Thioflavin T fluorescence of single D-amino acid substituted Aβ
The time dependence of ThT fluorescence of the singly substituted Aβ40 peptides produced three types of plots relative to that of wild type Aβ (Fig. 6a): (1) substantially increased fluorescence; (2) grossly similar; or (3) substantially decreased fluorescence. The biggest contrast in assembly was exhibited by D-L17, which had a t1/2 = 136 h, compared to 150 h for wild type, and a final fluorescence intensity of ≈1900, which was 16× higher than that of the wild type peptide (Table 3). D-K16, D-S26, D-N27 displayed substantially lower final ThT fluorescence intensities (38, 29, and 28 FU, respectively) (Fig. 6a, Table 3). With the exception of D-E3, which had a half time equivalent to that of WT Aβ42, all the other peptides had shorted half times.
The singly substituted Aβ42 peptides, relative to the wild type peptide, also demonstrated higher, lower, and equivalent assembly characteristics. As observed in the study of the doubly substituted versions, the magnitude of the differences between peptides with higher final fluorescence levels and the wild type peptide generally were much larger than those for peptides that displayed lower final fluorescence. D-F20 produced a hyperbolic increase (no discernible lag phase) in fluorescence that peaked at units, ~8× those of Aβ42. D-H14 and D-M35 produced very similar curves, each of which reached maximum fluorescence levels of 350 and 320 units, ~4.5× those of Aβ42. D-A21 displayed the largest decrease in final fluorescence intensity, which was ~5× lower than that of wild type. The remaining peptides produced final fluorescence intensities either equal to those of wild type or only modestly (|Δ| < 2) higher or lower.