Ideally amphipathic beta-sheeted peptides at interfaces: structure, orientation, affinities for lipids and hemolytic activity of (KL)(m)K peptides

Designed to model ideally amphipathic beta-sheets, the minimalist linear (K L)(m)K peptides (m = 4-7) were synthesized and proved to form stable films at the air/water interface, they insert into compressed dimyristoylphosphat idylcholine monolayers and interact with egg phosphatidylcholine vesicles. Whatever the interface or the lateral pressure applied to the films. FT-IR and polarization-modulated IRRAS spectroscopy developed in situ on the film s indicated that all the peptides totally fold into intermolecular antipara llel beta-sheets. Calculated spectra of the amide region allowed us to defi ne the orientation of the beta-strands compared to the interface. It is con cluded that such beta-sheets remain flat-oriented without deep perturbation of zwitterionic phospholipids. Dansyl labelling at the N-terminus indicate s that all the peptides are monomeric at a low concentration in aqueous buf fer and bind to lipids with similar Dns burying. The affinities for zwitter ionic lecithin mono- and bilayers, quantitatively estimated from buffer to lipid partition constants, monotonically increased with peptide length, ind icating that hydrophobicity is a limiting parameter for lipid and membrane affinities. Peptides induced permeability increases on zwitterionic liposom es, they are strongly hemolytic towards human erythrocytes and their activi ty increases concurrently with length. Taking into account the lipid affini ty, a hemolytic efficiency can be defined: at the same amount of peptide bo und! this efficiency strongly increases with the peptide length. It is prop osed that the first determinant step of membrane disturbance is the invasio n of the outer membrane leaflet by these ideally amphipathic beta-sheeted s tructures lying flat at the interface, like large rafts depending on the nu mber of beta-strands. (C) 2000 Elsevier Science B.V. All rights reserved.