Mg2+-induced conformational changes in the btuB riboswitch from E. coli
Mg2+-induced conformational changes in the btuB riboswitch from E. coli
复制标题
DOI：
10.1261/rna.039909.113
复制
发表时间：
2014-01-01
期刊：
影响因子：
4.5
通讯作者：
Sigel, Roland K. O.
中科院分区：
文献类型：
--
作者：
Choudhary, Pallavi K.;Sigel, Roland K. O.
Mg ~（2+）通过促进配体-核糖开关相互作用来调节核糖开关的功能。来自大肠杆菌的btu B核糖开关在与其配体辅酶B-12（腺苷钴胺素，Btcbl）结合后发生构象变化，并下调B-12转运蛋白Btu B的表达，以控制Btcbl的细胞水平。在这里，我们讨论的结构折叠所获得的btuB核糖开关从E。大肠杆菌对Mg 2+的反应，以及它如何影响RNA的配体结合能力构象。btuB核糖开关显著地根据Mg 2+的浓度采用不同的构象状态。在线探测的帮助下，我们显示存在至少两个特定的构象，一个是在完全不存在的Mg 2+（或低Mg 2+浓度）和其他出现以上类似于0.5 mM Mg 2+。核糖开关的不同区域对Mg 2+表现出不同的解离常数，表明btuB RNA的逐步折叠。增加Mg 2+浓度驱动从一种构象向另一种构象转变。存在于0.5 mM Mg 2+以上的构象状态定义了btu B核糖开关的结合能力构象，其可以与配体辅酶B-12有效地相互作用，并转换RNA构象。此外，提高Mg 2+浓度增强了在MgClCbl存在下转换的RNA的比率。在不存在Mg 2+的情况下，btuB核糖开关所经历的Btcbl诱导的构象转换的缺乏表明Mg 2+对于定义核糖开关的活性构象所起的关键作用。
Mg2+ has been shown to modulate the function of riboswitches by facilitating the ligand-riboswitch interactions. The btuB riboswitch from Escherichia coli undergoes a conformational change upon binding to its ligand, coenzyme B-12 (adenosylcobalamine, AdoCbl), and down-regulates the expression of the B-12 transporter protein BtuB in order to control the cellular levels of AdoCbl. Here, we discuss the structural folding attained by the btuB riboswitch from E. coli in response to Mg2+ and how it affects the ligand binding competent conformation of the RNA. The btuB riboswitch notably adopts different conformational states depending upon the concentration of Mg2+. With the help of in-line probing, we show the existence of at least two specific conformations, one being achieved in the complete absence of Mg2+ (or low Mg2+ concentration) and the other appearing above similar to 0.5 mM Mg2+. Distinct regions of the riboswitch exhibit different dissociation constants toward Mg2+, indicating a stepwise folding of the btuB RNA. Increasing the Mg2+ concentration drives the transition from one conformation toward the other. The conformational state existing above 0.5 mM Mg2+ defines the binding competent conformation of the btuB riboswitch which can productively interact with the ligand, coenzyme B-12, and switch the RNA conformation. Moreover, raising the Mg2+ concentration enhances the ratio of switched RNA in the presence of AdoCbl. The lack of a AdoCbl-induced conformational switch experienced by the btuB riboswitch in the absence of Mg2+ indicates a crucial role played by Mg2+ for defining an active conformation of the riboswitch.