@article{11673,
  keywords = {binding sites, manganese ribosweitch, RNA},
  author = {Hsuan-Lei Sung and David Nesbitt},
  title = {Single-Molecule FRET Kinetics of the Mn2+ Riboswitch: Evidence for Allosteric Mg2+ Control of “Induced-Fit” vs “Conformational Selection” Folding Pathways},
  abstract = {Gene expression in bacteria is often regulated dynamically by conformational changes in a riboswitch upon ligand binding, a detailed understanding of which is very much in its infancy. For example, the manganese riboswitch is a widespread RNA motif that conformationally responds in regulating bacterial gene expression to micromolar levels of its eponymous ligand, Mn2+, but the mechanistic pathways are poorly understood. In this work, we quantitatively explore the dynamic folding behavior of the manganese riboswitch by single-molecule fluorescence resonance energy transfer spectroscopy as a function of cation/ligand conditions. From the detailed analysis of the kinetics, the Mn2+ is shown to fold the riboswitch by a “bind-then-fold” (i.e., “induced-fit”, IF) mechanism, whereby the ligand binds first and then promotes folding. On the other hand, the data also clearly reveal the presence of a folded yet ligand-free structure predominating due to the addition of physiological Mg2+ to a nonselective metal ion binding site. Of particular kinetic interest, such a Mg2+ “prefolded” conformation of the riboswitch is shown to exhibit a significantly increased affinity for Mn2+ and further stabilization by subsequent binding of the ligand, thereby promoting efficient riboswitch folding by a “fold-then-bind” (i.e., “conformational selection”, CS) mechanism. Our results not only demonstrate Mg2+-controlled switching between IF and CS riboswitch folding pathways but also suggest a novel heterotropic allosteric control in the manganese riboswitch activity co-regulated by Mg2+ binding.},
  year = {2019},
  journal = {The Journal of Physical Chemistry B},
  volume = {123},
  pages = {2005-2015},
  month = {2019-02},
  issn = {1520-6106},
  url = {https://pubs.acs.org/doi/full/10.1021/acs.jpcb.8b11841},
  doi = {10.1021/acs.jpcb.8b11841},
}