Fast folding dynamics of α-helical peptides - Effect of solvent additives and pH

The fast folding/unfolding dynamics of an alanine-based α-helical model peptide was investigated using nanosecond temperature jump experiments in D2O. Temperature jumps were induced either by indirect heating, using visible laser pulses and a heat-transducing triphenylmethane dye, or by direct heating, using IR laser pulses. Although direct heating improves the quality, reliability and speed of the experiments, the heat-transducing dye was shown to not affect the helix-coil dynamics of alanine-based model peptides, thus validating the indirect heating method for this class of peptides. On the other hand, the presence of high concentrations of salt ions was found to alter the helix folding dynamics by screening of charged residues. We conclude that electrostatic interactions between residues have significant effects on the dynamics of helix folding. Similarly, the solvent pH was observed to affect the dynamics of helix folding, even in a range where no protonation/deprotonation is expected to occur.