemistry & Biophysics and Center for RNA Biology, University of Rochester Medical Center, Rochester, New York 14642, USA
| | - Joseph E Wedekind
- Department of Biochemistry & Biophysics and Center for RNA Biology, University of Rochester Medical Center, Rochester, New York 14642, USA
| | - David H Mathews
- Department of Biochemistry & Biophysics and Center for RNA Biology, University of Rochester Medical Center, Rochester, New York 14642, USA Department of Biostatistics and Computational Biology, University of Rochester Medical Center, Rochester, New York 14642, USA
| |
Collapse
|
65
|
Suddala KC, Wang J, Hou Q, Walter NG. Mg(2+) shifts ligand-mediated folding of a riboswitch from induced-fit to conformational selection. J Am Chem Soc 2015; 137:14075-83. [PMID: 26471732 DOI: 10.1021/jacs.5b09740] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bacterial riboswitches couple small-molecule ligand binding to RNA conformational changes that widely regulate gene expression, rendering them potential targets for antibiotic intervention. Despite structural insights, the ligand-mediated folding mechanisms of riboswitches are still poorly understood. Using single-molecule fluorescence resonance energy transfer (smFRET), we have investigated the folding mechanism of an H-type pseudoknotted preQ1 riboswitch in dependence of Mg(2+) and three ligands of distinct affinities. We show that, in the absence of Mg(2+), both weakly and strongly bound ligands promote pseudoknot docking through an induced-fit mechanism. By contrast, addition of as low as 10 μM Mg(2+) generally shifts docking toward conformational selection by stabilizing a folded-like conformation prior to ligand binding. Supporting evidence from transition-state analysis further highlights the particular importance of stacking interactions during induced-fit and of specific hydrogen bonds during conformational selection. Our mechanistic dissection provides unprecedented insights into the intricate synergy between ligand- and Mg(2+)-mediated RNA folding.
Collapse
Affiliation(s)
- Krishna C Suddala
- Biophysics, ‡Single Molecule Analysis Group, Department of Chemistry, University of Michigan , 930 N. University, Ann Arbor, Michigan 48109, United States
| | - Jiarui Wang
- Biophysics, ‡Single Molecule Analysis Group, Department of Chemistry, University of Michigan , 930 N. University, Ann Arbor, Michigan 48109, United States
| | - Qian Hou
- Biophysics, ‡Single Molecule Analysis Group, Department of Chemistry, University of Michigan , 930 N. University, Ann Arbor, Michigan 48109, United States
| | - Nils G Walter
- Biophysics, ‡Single Molecule Analysis Group, Department of Chemistry, University of Michigan , 930 N. University, Ann Arbor, Michigan 48109, United States
| |
Collapse
|
66
|
McCown PJ, Liang JJ, Weinberg Z, Breaker RR. Structural, functional, and taxonomic diversity of three preQ1 riboswitch classes. ACTA ACUST UNITED AC 2015; 21:880-889. [PMID: 25036777 DOI: 10.1016/j.chembiol.2014.05.015] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2013] [Revised: 04/17/2014] [Accepted: 05/07/2014] [Indexed: 12/31/2022]
Abstract
Previously, two riboswitch classes have been identified that sense and respond to the hypermodified nucleobase called prequeuosine1 (preQ1). The enormous expansion of available genomic DNA sequence data creates new opportunities to identify additional representatives of the known riboswitch classes and to discover novel classes. We conducted bioinformatics searches on microbial genomic DNA data sets to discover numerous additional examples belonging to the two previously known riboswitch classes for preQ1 (classes preQ1-I and preQ1-II), including some structural variants that further restrict ligand specificity. Additionally, we discovered a third preQ1-binding riboswitch class (preQ1-III) that is structurally distinct from previously known classes. These findings demonstrate that numerous organisms monitor the concentrations of this modified nucleobase by exploiting one or more riboswitch classes for this widespread compound.
Collapse
Affiliation(s)
- Phillip J McCown
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Jonathan J Liang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Zasha Weinberg
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA.,Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Ronald R Breaker
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520, USA.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.,Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| |
Collapse
|
67
|
Neuner S, Santner T, Kreutz C, Micura R. The "Speedy" Synthesis of Atom-Specific (15)N Imino/Amido-Labeled RNA. Chemistry 2015; 21:11634-11643. [PMID: 26237536 PMCID: PMC4946632 DOI: 10.1002/chem.201501275] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Although numerous reports on the synthesis of atom-specific (15)N-labeled nucleosides exist, fast and facile access to the corresponding phosphoramidites for RNA solid-phase synthesis is still lacking. This situation represents a severe bottleneck for NMR spectroscopic investigations on functional RNAs. Here, we present optimized procedures to speed up the synthesis of (15)N(1) adenosine and (15)N(1) guanosine amidites, which are the much needed counterparts of the more straightforward-to-achieve (15)N(3) uridine and (15)N(3) cytidine amidites in order to tap full potential of (1)H/(15)N/(15)N-COSY experiments for directly monitoring individual Watson-Crick base pairs in RNA. Demonstrated for two preQ1 riboswitch systems, we exemplify a versatile concept for individual base-pair labeling in the analysis of conformationally flexible RNAs when competing structures and conformational dynamics are encountered.
Collapse
Affiliation(s)
- Sandro Neuner
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Tobias Santner
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Christoph Kreutz
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Ronald Micura
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| |
Collapse
|
68
|
Rinaldi AJ, Suddala KC, Walter NG. Native purification and labeling of RNA for single molecule fluorescence studies. Methods Mol Biol 2015; 1240:63-95. [PMID: 25352138 DOI: 10.1007/978-1-4939-1896-6_6] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The recent discovery that non-coding RNAs are considerably more abundant and serve a much wider range of critical cellular functions than recognized over previous decades of research into molecular biology has sparked a renewed interest in the study of structure-function relationships of RNA. To perform their functions in the cell, RNAs must dominantly adopt their native conformations, avoiding deep, non-productive kinetic traps that may exist along a frustrated (rugged) folding free energy landscape. Intracellularly, RNAs are synthesized by RNA polymerase and fold co-transcriptionally starting from the 5' end, sometimes with the aid of protein chaperones. By contrast, in the laboratory RNAs are commonly generated by in vitro transcription or chemical synthesis, followed by purification in a manner that includes the use of high concentrations of urea, heat and UV light (for detection), resulting in the denaturation and subsequent refolding of the entire RNA. Recent studies into the nature of heterogeneous RNA populations resulting from this process have underscored the need for non-denaturing (native) purification methods that maintain the co-transcriptional fold of an RNA. Here, we present protocols for the native purification of an RNA after its in vitro transcription and for fluorophore and biotin labeling methods designed to preserve its native conformation for use in single molecule fluorescence resonance energy transfer (smFRET) inquiries into its structure and function. Finally, we present methods for taking smFRET data and for analyzing them, as well as a description of plausible overall preparation schemes for the plethora of non-coding RNAs.
Collapse
Affiliation(s)
- Arlie J Rinaldi
- W. M. Keck Science Center, The Claremont Colleges, Claremont, CA, 91711, USA
| | | | | |
Collapse
|
69
|
Structural analysis of a class III preQ1 riboswitch reveals an aptamer distant from a ribosome-binding site regulated by fast dynamics. Proc Natl Acad Sci U S A 2015; 112:E3485-94. [PMID: 26106162 DOI: 10.1073/pnas.1503955112] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
PreQ1-III riboswitches are newly identified RNA elements that control bacterial genes in response to preQ1 (7-aminomethyl-7-deazaguanine), a precursor to the essential hypermodified tRNA base queuosine. Although numerous riboswitches fold as H-type or HLout-type pseudoknots that integrate ligand-binding and regulatory sequences within a single folded domain, the preQ1-III riboswitch aptamer forms a HLout-type pseudoknot that does not appear to incorporate its ribosome-binding site (RBS). To understand how this unusual organization confers function, we determined the crystal structure of the class III preQ1 riboswitch from Faecalibacterium prausnitzii at 2.75 Å resolution. PreQ1 binds tightly (KD,app 6.5 ± 0.5 nM) between helices P1 and P2 of a three-way helical junction wherein the third helix, P4, projects orthogonally from the ligand-binding pocket, exposing its stem-loop to base pair with the 3' RBS. Biochemical analysis, computational modeling, and single-molecule FRET imaging demonstrated that preQ1 enhances P4 reorientation toward P1-P2, promoting a partially nested, H-type pseudoknot in which the RBS undergoes rapid docking (kdock ∼ 0.6 s(-1)) and undocking (kundock ∼ 1.1 s(-1)). Discovery of such dynamic conformational switching provides insight into how a riboswitch with bipartite architecture uses dynamics to modulate expression platform accessibility, thus expanding the known repertoire of gene control strategies used by regulatory RNAs.
Collapse
|
70
|
Jud L, Košutić M, Schwarz V, Hartl M, Kreutz C, Bister K, Micura R. Expanding the Scope of 2'-SCF3 Modified RNA. Chemistry 2015; 21:10400-7. [PMID: 26074479 PMCID: PMC4515092 DOI: 10.1002/chem.201500415] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Indexed: 11/14/2022]
Abstract
The 2′-trifluoromethylthio (2′-SCF3) modification endows ribonucleic acids with exceptional properties and has attracted considerable interest as a reporter group for NMR spectroscopic applications. However, only modified pyrimidine nucleosides have been generated so far. Here, the syntheses of 2′-SCF3 adenosine and guanosine phosphoramidites of which the latter was obtained in highly efficient manner by an unconventional Boc-protecting group strategy, are reported. RNA solid-phase synthesis provided site-specifically 2′-SCF3-modified oligoribonucleotides that were investigated intensively. Their excellent behavior in 19F NMR spectroscopic probing of RNA ligand binding was exemplified for a noncovalent small molecule–RNA interaction. Moreover, comparably to the 2′-SCF3 pyrimidine nucleosides, the purine counterparts were also found to cause a significant thermodynamic destabilization when located in double helical regions. This property was considered beneficial for siRNA design under the aspect to minimize off-target effects and their performance in silencing of the BASP1 gene was demonstrated.
Collapse
Affiliation(s)
- Lukas Jud
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Marija Košutić
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Veronika Schwarz
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Markus Hartl
- Institute of Biochemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Christoph Kreutz
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Klaus Bister
- Institute of Biochemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria)
| | - Ronald Micura
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80-82, 6020 Innsbruck (Austria).
| |
Collapse
|
71
|
Peselis A, Serganov A. Structure and function of pseudoknots involved in gene expression control. WILEY INTERDISCIPLINARY REVIEWS-RNA 2014; 5:803-22. [PMID: 25044223 DOI: 10.1002/wrna.1247] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 05/09/2014] [Accepted: 05/21/2014] [Indexed: 11/08/2022]
Abstract
Natural RNA molecules can have a high degree of structural complexity but even the most complexly folded RNAs are assembled from simple structural building blocks. Among the simplest RNA elements are double-stranded helices that participate in the formation of different folding topologies and constitute the major fraction of RNA structures. One common folding motif of RNA is a pseudoknot, defined as a bipartite helical structure formed by base-pairing of the apical loop in the stem-loop structure with an outside sequence. Pseudoknots constitute integral parts of the RNA structures essential for various cellular activities. Among many functions of pseudoknotted RNAs is feedback regulation of gene expression, carried out through specific recognition of various molecules. Pseudoknotted RNAs autoregulate ribosomal and phage protein genes in response to downstream encoded proteins, while many metabolic and transport genes are controlled by cellular metabolites interacting with pseudoknotted RNA elements from the riboswitch family. Modulation of some genes also depends on metabolite-induced messenger RNA (mRNA) cleavage performed by pseudoknotted ribozymes. Several regulatory pseudoknots have been characterized biochemically and structurally in great detail. These studies have demonstrated a plethora of pseudoknot-based folds and have begun uncovering diverse molecular principles of the ligand-dependent gene expression control. The pseudoknot-mediated mechanisms of gene control and many unexpected and interesting features of the regulatory pseudoknots have significantly advanced our understanding of the genetic circuits and laid the foundation for modulation of their outcomes.
Collapse
Affiliation(s)
- Alla Peselis
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | | |
Collapse
|
72
|
Eichhorn CD, Kang M, Feigon J. Structure and function of preQ 1 riboswitches. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1839:939-950. [PMID: 24798077 DOI: 10.1016/j.bbagrm.2014.04.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 04/22/2014] [Accepted: 04/25/2014] [Indexed: 12/17/2022]
Abstract
PreQ1 riboswitches help regulate the biosynthesis and transport of preQ1 (7-aminomethyl-7-deazaguanine), a precursor of the hypermodified guanine nucleotide queuosine (Q), in a number of Firmicutes, Proteobacteria, and Fusobacteria. Queuosine is almost universally found at the wobble position of the anticodon in asparaginyl, tyrosyl, histidyl and aspartyl tRNAs, where it contributes to translational fidelity. Two classes of preQ1 riboswitches have been identified (preQ1-I and preQ1-II), and structures of examples from both classes have been determined. Both classes form H-type pseudoknots upon preQ1 binding, each of which has distinct unusual features and modes of preQ1 recognition. These features include an unusually long loop 2 in preQ1-I pseudoknots and an embedded hairpin in loop 3 in preQ1-II pseudoknots. PreQ1-I riboswitches are also notable for their unusually small aptamer domain, which has been extensively investigated by NMR, X-ray crystallography, FRET, and other biophysical methods. Here we review the discovery, structural biology, ligand specificity, cation interactions, folding, dynamics, and applications to biotechnology of preQ1 riboswitches. This article is part of a Special Issue entitled: Riboswitches.
Collapse
Affiliation(s)
- Catherine D Eichhorn
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
| | - Mijeong Kang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA; UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, CA 90095, USA
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA; UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, CA 90095, USA
| |
Collapse
|
73
|
Gong Z, Zhao Y, Chen C, Duan Y, Xiao Y. Insights into ligand binding to PreQ1 Riboswitch Aptamer from molecular dynamics simulations. PLoS One 2014; 9:e92247. [PMID: 24663240 PMCID: PMC3963873 DOI: 10.1371/journal.pone.0092247] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Accepted: 02/19/2014] [Indexed: 11/19/2022] Open
Abstract
Riboswitches play roles in transcriptional or translational regulation through specific ligand binding of their aptamer domains. Although a number of ligand-bound aptamer complex structures have been solved, it is important to know ligand-free conformations of the aptamers in order to understand the mechanism of specific binding by ligands. In this paper, preQ1 riboswitch aptamer domain from Bacillus subtilis is studied by overall 1.5 μs all-atom molecular dynamics simulations We found that the ligand-free aptamer has a stable state with a folded P1-L3 and open binding pocket. The latter forms a cytosine-rich pool in which the nucleotide C19 oscillates between close and open positions, making it a potential conformation for preQ1 entrance. The dynamic picture further suggests that the specific recognition of preQ1 by the aptamer domain is not only facilitated by the key nucleotide C19 but also aided and enhanced by other cytosines around the binding pocket. These results should help to understand the details of preQ1 binding.
Collapse
Affiliation(s)
- Zhou Gong
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yunjie Zhao
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Changjun Chen
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yong Duan
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Genome Center and Department of Biomedical Engineering, University of California Davis, Davis, California, United States of America
| | - Yi Xiao
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
- * E-mail:
| |
Collapse
|
74
|
Peselis A, Serganov A. Themes and variations in riboswitch structure and function. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1839:908-918. [PMID: 24583553 DOI: 10.1016/j.bbagrm.2014.02.012] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Revised: 02/14/2014] [Accepted: 02/20/2014] [Indexed: 11/19/2022]
Abstract
The complexity of gene expression control by non-coding RNA has been highlighted by the recent progress in the field of riboswitches. Discovered a decade ago, riboswitches represent a diverse group of non-coding mRNA regions that possess a unique ability to directly sense cellular metabolites and modulate gene expression through formation of alternative metabolite-free and metabolite-bound conformations. Such protein-free metabolite sensing domains utilize sophisticated three-dimensional folding of RNA molecules to discriminate between a cognate ligand from related compounds so that only the right ligand would trigger a genetic response. Given the variety of riboswitch ligands ranging from small cations to large coenzymes, riboswitches adopt a great diversity of structures. Although many riboswitches share structural principles to build metabolite-competent folds, form precise ligand-binding pockets, and communicate a ligand-binding event to downstream regulatory regions, virtually all riboswitch classes possess unique features for ligand recognition, even those tuned to recognize the same metabolites. Here we present an overview of the biochemical and structural research on riboswitches with a major focus on common principles and individual characteristics adopted by these regulatory RNA elements during evolution to specifically target small molecules and exert genetic responses. This article is part of a Special Issue entitled: Riboswitches.
Collapse
Affiliation(s)
- Alla Peselis
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Alexander Serganov
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
| |
Collapse
|
75
|
Structural determinants for ligand capture by a class II preQ1 riboswitch. Proc Natl Acad Sci U S A 2014; 111:E663-71. [PMID: 24469808 DOI: 10.1073/pnas.1400126111] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Prequeuosine (preQ1) riboswitches are RNA regulatory elements located in the 5' UTR of genes involved in the biosynthesis and transport of preQ1, a precursor of the modified base queuosine universally found in four tRNAs. The preQ1 class II (preQ1-II) riboswitch regulates preQ1 biosynthesis at the translational level. We present the solution NMR structure and conformational dynamics of the 59 nucleotide Streptococcus pneumoniae preQ1-II riboswitch bound to preQ1. Unlike in the preQ1 class I (preQ1-I) riboswitch, divalent cations are required for high-affinity binding. The solution structure is an unusual H-type pseudoknot featuring a P4 hairpin embedded in loop 3, which forms a three-way junction with the other two stems. (13)C relaxation and residual dipolar coupling experiments revealed interhelical flexibility of P4. We found that the P4 helix and flanking adenine residues play crucial and unexpected roles in controlling pseudoknot formation and, in turn, sequestering the Shine-Dalgarno sequence. Aided by divalent cations, P4 is poised to act as a "screw cap" on preQ1 recognition to block ligand exit and stabilize the binding pocket. Comparison of preQ1-I and preQ1-II riboswitch structures reveals that whereas both form H-type pseudoknots and recognize preQ1 using one A, C, or U nucleotide from each of three loops, these nucleotides interact with preQ1 differently, with preQ1 inserting into different grooves. Our studies show that the preQ1-II riboswitch uses an unusual mechanism to harness exquisite control over queuosine metabolism.
Collapse
|
76
|
The AdoCbl–Riboswitch Interaction Investigated by In-Line Probing and Surface Plasmon Resonance Spectroscopy (SPR). Methods Enzymol 2014. [DOI: 10.1016/b978-0-12-801122-5.00020-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
77
|
Liberman JA, Bogue JT, Jenkins JL, Salim M, Wedekind JE. ITC analysis of ligand binding to preQ₁ riboswitches. Methods Enzymol 2014; 549:435-50. [PMID: 25432759 DOI: 10.1016/b978-0-12-801122-5.00018-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Riboswitches regulate genes by binding to small-molecule effectors. Isothermal titration calorimetry (ITC) provides a label-free method to quantify the equilibrium association constant, K(A), of a riboswitch interaction with its cognate ligand. In addition to probing affinity and specific chemical contributions that contribute to binding, ITC can be used to measure the thermodynamic parameters of an interaction (ΔG, ΔH, and ΔS), in addition to the binding stoichiometry (N). Here, we describe methods developed to measure the binding affinity of various preQ1 riboswitch classes for the pyrrolopyrimidine effector, preQ1. Example isotherms are provided along with a review of various preQ1-II (class 2) riboswitch mutants that were interrogated by ITC to quantify the energetic contributions of specific interactions visualized in the crystal structure. Protocols for ITC are provided in sufficient detail that the reader can reproduce experiments independently, or develop derivative methods suitable for analyzing novel riboswitch-ligand binding interactions.
Collapse
Affiliation(s)
- Joseph A Liberman
- Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Jarrod T Bogue
- Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Jermaine L Jenkins
- Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Structural Biology & Biophysics Facility, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Mohammad Salim
- Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Joseph E Wedekind
- Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Structural Biology & Biophysics Facility, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
| |
Collapse
|
78
|
Choudhary PK, Sigel RK. Mg(2+)-induced conformational changes in the btuB riboswitch from E. coli. RNA (NEW YORK, N.Y.) 2014; 20:36-45. [PMID: 24243114 PMCID: PMC3866643 DOI: 10.1261/rna.039909.113] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 10/09/2013] [Indexed: 06/02/2023]
Abstract
Mg(2+) has been shown to modulate the function of riboswitches by facilitating the ligand-riboswitch interactions. The btuB riboswitch from Escherichia coli undergoes a conformational change upon binding to its ligand, coenzyme B12 (adenosyl-cobalamine, AdoCbl), and down-regulates the expression of the B12 transporter protein BtuB in order to control the cellular levels of AdoCbl. Here, we discuss the structural folding attained by the btuB riboswitch from E. coli in response to Mg(2+) and how it affects the ligand binding competent conformation of the RNA. The btuB riboswitch notably adopts different conformational states depending upon the concentration of Mg(2+). With the help of in-line probing, we show the existence of at least two specific conformations, one being achieved in the complete absence of Mg(2+) (or low Mg(2+) concentration) and the other appearing above ∼0.5 mM Mg(2+). Distinct regions of the riboswitch exhibit different dissociation constants toward Mg(2+), indicating a stepwise folding of the btuB RNA. Increasing the Mg(2+) concentration drives the transition from one conformation toward the other. The conformational state existing above 0.5 mM Mg(2+) defines the binding competent conformation of the btuB riboswitch which can productively interact with the ligand, coenzyme B12, and switch the RNA conformation. Moreover, raising the Mg(2+) concentration enhances the ratio of switched RNA in the presence of AdoCbl. The lack of a AdoCbl-induced conformational switch experienced by the btuB riboswitch in the absence of Mg(2+) indicates a crucial role played by Mg(2+) for defining an active conformation of the riboswitch.
Collapse
|
79
|
Xia T, Yuan J, Fang X. Conformational dynamics of an ATP-binding DNA aptamer: a single-molecule study. J Phys Chem B 2013; 117:14994-5003. [PMID: 24245799 DOI: 10.1021/jp4099667] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nucleic acid aptamers are single-stranded RNA or DNA molecules that bind to their targets with high specificity and affinity. Although their biomedical applications have been booming, it is still debatable whether an aptamer recognizes its target through "induced fit" or "conformational selection", a central question in molecular recognition. To address this question, an ATP-binding DNA aptamer was selected as a model system and the conformational properties of this aptamer with and without the presence of ATP were investigated by single-pair Förster resonance energy transfer (spFRET) spectroscopy. The single-molecule results indicate that the aptamer can fold into a double-stranded-like structure, similar to the ligand-bound conformation, even without the presence of ATP. The folded structure is thermally stable at high salt concentrations and becomes rather dynamic at low salt concentrations. Although in the latter condition, the aptamer prefers unfolded structures, it can occasionally migrate to the folded conformation for a short time before being unfolded again. The binding of ATP to the aptamer stabilizes the folded structure, which populates the ligand-bound state of the aptamer, thus shifting the conformational equilibrium. Collectively, our data support that the ATP-binding DNA aptamer recognizes ATP ligand through "conformational selection".
Collapse
Affiliation(s)
- Tie Xia
- Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Key Laboratory of Molecular Nanostructure and Nanotechnology, Chinese Academy of Sciences , Beijing 100190, P. R. China
| | | | | |
Collapse
|
80
|
Suddala KC, Rinaldi AJ, Feng J, Mustoe AM, Eichhorn CD, Liberman JA, Wedekind JE, Al-Hashimi HM, Brooks CL, Walter NG. Single transcriptional and translational preQ1 riboswitches adopt similar pre-folded ensembles that follow distinct folding pathways into the same ligand-bound structure. Nucleic Acids Res 2013; 41:10462-75. [PMID: 24003028 PMCID: PMC3905878 DOI: 10.1093/nar/gkt798] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Riboswitches are structural elements in the 5′ untranslated regions of many bacterial messenger RNAs that regulate gene expression in response to changing metabolite concentrations by inhibition of either transcription or translation initiation. The preQ1 (7-aminomethyl-7-deazaguanine) riboswitch family comprises some of the smallest metabolite sensing RNAs found in nature. Once ligand-bound, the transcriptional Bacillus subtilis and translational Thermoanaerobacter tengcongensis preQ1 riboswitch aptamers are structurally similar RNA pseudoknots; yet, prior structural studies have characterized their ligand-free conformations as largely unfolded and folded, respectively. In contrast, through single molecule observation, we now show that, at near-physiological Mg2+ concentration and pH, both ligand-free aptamers adopt similar pre-folded state ensembles that differ in their ligand-mediated folding. Structure-based Gō-model simulations of the two aptamers suggest that the ligand binds late (Bacillus subtilis) and early (Thermoanaerobacter tengcongensis) relative to pseudoknot folding, leading to the proposal that the principal distinction between the two riboswitches lies in their relative tendencies to fold via mechanisms of conformational selection and induced fit, respectively. These mechanistic insights are put to the test by rationally designing a single nucleotide swap distal from the ligand binding pocket that we find to predictably control the aptamers′ pre-folded states and their ligand binding affinities.
Collapse
Affiliation(s)
- Krishna C Suddala
- Biophysics, University of Michigan, Ann Arbor, MI 48109, USA, Single Molecule Analysis Group, University of Michigan, Ann Arbor, MI 48109, USA, Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA, Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109, USA, Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA and Center for Theoretical Biological Physics, University of California San Diego, San Diego, CA 92037, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
81
|
Tuning a riboswitch response through structural extension of a pseudoknot. Proc Natl Acad Sci U S A 2013; 110:E3256-64. [PMID: 23940363 DOI: 10.1073/pnas.1304585110] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Structural and dynamic features of RNA folding landscapes represent critical aspects of RNA function in the cell and are particularly central to riboswitch-mediated control of gene expression. Here, using single-molecule fluorescence energy transfer imaging, we explore the folding dynamics of the preQ1 class II riboswitch, an upstream mRNA element that regulates downstream encoded modification enzymes of queuosine biosynthesis. For reasons that are not presently understood, the classical pseudoknot fold of this system harbors an extra stem-loop structure within its 3'-terminal region immediately upstream of the Shine-Dalgarno sequence that contributes to formation of the ligand-bound state. By imaging ligand-dependent preQ1 riboswitch folding from multiple structural perspectives, we reveal that the extra stem-loop strongly influences pseudoknot dynamics in a manner that decreases its propensity to spontaneously fold and increases its responsiveness to ligand binding. We conclude that the extra stem-loop sensitizes this RNA to broaden the dynamic range of the ON/OFF regulatory switch.
Collapse
|
82
|
Yu CH, Luo J, Iwata-Reuyl D, Olsthoorn RCL. Exploiting preQ(1) riboswitches to regulate ribosomal frameshifting. ACS Chem Biol 2013; 8:733-40. [PMID: 23327288 DOI: 10.1021/cb300629b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Knowing the molecular details of the interaction between riboswitch aptamers and their corresponding metabolites is important to understand gene expression. Here we report on a novel in vitro assay to study preQ(1) riboswitch aptamers upon binding of 7-aminomethyl-7-deazaguanine (preQ(1)). The assay is based on the ability of the preQ(1) aptamer to fold, upon ligand binding, into a pseudoknotted structure that is capable of stimulating -1 ribosomal frameshifting (-1 FS). Aptamers from three different species were found to induce between 7% and 20% of -1 FS in response to increasing preQ(1) levels, whereas preQ(1) analogues were 100-1000-fold less efficient. In depth mutational analysis of the Fusobacterium nucleatum aptamer recapitulates most of the structural details previously identified for preQ(1) aptamers from other bacteria by crystallography and/or NMR spectroscopy. In addition to providing insight into the role of individual nucleotides of the preQ(1) riboswitch aptamer in ligand binding, the presented system provides a valuable tool to screen small molecules against bacterial riboswitches in a eukaryotic background.
Collapse
Affiliation(s)
| | | | - Dirk Iwata-Reuyl
- Department of Chemistry, Portland State University, Portland, Oregon 97201,
United States
| | | |
Collapse
|
83
|
Structure of a class II preQ1 riboswitch reveals ligand recognition by a new fold. Nat Chem Biol 2013; 9:353-5. [PMID: 23584677 PMCID: PMC3661761 DOI: 10.1038/nchembio.1231] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2012] [Accepted: 03/14/2013] [Indexed: 11/26/2022]
Abstract
PreQ1 riboswitches regulate genes by binding the pyrrolopyrimidine intermediate preQ1 during biosynthesis of the essential tRNA base queuosine. We report the first preQ1-II riboswitch structure at 2.3 Å resolution, which uses a novel fold to achieve effector recognition at the confluence of a three-way-helical junction flanking a pseudoknotted ribosome-binding site (RBS). The results account for preQ1-II-riboswitch-mediated translational control, and expand the known repertoire of ligand binding modes utilized by regulatory RNAs.
Collapse
|
84
|
Serganov A, Patel DJ. Metabolite recognition principles and molecular mechanisms underlying riboswitch function. Annu Rev Biophys 2013; 41:343-70. [PMID: 22577823 DOI: 10.1146/annurev-biophys-101211-113224] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Riboswitches are mRNA elements capable of modulating gene expression in response to specific binding by cellular metabolites. Riboswitches exert their function through the interplay of alternative ligand-free and ligand-bound conformations of the metabolite-sensing domain, which in turn modulate the formation of adjacent gene expression controlling elements. X-ray crystallography and NMR spectroscopy have determined three-dimensional structures of virtually all the major riboswitch classes in the ligand-bound state and, for several riboswitches, in the ligand-free state. The resulting spatial topologies have demonstrated the wide diversity of riboswitch folds and revealed structural principles for specific recognition by cognate metabolites. The available three-dimensional information, supplemented by structure-guided biophysical and biochemical experimentation, has led to an improved understanding of how riboswitches fold, what RNA conformations are required for ligand recognition, and how ligand binding can be transduced into gene expression modulation. These studies have greatly facilitated the dissection of molecular mechanisms underlying riboswitch action and should in turn guide the anticipated development of tools for manipulating gene regulatory circuits.
Collapse
Affiliation(s)
- Alexander Serganov
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York 10016, USA.
| | | |
Collapse
|
85
|
Daddacha W, Noble E, Nguyen LA, Kennedy EM, Kim B. Effect of ribonucleotides embedded in a DNA template on HIV-1 reverse transcription kinetics and fidelity. J Biol Chem 2013; 288:12522-32. [PMID: 23479739 DOI: 10.1074/jbc.m113.458398] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
HIV-1 reverse transcriptase (RT) frequently incorporates ribonucleoside triphosphates (rNTPs) during proviral DNA synthesis, particularly under the limited dNTP conditions found in macrophages. We investigated the mechanistic impacts of an rNMP embedded in DNA templates on HIV-1 RT-mediated DNA synthesis. We observed that the template-embedded rNMP induced pausing of RT and delayed DNA synthesis kinetics at low macrophage dNTP concentrations but not at high T cell dNTP concentrations. Although the binding affinity of RT to the rNMP-containing template-primer was not altered, the dNTP incorporation kinetics of RT were significantly reduced at one nucleotide upstream and downstream of the rNMP site, leading to pause sites. Finally, HIV-1 RT becomes more error-prone at rNMP sites with an elevated mismatch extension capability but not enhanced misinsertion capability. Together these data suggest that rNMPs embedded in DNA templates may influence reverse transcription kinetics and impact viral mutagenesis in macrophages.
Collapse
Affiliation(s)
- Waaqo Daddacha
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York 14642, USA
| | | | | | | | | |
Collapse
|
86
|
Schill M, Koslowski T. Sensing organic molecules by charge transfer through aptamer-target complexes: theory and simulation. J Phys Chem B 2013; 117:475-83. [PMID: 23227783 DOI: 10.1021/jp308042n] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Aptamers, i.e., short sequences of RNA and single-stranded DNA, are capable of specificilly binding objects ranging from small molecules over proteins to entire cells. Here, we focus on the structure, stability, dynamics, and electronic properties of oligonucleotides that interact with aromatic or heterocyclic targets. Large-scale molecular dynamics simulations indicate that aromatic rings such as dyes, metabolites, or alkaloides form stable adducts with their oligonucleotide host molecules at least on the simulation time scale. From molecular dynamics snapshots, the energy parameters relevant to Marcus' theory of charge transfer are computed using a modified Su-Schrieffer-Heeger Hamiltonian, permitting an estimate of the charge transfer rates. In many cases, aptamer binding seriously influences the charge transfer kinetics and the charge carrier mobility within the complex, with conductivities up to the nanoampere range for a single complex. We discuss the conductivity properties with reference to potential applications as biosensors.
Collapse
Affiliation(s)
- Maria Schill
- Institut für Physikalische Chemie, Universität Freiburg, Albertstrasse 23a, D-79104 Freiburg im Breisgau, Germany
| | | |
Collapse
|
87
|
Singh TS, Rao BJ, Krishnamoorthy G. GTP binding leads to narrowing of the conformer population while preserving the structure of the RNA aptamer: a site-specific time-resolved fluorescence dynamics study. Biochemistry 2012; 51:9260-9. [PMID: 23110669 DOI: 10.1021/bi301110u] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, we employed a combination of steady-state and time-resolved fluorescence spectroscopy and studied the site-specific dynamics in a GTP aptamer using 2-aminopurine as a fluorescent probe. We compared the dynamics of the GTP-bound aptamer with that of the free aptamer as well as when it is denatured. GTP binding leads to an overall compaction of structure in the aptamer. The general pattern of fluorescence lifetimes and correlation times scanned across several locations in the aptamer does not seem to change following GTP binding. However, a remarkable narrowing of the lifetime distribution of the aptamer ensues following its compaction by GTP binding. Interestingly, such a "conformational narrowing" is evident from the lifetime readouts of the nucleotide belonging to the stem as well as the "bulge" part of the aptamer, independent of whether it is directly interacting with GTP. Taken together, these results underscore the importance of an overall intrinsic structure associated with the free aptamer that is further modulated following GTP binding. This work provides strong support for the "conformational selection" hypothesis of ligand binding.
Collapse
Affiliation(s)
- T Sanjoy Singh
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400 005, India
| | | | | |
Collapse
|
88
|
Banáš P, Sklenovský P, Wedekind JE, Šponer J, Otyepka M. Molecular mechanism of preQ1 riboswitch action: a molecular dynamics study. J Phys Chem B 2012; 116:12721-34. [PMID: 22998634 PMCID: PMC3505677 DOI: 10.1021/jp309230v] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Riboswitches often occur in the 5'-untranslated regions of bacterial mRNA where they regulate gene expression. The preQ(1) riboswitch controls the biosynthesis of a hypermodified nucleoside queuosine in response to binding the queuosine metabolic intermediate. Structures of the ligand-bound and ligand-free states of the preQ(1) riboswitch from Thermoanaerobacter tengcongensis were determined recently by X-ray crystallography. We used multiple, microsecond-long molecular dynamics simulations (29 μs in total) to characterize the structural dynamics of preQ(1) riboswitches in both states. We observed different stabilities of the stem in the bound and free states, resulting in different accessibilities of the ribosome-binding site. These differences are related to different stacking interactions between nucleotides of the stem and the associated loop, which itself adopts different conformations in the bound and free states. We suggest that the loop not only serves to bind preQ(1) but also transmits information about ligand binding from the ligand-binding pocket to the stem, which has implications for mRNA accessibility to the ribosome. We explain functional results obscured by a high salt crystallization medium and help to refine regions of disordered electron density, which demonstrates the predictive power of our approach. Besides investigating the functional dynamics of the riboswitch, we have also utilized this unique small folded RNA system for analysis of performance of the RNA force field on the μs time scale. The latest AMBER parmbsc0χ(OL3) RNA force field is capable of providing stable trajectories of the folded molecule on the μs time scale. On the other hand, force fields that are not properly balanced lead to significant structural perturbations on the sub-μs time scale, which could easily lead to inappropriate interpretation of the simulation data.
Collapse
Affiliation(s)
- Pavel Banáš
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, tr. 17. listopadu 12, 771 46 Olomouc, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Kralovopolska 135, 612 65 Brno, Czech Republic
| | - Petr Sklenovský
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, tr. 17. listopadu 12, 771 46 Olomouc, Czech Republic
| | - Joseph E. Wedekind
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, 601 Elmwood Ave, Box 712, Rochester, NY 14620, USA
| | - Jiří Šponer
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, tr. 17. listopadu 12, 771 46 Olomouc, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Kralovopolska 135, 612 65 Brno, Czech Republic
- CEITEC – Central European Institute of Technology, Masaryk University, Campus Bohunice, Kamenice 5, 625 00 Brno, Czech Republic
| | - Michal Otyepka
- Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, tr. 17. listopadu 12, 771 46 Olomouc, Czech Republic
| |
Collapse
|
89
|
Gong Z, Zhao Y, Chen C, Xiao Y. Computational study of unfolding and regulation mechanism of preQ1 riboswitches. PLoS One 2012; 7:e45239. [PMID: 23028870 PMCID: PMC3444477 DOI: 10.1371/journal.pone.0045239] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Accepted: 08/17/2012] [Indexed: 11/18/2022] Open
Abstract
Riboswitches are novel RNA regulatory elements. Each riboswitch molecule consists of two domains: aptamer and express platform. The three-dimensional (3D) structure of the aptamer domain, depending on ligand binding or not, controls that of the express platform, which then switches on or off transcriptional or translational process. Here we study the two types of preQ(1) riboswitch aptamers from T. Tengcongensis (denoted as Tte preQ(1) riboswitch for short below) and Bacillus subtilis (denoted as Bsu preQ(1) riboswitch for short below), respectively. The free-state 3D structure of the Tte preQ(1) riboswitch is the same as its bound state but the Bsu preQ(1) riboswitch is not. Therefore, it is very interesting to investigate how these riboswitches realize their different regulation functions. We simulated the unfolding of these two aptamers through all-atom molecular dynamic simulation and found that they have similar unfolding or folding pathways and ligand-binding processes. The main difference between them is the folding intermediate states. The similarity and difference of their unfolding or folding dynamics may suggest their similar regulation mechanisms and account for their different functions, respectively. These results are also useful to understand the regulation mechanism of other riboswitches with free-state 3D structures similar to their bound states.
Collapse
Affiliation(s)
- Zhou Gong
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yunjie Zhao
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Changjun Chen
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yi Xiao
- Biomolecular Physics and Modeling Group, Department of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| |
Collapse
|
90
|
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.
Collapse
|
91
|
Santner T, Rieder U, Kreutz C, Micura R. Pseudoknot preorganization of the preQ1 class I riboswitch. J Am Chem Soc 2012; 134:11928-31. [PMID: 22775200 DOI: 10.1021/ja3049964] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To explore folding and ligand recognition of metabolite-responsive RNAs is of major importance to comprehend gene regulation by riboswitches. Here, we demonstrate, using NMR spectroscopy, that the free aptamer of a preQ(1) class I riboswitch preorganizes into a pseudoknot fold in a temperature- and Mg(2+)-dependent manner. The preformed pseudoknot represents a structure that is close to the ligand-bound state and that likely represents the conformation selected by the ligand. Importantly, a defined base pair mutation within the pseudoknot interaction stipulates whether, in the absence of ligand, dimer formation of the aptamer competes with intramolecular pseudoknot formation. This study pinpoints how RNA preorganization is a crucial determinant for the adaptive recognition process of RNA and ligand.
Collapse
Affiliation(s)
- Tobias Santner
- Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, Austria
| | | | | | | |
Collapse
|
92
|
Serganov A, Patel DJ. Molecular recognition and function of riboswitches. Curr Opin Struct Biol 2012; 22:279-86. [PMID: 22579413 DOI: 10.1016/j.sbi.2012.04.005] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 04/22/2012] [Accepted: 04/23/2012] [Indexed: 11/27/2022]
Abstract
Regulatory mRNAs elements termed riboswitches respond to elevated concentrations of cellular metabolites by modulating expression of associated genes. Riboswitches attain their high metabolite selectivity by capitalizing on the intrinsic tertiary structures of their sensor domains. Over the years, riboswitch structure and folding have been amongst the most researched topics in the RNA field. Most recently, novel structures of single-ligand and cooperative double-ligand sensors have broadened our knowledge of architectural and molecular recognition principles exploited by riboswitches. The structural information has been complemented by extensive folding studies, which have provided several important clues on the formation of ligand-competent conformations and mechanisms of ligand discrimination. These studies have greatly improved our understanding of molecular events in riboswitch-mediated gene expression control and provided the molecular basis for intervention into riboswitch-controlled genetic circuits.
Collapse
Affiliation(s)
- Alexander Serganov
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, 550 First Ave., MSB-393, New York, NY 10016, USA
| | | |
Collapse
|
93
|
Wacker A, Buck J, Richter C, Schwalbe H, Wöhnert J. Mechanisms for differentiation between cognate and near-cognate ligands by purine riboswitches. RNA Biol 2012; 9:672-80. [PMID: 22647526 DOI: 10.4161/rna.20106] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Riboswitches are elements in the 5'-untranslated region of mRNAs that regulate gene expression by directly interacting with metabolites related to their own gene products. A remarkable feature of this gene regulation mechanism is the high specificity of riboswitches for their cognate ligands. In this study, we used a combination of static and time-resolved NMR-spectroscopic methods to investigate the mechanisms for ligand specificity in purine riboswitches. We investigate the xpt-aptamer domain from a guanine-responsive riboswitch and the mfl-aptamer domain from a 2'-deoxyguanosine-responsive riboswitch. The xpt-aptamer binds the purine nucleobases guanine/hypoxanthine with high affinity, but, unexpectedly, also the nucleoside 2'-deoxyguanosine. On the other hand, the mfl-aptamer is highly specific for its cognate ligand 2'-deoxyguanosine, and does not bind purine ligands. We addressed the question of aptamer`s ligand specificity by real-time NMR spectroscopy. Our studies of ligand binding and subsequently induced aptamer folding revealed that the xpt-aptamer discriminates against non-cognate ligands by enhanced life-times of the cognate complex compared with non-cognate complexes, whereas the mfl-aptamer rejects non-cognate ligands at the level of ligand association, employing a kinetic proofreading mechanism.
Collapse
Affiliation(s)
- Anna Wacker
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany
| | | | | | | | | |
Collapse
|
94
|
McCarty RM, Bandarian V. Biosynthesis of pyrrolopyrimidines. Bioorg Chem 2012; 43:15-25. [PMID: 22382038 DOI: 10.1016/j.bioorg.2012.01.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 01/05/2012] [Accepted: 01/06/2012] [Indexed: 12/17/2022]
Abstract
Pyrrolopyrimidine containing compounds, also known as 7-deazapurines, are a collection of purine-based metabolites that have been isolated from a variety of biological sources and have diverse functions which range from secondary metabolism to RNA modification. To date, nearly 35 compounds with the common 7-deazapurine core structure have been described. This article will illustrate the structural diversity of these compounds and review the current state of knowledge on the biosynthetic pathways that give rise to them.
Collapse
Affiliation(s)
- Reid M McCarty
- Department of Chemistry and Biochemistry, University of Arizona, 1041 E. Lowell St., Tucson, AZ 85721, USA
| | | |
Collapse
|
95
|
Boehr DD. Promiscuity in protein-RNA interactions: conformational ensembles facilitate molecular recognition in the spliceosome: conformational diversity in U2AF⁶⁵ facilitates binding to diverse RNA sequences. Bioessays 2011; 34:174-80. [PMID: 22144099 DOI: 10.1002/bies.201100152] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Here I discuss findings that suggest a universal mechanism for proteins (and RNA) to recognize and interact with various binding partners by selectively binding to different conformations that pre-exist in the free protein's conformational ensemble. The tandem RNA recognition motif domains of splicing factor U2AF⁶⁵ fluctuate in solution between a predominately closed conformation in which the RNA binding site of one of the domains is blocked, and a lowly populated open conformation in which both RNA binding pockets are accessible. RNA binding to U2AF⁶⁵ may thus occur through the weakly populated open conformation, and the binding interaction stabilizes the open conformation. The conformational diversity observed in U2AF⁶⁵ might also facilitate binding to diverse RNA sequences as found in the polypyrimidine tracts that help define 3' splice sites. Similar binding pathways in other systems have important consequences in biological regulation, molecular evolution, and information storage.
Collapse
Affiliation(s)
- David D Boehr
- Department of Chemistry, The Pennsylvania State University, 240 Chemistry Building, University Park, PA, USA.
| |
Collapse
|
96
|
Vicens Q, Mondragón E, Batey RT. Molecular sensing by the aptamer domain of the FMN riboswitch: a general model for ligand binding by conformational selection. Nucleic Acids Res 2011; 39:8586-98. [PMID: 21745821 PMCID: PMC3201879 DOI: 10.1093/nar/gkr565] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Revised: 06/20/2011] [Accepted: 06/21/2011] [Indexed: 12/25/2022] Open
Abstract
Understanding the nature of the free state of riboswitch aptamers is important for illuminating common themes in gene regulation by riboswitches. Prior evidence indicated the flavin mononucleotide (FMN)-binding riboswitch aptamer adopted a 'bound-like' structure in absence of FMN, suggesting only local conformational changes upon ligand binding. In the scope of pinpointing the general nature of such changes at the nucleotide level, we performed SHAPE mapping experiments using the aptamer domain of two phylogenetic variants, both in absence and in presence of FMN. We also solved the crystal structures of one of these domains both free (3.3 Å resolution) and bound to FMN (2.95 Å resolution). Our comparative study reveals that structural rearrangements occurring upon binding are restricted to a few of the joining regions that form the binding pocket in both RNAs. This type of binding event with minimal structural perturbations is reminiscent of binding events by conformational selection encountered in other riboswitches and various RNAs.
Collapse
Affiliation(s)
| | | | - Robert T. Batey
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA
| |
Collapse
|
97
|
Liberman JA, Wedekind JE. Riboswitch structure in the ligand-free state. WILEY INTERDISCIPLINARY REVIEWS-RNA 2011; 3:369-84. [PMID: 21957061 DOI: 10.1002/wrna.114] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Molecular investigations of riboswitches bound to small-molecule effectors have produced a wealth of information on how these molecules achieve high affinity and specificity for a target ligand. X-ray crystal structures have been determined for the ligand-free state for representatives of the preQ₁-I, S-adenosylmethionine I, lysine, and glycine aptamer classes. These structures in conjunction with complimentary techniques, such as in-line probing, NMR spectroscopy, Förster resonance energy transfer, small-angle scattering, and computational simulations, have demonstrated that riboswitches adopt multiple conformations in the absence of ligand. Despite a number of investigations that support ligand-dependent folding, mounting evidence suggests that free-state riboswitches interact with their effectors in the sub-populations of largely prefolded states as embodied by the principle of conformational selection, which has been documented extensively for protein-mediated ligand interactions. Fundamental riboswitch investigations of the bound and free states have advanced our understanding of RNA folding, ligand recognition, and how these factors culminate in communication between an aptamer and its expression platform. An understanding of these topics is essential to comprehend riboswitch gene regulation at the molecular level, which has already provided a basis to understand the mechanism of action of natural antimicrobials.
Collapse
Affiliation(s)
- Joseph A Liberman
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
| | | |
Collapse
|