1
|
Olenginski LT, Spradlin SF, Batey RT. Flipping the script: Understanding riboswitches from an alternative perspective. J Biol Chem 2024; 300:105730. [PMID: 38336293 PMCID: PMC10907184 DOI: 10.1016/j.jbc.2024.105730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 01/14/2024] [Accepted: 01/19/2024] [Indexed: 02/12/2024] Open
Abstract
Riboswitches are broadly distributed regulatory elements most frequently found in the 5'-leader sequence of bacterial mRNAs that regulate gene expression in response to the binding of a small molecule effector. The occupancy status of the ligand-binding aptamer domain manipulates downstream information in the message that instructs the expression machinery. Currently, there are over 55 validated riboswitch classes, where each class is defined based on the identity of the ligand it binds and/or sequence and structure conservation patterns within the aptamer domain. This classification reflects an "aptamer-centric" perspective that dominates our understanding of riboswitches. In this review, we propose a conceptual framework that groups riboswitches based on the mechanism by which RNA manipulates information directly instructing the expression machinery. This scheme does not replace the established aptamer domain-based classification of riboswitches but rather serves to facilitate hypothesis-driven investigation of riboswitch regulatory mechanisms. Based on current bioinformatic, structural, and biochemical studies of a broad spectrum of riboswitches, we propose three major mechanistic groups: (1) "direct occlusion", (2) "interdomain docking", and (3) "strand exchange". We discuss the defining features of each group, present representative examples of riboswitches from each group, and illustrate how these RNAs couple small molecule binding to gene regulation. While mechanistic studies of the occlusion and docking groups have yielded compelling models for how these riboswitches function, much less is known about strand exchange processes. To conclude, we outline the limitations of our mechanism-based conceptual framework and discuss how critical information within riboswitch expression platforms can inform gene regulation.
Collapse
Affiliation(s)
| | | | - Robert T Batey
- Department of Biochemistry, University of Colorado, Boulder, Colorado, USA.
| |
Collapse
|
2
|
Acosta-Reyes FJ, Bhattacharjee S, Gottesman M, Frank J. How Dedicated Ribosomes Translate a Leaderless mRNA. J Mol Biol 2024; 436:168423. [PMID: 38185325 PMCID: PMC11003707 DOI: 10.1016/j.jmb.2023.168423] [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: 10/13/2023] [Revised: 12/15/2023] [Accepted: 12/26/2023] [Indexed: 01/09/2024]
Abstract
In bacteriophage λ lysogens, the λcI repressor is encoded by the leaderless transcript (lmRNA) initiated at the λpRM promoter. Translation is enhanced in rpsB mutants deficient in ribosomal protein uS2. Although translation initiation of lmRNA is conserved in bacteria, archaea, and eukaryotes, structural insight of a lmRNA translation initiation complex is missing. Here, we use cryo-EM to solve the structures of the uS2-deficient 70S ribosome of host E. coli mutant rpsB11 and the wild-type 70S complex with λcI lmRNA and fMet-tRNAfMet. Importantly, the uS2-deficient 70S ribosome also lacks protein bS21. The anti-Shine-Dalgarno (aSD) region is structurally supported by bS21, so that the absence of the latter causes the aSD to divert from the normal mRNA exit pathway, easing the exit of lmRNA. A π-stacking interaction between the monitor base A1493 and A(+4) of lmRNA potentially acts as a recognition signal. Coulomb charge flow, along with peristalsis-like dynamics within the mRNA entrance channel due to the increased 30S head rotation caused by the absence of uS2, are likely to facilitate the propagation of lmRNA through the ribosome. These findings lay the groundwork for future research on the mechanism of translation and the co-evolution of lmRNA and mRNA that includes the emergence of a defined ribosome-binding site of the transcript.
Collapse
Affiliation(s)
- Francisco J Acosta-Reyes
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Sayan Bhattacharjee
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Max Gottesman
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Department of Microbiology & Immunology, Columbia University, New York, NY 10032, USA
| | - Joachim Frank
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| |
Collapse
|
3
|
Acosta-Reyes FJ, Bhattacharjee S, Gottesman M, Frank J. Structural insight into translation initiation of the λcl leaderless mRNA. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.02.556006. [PMID: 37693525 PMCID: PMC10491246 DOI: 10.1101/2023.09.02.556006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
In bacteriophage λ lysogens, the λcI repressor is encoded by the leaderless transcript (lmRNA) initiated at the λpRM promoter. Translation is enhanced in rpsB mutants deficient in ribosomal protein uS2. Although translation initiation of lmRNA is conserved in bacteria, archaea, and eukaryotes, structural insight of a lmRNA translation initiation complex is missing. Here, we use cryo-EM to solve the structures of the uS2-deficient 70S ribosome of host E. coli mutant rpsB11 and the wild-type 70S complex with λcI lmRNA and fmet-tRNAfMet. Importantly, the uS2-deficient 70S ribosome also lacks protein bS21. The anti-Shine-Dalgarno (aSD) region is structurally supported by bS21, so that the absence of the latter causes the aSD to divert from the normal mRNA exit pathway, easing the exit of lmRNA. A π-stacking interaction between the monitor base A1493 and A(+4) of lmRNA potentially acts as a recognition signal. Coulomb charge flow, along with peristalsis-like dynamics within the mRNA entry channel due to the increased 30S head rotation caused by the absence of uS2, are likely to facilitate the propagation of lmRNA through the ribosome. These findings lay the groundwork for future research on the mechanism of translation and the co-evolution of lmRNA and mRNA that includes the emergence of a defined ribosome-binding site of the transcript.
Collapse
Affiliation(s)
- Francisco J Acosta-Reyes
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Sayan Bhattacharjee
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Max Gottesman
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
- Department of Microbiology & Immunology, Columbia University, New York, NY, 10032, USA
| | - Joachim Frank
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| |
Collapse
|
4
|
Wu Y, Zhu L, Li S, Chu H, Wang X, Xu W. High content design of riboswitch biosensors: All-around rational module-by-module design. Biosens Bioelectron 2022; 220:114887. [DOI: 10.1016/j.bios.2022.114887] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 09/27/2022] [Accepted: 11/03/2022] [Indexed: 11/11/2022]
|
5
|
Petersen SD, Zhang J, Lee JS, Jakociunas T, Grav LM, Kildegaard HF, Keasling JD, Jensen MK. Modular 5'-UTR hexamers for context-independent tuning of protein expression in eukaryotes. Nucleic Acids Res 2019; 46:e127. [PMID: 30124898 PMCID: PMC6265478 DOI: 10.1093/nar/gky734] [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: 03/09/2018] [Accepted: 08/01/2018] [Indexed: 11/25/2022] Open
Abstract
Functional characterization of regulatory DNA elements in broad genetic contexts is a prerequisite for forward engineering of biological systems. Translation initiation site (TIS) sequences are attractive to use for regulating gene activity and metabolic pathway fluxes because the genetic changes are minimal. However, limited knowledge is available on tuning gene outputs by varying TISs in different genetic and environmental contexts. Here, we created TIS hexamer libraries in baker’s yeast Saccharomyces cerevisiae directly 5′ end of a reporter gene in various promoter contexts and measured gene activity distributions for each library. Next, selected TIS sequences, resulted in almost 10-fold changes in reporter outputs, were experimentally characterized in various environmental and genetic contexts in both yeast and mammalian cells. From our analyses, we observed strong linear correlations (R2 = 0.75–0.98) between all pairwise combinations of TIS order and gene activity. Finally, our analysis enabled the identification of a TIS with almost 50% stronger output than a commonly used TIS for protein expression in mammalian cells, and selected TISs were also used to tune gene activities in yeast at a metabolic branch point in order to prototype fitness and carotenoid production landscapes. Taken together, the characterized TISs support reliable context-independent forward engineering of translation initiation in eukaryotes.
Collapse
Affiliation(s)
- Søren D Petersen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Jie Zhang
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Jae S Lee
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Tadas Jakociunas
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Lise M Grav
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Helene F Kildegaard
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Jay D Keasling
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.,Joint BioEnergy Institute, Emeryville, CA 94608, USA.,Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.,Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720, USA.,Department of Bioengineering, University of California, Berkeley, CA 94720, USA.,Center for Synthetic Biochemistry, Institute for Synthetic Biology, Shenzhen Institutes of Advanced Technologies, Shenzhen 518055, China
| | - Michael K Jensen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| |
Collapse
|