Temperature-Induced Collapse of Elastin-Like Peptides Studied by 2DIR Spectroscopy

Elastin-like peptides (ELP) are hydrophobic biopolymers that exhibit a reversible coacervation transition when the temperature is raised above a critical point. Here we use a combination of linear infrared spectroscopy, two-dimensional infrared (2DIR) spectroscopy and molecular dynamics simulations to study the structural dynamics of two elastin-like peptides. Specfically, we investigate the effect of the solvent environ- ment and temperature on the structural dynamics of a short (5-residue) elastin-like peptide and of a long (450-residue) elastin-like peptide. We identify two vibrational energy transfer processes that take place within the amide I0 band of both peptides. We observe that the rate constant of one of the exchange processes is strongly dependent on the solvent environment and argue that the coacervation transition is accompanied by a desolvation of the peptide backbone where up to 75% of the water molecules are displaced. We also study the spectral diffusion dynamics of a valine residue that is present in both peptides. We find that these dynamics are relatively slow and indicative of an amide group that is shielded from the solvent. We conclude that the coacerva- tion transition of elastin-like peptides is probably not associated with a conformational change involving this residue.