Conformational capture of the SAM-II riboswitch
Conformational capture of the SAM-II riboswitch
复制标题
DOI：
10.1038/nchembio.562
复制
发表时间：
2011-06-01
影响因子：
14.8
通讯作者：
Micura, Ronald
中科院分区：
文献类型：
--
作者：
Haller, Andrea;Rieder, Ulrike;Micura, Ronald
核糖开关是mRNA中的基因调控元件，其通过特异性响应代谢物而起作用。虽然核糖开关的代谢物结合状态已被证明适合于结构确定的努力，核糖开关在其配体的自由形式和它们的配体反应机制引起的监管控制的结构特征的知识是缺乏的。在这里，我们探讨了配体诱导的折叠过程中的S-腺苷甲硫氨酸II型（SAM-II）核糖开关使用化学和生物物理方法，包括NMR和荧光光谱，单分子荧光成像。数据显示，未配体的SAM-II核糖开关本质上是动态的，因为其茎环元件通过与包含Shine-Dalgarno序列的3'突出端中的核苷进行碱基配对而参与假结折叠。尽管假结结构在其配体S-腺苷甲硫氨酸（SAM）不存在的情况下是高度瞬时的，但其通过构象捕获机制在配体识别后变得构象受限。这些见解提供了核糖开关动力学的分子理解，揭示了核糖开关介导的翻译调控机制的新的光。
Riboswitches are gene regulation elements in mRNA that function by specifically responding to metabolites. Although the metabolite-bound states of riboswitches have proven amenable to structure determination efforts, knowledge of the structural features of riboswitches in their ligand-free forms and their ligand-response mechanisms giving rise to regulatory control is lacking. Here we explore the ligand-induced folding process of the S-adenosylmethionine type II (SAM-II) riboswitch using chemical and biophysical methods, including NMR and fluorescence spectroscopy, and single-molecule fluorescence imaging. The data reveal that the unliganded SAM-II riboswitch is dynamic in nature, in that its stem-loop element becomes engaged in a pseudoknot fold through base-pairing with nucleosides in the 3' overhang containing the Shine-Dalgarno sequence. Although the pseudoknot structure is highly transient in the absence of its ligand, S-adenosylmethionine (SAM), it becomes conformationally restrained upon ligand recognition, through a conformational capture mechanism. These insights provide a molecular understanding of riboswitch dynamics that shed new light on the mechanism of riboswitch-mediated translational regulation.