1
|
Schroeder GM, Kiliushik D, Jenkins JL, Wedekind JE. Structure and function analysis of a type III preQ 1-I riboswitch from Escherichia coli reveals direct metabolite sensing by the Shine-Dalgarno sequence. J Biol Chem 2023; 299:105208. [PMID: 37660906 PMCID: PMC10622847 DOI: 10.1016/j.jbc.2023.105208] [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: 06/27/2023] [Revised: 08/18/2023] [Accepted: 08/22/2023] [Indexed: 09/05/2023] Open
Abstract
Riboswitches are small noncoding RNAs found primarily in the 5' leader regions of bacterial messenger RNAs where they regulate expression of downstream genes in response to binding one or more cellular metabolites. Such noncoding RNAs are often regulated at the translation level, which is thought to be mediated by the accessibility of the Shine-Dalgarno sequence (SDS) ribosome-binding site. Three classes (I-III) of prequeuosine1 (preQ1)-sensing riboswitches are known that control translation. Class I is divided into three subtypes (types I-III) that have diverse mechanisms of sensing preQ1, which is involved in queuosine biosynthesis. To provide insight into translation control, we determined a 2.30 Å-resolution cocrystal structure of a class I type III preQ1-sensing riboswitch identified in Escherichia coli (Eco) by bioinformatic searches. The Eco riboswitch structure differs from previous preQ1 riboswitch structures because it has the smallest naturally occurring aptamer and the SDS directly contacts the preQ1 metabolite. We validated structural observations using surface plasmon resonance and in vivo gene-expression assays, which showed strong switching in live E. coli. Our results demonstrate that the Eco riboswitch is relatively sensitive to mutations that disrupt noncanonical interactions that form the pseudoknot. In contrast to type II preQ1 riboswitches, a kinetic analysis showed that the type III Eco riboswitch strongly prefers preQ1 over the chemically similar metabolic precursor preQ0. Our results reveal the importance of noncanonical interactions in riboswitch-driven gene regulation and the versatility of the class I preQ1 riboswitch pseudoknot as a metabolite-sensing platform that supports SDS sequestration.
Collapse
Affiliation(s)
- Griffin M Schroeder
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Daniil Kiliushik
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Jermaine L Jenkins
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
| | - Joseph E Wedekind
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
| |
Collapse
|
2
|
Liao TW, Huang L, Wilson TJ, Ganser LR, Lilley DMJ, Ha T. Linking folding dynamics and function of SAM/SAH riboswitches at the single molecule level. Nucleic Acids Res 2023; 51:8957-8969. [PMID: 37522343 PMCID: PMC10516623 DOI: 10.1093/nar/gkad633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 06/27/2023] [Accepted: 07/18/2023] [Indexed: 08/01/2023] Open
Abstract
Riboswitches are regulatory elements found in bacterial mRNAs that control downstream gene expression through ligand-induced conformational changes. Here, we used single-molecule FRET to map the conformational landscape of the translational SAM/SAH riboswitch and probe how co-transcriptional ligand-induced conformational changes affect its translation regulation function. Riboswitch folding is highly heterogeneous, suggesting a rugged conformational landscape that allows for sampling of the ligand-bound conformation even in the absence of ligand. The addition of ligand shifts the landscape, favoring the ligand-bound conformation. Mutation studies identified a key structural element, the pseudoknot helix, that is crucial for determining ligand-free conformations and their ligand responsiveness. We also investigated ribosomal binding site accessibility under two scenarios: pre-folding and co-transcriptional folding. The regulatory function of the SAM/SAH riboswitch involves kinetically favoring ligand binding, but co-transcriptional folding reduces this preference with a less compact initial conformation that exposes the Shine-Dalgarno sequence and takes min to redistribute to more compact conformations of the pre-folded riboswitch. Such slow equilibration decreases the effective ligand affinity. Overall, our study provides a deeper understanding of the complex folding process and how the riboswitch adapts its folding pattern in response to ligand, modulates ribosome accessibility and the role of co-transcriptional folding in these processes.
Collapse
Affiliation(s)
- Ting-Wei Liao
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Lin Huang
- Guangdong Provincial Key Laboratory of Malignant Tumor Epigenetics and Gene Regulation, Guangdong-Hong Kong Joint Laboratory for RNA Medicine, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, China
| | - Timothy J Wilson
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Laura R Ganser
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - David M J Lilley
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Taekjip Ha
- Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Howard Hughes Medical Institute, Baltimore, MD, USA
| |
Collapse
|
3
|
Schroeder GM, Akinyemi O, Malik J, Focht CM, Pritchett E, Baker C, McSally JP, Jenkins JL, Mathews D, Wedekind J. A riboswitch separated from its ribosome-binding site still regulates translation. Nucleic Acids Res 2023; 51:2464-2484. [PMID: 36762498 PMCID: PMC10018353 DOI: 10.1093/nar/gkad056] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 01/14/2023] [Accepted: 02/07/2023] [Indexed: 02/11/2023] Open
Abstract
Riboswitches regulate downstream gene expression by binding cellular metabolites. Regulation of translation initiation by riboswitches is posited to occur by metabolite-mediated sequestration of the Shine-Dalgarno sequence (SDS), causing bypass by the ribosome. Recently, we solved a co-crystal structure of a prequeuosine1-sensing riboswitch from Carnobacterium antarcticum that binds two metabolites in a single pocket. The structure revealed that the second nucleotide within the gene-regulatory SDS, G34, engages in a crystal contact, obscuring the molecular basis of gene regulation. Here, we report a co-crystal structure wherein C10 pairs with G34. However, molecular dynamics simulations reveal quick dissolution of the pair, which fails to reform. Functional and chemical probing assays inside live bacterial cells corroborate the dispensability of the C10-G34 pair in gene regulation, leading to the hypothesis that the compact pseudoknot fold is sufficient for translation attenuation. Remarkably, the C. antarcticum aptamer retained significant gene-regulatory activity when uncoupled from the SDS using unstructured spacers up to 10 nucleotides away from the riboswitch-akin to steric-blocking employed by sRNAs. Accordingly, our work reveals that the RNA fold regulates translation without SDS sequestration, expanding known riboswitch-mediated gene-regulatory mechanisms. The results infer that riboswitches exist wherein the SDS is not embedded inside a stable fold.
Collapse
Affiliation(s)
- Griffin M Schroeder
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - Olayinka Akinyemi
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Department of Physics, University of Rochester, Rochester, NY 14642, USA
| | - Jeffrey Malik
- Genomics Research Center, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - Caroline M Focht
- Department of Molecular Biophysics and Biochemistry and the Institute of Biomolecular Design and Discovery, Yale University, New Haven, CT 06516, USA
| | - Elizabeth M Pritchett
- Genomics Research Center, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - Cameron D Baker
- Genomics Research Center, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - James P McSally
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - Jermaine L Jenkins
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - David H Mathews
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| | - Joseph E Wedekind
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
- Center for RNA Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
| |
Collapse
|
4
|
Bessler L, Kaur N, Vogt LM, Flemmich L, Siebenaller C, Winz ML, Tuorto F, Micura R, Ehrenhofer-Murray AE, Helm M. Functional integration of a semi-synthetic azido-queuosine derivative into translation and a tRNA modification circuit. Nucleic Acids Res 2022; 50:10785-10800. [PMID: 36169220 PMCID: PMC9561289 DOI: 10.1093/nar/gkac822] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 09/09/2022] [Accepted: 09/27/2022] [Indexed: 11/17/2022] Open
Abstract
Substitution of the queuine nucleobase precursor preQ1 by an azide-containing derivative (azido-propyl-preQ1) led to incorporation of this clickable chemical entity into tRNA via transglycosylation in vitro as well as in vivo in Escherichia coli, Schizosaccharomyces pombe and human cells. The resulting semi-synthetic RNA modification, here termed Q-L1, was present in tRNAs on actively translating ribosomes, indicating functional integration into aminoacylation and recruitment to the ribosome. The azide moiety of Q-L1 facilitates analytics via click conjugation of a fluorescent dye, or of biotin for affinity purification. Combining the latter with RNAseq showed that TGT maintained its native tRNA substrate specificity in S. pombe cells. The semi-synthetic tRNA modification Q-L1 was also functional in tRNA maturation, in effectively replacing the natural queuosine in its stimulation of further modification of tRNAAsp with 5-methylcytosine at position 38 by the tRNA methyltransferase Dnmt2 in S. pombe. This is the first demonstrated in vivo integration of a synthetic moiety into an RNA modification circuit, where one RNA modification stimulates another. In summary, the scarcity of queuosinylation sites in cellular RNA, makes our synthetic q/Q system a ‘minimally invasive’ system for placement of a non-natural, clickable nucleobase within the total cellular RNA.
Collapse
Affiliation(s)
- Larissa Bessler
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
| | - Navpreet Kaur
- Institute of Biology, Humboldt-Universität zu Berlin, 10117 Berlin, Germany
| | - Lea-Marie Vogt
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
| | - Laurin Flemmich
- Department of Organic Chemistry, University of Innsbruck, 6020 Innsbruck, Austria
| | - Carmen Siebenaller
- Department of Chemistry - Biochemistry, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
| | - Marie-Luise Winz
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
| | - Francesca Tuorto
- Division of Biochemistry, Mannheim Institute for Innate Immunoscience (MI3), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Ronald Micura
- Department of Organic Chemistry, University of Innsbruck, 6020 Innsbruck, Austria
| | | | - Mark Helm
- Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
| |
Collapse
|
5
|
A small RNA that cooperatively senses two stacked metabolites in one pocket for gene control. Nat Commun 2022; 13:199. [PMID: 35017488 PMCID: PMC8752633 DOI: 10.1038/s41467-021-27790-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 12/02/2021] [Indexed: 11/16/2022] Open
Abstract
Riboswitches are structured non-coding RNAs often located upstream of essential genes in bacterial messenger RNAs. Such RNAs regulate expression of downstream genes by recognizing a specific cellular effector. Although nearly 50 riboswitch classes are known, only a handful recognize multiple effectors. Here, we report the 2.60-Å resolution co-crystal structure of a class I type I preQ1-sensing riboswitch that reveals two effectors stacked atop one another in a single binding pocket. These effectors bind with positive cooperativity in vitro and both molecules are necessary for gene regulation in bacterial cells. Stacked effector recognition appears to be a hallmark of the largest subgroup of preQ1 riboswitches, including those from pathogens such as Neisseria gonorrhoeae. We postulate that binding to stacked effectors arose in the RNA World to closely position two substrates for RNA-mediated catalysis. These findings expand known effector recognition capabilities of riboswitches and have implications for antimicrobial development. Riboswitches contain an aptamer domain that recognizes a metabolite and an expression platform that regulates gene expression. Here the authors report the crystal structure of a preQ1-sensing riboswitch from Carnobacterium antarcticus that shows two metabolites in a single binding pocket.
Collapse
|
6
|
Balaratnam S, Rhodes C, Bume DD, Connelly C, Lai CC, Kelley JA, Yazdani K, Homan PJ, Incarnato D, Numata T, Schneekloth Jr JS. A chemical probe based on the PreQ 1 metabolite enables transcriptome-wide mapping of binding sites. Nat Commun 2021; 12:5856. [PMID: 34615874 PMCID: PMC8494917 DOI: 10.1038/s41467-021-25973-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 08/26/2021] [Indexed: 02/08/2023] Open
Abstract
The role of metabolite-responsive riboswitches in regulating gene expression in bacteria is well known and makes them useful systems for the study of RNA-small molecule interactions. Here, we study the PreQ1 riboswitch system, assessing sixteen diverse PreQ1-derived probes for their ability to selectively modify the class-I PreQ1 riboswitch aptamer covalently. For the most active probe (11), a diazirine-based photocrosslinking analog of PreQ1, X-ray crystallography and gel-based competition assays demonstrated the mode of binding of the ligand to the aptamer, and functional assays demonstrated that the probe retains activity against the full riboswitch. Transcriptome-wide mapping using Chem-CLIP revealed a highly selective interaction between the bacterial aptamer and the probe. In addition, a small number of RNA targets in endogenous human transcripts were found to bind specifically to 11, providing evidence for candidate PreQ1 aptamers in human RNA. This work demonstrates a stark influence of linker chemistry and structure on the ability of molecules to crosslink RNA, reveals that the PreQ1 aptamer/ligand pair are broadly useful for chemical biology applications, and provides insights into how PreQ1, which is similar in structure to guanine, interacts with human RNAs.
Collapse
Affiliation(s)
- Sumirtha Balaratnam
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Curran Rhodes
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Desta Doro Bume
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Colleen Connelly
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Christopher C. Lai
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - James A. Kelley
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Kamyar Yazdani
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| | - Philip J. Homan
- grid.48336.3a0000 0004 1936 8075Center for Cancer Research Collaborative Bioinformatics Resource, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892 USA ,grid.418021.e0000 0004 0535 8394Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD 21702 USA
| | - Danny Incarnato
- grid.4830.f0000 0004 0407 1981Department of Molecular Genetics, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands
| | - Tomoyuki Numata
- grid.177174.30000 0001 2242 4849Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka-shi Fukuoka, 812-8582 Japan ,grid.208504.b0000 0001 2230 7538Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba-shi, Ibaraki, 305-8566 Japan
| | - John S. Schneekloth Jr
- grid.48336.3a0000 0004 1936 8075Chemical Biology Laboratory, National Cancer Institute, Frederick, MD 21702 USA
| |
Collapse
|
7
|
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] [Grants] [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-O 6-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 O 6-alkylated preQ1 derivatives. Here, we report a robust synthesis for this class of pyrrolo[2,3-d]pyrimidines starting from readily accessible N 2-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 O 6-alkylated 7-aminomethyl-7-deazaguanines for the development of RNA labeling tools based on the preQ1 class-I riboswitch scaffold.
Collapse
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
| |
Collapse
|
8
|
Frommer J, Müller S. Changed reactivity of secondary hydroxy groups in C8-modified adenosine - lessons learned from silylation. Beilstein J Org Chem 2020; 16:2854-2861. [PMID: 33299483 PMCID: PMC7705864 DOI: 10.3762/bjoc.16.234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 11/03/2020] [Indexed: 12/03/2022] Open
Abstract
Synthesis of site-specifically modified oligonucleotides has become a major tool for RNA structure and function studies. Reporter groups or specific functional entities are required to be attached at a pre-defined site of the oligomer. An attractive strategy is the incorporation of suitably functionalized building blocks that allow post-synthetic conjugation of the desired moiety. A C8-alkynyl-modified adenosine derivative was synthesized, reviving an old synthetic pathway for iodination of purine nucleobases. Silylation of the C8-alkynyl-modified adenosine revealed unexpected selectivity of the two secondary sugar hydroxy groups, with the 3'-O-isomer being preferentially formed. Optimization of the protection scheme lead to a new and economic route to the desired C8-alkynylated building block and its incorporation in RNA.
Collapse
Affiliation(s)
- Jennifer Frommer
- Institute for Biochemistry, University Greifswald, Felix-Hausdorff Str. 4, D-17487 Greifswald, Germany
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Sabine Müller
- Institute for Biochemistry, University Greifswald, Felix-Hausdorff Str. 4, D-17487 Greifswald, Germany
| |
Collapse
|
9
|
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: 37] [Impact Index Per Article: 9.3] [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
Collapse
Affiliation(s)
- Jessica A Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, USA
| |
Collapse
|
10
|
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.
Collapse
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.
| |
Collapse
|