Figure 7. The monomer-dimer-hexamer model describes the thermodynamics and kinetics of fibril elongation.
(a) Global fits (blue solid lines) to the fibril elongation kinetics monitored by ThT fluorescence assuming a hexamer addition model at different concentrations of soluble ΔN6 (dots) (Materials and methods and Table 4). The concentrations of ΔN6 are colored according to the key. The average of five replicates is shown. (b) Protein correlation times (τc) measured using NMR (red) and back-calculated values (green) using the populations of monomers, dimers and hexamers predicted from the monomer-dimer-hexamer model and the correlation times of the dimers and hexamer structural models shown in Figures 4 and 5. (c) The fibril yield (after 100 hr) of each elongation reaction. SDS-PAGE analysis of the whole reaction (shown in (a)) before centrifugation (W) or of the supernatant (S/N) after centrifugation at the different concentrations of ΔN6, as indicated. (d) Bar-charts showing the % of insoluble material (gray) measured using densitometry of the gel shown in (c). The % hexamer population in the absence of seeds (black) predicted by the monomer-dimer-hexamer model at each ΔN6 concentration correlates with the % insoluble material (gray). Note that the fibril yield is low since fibrils cannot form when the monomer concentration falls significantly below the Kd for dimer formation (50 μM).
Figure 7—figure supplement 1. Alternative kinetic models do not describe the kinetics of seeded fibril growth.
