Figure 3. Experimental shape stability diagram agrees well with curvature instability theory.

Filled triangles represent the measured transition-density (expressed as a cover fraction, using the close-packed N-BAR dimer density of 30000 µm⁻²)²⁹ of GUVs under corresponding tensions. The open data points represent the maximum protein cover fraction reached by a GUV with (triangle) or without (circle) tubulation during protein-membrane binding. The solid line represents the best fit of experimental data with the proposed curvature instability model (r²=0.85). The dashed lines are 95% confidence intervals for the fit. The shaded area represents the region where the membrane is tubulated by endophilin N-BAR. The arrows indicate two ways of inducing membrane tubulation: 1), by increasing protein coverage on the membrane at constant tension or 2), by decreasing membrane tension at constant coverage. The large circle (non-tubulated state), and triangle (tubulated state), represent the state of the membrane before and after tension reduction (compare Figure 1d), respectively. The inset shows the same data using linear axes. Error bars represent the standard errors associated with determining each data point. Concentrations of endophilin N-BAR used in the experiment ranged from 25nM to 400nM (also note Supplementary Figure 5a).