Elastomeric Polypeptide Biomaterials: Structure and Free Energy Transduction

Abstract

The primary, secondary, tertiary and quaternary structures are presented and discussed for elastomeric polypeptides capable of undergoing inverse temperature transitions, that is, these polypeptides fold with the extrusion of water on raising the temperature through a transition. The elastomeric polypeptides, which are comprised of repeating peptide sequences, appear to be dominantly entropic elastomers. As these elastomers exhibit preferred secondary, tertiary and quarternary structure, they are not properly characterized as the random chain networks commonly ascribed to entropic elastomers. Instead, a mechanism of damping of internal chain dynamics on extension is described and referred to as the librational entropy mechanism of elasticity. Indeed, there are emerging a set of structural concepts for elastomeric polypeptides.

Of particular interest is that these elastomers are capable of exhibiting free energy transduction, e.g., thermomechanical and chemomechanical. A principle is stated for thermomechanical transduction and a postulate is given for chemomechanical transduction which is supported by prediction and experimental verification. The underlying mechanism is considered to be an aqueous(hydration) mediated apolar(hydrophobic)-polar interaction free energy which arises out of a competition between apolar and polar groups for limited waters of hydration. In general, there emerges a simple structural perspective of free energy transduction in elastomeric polypeptide biomaterials that involves thermal, mechanical or chemical means of altering the equilibrium between folded and unfolded states, where the folded states are dynamic helices called β-spirals with dominantly hydrophobic intramolecular interturn contacts and the unfolded states have the hydrophobic groups exposed to water.