Modulation of the folding energy landscape of cytochrome C with salt.

The folding reaction of acid-unfolded cytochrome c in the presence of various amounts of KCl was investigated with Trp fluorescence and resonance Raman spectroscopies. It was found that the too-early-too-much polypeptide chain collapse induced by KCl yields some stable folding intermediates, which need to overcome a higher energy barrier to fold into their native conformation. We propose that the charge distribution on the polypeptide chain is part of the folding codon encoded in the linear amino acid sequence. The charge screening effect introduced by KCl alters the shape of the energy landscape by raising the slope of the upper rim and introduces a rugged energy surface toward the bottom of the folding funnel.