FIGURE 4.
Influence of membrane surface charge on AS interaction. A, fluorescence emission spectra of AS-18MFE in buffer (dashed and dotted line) or in the presence of neutral (DOPC, gray) or negatively charged (DOPG, black) SUVs (solid lines) and LUVs (dashed lines). Lipid and protein concentrations were 100 μm and 100 nm, respectively. B, titration of AS-18MFE by SUVs composed of DOPG/DOPC mixtures containing 0% (□), 25% (○), 50% (△), and 100% (♢) of negatively charged DOPG. Lines are fits of the data by Equation 1, assuming equivalent binding sites. CAS = 200 nm. C, dependence of the concentration of lipids needed for 50% AS binding on membrane charge (CAS = 100 nm). Shown are means of at least three measurements ± 2 maximal differences. All experiments were performed at 37 °C in 25 mm Na-PO4, pH 6.5, 150 mm NaCl. Excitation was at 420 nm.