Structural transitions and thermodynamics of a glycine-dependent riboswitch from Vibrio cholerae

JOURNAL OF MOLECULAR BIOLOGY

卷:365

Article

Lipfert, Jan ; Das, Rhiju ; Chu, Vincent B. ; Kudaravalli, Madhuri ; Boyd, Nathan ; Herschlag, Daniel ; Doniach, Sebastian

关键词: riboswitches;    small-angle X-ray scattering;    RNA folding;    RNA aptamers;   

DOI  :  10.1016/j.jmb.2006.10.022

来源: Elsevier

【 摘 要 】

Riboswitches are complex folded RNA domains found in noncoding regions of mRNA that regulate gene expression upon small molecule binding. Recently, Breaker and coworkers reported a tandem aptamer riboswitch (VCI-II) that binds glycine cooperatively. Here, we use hydroxyl radical footprinting and small-angle X-ray scattering (SAX to study the S) conformations of this tandem aptamer as a function of Mg2+ and glycine concentration. We fit a simple three-state thermodynamic model that describes the energetic coupling between magnesium-induced folding and glycine binding. Furthermore, we characterize the structural conformations of each of the three states: In low salt with no magnesium present, the VCI-II construct has an extended overall conformation, presumably representing unfolded structures. Addition of millimolar concentrations of Mg2+ in the absence of glycine leads to a significant compaction and partial folding as judged by hydroxyl radical protections. In the presence of millimolar Mg2+ concentrations, the tandem aptamer binds glycine cooperatively. The glycine binding transition involves a further compaction, additional tertiary packing interactions and further uptake of magnesium ions relative to the state in high Mg2+ but no glycine. Employing density reconstruction algorithms, we obtain low resolution 3-D structures for all three states from the SAXS measurements. These data provide a first glimpse into the structural conformations of the VCI-II aptamer, establish rigorous constraints for further modeling, and provide a framework for future mechanistic studies. (c) 2006 Elsevier Ltd. All rights reserved.

【 授权许可】

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