Abstract
A decapeptide Ala-Nle-Ala-Lys-Ala-Ala-Ala-Ala-Nle-Ala showed conformational transition from α-helix to β-sheet and further formed amyloid fibrils in a micellar environment in previous work with lysine-scanning decapeptides. In the present work we used norleucine-scanning decapeptides to evaluate amyloid formation under the same conditions. The decapeptides were synthesized, and their conformations were determined by circular dichroism (CD). Conformational transition from α-helix to β-structure was noted in nearly every decapeptide. However, only the decapeptide Ala-Ala-Ala-Lys-Ala-Ala-Ala-Nle-Ala-Ala (8X4K), which has one norleucine (Nle) and one lysine (Lys) in an alanine(Ala)-based decapeptide, formed the β-structure immediately and not via α-helices. A series of norleucine-scanning decapeptides were examined for amyloid-forming capacity, by using a fluorescence dye, Thioflavin T. An increase in fluorescence was also a clear indication of the high capacity of 8X4K to form amyloids. The amyloid aggregates were observed by transmission electron microscopy (TEM) and identified as parallel β-sheet structures by fourier transform infrared spectroscopy (FTIR).
