Tuning the Continuum of Structural States in the Native Ensemble of a Regulatory Protein.

The mesoscale nature of proteins allows for an efficient coupling between environmental cues and conformational changes, enabling their function as molecular transducers. Delineating the precise structural origins of such a connection and the expected spectroscopic response has, however, been challenging. In this work, we perform a combination of urea-temperature double perturbation experiments and theoretical modeling to probe the conformational landscape of Cnu, a natural thermosensor protein. We observe unique ensemble signatures that point to a continuum of conformational substates in the native ensemble and that respond intricately to perturbations upon monitoring secondary and tertiary structures, distances between an intrinsic FRET pair, and hydrodynamic volumes. Binding assays further reveal a weakening of the Cnu functional complex with temperature, highlighting the molecular origins of signal transduction critical for pathogenic response in enterobacteriaceae.