Amyloid Fibrils in Bionanomaterials

Abstract

Amyloid fibrils are a type of protein nanofibres that form when a normally soluble protein aggregates in a regular fashion via self-association. Their organised and repetitive β-sheet structure is thought to be a generic property of all proteins, depending on the environmental conditions. The nanometre size and high stability of these protein nanofibres are attractive features to exploit in bionanomaterials.

This thesis aimed to manipulate insulin amyloid fibrils, as a model protein nanofibre system, through investigating the effect of chemical modification on insulin fibril formation in heterogeneous mixtures. Using acetylation, reduction carboxymethylation, reduction pyridylethylation, trypsin digestion and chymotrypsin digestion, it was shown that nanofibres can form in heterogeneous mixtures of modified insulin at variable rates to produce fibrils of distinct morphologies. Distinctively well defined, long, unbranched nanofibres were observed in the crude reduced carboxymethylated insulin mixture after incubation at 60°C (pH 7.4), which formed at a faster rate than native insulin. The crude reduced pyridylethylated insulin revealed the formation of “wavy” fibrils when exposed to 60°C and pH 1.6, compared to the straight native insulin amyloid fibrils. Although, the trypsin digestion inhibited nanofibre formation at 60°C and pH 1.6, chymotrypsin digestion of insulin produced a mixture of long and short nanofibres under the same conditons. Thus chemical modification provides a simple means of manipulating protein nanofibre assembly for use in bionanotechnology.

Protein nanofibres were incorporated into a model polymer polyvinylalcohol (PVOH) film in order to assess the impact on material properties. A systematic study involving both insulin and a crude source of crystallin proteins derived from bovine eye lens was undertaken. A protein nanofibre-PVOH nanocomposite was successfully fabricated by a procedure of solution mixing and casting. Dynamic mechanical analysis showed that the addition of insulin fibrils did not change the stiffness of the PVOH. However, an increase in the stiffness of the PVOH-crude bovine eye lens composites was found. Both insulin and bovine eye lens nanofibres reduced the damping properties of the polymer, which suggested a reduction in molecular mobility/slipping.

The results revealed that protein nanofibre formation can be controlled through the modification of the protein and that nanofibres may alter polymer properties in a protein specific manner. Employing these findings in the development of novel bionanomaterials that use the protein nanofibres as a form of natural scaffolding offers a fruitful avenue of future research.