Figure 3. Mechanical effect of I-BAR binding to the inner leaflet of membrane tubes.

(a) Pulling force, f, as a function of the square root of tension, , for three different values of φ_v : 1% (magenta, N=9 GUVs), 2% (green, N=5 GUVs) and 5% (cyan, N=10 GUVs). Fitting yields (see Supplementary Note 1 for details) an average value of the protein-membrane elastic parameter =(32±12) k_BT. The dashed line corresponds to a fit to the data obtained for bare GUVs (Supplementary Fig. 5a). (b) Tube radius, R, as a function of σ_v, for the same conditions as in (a). Fitting yields =(60±30) k_BT. The dashed line corresponds to a fit to the data obtained for bare GUVs (Supplementary Fig. 5b). Data and fit for φ_v=5% indicate that R extrapolates to a finite value at zero tension, whereas for φ_v=1 and 2% it diverges. Inset shows calculated jump in tube curvature (1/R) at zero tension as a function of φ_v.