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tRNA Fusion to Streamline RNA Structure Determination: Case Studies in Probing Aminoacyl-tRNA Sensing Mechanisms by the T-Box Riboswitch. CRYSTALS 2022. [DOI: 10.3390/cryst12050694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
RNAs are prone to misfolding and are often more challenging to crystallize and phase than proteins. Here, we demonstrate that tRNA fusion can streamline the crystallization and structure determination of target RNA molecules. This strategy was applied to the T-box riboswitch system to capture a dynamic interaction between the tRNA 3′-UCCA tail and the T-box antiterminator, which senses aminoacylation. We fused the T-box antiterminator domain to the tRNA anticodon arm to capture the intended interaction through crystal packing. This approach drastically improved the probability of crystallization and successful phasing. Multiple structure snapshots captured the antiterminator loop in an open conformation with some resemblance to that observed in the recent co-crystal structures of the full-length T box riboswitch–tRNA complex, which contrasts the resting, closed conformation antiterminator observed in an earlier NMR study. The anticipated tRNA acceptor–antiterminator interaction was captured in a low-resolution crystal structure. These structures combined with our previous success using prohead RNA–tRNA fusions demonstrates tRNA fusion is a powerful method in RNA structure determination.
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Li S, Su Z, Lehmann J, Stamatopoulou V, Giarimoglou N, Henderson FE, Fan L, Pintilie GD, Zhang K, Chen M, Ludtke SJ, Wang YX, Stathopoulos C, Chiu W, Zhang J. Structural basis of amino acid surveillance by higher-order tRNA-mRNA interactions. Nat Struct Mol Biol 2019; 26:1094-1105. [PMID: 31740854 PMCID: PMC6899168 DOI: 10.1038/s41594-019-0326-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 10/07/2019] [Indexed: 12/11/2022]
Abstract
Amino acid availability in Gram-positive bacteria is monitored by T-box riboswitches. T-boxes directly bind tRNAs, assess their aminoacylation state, and regulate the transcription or translation of downstream genes to maintain nutritional homeostasis. Here, we report cocrystal and cryo-EM structures of Geobacillus kaustophilus and Bacillus subtilis T-box-tRNA complexes, detailing their multivalent, exquisitely selective interactions. The T-box forms a U-shaped molecular vise that clamps the tRNA, captures its 3' end using an elaborate 'discriminator' structure, and interrogates its aminoacylation state using a steric filter fashioned from a wobble base pair. In the absence of aminoacylation, T-boxes clutch tRNAs and form a continuously stacked central spine, permitting transcriptional readthrough or translation initiation. A modeled aminoacyl disrupts tRNA-T-box stacking, severing the central spine and blocking gene expression. Our data establish a universal mechanism of amino acid sensing on tRNAs and gene regulation by T-box riboswitches and exemplify how higher-order RNA-RNA interactions achieve multivalency and specificity.
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Affiliation(s)
- Shuang Li
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA
| | - Zhaoming Su
- Department of Bioengineering and Department of Microbiology and Immunology, James H. Clark Center, Stanford University, Stanford, CA, USA
| | - Jean Lehmann
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Campus Paris-Saclay, Gif-sur-Yvette, France
| | | | - Nikoleta Giarimoglou
- Department of Biochemistry, School of Medicine, University of Patras, Patras, Greece
| | - Frances E Henderson
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA
| | - Lixin Fan
- Small-Angle X-ray Scattering Core Facility, Center for Cancer Research of the National Cancer Institute, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research, Inc, Frederick, MD, USA
| | - Grigore D Pintilie
- Department of Bioengineering and Department of Microbiology and Immunology, James H. Clark Center, Stanford University, Stanford, CA, USA
| | - Kaiming Zhang
- Department of Bioengineering and Department of Microbiology and Immunology, James H. Clark Center, Stanford University, Stanford, CA, USA
| | - Muyuan Chen
- Verna Marrs and McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Steven J Ludtke
- Verna Marrs and McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Yun-Xing Wang
- Small-Angle X-ray Scattering Core Facility, Center for Cancer Research of the National Cancer Institute, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research, Inc, Frederick, MD, USA.,Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
| | | | - Wah Chiu
- Department of Bioengineering and Department of Microbiology and Immunology, James H. Clark Center, Stanford University, Stanford, CA, USA. .,Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Menlo Park, Stanford University, Stanford, CA, USA.
| | - Jinwei Zhang
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA.
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Suddala KC, Zhang J. An evolving tale of two interacting RNAs-themes and variations of the T-box riboswitch mechanism. IUBMB Life 2019; 71:1167-1180. [PMID: 31206978 DOI: 10.1002/iub.2098] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 05/10/2019] [Indexed: 01/10/2023]
Abstract
T-box riboswitches are a widespread class of structured noncoding RNAs in Gram-positive bacteria that regulate the expression of amino acid-related genes. They form negative feedback loops to maintain steady supplies of aminoacyl-transfer RNAs (tRNAs) to the translating ribosomes. T-box riboswitches are located in the 5' leader regions of mRNAs that they regulate and directly bind to their cognate tRNA ligands. T-boxes further sense the aminoacylation state of the bound tRNAs and, based on this readout, regulate gene expression at the level of transcription or translation. T-box riboswitches consist of two conserved domains-a 5' Stem I domain that is involved in specific tRNA recognition and a 3' antiterminator/antisequestrator (or discriminator) domain that senses the amino acid on the 3' end of the bound tRNA. Interaction of the 3' end of an uncharged but not charged tRNA with a thermodynamically weak discriminator domain stabilizes it to promote transcription readthrough or translation initiation. Recent biochemical, biophysical, and structural studies have provided high-resolution insights into the mechanism of tRNA recognition by Stem I, several structural models of full-length T-box-tRNA complexes, mechanism of amino acid sensing by the antiterminator domain, as well as kinetic details of tRNA binding to the T-box riboswitches. In addition, translation-regulating T-box riboswitches have been recently characterized, which presented key differences from the canonical transcriptional T-boxes. Here, we review the recent developments in understanding the T-box riboswitch mechanism that have employed various complementary approaches. Further, the regulation of multiple essential genes by T-boxes makes them very attractive drug targets to combat drug resistance. The recent progress in understanding the biochemical, structural, and dynamic aspects of the T-box riboswitch mechanism will enable more precise and effective targeting with small molecules. © 2019 IUBMB Life, 2019 © 2019 IUBMB Life, 71(8):1167-1180, 2019.
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Affiliation(s)
- Krishna C Suddala
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Jinwei Zhang
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA
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Abstract
The T-box riboswitch is a unique, RNA-based regulatory mechanism that modulates expression of a wide variety of amino acid-related genes, predominantly in Firmicutes. RNAs of this class selectively bind a specific cognate tRNA, utilizing recognition of the tRNA anticodon and other tRNA features. The riboswitch monitors the aminoacylation status of the tRNA to induce expression of the regulated downstream gene(s) at the level of transcription antitermination or derepression of translation initiation in response to reduced tRNA charging via stabilization of an antiterminator or antisequestrator. Recent biochemical and structural studies have revealed new features of tRNA recognition that extend beyond the initially identified Watson-Crick base-pairing of a codon-like sequence in the riboswitch with the tRNA anticodon, and residues in the antiterminator or antisequestrator with the tRNA acceptor end. These studies have revealed new tRNA contacts and new modes of riboswitch function and ligand recognition that expand our understanding of RNA-RNA recognition and the biological roles of tRNA.
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Zhang J, Chetnani B, Cormack ED, Alonso D, Liu W, Mondragón A, Fei J. Specific structural elements of the T-box riboswitch drive the two-step binding of the tRNA ligand. eLife 2018; 7:39518. [PMID: 30251626 PMCID: PMC6197855 DOI: 10.7554/elife.39518] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Accepted: 09/24/2018] [Indexed: 12/29/2022] Open
Abstract
T-box riboswitches are cis-regulatory RNA elements that regulate the expression of proteins involved in amino acid biosynthesis and transport by binding to specific tRNAs and sensing their aminoacylation state. While the T-box modular structural elements that recognize different parts of a tRNA have been identified, the kinetic trajectory describing how these interactions are established temporally remains unclear. Using smFRET, we demonstrate that tRNA binds to the riboswitch in two steps, first anticodon recognition followed by the sensing of the 3’ NCCA end, with the second step accompanied by a T-box riboswitch conformational change. Studies on site-specific mutants highlight that specific T-box structural elements drive the two-step binding process in a modular fashion. Our results set up a kinetic framework describing tRNA binding by T-box riboswitches, and suggest such binding mechanism is kinetically beneficial for efficient, co-transcriptional recognition of the cognate tRNA ligand. Living organisms depend upon a group of chemicals called amino acids to survive. Amino acids are the building blocks of proteins, and proteins have many important roles within and around cells. Bacteria regulate certain genes to ensure they have the right balance of different amino acids to survive. By controlling the availability of certain proteins that help them to make or collect certain amino acids, bacteria can control their overall amino acid balance. Before a protein is made, a molecular machine called RNA polymerase must first copy the information in a gene to make a molecule called a messenger RNA (mRNA). The mRNA is then translated to make the protein from individual amino acids. In this process, each amino acid needs to be first attached to another molecule called a transfer RNA (tRNA). In many bacteria species, the mRNAs involved in making or transporting amino acids contain structures called T-boxes. These structures guide the RNA polymerase to make more of the mRNAs when the levels of the amino acid become too low. A T-box, however, does not sense the level of the amino acid directly. Instead it senses the number of tRNA molecules that do not carry an amino acid. Zhang, Chetnani et al. examined a particular T-box interacting with tRNA using pairs of fluorescent dyes to detect distances between molecules. The T-box first recognizes a part of the tRNA called the anticodon to make sure it binds the correct type of tRNA. It then changes its shape to detect whether the tRNA is attached to an amino acid. This two-step process is driven by multiple structural elements within the T-box, and the flexibility of the T-box plays a critical role. A cell’s survival depends on it keeping amino acid levels under control. Understanding how bacteria do this could lead to new antibiotic drugs that target the T-box to kill cells. This study also provides insights into the workings of mRNA components like T-boxes – a type of riboswitch – which is an unusual means of controlling gene activity.
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Affiliation(s)
- Jiacheng Zhang
- Institute for Biophysical Dynamics, University of Chicago, Chicago, United States
| | - Bhaskar Chetnani
- Department of Molecular Biosciences, Northwestern University, Evanston, United States
| | | | - Dulce Alonso
- Department of Molecular Biosciences, Northwestern University, Evanston, United States
| | - Wei Liu
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Alfonso Mondragón
- Department of Molecular Biosciences, Northwestern University, Evanston, United States
| | - Jingyi Fei
- Institute for Biophysical Dynamics, University of Chicago, Chicago, United States.,Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
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Hierarchical mechanism of amino acid sensing by the T-box riboswitch. Nat Commun 2018; 9:1896. [PMID: 29760498 PMCID: PMC5951919 DOI: 10.1038/s41467-018-04305-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 04/16/2018] [Indexed: 11/08/2022] Open
Abstract
In Gram-positive bacteria, T-box riboswitches control gene expression to maintain the cellular pools of aminoacylated tRNAs essential for protein biosynthesis. Co-transcriptional binding of an uncharged tRNA to the riboswitch stabilizes an antiterminator, allowing transcription read-through, whereas an aminoacylated tRNA does not. Recent structural studies have resolved two contact points between tRNA and Stem-I in the 5' half of the T-box riboswitch, but little is known about the mechanism empowering transcriptional control by a small, distal aminoacyl modification. Using single-molecule fluorescence microscopy, we have probed the kinetic and structural underpinnings of tRNA binding to a glycyl T-box riboswitch. We observe a two-step mechanism where fast, dynamic recruitment of tRNA by Stem-I is followed by ultra-stable anchoring by the downstream antiterminator, but only without aminoacylation. Our results support a hierarchical sensing mechanism wherein dynamic global binding of the tRNA body is followed by localized readout of its aminoacylation status by snap-lock-based trapping.
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New tRNA contacts facilitate ligand binding in a Mycobacterium smegmatis T box riboswitch. Proc Natl Acad Sci U S A 2018; 115:3894-3899. [PMID: 29581302 DOI: 10.1073/pnas.1721254115] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
T box riboswitches are RNA regulatory elements widely used by organisms in the phyla Firmicutes and Actinobacteria to regulate expression of amino acid-related genes. Expression of T box family genes is down-regulated by transcription attenuation or inhibition of translation initiation in response to increased charging of the cognate tRNA. Three direct contacts with tRNA have been described; however, one of these contacts is absent in a subclass of T box RNAs and the roles of several structural domains conserved in most T box RNAs are unknown. In this study, structural elements of a Mycobacterium smegmatis ileS T box riboswitch variant with an Ultrashort (US) Stem I were sequentially deleted, which resulted in a progressive decrease in binding affinity for the tRNAIle ligand. Selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE) revealed structural changes in conserved riboswitch domains upon interaction with the tRNA ligand. Cross-linking and mutational analyses identified two interaction sites, one between the S-turn element in Stem II and the T arm of tRNAIle and the other between the Stem IIA/B pseudoknot and the D loop of tRNAIle These newly identified RNA contacts add information about tRNA recognition by the T box riboswitch and demonstrate a role for the S-turn and pseudoknot elements, which resemble structural elements that are common in many cellular RNAs.
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