1
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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 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] [What about the content of this article? (0)] [Affiliation(s)] [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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2
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Hansen LN, Kletzien OA, Urquijo M, Schwanz LT, Batey RT. Context-dependence of T-loop mediated long-range RNA tertiary interactions. J Mol Biol 2023; 435:168070. [PMID: 37003469 PMCID: PMC10152882 DOI: 10.1016/j.jmb.2023.168070] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Revised: 03/03/2023] [Accepted: 03/06/2023] [Indexed: 04/03/2023]
Abstract
The architecture and folding of complex RNAs is governed by a limited set of highly recurrent structural motifs that form long-range tertiary interactions. One of these motifs is the T-loop, which was first identified in tRNA but is broadly distributed across biological RNAs. While the T-loop has been examined in detail in different biological contexts, the various receptors that it interacts with are not as well defined. In this study, we use a cell-based genetic screen in concert with bioinformatic analysis to examine three different, but related, T-loop receptor motifs found in the flavin mononucleotide (FMN) and cobalamin (Cbl) riboswitches. As a host for different T-loop receptors, we employed the env8 class-II Cbl riboswitch, an RNA that uses two T-loop motifs for both folding and supporting the ligand binding pocket. A set of libraries was created in which select nucleotides that participate in the T-loop/T-loop receptor (TL/TLR) interaction were fully randomized. Library members were screened for their ability to support Cbl-dependent expression of a reporter gene. While T-loops appear to be variable in sequence, we find that the functional sequence space is more restricted in the Cbl riboswitch, suggesting that TL/TLR interactions are context dependent. Our data reveal clear sequence signatures for the different types of receptor motifs that align with phylogenic analysis of these motifs in the FMN and Cbl riboswitches. Finally, our data suggest the functional contribution of various nucleobase-mediated long-range interactions within the riboswitch subclass of TL/TLR interactions that are distinct from those found in other RNAs.
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Affiliation(s)
- Lisa N Hansen
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309-0596, USA
| | - Otto A Kletzien
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309-0596, USA
| | - Marcus Urquijo
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309-0596, USA
| | - Logan T Schwanz
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309-0596, USA
| | - Robert T Batey
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309-0596, USA.
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3
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Kiliszek A, Pluta M, Bejger M, Rypniewski W. Structure and thermodynamics of a UGG motif interacting with Ba2+ and other metal ions: accommodating changes in the RNA structure and the presence of a G(syn)-G(syn) pair. RNA 2022; 29:rna.079414.122. [PMID: 36319090 PMCID: PMC9808570 DOI: 10.1261/rna.079414.122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 10/11/2022] [Indexed: 06/16/2023]
Abstract
The self-complementary triplet 5'UGG3'/5'UGG3' is a particular structural motif containing noncanonical G-G pair and two U·G wobble pairs. It constitutes a specific structural and electrostatic environment attracting metal ions, particularly Ba2+ ions. Crystallographic research has shown that two Ba2+ cations are located in the major groove of the helix and interact directly with the UGG triplet. A comparison with the unliganded structure has revealed global changes in the RNA structure in the presence of metal ions, whereas thermodynamic measurements have shown increased stability. Moreover, in the structure with Ba2+, an unusual noncanonical G(syn)-G(syn) pair is observed instead of the common G(anti)-G(syn). We further elucidate the metal binding properties of the UGG/UGG triplet by performing crystallographic and thermodynamic studies using DSC and UV melting with other metal ions. The results explain the preferences of the UGG sequence for Ba2+ cations and point to possible applications of this metal-binding propensity.
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4
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Matoušková E, Dršata T, Pfeifferová L, Šponer J, Réblová K, Lankaš F. RNA kink-turns are highly anisotropic with respect to lateral displacement of the flanking stems. Biophys J 2022; 121:705-714. [PMID: 35122735 PMCID: PMC8943727 DOI: 10.1016/j.bpj.2022.01.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 12/23/2021] [Accepted: 01/28/2022] [Indexed: 11/02/2022] Open
Abstract
Kink-turns are highly bent internal loop motifs commonly found in the ribosome and other RNA complexes. They frequently act as binding sites for proteins and mediate tertiary interactions in larger RNA structures. Kink-turns have been a topic of intense research, but their elastic properties in the folded state are still poorly understood. Here we use extensive all-atom molecular dynamics simulations to parameterize a model of kink-turn in which the two flanking helical stems are represented by effective rigid bodies. Time series of the full set of six interhelical coordinates enable us to extract minimum energy shapes and harmonic stiffness constants for kink-turns from different RNA functional classes. The analysis suggests that kink-turns exhibit isotropic bending stiffness but are highly anisotropic with respect to lateral displacement of the stems. The most flexible lateral displacement mode is perpendicular to the plane of the static bend. These results may help understand the structural adaptation and mechanical signal transmission by kink-turns in complex natural and artificial RNA structures.
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Affiliation(s)
- Eva Matoušková
- Department of Informatics and Chemistry, University of Chemistry and Technology, Prague, Czech Republic
| | - Tomáš Dršata
- Department of Informatics and Chemistry, University of Chemistry and Technology, Prague, Czech Republic
| | - Lucie Pfeifferová
- Department of Informatics and Chemistry, University of Chemistry and Technology, Prague, Czech Republic
| | - Jiří Šponer
- Institute of Biophysics of the Czech Academy of Sciences, Brno, Czech Republic
| | - Kamila Réblová
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic; Centre of Molecular Biology and Genetics, University Hospital Brno, Czech Republic.
| | - Filip Lankaš
- Department of Informatics and Chemistry, University of Chemistry and Technology, Prague, Czech Republic.
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5
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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6
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Abstract
The crystallization and structural determination of large RNAs and their complexes remain major bottlenecks in the mechanistic analysis of cellular and viral RNAs. Here, we describe a protocol that combines postcrystallization dehydration and ion replacement that dramatically improved the diffraction quality of crystals of a large gene-regulatory tRNA-mRNA complex. Through this method, the resolution limit of X-ray data extended from 8.5 to 3.2 Å, enabling structure determination. Although this protocol was developed for a particular RNA complex, the general importance of solvent and counterions in nucleic acid structure may render it generally useful for crystallographic analysis of other RNAs.
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7
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Lai SM, Gopalan V. Using an L7Ae-Tethered, Hydroxyl Radical-Mediated Footprinting Strategy to Identify and Validate Kink-Turns in RNAs. Methods Mol Biol 2021; 2167:147-169. [PMID: 32712919 DOI: 10.1007/978-1-0716-0716-9_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Kink-turns are important RNA structural modules that facilitate long-range tertiary interactions and form binding sites for members of the L7Ae family of proteins. Present in a wide variety of functional RNAs, kink-turns play key organizational roles in many RNA-based cellular processes, including translation, modification, and tRNA biogenesis. It is important to determine the contribution of kink-turns to the overall architecture of resident RNAs, as these modules dictate ribonucleoprotein (RNP) assembly and function. This chapter describes a site-directed, hydroxyl radical-mediated footprinting strategy that utilizes L7Ae-tethered chemical nucleases to experimentally validate computationally identified kink-turns in any RNA and under a wide variety of conditions. The work plan described here uses the catalytic RNase P RNA as an example to provide a blueprint for using this footprinting method to map RNA-protein interactions in other RNP complexes.
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Affiliation(s)
- Stella M Lai
- Department of Chemistry and Biochemistry and Center for RNA Biology, The Ohio State University, Columbus, OH, USA
| | - Venkat Gopalan
- Department of Chemistry and Biochemistry and Center for RNA Biology, The Ohio State University, Columbus, OH, USA.
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8
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Zhang H, Zhang H, Chen C. Simulation Study of the Plasticity of k-Turn Motif in Different Environments. Biophys J 2020; 119:1416-1426. [PMID: 32918889 DOI: 10.1016/j.bpj.2020.08.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 07/15/2020] [Accepted: 08/12/2020] [Indexed: 10/23/2022] Open
Abstract
The k-turn is a widespread and important motif in RNA. According to the internal hydrogen bond network, it has two stable states, called N1 and N3. The relative stability between the states changes with the environment. It is able to accept different conformations in different environments. This is called the "plasticity" of a molecule. In this work, we study the plasticity of k-turn by the mixing REMD method in explicit solvent. The results are concluded as follows. First, N1 and N3 are almost equally stable when k-turn is in the solvent alone. The molecule is quite flexible as a hinge. However, after binding to different proteins, such as the proteins L7Ae and L24e, k-turn falls into one global minimum. The preferred state could be either N1 or N3. On the contrary, the other nonpreferred state becomes unstable with a weaker binding affinity to the protein. It reveals that RNA-binding protein is able to modulate the representative state of k-turn at equilibrium. This is in agreement with the findings in experiments. Moreover, free energy calculations show that the free energy barrier between the N1 and N3 states of k-turn increases in the complexes. The state-to-state transition is greatly impeded. We also give a deep discussion on the mechanism of the high plasticity of k-turn in different environments.
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Affiliation(s)
- Haomiao Zhang
- Biomolecular Physics and Modeling Group, School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Haozhe Zhang
- Biomolecular Physics and Modeling Group, School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Changjun Chen
- Biomolecular Physics and Modeling Group, School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, China.
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9
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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10
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Abstract
The kink-turn (k-turn) is a widespread structural motif found in functional RNA species. It typically comprises a three-nucleotide bulge followed by tandem trans sugar edge-Hoogsteen G:A base pairs. It introduces a sharp kink into the axis of duplex RNA, juxtaposing the minor grooves. Cross-strand H-bonds form at the interface, accepted by the conserved adenine nucleobases of the G:A basepairs. Alternative acceptors for one of these divides the k-turns into two conformational classes N3 and N1. The base pair that follows the G:A pairs (3b:3n) determines which conformation is adopted by a given k-turn. k-turns often mediate tertiary contacts in folded RNA species and frequently bind proteins. Common k-turn binding proteins include members of the L7Ae family, such as the human 15·5k protein. A recognition helix within these proteins binds in the widened major groove on the outside of the k-turn, that makes specific H-bonds with the conserved guanine nucleobases of the G:A pairs. L7Ae binds with extremely high affinity, and single-molecule data are consistent with folding by conformational selection. The standard, simple k-turn can be elaborated in a variety of ways, that include the complex k-turns and the k-junctions. In free solution in the absence of added metal ions or protein k-turns do not adopt the tightly-kinked conformation. They undergo folding by the binding of proteins, by the formation of tertiary contacts, and some (but not all) will fold on the addition of metal ions. Whether or not folding occurs in the presence of metal ions depends on local sequence, including the 3b:3n position, and the -1b:-1n position (5' to the bulge). In most cases -1b:-1n = C:G, so that the 3b:3n position is critical since it determines both folding properties and conformation. In general, the selection of these sequence matches a given k-turn to its biological requirements. The k-turn structure is now very well understood, to the point at which they can be used as a building block for the formation of RNA nano-objects, including triangles and squares.
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11
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Huang L, Ashraf S, Lilley DMJ. The role of RNA structure in translational regulation by L7Ae protein in archaea. RNA 2019; 25:60-69. [PMID: 30327333 PMCID: PMC6298567 DOI: 10.1261/rna.068510.118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Accepted: 10/07/2018] [Indexed: 05/03/2023]
Abstract
A recent study has shown that archaeal L7Ae binds to a putative k-turn structure in the 5'-leader of the mRNA of its structural gene to regulate translation. To function as a regulator, the RNA should be unstructured in the absence of protein, but it should adopt a k-turn-containing stem-loop on binding L7Ae. Sequence analysis of UTR sequences indicates that their k-turn elements will be unable to fold in the absence of L7Ae, and we have demonstrated this experimentally in solution using FRET for the Archaeoglobus fulgidus sequence. We have solved the X-ray crystal structure of the complex of the A. fulgidus RNA bound to its cognate L7Ae protein. The RNA adopts a standard k-turn conformation that is specifically recognized by the L7Ae protein, so stabilizing the stem-loop. In-line probing of the natural-sequence UTR shows that the RNA is unstructured in the absence of L7Ae binding, but folds on binding the protein such that the ribosome binding site is occluded. Thus, L7Ae regulates its own translation by switching the conformation of the RNA to alter accessibility.
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Affiliation(s)
- Lin Huang
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Saira Ashraf
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, The University of Dundee, Dundee DD1 5EH, United Kingdom
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12
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Fischer NM, Polêto MD, Steuer J, van der Spoel D. Influence of Na+ and Mg2+ ions on RNA structures studied with molecular dynamics simulations. Nucleic Acids Res 2018; 46:4872-4882. [PMID: 29718375 PMCID: PMC6007214 DOI: 10.1093/nar/gky221] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 02/16/2018] [Accepted: 04/23/2018] [Indexed: 01/11/2023] Open
Abstract
The structure of ribonucleic acid (RNA) polymers is strongly dependent on the presence of, in particular Mg2+ cations to stabilize structural features. Only in high-resolution X-ray crystallography structures can ions be identified reliably. Here, we perform molecular dynamics simulations of 24 RNA structures with varying ion concentrations. Twelve of the structures were helical and the others complex folded. The aim of the study is to predict ion positions but also to evaluate the impact of different types of ions (Na+ or Mg2+) and the ionic strength on structural stability and variations of RNA. As a general conclusion Mg2+ is found to conserve the experimental structure better than Na+ and, where experimental ion positions are available, they can be reproduced with reasonable accuracy. If a large surplus of ions is present the added electrostatic screening makes prediction of binding-sites less reproducible. Distinct differences in ion-binding between helical and complex folded structures are found. The strength of binding (ΔG‡ for breaking RNA atom-ion interactions) is found to differ between roughly 10 and 26 kJ/mol for the different RNA atoms. Differences in stability between helical and complex folded structures and of the influence of metal ions on either are discussed.
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Affiliation(s)
- Nina M Fischer
- Uppsala Centre for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
| | - Marcelo D Polêto
- Uppsala Centre for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
- Center of Biotechnology, Universidade Federal do Rio Grande do Sul, Bento Gonçalves 9500, BR-91500-970 Porto Alegre, Brazil
| | - Jakob Steuer
- Uppsala Centre for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
- Department of Chemistry, University of Konstanz, Universitätstraße 10, D-78457 Konstanz, Germany
| | - David van der Spoel
- Uppsala Centre for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
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13
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Ashraf S, Huang L, Lilley DMJ. Sequence determinants of the folding properties of box C/D kink-turns in RNA. RNA 2017; 23:1927-1935. [PMID: 28956757 PMCID: PMC5689011 DOI: 10.1261/rna.063453.117] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 09/15/2017] [Indexed: 05/20/2023]
Abstract
Folding properties differ markedly between kink-turns (k-turns) that have different biological functions. While ribosomal and riboswitch k-turns generally fold into their kinked conformation on addition of metal ions, box C/D snoRNP k-turns remain completely unfolded under these conditions, although they fold on addition of L7Ae protein. Sequence elements have been systematically exchanged between a standard ribosomal k-turn (Kt-7) that folds on addition of metal ions, and a box C/D k-turn. Folding was studied using fluorescence resonance energy transfer and gel electrophoresis. Three sequence elements each contribute in an approximately additive manner to the different folding properties of Kt-7 and box C/D k-turns from archaea. Bioinformatic analysis indicates that k-turn sequences evolve sequences that suit their folding properties to their biological function. The majority of ribosomal and riboswitch k-turns have sequences allowing unassisted folding in response to the presence of metal ions. In contrast, box C/D k-turns have sequences that require the binding of proteins to drive folding into the kinked conformation, consistent with their role in the assembly of the box C/D snoRNP apparatus. The rules governing the influence of sequence on folding properties can be applied to other standard k-turns to predict their folding characteristics.
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Affiliation(s)
- Saira Ashraf
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Lin Huang
- 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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14
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Bayrak CS, Kim N, Schlick T. Using sequence signatures and kink-turn motifs in knowledge-based statistical potentials for RNA structure prediction. Nucleic Acids Res 2017; 45:5414-5422. [PMID: 28158755 PMCID: PMC5435971 DOI: 10.1093/nar/gkx045] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/22/2017] [Indexed: 12/15/2022] Open
Abstract
Kink turns are widely occurring motifs in RNA, located in internal loops and associated with many biological functions including translation, regulation and splicing. The associated sequence pattern, a 3-nt bulge and G-A, A-G base-pairs, generates an angle of ∼50° along the helical axis due to A-minor interactions. The conserved sequence and distinct secondary structures of kink-turns (k-turn) suggest computational folding rules to predict k-turn-like topologies from sequence. Here, we annotate observed k-turn motifs within a non-redundant RNA dataset based on sequence signatures and geometrical features, analyze bending and torsion angles, and determine distinct knowledge-based potentials with and without k-turn motifs. We apply these scoring potentials to our RAGTOP (RNA-As-Graph-Topologies) graph sampling protocol to construct and sample coarse-grained graph representations of RNAs from a given secondary structure. We present graph-sampling results for 35 RNAs, including 12 k-turn and 23 non k-turn internal loops, and compare the results to solved structures and to RAGTOP results without special k-turn potentials. Significant improvements are observed with the updated scoring potentials compared to the k-turn-free potentials. Because k-turns represent a classic example of sequence/structure motif, our study suggests that other such motifs with sequence signatures and unique geometrical features can similarly be utilized for RNA structure prediction and design.
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Affiliation(s)
- Cigdem Sevim Bayrak
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA
| | - Namhee Kim
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA
| | - Tamar Schlick
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA
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15
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Abstract
Mammalian cells express hundreds of intron-encoded box H/ACA RNAs which fold into a common hairpin-hinge-hairpin-tail structure, interact with 4 evolutionarily conserved proteins, dyskerin, Nop10, Nhp2 and Gar1, and function mainly in RNA pseudouridylation. The human telomerase H/ACA RNA (hTR) directs telomeric DNA synthesis and it carries a 5'-terminal domain encompassing the telomeric template sequence. The primary hTR transcript is synthesized from an independent gene by RNA polymerase II and undergoes 3' end processing controlled by the 3'-terminal H/ACA domain. The apical stem-loop of the 3' hairpin of hTR carries a unique biogenesis-promoting element, the BIO motif that promotes hTR processing and RNP assembly. AluACA RNAs represent a distinct class of human H/ACA RNAs; they are processed from intronic Alu repetitive sequences. As compared to canonical H/ACA RNAs, the AluACA RNAs carry unusually short or long 5' hairpins and generally, they accumulate at low levels. Here, we demonstrate that the suboptimal 5' hairpins are responsible for the weak expression of AluACA RNAs. We also show that AluACA RNAs frequently carry a processing/stabilization element that is structurally and functionally indistinguishable from the hTR BIO motif. Both hTR and AluACA biogenesis-promoting elements are located in the terminal stem-loop of the 3'-terminal H/ACA hairpin, they show perfect structural conservation and are functionally interchangeable in in vivo RNA processing reactions. Our results demonstrate that the BIO motif, instead of being confined to hTR, is a more general H/ACA RNP biogenesis-facilitating element that can also promote processing/assembly of intron-encoded AluACA RNPs.
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Affiliation(s)
- Amandine Ketele
- a Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, Center de Biologie Intégrative, Université Paul Sabatier , Toulouse Cedex 9, France
| | - Tamás Kiss
- a Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, Center de Biologie Intégrative, Université Paul Sabatier , Toulouse Cedex 9, France.,b Biological Research Center, Hungarian Academy of Sciences , Szeged , Hungary
| | - Beáta E Jády
- a Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, Center de Biologie Intégrative, Université Paul Sabatier , Toulouse Cedex 9, France
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16
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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17
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Esquiaqui JM, Sherman EM, Ye JD, Fanucci GE. Conformational Flexibility and Dynamics of the Internal Loop and Helical Regions of the Kink–Turn Motif in the Glycine Riboswitch by Site-Directed Spin-Labeling. Biochemistry 2016; 55:4295-305. [DOI: 10.1021/acs.biochem.6b00287] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jackie M. Esquiaqui
- Department
of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
| | - Eileen M. Sherman
- Department
of Chemistry, University of Central Florida, 4000 Central Florida Boulevard, Orlando, Florida 32816, United States
| | - Jing-Dong Ye
- Department
of Chemistry, University of Central Florida, 4000 Central Florida Boulevard, Orlando, Florida 32816, United States
| | - Gail E. Fanucci
- Department
of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
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18
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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19
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Shi X, Huang L, Lilley DMJ, Harbury PB, Herschlag D. The solution structural ensembles of RNA kink-turn motifs and their protein complexes. Nat Chem Biol 2016; 12:146-52. [PMID: 26727239 PMCID: PMC4755865 DOI: 10.1038/nchembio.1997] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2015] [Accepted: 11/04/2015] [Indexed: 12/22/2022]
Abstract
With the growing number of crystal structures of RNA and RNA-protein complexes, a critical next step is understanding the dynamic solution behavior of these entities in terms of conformational ensembles and energy landscapes. To this end, we have used X-ray scattering interferometry (XSI) to probe the ubiquitous RNA kink-turn motif and its complexes with the canonical kink-turn binding protein L7Ae. XSI revealed that the folded kink-turn is best described as a restricted conformational ensemble. The ions present in solution alter the nature of this ensemble, and protein binding can perturb the kink-turn ensemble without collapsing it to a unique state. This study demonstrates how XSI can reveal structural and ensemble properties of RNAs and RNA-protein complexes and uncovers the behavior of an important RNA-protein motif. This type of information will be necessary to understand, predict and engineer the behavior and function of RNAs and their protein complexes.
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Affiliation(s)
- Xuesong Shi
- Department of Biochemistry, Stanford University, Stanford, California, USA
| | - Lin Huang
- Nucleic Acid Structure Research Group, School of Life Sciences, University of Dundee, Dundee, UK
| | - David M J Lilley
- Nucleic Acid Structure Research Group, School of Life Sciences, University of Dundee, Dundee, UK
| | - Pehr B Harbury
- Department of Biochemistry, Stanford University, Stanford, California, USA
- ChEM-H, Stanford University, Stanford, California, USA
| | - Daniel Herschlag
- Department of Biochemistry, Stanford University, Stanford, California, USA
- ChEM-H, Stanford University, Stanford, California, USA
- Department of Chemistry, Stanford University, Stanford, California, USA
- Department of Chemical Engineering, Stanford University, Stanford, California, USA
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20
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Abstract
Kink turns (k-turns) are widespread structural elements that introduce an axial bend into duplex RNA with an included angle of 50°. These mediate key tertiary interactions and bind specific proteins including members of the L7Ae family. The standard k-turn comprises a three-nucleotide bulge followed by G·A and A·G pairs. The RNA kinks by an association of the two minor grooves, stabilized by the formation of a number of key cross-strand hydrogen bonds mostly involving the adenine bases of the G·A and A·G pairs. The k-turns may be divided into two conformational classes, depending on the receptor for one of these hydrogen bonds. k-turns become folded by one of three different processes. Some, but not all, k-turns become folded in the presence of metal ions. Whether or not a given k-turn is folded under these conditions is determined by its sequence. We present a set of rules for the prediction of folding properties and the structure adopted on local sequence.
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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, United Kingdom
| | - David M J Lilley
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, United Kingdom.
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21
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Abstract
The crystallization and structural determination of large RNAs and their complexes remain major bottlenecks in the mechanistic analysis of cellular and viral RNAs. Here, we describe a protocol that combines post-crystallization dehydration and ion replacement that dramatically improved the diffraction quality of crystals of a large gene-regulatory tRNA-mRNA complex. Through this method, the resolution limit of X-ray data extended from 8.5 to 3.2 Å, enabling structure determination. Although this protocol was developed for a particular RNA complex, the general importance of solvent and counterions in nucleic acid structure may render it generally useful for crystallographic analysis of other RNAs.
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Affiliation(s)
- Jinwei Zhang
- National Heart, Lung and Blood Institute, 50 South Drive, MSC 8012, Bethesda, MD, 20892-8012, USA
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22
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Kim N, Zahran M, Schlick T. Computational Prediction of Riboswitch Tertiary Structures Including Pseudoknots by RAGTOP. Methods Enzymol 2015; 553:115-35. [DOI: 10.1016/bs.mie.2014.10.054] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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23
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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24
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Esquiaqui JM, Sherman EM, Ionescu SA, Ye JD, Fanucci GE. Characterizing the dynamics of the leader-linker interaction in the glycine riboswitch with site-directed spin labeling. Biochemistry 2014; 53:3526-8. [PMID: 24849816 PMCID: PMC4059530 DOI: 10.1021/bi500404b] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Site-directed
spin labeling with continuous wave electron paramagnetic
resonance (EPR) spectroscopy was utilized to characterize dynamic
features of the kink–turn motif formed through a leader–linker
interaction in the Vibrio cholerae glycine riboswitch.
Efficient incorporation of spin-labels into select sites within the
phosphate backbone of the leader–linker region proceeded via
splinted ligation of chemically synthesized spin-labeled oligonucleotides
to in vitro transcribed larger RNA fragments. The
resultant nitroxide EPR line shapes have spectral characteristics
consistent with a kink–turn motif and reveal differential backbone
dynamics that are modulated by the presence of magnesium, potassium,
and glycine.
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Affiliation(s)
- Jackie M Esquiaqui
- Department of Chemistry, University of Florida , P.O. Box 117200, Gainesville, Florida 32611, United States
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25
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Lilley DM. The K-turn motif in riboswitches and other RNA species. Biochim Biophys Acta 2014; 1839:995-1004. [PMID: 24798078 DOI: 10.1016/j.bbagrm.2014.04.020] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Revised: 04/15/2014] [Accepted: 04/25/2014] [Indexed: 01/12/2023]
Abstract
The kink turn is a widespread structure motif that introduces a tight bend into the axis of duplex RNA. This generally functions to mediate tertiary interactions, and to serve as a specific protein binding site. K-turns or closely related structures are found in at least seven different riboswitch structures, where they function as key architectural elements that help generate the ligand binding pocket. This article is part of a Special Issue entitled: Riboswitches.
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26
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Zhang J, Ferré-D'Amaré AR. New molecular engineering approaches for crystallographic studies of large RNAs. Curr Opin Struct Biol 2014; 26:9-15. [PMID: 24607443 DOI: 10.1016/j.sbi.2014.02.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 02/04/2014] [Accepted: 02/05/2014] [Indexed: 01/01/2023]
Abstract
Crystallization of RNAs with complex three-dimensional architectures remains a formidable experimental challenge. We review a number of successful heuristics involving engineering of the target RNAs to facilitate crystal contact formation, such as those that enabled the crystallization and structure determination of the cognate tRNA complexes of RNase P holoenzyme and the Stem I domain of the T-box riboswitch. Recently, RNA-targeted antibody Fab fragments and Kink-turn binding proteins have joined the ranks of successful chaperones for RNA crystallization. Lastly, we review the use of structured RNAs to facilitate crystallization of RNA-binding proteins and other RNAs.
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Affiliation(s)
- Jinwei Zhang
- National Heart, Lung and Blood Institute, 50 South Drive, MSC 8012, Bethesda, MD 20892-8012, USA
| | - Adrian R Ferré-D'Amaré
- National Heart, Lung and Blood Institute, 50 South Drive, MSC 8012, Bethesda, MD 20892-8012, USA.
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27
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Abstract
The k-junction is a structural motif in RNA comprising a three-way helical junction based upon kink turn (k-turn) architecture. A computer program written to examine relative helical orientation identified the three-way junction of the Arabidopsis TPP riboswitch as an elaborated k-turn. The Escherichia coli TPP riboswitch contains a related k-junction, and analysis of >11 000 sequences shows that the structure is common to these riboswitches. The k-junction exhibits all the key features of an N1-class k-turn, including the standard cross-strand hydrogen bonds. The third helix of the junction is coaxially aligned with the C (canonical) helix, while the k-turn loop forms the turn into the NC (non-canonical) helix. Analysis of ligand binding by ITC and global folding by gel electrophoresis demonstrates the importance of the k-turn nucleotides. Clearly the basic elements of k-turn structure are structurally well suited to generate a three-way helical junction, retaining all the key features and interactions of the k-turn.
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Affiliation(s)
- Jia Wang
- 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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28
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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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29
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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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30
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Sheth P, Cervantes-Cervantes M, Nagula A, Laing C, Wang JTL. Novel features for identifying A-minors in three-dimensional RNA molecules. Comput Biol Chem 2013; 47:240-5. [PMID: 24211672 DOI: 10.1016/j.compbiolchem.2013.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2013] [Revised: 10/15/2013] [Accepted: 10/16/2013] [Indexed: 01/08/2023]
Abstract
RNA tertiary interactions or tertiary motifs are conserved structural patterns formed by pairwise interactions between nucleotides. They include base-pairing, base-stacking, and base-phosphate interactions. A-minor motifs are the most common tertiary interactions in the large ribosomal subunit. The A-minor motif is a nucleotide triple in which minor groove edges of an adenine base are inserted into the minor groove of neighboring helices, leading to interaction with a stabilizing base pair. We propose here novel features for identifying and predicting A-minor motifs in a given three-dimensional RNA molecule. By utilizing the features together with machine learning algorithms including random forests and support vector machines, we show experimentally that our approach is capable of predicting A-minor motifs in the given RNA molecule effectively, demonstrating the usefulness of the proposed approach. The techniques developed from this work will be useful for molecular biologists and biochemists to analyze RNA tertiary motifs, specifically A-minor interactions.
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Affiliation(s)
- Palak Sheth
- Bioinformatics Program, New Jersey Institute of Technology, Newark, NJ 07102, USA
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31
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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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