1
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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.
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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
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2
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Li M, Deng J, Peng X, Wang J, Wilson TJ, Huang L, Lilley DMJ. Structure and ion-dependent folding of k-junctions. RNA (NEW YORK, N.Y.) 2023; 29:1411-1422. [PMID: 37311599 PMCID: PMC10573300 DOI: 10.1261/rna.079678.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Accepted: 05/22/2023] [Indexed: 06/15/2023]
Abstract
k-Junctions are elaborated forms of kink turns with an additional helix on the nonbulged strand, thus forming a three-way helical junction. Two were originally identified in the structures of Arabidopsis and Escherichia coli thiamine pyrophosphate (TPP) riboswitches, and another called DUF-3268 was tentatively identified from sequence information. In this work we show that the Arabidopsis and E. coli riboswitch k-junctions fold in response to the addition of magnesium or sodium ions, and that atomic mutations that should disrupt key hydrogen bonding interactions greatly impair folding. Using X-ray crystallography, we have determined the structure of the DUF-3268 RNA and thus confirmed that it is a k-junction. It also folds upon the addition of metal ions, though requiring a 40-fold lower concentration of either divalent or monovalent ions. The key difference between the DUF-3268 and riboswitch k-junctions is the lack of nucleotides inserted between G1b and A2b in the former. We show that this insertion is primarily responsible for the difference in folding properties. Finally, we show that the DUF-3268 can functionally substitute for the k-junction in the E. coli TPP riboswitch such that the chimera can bind the TPP ligand, although less avidly.
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Affiliation(s)
- Mengxiao Li
- 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
| | - Jie Deng
- 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
| | - Xuemei Peng
- 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
| | - Jia Wang
- College of Pharmacy, Shenzhen Technology University, Shenzhen 518118, China
| | - Timothy J Wilson
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - 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
| | - David M J Lilley
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
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3
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Peng X, Liao W, Lin X, Lilley DMJ, Huang L. Crystal structures of the NAD+-II riboswitch reveal two distinct ligand-binding pockets. Nucleic Acids Res 2023; 51:2904-2914. [PMID: 36840714 PMCID: PMC10085692 DOI: 10.1093/nar/gkad102] [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: 11/21/2022] [Revised: 02/01/2023] [Accepted: 02/16/2023] [Indexed: 02/26/2023] Open
Abstract
We present crystal structures of a new NAD+-binding riboswitch termed NAD+-II, bound to nicotinamide mononucleotide (NMN), nicotinamide adenine dinucleotide (NAD+) and nicotinamide riboside (NR). The RNA structure comprises a number of structural features including three helices, one of which forms a triple helix by interacting with an A5 strand in its minor-groove, and another formed from a long-range pseudoknot. The core of the structure (centrally located and coaxial with the triplex and the pseudoknot) includes two consecutive quadruple base interactions. Unusually the riboswitch binds two molecules of ligand, bound at distinct, non-overlapping sites in the RNA. Binding occurs primarily through the nicotinamide moiety of each ligand, held by specific hydrogen bonding and stacking interactions with the pyridyl ring. The mode of binding is the same for NMN, NR and the nicotinamide moiety of NAD+. In addition, when NAD+ is bound into one site it adopts an elongated conformation such that its diphosphate linker occupies a groove on the surface of the RNA, following which the adenine portion inserts into a pocket and makes specific hydrogen bonding interactions. Thus the NAD+-II riboswitch is distinct from the NAD+-I riboswitch in that it binds two molecules of ligand at separate sites, and that binding occurs principally through the nicotinamide moiety.
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Affiliation(s)
- Xuemei Peng
- 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, China
- Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Wenjian Liao
- 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, China
- Department of Urology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Xiaowei Lin
- 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, China
- Department of Urology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - 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
| | - 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, China
- Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
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4
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Deng J, Wilson TJ, Wang J, Peng X, Li M, Lin X, Liao W, Lilley DMJ, Huang L. Structure and mechanism of a methyltransferase ribozyme. Nat Chem Biol 2022; 18:556-564. [PMID: 35301479 PMCID: PMC9050513 DOI: 10.1038/s41589-022-00982-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 01/26/2022] [Indexed: 11/09/2022]
Abstract
Known ribozymes in contemporary biology perform a limited range of chemical catalysis, but in vitro selection has generated species that catalyze a broader range of chemistry; yet, there have been few structural and mechanistic studies of selected ribozymes. A ribozyme has recently been selected that can catalyze a site-specific methyl transfer reaction. We have solved the crystal structure of this ribozyme at a resolution of 2.3 Å, showing how the RNA folds to generate a very specific binding site for the methyl donor substrate. The structure immediately suggests a catalytic mechanism involving a combination of proximity and orientation and nucleobase-mediated general acid catalysis. The mechanism is supported by the pH dependence of the rate of catalysis. A selected methyltransferase ribozyme can thus use a relatively sophisticated catalytic mechanism, broadening the range of known RNA-catalyzed chemistry. ![]()
The authors present the crystal structure of the MTR1 ribozyme that transfers the methyl group from O6-methylguanine to an adenine N1 in the target RNA and propose a catalytic mechanism based upon proximity, orientation and general acid catalysis.
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Affiliation(s)
- Jie Deng
- 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, China.,Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK
| | - Jia Wang
- College of Life Sciences, Guangzhou University, Guangzhou, China
| | - Xuemei Peng
- 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, China.,Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Mengxiao Li
- 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, China.,Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Xiaowei Lin
- 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, China.,Department of Urology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - Wenjian Liao
- 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, China.,Department of Urology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK.
| | - 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, China. .,Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, China.
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5
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Weinberg CE, Olzog VJ, Eckert I, Weinberg Z. Identification of over 200-fold more hairpin ribozymes than previously known in diverse circular RNAs. Nucleic Acids Res 2021; 49:6375-6388. [PMID: 34096583 PMCID: PMC8216279 DOI: 10.1093/nar/gkab454] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 05/12/2021] [Indexed: 11/18/2022] Open
Abstract
Self-cleaving ribozymes are catalytic RNAs that cut themselves at a specific inter-nucleotide linkage. They serve as a model of RNA catalysis, and as an important tool in biotechnology. For most of the nine known structural classes of self-cleaving ribozymes, at least hundreds of examples are known, and some are present in multiple domains of life. By contrast, only four unique examples of the hairpin ribozyme class are known, despite its discovery in 1986. We bioinformatically predicted 941 unique hairpin ribozymes of a different permuted form from the four previously known hairpin ribozymes, and experimentally confirmed several diverse predictions. These results profoundly expand the number of natural hairpin ribozymes, enabling biochemical analysis based on natural sequences, and suggest that a distinct permuted form is more biologically relevant. Moreover, all novel hairpins were discovered in metatranscriptomes. They apparently reside in RNA molecules that vary both in size—from 381 to 5170 nucleotides—and in protein content. The RNA molecules likely replicate as circular single-stranded RNAs, and potentially provide a dramatic increase in diversity of such RNAs. Moreover, these organisms have eluded previous attempts to isolate RNA viruses from metatranscriptomes—suggesting a significant untapped universe of viruses or other organisms hidden within metatranscriptome sequences.
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Affiliation(s)
- Christina E Weinberg
- Institute for Biochemistry, Leipzig University, Brüderstraße 34, 04103 Leipzig, Germany
| | - V Janett Olzog
- Institute for Biochemistry, Leipzig University, Brüderstraße 34, 04103 Leipzig, Germany
| | - Iris Eckert
- Bioinformatics Group, Department of Computer Science and Interdisciplinary Centre for Bioinformatics, Leipzig University, Härtelstraße 16-18, 04107 Leipzig, Germany
| | - Zasha Weinberg
- Bioinformatics Group, Department of Computer Science and Interdisciplinary Centre for Bioinformatics, Leipzig University, Härtelstraße 16-18, 04107 Leipzig, Germany
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6
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Huang L, Liao X, Li M, Wang J, Peng X, Wilson TJ, Lilley DMJ. Structure and folding of four putative kink turns identified in structured RNA species in a test of structural prediction rules. Nucleic Acids Res 2021; 49:5916-5924. [PMID: 33978763 PMCID: PMC8191799 DOI: 10.1093/nar/gkab333] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 04/13/2021] [Accepted: 05/09/2021] [Indexed: 01/25/2023] Open
Abstract
k-Turns are widespread key architectural elements that occur in many classes of RNA molecules. We have shown previously that their folding properties (whether or not they fold into their tightly kinked structure on addition of metal ions) and conformation depend on their local sequence, and we have elucidated a series of rules for prediction of these properties from sequence. In this work, we have expanded the rules for prediction of folding properties, and then applied the full set to predict the folding and conformation of four probable k-turns we have identified amongst 224 structured RNA species found in bacterial intergenenic regions by the Breaker lab (1). We have analyzed the ion-dependence of folding of the four k-turns using fluorescence resonance energy transfer, and determined the conformation of two of them using X-ray crystallography. We find that the experimental data fully conform to both the predicted folding and conformational properties. We conclude that our folding rules are robust, and can be applied to new k-turns of unknown characteristics with confidence.
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Affiliation(s)
- Lin Huang
- Guangdong Provincial Key Laboratory of Malignant Tumor Epigenetics and Gene Regulation, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, PR China
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Xinli Liao
- Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, PR China
| | - Mengxiao Li
- Guangdong Provincial Key Laboratory of Malignant Tumor Epigenetics and Gene Regulation, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, PR China
| | - Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Xuemei Peng
- Guangdong Provincial Key Laboratory of Malignant Tumor Epigenetics and Gene Regulation, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, PR China
| | - 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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7
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Huang L, Liao TW, Wang J, Ha T, Lilley DMJ. Crystal structure and ligand-induced folding of the SAM/SAH riboswitch. Nucleic Acids Res 2020; 48:7545-7556. [PMID: 32520325 PMCID: PMC7367207 DOI: 10.1093/nar/gkaa493] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 05/25/2020] [Accepted: 05/30/2020] [Indexed: 01/09/2023] Open
Abstract
While most SAM riboswitches strongly discriminate between SAM and SAH, the SAM/SAH riboswitch responds to both ligands with similar apparent affinities. We have determined crystal structures of the SAM/SAH riboswitch bound to SAH, SAM and other variant ligands at high resolution. The riboswitch forms an H-type pseudoknot structure with coaxial alignment of the stem–loop helix (P1) and the pseudoknot helix (PK). An additional three base pairs form at the non-open end of P1, and the ligand is bound at the interface between the P1 extension and the PK helix. The adenine nucleobase is stacked into the helix and forms a trans Hoogsteen–Watson–Crick base pair with a uridine, thus becoming an integral part of the helical structure. The majority of the specific interactions are formed with the adenosine. The methionine or homocysteine chain lies in the groove making a single hydrogen bond, and there is no discrimination between the sulfonium of SAM or the thioether of SAH. Single-molecule FRET analysis reveals that the riboswitch exists in two distinct conformations, and that addition of SAM or SAH shifts the population into a stable state that likely corresponds to the form observed in the crystal. A model for translational regulation is presented whereby in the absence of ligand the riboswitch is largely unfolded, lacking the PK helix so that translation can be initiated at the ribosome binding site. But the presence of ligand stabilizes the folded conformation that includes the PK helix, so occluding the ribosome binding site and thus preventing the initiation of translation.
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Affiliation(s)
- Lin Huang
- Guangdong Provincial Key Laboratory of Malignant Tumor Epigenetics and Gene Regulation, Medical Research Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, P. R. China.,RNA Biomedical Institute, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou 510120, P. R. China.,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
| | - Taekjip Ha
- Department of Biophysics.,Department of Biophysics and Biophysical Chemistry.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, USA.,Howard Hughes Medical Institute, Baltimore, MD, USA
| | - 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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8
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Huang L, Wang J, Lilley DMJ. Structure and ligand binding of the ADP-binding domain of the NAD + riboswitch. RNA (NEW YORK, N.Y.) 2020; 26:878-887. [PMID: 32295864 PMCID: PMC7297122 DOI: 10.1261/rna.074898.120] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 03/22/2020] [Indexed: 06/02/2023]
Abstract
The nadA motif is the first known NAD+-dependent riboswitch, comprising two similar tandem bulged stem-loop structures. We have determined the structure of the 5' domain 1 of the riboswitch. It has three coaxial helical segments, separated by an ACANCCCC bulge and by an internal loop, with a tertiary contact between them that includes two C:G base pairs. We have determined the structure with a number of ligands related to NADH, but in each case only the ADP moiety is observed. The adenosine adopts an anti conformation, forms multiple hydrogen bonds across the width of the sugar edge of the penultimate C:G base pair of the helix preceding the bulge, and the observed contacts have been confirmed by mutagenesis and calorimetry. Two divalent metal ions play a key structural role at the narrow neck of the bulge. One makes direct bonding contacts to the diphosphate moiety, locking it into position. Thus the nucleobase, ribose, and phosphate groups of the ADP moiety are all specifically recognized by the RNA. The NAD+ riboswitch is modular. Domain 1 is an ADP binding domain that may be ancient and could potentially be used in combination with other ligand binding motifs such as CoA.
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Affiliation(s)
- Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
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9
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Huang L, Wang J, Watkins AM, Das R, Lilley DMJ. Structure and ligand binding of the glutamine-II riboswitch. Nucleic Acids Res 2019; 47:7666-7675. [PMID: 31216023 PMCID: PMC6698751 DOI: 10.1093/nar/gkz539] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 05/31/2019] [Accepted: 06/06/2019] [Indexed: 12/14/2022] Open
Abstract
We have determined the structure of the glutamine-II riboswitch ligand binding domain using X-ray crystallography. The structure was solved using a novel combination of homology modeling and molecular replacement. The structure comprises three coaxial helical domains, the central one of which is a pseudoknot with partial triplex character. The major groove of this helix provides the binding site for L-glutamine, which is extensively hydrogen bonded to the RNA. Atomic mutation of the RNA at the ligand binding site leads to loss of binding shown by isothermal titration calorimetry, explaining the specificity of the riboswitch. A metal ion also plays an important role in ligand binding. This is directly bonded to a glutamine carboxylate oxygen atom, and its remaining inner-sphere water molecules make hydrogen bonding interactions with the RNA.
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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
| | - Andrew M Watkins
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Rhiju Das
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - 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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10
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Ashraf S, Huang L, Lilley DMJ. Effect of methylation of adenine N 6 on kink turn structure depends on location. RNA Biol 2019; 16:1377-1385. [PMID: 31234702 PMCID: PMC6779385 DOI: 10.1080/15476286.2019.1630797] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 05/30/2019] [Accepted: 06/03/2019] [Indexed: 12/22/2022] Open
Abstract
N6-methyladenine is the most common covalent modification in cellular RNA species, with demonstrated functional consequences. At the molecular level this methylation could alter local RNA structure, and/or modulate the binding of specific proteins. We have previously shown that trans-Hoogsteen-sugar (sheared) A:G base pairs can be completely disrupted by methylation, and that this occurs in a sub-set ofD/D k-turn structures. In this work we have investigated to what extent sequence context affects the severity with which inclusion of N6-methyladenine into different A:G base pairs of a standard k-turn affects RNA folding and L7Ae protein binding. We find that local sequence has a major influence, ranging from complete absence of folding and protein binding to a relatively mild effect. We have determined the crystal structure of one of these species both free and protein-bound, showing the environment of the methyl group and the way the modification is accommodated into the k-turn structure.
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Affiliation(s)
- Saira Ashraf
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, U.K
| | - Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, U.K
| | - David M. J. Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, U.K
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11
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Wilson T, Liu Y, Li NS, Dai Q, Piccirilli JA, Lilley DMJ. Comparison of the Structures and Mechanisms of the Pistol and Hammerhead Ribozymes. J Am Chem Soc 2019; 141:7865-7875. [PMID: 31017785 PMCID: PMC6523996 DOI: 10.1021/jacs.9b02141] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Indexed: 01/10/2023]
Abstract
Comparison of the secondary and three-dimensional structures of the hammerhead and pistol ribozymes reveals many close similarities, so in this work we have asked if they are mechanistically identical. We have determined a new crystal structure of the pistol ribozyme and have shown that G40 acts as general base in the cleavage reaction. The conformation in the active site ensures an in-line attack of the O2' nucleophile, and the conformation at the scissile phosphate and the position of the general base are closely similar to those in the hammerhead ribozyme. However, the two ribozymes differ in the nature of the general acid. 2'-Amino substitution experiments indicate that the general acid of the hammerhead ribozyme is the O2' of G8, while that of the pistol ribozyme is a hydrated metal ion. The two ribozymes are related but mechanistically distinct.
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Affiliation(s)
- Timothy
J. Wilson
- Cancer
Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K.
| | - Yijin Liu
- Cancer
Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K.
| | - Nan-Sheng Li
- Department
of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Qing Dai
- Department
of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Joseph A. Piccirilli
- Department
of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - David M. J. Lilley
- Cancer
Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K.
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12
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Huang L, Wang J, Wilson TJ, Lilley DMJ. Structure-guided design of a high-affinity ligand for a riboswitch. RNA (NEW YORK, N.Y.) 2019; 25:423-430. [PMID: 30609994 PMCID: PMC6426286 DOI: 10.1261/rna.069567.118] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Accepted: 12/28/2018] [Indexed: 06/09/2023]
Abstract
We have designed structure-based ligands for the guanidine-II riboswitch that bind with enhanced affinity, exploiting the twin binding sites created by loop-loop interaction. We synthesized diguanidine species, comprising two guanidino groups covalently connected by Cn linkers where n = 4 or 5. Calorimetric and fluorescent analysis shows that these ligands bind with a 10-fold higher affinity to the riboswitch compared to guanidine. We determined X-ray crystal structures of the riboswitch bound to the new ligands, showing that the guanidino groups are bound to both nucleobases and backbone within the binding pockets, analogously to guanidine binding. The connecting chain passes through side openings in the binding pocket and traverses the minor groove of the RNA. The combination of the riboswitch loop-loop interaction and our novel ligands has potential applications in chemical biology.
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Affiliation(s)
- Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
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13
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Huang L, Lilley DMJ. Structure and ligand binding of the SAM-V riboswitch. Nucleic Acids Res 2018; 46:6869-6879. [PMID: 29931337 PMCID: PMC6061858 DOI: 10.1093/nar/gky520] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 05/22/2018] [Accepted: 05/25/2018] [Indexed: 11/29/2022] Open
Abstract
SAM-V is one of the class of riboswitches that bind S-adenosylmethione, regulating gene expression by controlling translation. We have solved the crystal structure of the metY SAM-V riboswitch bound to its SAM ligand at 2.5 Å resolution. The RNA folds as an H-type pseudoknot, with a major-groove triple helix in which resides the SAM ligand binding site. The bound SAM adopts an elongated conformation aligned with the axis of the triple helix, and is held at either end by hydrogen bonding to the adenine and the amino acid moieties. The central sulfonium cation makes electrostatic interactions with an U:A.U base triple, so conferring specificity. We propose a model in which SAM binding leads to association of the triplex third strand that stabilizes a short helix and occludes the ribosome binding site. Thus the new structure explains both ligand specificity and the mechanism of genetic control.
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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
| | - 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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14
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Seith DD, Bingaman JL, Veenis AJ, Button AC, Bevilacqua PC. Elucidation of Catalytic Strategies of Small Nucleolytic Ribozymes From Comparative Analysis of Active Sites. ACS Catal 2018; 8:314-327. [PMID: 32547833 PMCID: PMC7296830 DOI: 10.1021/acscatal.7b02976] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A number of small, self-cleaving ribozyme classes have been identified including the hammerhead, hairpin, hepatitis delta virus (HDV), Varkud satellite (VS), glmS, twister, hatchet, pistol, and twister sister ribozymes. Within the active sites of these ribozymes, myriad functional groups contribute to catalysis. There has been extensive structure-function analysis of individual ribozymes, but the extent to which catalytic devices are shared across different ribozyme classes is unclear. As such, emergent catalytic principles for ribozymes may await discovery. Identification of conserved catalytic devices can deepen our understanding of RNA catalysis specifically and of enzymic catalysis generally. To probe similarities and differences amongst ribozyme classes, active sites from more than 80 high-resolution crystal structures of self-cleaving ribozymes were compared computationally. We identify commonalities amongst ribozyme classes pertaining to four classic catalytic devices: deprotonation of the 2'OH nucleophile (γ), neutralization of the non-bridging oxygens of the scissile phosphate (β), neutralization of the O5' leaving group (δ), and in-line nucleophilic attack (α). In addition, we uncover conservation of two catalytic devices, each of which centers on the activation of the 2'OH nucleophile by a guanine: one to acidify the 2'OH by hydrogen bond donation to it (γ') and one to acidify the 2'OH by releasing it from non-productive interactions by competitive hydrogen bonding (γ''). Our findings reveal that the amidine functionalities of G, A, and C are especially important for these strategies, and help explain absence of U at ribozyme active sites. The identified γ' and γ'' catalytic strategies help unify the catalytic strategies shared amongst catalytic RNAs and may be important for large ribozymes, as well as protein enzymes that act on nucleic acids.
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Affiliation(s)
- Daniel D. Seith
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- These two authors contributed equally to this work
| | - Jamie L. Bingaman
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- These two authors contributed equally to this work
| | - Andrew J. Veenis
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Aileen C. Button
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Biochemistry, The University of Vermont, Burlington, Vermont 05405
| | - Philip C. Bevilacqua
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
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15
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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: 34] [Impact Index Per Article: 4.9] [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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16
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White NA, Hoogstraten CG. Thermodynamics and kinetics of RNA tertiary structure formation in the junctionless hairpin ribozyme. Biophys Chem 2017; 228:62-68. [PMID: 28710920 PMCID: PMC5572644 DOI: 10.1016/j.bpc.2017.07.001] [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: 05/05/2017] [Revised: 06/24/2017] [Accepted: 07/02/2017] [Indexed: 11/15/2022]
Abstract
The hairpin ribozyme consists of two RNA internal loops that interact to form the catalytically active structure. This docking transition is a rare example of intermolecular formation of RNA tertiary structure without coupling to helix annealing. We have used temperature-dependent surface plasmon resonance (SPR) to characterize the thermodynamics and kinetics of RNA tertiary structure formation for the junctionless form of the ribozyme, in which loops A and B reside on separate molecules. We find docking to be strongly enthalpy-driven and to be accompanied by substantial activation barriers for association and dissociation, consistent with the structural reorganization of both internal loops upon complex formation. Comparisons with the parallel analysis of a ribozyme variant carrying a 2'-O-methyl modification at the self-cleavage site and with published data in other systems reveal a surprising diversity of thermodynamic signatures, emphasizing the delicate balance of contributions to the free energy of formation of RNA tertiary structure.
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Affiliation(s)
- Neil A White
- Department of Biochemistry and Molecular Biology, 603 Wilson Road, Room 302D, Michigan State University, East Lansing, MI 48824, USA
| | - Charles G Hoogstraten
- Department of Biochemistry and Molecular Biology, 603 Wilson Road, Room 302D, Michigan State University, East Lansing, MI 48824, USA.
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17
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Huang L, Ashraf S, Wang J, Lilley DM. Control of box C/D snoRNP assembly by N 6-methylation of adenine. EMBO Rep 2017; 18:1631-1645. [PMID: 28623187 PMCID: PMC5579392 DOI: 10.15252/embr.201743967] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 05/21/2017] [Accepted: 05/22/2017] [Indexed: 01/03/2023] Open
Abstract
N6-methyladenine is the most widespread mRNA modification. A subset of human box C/D snoRNA species have target GAC sequences that lead to formation of N6-methyladenine at a key trans Hoogsteen-sugar A·G base pair, of which half are methylated in vivo The GAC target is conserved only in those that are methylated. Methylation prevents binding of the 15.5-kDa protein and the induced folding of the RNA Thus, the assembly of the box C/D snoRNP could in principle be regulated by RNA methylation at its critical first stage. Crystallography reveals that N6-methylation of adenine prevents the formation of trans Hoogsteen-sugar A·G base pairs, explaining why the box C/D RNA cannot adopt its kinked conformation. More generally, our data indicate that sheared A·G base pairs (but not Watson-Crick base pairs) are more susceptible to disruption by N6mA methylation and are therefore possible regulatory sites. The human signal recognition particle RNA and many related Alu retrotransposon RNA species are also methylated at N6 of an adenine that forms a sheared base pair with guanine and mediates a key tertiary interaction.
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Affiliation(s)
- Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee, UK
| | - Saira Ashraf
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee, UK
| | - Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee, UK
| | - David Mj Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee, UK
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18
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Huang L, Wang J, Lilley DMJ. The Structure of the Guanidine-II Riboswitch. Cell Chem Biol 2017; 24:695-702.e2. [PMID: 28529131 PMCID: PMC5486947 DOI: 10.1016/j.chembiol.2017.05.014] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Revised: 04/13/2017] [Accepted: 05/09/2017] [Indexed: 11/10/2022]
Abstract
The guanidine-II (mini-ykkC) riboswitch is the smallest of the guanidine-responsive riboswitches, comprising two stem loops of similar sequence. We have solved high-resolution crystal structures of both stem loops for the riboswitch from Gloeobacter violaceus. The stem loops have a strong propensity to dimerize by intimate loop-loop interaction. The dimerization creates specific binding pockets for two guanidine molecules, explaining their cooperative binding. Within the binding pockets the ligands are hydrogen bonded to a guanine at O6 and N7, and to successive backbone phosphates. Additionally they are each stacked upon a guanine nucleobase. One side of the pocket has an opening to the solvent, slightly lowering the specificity of ligand binding, and structures with bound methylguanidine, aminoguanidine, and agmatine show how this is possible.
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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
| | - 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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19
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Lilley DMJ. How RNA acts as a nuclease: some mechanistic comparisons in the nucleolytic ribozymes. Biochem Soc Trans 2017; 45:683-691. [PMID: 28620029 DOI: 10.1042/bst20160158] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 02/28/2017] [Accepted: 03/02/2017] [Indexed: 02/11/2024]
Abstract
Recent structural and mechanistic studies have shed considerable light on the catalytic mechanisms of nucleolytic ribozymes. The discovery of several new ribozymes in this class has now allowed comparisons to be made, and the beginnings of mechanistic groupings to emerge.
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Affiliation(s)
- David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K.
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20
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Liu Y, Wilson TJ, Lilley DM. The structure of a nucleolytic ribozyme that employs a catalytic metal ion. Nat Chem Biol 2017; 13:508-513. [PMID: 28263963 PMCID: PMC5392355 DOI: 10.1038/nchembio.2333] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 12/21/2016] [Indexed: 01/05/2023]
Abstract
The TS ribozyme (originally called "twister sister") is a catalytic RNA. We present a crystal structure of the ribozyme in a pre-reactive conformation. Two co-axial helical stacks are organized by a three-way junction and two tertiary contacts. Five divalent metal ions are directly coordinated to RNA ligands, making important contributions to the RNA architecture. The scissile phosphate lies in a quasihelical loop region that is organized by a network of hydrogen bonding. A divalent metal ion is directly bound to the nucleobase 5' to the scissile phosphate, with an inner-sphere water molecule positioned to interact with the O2' nucleophile. The rate of ribozyme cleavage correlated in a log-linear manner with divalent metal ion pKa, consistent with proton transfer in the transition state, and we propose that the bound metal ion is a likely general base for the cleavage reaction. Our data indicate that the TS ribozyme functions predominantly as a metalloenzyme.
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Affiliation(s)
- Yijin Liu
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K
| | - Timothy J. Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K
| | - David M.J. Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, U.K
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21
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Ochieng PO, White NA, Feig M, Hoogstraten CG. Intrinsic Base-Pair Rearrangement in the Hairpin Ribozyme Directs RNA Conformational Sampling and Tertiary Interface Formation. J Phys Chem B 2016; 120:10885-10898. [PMID: 27701852 DOI: 10.1021/acs.jpcb.6b05606] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Dynamic fluctuations in RNA structure enable conformational changes that are required for catalysis and recognition. In the hairpin ribozyme, the catalytically active structure is formed as an intricate tertiary interface between two RNA internal loops. Substantial alterations in the structure of each loop are observed upon interface formation, or docking. The very slow on-rate for this relatively tight interaction has led us to hypothesize a double conformational capture mechanism for RNA-RNA recognition. We used extensive molecular dynamics simulations to assess conformational sampling in the undocked form of the loop domain containing the scissile phosphate (loop A). We observed several major accessible conformations with distinctive patterns of hydrogen bonding and base stacking interactions in the active-site internal loop. Several important conformational features characteristic of the docked state were observed in well-populated substates, consistent with the kinetic sampling of docking-competent states by isolated loop A. Our observations suggest a hybrid or multistage binding mechanism, in which initial conformational selection of a docking-competent state is followed by induced-fit adjustment to an in-line, chemically reactive state only after formation of the initial complex with loop B.
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Affiliation(s)
- Patrick O Ochieng
- Department of Biochemistry and Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
| | - Neil A White
- Department of Biochemistry and Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
| | - Michael Feig
- Department of Biochemistry and Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
| | - Charles G Hoogstraten
- Department of Biochemistry and Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
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22
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Huang L, Lilley DMJ. A quasi-cyclic RNA nano-scale molecular object constructed using kink turns. NANOSCALE 2016; 8:15189-95. [PMID: 27506301 PMCID: PMC5058347 DOI: 10.1039/c6nr05186c] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 08/01/2016] [Indexed: 05/25/2023]
Abstract
k-Turns are widespread RNA architectural elements that mediate tertiary interactions. We describe a double-kink-turn motif comprising two inverted k-turns that forms a tight horse-shoe structure that can assemble into a variety of shapes by coaxial association of helical ends. Using X-ray crystallography we show that these assemble with two (dumbell), three (triangle) and four units (square), with or without bound protein, within the crystal lattice. In addition, exchange of a single basepair can almost double the pore radius or shape of a molecular assembly. On the basis of this analysis we synthesized a 114 nt self-complementary RNA containing six k-turns. The crystal structure of this species shows that it forms a quasi-cyclic triangular object. These are randomly disposed about the three-fold axis in the crystal lattice, generating a circular RNA of quasi D3 symmetry with a shape reminiscent of that of a cyclohexane molecule in its chair conformation. This work demonstrates that the k-turn is a powerful building block in the construction of nano-scale molecular objects, and illustrates why k-turns are widely used in natural RNA molecules to organize long-range architecture and mediate tertiary contacts.
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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.
| | - 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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23
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Huang L, Wang J, Lilley DMJ. A critical base pair in k-turns determines the conformational class adopted, and correlates with biological function. Nucleic Acids Res 2016; 44:5390-8. [PMID: 27016741 PMCID: PMC4914095 DOI: 10.1093/nar/gkw201] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Revised: 03/08/2016] [Accepted: 03/14/2016] [Indexed: 11/20/2022] Open
Abstract
k-turns are commonly-occurring motifs that introduce sharp kinks into duplex RNA, thereby facilitating tertiary contacts. Both the folding and conformation of k-turns are determined by their local sequence. k-turns fall into two conformational classes, called N3 and N1, that differ in the pattern of hydrogen bonding in the core. We show here that this is determined by the basepair adjacent to the critical G•A pairs. We determined crystal structures of a series of Kt-7 variants in which this 3b,3n position has been systematically varied, showing that this leads to a switch in the conformation. We have previously shown that the 3b,3n position also determines the folding characteristics of the k-turn, i.e. whether or not the k-turn can fold in the presence of metal ions alone. We have analyzed the distribution of 3b,3n sequences from four classes of k-turns from ribosomes, riboswitches and U4 snRNA, finding a strong conservation of properties for a given k-turn type. We thus demonstrate a strong association between biological function, 3b,3n sequence and k-turn folding and conformation. This has strong predictive power, and can be applied to the modeling of large RNA architectures.
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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
| | - 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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24
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Wilson TJ, Liu Y, Domnick C, Kath-Schorr S, Lilley DMJ. The Novel Chemical Mechanism of the Twister Ribozyme. J Am Chem Soc 2016; 138:6151-62. [PMID: 27153229 DOI: 10.1021/jacs.5b11791] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We describe the multifactorial origins of catalysis by the twister ribozyme. We provide evidence that the adenine immediately 3' to the scissile phosphate (A1) acts as a general acid. Substitution of ring nitrogen atoms indicates that very unusually the N3 of A1 is the proton donor to the oxyanion leaving group. A1 is accommodated in a specific binding pocket that raises its pKa toward neutrality, juxtaposes its N3 with the O5' to be protonated, and helps create the in-line trajectory required for nucleophilic attack. A1 performs general acid catalysis while G33 acts as a general base. A 100-fold stereospecific phosphorothioate effect at the scissile phosphate is consistent with a significant stabilization of the transition state by the ribozyme, and functional group substitution at G33 indicates that its exocyclic N2 interacts directly with the scissile phosphate. A model of the ribozyme active site is proposed that accommodates these catalytic strategies.
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Affiliation(s)
- Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee , Dow Street, Dundee DD1 5EH, U.K
| | - Yijin Liu
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee , Dow Street, Dundee DD1 5EH, U.K
| | - Christof Domnick
- Life and Medical Sciences Institute, University of Bonn , Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany
| | - Stephanie Kath-Schorr
- Life and Medical Sciences Institute, University of Bonn , Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee , Dow Street, Dundee DD1 5EH, U.K
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25
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Lee HT, Kilburn D, Behrouzi R, Briber RM, Woodson SA. Molecular crowding overcomes the destabilizing effects of mutations in a bacterial ribozyme. Nucleic Acids Res 2015; 43:1170-6. [PMID: 25541198 PMCID: PMC4333387 DOI: 10.1093/nar/gku1335] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 12/01/2014] [Accepted: 12/05/2014] [Indexed: 11/13/2022] Open
Abstract
The native structure of the Azoarcus group I ribozyme is stabilized by the cooperative formation of tertiary interactions between double helical domains. Thus, even single mutations that break this network of tertiary interactions reduce ribozyme activity in physiological Mg(2+) concentrations. Here, we report that molecular crowding comparable to that in the cell compensates for destabilizing mutations in the Azoarcus ribozyme. Small angle X-ray scattering, native polyacrylamide gel electrophoresis and activity assays were used to compare folding free energies in dilute and crowded solutions containing 18% PEG1000. Crowder molecules allowed the wild-type and mutant ribozymes to fold at similarly low Mg(2+) concentrations and stabilized the active structure of the mutant ribozymes under physiological conditions. This compensation helps explains why ribozyme mutations are often less deleterious in the cell than in the test tube. Nevertheless, crowding did not rescue the high fraction of folded but less active structures formed by double and triple mutants. We conclude that crowding broadens the fitness landscape by stabilizing compact RNA structures without improving the specificity of self-assembly.
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Affiliation(s)
- Hui-Ting Lee
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
| | - Duncan Kilburn
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA Center for Neutron Scattering Research, National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, MD 20899, USA
| | - Reza Behrouzi
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
| | - Robert M Briber
- Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | - Sarah A Woodson
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
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26
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McPhee SA, Huang L, Lilley DMJ. A critical base pair in k-turns that confers folding characteristics and correlates with biological function. Nat Commun 2014; 5:5127. [PMID: 25351101 PMCID: PMC4382518 DOI: 10.1038/ncomms6127] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 09/02/2014] [Indexed: 12/28/2022] Open
Abstract
Kink turns (k-turns) are widespread elements in RNA that mediate tertiary contacts by kinking the helical axis. We have found that the ability of k-turns to undergo ion-induced folding is conferred by a single base pair that follows the conserved A·G pairs, that is, the 3b·3n position. A Watson–Crick pair leads to an inability to fold in metal ions alone, while 3n=G or 3b=C (but not both) permits folding. Crystallographic study reveals two hydrated metal ions coordinated to O6 of G3n and G2n of Kt-7. Removal of either atom impairs Mg2+-induced folding in solution. While SAM-I riboswitches have 3b·3n sequences that would predispose them to ion-induced folding, U4 snRNA are strongly biased to an inability to such folding. Thus riboswitch sequences allow folding to occur independently of protein binding, while U4 should remain unfolded until bound by protein. The empirical rules deduced for k-turn folding have strong predictive value. The k-turn is a widespread RNA element that adopts a kinked structure that mediates tertiary contacts and frequently binds specific proteins. Here, McPhee et al. show that the ability of a given k-turn to fold in the presence of metal ions alone—or to otherwise require protein binding—is attributable to a specific base pair.
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Affiliation(s)
- Scott A McPhee
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Lin Huang
- 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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Crystal structure and mechanistic investigation of the twister ribozyme. Nat Chem Biol 2014; 10:739-44. [DOI: 10.1038/nchembio.1587] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 06/16/2014] [Indexed: 02/07/2023]
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Measurement of the change in twist at a helical junction in RNA using the orientation dependence of FRET. Biophys J 2014; 105:2175-81. [PMID: 24209863 DOI: 10.1016/j.bpj.2013.09.042] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/04/2013] [Accepted: 09/23/2013] [Indexed: 02/05/2023] Open
Abstract
Indocarbocyanine fluorophores attached via the 5' terminus of double-stranded nucleic acids have a strong propensity to stack onto the terminal basepair. We previously demonstrated that the efficiency of fluorescence resonance energy transfer between cyanine 3 and 5 terminally attached to duplex species exhibits a pronounced modulation with helix length. This results from a systematic variation in the orientation parameter κ(2) as the relative rotation of the fluorophore transition moments changes due to the helical geometry. Analysis of such profiles provides a rich source of orientational information. In this work, we applied this methodology to the structure of a three-way helical junction that plays an important role in the hepatitis C virus internal ribosome entry site. By comparing matched pairs of duplex and junction species, we were able to measure the change in rotation at the junction. The data reveal a 29.5° overwinding and a small axial extension. This shows the power of this approach for measuring orientational information in biologically important RNA junctions.
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Huang L, Lilley DMJ. Structure of a rare non-standard sequence k-turn bound by L7Ae protein. Nucleic Acids Res 2014; 42:4734-40. [PMID: 24482444 PMCID: PMC3985660 DOI: 10.1093/nar/gku087] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Kt-23 from Thelohania solenopsae is a rare RNA kink turn (k-turn) where an adenine replaces the normal guanine at the 2n position. L7Ae is a member of a strongly conserved family of proteins that bind a range of k-turn structures in the ribosome, box C/D and H/ACA small nucleolar RNAs and U4 small nuclear RNA. We have solved the crystal structure of T. solenopsae Kt-23 RNA bound to Archeoglobus fulgidus L7Ae protein at a resolution of 2.95 Å. The protein binds in the major groove displayed on the outer face of the k-turn, in a manner similar to complexes with standard k-turn structures. The k-turn adopts a standard N3 class conformation, with a single hydrogen bond from A2b N6 to A2n N3. This contrasts with the structure of the same sequence located in the SAM-I riboswitch, where it adopts an N1 structure, showing the inherent plasticity of k-turn structure. This potentially can affect any tertiary interactions in which the RNA participates.
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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
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Huang L, Lilley DM. The molecular recognition of kink-turn structure by the L7Ae class of proteins. RNA (NEW YORK, N.Y.) 2013; 19:1703-10. [PMID: 24149842 PMCID: PMC3884654 DOI: 10.1261/rna.041517.113] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2013] [Accepted: 08/29/2013] [Indexed: 05/20/2023]
Abstract
L7Ae is a member of a protein family that binds kink-turns (k-turns) in many functional RNA species. We have solved the X-ray crystal structure of the near-consensus sequence Kt-7 of Haloarcula marismortui bound by Archaeoglobus fulgidus L7Ae at 2.3-Å resolution. We also present a structure of Kt-7 in the absence of bound protein at 2.2-Å resolution. As a result, we can describe a general mode of recognition of k-turn structure by the L7Ae family proteins. The protein makes interactions in the widened major groove on the outer face of the k-turn. Two regions of the protein are involved. One is an α-helix that enters the major groove of the NC helix, making both nonspecific backbone interactions and specific interactions with the guanine nucleobases of the conserved G • A pairs. A hydrophobic loop makes close contact with the L1 and L2 bases, and a glutamate side chain hydrogen bonds with L1. Taken together, these interactions are highly selective for the structure of the k-turn and suggest how conformational selection of the folded k-turn occurs.
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31
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Daldrop P, Masquida B, Lilley DMJ. The functional exchangeability of pk- and k-turns in RNA structure. RNA Biol 2013; 10:445-52. [PMID: 23364423 PMCID: PMC3672288 DOI: 10.4161/rna.23673] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Ribonuclease P RNA requires a sharply kinked RNA helix to make a loop-receptor interaction that creates the binding site for the substrate. In some forms of the ribozyme, this is accomplished by a k-turn, while others have a different element called the pk-turn. The structure of the pk-turn in RNase P of Thermotoga maritima is globally very similar to a k-turn, but lacks all the standard features of that structure, including long-range hydrogen bonds between the two helical arms. We show here that in an isolated RNA duplex, the pk-turn fails to adopt a tightly kinked structure, but rather is a flexible element. This suggests that the tertiary contacts of RNase P assist its folding into the required kinked structure. We find that we can replace the k-turn of the SAM-I riboswitch with the pk-turn, such that the resulting RNA retains its ability to bind SAM, although with lower affinity. We also find that we can replace the pk-turn of T. maritima RNase P with a standard k-turn (in either orientation) with retention of ribozyme activity. Thus, although the pk-turn cannot intrinsically fold into the kinked structure, it can be induced to fold correctly in context. And the pk-turn and k-turns can substitute functionally for one another.
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Affiliation(s)
- Peter Daldrop
- Cancer Research UK Nucleic Acid Structure Research Group; MSI/WTB Complex; The University of Dundee; Dundee, UK
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Wilson TJ, Lilley DM. A Mechanistic Comparison of the Varkud Satellite and Hairpin Ribozymes. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 120:93-121. [DOI: 10.1016/b978-0-12-381286-5.00003-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Wang J, Fessl T, Schroeder KT, Ouellet J, Liu Y, Freeman ADJ, Lilley DMJ. Single-molecule observation of the induction of k-turn RNA structure on binding L7Ae protein. Biophys J 2012; 103:2541-8. [PMID: 23260056 DOI: 10.1016/j.bpj.2012.11.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Revised: 11/02/2012] [Accepted: 11/06/2012] [Indexed: 10/27/2022] Open
Abstract
The k-turn is a commonly occurring structural motif that introduces a tight kink into duplex RNA. In free solution, it can exist in an extended form, or by folding into the kinked structure. Binding of proteins including the L7Ae family can induce the formation of the kinked geometry, raising the question of whether this occurs by passive selection of the kinked structure, or a more active process in which the protein manipulates the RNA structure. We have devised a single-molecule experiment whereby immobilized L7Ae protein binds Cy3-Cy5-labeled RNA from free solution. We find that all bound RNA is in the kinked geometry, with no evidence for transitions to an extended form at the millisecond timescale of the camera. Furthermore, real-time binding experiments provide no evidence for a more extended intermediate even at the earliest times, at a time resolution of 16 ms. The data support a passive conformational selection model by which the protein selects a fraction of RNA that is already in the kinked conformation, thereby drawing the equilibrium into this form.
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Affiliation(s)
- Jia Wang
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee, United Kingdom
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Kath-Schorr S, Wilson TJ, Li NS, Lu J, Piccirilli JA, Lilley DMJ. General acid-base catalysis mediated by nucleobases in the hairpin ribozyme. J Am Chem Soc 2012; 134:16717-24. [PMID: 22958171 DOI: 10.1021/ja3067429] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The catalytic mechanism by which the hairpin ribozyme accelerates cleavage or ligation of the phosphodiester backbone of RNA has been incompletely understood. There is experimental evidence for an important role for an adenine (A38) and a guanine (G8), and it has been proposed that these act in general acid-base catalysis. In this work we show that a large reduction in cleavage rate on substitution of A38 by purine (A38P) can be reversed by replacement of the 5'-oxygen atom at the scissile phosphate by sulfur (5'-PS), which is a much better leaving group. This is consistent with A38 acting as the general acid in the unmodified ribozyme. The rate of cleavage of the 5'-PS substrate by the A38P ribozyme increases with pH log-linearly, indicative of a requirement for a deprotonated base with a relatively high pK(a). On substitution of G8 by diaminopurine, the 5'-PS substrate cleavage rate at first increases with pH and then remains at a plateau, exhibiting an apparent pK(a) consistent with this nucleotide acting in general base catalysis. Alternative explanations for the pH dependence of hairpin ribozyme reactivity are discussed, from which we conclude that general acid-base catalysis by A38 and G8 is the simplest and most probable explanation consistent with all the experimental data.
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Affiliation(s)
- Stephanie Kath-Schorr
- 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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35
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Schroeder KT, Daldrop P, McPhee SA, Lilley DM. Structure and folding of a rare, natural kink turn in RNA with an A*A pair at the 2b*2n position. RNA (NEW YORK, N.Y.) 2012; 18:1257-66. [PMID: 22539525 PMCID: PMC3358647 DOI: 10.1261/rna.032409.112] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Accepted: 03/28/2012] [Indexed: 05/20/2023]
Abstract
The kink turn (k-turn) is a frequently occurring motif, comprising a bulge followed by G•A and A•G pairs that introduces a sharp axial bend in duplex RNA. Natural k-turn sequences exhibit significant departures from the consensus, including the A•G pairs that form critical interactions stabilizing the core of the structure. Kt-23 found in the small ribosomal subunit differs from the consensus in many organisms, particularly in the second A•G pair distal to the bulge (2b•2n). Analysis of many Kt-23 sequences shows that the frequency of occurrence at the 2n position (i.e., on the nonbulged strand, normally G in standard k-turns) is U>C>G>A. Less than 1% of sequences have A at the 2n position, but one such example occurs in Thelohania solenopsae Kt-23. This sequence folds only weakly in the presence of Mg²⁺ ions but is induced to fold normally by the binding of L7Ae protein. Introduction of this sequence into the SAM-I riboswitch resulted in normal binding of SAM ligand, indicating that tertiary RNA contacts have resulted in k-turn folding. X-ray crystallography shows that the T. solenopsae Kt-23 adopts a standard k-turn geometry, making the key, conserved hydrogen bonds in the core and orienting the 1n (of the bulge-proximal A•G pair) and 2b adenine nucleobases in position facing the opposing minor groove. The 2b and 2n adenine nucleobases are not directly hydrogen bonded, but each makes hydrogen bonds to their opposing strands.
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Affiliation(s)
- Kersten T. Schroeder
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Peter Daldrop
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Scott A. McPhee
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - David M.J. Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
- Corresponding author.E-mail .
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36
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Schroeder KT, Daldrop P, Lilley DMJ. RNA tertiary interactions in a riboswitch stabilize the structure of a kink turn. Structure 2011; 19:1233-40. [PMID: 21893284 PMCID: PMC3651934 DOI: 10.1016/j.str.2011.07.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 06/26/2011] [Accepted: 07/02/2011] [Indexed: 01/31/2023]
Abstract
The kink turn is a widespread RNA motif that introduces an acute kink into the axis of duplex RNA, typically comprising a bulge followed by a G⋅A and A⋅G pairs. The kinked conformation is stabilized by metal ions, or the binding of proteins including L7Ae. We now demonstrate a third mechanism for the stabilization of k-turn structure, involving tertiary interactions within a larger RNA structure. The SAM-I riboswitch contains an essential standard k-turn sequence that kinks a helix so that its terminal loop can make a long-range interaction. We find that some sequence variations in the k-turn within the riboswitch do not prevent SAM binding, despite preventing the folding of the k-turn in isolation. Furthermore, two crystal structures show that the sequence-variant k-turns are conventionally folded within the riboswitch. This study shows that the folded structure of the k-turn can be stabilized by tertiary interactions within a larger RNA structure.
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Affiliation(s)
- Kersten T Schroeder
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, UK
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37
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Abstract
The nucleolytic ribozymes use general acid-base catalysis to contribute significantly to their rate enhancement. The VS (Varkud satellite) ribozyme uses a guanine and an adenine nucleobase as general base and acid respectively in the cleavage reaction. The hairpin ribozyme is probably closely similar, while the remaining nucleolytic ribozymes provide some interesting contrasts.
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38
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Wilson TJ, Lilley DMJ. Do the hairpin and VS ribozymes share a common catalytic mechanism based on general acid-base catalysis? A critical assessment of available experimental data. RNA (NEW YORK, N.Y.) 2011; 17:213-21. [PMID: 21173201 PMCID: PMC3022271 DOI: 10.1261/rna.2473711] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The active centers of the hairpin and VS ribozymes are both generated by the interaction of two internal loops, and both ribozymes use guanine and adenine nucleobases to accelerate cleavage and ligation reactions. The centers are topologically equivalent and the relative positioning of key elements the same. There is good evidence that the cleavage reaction of the VS ribozyme is catalyzed by the guanine (G638) acting as general base and the adenine (A756) as general acid. We now critically evaluate the experimental mechanistic evidence for the hairpin ribozyme. We conclude that all the available data are fully consistent with a major contribution to catalysis by general acid-base catalysis involving the adenine (A38) and guanine (G8). It appears that the two ribozymes are mechanistically equivalent.
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Affiliation(s)
- Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD15EH, United Kingdom
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39
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Ouellet J, Melcher S, Iqbal A, Ding Y, Lilley DMJ. Structure of the three-way helical junction of the hepatitis C virus IRES element. RNA (NEW YORK, N.Y.) 2010; 16:1597-1609. [PMID: 20581129 PMCID: PMC2905758 DOI: 10.1261/rna.2158410] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Accepted: 05/04/2010] [Indexed: 05/29/2023]
Abstract
The hepatitis C virus internal ribosome entry site (IRES) element contains a three-way junction that is important in the overall RNA conformation, and for its role in the internal initiation of translation. The junction also illustrates some important conformational principles in the folding of three-way helical junctions. It is formally a 3HS(4) junction, with the possibility of two alternative stacking conformers. However, in principle, the junction can also undergo two steps of branch migration that would form 2HS(1)HS(3) and 2HS(2)HS(2) junctions. Comparative gel electrophoresis and ensemble fluorescence resonance energy transfer (FRET) studies show that the junction is induced to fold by the presence of Mg(2+) ions in low micromolar concentrations, and suggest that the structure adopted is based on coaxial stacking of the two helices that do not terminate in a hairpin loop (i.e., helix IIId). Single-molecule FRET studies confirm this conclusion, and indicate that there is no minor conformer present based on an alternative choice of helical stacking partners. Moreover, analysis of single-molecule FRET data at an 8-msec resolution failed to reveal evidence for structural transitions. It seems probable that this junction adopts a single conformation as a unique and stable fold.
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Affiliation(s)
- Jonathan Ouellet
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
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40
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Schroeder KT, Lilley DMJ. Ion-induced folding of a kink turn that departs from the conventional sequence. Nucleic Acids Res 2010; 37:7281-9. [PMID: 19783814 PMCID: PMC2790904 DOI: 10.1093/nar/gkp791] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Kink turns (k-turns) are important structural motifs that create a sharp axial bend in RNA. Most conform to a consensus in which a three-nucleotide bulge is followed by consecutive G*A and A*G base pairs, and when these G*A pairs are modified in vitro this generally leads to a failure to adopt the k-turn conformation. Kt-23 in the 30S ribosomal subunit of Thermus thermophilus is a rare exception in which the bulge-distal A*G pair is replaced by a non-Watson-Crick A*U pair. In the context of the ribosome, Kt-23 adopts a completely conventional k-turn geometry. We show here that this sequence is induced to fold into a k-turn structure in an isolated RNA duplex by Mg(2+) or Na(+) ions. Therefore, the Kt-23 is intrinsically stable despite lacking the key A*G pair; its formation requires neither tertiary interactions nor protein binding. Moreover, the Kt-23 k-turn is stabilized by the same critical hydrogen-bonding interactions within the core of the structure that are found in more conventional sequences such as the near-consensus Kt-7. T. thermophilus Kt-23 has two further non-Watson-Crick base pairs within the non-canonical helix, three and four nucleotides from the bulge, and we find that the nature of these pairs influences the ability of the RNA to adopt k-turn conformation, although the base pair adjacent to the A*U pair is more important than the other.
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Affiliation(s)
- Kersten T Schroeder
- 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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41
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Vámosi G, Clegg RM. Helix−Coil Transition of a Four-Way DNA Junction Observed by Multiple Fluorescence Parameters. J Phys Chem B 2008; 112:13136-48. [DOI: 10.1021/jp8034055] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- György Vámosi
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Department of Biophysics and Cell Biology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary HU H-4012, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080
| | - Robert M. Clegg
- Cell Biology and Signaling Research Group of the Hungarian Academy of Sciences, Department of Biophysics and Cell Biology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary HU H-4012, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080
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42
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Orientation dependence in fluorescent energy transfer between Cy3 and Cy5 terminally attached to double-stranded nucleic acids. Proc Natl Acad Sci U S A 2008; 105:11176-81. [PMID: 18676615 DOI: 10.1073/pnas.0801707105] [Citation(s) in RCA: 252] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have found that the efficiency of fluorescence resonance energy transfer between Cy3 and Cy5 terminally attached to the 5' ends of a DNA duplex is significantly affected by the relative orientation of the two fluorophores. The cyanine fluorophores are predominantly stacked on the ends of the helix in the manner of an additional base pair, and thus their relative orientation depends on the length of the helix. Observed fluorescence resonance energy transfer (FRET) efficiency depends on the length of the helix, as well as its helical periodicity. By changing the helical geometry from B form double-stranded DNA to A form hybrid RNA/DNA, a marked phase shift occurs in the modulation of FRET efficiency with helix length. Both curves are well explained by the standard geometry of B and A form helices. The observed modulation for both polymers is less than that calculated for a fully rigid attachment of the fluorophores. However, a model involving lateral mobility of the fluorophores on the ends of the helix explains the observed experimental data. This has been further modified to take account of a minor fraction of unstacked fluorophore observed by fluorescent lifetime measurements. Our data unequivocally establish that Förster transfer obeys the orientation dependence as expected for a dipole-dipole interaction.
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43
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The Importance of G·A Hydrogen Bonding in the Metal Ion- and Protein-induced Folding of a Kink Turn RNA. J Mol Biol 2008; 381:431-42. [DOI: 10.1016/j.jmb.2008.05.052] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Revised: 05/20/2008] [Accepted: 05/20/2008] [Indexed: 02/06/2023]
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44
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Lilley DMJ. A chemo-genetic approach for the study of nucleobase participation in nucleolytic ribozymes. Biol Chem 2007; 388:699-704. [PMID: 17570822 DOI: 10.1515/bc.2007.069] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A novel chemo-genetic approach for the analysis of general acid-base catalysis by nucleobases in ribozymes is reviewed. This involves substitution of a C-nucleoside with imidazole in place of a natural nucleobase. The Varkud satellite ribozyme in which the nucleobase at the critical 756 position has been replaced by imidazole is active in both cleavage and ligation reactions. Similarly, a modified hairpin ribozyme with the nucleobase at position 8 substituted by imidazole is active in cleavage and ligation reactions. Although the rates are lower than those of the natural ribozymes, they are significantly greater than other variants at these positions. The dependence of the hairpin ribozyme reaction rates on pH has been studied. Both cleavage and ligation reactions display a bell-shaped pH dependence, consistent with general acid-base catalysis involving the nucleotide at position 8.
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Affiliation(s)
- David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK.
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45
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Cottrell JW, Kuzmin YI, Fedor MJ. Functional Analysis of Hairpin Ribozyme Active Site Architecture. J Biol Chem 2007; 282:13498-507. [PMID: 17351263 DOI: 10.1074/jbc.m700451200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The hairpin ribozyme is a small catalytic motif found in plant satellite RNAs where it catalyzes a reversible self-cleavage reaction during processing of replication intermediates. Crystallographic studies of hairpin ribozymes have provided high resolution views of the RNA functional groups that comprise the active site and stimulated biochemical studies that probed the contributions of nucleobase functional groups to catalytic chemistry. The dramatic loss of activity that results from perturbation of active site architecture points to the importance of positioning and orientation in catalytic rate acceleration. The current study focuses on the network of noncovalent interactions that align nucleophilic and leaving group oxygens in the orientation required for the S(N)2-type reaction mechanism and orient the active site nucleobases near the reactive phosphate to facilitate catalytic chemistry. Nucleotide modifications that alter or eliminate individual hydrogen bonding partners had different effects on the activation barrier to catalysis, the stability of ribozyme complexes in the ground state, and the internal equilibrium between cleavage and ligation of bound products. Furthermore, substitution of hydrogen bond donors and acceptors with seemingly equivalent pairs sometimes had very different functional consequences. These biochemical analyses augment high resolution structural information to provide insights into the functional significance of active site architecture.
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Affiliation(s)
- Joseph W Cottrell
- Department of Molecular Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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Liu J, Lilley DMJ. The role of specific 2'-hydroxyl groups in the stabilization of the folded conformation of kink-turn RNA. RNA (NEW YORK, N.Y.) 2007; 13:200-10. [PMID: 17158708 PMCID: PMC1781366 DOI: 10.1261/rna.285707] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The role of 2'-hydroxyl groups in stabilizing the tightly kinked geometry of the kink-turn (K-turn) has been investigated. Individual 2'-OH groups have been removed by chemical synthesis, and the kinking of the RNA has been studied by gel electrophoresis and fluorescence resonance energy transfer. The results have been analyzed by reference to a database of 11 different crystallographic structures of K-turns. The potential hydrogen bonds fall into several classes. The most important are those in the core of the turn and ribose-phosphate interactions around the bulge. Of these the single most important hydrogen bond is one donated from the 2'-OH of the 5' nucleotide of the bulge to the N1 of the adenine of the kink-proximal A*G pair. This is present in all known K-turn structures, and removal of the 2'-OH completely prevents metal ion-induced folding. Hydrogen bonds formed in the minor grooves of the helical stems are less important, and removal of the participating 2'-OH groups leads to reduced impairment of folding. These interactions are generally more polymorphic, and hydrogen bonds probably form where possible, as permitted by the global structure.
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Affiliation(s)
- Jia Liu
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, UK
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Wilson TJ, Nahas M, Araki L, Harusawa S, Ha T, Lilley DMJ. RNA folding and the origins of catalytic activity in the hairpin ribozyme. Blood Cells Mol Dis 2006; 38:8-14. [PMID: 17150385 DOI: 10.1016/j.bcmd.2006.10.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2006] [Accepted: 10/10/2006] [Indexed: 11/26/2022]
Abstract
The nucleolytic ribozymes catalyse site-specific phosphodiester cleavage and ligation transesterification reactions in RNA. The hairpin ribozyme folds to generate an intimate loop-loop interaction to create the local environment in which catalysis can proceed. We have studied the ion-induced folding using single-molecule FRET experiments, showing that the four-way helical junction accelerates the folding 500-fold by introducing a discrete intermediate that juxtaposes the loops. Using FRET we can observe individual hairpin ribozyme molecules as they undergo multiple cycles of cleavage and ligation, and measure the rates of the internal reactions, free of uncertainties in the contributions of docking and substrate dissociation processes. On average, the cleaved ribozyme undergoes several docking-undocking events before a ligation reaction occurs. On the basis of these experiments, we have explored the role of the nucleobases G8 and A38 in the catalysis. Both cleavage and ligation reactions are pH dependent, corresponding to the titration of a group with pKa=6.2. We have used a novel ribonucleoside in which these bases are replaced by imidazole to investigate the role of acid-base catalysis in this ribozyme. We observe significant rates of cleavage and ligation, and a bell-shaped pH dependence for both.
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Affiliation(s)
- Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, UK
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Jones C, Spencer AC, Hsu JL, Spremulli L, Martinis SA, DeRider M, Agris PF. A counterintuitive Mg2+-dependent and modification-assisted functional folding of mitochondrial tRNAs. J Mol Biol 2006; 362:771-86. [PMID: 16949614 PMCID: PMC1781928 DOI: 10.1016/j.jmb.2006.07.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2006] [Revised: 07/05/2006] [Accepted: 07/19/2006] [Indexed: 10/24/2022]
Abstract
Mitochondrial tRNAs (mtRNAs) often lack domains and posttranscriptional modifications that are found in cytoplasmic tRNAs. These structural and chemical elements normally stabilize the folding of cytoplasmic tRNAs into canonical structures that are competent for aminoacylation and translation. For example, the dihydrouridine (D) stem and loop domain is involved in the tertiary structure of cytoplasmic tRNAs through hydrogen bonds and a Mg2+ bridge to the ribothymidine (T) stem and loop domain. These interactions are often absent in mtRNA because the D-domain is truncated or missing. Using gel mobility shift analyses, UV, circular dichroism and NMR spectroscopies and aminoacylation assays, we have investigated the functional folding interactions of chemically synthesized and site-specifically modified mitochondrial and cytoplasmic tRNAs. We found that Mg2+ is critical for folding of the truncated D-domain of bovine mtRNAMet with the tRNA's T-domain. Contrary to the expectation that Mg2+ stabilizes RNA folding, the mtRNAMet D-domain structure was unfolded and relaxed, rather than stabilized in the presence of Mg2+. Because the D-domain is transcribed prior to the T-domain, we conclude that Mg2+ prevents misfolding of the 5'-half of bovine mtRNAMet facilitating its correct interaction with the T-domain. The interaction of the mtRNAMet D-domain with the T-domain was enhanced by a pseudouridine located in either the D or T-domains compared to that of the unmodified RNAs (Kd=25.3, 24.6 and 44.4 microM, respectively). Mg2+ also affected the folding interaction of a yeast mtRNALeu1, but had minimal effect on the folding of an Escherichia coli cytoplasmic tRNALeu. The D-domain modification, dihydrouridine, facilitated mtRNALeu folding. These data indicate that conserved modifications assist and stabilize the formation of the functional mtRNA tertiary structure.
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Affiliation(s)
- Christopher Jones
- Department of Structural and Molecular Biology, 128 Polk Hall, Campus Box 7622, North Carolina State University, Raleigh, NC 27695-7622
| | - Angela C. Spencer
- Department of Chemistry, Campus Box 3290, Venable and Kenan Laboratories, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599-3290
| | - Jennifer L. Hsu
- Department of Biochemistry, 419 Roger Adams Laboratory, Box B-4, 600 S. Mathews Ave., University of Illinois at Urbana-Champaign, Urbana, Il 61801
| | - Linda Spremulli
- Department of Chemistry, Campus Box 3290, Venable and Kenan Laboratories, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599-3290
| | - Susan A. Martinis
- Department of Biochemistry, 419 Roger Adams Laboratory, Box B-4, 600 S. Mathews Ave., University of Illinois at Urbana-Champaign, Urbana, Il 61801
| | - Michele DeRider
- Department of Structural and Molecular Biology, 128 Polk Hall, Campus Box 7622, North Carolina State University, Raleigh, NC 27695-7622
| | - Paul F. Agris
- Department of Structural and Molecular Biology, 128 Polk Hall, Campus Box 7622, North Carolina State University, Raleigh, NC 27695-7622
- Corresponding author; E-mail address of corresponding author:
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Wilson TJ, Ouellet J, Zhao ZY, Harusawa S, Araki L, Kurihara T, Lilley DMJ. Nucleobase catalysis in the hairpin ribozyme. RNA (NEW YORK, N.Y.) 2006; 12:980-7. [PMID: 16601203 PMCID: PMC1464849 DOI: 10.1261/rna.11706] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
RNA catalysis is important in the processing and translation of RNA molecules, yet the mechanisms of catalysis are still unclear in most cases. We have studied the role of nucleobase catalysis in the hairpin ribozyme, where the scissile phosphate is juxtaposed between guanine and adenine bases. We show that a modified ribozyme in which guanine 8 has been substituted by an imidazole base is active in both cleavage and ligation, with ligation rates 10-fold faster than cleavage. The rates of both reactions exhibit bell-shaped dependence on pH, with pK(a) values of 5.7 +/- 0.1 and 7.7 +/- 0.1 for cleavage and 6.1 +/- 0.3 and 6.9 +/- 0.3 for ligation. The data provide good evidence for general acid-base catalysis by the nucleobases.
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Affiliation(s)
- Timothy J Wilson
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee
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Salter J, Krucinska J, Alam S, Grum-Tokars V, Wedekind JE. Water in the active site of an all-RNA hairpin ribozyme and effects of Gua8 base variants on the geometry of phosphoryl transfer. Biochemistry 2006; 45:686-700. [PMID: 16411744 PMCID: PMC2546605 DOI: 10.1021/bi051887k] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The hairpin ribozyme requires functional group contributions from G8 to assist in phosphodiester bond cleavage. Previously, replacement of G8 by a series of nucleobase variants showed little effect on interdomain docking, but a 3-250-fold effect on catalysis. To identify G8 features that contribute to catalysis within the hairpin ribozyme active site, structures for five base variants were determined by X-ray crystallography in a resolution range between 2.3 and 2.7 A. For comparison, a native all-RNA "G8" hairpin ribozyme structure was refined to 2.05 A resolution. The native structure revealed a scissile bond angle (tau) of 158 degrees, which is close to the requisite 180 degrees "in-line" geometry. Mutations G8(inosine), G8(diaminopurine), G8(aminopurine), G8(adenosine), and G8(uridine) folded properly, but exhibited nonideal scissile bond geometries (tau ranging from 118 degrees to 93 degrees) that paralleled their diminished solution activities. A superposition ensemble of all structures, including a previously described hairpin ribozyme-vanadate complex, indicated the scissile bond can adopt a variety of conformations resulting from perturbation of the chemical environment and provided a rationale for how the exocyclic amine of nucleobase 8 promotes productive, in-line geometry. Changes at position 8 also caused variations in the A-1 sugar pucker. In this regard, variants A8 and U8 appeared to represent nonproductive ground states in which their 2'-OH groups mimicked the pro-R, nonbridging oxygen of the vanadate transition-state complex. Finally, the results indicated that ordered water molecules bind near the 2'-hydroxyl of A-1, lending support to the hypothesis that solvent may play an important role in the reaction.
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Affiliation(s)
- Jason Salter
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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