Fig. 3: Morphology of septin filaments on yeast polar extract SLBs compared to septin filaments on mica.

HS-AFM movie frame (a) and 5 frame average (b) of septin filaments on yeast polar extract SLBs in buffer 20 mM HEPES, pH 6, 50 mM KCl. c Section profile across the dashed line in (b) showing the periodic inter-filament distance, d_(f-f), of the laterally aligned filaments. d Lateral inter-filament distance distribution: <d_(f-f)> = 10.7 ± 2.0 nm (n = 401, from 26 images from 8 biological replicates). e Filament height, h, distribution above membrane, <h > = 4.9 ± 0.6 nm (n = 31, from 18 images from 9 biological replicates). Inset in (e) shows 4 septin filaments in section (ovals) on a lipid bilayer. Each filament interacts with the membrane via the face exposing the C-termini (C) and exposing the N-termini (N) to the bulk. HS-AFM movie frame (f) and 5 frame average (g) of septin filaments on mica in buffer 20 mM HEPES, pH 7.5, 600 mM KCl. h Section profile across the dashed line in (g) showing the inter-filament distance, d_(f-f), within, and the inter-pair distance, d_(p-p), between aligned filament pairs. i Lateral inter-filament distance, d_(f-f), and lateral inter-filament-pair distance, d_(p-p), distributions: <d_(f-f)> = 7.1 ± 1.1 nm (n = 269) and <d_(p-p)> = 19.3 ± 2.4 nm (n = 113, from 5 images from 4 biological replicates). j Filament height, h, distribution above mica, <h > = 4.0 ± 0.4 nm (n = 86, from 38 images from 13 biological replicates). Inset in (j) shows 4 septin filaments in section (ovals) on mica, grouped in 2 pairs of 2 filaments. The filaments in pairs interact with each other via the face exposing the N-termini (N) exposing the C-termini (C) to the sides. All values are mean ± stdev.