title: Unusually high-affinity Mg(2+) binding at the AU-rich sequence within the antiterminator hairpin of a Mg(2+) riboswitch.
abstract: Mg(2+)-Responsive riboswitches represent a fascinating example of bifunctional RNAs that sense Mg(2+) ions with high selectivity and autonomously regulate the expression of Mg(2+)-transporter proteins. The mechanism of the mgtA riboswitch is scarcely understood, and a detailed structural analysis is called for to study how this RNA can selectively recognize Mg(2+) and respond by switching between two alternative stem loop structures. In this work, we investigated the structure and Mg(2+)-binding properties of the lower part of the antiterminator loop C from the mgtA riboswitch of Yersinia enterocolitica by solution NMR and report a discrete Mg(2+)-binding site embedded in the AU-rich sequence. At the position of Mg(2+) binding, the helical axis exhibits a distinct kink accompanied by a widening of the major groove, which accommodates the Mg(2+)-binding pocket. An unusually large overlap between two adenine residues on the opposite strands suggests that the bending may be sequence-induced by strong stacking interactions, enabling Mg(2+) to bind at this so-far not described metal-ion binding site.
authors.affiliation: Institute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, (phone: +41 44 635 4652; fax: +41 44 635 6802).
authors.forename: Maximiliane M T
authors.initials: MM
authors.lastname: Korth
authors.forename: Roland K O
authors.initials: RK
authors.lastname: Sigel
mesh_terms: D063307:AU Rich Elements / Q000235:genetics*; D020816:Amino Acid Motifs; D001665:Binding Sites; D018388:Codon, Terminator / Q000737:chemistry* / Q000235:genetics; D008274:Magnesium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D058928:Riboswitch / Q000235:genetics*
chemical_list: D018388:Codon, Terminator; D058928:Riboswitch; D008274:Magnesium