Figure 1

In vitro cross‐seeding between FapC fragments (FapCS) and Aβ. A) ThT assay of Aβ (50 × 10⁻⁶m, incubated at 37 °C) in the presence or absence of FapCS, FapC monomers or preformed FapC fibrils (5 × 10⁻⁶m) (n = 3). B‐D) ThT kinetic parameters of fibrillization rate constant k (B), half‐life t_1/2 (C) and lag time (D) (n = 3). FapCS significantly increased (*, p < 0.05) k of Aβ, while the parameter was significantly suppressed (**, p < 0.005) with FapC monomer and fibrils. t_1/2 and lag time of Aβ were significantly shortened (**, p < 0.005) by FapCS. E) Static light scattering (SLS) indicating a rapid growth in the size of Aβ fibrils, immediately after mixing with FapCS (n = 3). F) TEM images of Aβ (at 12 h showing prefibrillar species) and G) FapCS (scale bar: 100 nm). H) TEM and I) AFM images of Aβ incubated with FapCS at 12 h (scale bar: 100 nm). J) CD spectra and K) secondary structure of Aβ alone and with FapCS (n = 3). After 12 h of incubation, the negative peaks of Aβ at 215 and 198 nm were slightly increased and decreased in intensity, respectively, indicating a transition from random coil (decreased from 34 ± 6 to 28 ± 1.5%) to β‐sheet (slightly increased from 28 ± 9 to 33 ± 6%). At 48 h, a strong negative peak appeared at 201 nm representing formation β‐sheets rich (54 ± 4.5%) fibrils. However, similar β‐sheets rich structure (59 ± 6%) were observed in Aβ + FapCS sample at 12 h time point. L) Enthalpy (ΔH) and free energy (ΔG), M) entropic factor (TΔS) for binding between FapCS and Aβ monomers or oligomers (Aβo) (n = 3). N) Immunolabeling of Aβ with β‐amyloid specific antibodies (scale bar: 10 × 10⁻⁶m). O) Quantification of green fluorescence intensity from (N) (n = 3). Significantly higher immune‐recognition (**, p < 0.005) was observed with Aβ + FapCS than Aβ alone, after 12 h incubation. P) STED microscopy of Aβ + FapCS (scale bar: 1 × 10⁻⁶m). FapCS labeled with Alexa 647 appeared to be adsorbed onto or integrated into Aβ fibrils that were labeled with ThT.