From peptides and proteins to micro-structure mechanics and rheological properties of fibril systems

This article provides a summary of an example of how relationships between molecular scale properties and macroscopic properties are formulated, in this case with a focus on fibril microstructures and according system elasticity. Entropy plays a dominant role on all length scales. The elasticity is reviewed in terms of the micro-mechanical properties of the fibrils over a wide range of concentrations. The elasticity is concluded to be of an entropic nature. The micro-mechanical fibril property is the persistence length. For fibrils based on globular proteins the response to temperature change and flow has been reported to be either reversible or non-reversible, dependent on the age of the fibril. The reversibility is argued to be related to the fact that the fibril consists of peptides originating from hydrolysis of the globular proteins, and that the initial step of fibrillar peptide assembly is entropic of nature. The longer term irreversibility is speculated to be caused by a secondary assembly step being a collective transition into inter-beta-sheets.