How Proteins Unfold

A lot of research has been performed in the area of protein folding and denaturation. Although different denaturing salts are commonly used to induce the unfolding process, salt-specific effects on protein structure remain controversial despite decades of research. in this work, we combine accurate multi-parameter single-molecule Forster Resonance Energy Transfer (smFRET) experiments, Circular Dichroism (CD) measurements and explicit-water Molecular Dynamics (MD) simulations to investigate salt-specific effects on a short charged α-helix peptide.Using CD and MD, we explored the structural influence of guanidinium chloride (GndCl), sodium perchlorate (NaClO4) and potassium chloride (KCl). NaClO4 behaved as a folding aid in CD, contradictory to what is observed in the MD simulations and what is expected from its ranking in the Hofmeister series. Multi-parameter smFRET experiments on the α-helix under varying salt concentrations were carried out to gain a more detailed insight into the induced conformations.Addition of KCl allowed the peptide to adopt an α-helical conformation whereas GndCl denatured by swelling the chain. NaClO4 at 4M condenses the chain into a rapidly fluctuating collapsed state. With the help of CD, MD and spFRET we could show that two denaturing ions (Gnd, ClO4-) work in two very different mechanisms.View Large Image | View Hi-Res Image | Download PowerPoint Slide