Mg2+ Shifts Ligand-Mediated Folding of a Riboswitch from Induced-Fit to Conformational Selection
Bacterial riboswitches couple small-molecule ligand binding to RNA conformational changes that widely regulate gene expression, rendering them potential targets for antibiotic intervention. Despite structural insights, the ligand-mediated folding mechanisms of riboswitches are still poorly understoo...
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Published in | Journal of the American Chemical Society Vol. 137; no. 44; pp. 14075 - 14083 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
American Chemical Society
11.11.2015
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Online Access | Get full text |
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Summary: | Bacterial riboswitches couple small-molecule ligand binding to RNA conformational changes that widely regulate gene expression, rendering them potential targets for antibiotic intervention. Despite structural insights, the ligand-mediated folding mechanisms of riboswitches are still poorly understood. Using single-molecule fluorescence resonance energy transfer (smFRET), we have investigated the folding mechanism of an H-type pseudoknotted preQ1 riboswitch in dependence of Mg2+ and three ligands of distinct affinities. We show that, in the absence of Mg2+, both weakly and strongly bound ligands promote pseudoknot docking through an induced-fit mechanism. By contrast, addition of as low as 10 μM Mg2+ generally shifts docking toward conformational selection by stabilizing a folded-like conformation prior to ligand binding. Supporting evidence from transition-state analysis further highlights the particular importance of stacking interactions during induced-fit and of specific hydrogen bonds during conformational selection. Our mechanistic dissection provides unprecedented insights into the intricate synergy between ligand- and Mg2+-mediated RNA folding. |
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ISSN: | 0002-7863 1520-5126 |
DOI: | 10.1021/jacs.5b09740 |