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 dominantsupramolecular 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), whensuspended in methyl alcohol. Comparative experiments with poly (LeuGlyGlyValGly) havefurther indicated that the interface energy plays a significant role and that solvation effects act inconcomitance 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 influenceof sequence specificities has been studied by comparing poly(ValGlyGlyValGly) andpoly(LeuGlyGlyValGly) with a similar degree of polymerization. Deposits on substrates of thepolypeptides 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 3Dmodelling previously proposed for the supramolecular assembly in water ofpoly(ValGlyGlyValGly). The results were discussed and rationalized also on the light of published data.