Biophysical studies of the development of amyloid fibrils from a peptide fragment of cold shock protein B

The peptide CspB-1, which represents residues 1-22 of the cold shock protei n CspB from Bacillus subtilis, has been shown to form amyloid fibrils when solutions containing this peptide in aqueous (50%) acetonitrile are diluted in water [M. Gro beta et al. (1999) Protein Science 8, 1350-1357] We estab lished conditions in which reproducible kinetic steps associated with the f ormation of these fibrils can be observed. Studies combining these conditio ns with a range of biophysical methods reveal that a variety of distinct ev ents occurs during the process that results in amyloid fibrils. A CD spectr um indicative of beta structure is observed within 1 min of the solvent shi ft, and its intensity increases on a longer timescale in at least two kinet ic phases. The characteristic wavelength shift of the amyloid-binding dye C ongo Red is established within 30 min of the initiation of the aggregation process and corresponds to one of the phases observed by CD and to changes in the Fourier transform-infrared spectrum indicative of beta structure. Sh ort fibrillar structures begin to be visible under the electron microscope after these events, and longer, well-defined amyloid fibrils are establishe d on a timescale of hours. NMR spectroscopy shows that there are no signifi cant changes in the concentration of monomeric species in solution during t he events leading to fibril formation, but that soluble aggregates too larg e to be visible in NMR spectra are present throughout the process. A model for amyloid formation by this peptide is presented which is consistent with these kinetic data and with published work on a variety of disease-related systems. These findings support the concept that the ability to form amylo id fibrils is a generic property of polypeptide chains, and that the mechan ism of their formation is similar for different peptides and proteins.