Institute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, (phone: +41 44 635 4652; fax: +41 44 635 6802).
Chem Biodivers. 2012 Sep;9(9):2035-49. doi: 10.1002/cbdv.201200031.
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.
Mg(2+)-响应型核糖开关是一类具有双功能的 RNA 分子，能够高度选择性地感应 Mg(2+)离子，并自主调节 Mg(2+)转运蛋白的表达。尽管 mgtA 核糖开关的作用机制尚不清楚，但需要进行详细的结构分析，以研究这种 RNA 如何选择性地识别 Mg(2+)并通过在两种替代的茎环结构之间切换来做出响应。在这项工作中，我们通过溶液 NMR 研究了来自肠炎沙门氏菌 mgtA 核糖开关的终止子环 C 的下部结构和 Mg(2+)结合特性，并报告了一个嵌入在富含 AU 序列中的离散 Mg(2+)结合位点。在 Mg(2+)结合位置，螺旋轴表现出明显的扭曲，同时主沟变宽，从而容纳 Mg(2+)-结合口袋。相反链上两个腺嘌呤残基之间的异常大重叠表明，这种弯曲可能是由强烈的堆积相互作用引起的序列诱导，从而使 Mg(2+)能够结合到这个迄今为止尚未描述的金属离子结合位点。
