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We have investigated the structural time-evolution of multistranded β-lactoglobulin protein fibrils at pH 2 and 90 °C by combining small angle neutron scattering (SANS), dynamic (DLS) and depolarized light scattering (DDLS) as well as atomic force microscopy (AFM). Light scattering techniques, combined with SANS clearly demonstrate the different stages of conversion of β-lactoglobulin monomers (2 wt %) into semiflexible protein fibrils upon heating at 90 °C. In addition, atomic force microscopy allows the resolution of some details of the fibrils at the molecular length scale which bulk scattering techniques cannot capture. Thus, we were able to resolve and identify different individual stages of the fibrillation process, including the formation of protofilaments, their alignment and aggregation into mature multistranded fibrils, and the development of a periodic pitch along their contour length. The picture emerging from combination of the scattering and single molecule techniques is consistent with three critical steps: (i) individual protofilaments align upon approaching due to liquid crystalline interactions; (ii) short range attractions among filaments—presumably of Lennard–Jones or hydrophobicity type—lead to irreversible aggregation of nearly perfectly aligned protofilaments into multistranded ribbon-like fibrils; (iii) intramolecular electrostatic repulsion of fibrils leads to twisting of the ribbon along the axis leading to the development of a periodic pitch along the fibrils contour length. The individual stages of the fibrillation and aggregation process are discussed in detail, in terms of the colloidal physics involved.

We present a study of the spatial structure of cationic cylindrical polymer brushes in the presence of counterions of different valencies. Dynamic light scattering (DLS), atomic force microscopy (AFM) and cryogenic transmission electron microscope (cryo-TEM) studies demonstrate that the brushes undergo a transition from an extended to a collapsed state when the ionic strength is raised. In the presence of a di- or trivalent salt this collapse passes through an intermediate state in which the cylindrical polymer brushes assume a helical conformation. The helical pitch (25 nm) is in the range expected from theoretical considerations. Moreover, we demonstrate that the collapse can be reversed by a photochemical cleavage of the complex trivalent counterion into one monovalent and one divalent ion (photoaquation). All data demonstrate that the spatial structure of cylindrical polymer brushes can be manipulated on the nanoscale in a defined fashion.

Self-assembly of Fmoc-L-DOPA leads to the formation of twisted fibers at pH 2. Temperature dependent circular dichroism (CD) reveals the formation of a linear superstructure via π–π stacking. SAXS experiments together with TEM imaging confirm the existence of semi-flexible twisted-multistranded fibers. The self-assembly is found to be pH-dependent, with no aggregation at pH 5 and 7.

We present a new strategy to disassemble amyloid fibrils consisting of a supramolecular attachment along the fibrils’ contour length of end-terminated counter charged hydrophilic polymers. We chose as a model system to work with positively charged β-lactoglobulin fibrils (pH 2), to which sulfonic acid terminated poly(ethylene glycol) (PEG) chains are ionically attached. The attachment of PEG to the β-lactoglobulin fibrils was confirmed by electrophoretic mobility measurements and small-angle neutron scattering (SANS). This complexation results in a supramolecular bottle-brush system, in which the PEG chains, attached at high grafting densities, stretch out due to excluded volume interactions. The increase in free energy resulting from this entropy loss causes the amyloid fibrils to disassemble, which in turn allows the chains to relax. The decrease in the average contour length of the fibrils was analyzed with atomic force microscopy (AFM) by varying the molecular weight and concentration of the supramolecularly attached polymer. The resulting average contour length distributions were fitted by a Boltzmann distribution law, which yielded an average energy per unit length of the amyloid fibrils. The dependence of this energy on the molecular weight (Mw) and the grafting density of the attached polymers was calculated and compared with available polymer bottle-brush theories. Both the increase in Mw and grafting density the polymer led to a decrease in average contour length. In particular, the characteristic exponent of the Mw-dependence of the energy was found to be identical (0.51) to predictions by Semenov (0.50 in Polym. Sci. Ser. A, 2007) and close to predictions by Wang and Safran (0.375 in J. Chem. Phys., 1988). The present findings demonstrate the dynamic association among amyloid fibril building blocks and offer a new appealing supramolecular route to tune their thermodynamic characteristics and their structural properties.