Surface science aspects of supramolecular conformation in elastin‐like polypeptides

Abstract

Polypeptides can form helical fibres in aqueous media: potentially useful for the production of biocompatible fabric and yarns. A previous work has shown that fibre formation occurs readily with elastin-like polypeptides constructed from hydrophobic amino acids, such as valine, glycine and leucine. However, elastin-like polypeptides, when suspended in methyl alcohol, are observed to form globules and 'string of bead' structures. Thus, it seems probable that the interface energy is important. Interface energy is minimised by the formation of bonds extending from one phase to the other: a phenomenon that is central to adhesion science. We have looked for evidence of such bonding using XPS to study structures formed by poly(ValGlyGlyLeuGly). The structures formed were first characterised by atomic force microscopy. Differences were found between structures and spectra formed in either water or methanol. No evidence for the presence of unique bonds characterising the interface was found, but evidence was found for the influence of a water environment on the internal structure, suggesting that it is the increase in intermolecular bonding opportunities associated with the influence of water on the growth of fibres that is the thermodynamic driver for the observed transformation into fibre deposits.

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

“…In Figure 1, results from surface analyses of poly(ValGlyGlyValGly) suspended in 50% MeOH, that is, MeOH/H 2 O 1:1 mixture deposited on gold are summarized. These experiments with poly(ValGlyGlyValGly) in methanol/water mixtures retrace those previously performed with poly(ValGlyGlyLeuGly) in MeOH, MeOH:H 2 O 1:1, MeOH:H 2 O 1:213 and further support the evidence of AFM and XPS, that these polypeptides have similar solvation paths: the proportions of different, coexisting, structures correlate with the relative water/methanol activities and the relative evaporation rate of the two solvents (vapor pressure of 13.02 kPa for methanol and 2.3 kPa for water, at 20°C).…”

“…In accord with findings of previous work9–13 and literature,14–17 we show that water molecules have a unique role in organizing the fibrillar structure. Supported by computation, these studies have allowed the revaluation of the 3D model previously proposed11 for the self‐assembly of poly(ValGlyGlyValGly), the polypeptide most inclined to form helical fibers in water.…”

“…These correlated contributions, peak n.4 in C1s and peak n.2 in O1s can be seen in Figure 1. As previously found,9–11, 13 such interactions induce both carbon and oxygen of >CO peptide groups to undergo a chemical shift in the same direction and in the same proportion while leaving nitrogen quite unperturbed, apart from some broadening and asymmetry, with its BE peaked at 400.2 eV 20…”

“…The low roughness of silicon surfaces, suitable for AFM imaging, and its capability of making “reversible” H‐bonds with our polypeptides have made silicon wafer the most suitable substrate for our studies. Thus it is used in this work unless it was necessary to reduce the influence of substrate oxides on analysis of the O1s region, in which case gold substrates were used 9–11, 13…”

Characterisation of helical structure in AFM micrographs of a trimer of the peptide sequence (ValGlyGlyValGly)

“…A discussion of the possible impact of surface chemistry on amyloid-like fibre conformation has been given. [4] More recently, a multi-technique study of the trimer, (ValGlyGlyValGly) 3 , has been carried out. [4,5] This contribution, part of the multi-technique study, deals specifically with the helical formations that were found when samples of the trimer in aqueous suspension were examined within a few hours of its preparation.…”