Detergent-Like Action of the Antibiotic Peptide Surfactin on Lipid Membranes  Heiko Heerklotz, Joachim Seelig  Biophysical Journal  Volume 81, Issue 3, Pages 1547-1554 (September 2001) DOI: 10.1016/S0006-3495(01)75808-0 Copyright © 2001 The Biophysical Society Terms and Conditions

Figure 1 ITC demicellization experiments. (A). Raw data for a set of 7-μL injections of a 0.5-mM surfactin solution into buffer (10mM Tris, 100mM NaCl, pH 8.5) at 15°C, showing the heat flow per injection. (B) Heats of injection, δhi, per mole of surfactin injected, δni, versus the surfactin concentration in the cell, CS0 at 5°C (▾), 15°C (♢), 25°C (bold line, ●), 35°C (○), and 45°C (▴). (C) Normalized first derivative of the 25°C curve of (B). The maximum is defined as the CMC. Biophysical Journal 2001 81, 1547-1554DOI: (10.1016/S0006-3495(01)75808-0) Copyright © 2001 The Biophysical Society Terms and Conditions

Figure 2 (A, log scale) the critical micelle concentration, CMC, and (B) Temperature dependence of the enthalpy of micelle formation ΔHSuw→m. The data are taken from Fig. 1. The slope of the linear fit in (B) is ΔCPw→m=−(250±10) cal/(molK) and the isocaloric temperature is 41°C (solid line). The fit of log(CMC) versus T (solid line in A, cf. Kresheck, 1998) predicts the van’t Hoff enthalpy indicated by the dash/dot line in (B). Biophysical Journal 2001 81, 1547-1554DOI: (10.1016/S0006-3495(01)75808-0) Copyright © 2001 The Biophysical Society Terms and Conditions

Figure 3 Partitioning of surfactin into 100-nm POPC vesicles. (A) ITC experiment. Injection of 7.5-μL aliquots of lipid vesicles (2nm POPC) into a 7.5-μM surfactin solution. (B) The heat of reaction, δhi, divided by the molar amount of injected lipid is plotted versus the lipid concentration in the calorimeter cell, CL0. The different symbols refer to four different experiments with the following surfactin concentrations 5μM (▾), 7.5μM (○, □), 10μM (▴). The solid lines are theoretical fits according to Eq. 5 with the following parameters K=2.2×104 M−1, ΔHSuw→b=9.0 kcal/mol, qdil=−0.23 kcal/mol. (C) Variation of the surfactin (bound)-to-lipid ratio, Rb as a function of the lipid concentration in the calorimeter cell. The solid line SAT denotes the limiting detergent-to-lipid ratio at which membrane micellization occurs. Biophysical Journal 2001 81, 1547-1554DOI: (10.1016/S0006-3495(01)75808-0) Copyright © 2001 The Biophysical Society Terms and Conditions

Figure 4 Double logarithmic plot of the partition coefficient, K, versus the critical micelle concentration, CMC, of surfactin compared to C12EO9 (nonaethyleneglycol dodecyl ether), FOSMEA (dodecyl phospho-n-methylethanolamine) (details not shown) and other non-ionic surfactants as described in Heerklotz and Seelig (2000a). The diagonal line corresponds to K · CMC=1. An offset from the diagonal to lower K values (i.e., K ·CMC<1) indicates strong membrane destabilization by the respective compound. Biophysical Journal 2001 81, 1547-1554DOI: (10.1016/S0006-3495(01)75808-0) Copyright © 2001 The Biophysical Society Terms and Conditions

Figure 5 Correlation between the surfactant-to-lipid mole ratio in the membrane at the onset of solubilization, Rbsat, and the membrane destabilization specified in terms of K · CMC. Surfactin is compared to non-ionic surfactants as characterized in Heerklotz and Seelig (2000a). The bold line represents Rbsat=KCMC. Biophysical Journal 2001 81, 1547-1554DOI: (10.1016/S0006-3495(01)75808-0) Copyright © 2001 The Biophysical Society Terms and Conditions