Fig 1.
Structure of Aβ peptides 1-40/42 showing the position of residues 14–23 in the fibril formed.
(A) Aβ 1–40, two fold symmetry; (B) Aβ 1–40, three fold symmetry; and (C) Aβ 1–42, two fold symmetry. (D) The position of the Phe19 and Phe20 within the PDB:2BEG structure. (E) Amino acid sequence of Aβ 14–23, the substrate for peptide substitution in this study.
Fig 2.
10 μM Aβ 1–42 fibril aggregation in the presence of 20 μM peptides over 40 hours.
(A-B) Data from eight experiments (total n = 22 for Aβ 1–42) is shown. Error bars = SD. * p < 0.05, ** P < 0.01, *** p < 0.001, **** p < 0.0001. (A) Average changes in lag time relative to Aβ 1–42 alone (normalized to 1). (B) Average changes in ThT fluorescence relative to Aβ 1–42 alone (normalized to 1). (C-F) A representative kinetic experiment showing the inherent variability of Aβ 1–42 aggregation in the absence (C) or presence of D19 (D), D20 (E) or D19/20 (F) in replicate wells (n = 3). Despite this variability, the lag phases are always prolonged in the presence of D-peptide.
Fig 3.
Transmission electron micrographs of end-products of 48 hour Aβ 1–42 fibril (37°C) reactions in the presence or absence of peptides.
(A) Aβ 1–42 fibrils alone. (B) Aβ 1–42 fibrils after co-incubation with D19. A number of laterally associated fibrils are seen (arrow). (C) Aβ 1–42 fibrils after co-incubation with D20. Frequent oligomeric structures are associated along the length of many fibrils (arrow). (D) Aβ 1–42 fibrils after co-incubation with D19/20. Many fibrils had kinks or bends (arrow). Scale bars are 100 nm.
Table 1.
Properties of Aβ 1–42 fibrils generated in the presence or absence of peptides.
Fig 4.
Electron microscopy and dynamic light scattering analysis of end-products of 24 hour oligomer (4°C) preparations in the presence or absence of peptides.
(A) Aβ 1–42, (B) D19, (C) D20, (D) D19/20, (E) Aβ 1–42 + D19, (F) Aβ 1–42 + D20 and (G) Aβ 1–42 + D19/20. Scale bars are 100 nm. The size (Rh) distribution by mass has been plotted. Averages of ten readings are shown with error bars representing standard deviation.
Fig 5.
Morphology of D19/20 large spherical aggregates.
(A-B) Electron micrographs of occasionally observed large aggregates from D19/20 oligomer incubation reactions. Scale bar 1000 nm. (C) Rh distribution of aggregates. Average of twelve readings shown. Error bars represent standard deviation.
Fig 6.
Rescue of cell viability after treatment with Aβ 1–42 oligomers co-incubated with D19, D20 or D19/20, as measured by MTS assay in primary cortical neurons.
Cell toxicity was partially rescued when cells were treated with oligomer reactions of Aβ 1–42 co-incubated with peptide (Aβ42+peptide). No rescue was observed if cells were treated sequentially with Aβ 1–42 oligomers and then peptide oligomers (Aβ 1-42(+peptide)), without prior co-incubation. Values shown are normalized to Aβ 1–42 toxicity levels. n ≥ 6. ** p < 0.01.
Fig 7.
Dynamic light scattering during fibrillization.
Size (Rh) distribution by mass for Aβ 1–42 alone (A) and in presence of D19 (B), D20 (C) and D19/20 (D) observed at 0, 2, 8, 12 and 14 hours under fibril forming conditions at 37°C. The starting material was first oligomerized by incubation at 4°C for 24 hours.
Fig 8.
Aβ 1–42 toxicity correlated with hydrodynamic radii of oligomers.
A bubble plot correlates the size and toxicity observed for Aβ 1–42 oligomers with or without peptide co-incubation at 4°C. The size of each bubble represents the percentage of mass with that particular radius.