Permeation of the cell membrane leading to cell death is a mechanism used by a large number of membrane-lytic peptides. Some are linear, mostly helical, and others contain one or more disulfide bonds forming beta-sheet or both beta-sheet and alpha-helix structures. They are all soluble in solution but when they reach the target membrane, conformational changes occur which let them associate with and lyse the membrane. Some lytic peptides are not cell-selective and lyse different microorganisms and normal mammalian cells, while others are specific to either type of cells. Despite extensive studies, the mode of action of membrane-lytic peptides is not fully understood and the basis for their selectivity towards specific target cells is not known. Many studies have shown that peptide-lipid interactions leading to membrane permeation play a major role in their activity. Membrane permeation by amphipathic alpha-helical peptides has been proposed to occur via one of two general mechanisms: (i) transmembrane pore formation via a 'barrel-stave' mechanism; and (ii) membrane destruction/solubilization via a 'carpet' mechanism. This review, which is focused on the different stages of membrane permeation induced by representatives of amphipathic alpha-helical antimicrobial and cell non-selective lytic peptides distinguishes between the 'carpet' mechanism, which holds for antimicrobial peptides versus the 'barrel-stave' mechanism, which holds for cell non-selective lytic peptides.
