Figure 3.

Immobilization experiment to probe the conformational dynamics of Aβ40 (left) and Aβ42 (right) on the timescale of microseconds to milliseconds. Experiments were performed at the native condition (PBS, 22°C). (A) Representative fluorescence (D, donor; A, acceptor) and FRET efficiency (E) trajectories of Aβ40 and Aβ42 (1 ms bin time) obtained by continuous-wave excitation. Photon count rates were 50–100 ms⁻¹. Both trajectories show a constant FRET efficiency (E = 0.5–0.6) followed by successive acceptor (red arrow) and donor (green arrow) photobleaching. (B) The FRET efficiency histograms in the upper panels are constructed using the FRET efficiency values calculated from the initial segment of the trajectory of each molecule. The histograms in the lower panels are constructed using the FRET efficiency values of all 1 ms bins in the initial segment of each trajectory. FRET efficiencies were corrected for background photons. (C) Donor-acceptor cross correlation averaged over the initial segments of trajectories in (B). Experimental data (green circles) are fitted to a single exponential function (red). The relaxation rates are 15.3 and 16.5 ms⁻¹ for Aβ40 and Aβ42, respectively. To see this figure in color, go online.