Unusually High-Affinity Mg(2+) Binding at the AU-Rich Sequence within the Antiterminator Hairpin of a Mg(2+) Riboswitch |
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Authors: | Maximiliane M T Korth Roland K O Sigel |
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Institution: | Institute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, (phone: +41?44?635?4652; fax: +41?44?635?6802). |
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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. |
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