Exploring the Folding Landscape of RNA in Crowded Solutions

Abstract

Crowder molecules in solution alter the configuration potential energy landscape of biological macromolecules. It is therefore critical to account for the influence of these other molecules when describing the folding of RNA inside the cell. Small angle x-ray scattering experiments were used to measure folding of a 64 kDa bacterial group I ribozyme in the presence of polyethylene-glycol with different molecular weights. We find that crowder molecules stabilize more compact states of the unfolded RNA, and also stabilize the folded state with respect to the unfolded state, as measured via the lowering of the folding midpoint on a MgCl2 titration. In addition, stopped-flow SAXS experiments with millisecond resolution show that the addition of crowder molecules speeds up the folding of RNA, even when the stability of the final folded state is held constant. These data indicate that crowder molecules change the folding landscape for RNA, allowing it to fold efficiently in Mg2+ concentrations that are well within the physiological range.