Self-assembly of beta-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 beta-sheet complexes. The present work describes water-soluble de novo beta-sheet peptides which self-assemble into fibrillar structures. The model peptides enable studies of the relationship between beta-sheet stability and association behavior. The peptides [DPKGDPKG-(VT)n-GKGDPKPD-NH2, n = 3-8] are composed of a central beta-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 beta-sheet structures. The association behavior investigated by analytical ultracentrifugation and dynamic light scattering was found to correlate strongly with the stability of a beta-sheet conformation. Model peptides with n >/= 6 form stable, water-soluble beta-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.
Infrared spectroscopy provides molecular information in systems that range from the level of peptides, isolate proteins and enzymes, to even more complex systems such as peptide–protein complexes and membrane‐bound proteins. The information may be a global one such as the secondary structure composition of a protein, or it may be highly specific such as the alteration of individual vibrating bonds in an enzyme. Furthermore, the structural information is not restricted to a static picture, but can also be obtained at high time resolution to allow true structure–function correlation. Illustrative examples are given to demonstrate the sort of information, which infrared techniques can provide and how this information can be extracted from the experimental data. In addition, strengths and limitations of the infrared approach are discussed. This should help the reader to evaluate whether a particular system is appropriate for study by infrared spectroscopy, and what specific advantages are gained when applying infrared techniques.
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