The monolayer technique: a potent tool for studying the interfacial properties of antimicrobial and membrane-lytic peptides and their interactions with lipid membranes

Erudites of the antiquity already knew the calming effect of oil films on t he sea waves. But one had to wait until 1774 to read the first scientific r eport on oil films from B. Franklin and again 1878 to learn the thermodynam ic analysis on adsorption developed by J. Gibbs. Then, in 1891, Agnes Pocke ls described a technique to manipulate oil films by using barriers. Finally , in 1917, I. Langmuir introduced the experimental and theoretical modern c oncepts on insoluble monolayers. Since that time, and because it has been f ound to provide invaluable information at the molecular scale, the monolaye r technique has been more and more extensively used, and, during the past d ecade, an explosive increase in the number of publications has occurred. Ov er the same period, considerable and ever-increasing interest in the antimi crobial peptides of various plants, bacteria, insects, amphibians and mamma ls has grown. Because many of these antimicrobial peptides act at the cell membrane level, the monolayer technique is entirely suitable for studying t heir physicochemical and biological properties. This review describes monol ayer experiments performed with some of these antimicrobial peptides, espec ially gramicidin A, melittin, cardiotoxins and defensin A. After giving a f ew basic notions of surface chemistry, the surface-active properties of the se peptides and their behavior when they are arranged in monomolecular film s are reported and discussed in relation to their tridimensional structure and their amphipathic character. The penetration of these antimicrobial pep tides into phospholipid monolayer model membranes, as well as their interac tions with lipids in mixed films, are also emphasized. (C) 1999 Elsevier Sc ience B.V. All rights reserved.