Fig. 5.

The effect of Rs1 on membrane fluidity. PS bilayer indentations were performed using the AFM cantilever and the cantilever deflection at which the bilayer ruptured were measured. The effect of Ca²⁺ and of Rs1 on PS bilayer fluidity is reflected in the membrane yield strength. A. PS bilayer in 20 mM HEPES-150 mM NaCl. Although “phases” appear in PS even without Ca²⁺, punch-through forces differ little in the two domains. B. PS bilayer in 20 mM HEPES, 150 mM NaCl, 0.5 mM CaCl₂. In the presence of Ca²⁺, the punch through deflection shows two separate peaks with different yield strengths. C. PS bilayer in 20 mM HEPES, 150 mM NaCl, 0.5 mM CaCl₂ after injection of Rs1. Protein binding greatly enhances membrane robustness of the ordered phase as opposed to the fluid phase that remains unaffected. D. A pair of force curves obtained by indenting PS ordered domain in the presence of calcium (red) and the same phase after Rs1 adsorption (blue). The discontinuities in the deflection curve due to the bilayer break-through (yield) and the cantilever deflections at which the bilayers are punctured are indicated.