Salt Interactions in Solution Prevent Direct Association of Urea with a Peptide Backbone.

There is an ongoing debate as to how urea denatures proteins in solution. Using a combination of neutron scattering and computer simulation of a model peptide, KGPGK, it was found that the ionic strength and pH have a significant impact on the urea-peptide interaction. From the work presented here, it appears that urea first and foremost decreases the charge-based interactions in solution, such as the TFA-TFA association, before interacting with the peptide backbone via hydrogen bonds. This gives insight into the pH and salt concentration dependency of urea-caused protein denaturation and might unify direct and indirect theories of urea-induced protein denaturation. The observed differences between MD and neutron and X-ray diffraction data might show that MD, in this particular case, underestimates the influence of charged fluorinated solutes.