Water-Soluble β-Sheet Models Which Self-Assemble into Fibrillar Structures

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Abstract
Self-assembly of β-sheet domains resulting in the formation of pathogenic, fibrillar protein aggregates (amyloids) is a characteristic feature of various medical disorders. These include neurodegenerative diseases, such as Alzheimer's, Huntington's, and Creutzfeldt−Jacob's. A significant problem in studying such aggregation processes is the poor solubility of these β-sheet complexes. The present work describes water-soluble de novo β-sheet peptides which self-assemble into fibrillar structures. The model peptides enable studies of the relationship between β-sheet stability and association behavior. The peptides [DPKGDPKG-(VT)n-GKGDPKPD-NH2, n = 3−8] are composed of a central β-sheet-forming domain (VT-sequence), and N- and C-terminal nonstructured octapeptide sequences which promote water solubility. Conformational analyses by circular dichroism and Fourier transform infrared spectroscopy indicate the influence of peptide length, d-amino acid substitution, and concentration on the ability of the peptides to form stable β-sheet structures. The association behavior investigated by analytical ultracentrifugation and dynamic light scattering was found to correlate strongly with the stability of a β-sheet conformation. Model peptides with n ≥ 6 form stable, water-soluble β-sheet complexes with molecular masses of more than 2000 kDa, which are organized in fibrillar structures. The fibrils examined by Congo Red staining and electron microscopy show some similarities with naturally occurring amyloid fibrils.

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