Fluoride ion encapsulation by Mg2+ ions and phosphates in a fluoride riboswitch.
Publication Type:Journal Article
Source:Nature, Volume 486, Issue 7401, p.85-9 (2012)
Keywords:Base Sequence, Binding Sites, Cations, Divalent, Fluorides, Gene Expression Regulation, Bacterial, Gram-Negative Anaerobic Straight, Curved, and Helical Rods, Ligands, Magnesium, Models, Molecular, Nucleic Acid Conformation, Nucleotide Motifs, Phosphates, Riboswitch, Structure-Activity Relationship, Substrate Specificity, Water
<p>Significant advances in our understanding of RNA architecture, folding and recognition have emerged from structure-function studies on riboswitches, non-coding RNAs whose sensing domains bind small ligands and whose adjacent expression platforms contain RNA elements involved in the control of gene regulation. We now report on the ligand-bound structure of the Thermotoga petrophila fluoride riboswitch, which adopts a higher-order RNA architecture stabilized by pseudoknot and long-range reversed Watson-Crick and Hoogsteen A•U pair formation. The bound fluoride ion is encapsulated within the junctional architecture, anchored in place through direct coordination to three Mg(2+) ions, which in turn are octahedrally coordinated to water molecules and five inwardly pointing backbone phosphates. Our structure of the fluoride riboswitch in the bound state shows how RNA can form a binding pocket selective for fluoride, while discriminating against larger halide ions. The T. petrophila fluoride riboswitch probably functions in gene regulation through a transcription termination mechanism.</p>