D-amino acid substituted Aβ.
Peptides were prepared and mixed with Thioflavin T, which binds β-sheet
and can serve as a surrogate marker for aggregation. Error bars
represent standard deviations of three experiments. (A) Variants of Aβ40
with single D-amino acid substitutions. (B) Variants of Aβ42 with single
D-amino acid substitutions.
Figure 7. Secondary structure of Aβ40 and single
D-amino acid substituted variants . Secondary structure formation
of D-amino acid substituted Aβ40 variants was assessed using CD. Aβ40 is
unstructured initially, with a minimum of molar ellipticity at 196 nm.
The secondary structure formation transitions are shown for (A) WT, (B)
D-L17 and (C) D-N27. (D) Comparisons of final secondary structure
between WT and mono-D-amino acid substituted variants. (E) Rates of
transition to secondary structure. These rates were plotted as a
function of the molar ellipticity at the wavelength at which the molar
ellipticity was at a minimum in the final secondary structure formed and
time (in hours).
Figure 8. Secondary structure of Aβ42 and single
D-amino acid substituted variants . Secondary structure formation
of D-amino acid substituted Aβ42 variants was assessed using CD. Aβ42 is
unstructured initially, with a minimum of molar ellipticity at 196 nm.
Over time, Aβ42 undergoes structural transitions to predominately
β-sheet (minimum at 216 nm). Differences in the time course of this
structural transition are observed. The secondary structure formation
transitions are shown for (A) WT, (B) D-H14, (C) D-F20, (D) D-A21, and
(E) D-M35. (F) Comparisons of final secondary structure between WT and
mono-D-amino acid substituted variants. (G) Rates of transition to
secondary structure. These rates were plotted as a function of the molar
ellipticity at the wavelength at which the molar ellipticity was at a
minimum in the final secondary structure formed and time (in hours).
Figure 9. Morphology of WT and single D-amino acid
substituted Aβ40 and Aβ42 .
The morphology of WT and single D-amino acid substituted variants of
Aβ42 was studied using transmission electron microscopy. Electron
micrographs of fibrils formed by WT, D-H14, D-F20, D-A21, and M35 after
transitioning to their final secondary structures.
Figure 10. Map of individual amino acids important in
controlling Aβ folding and assembly.
Using a scanning D-amino acid substitution approach, we identified
specific amino acids that may play an important role in controlling the
oligomer formation, fibril formation kinetics, and secondary structure
formation of Aβ.