Roles of Mg2+ in TPP-dependent riboswitch

We quantified the effect of Mg2+ on thiamine pyrophosphate (TPP) binding to TPP-dependent thiA riboswitch RNA. The association constant of TPP binding to the riboswitch at 20 °C increased from 1.2 × 106 to 50 × 106 M−1 as the Mg2+ concentration increased from 0 to 1 mM. Furthermore, circular dichroic spectra under various conditions showed that 1 mM Mg2+ induced a local structural change of the riboswitch, which might be pivotal for TPP binding. These results indicate that a physiological concentration of Mg2+ can regulate TPP binding to the thiA riboswitch.