Spread layers of recombinant vicilin amyloid fibrils at the water - air interface

Practically all the publications on properties of spread and adsorbed plant protein fibrils deal with the aggregates obtained from protein isolates containing the admixtures of other proteins. On the contrary, this work is devoted to layers of amyloid fibrils of recombinant vicilin, storage 7S globulin from garden pea, at an aqueous surface. The application of surface tensiometry, dilational surface rheology and ellipsometry allowed discovering that, unlike the layers of non-fibrillar protein, the spreading occurred only if the ionic strength of the spreading dispersion or of the subphase exceeded a certain value. The dynamic surface elasticity of the layers of vicilin fibrils proved to be a non-monotonic function of the surface pressure but reached much lower values at high surface compressions than in the case of layers of the non-fibrillar protein. The observed distinction can be explained by different structures of the surface aggregates in the two systems. Relatively rigid and long fibrils cannot form dense and rigid surface aggregates unlike the non-fibrillar state of the vicilin protein. At the same time, atomic force microscopy shows that the layers of fibrils still have some holes at high surface pressures. These finding highlight how fibril rigidity and salt screening control interfacial organization and may guide the design of plant protein-based stabilizers for foams and emulsions.