β-Sheet Recognition by Time-Resolved Fluorescence Spectroscopy

A cyanine dye is used for the determination of β-sheet protein structures above the critical protein aggregation concentration through a bathochromic shift of the longwavelength absorption band. Simultaneously the fluorescence quantum yield of the dye increases strongly in the presence of β-sheet protein as compared to aqueous solution. Results from fluorescence lifetime experiments exhibit a short component (100 ps) of the dye in aqueous solution, which increases to about 1800 ps in protein-containing solutions. In contrast to absorption properties, the values of fluorescence lifetime and fluorescence intensity also depend on protein concentration and can be used not only to determine the protein structure but also to roughly estimate the concentration of the protein. Due to the protein-induced formation of H-aggregates, the absorption, the fluorescence intensity, and the amplitude of the fluorescence lifetime depend on time delay between sample preparation and measurement.