(595a) Pore Formation in 1,2-Dimyristoyl-Sn-Glycero-3-Phosphocholine Bilayers and Listeria Moncytogenes By Low Concentrations of Antimicrobial Peptide Melittin

Antimicrobial peptides belong to a large and varied class of relatively short peptides family, which usually are largely positively charged, and constitute host-defense system in many living organisms, capable of killing inter alia, Gram negative and Gram positive bacteria by permeabilzation of cell membrane through pore formation. In the first part of this study, pore formation in DMPC bilayers by antimicrobial peptide melittin was monitored by leakage of fluorescent dyes (calcein, FD4 and FD20) of different molecular weights encapsulated within liposomes which indicated a lagtime which was larger for smaller melittin/liposome ratio and larger molecular weight of dye. Pore formation was also demonstrated through direct observation of dye leakage using confocal microscopy. A mathematical model for the prediction of time of pore formation was proposed accounting for (i) adsorption of melittin onto bilayer (ii) surface aggregation and (iii) energy barrier for formation of pore by melittin aggregates that may be interspersed with phospholipid heads. Model predictions were compared with experimental data. In the second part of this study, the antimicrobial activity of native melittin as well as its mutant (26 amino acids: GIGAVLKVLTTGLPALKSWIKRKRQQ in which Ile-17 residue of melittin was replaced by a Lys residue in order to decrease its hydrophobicity with more charge) against different strains of Gram positive bacteria listeria monocytogenes was characterized by absorbance and plate count which also indicated a lagtime for deactivation that was concentration dependent. Because of decreased interaction with mammalian cell, the cytotoxicity of mutant melittin was found to be less than that for native.