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.