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Deposits of protein misfolding and/or aggregates are a pathological hallmark of amyloid-related diseases. For instance, insulin amyloid fibril deposits have been observed in patients with insulin-dependent diabetes mellitus after insulin administration. Here, we report on the use of AuNPs functionalized with linear- (i.e. dextrin and chitosan) and branched- (i.e. dextran-40 and dextran-10) biopolymers as potential agents to inhibit insulin fibril formation. Our dynamic light scattering analyses showed a size decrease of the amyloid fibrils in the presence of functionalized AuNPs. Circular dichroism spectroscopy as well as enzyme-linked immunosorbent assay data demonstrated that the secondary structural transition from α-helix to β-sheet (which is characteristic for insulin amyloid fibril formation) was significantly suppressed by all biopolymer-coated AuNPs, and in particular, by those functionalized with linear biopolymers. Both transmission electron microscopy and atomic force microscopy analyses showed that the long thick amyloid fibrils formed by insulin alone become shorter, thinner or cluster when incubated with biopolymer-coated AuNPs. Dextrin- and chitosan-coated AuNPs were found to be the best inhibitors of the fibril formation. Based on these results, we propose a mechanism for the inhibition of insulin amyloid fibrils: biopolymer-coated AuNPsstrongly interact with the insulin monomers and inhibit the oligomer formation as well as elongation of the protofibrils.Moreover, cytotoxicity experiments showed that AuNP-insulin amyloid fibrils are less toxic compared to insulin amyloid fibrils alone. Our results suggest that both dextrin- and chitosan-AuNPs could be used as therapeutic agents for the treatment of amyloid-related disorders.

Functional amyloids (protein nanofibrils, PNF) synthesized from plant sources exhibit unique physicochemical and nanomechanical properties that could improve food texture. While environmental factors affecting PNFs are well-known, scientific evidence on how cells (focus on the oral cavity) respond to them under physiological conditions is lacking. Self-assembled PNFs synthesized from fava bean whole protein isolate show a strong pH- and solvent-dependent morphology and elasticity modification measured by atomic force microscopy (AFM). After incubation of PNFs with an oral mechanosensitive model cell line at pH 7.3, difference in cell-surface roughness without significant changes in the overall cell elasticity were measured. The role of cell membrane composition on supported lipid bilayers was also tested, showing an increase in membrane elasticity with increasing fibril concentration and the possible impact of annular phospholipids in binding. Genetic responses of membrane proteins involved in texture and fat perception were detected at the mRNA level by RT-qPCR assay and both mechano- and chemosensing proteins displayed responses highlighting an interface dependent interaction. The outcomes of this study provide a basis for understanding the changing physicochemical properties of PNFs and their effect on flavor perception by altering mouthfeel and fat properties. This knowledge is important in the development of plant-based texture enhancers for sensory-appealing foods that require consumer acceptance and further promote healthy diets.