De novo Designed Peptide-Based Amyloid Fibrils

Identification of therapeutic strategies to prevent or cure diseases associated with amyloid fibril deposition in tissue (Alzheimer's disease, spongiform encephalopathies, etc.) requires a rational understanding of the driving forces involved in the formation of these organized assemblies rich in β-sheet structure. To this end, we used a computer-designed algorithm to search for hexapeptide sequences with a high propensity to form homopolymeric β-sheets. Sequences predicted to be highly favorable on this basis were found experimentally to self-associate efficiently into β-sheets, whereas point mutations predicted to be unfavorable for this structure inhibited polymerization. However, the property to form polymeric β-sheets is not a sufficient requirement for fibril formation because, under the conditions used here, preformed β-sheets from these peptides with charged residues form well defined fibrils only if the total net charge of the molecule is ±1. This finding illustrates the delicate balance of interactions involved in the formation of fibrils relative to more disordered aggregates. The present results, in conjunction with x-ray fiber diffraction, electron microscopy, and Fourier transform infrared measurements, have allowed us to propose a detailed structural model of the fibrils.