Novel Amyloid Fibrillar Networks Derived from a Globular Protein:  β-Lactoglobulin

Biology provides us with a unique set of self-assembled fibrillar networks in the form of amyloid fibrils, derived from the self-assembly of a number of peptides or misfolded proteins. These, in turn, are associated with a number of diseases such as Alzheimer's, Creutzfeldt−Jakob disease (CJD), and type II diabetes. Recently, generating such supramolecular peptidic structures in vitro has led to a class of novel materials. In this multidistance scale, multidisciplinary study, we highlight various regimes whereby fibrils may be engineered by initiating self-assembly through the unfolding of a non-disease- associated globular protein, β-lactoglobulin ( M w ∼ 18 000, 162 residues). In particular, fibrils were generated by traditional thermal methods at pH 2, or, in a novel approach, by incubation in solvent−water mixtures such as water−2,2,2-trifluoroethanol. These treatments lead to fibrils of distinct structure and morphology. Secondary structure analyses of these by Fourier transform infrared spectroscopy (FTIR) and Raman vibrational spectroscopy confirm β-sheet-mediated aggregation which is especially surprising for solvent-mediated fibril formation where an expanded helical conformation is expected. The same systems have been studied with both atomic force (AFM) and electron (EM) microscopy. The systems form gels above certain critical concentrations, which have, in turn, been characterized by rheological measurements. Again contrasts between the heat-set and cold-set solvent-induced protein gels can be seen, the latter showing features reminiscent of gelatin gels.