Van der Waals and electrostatic interactions synergistically contribute to the hLz peptidemembrane interaction and potentiate its action against bacteria

A.M. BOUCHET; N. IANUCCI; M.B. PASTRIAN; O. CASCONE; N.C. SANTOS ; E. A. DISALVO; A HOLLMANN

Philadelphia

Conferencia; Biophysical Society 57th Annual Meeting; 2013

Biophysical Society

Substitution of Ala 108 and Ala 111 in the 107-115 human lysozyme peptide results in a 20-fold increase in the anti-staphylococcal activity and decreases its hemolytic activity, which becomes significant only at 10-fold its Microbial Inhibition Concentration (MIC). This analog displays an additional positive charge near the N-terminus (108) and an extra Trp residue at the center of the molecule (111), indicating that this particular amino acid sequence improves its interaction with the bacterial membrane. In order to understand the role of this arrangement in the membrane interaction, studies with model lipid membranes were carried out. The interactions of peptides, 107-115 hLz and the novel analog ([K108W111]107-115 hLz) with liposomes and lipid monolayers were evaluated by monitoring the changes in the fluorescence of the Trp residues and the variation of the surface pressure, respectively. Results obtained with both techniques revealed significant increase of lipid affinity of [K108W111]107-115 hLz, specially when the membranes containing negatively charged lipids, such as phosphatidylglycerol (PG). However, there is also a significant interaction with zwitterionic lipids, suggesting that other forces in addition to electrostatic interactions are involved in the binding. The locations of both peptides in the membranes showed no significant difference, as evaluated by fluorescence quenching techniques, suggesting that the enhancement in the antimicrobial activity cannot be only ascribed to the average membrane location of the peptides. In contrast to this more static picture, tThe analysis of adsorption isotherms and the kinetics of insertion suggest that relaxation processes of the membrane structure are involved in this process, probably by imposing a reorganization of water at the interphases. In this regard, the enhanced activity of peptide [K108W111]107-115 hLz may be explained by a synergistic effect between the increased electrostatic forces (substitution of Ala by Lys at position 108), as well as the increased hydrophobic interactions (substitution of Ala by Trp at position 111).