Amyloid gels: Morphological and dynamical properties of an amyloid fibrillar network.

Amyloid fibrils are linearly elongated protein aggregates, characterized by a cross-? sheet quaternary structure running along the main fiber axis. Amyloid fibrils and deposits have a high clinical relevance, because they are related to several diseases, including Alzheimer's and prion disease. In addition, they have a general biological importance as underlined by the existence of functional amyloids with a positive physiological activity. Lower organisms, like bacteria or fungi, use amyloid fibers as structural components, for their unique mechanical and biological properties, such their high yield-strength and their protease resistance. Some bacteria, e.g., employ an extracellular amyloid matrix to help surface adhesion and colony formation. The hormone insulin has long been known to form amyloid fibrils under given conditions. The formation of insulin fibrils is important not only for the development of reliable formulations or delivery systems, but also for modeling the basic properties of protein self-organization. Insulin aggregation is enriched by a complex hierarchy of different morphologies, including fibrils, larger bundles and floccules, which may eventually assemble to form a gel. In our previous work, we have shown the appearance of a noteworthy elastic network of fibers, associated with the initial fibril nucleation and elongation more than to the formation of large structures and gelation. Here, we focus on morphological and dynamical properties of this amyloid fibrillar network, by exploiting the possibility of dynamic light scattering techniques. The dynamical behavior of the gel matrix was studied by a novel device and software, both developed in our laboratory, for Dynamic Small Angle Light Scattering (D-SALS), which is intrinsically suitable for slow, gelling, nonergodic samples due to multi-pixel detection. The dynamical relaxation within the gel matrix was studied by Dynamic Large Angle Light Scattering (D-LALS), opportunely adapted on order to perform the spatial averaging necessary to restore ergodicity. We observed a distribution of non-diffusive relaxation times and processes over a wide range of time scales evidencing the structural heterogeneity and peculiarity of this potentially new material.