Gomesin (Gm) is a potent cationic antimicrobial peptide that was isolated and characterized from hemocytes of the Brazilian spider Acanthoscurria gomesiana [1]. The peptide contains eighteen amino acid residues, including four cysteines that form two disulfide bridges: Cys~(2-15) and Cys~(6-11). The molecule adopts a β-hairpin-like structure, as determined by 2-D nuclear magnetic resonance and molecular dynamics studies [2] (Figure 1), The presence of two internal disulfide bridges plus a C-terminal amidation and a pyroglutamic acid in the N-terminus, certainly contributes to the stability of the peptide to human serum proteases. Due to its large range of antimicrobial and antifungical activities Gm seems to be an interesting lead peptide in the development of alternative new drug for human therapy [3-5]. To further understand the mechanism of the interaction of this peptide with membranes, we studied here the lytic action of Gm and its poorly active linear analogue ([Ser~(2,6,11,15)]-Gm) [6] on giant unilamellar vesicles (GUVs) [7], composed of mixtures of neutral [l-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)] and anionic [l-palmitoyl-2-oleoylphosphatidylglycerol (POPG)] phospholipids by using optical and fluorescence microscopies.
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