Figure 4
Transthyretin fibrillation process described using SAXS data.
(A) SAXS scattering intensity against the scattering vector q (q = 4π sin θ/λ, 2θ equals the scattering angle) at different time points during the fibrillation (black) and the fitted curves (red). The fitted curves are obtained by linear combination of the scattering curves for the pre-initiation tetramer and protofibril after 21½ hours of incubation. Curves show pre-initiation condition (top), kinetics (3½ min to 21½ hours) and mature protofibrils (1 month) (bottom). Curves are translated arbitrarily to provide a clear view of each curve. (B) Normalized pair distance distribution function (P(r)) calculated from the corresponding scattering curves. The sequence of curves follows that of the raw scattering curves in A and again curves are translated arbitrarily for viewing purposes. The inset shows selected P(r) functions scaled to the same volume. Pre-initiation (grey), 40 minutes (yellow), 2 hours (orange), 4 hours (red), 7 hours (blue), 11 hours (cyan), 21½ hours (green) and mature protofibrils (black). (C) Zoom of the lowest scattering angles of SAXS scattering curves at 40 minutes (yellow), 2 hours (orange), 4 hours (red), 7 hours (blue), 11 hours (cyan), 18 hours (grey) and 21½ hours (green) after fibrillation initiation. Arrows indicate the time development and cross-over points are marked with arrow heads. (D) The estimated average radius of gyration (Rg) and average molecular weight (MW) at various time points during the fibrillation process. Rg is estimated using GNOM (grey triangles). MW estimates (red spheres) are based on the scattering intensity at zero angle (I0) from the Guinier approximation. The solid lines are guides for the eye. For comparison the ThT fluorescence intensity (open spheres) are normalised on a scale from three to 20. In all panels the data from the outlier at 14½ hours of incubation are left (included in Table S1).
