Three-state mechanism couples ligand and temperature sensing in riboswitches
Three-state mechanism couples ligand and temperature sensing in riboswitches
复制标题
DOI：
10.1038/nature12378
复制
发表时间：
2013-07-18
期刊：
影响因子：
64.8
通讯作者：
Schwalbe, Harald
中科院分区：
文献类型：
--
作者：
Reining, Anke;Nozinovic, Senada;Schwalbe, Harald
核糖开关是顺式作用的基因调控的RNA元件，可以在转录、翻译和RNA切割水平上发挥作用(1-3)。普遍接受的核糖开关功能的分子机制提出了两个相互排斥的状态之间的配体依赖的构象开关(4)。根据这一机制，配体与适配子结构域结合诱导表达平台的变构构象切换，导致配体相关基因表达的激活或抑制(5)。然而，许多核糖开关的性质不能用纯粹的两态机制来解释。在这里，我们证明了由人类革兰氏阴性病原菌创伤弧菌(Vibrio Vernificus)(6)染色体II上的Add基因编码的腺嘌呤敏感核糖开关的调节机制与两态开关机制显著不同，因为它涉及三个不同的稳定构象。我们表征了三种构象的布居比与温度和镁离子的依赖关系，以及它们在核苷酸分辨下的相互转化动力学。所观察到的包括两个结构不同的ADD核糖开关的无配体构象的预平衡的温度依赖性在生理上相关的温度范围内提供了有效的调节。这种强大的开关是细菌基因调控的关键要求，因为细菌必须适应不同温度的环境。据我们所知，翻译性腺嘌呤敏感核糖开关是温度补偿调节RNA元件的第一个例子。
Riboswitches are cis-acting gene-regulatory RNA elements that can function at the level of transcription, translation and RNA cleavage(1-3). The commonly accepted molecular mechanism for riboswitch function proposes a ligand-dependent conformational switch between two mutually exclusive states(4). According to this mechanism, ligand binding to an aptamer domain induces an allosteric conformational switch of an expression platform, leading to activation or repression of ligand-related gene expression(5). However, many riboswitch properties cannot be explained by a pure two-state mechanism. Here we show that the regulation mechanism of the adenine-sensing riboswitch, encoded by the add gene on chromosome II of the human Gram-negative pathogenic bacterium Vibrio vulnificus(6), is notably different from a two-state switch mechanism in that it involves three distinct stable conformations. We characterized the temperature and Mg2+ dependence of the population ratios of the three conformations and the kinetics of their interconversion at nucleotide resolution. The observed temperature dependence of a pre-equilibrium involving two structurally distinct ligand-free conformations of the add riboswitch conferred efficient regulation over a physiologically relevant temperature range. Such robust switching is a key requirement for gene regulation in bacteria that have to adapt to environments with varying temperatures. The translational adenine-sensing riboswitch represents the first example, to our knowledge, of a temperature-compensated regulatory RNA element.