Fig. 3.

Results of sm-FRET measurements after addition of two equivalents of unlabeled nanobodies to pre-formed high-FRET oligomers. The oligomers were pre-formed by the aggregation of 70 μM ɑS without nanobodies for 29 h under the same incubation conditions as for the sm-FRET kinetic assays. a Representative contour plots of FRET efficiency versus apparent oligomer size resulting from sm-FRET measurements performed immediately after addition of nanobodies to aggregated solutions of ɑS (after 29 h). b Corresponding FRET efficiency histograms split into two size populations, small (2- to 5-mers) and large (6- to 150-mers) species. In the absence of nanobodies and upon addition of the control NbHul5g, the majority of the large oligomeric species observed in the experiment had FRET efficiency values above 0.6, characteristic of high-FRET oligomers (first two panels). Upon addition of either NbSyn2 (third panel) or NbSyn87 (fourth panel), the average FRET efficiency distributions shifted to lower values, an effect that was particularly pronounced in the presence of NbSyn87