Fig. 4: Septin interaction with and on yeast membranes.

a Septin filament surface coverage on yeast polar lipid SLBs as a function of the KCl concentration during an in-situ titration (black data points), as well as individual incubation experiments (grey data points). Data points are mean ± standard deviation of the septin surface coverage in the first 10 HS-AFM frames in 3 different movies in each set of conditions. The titration data is fit with a Boltzmann function. b HS-AFM movie frames of septin filaments on yeast polar lipid SLB (in 20 mM HEPES, pH 6, 50 mM KCl) prior to the HS-AFM line scanning (HS-AFM-LS) force-sweep experiment. c HS-AFM-LS force-sweep experiment. Kymograph of filament cutting along a line in the middle of the dashed box in (b) and (d). As the force is increased the septin filaments break (white arrows). d HS-AFM movie frames of septin filament recovery after the HS-AFM-LS force-sweep experiment. Filament destruction at time t = +4 s was largely reformed at t = +116 s (dashed outlines). Imaging before, during, and after the HS-AFM-LS force-sweep experiment is shown in Supplementary Movie 2. e Individually flattened image areas of dashed outlines in (b) and (d) showing filament structure before and their recovery after the HS-AFM-LS force-sweep experiment. f Image entropy of panels in (e). The experiment is representative of 22 HS-AFM-LS filament cutting experiments from 4 biological replicates, where full or partial filament alignment recovery was observed. Data points are mean ± standard error of the image entropy in all image kernels of size 9 × 9 pixels.