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Fig. 2. (A) Integrated heat per injection normalized with respect to the number of moles oflipids (all, left or POPG only, right). (B) Relative intensity of 90 o light scattering.fluorescently labeled Gm (Gm with a rhodamine group attached to the N -amino group ofthe lysine residue; denoted Gm-Rh) by a micropipette placed at the vicinities of a GUV byoptical microscopy (data not shown). Generally, we observed that Gm-Rh first binds to thevesicle surface, then accumulates at certain points (small high-contrast regions).Afterwards, the vesicles suddenly burst through the opening of a large hole, and themembrane rearranges into an interconnected tubular structure. As control, in the absence ofpeptide, the GUVs were never spontaneously disrupted [3].Still using the optical microscopy, GUV solutions of different composition weremixed with increasing concentrations of Gm or [Ser 2,6,11,15 ]-Gm (data not shown). Thenumber of GUVs as a function of time was used to quantify the lytic activity of thepeptides. The measurements were done for different compositions of GUVs andconcentrations of Gm and [Ser 2,6,11,15 ]-Gm. In the other setup, we tested the interactionbetween these peptides (Gm and GmL) and LUVs by using ITC. As shown in Figure 1, themagnitude of H increased with the mol% of POPG. Besides that, the interaction of Gmwith one bilayer composition was always stronger than its linear analogue interaction [4].The sigmoidal curves obtained at high mol% POPG fall close to a mastercurve when thedata is shown relative to the mol% POPG only (Figure 2A). In our last experiment, the 90 olight scattering ( = 400 nm) of dispersions of LUVs with peptides was measured in thesame conditions as in the ITC experiments. The data, Figure 2B, are shown as relativeintensities: positive values indicate aggregation of LUVs driven by the peptides andnegative values indicate destruction of LUVs induced by peptide action. High bindingaffinity (both peptides against 50 and 100 mol% POPG) is accompanied by extensivevesicle aggregation. The interaction of both Gm and GmL with POPC/POPG is mainly anenthalpy-driven process ( H < 0), which seems to happen with POPG lipids only. Anendothermic component appears under some conditions.AcknowledgmentsThis work was supported by FAPESP, CNPq, and CAPES.References1. Silva Jr., P.I., et al. J. Biol. Chem. 275, 33464-33470 (2000).2. Fazio, M.A., et al. Biopolymers 84, 205-218 (2006).3. Domingues, T.M., et al. Langmuir. 26, 11077-11084 (2010).4. Seelig, J. Biochim. Biophys. Acta. 1331, 103-116 (1997).401