Combined effects of solvation and aggregation propensity on the final supramolecular structures adopted by hydrophobic- glycine-rich, elastin-like polypeptides

Previous work on elastin-like polypeptides (ELPs) made of hydrophobic amino acids of the type XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu) has consistently shown that differing dominant supramolecular structures were formed when the suspending media were varied: helical, amyloid-like fibers when suspended in water and globules evolving into ‘string of bead’ structures, poly(ValGlyGlyValGly), or cigar-like bundles, poly (ValGlyGlyLeuGly), when suspended in methyl alcohol. Comparative experiments with poly (LeuGlyGlyValGly) have further indicated that the interface energy plays a significant role and that solvation effects act in concomitance with the intrinsic aggregation propensity of the repeat sequence. Continuing our investigation on ELPs using surface (XPS, AFM) and bulk (CD, FTIR) techniques for their characterization, here we have compared the effect of suspending solvents (H2O, DMSO, EG, MeOH) on poly(ValGlyGlyValGly), the polypeptide most inclined to form long and well refined helical fibers in water, searching for the signature of intermolecular interactions occurring between the polypeptide chains in the given suspension. The influence of sequence specificities has been studied by comparing poly(ValGlyGlyValGly) and poly(LeuGlyGlyValGly) with a similar degree of polymerization. Deposits on substrates of the polypeptides were characterized taking into account the differing evaporation rate of solvents, and tests on their stability in ultra high vacuum (UHV) were performed. Finally, combining experimental and computational studies, we have revaluated the 3D modelling previously proposed for the supramolecular assembly in water of poly(ValGlyGlyValGly). The results were discussed and rationalized also on the light of published data.