Phase behavior and chain dynamics of elastin-like peptides versus amino acid sequences

Abstract

Elastin fibrillogenesis is conditioned by multiple self-assembly processes. Previous studies have evidenced the crucial influence of amino acid specificities on molecular organization of glycine-rich elastin-like peptides, but also the important role of environment on the self-assembly processes. For the first time, we combined a differential scanning calorimetry (DSC) study on aqueous solutions of three elastin-like peptides with thermally stimulated currents (TSC) experiments in the condensed state. We have studied three pentadecapeptides having the XGGZG motif threefold repeated with X and Z residues constituted of valine and leucine, known to form fiber structures. Valine and leucine moieties differ only by the presence of –CH2– spacer occupying in the pattern the first or the fourth position. Both of the residues are among the most abundant in elastin. Via DSC, we showed that the simple substitution of one amino acid strongly influences the surrounding hydration of the pentadecapeptides. During the self-assembly process, a slow exchange between bound water and bulk water is highlighted for (VGGLG)3, whereas a fast exchange of water molecules is found for(VGGVG)3 and (LGGVG)3. In the pre-fibrillar condensed state, TSC analysis reveals localized and delocalized motions and gives a fingerprint of the dynamics via activation parameters. At the localized level, a profound difference in the carbonyl environment is observed between(VGGLG)3 and the other peptides. The delocalized chain dynamics of the three peptides can be connected to the different conformations. The dominant unordered conformation of (VGGLG)3 leads to a softer system, while the large amount of b sheets and b turns in (VGGVG)3 and (LGGVG)3 leads to stiffer systems. Around the physiological temperature occurs a structural, isochronal phasetransition, sequence specific, suggested to be associated with the ferroelectricity of such elastin-like peptides.