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de Crécy-Lagard V, Hutinet G, Cediel-Becerra JDD, Yuan Y, Zallot R, Chevrette MG, Ratnayake RMMN, Jaroch M, Quaiyum S, Bruner S. Biosynthesis and function of 7-deazaguanine derivatives in bacteria and phages. Microbiol Mol Biol Rev 2024; 88:e0019923. [PMID: 38421302 PMCID: PMC10966956 DOI: 10.1128/mmbr.00199-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2024] Open
Abstract
SUMMARYDeazaguanine modifications play multifaceted roles in the molecular biology of DNA and tRNA, shaping diverse yet essential biological processes, including the nuanced fine-tuning of translation efficiency and the intricate modulation of codon-anticodon interactions. Beyond their roles in translation, deazaguanine modifications contribute to cellular stress resistance, self-nonself discrimination mechanisms, and host evasion defenses, directly modulating the adaptability of living organisms. Deazaguanine moieties extend beyond nucleic acid modifications, manifesting in the structural diversity of biologically active natural products. Their roles in fundamental cellular processes and their presence in biologically active natural products underscore their versatility and pivotal contributions to the intricate web of molecular interactions within living organisms. Here, we discuss the current understanding of the biosynthesis and multifaceted functions of deazaguanines, shedding light on their diverse and dynamic roles in the molecular landscape of life.
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Affiliation(s)
- Valérie de Crécy-Lagard
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
- University of Florida Genetics Institute, Gainesville, Florida, USA
| | - Geoffrey Hutinet
- Department of Biology, Haverford College, Haverford, Pennsylvania, USA
| | | | - Yifeng Yuan
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | - Rémi Zallot
- Department of Life Sciences, Manchester Metropolitan University, Manchester, United Kingdom
| | - Marc G. Chevrette
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | | | - Marshall Jaroch
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | - Samia Quaiyum
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | - Steven Bruner
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
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2
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Olenginski LT, Spradlin SF, Batey RT. Flipping the script: Understanding riboswitches from an alternative perspective. J Biol Chem 2024; 300:105730. [PMID: 38336293 PMCID: PMC10907184 DOI: 10.1016/j.jbc.2024.105730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 01/14/2024] [Accepted: 01/19/2024] [Indexed: 02/12/2024] Open
Abstract
Riboswitches are broadly distributed regulatory elements most frequently found in the 5'-leader sequence of bacterial mRNAs that regulate gene expression in response to the binding of a small molecule effector. The occupancy status of the ligand-binding aptamer domain manipulates downstream information in the message that instructs the expression machinery. Currently, there are over 55 validated riboswitch classes, where each class is defined based on the identity of the ligand it binds and/or sequence and structure conservation patterns within the aptamer domain. This classification reflects an "aptamer-centric" perspective that dominates our understanding of riboswitches. In this review, we propose a conceptual framework that groups riboswitches based on the mechanism by which RNA manipulates information directly instructing the expression machinery. This scheme does not replace the established aptamer domain-based classification of riboswitches but rather serves to facilitate hypothesis-driven investigation of riboswitch regulatory mechanisms. Based on current bioinformatic, structural, and biochemical studies of a broad spectrum of riboswitches, we propose three major mechanistic groups: (1) "direct occlusion", (2) "interdomain docking", and (3) "strand exchange". We discuss the defining features of each group, present representative examples of riboswitches from each group, and illustrate how these RNAs couple small molecule binding to gene regulation. While mechanistic studies of the occlusion and docking groups have yielded compelling models for how these riboswitches function, much less is known about strand exchange processes. To conclude, we outline the limitations of our mechanism-based conceptual framework and discuss how critical information within riboswitch expression platforms can inform gene regulation.
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Affiliation(s)
| | | | - Robert T Batey
- Department of Biochemistry, University of Colorado, Boulder, Colorado, USA.
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3
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Parmar S, Bume DD, Conelly C, Boer R, Prestwood PR, Wang Z, Labuhn H, Sinnadurai K, Feri A, Ouellet J, Homan P, Numata T, Schneekloth JS. Mechanistic Analysis of Riboswitch Ligand Interactions Provides Insights into Pharmacological Control over Gene Expression. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.23.581746. [PMID: 38903087 PMCID: PMC11188086 DOI: 10.1101/2024.02.23.581746] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/22/2024]
Abstract
Riboswitches are structured RNA elements that regulate gene expression upon binding to small molecule ligands. Understanding the mechanisms by which small molecules impact riboswitch activity is key to developing potent, selective ligands for these and other RNA targets. We report the structure-informed design of chemically diverse synthetic ligands for PreQ1 riboswitches. Multiple X-ray co-crystal structures of synthetic ligands with the Thermoanaerobacter tengcongensis (Tte)-PreQ1 riboswitch confirm a common binding site with the cognate ligand, despite considerable chemical differences among the ligands. Structure probing assays demonstrate that one ligand causes conformational changes similar to PreQ1 in six structurally and mechanistically diverse PreQ1 riboswitch aptamers. Single-molecule force spectroscopy is used to demonstrate differential modes of riboswitch stabilization by the ligands. Binding of the natural ligand brings about the formation of a persistent, folded pseudoknot structure, whereas a synthetic ligand decreases the rate of unfolding through a kinetic mechanism. Single round transcription termination assays show the biochemical activity of the ligands, while a GFP reporter system reveals compound activity in regulating gene expression in live cells without toxicity. Taken together, this study reveals that diverse small molecules can impact gene expression in live cells by altering conformational changes in RNA structures through distinct mechanisms.
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Affiliation(s)
- Shaifaly Parmar
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
| | - Desta Doro Bume
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
| | - Colleen Conelly
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
| | - Robert Boer
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
| | - Peri R. Prestwood
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
| | - Zhen Wang
- Depixus SAS, 3-5 Impasse Reille, 75014 Paris, France
| | | | | | - Adeline Feri
- Depixus SAS, 3-5 Impasse Reille, 75014 Paris, France
| | - Jimmy Ouellet
- Depixus SAS, 3-5 Impasse Reille, 75014 Paris, France
| | - Philip Homan
- Center for Cancer Research Collaborative Bioinformatics Resource, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA
| | - Tomoyuki Numata
- Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka 819-0395, Japan
| | - John S. Schneekloth
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
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4
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Singh K, Reddy G. Excited States of apo-Guanidine-III Riboswitch Contribute to Guanidinium Binding through Both Conformational and Induced-Fit Mechanisms. J Chem Theory Comput 2024; 20:421-435. [PMID: 38134376 DOI: 10.1021/acs.jctc.3c00999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2023]
Abstract
Riboswitches are mRNA segments that regulate gene expression through conformational changes driven by their cognate ligand binding. The ykkC motif forms a riboswitch class that selectively senses a guanidinium ion (Gdm+) and regulates the downstream expression of proteins which aid in the efflux of excess Gdm+ from the cells. The aptamer domain (AD) of the guanidine-III riboswitch forms an H-type pseudoknot with a triple helical domain that binds a Gdm+. We studied the binding of Gdm+ to the AD of the guanidine (ykkC)-III riboswitch using computer simulations to probe the specificity of the riboswitch to Gdm+ binding. We show that Gdm+ binding is a fast process occurring on the nanosecond time scale, with minimal conformational changes to the AD. Using machine learning and Markov-state models, we identified the excited conformational states of the AD, which have a high Gdm+ binding propensity, making the Gdm+ binding landscape complex exhibiting both conformational selection and induced-fit mechanisms. The proposed apo-AD excited states and their role in the ligand-sensing mechanism are amenable to experimental verification. Further, targeting these excited-state conformations in discovering new antibiotics can be explored.
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Affiliation(s)
- Kushal Singh
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012 Karnataka, India
| | - Govardhan Reddy
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012 Karnataka, India
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5
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Hamal Dhakal S, Kavita K, Panchapakesan SSS, Roth A, Breaker RR. 8-oxoguanine riboswitches in bacteria detect and respond to oxidative DNA damage. Proc Natl Acad Sci U S A 2023; 120:e2307854120. [PMID: 37748066 PMCID: PMC10556655 DOI: 10.1073/pnas.2307854120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 08/25/2023] [Indexed: 09/27/2023] Open
Abstract
Riboswitches rely on structured aptamer domains to selectively sense their target ligands and regulate gene expression. However, some riboswitch aptamers in bacteria carry mutations in their otherwise strictly conserved binding pockets that change ligand specificities. The aptamer domain of a riboswitch class originally found to selectively sense guanine forms a three-stem junction that has since been observed to exploit numerous alterations in its ligand-binding pocket. These rare variants have modified their ligand specificities to sense other purines or purine derivatives, including adenine, 2'-deoxyguanosine (three classes), and xanthine. Herein, we report the characteristics of a rare variant that is narrowly distributed in the Paenibacillaceae family of bacteria. Known representatives are always associated with genes encoding 8-oxoguanine deaminase. As predicted from this gene association, these variant riboswitches tightly bind 8-oxoguanine (8-oxoG), strongly discriminate against other purine derivatives, and function as genetic "ON" switches. Following exposure of cells to certain oxidative stresses, a representative 8-oxoG riboswitch activates gene expression, likely caused by the accumulation of 8-oxoG due to oxidative damage to G nucleobases in DNA, RNA, and the nucleotide pool. Furthermore, an engineered version of the variant aptamer was prepared that exhibits specificity for 8-oxoadenine, further demonstrating that RNA aptamers can acquire mutations that expand their ability to detect and respond to oxidative damage.
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Affiliation(s)
- Siddhartha Hamal Dhakal
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT06511-8103
| | - Kumari Kavita
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT06511-8103
| | | | - Adam Roth
- HHMI, Yale University, New Haven, CT06511-8103
| | - Ronald R. Breaker
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT06511-8103
- HHMI, Yale University, New Haven, CT06511-8103
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT06511-8103
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6
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Hu G, Zhang Y, Yu Z, Cui T, Cui W. Dynamical characterization and multiple unbinding paths of two PreQ 1 ligands in one pocket. Phys Chem Chem Phys 2023; 25:24004-24015. [PMID: 37646322 DOI: 10.1039/d3cp03142j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
Riboswitches naturally regulate gene expression in bacteria by binding to specific small molecules. Class 1 preQ1 riboswitch aptamer is an important model not only for RNA folding but also as a target for designing small molecule antibiotics due to its well-known minimal aptamer domain. Here, we ran a total of 62.4 μs conventional and enhanced-sampling molecular dynamics (MD) simulations to characterize the determinants underlying the binding of the preQ1-II riboswitch aptamer to two preQ1 ligands in one binding pocket. Decomposition of binding free energy suggested that preQ1 ligands at α and β sites interact with four nucleotides (G5, C17, C18, and A30) and two nucleotides (A12 and C31), respectively. Mg2+ ions play a crucial role in both stabilizing the binding pocket and facilitating ligand binding. The flexible preQ1 ligand at the β site leads to the top of the binding pocket loosening and thus pre-organizes the riboswitch for ligand entry. Enhanced sampling simulations further revealed that the preQ1 ligand at the α site unbinds through two orthogonal pathways, which are dependent on whether or not a β site preQ1 ligand is present. One of the two preQ1 ligands has been identified in the binding pocket, which will aid to identify the second preQ1 Ligand. Our work provides new information for designing robust ligands.
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Affiliation(s)
- Guodong Hu
- Shandong Key Laboratory of Biophysics, Dezhou University, Dezhou 253023, China.
- Laoling People's Hospital, Dezhou 253600, China
| | | | - Zhiping Yu
- Shandong Key Laboratory of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Tiejun Cui
- Laoling People's Hospital, Dezhou 253600, China
| | - Wanling Cui
- Shandong Key Laboratory of Biophysics, Dezhou University, Dezhou 253023, China.
- Laoling People's Hospital, Dezhou 253600, China
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7
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Xu L, Xiao Y, Zhang J, Fang X. Structural insights into translation regulation by the THF-II riboswitch. Nucleic Acids Res 2023; 51:952-965. [PMID: 36620887 PMCID: PMC9881143 DOI: 10.1093/nar/gkac1257] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 12/12/2022] [Accepted: 12/15/2022] [Indexed: 01/10/2023] Open
Abstract
In bacteria, expression of folate-related genes is controlled by the tetrahydrofolate (THF) riboswitch in response to specific binding of THF and its derivatives. Recently, a second class of THF riboswitches, named THF-II, was identified in Gram-negative bacteria, which exhibit distinct architecture from the previously characterized THF-I riboswitches found in Gram-positive bacteria. Here, we present the crystal structures of the ligand-bound THF-II riboswitch from Mesorhizobium loti. These structures exhibit a long rod-like fold stabilized by continuous base pair and base triplet stacking across two helices of P1 and P2 and their interconnecting ligand-bound binding pocket. The pterin moiety of the ligand docks into the binding pocket by forming hydrogen bonds with two highly conserved pyrimidines in J12 and J21, which resembles the hydrogen-bonding pattern at the ligand-binding site FAPK in the THF-I riboswitch. Using small-angle X-ray scattering and isothermal titration calorimetry, we further characterized the riboswitch in solution and reveal that Mg2+ is essential for pre-organization of the binding pocket for efficient ligand binding. RNase H cleavage assay indicates that ligand binding reduces accessibility of the ribosome binding site in the right arm of P1, thus down-regulating the expression of downstream genes. Together, these results provide mechanistic insights into translation regulation by the THF-II riboswitch.
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Affiliation(s)
| | | | - Jie Zhang
- Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing 100084, China,Center for Synthetic and Systems Biology, Tsinghua University, Beijing 100084, China
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8
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Chen J, Zeng Q, Wang W, Sun H, Hu G. Decoding the Identification Mechanism of an SAM-III Riboswitch on Ligands through Multiple Independent Gaussian-Accelerated Molecular Dynamics Simulations. J Chem Inf Model 2022; 62:6118-6132. [PMID: 36440874 DOI: 10.1021/acs.jcim.2c00961] [Citation(s) in RCA: 49] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
S-Adenosyl-l-methionine (SAM)-responsive riboswitches play a central role in the regulation of bacterial gene expression at the level of transcription attenuation or translation inhibition. In this study, multiple independent Gaussian-accelerated molecular dynamics simulations were performed to decipher the identification mechanisms of SAM-III (SMK) on ligands SAM, SAH, and EEM. The results reveal that ligand binding highly affects the structural flexibility, internal dynamics, and conformational changes of SAM-III. The dynamic analysis shows that helices P3 and P4 as well as two junctions J23 and J24 of SAM-III are highly susceptible to ligand binding. Analyses of free energy landscapes suggest that ligand binding induces different free energy profiles of SAM-III, which leads to the difference in identification sites of SAM-III on ligands. The information on ligand-nucleotide interactions not only uncovers that the π-π, cation-π, and hydrogen bonding interactions drive identification of SAM-III on the three ligands but also reveals that different electrostatic properties of SAM, SAH, and EEM alter the active sites of SAM-III. Meanwhile, the results also verify that the adenine group of SAM, SAH, and EEM is well recognized by conserved nucleotides G7, A29, U37, A38, and G48. We expect that this study can provide useful information for understanding the applications of SAM-III in chemical, synthetic RNA biology, and biomedical fields.
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Affiliation(s)
- Jianzhong Chen
- School of Science, Shandong Jiaotong University, Jinan250357, China
| | - Qingkai Zeng
- School of Science, Shandong Jiaotong University, Jinan250357, China
| | - Wei Wang
- School of Science, Shandong Jiaotong University, Jinan250357, China
| | - Haibo Sun
- School of Science, Shandong Jiaotong University, Jinan250357, China
| | - Guodong Hu
- Shandong Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou253023, China
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9
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Hamal Dhakal S, Panchapakesan SSS, Slattery P, Roth A, Breaker RR. Variants of the guanine riboswitch class exhibit altered ligand specificities for xanthine, guanine, or 2'-deoxyguanosine. Proc Natl Acad Sci U S A 2022; 119:e2120246119. [PMID: 35622895 PMCID: PMC9295807 DOI: 10.1073/pnas.2120246119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 03/12/2022] [Indexed: 12/30/2022] Open
Abstract
The aptamer portions of previously reported riboswitch classes that sense guanine, adenine, or 2′-deoxyguanosine are formed by a highly similar three-stem junction with distinct nucleotide sequences in the regions joining the stems. The nucleotides in these joining regions form the major features of the selective ligand-binding pocket for each aptamer. Previously, we reported the existence of additional, rare variants of the predominant guanine-sensing riboswitch class that carry nucleotide differences in the ligand-binding pocket, suggesting that these RNAs have further diversified their structures and functions. Herein, we report the discovery and analysis of three naturally occurring variants of guanine riboswitches that are narrowly distributed across Firmicutes. These RNAs were identified using comparative sequence analysis methods, which also revealed that some of the gene associations for these variants are atypical for guanine riboswitches or their previously known natural variants. Binding assays demonstrate that the newfound variant riboswitch representatives recognize xanthine, guanine, or 2′-deoxyguanosine, with the guanine class exhibiting greater discrimination against related purines than the more common guanine riboswitch class reported previously. These three additional variant classes, together with the four previously discovered riboswitch classes that employ the same three-stem junction architecture, reveal how a simple structural framework can be diversified to expand the range of purine-based ligands sensed by RNA.
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Affiliation(s)
- Siddhartha Hamal Dhakal
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
| | | | - Paul Slattery
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
| | - Adam Roth
- HHMI, Yale University, New Haven, CT 06520-8103
| | - Ronald R. Breaker
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
- HHMI, Yale University, New Haven, CT 06520-8103
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8103
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10
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Abstract
More than 55 distinct classes of riboswitches that respond to small metabolites or elemental ions have been experimentally validated to date. The ligands sensed by these riboswitches are biased in favor of fundamental compounds or ions that are likely to have been relevant to ancient forms of life, including those that might have populated the "RNA World", which is a proposed biochemical era that predates the evolutionary emergence of DNA and proteins. In the following text, I discuss the various types of ligands sensed by some of the most common riboswitches present in modern bacterial cells and consider implications for ancient biological processes centered on the proven capabilities of these RNA-based sensors. Although most major biochemical aspects of metabolism are represented by known riboswitch classes, there are striking sensory gaps in some key areas. These gaps could reveal weaknesses in the performance capabilities of RNA that might have hampered RNA World evolution, or these could highlight opportunities to discover additional riboswitch classes that sense essential metabolites.
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Affiliation(s)
- Ronald R. Breaker
- Corresponding Author: Ronald R. Breaker - Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103, United States; Phone: 203-432-9389; , Twitter: @RonBreaker
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11
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Negi I, Mahmi AS, Seelam Prabhakar P, Sharma P. Molecular Dynamics Simulations of the Aptamer Domain of Guanidinium Ion Binding Riboswitch ykkC-III: Structural Insights into the Discrimination of Cognate and Alternate Ligands. J Chem Inf Model 2021; 61:5243-5255. [PMID: 34609872 DOI: 10.1021/acs.jcim.1c01022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Guanidinium ion is a toxic cellular metabolite. The ykkC-III riboswitch, an mRNA stretch, regulates the gene expression by undergoing a conformational change in response to the binding of a free guanidinium ion and thereby plays a potentially important role in alleviating guanidinium toxicity in cells. An experimental crystal structure of the guanidinium-bound aptamer domain of the riboswitch from Thermobifida Fusca revealed the overall RNA architecture and mapped the specific noncovalent interactions that stabilize the ligand within the binding pocket aptamer. However, details of how the aptamer domain discriminates the cognate ligand from its closest structurally analogous physiological metabolites (arginine and urea), and how the binding of cognate ligand arrays information from the aptamer domain to the expression platform for regulating the gene expression, are not well understood. To fill this void, we perform a cumulative of 2 μs all-atom explicit-solvent molecular dynamics (MD) simulations on the full aptamer domain, augmented with quantum-chemical calculations on the ligand-binding pocket, to compare the structural and dynamical details of the guanidinium-bound state with the arginine or urea bound states, as well as the unbound (open) state. Analysis of the ligand-binding pocket reveals that due to unfavorable interactions with the binding-pocket residues, urea cannot bind the aptamer domain and thereby cannot alter the gene expression. Although interaction of the guanidyl moiety of arginine within the binding pocket is either comparable or stronger than the guanidinium ion, additional non-native hydrogen-bonding networks, as well as differences in the dynamical details of the arginine-bound state, explain why arginine cannot transmit the information from the aptamer domain to the expression platform. Based on our simulations, we propose a mechanism of how the aptamer domain communicates with the expression platform. Overall, our work provides interesting insights into the ligand recognition by a specific class of riboswitches and may hopefully inspire future studies to further understand the gene regulation by riboswitches.
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Affiliation(s)
- Indu Negi
- Computational Biochemistry Laboratory, Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India
| | - Amanpreet Singh Mahmi
- Computational Biochemistry Laboratory, Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India
| | - Preethi Seelam Prabhakar
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology (IIIT-H), Gachibowli, Hyderabad, Telangana 500032, India
| | - Purshotam Sharma
- Computational Biochemistry Laboratory, Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India
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12
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Flemmich L, Moreno S, Micura R. Synthesis of O 6-alkylated preQ 1 derivatives. Beilstein J Org Chem 2021; 17:2295-2301. [PMID: 34621392 PMCID: PMC8450960 DOI: 10.3762/bjoc.17.147] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2021] [Accepted: 08/27/2021] [Indexed: 12/23/2022] Open
Abstract
A naturally occurring riboswitch can utilize 7-aminomethyl-O6-methyl-7-deazaguanine (m6preQ1) as cofactor for methyl group transfer resulting in cytosine methylation. This recently discovered riboswitch-ribozyme activity opens new avenues for the development of RNA labeling tools based on tailored O6-alkylated preQ1 derivatives. Here, we report a robust synthesis for this class of pyrrolo[2,3-d]pyrimidines starting from readily accessible N2-pivaloyl-protected 6-chloro-7-cyano-7-deazaguanine. Substitution of the 6-chloro atom with the alcoholate of interest proceeds straightforward. The transformation of the 7-cyano substituent into the required aminomethyl group turned out to be challenging and was solved by a hydration reaction sequence on a well-soluble dimethoxytritylated precursor via in situ oxime formation. The synthetic path now provides a solid foundation to access O6-alkylated 7-aminomethyl-7-deazaguanines for the development of RNA labeling tools based on the preQ1 class-I riboswitch scaffold.
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Affiliation(s)
- Laurin Flemmich
- Institute of Organic Chemistry, Center for molecular Biosciences Innsbruck (CMBI), Innrain 80-82, 6020 Innsbruck, Austria
| | - Sarah Moreno
- Institute of Organic Chemistry, Center for molecular Biosciences Innsbruck (CMBI), Innrain 80-82, 6020 Innsbruck, Austria
| | - Ronald Micura
- Institute of Organic Chemistry, Center for molecular Biosciences Innsbruck (CMBI), Innrain 80-82, 6020 Innsbruck, Austria
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13
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Beyene SS, Ling T, Ristevski B, Chen M. A novel riboswitch classification based on imbalanced sequences achieved by machine learning. PLoS Comput Biol 2020; 16:e1007760. [PMID: 32687488 PMCID: PMC7392346 DOI: 10.1371/journal.pcbi.1007760] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 07/30/2020] [Accepted: 05/13/2020] [Indexed: 11/24/2022] Open
Abstract
Riboswitch, a part of regulatory mRNA (50-250nt in length), has two main classes: aptamer and expression platform. One of the main challenges raised during the classification of riboswitch is imbalanced data. That is a circumstance in which the records of a sequences of one group are very small compared to the others. Such circumstances lead classifier to ignore minority group and emphasize on majority ones, which results in a skewed classification. We considered sixteen riboswitch families, to be in accord with recent riboswitch classification work, that contain imbalanced sequences. The sequences were split into training and test set using a newly developed pipeline. From 5460 k-mers (k value 1 to 6) produced, 156 features were calculated based on CfsSubsetEval and BestFirst function found in WEKA 3.8. Statistically tested result was significantly difference between balanced and imbalanced sequences (p < 0.05). Besides, each algorithm also showed a significant difference in sensitivity, specificity, accuracy, and macro F-score when used in both groups (p < 0.05). Several k-mers clustered from heat map were discovered to have biological functions and motifs at the different positions like interior loops, terminal loops and helices. They were validated to have a biological function and some are riboswitch motifs. The analysis has discovered the importance of solving the challenges of majority bias analysis and overfitting. Presented results were generalized evaluation of both balanced and imbalanced models, which implies their ability of classifying, to classify novel riboswitches. The Python source code is available at https://github.com/Seasonsling/riboswitch.
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Affiliation(s)
- Solomon Shiferaw Beyene
- Department of Bioinformatics, College of Life Sciences, Zhejiang University, Hangzhou, China
| | - Tianyi Ling
- Department of Bioinformatics, College of Life Sciences, Zhejiang University, Hangzhou, China
- School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
| | - Blagoj Ristevski
- Faculty of Information and Communication Technologies, Bitola, St. Kliment Ohridski University Bitola, ul. Partizanska Bitola, Republic of North Macedonia
| | - Ming Chen
- Department of Bioinformatics, College of Life Sciences, Zhejiang University, Hangzhou, China
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14
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Sherlock ME, Breaker RR. Former orphan riboswitches reveal unexplored areas of bacterial metabolism, signaling, and gene control processes. RNA (NEW YORK, N.Y.) 2020; 26:675-693. [PMID: 32165489 PMCID: PMC7266159 DOI: 10.1261/rna.074997.120] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Comparative sequence analyses have been used to discover numerous classes of structured noncoding RNAs, some of which are riboswitches that specifically recognize small-molecule or elemental ion ligands and influence expression of adjacent downstream genes. Determining the correct identity of the ligand for a riboswitch candidate typically is aided by an understanding of the genes under its regulatory control. Riboswitches whose ligands were straightforward to identify have largely been associated with well-characterized metabolic pathways, such as coenzyme or amino acid biosynthesis. Riboswitch candidates whose ligands resist identification, collectively known as orphan riboswitches, are often associated with genes coding for proteins of unknown function, or genes for various proteins with no established link to one another. The cognate ligands for 16 former orphan riboswitch motifs have been identified to date. The successful pursuit of the ligands for these classes has provided insight into areas of biology that are not yet fully explored, such as ion homeostasis, signaling networks, and other previously underappreciated biochemical or physiological processes. Herein we discuss the strategies and methods used to match ligands with orphan riboswitch classes, and overview the lessons learned to inform and motivate ongoing efforts to identify ligands for the many remaining candidates.
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Affiliation(s)
- Madeline E Sherlock
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
| | - Ronald R Breaker
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
- Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA
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15
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Brown JA. Unraveling the structure and biological functions of RNA triple helices. WILEY INTERDISCIPLINARY REVIEWS-RNA 2020; 11:e1598. [PMID: 32441456 PMCID: PMC7583470 DOI: 10.1002/wrna.1598] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 04/06/2020] [Accepted: 04/15/2020] [Indexed: 02/06/2023]
Abstract
It has been nearly 63 years since the first characterization of an RNA triple helix in vitro by Gary Felsenfeld, David Davies, and Alexander Rich. An RNA triple helix consists of three strands: A Watson–Crick RNA double helix whose major‐groove establishes hydrogen bonds with the so‐called “third strand”. In the past 15 years, it has been recognized that these major‐groove RNA triple helices, like single‐stranded and double‐stranded RNA, also mediate prominent biological roles inside cells. Thus far, these triple helices are known to mediate catalysis during telomere synthesis and RNA splicing, bind to ligands and ions so that metabolite‐sensing riboswitches can regulate gene expression, and provide a clever strategy to protect the 3′ end of RNA from degradation. Because RNA triple helices play important roles in biology, there is a renewed interest in better understanding the fundamental properties of RNA triple helices and developing methods for their high‐throughput discovery. This review provides an overview of the fundamental biochemical and structural properties of major‐groove RNA triple helices, summarizes the structure and function of naturally occurring RNA triple helices, and describes prospective strategies to isolate RNA triple helices as a means to establish the “triplexome”. This article is categorized under:RNA Structure and Dynamics > RNA Structure and Dynamics RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems
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Affiliation(s)
- Jessica A Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, USA
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16
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Dutta D, Wedekind JE. Nucleobase mutants of a bacterial preQ 1-II riboswitch that uncouple metabolite sensing from gene regulation. J Biol Chem 2020; 295:2555-2567. [PMID: 31659117 PMCID: PMC7049981 DOI: 10.1074/jbc.ra119.010755] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 10/20/2019] [Indexed: 11/06/2022] Open
Abstract
Riboswitches are a class of nonprotein-coding RNAs that directly sense cellular metabolites to regulate gene expression. They are model systems for analyzing RNA-ligand interactions and are established targets for antibacterial agents. Many studies have analyzed the ligand-binding properties of riboswitches, but this work has outpaced our understanding of the underlying chemical pathways that govern riboswitch-controlled gene expression. To address this knowledge gap, we prepared 15 mutants of the preQ1-II riboswitch-a structurally and biochemically well-characterized HLout pseudoknot that recognizes the metabolite prequeuosine1 (preQ1). The mutants span the preQ1-binding pocket through the adjoining Shine-Dalgarno sequence (SDS) and include A-minor motifs, pseudoknot-insertion helix P4, U·A-U base triples, and canonical G-C pairs in the anti-SDS. As predicted-and confirmed by in vitro isothermal titration calorimetry measurements-specific mutations ablated preQ1 binding, but most aberrant binding effects were corrected by compensatory mutations. In contrast, functional analysis in live bacteria using a riboswitch-controlled GFPuv-reporter assay revealed that each mutant had a deleterious effect on gene regulation, even when compensatory changes were included. Our results indicate that effector binding can be uncoupled from gene regulation. We attribute loss of function to defects in a chemical interaction network that links effector binding to distal regions of the fold that support the gene-off RNA conformation. Our findings differentiate effector binding from biological function, which has ramifications for riboswitch characterization. Our results are considered in the context of synthetic ligands and drugs that bind tightly to riboswitches without eliciting a biological response.
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Affiliation(s)
- Debapratim Dutta
- Department of Biochemistry and Biophysics and Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642
| | - Joseph E Wedekind
- Department of Biochemistry and Biophysics and Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642.
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17
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Abstract
In bacteria and archaea, small RNAs (sRNAs) regulate complex networks through antisense interactions with target mRNAs in trans, and riboswitches regulate gene expression in cis based on the ability to bind small-molecule ligands. Although our understanding and characterization of these two important regulatory RNA classes is far from complete, these RNA-based mechanisms have proven useful for a wide variety of synthetic biology applications. Besides classic and contemporary applications in the realm of metabolic engineering and orthogonal gene control, this review also covers newer applications of regulatory RNAs as biosensors, logic gates, and tools to determine RNA-RNA interactions. A separate section focuses on critical insights gained and challenges posed by fundamental studies of sRNAs and riboswitches that should aid future development of synthetic regulatory RNAs.
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18
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Abstract
RNA is a versatile biomolecule capable of transferring information, taking on distinct three-dimensional shapes, and reacting to ambient conditions. RNA molecules utilize a wide range of mechanisms to control gene expression. An example of such regulation is riboswitches. Consisting exclusively of RNA, they are able to control important metabolic processes, thus providing an elegant and efficient RNA-only regulation system. Existing across all domains of life, riboswitches appear to represent one of the most highly conserved mechanisms for the regulation of a broad range of biochemical pathways. Through binding of a wide range of small-molecule ligands to their so-called aptamer domain, riboswitches undergo a conformational change in their downstream "expression platform." In consequence, the pattern of gene expression changes, which in turn results in increased or decreased protein production. Riboswitches unite the sensing and transduction of a signal that can directly be coupled to the metabolism of the cell; thus they constitute a very potent regulatory mechanism for many organisms. Highly specific RNA-binding domains not only occur in vivo but can also be evolved by means of the SELEX (systematic evolution of ligands by exponential enrichment) method, which allows in vitro selection of aptamers against almost any ligand. Coupling of these aptamers with an expression platform has led to the development of synthetic riboswitches, a highly active research field of great relevance and immense potential. The aim of this review is to summarize developments in the riboswitch field over the last decade and address key questions of recent research.
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19
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Sinumvayo JP, Zhao C, Tuyishime P. Recent advances and future trends of riboswitches: attractive regulatory tools. World J Microbiol Biotechnol 2018; 34:171. [PMID: 30413889 DOI: 10.1007/s11274-018-2554-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 11/02/2018] [Indexed: 01/06/2023]
Abstract
Bacterial genomes contain a huge amount of different genes. These genes are spatiotemporally expressed to accomplish some required functions within the organism. Inside the cell, any step of gene expression may be modulated at four possible places such as transcription initiation, translation regulation, mRNA stability and protein stability. To achieve this, there is a necessity of strong regulators either natural or synthetic which can fine-tune gene expression regarding the required function. In recent years, riboswitches as metabolite responsive control elements residing in the untranslated regions of certain messenger RNAs, have been known to control gene expression at transcription or translation level. Importantly, these control elements do not prescribe the involvement of protein factors for metabolite binding. However, they own their particular properties to sense intramolecular metabolites (ligands). Herein, we highlighted current important bacterial riboswitches, their applications to support genetic control, ligand-binding domain mechanisms and current progress in synthetic riboswitches.
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Affiliation(s)
- Jean Paul Sinumvayo
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China. .,University of Chinese Academy of Sciences, Beijing, China.
| | - Chunhua Zhao
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Philibert Tuyishime
- University of Chinese Academy of Sciences, Beijing, China.,Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
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20
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Warnasooriya C, Ling C, Belashov IA, Salim M, Wedekind JE, Ermolenko DN. Observation of preQ 1-II riboswitch dynamics using single-molecule FRET. RNA Biol 2018; 16:1086-1092. [PMID: 30328747 DOI: 10.1080/15476286.2018.1536591] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
PreQ1 riboswitches regulate the synthesis of the hypermodified tRNA base queuosine by sensing the pyrrolopyrimidine metabolite preQ1. Here, we use single-molecule FRET to interrogate the structural dynamics of apo and preQ1-bound states of the preQ1-II riboswitch from Lactobacillus rhamnosus. We find that the apo-form of the riboswitch spontaneously samples multiple conformations. Magnesium ions and preQ1 stabilize conformations that sequester the ribosome-binding site of the mRNA within the pseudoknotted structure, thus inhibiting translation initiation. Our results reveal that folding of the preQ1-II riboswitch is complex and provide evidence favoring a conformational selection model of effector binding by riboswitches of this class.
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Affiliation(s)
- Chandani Warnasooriya
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
| | - Clarence Ling
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
| | - Ivan A Belashov
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
| | - Mohammad Salim
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
| | - Joseph E Wedekind
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
| | - Dmitri N Ermolenko
- a Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester , Rochester , NY , USA
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21
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Neuner E, Frener M, Lusser A, Micura R. Superior cellular activities of azido- over amino-functionalized ligands for engineered preQ 1 riboswitches in E.coli. RNA Biol 2018; 15:1376-1383. [PMID: 30332908 PMCID: PMC6284575 DOI: 10.1080/15476286.2018.1534526] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 10/05/2018] [Indexed: 01/29/2023] Open
Abstract
For this study, we utilized class-I and class-II preQ1-sensing riboswitches as model systems to decipher the structure-activity relationship of rationally designed ligand derivatives in vitro and in vivo. We found that synthetic preQ1 ligands with amino-modified side chains that protrude from the ligand-encapsulating binding pocket, and thereby potentially interact with the phosphate backbone in their protonated form, retain or even increase binding affinity for the riboswitches in vitro. They, however, led to significantly lower riboswitch activities in a reporter system in vivo in E. coli. Importantly, when we substituted the amino- by azido-modified side chains, the cellular activities of the ligands were restored for the class-I conditional gene expression system and even improved for the class-II counterpart. Kinetic analysis of ligand binding in vitro revealed enhanced on-rates for amino-modified derivatives while they were attenuated for azido-modified variants. This shows that neither high affinities nor fast on-rates are necessarily translated into efficient cellular activities. Taken together, our comprehensive study interconnects in vitro kinetics and in vitro thermodynamics of RNA-ligand binding with the ligands' in vivo performance and thereby encourages azido- rather than amino-functionalized design for enhanced cellular activity.
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Affiliation(s)
- Eva Neuner
- Institute of Organic Chemistry and Center for Molecular Biosciences Innsbruck CMBI, Leopold-Franzens University, Innsbruck, Austria
| | - Marina Frener
- Institute of Organic Chemistry and Center for Molecular Biosciences Innsbruck CMBI, Leopold-Franzens University, Innsbruck, Austria
| | - Alexandra Lusser
- Division of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Ronald Micura
- Institute of Organic Chemistry and Center for Molecular Biosciences Innsbruck CMBI, Leopold-Franzens University, Innsbruck, Austria
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22
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Classification of riboswitch sequences using k-mer frequencies. Biosystems 2018; 174:63-76. [PMID: 30205141 DOI: 10.1016/j.biosystems.2018.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 08/16/2018] [Accepted: 09/05/2018] [Indexed: 12/24/2022]
Abstract
Riboswitches are non-coding RNAs that regulate gene expression by altering the structural conformation of mRNA transcripts. Their regulation mechanism might be exploited for interesting biomedical applications such as drug targets and biosensors. A major challenge consists in accurately identifying metabolite-binding RNA switches which are structurally complex and diverse. In this regard, we investigated the classification of 16 riboswitch families using supervised learning algorithms trained solely with sequence-based features. We generated a reduced feature set and proposed a visual representation to explore its components. We induced Support Vector Machine, Random Forest, Naive Bayes, J48, and HyperPipes classifiers with our proposed feature set and tested their performance over independent data. Our best multi-class classifier achieved F-measure values of 0.996 and 0.966 in the training and test phases, respectively, outperforming those of a previous approach. When compared against BLAST, our best classifiers yielded competitive results. This work shows that the classifiers trained with our sequence-based feature set accurately discriminate riboswitches.
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23
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Dutta D, Belashov IA, Wedekind JE. Coupling Green Fluorescent Protein Expression with Chemical Modification to Probe Functionally Relevant Riboswitch Conformations in Live Bacteria. Biochemistry 2018; 57:4620-4628. [PMID: 29897738 DOI: 10.1021/acs.biochem.8b00316] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Noncoding RNAs engage in numerous biological activities including gene regulation. To fully understand RNA function it is necessary to probe biologically relevant conformations in living cells. To address this challenge, we coupled RNA-mediated regulation of the green fluorescent protein (GFP)uv-reporter gene to icSHAPE (in cell Selective 2'-Hydroxyl Acylation analyzed by Primer Extension). Our transcript-specific approach provides sensitive, fluorescence-based readout of the regulatory-RNA status as a means to coordinate chemical modification experiments. We chose a plasmid-based reporter compatible with Escherichia coli to allow use of knockout strains that eliminate endogenous effector biosynthesis. The approach was piloted using the Lactobacillus rhamnosus ( Lrh) preQ1-II riboswitch, which senses the pyrrolopyrimidine metabolite preQ1. Using an E. coli Δ queF strain incapable of preQ1 anabolism, the Lrh riboswitch yielded nearly one log unit of GFPuv-gene repression resulting from exogenously added preQ1. We then subjected cells in gene "on" and "off" states to icSHAPE. The resulting differential analysis indicated reduction in Lrh riboswitch flexibility in the P3 helix of the pseudoknot, which comprises the ribosome-binding site (RBS) paired with the anti-RBS. Such expression platform modulation was not observed by in vitro chemical probing and demonstrates that the crowded cellular environment does not preclude detection of compact and loose RNA-regulatory conformations. Here we describe the design, methods, interpretation, and caveats of Reporter Coupled (ReCo) icSHAPE. We also describe mapping of the differential ReCo-icSHAPE results onto the Lrh riboswitch-preQ1 cocrystal structure. The approach should be readily applicable to functional RNAs triggered by effectors or environmental variations.
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Affiliation(s)
- Debapratim Dutta
- Department of Biochemistry & Biophysics and Center for RNA Biology , University of Rochester School of Medicine & Dentistry , Rochester , New York 14642 , United States
| | - Ivan A Belashov
- Department of Biochemistry & Biophysics and Center for RNA Biology , University of Rochester School of Medicine & Dentistry , Rochester , New York 14642 , United States
| | - Joseph E Wedekind
- Department of Biochemistry & Biophysics and Center for RNA Biology , University of Rochester School of Medicine & Dentistry , Rochester , New York 14642 , United States
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24
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Bala J, Chinnapaiyan S, Dutta RK, Unwalla H. Aptamers in HIV research diagnosis and therapy. RNA Biol 2018; 15:327-337. [PMID: 29431588 PMCID: PMC5927724 DOI: 10.1080/15476286.2017.1414131] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 11/07/2017] [Accepted: 12/03/2017] [Indexed: 12/30/2022] Open
Abstract
Aptamers are high affinity single-stranded nucleic acid or protein ligands which exhibit specificity and avidity comparable to, or exceeding that of antibodies and can be generated against most targets. The functionality of aptamers is based on their unique tertiary structure, complexity and their ability to attain unique binding pockets by folding. Aptamers are selected in vitro by a process called Systematic Evolution of Ligands by Exponential enrichment (SELEX). The Kd values for the selected aptamer are often in the picomolar to low nanomolar range. Stable and nontoxic aptamers could be selected for a wide range of ligands including small molecules to large proteins. Aptamers have shown tremendous potential and have found multipurpose application in the field of therapeutic, diagnostic, biosensor and bio-imaging. While their mechanism of action can be similar to that of monoclonal antibodies, aptamers provide additional advantages in terms of production cost, simpler regulatory approval and lower immunogenicity as they are synthesized chemically. Human immunodeficiency virus (HIV) is the primary cause of acquired immune deficiency syndrome (AIDS), which causes significant morbidity and mortality with a significant consequent decrease in the quality of patient's lives. While cART has led to good viral control, people living with HIV now suffer from non-HIV comorbidities due to viral protein expression that cannot be controlled by cART. Hence pathophysiological mechanisms that govern these comorbidities with a focus on therapies that neutralize these HIV effects gained increased attention. Recent advances in HIV/AIDS research have identified several molecular targets and for the development of therapeutic and diagnostic using aptamers against HIV/AIDS. This review presents recent advances in aptamers technology for potential application in HIV diagnostics and therapeutics towards improving the quality of life of people living with HIV.
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Affiliation(s)
- Jyoti Bala
- Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA
| | - Srinivasan Chinnapaiyan
- Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA
| | - Rajib Kumar Dutta
- Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA
| | - Hoshang Unwalla
- Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA
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25
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Mirihana Arachchilage G, Sherlock ME, Weinberg Z, Breaker RR. SAM-VI RNAs selectively bind S-adenosylmethionine and exhibit similarities to SAM-III riboswitches. RNA Biol 2018; 15:371-378. [PMID: 29106323 DOI: 10.1080/15476286.2017.1399232] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Five distinct riboswitch classes that regulate gene expression in response to the cofactor S-adenosylmethionine (SAM) or its metabolic breakdown product S-adenosylhomocysteine (SAH) have been reported previously. Collectively, these SAM- or SAH-sensing RNAs constitute the most abundant collection of riboswitches, and are found in nearly every major bacterial lineage. Here, we report a potential sixth member of this pervasive riboswitch family, called SAM-VI, which is predominantly found in Bifidobacterium species. SAM-VI aptamers selectively bind the cofactor SAM and strongly discriminate against SAH. The consensus sequence and structural model for SAM-VI share some features with the consensus model for the SAM-III riboswitch class, whose members are mainly found in lactic acid bacteria. However, there are sufficient differences between the two classes such that current bioinformatics methods separately cluster representatives of the two motifs. These findings highlight the abundance of RNA structures that can form to selectively recognize SAM, and showcase the ability of RNA to utilize diverse strategies to perform similar biological functions.
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Affiliation(s)
| | - Madeline E Sherlock
- b Department of Molecular Biophysics and Biochemistry , Yale University , New Haven , CT , USA
| | - Zasha Weinberg
- a Howard Hughes Medical Institute, Yale University , New Haven , CT , USA
| | - Ronald R Breaker
- a Howard Hughes Medical Institute, Yale University , New Haven , CT , USA.,b Department of Molecular Biophysics and Biochemistry , Yale University , New Haven , CT , USA.,c Department of Molecular , Cellular and Developmental Biology, Yale University , New Haven , CT , USA
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26
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Huang L, Wang J, Wilson TJ, Lilley DMJ. Structure of the Guanidine III Riboswitch. Cell Chem Biol 2017; 24:1407-1415.e2. [PMID: 28988949 PMCID: PMC5696562 DOI: 10.1016/j.chembiol.2017.08.021] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Revised: 07/20/2017] [Accepted: 08/29/2017] [Indexed: 01/09/2023]
Abstract
Riboswitches are structural elements found in mRNA molecules that couple small-molecule binding to regulation of gene expression, usually by controlling transcription or translation. We have determined high-resolution crystal structures of the ykkC guanidine III riboswitch from Thermobifida fusca. The riboswitch forms a classic H-type pseudoknot that includes a triple helix that is continuous with a central core of conserved nucleotides. These form a left-handed helical ramp of inter-nucleotide interactions, generating the guanidinium cation binding site. The ligand is hydrogen bonded to the Hoogsteen edges of two guanine bases. The binding pocket has a side opening that can accommodate a small side chain, shown by structures with bound methylguanidine, aminoguanidine, ethylguanidine, and agmatine. Comparison of the new structure with those of the guanidine I and II riboswitches reveals that evolution generated three different structural solutions for guanidine binding and subsequent gene regulation, although with some common elements.
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Affiliation(s)
- Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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27
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Ignatov D, Johansson J. RNA-mediated signal perception in pathogenic bacteria. WILEY INTERDISCIPLINARY REVIEWS-RNA 2017; 8. [PMID: 28792118 DOI: 10.1002/wrna.1429] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Revised: 05/11/2017] [Accepted: 05/11/2017] [Indexed: 11/09/2022]
Abstract
Bacterial pathogens encounter several different environments during an infection, many of them possibly being detrimental. In order to sense its surroundings and adjust the gene expression accordingly, different regulatory schemes are undertaken. With these, the bacterium appropriately can differentiate between various environmental cues to express the correct virulence factor at the appropriate time and place. An attractive regulator device is RNA, which has an outstanding ability to alter its structure in response to external stimuli, such as metabolite concentration or alterations in temperature, to control its downstream gene expression. This review will describe the function of riboswitches and thermometers, with a particular emphasis on regulatory RNAs being important for bacterial pathogenicity. WIREs RNA 2017, 8:e1429. doi: 10.1002/wrna.1429 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Dmitriy Ignatov
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden.,Department of Molecular Biology, Umeå University, Umeå, Sweden.,Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå, Sweden
| | - Jörgen Johansson
- Umeå Centre for Microbial Research, Umeå University, Umeå, Sweden.,Department of Molecular Biology, Umeå University, Umeå, Sweden.,Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå, Sweden
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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.
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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;
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Hallberg ZF, Su Y, Kitto RZ, Hammond MC. Engineering and In Vivo Applications of Riboswitches. Annu Rev Biochem 2017; 86:515-539. [PMID: 28375743 DOI: 10.1146/annurev-biochem-060815-014628] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Riboswitches are common gene regulatory units mostly found in bacteria that are capable of altering gene expression in response to a small molecule. These structured RNA elements consist of two modular subunits: an aptamer domain that binds with high specificity and affinity to a target ligand and an expression platform that transduces ligand binding to a gene expression output. Significant progress has been made in engineering novel aptamer domains for new small molecule inducers of gene expression. Modified expression platforms have also been optimized to function when fused with both natural and synthetic aptamer domains. As this field expands, the use of these privileged scaffolds has permitted the development of tools such as RNA-based fluorescent biosensors. In this review, we summarize the methods that have been developed to engineer new riboswitches and highlight applications of natural and synthetic riboswitches in enzyme and strain engineering, in controlling gene expression and cellular physiology, and in real-time imaging of cellular metabolites and signals.
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Affiliation(s)
- Zachary F Hallberg
- Department of Chemistry, University of California, Berkeley, California 94720;
| | - Yichi Su
- Department of Chemistry, University of California, Berkeley, California 94720;
| | - Rebekah Z Kitto
- Department of Chemistry, University of California, Berkeley, California 94720;
| | - Ming C Hammond
- Department of Chemistry, University of California, Berkeley, California 94720; .,Department of Molecular and Cell Biology, University of California, Berkeley, California 94720
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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.
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31
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Zallot R, Yuan Y, de Crécy-Lagard V. The Escherichia coli COG1738 Member YhhQ Is Involved in 7-Cyanodeazaguanine (preQ₀) Transport. Biomolecules 2017; 7:E12. [PMID: 28208705 PMCID: PMC5372724 DOI: 10.3390/biom7010012] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 01/27/2017] [Accepted: 01/30/2017] [Indexed: 11/17/2022] Open
Abstract
Queuosine (Q) is a complex modification of the wobble base in tRNAs with GUN anticodons. The full Q biosynthesis pathway has been elucidated in Escherichia coli. FolE, QueD, QueE and QueC are involved in the conversion of guanosine triphosphate (GTP) to 7-cyano-7-deazaguanine (preQ₀), an intermediate of increasing interest for its central role in tRNA and DNA modification and secondary metabolism. QueF then reduces preQ₀ to 7-aminomethyl-7-deazaguanine (preQ₁). PreQ₁ is inserted into tRNAs by tRNA guanine(34) transglycosylase (TGT). The inserted base preQ₁ is finally matured to Q by two additional steps involving QueA and QueG or QueH. Most Eubacteria harbor the full set of Q synthesis genes and are predicted to synthesize Q de novo. However, some bacteria only encode enzymes involved in the second half of the pathway downstream of preQ₀ synthesis, including the signature enzyme TGT. Different patterns of distribution of the queF, tgt, queA and queG or queH genes are observed, suggesting preQ₀, preQ₁ or even the queuine base being salvaged in specific organisms. Such salvage pathways require the existence of specific 7-deazapurine transporters that have yet to be identified. The COG1738 family was identified as a candidate for a missing preQ₀/preQ₁ transporter in prokaryotes, by comparative genomics analyses. The existence of Q precursor salvage was confirmed for the first time in bacteria, in vivo, through an indirect assay. The involvement of the COG1738 in salvage of a Q precursor was experimentally validated in Escherichia coli, where it was shown that the COG1738 family member YhhQ is essential for preQ₀ transport.
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Affiliation(s)
- Rémi Zallot
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA.
| | - Yifeng Yuan
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA.
| | - Valérie de Crécy-Lagard
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA.
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Colameco S, Elliot MA. Non-coding RNAs as antibiotic targets. Biochem Pharmacol 2016; 133:29-42. [PMID: 28012959 DOI: 10.1016/j.bcp.2016.12.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 12/12/2016] [Indexed: 02/07/2023]
Abstract
Antibiotics inhibit a wide range of essential processes in the bacterial cell, including replication, transcription, translation and cell wall synthesis. In many instances, these antibiotics exert their effects through association with non-coding RNAs. This review highlights many classical antibiotic targets (e.g. rRNAs and the ribosome), explores a number of emerging targets (e.g. tRNAs, RNase P, riboswitches and small RNAs), and discusses the future directions and challenges associated with non-coding RNAs as antibiotic targets.
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Affiliation(s)
- Savannah Colameco
- Department of Biology and Institute for Infectious Disease Research, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada
| | - Marie A Elliot
- Department of Biology and Institute for Infectious Disease Research, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
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Slinger BL, Meyer MM. RNA regulators responding to ribosomal protein S15 are frequent in sequence space. Nucleic Acids Res 2016; 44:9331-9341. [PMID: 27580716 PMCID: PMC5100602 DOI: 10.1093/nar/gkw754] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 08/19/2016] [Indexed: 02/07/2023] Open
Abstract
There are several natural examples of distinct RNA structures that interact with the same ligand to regulate the expression of homologous genes in different organisms. One essential question regarding this phenomenon is whether such RNA regulators are the result of convergent or divergent evolution. Are the RNAs derived from some common ancestor and diverged to the point where we cannot identify the similarity, or have multiple solutions to the same biological problem arisen independently? A key variable in assessing these alternatives is how frequently such regulators arise within sequence space. Ribosomal protein S15 is autogenously regulated via an RNA regulator in many bacterial species; four apparently distinct regulators have been functionally validated in different bacterial phyla. Here, we explore how frequently such regulators arise within a partially randomized sequence population. We find many RNAs that interact specifically with ribosomal protein S15 from Geobacillus kaustophilus with biologically relevant dissociation constants. Furthermore, of the six sequences we characterize, four show regulatory activity in an Escherichia coli reporter assay. Subsequent footprinting and mutagenesis analysis indicates that protein binding proximal to regulatory features such as the Shine–Dalgarno sequence is sufficient to enable regulation, suggesting that regulation in response to S15 is relatively easily acquired.
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Affiliation(s)
- Betty L Slinger
- Biology Department, Boston College, Chestnut Hill, MA 02467, USA
| | - Michelle M Meyer
- Biology Department, Boston College, Chestnut Hill, MA 02467, USA
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34
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Dynamics Correlation Network for Allosteric Switching of PreQ1 Riboswitch. Sci Rep 2016; 6:31005. [PMID: 27484311 PMCID: PMC4971525 DOI: 10.1038/srep31005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 07/11/2016] [Indexed: 02/06/2023] Open
Abstract
Riboswitches are a class of metabolism control elements mostly found in bacteria. Due to their fundamental importance in bacteria gene regulation, riboswitches have been proposed as antibacterial drug targets. Prequeuosine (preQ1) is the last free precursor in the biosynthetic pathway of queuosine that is crucial for translation efficiency and fidelity. However, the regulation mechanism for the preQ1 riboswitch remains unclear. Here we constructed fluctuation correlation network based on all-atom molecular dynamics simulations to reveal the regulation mechanism. The results suggest that the correlation network in the bound riboswitch is distinctly different from that in the apo riboswitch. The community network indicates that the information freely transfers from the binding site of preQ1 to the expression platform of the P3 helix in the bound riboswitch and the P3 helix is a bottleneck in the apo riboswitch. Thus, a hypothesis of “preQ1-binding induced allosteric switching” is proposed to link riboswitch and translation regulation. The community networks of mutants support this hypothesis. Finally, a possible allosteric pathway of A50-A51-A52-U10-A11-G12-G56 was also identified based on the shortest path algorithm and confirmed by mutations and network perturbation. The novel fluctuation network analysis method can be used as a general strategy in studies of riboswitch structure-function relationship.
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35
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Meyer MM. The role of mRNA structure in bacterial translational regulation. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 8. [PMID: 27301829 DOI: 10.1002/wrna.1370] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 05/12/2016] [Accepted: 05/16/2016] [Indexed: 01/08/2023]
Abstract
The characteristics of bacterial messenger RNAs (mRNAs) that influence translation efficiency provide many convenient handles for regulation of gene expression, especially when coupled with the processes of transcription termination and mRNA degradation. An mRNA's structure, especially near the site of initiation, has profound consequences for how readily it is translated. This property allows bacterial gene expression to be altered by changes to mRNA structure induced by temperature, or interactions with a wide variety of cellular components including small molecules, other RNAs (such as sRNAs and tRNAs), and RNA-binding proteins. This review discusses the links between mRNA structure and translation efficiency, and how mRNA structure is manipulated by conditions and signals within the cell to regulate gene expression. The range of RNA regulators discussed follows a continuum from very complex tertiary structures such as riboswitch aptamers and ribosomal protein-binding sites to thermosensors and mRNA:sRNA interactions that involve only base-pairing interactions. Furthermore, the high degrees of diversity observed for both mRNA structures and the mechanisms by which inhibition of translation occur have significant consequences for understanding the evolution of bacterial translational regulation. WIREs RNA 2017, 8:e1370. doi: 10.1002/wrna.1370 For further resources related to this article, please visit the WIREs website.
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36
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Su Y, Hickey SF, Keyser SGL, Hammond MC. In Vitro and In Vivo Enzyme Activity Screening via RNA-Based Fluorescent Biosensors for S-Adenosyl-l-homocysteine (SAH). J Am Chem Soc 2016; 138:7040-7. [PMID: 27191512 DOI: 10.1021/jacs.6b01621] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
High-throughput enzyme activity screens are essential for target characterization and drug development, but few assays employ techniques or reagents that are applicable to both in vitro and live cell settings. Here, we present a class of selective and sensitive fluorescent biosensors for S-adenosyl-l-homocysteine (SAH) that provide a direct "mix and go" activity assay for methyltransferases (MTases), an enzyme class that includes several cancer therapeutic targets. Our riboswitch-based biosensors required an alternate inverted fusion design strategy, but retained full selectivity for SAH over its close structural analogue, the highly abundant methylation cofactor S-adenosyl-l-methionine (SAM). The level of ligand selectivity for these fluorescent biosensors exceeded that of commercial antibodies for SAH and proved critical to cellular applications, as we employed them to measure methylthioadenosine nucleosidase (MTAN) activity in live Escherichia coli. In particular, we were able to monitor in vivo increase of SAH levels upon chemical inhibition of MTAN using flow cytometry, which demonstrates high-throughput, single cell measurement of an enzyme activity associated with the biosynthesis of quorum sensing signal AI-2. Thus, this study presents RNA-based fluorescent biosensors as promising molecular reagents for high-throughput enzymatic assays that successfully bridge the gap between in vitro and in vivo applications.
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Affiliation(s)
- Yichi Su
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Scott F Hickey
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Samantha G L Keyser
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Ming C Hammond
- Department of Chemistry, University of California , Berkeley, California 94720, United States
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37
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Slinger BL, Newman H, Lee Y, Pei S, Meyer MM. Co-evolution of Bacterial Ribosomal Protein S15 with Diverse mRNA Regulatory Structures. PLoS Genet 2015; 11:e1005720. [PMID: 26675164 PMCID: PMC4684408 DOI: 10.1371/journal.pgen.1005720] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2015] [Accepted: 11/10/2015] [Indexed: 11/19/2022] Open
Abstract
RNA-protein interactions are critical in many biological processes, yet how such interactions affect the evolution of both partners is still unknown. RNA and protein structures are impacted very differently by mechanisms of genomic change. While most protein families are identifiable at the nucleotide level across large phylogenetic distances, RNA families display far less nucleotide similarity and are often only shared by closely related bacterial species. Ribosomal protein S15 has two RNA binding functions. First, it is a ribosomal protein responsible for organizing the rRNA during ribosome assembly. Second, in many bacterial species S15 also interacts with a structured portion of its own transcript to negatively regulate gene expression. While the first interaction is conserved in most bacteria, the second is not. Four distinct mRNA structures interact with S15 to enable regulation, each of which appears to be independently derived in different groups of bacteria. With the goal of understanding how protein-binding specificity may influence the evolution of such RNA regulatory structures, we examine whether examples of these mRNA structures are able to interact with, and regulate in response to, S15 homologs from organisms containing distinct mRNA structures. We find that despite their shared RNA binding function in the rRNA, S15 homologs have distinct RNA recognition profiles. We present a model to explain the specificity patterns observed, and support this model by with further mutagenesis. After analyzing the patterns of conservation for the S15 protein coding sequences, we also identified amino acid changes that alter the binding specificity of an S15 homolog. In this work we demonstrate that homologous RNA-binding proteins have different specificity profiles, and minor changes to amino acid sequences, or to RNA structural motifs, can have large impacts on RNA-protein recognition.
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Affiliation(s)
- Betty L. Slinger
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
| | - Hunter Newman
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
| | - Younghan Lee
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
| | - Shermin Pei
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
| | - Michelle M. Meyer
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
- * E-mail:
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38
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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.
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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
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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.
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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
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40
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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.
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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)
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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.
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42
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Imaging metabolite dynamics in living cells using a Spinach-based riboswitch. Proc Natl Acad Sci U S A 2015; 112:E2756-65. [PMID: 25964329 DOI: 10.1073/pnas.1504354112] [Citation(s) in RCA: 145] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Riboswitches are natural ligand-sensing RNAs typically that are found in the 5' UTRs of mRNA. Numerous classes of riboswitches have been discovered, enabling mRNA to be regulated by diverse and physiologically important cellular metabolites and small molecules. Here we describe Spinach riboswitches, a new class of genetically encoded metabolite sensor derived from naturally occurring riboswitches. Drawing upon the structural switching mechanism of natural riboswitches, we show that Spinach can be swapped for the expression platform of various riboswitches, allowing metabolite binding to induce Spinach fluorescence directly. In the case of the thiamine 5'-pyrophosphate (TPP) riboswitch from the Escherichia coli thiM gene encoding hydroxyethylthiazole kinase, we show that insertion of Spinach results in an RNA sensor that exhibits fluorescence upon binding TPP. This TPP Spinach riboswitch binds TPP with affinity and selectivity similar to that of the endogenous riboswitch and enables the discovery of agonists and antagonists of the TPP riboswitch using simple fluorescence readouts. Furthermore, expression of the TPP Spinach riboswitch in Escherichia coli enables live imaging of dynamic changes in intracellular TPP concentrations in individual cells. Additionally, we show that other riboswitches that use a structural mechanism similar to that of the TPP riboswitch, including the guanine and adenine riboswitches from the Bacillus subtilis xpt gene encoding xanthine phosphoribosyltransferase, and the S-adenosyl-methionine-I riboswitch from the B. subtilis yitJ gene encoding methionine synthase, can be converted into Spinach riboswitches. Thus, Spinach riboswitches constitute a novel class of RNA-based fluorescent metabolite sensors that exploit the diversity of naturally occurring ligand-binding riboswitches.
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Manzourolajdad A, Arnold J. Secondary structural entropy in RNA switch (Riboswitch) identification. BMC Bioinformatics 2015; 16:133. [PMID: 25928324 PMCID: PMC4448311 DOI: 10.1186/s12859-015-0523-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 03/02/2015] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND RNA regulatory elements play a significant role in gene regulation. Riboswitches, a widespread group of regulatory RNAs, are vital components of many bacterial genomes. These regulatory elements generally function by forming a ligand-induced alternative fold that controls access to ribosome binding sites or other regulatory sites in RNA. Riboswitch-mediated mechanisms are ubiquitous across bacterial genomes. A typical class of riboswitch has its own unique structural and biological complexity, making de novo riboswitch identification a formidable task. Traditionally, riboswitches have been identified through comparative genomics based on sequence and structural homology. The limitations of structural-homology-based approaches, coupled with the assumption that there is a great diversity of undiscovered riboswitches, suggests the need for alternative methods for riboswitch identification, possibly based on features intrinsic to their structure. As of yet, no such reliable method has been proposed. RESULTS We used structural entropy of riboswitch sequences as a measure of their secondary structural dynamics. Entropy values of a diverse set of riboswitches were compared to that of their mutants, their dinucleotide shuffles, and their reverse complement sequences under different stochastic context-free grammar folding models. Significance of our results was evaluated by comparison to other approaches, such as the base-pairing entropy and energy landscapes dynamics. Classifiers based on structural entropy optimized via sequence and structural features were devised as riboswitch identifiers and tested on Bacillus subtilis, Escherichia coli, and Synechococcus elongatus as an exploration of structural entropy based approaches. The unusually long untranslated region of the cotH in Bacillus subtilis, as well as upstream regions of certain genes, such as the sucC genes were associated with significant structural entropy values in genome-wide examinations. CONCLUSIONS Various tests show that there is in fact a relationship between higher structural entropy and the potential for the RNA sequence to have alternative structures, within the limitations of our methodology. This relationship, though modest, is consistent across various tests. Understanding the behavior of structural entropy as a fairly new feature for RNA conformational dynamics, however, may require extensive exploratory investigation both across RNA sequences and folding models.
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Affiliation(s)
- Amirhossein Manzourolajdad
- Institute of Bioinformatics, University of Georgia, Davison Life Sciences Bldg, Room B118B, 120 Green St, Athens, 30602, USA. .,National Center for Biotechnology Information (NCBI), NIH, Building 38A, RM 6S614K, 8600 Rockville Pike, Bethesda, 20894, USA.
| | - Jonathan Arnold
- Institute of Bioinformatics, University of Georgia, Davison Life Sciences Bldg, Room B118B, 120 Green St, Athens, 30602, USA. .,Department of Genetics, University of Georgia, Davison Life Sciences Bldg, 120 Green St, Athens, 30602, USA.
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Levic J, Micura R. Syntheses of (15)N-labeled pre-queuosine nucleobase derivatives. Beilstein J Org Chem 2014; 10:1914-8. [PMID: 25246950 PMCID: PMC4168690 DOI: 10.3762/bjoc.10.199] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2014] [Accepted: 07/14/2014] [Indexed: 01/21/2023] Open
Abstract
Pre-queuosine or queuine (preQ1) is a guanine derivative that is involved in the biosynthetic pathway of the hypermodified tRNA nucleoside queuosine (Que). The core structure of preQ1 is represented by 7-(aminomethyl)-7-deazaguanine (preQ1 base). Here, we report the synthesis of three preQ1 base derivatives with complementary 15N-labeling patterns, utilizing [15N]-KCN, [15N]-phthalimide, and [15N3]-guanidine as cost-affordable 15N sources. Such derivatives are required to explore the binding process of the preQ1 base to RNA targets using advanced NMR spectroscopic methods. PreQ1 base specifically binds to bacterial mRNA domains and thereby regulates genes that are required for queuosine biosynthesis.
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Affiliation(s)
- Jasmin Levic
- Institute of Organic Chemistry, University of Innsbruck and Center for Molecular Biosciences Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Ronald Micura
- Institute of Organic Chemistry, University of Innsbruck and Center for Molecular Biosciences Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
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Zallot R, Brochier-Armanet C, Gaston KW, Forouhar F, Limbach PA, Hunt JF, de Crécy-Lagard V. Plant, animal, and fungal micronutrient queuosine is salvaged by members of the DUF2419 protein family. ACS Chem Biol 2014; 9:1812-25. [PMID: 24911101 PMCID: PMC4136680 DOI: 10.1021/cb500278k] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
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Queuosine (Q) is a modification found
at the wobble position of
tRNAs with GUN anticodons. Although Q is present in most eukaryotes
and bacteria, only bacteria can synthesize Q de novo. Eukaryotes acquire queuine (q), the free base of Q, from diet and/or
microflora, making q an important but under-recognized micronutrient
for plants, animals, and fungi. Eukaryotic type tRNA-guanine transglycosylases
(eTGTs) are composed of a catalytic subunit (QTRT1) and a homologous
accessory subunit (QTRTD1) forming a complex that catalyzes q insertion
into target tRNAs. Phylogenetic analysis of eTGT subunits revealed
a patchy distribution pattern in which gene losses occurred independently
in different clades. Searches for genes co-distributing with eTGT
family members identified DUF2419 as a potential Q salvage protein
family. This prediction was experimentally validated in Schizosaccharomyces
pombe by confirming that Q was present by analyzing tRNAAsp with anticodon GUC purified from wild-type cells and by
showing that Q was absent from strains carrying deletions in the QTRT1
or DUF2419 encoding genes. DUF2419 proteins occur in most Eukarya
with a few possible cases of horizontal gene transfer to bacteria.
The universality of the DUF2419 function was confirmed by complementing
the S. pombe mutant with the Zea mays (maize), human, and Sphaerobacter thermophilus homologues.
The enzymatic function of this family is yet to be determined, but
structural similarity with DNA glycosidases suggests a ribonucleoside
hydrolase activity.
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Affiliation(s)
- Rémi Zallot
- Department
of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611, United States
| | - Céline Brochier-Armanet
- Université
Lyon 1, CNRS, UMR5558, Laboratoire de Biométrie et Biologie
Evolutive, Université de Lyon, 69622 Villeurbanne, France
| | - Kirk W. Gaston
- Rieveschl
Laboratories for Mass Spectrometry, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Farhad Forouhar
- Department
of Biological Sciences and Northeast Structural Genomics Consortium, Columbia University, New York, New York 10027, United States
| | - Patrick A. Limbach
- Rieveschl
Laboratories for Mass Spectrometry, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - John F. Hunt
- Department
of Biological Sciences and Northeast Structural Genomics Consortium, Columbia University, New York, New York 10027, United States
| | - Valérie de Crécy-Lagard
- Department
of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611, United States
- University of Florida Genetics Institute, Gainesville, Florida 32611, United States
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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.
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Affiliation(s)
- Alla Peselis
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
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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.
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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
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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.
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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.
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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.
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Fowler CC, Li Y. Construction and application of riboswitch-based sensors that detect metabolites within bacterial cells. Methods Mol Biol 2014; 1103:177-97. [PMID: 24318895 DOI: 10.1007/978-1-62703-730-3_14] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A riboswitch is an RNA element that detects the level of a specific metabolite within the cell and regulates the expression of co-transcribed genes. By fusing a riboswitch to a reporter protein in a carefully designed and tested construct, this ability can be exploited to create an intracellular sensor that detects the level of a particular small molecule within live bacterial cells. There is a great deal of flexibility in the design of such a sensor and factors such as the molecule to be detected and the downstream experiments in which the sensor will be applied should guide the specific blueprint of the final construct. The completed sensor plasmid needs to be rigorously tested with appropriate controls to ensure that its dynamic range, signal strength, sensitivity and specificity are suitable for its intended applications. In this chapter, methods for the design, assessment and use of riboswitch sensors are provided along with those for one example application for which riboswitch sensors are ideally suited.
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Affiliation(s)
- Casey C Fowler
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
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