The Effects of Proline Isomerization on the Solvation Behavior of Elastin-Like Polypeptides in Water-Ethanol Mixtures

Elastin-like polypeptides (ELPs) are well-known proline-rich stimulus-responsive polymers. They have broad applications ranging from drug delivery to green chemistry. Recently, the authors have shown that the cis/trans proline isomerization can be used to regulate their conformational behavior while keeping the lower critical solution temperature (LCST) unchanged in pure water. In aqueous ethanol mixtures, ELPs typically exhibit an expanded-collapsed-expanded transition known as the co-non-solvency phenomenon. Since it is unclear how proline isomerization affects the solvation behavior of ELPs in aqueous ethanol mixtures, an all-atom insight on single ELPs has been provided to address this question. It is found that if all proline residues are in the cis state, the peptides only experience a collapsed-expanded transition as ethanol concentration increases, i.e., the initial collapse vanishes because cis isomers prefer the compact structures in pure water. The data from the authors also suggest that proline isomerization does not change the shift in solvation free energy of an ELP with given sequence, but it varies the affinity of the peptide to both the solvent and cosolvent molecules.