Permeabilization of raft-containing lipid vesicles by delta-lysin: a mechanism for cell sensitivity to cytotoxic peptides.
Delta-lysin is a linear, 26-residue peptide that adopts an alpha-helical, amphipathic structure upon binding to membranes. Delta-lysin preferentially binds to mammalian cell membranes, the outer leaflets of which are enriched in sphingomyelin, cholesterol, and unsaturated phosphatidylcholine. Mixtures including these lipids have been shown to exhibit separation between liquid-disordered (l(d)) and liquid-ordered (l(o)) domains. When rich in sphingomyelin and cholesterol, these ordered domains have been called lipid "rafts". We found that delta-lysin binds poorly to the l(o) (raft) domains; therefore, in mixed-phase lipid vesicles, delta-lysin preferentially binds to the l(d) domains. This leads to the concentration of delta-lysin in l(d) domains, enhancing peptide aggregation and, consequently, the rate of peptide-induced dye efflux from lipid vesicles. The efficient lysis of eukaryotic cells by delta-lysin can thus be attributed not to specific delta-lysin-cholesterol or delta-lysin-sphingomyelin interactions but, rather, to the exclusion of delta-lysin from ordered rafts. The degree to which the kinetics of dye efflux are enhanced in mixed-phase vesicles over those observed in pure, unsaturated phosphatidylcholine vesicles directly reflects the amount of l(d) phase present in mixed-phase systems. This effect of lipid domains has broader consequences, beyond the hemolytic efficiency of delta-lysin. We discuss the hypothesis that bacterial sensitivity to antimicrobial peptides may be determined by a similar mechanism.
Pokorny
Antje
A
Department of Chemistry and Biochemistry, University of North Carolina-Wilmington, North Carolina 28403, USA.
Almeida
Paulo F F
PF
D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D002463:Cell Membrane Permeability / Q000187:drug effects; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D005452:Fluoresceins / Q000737:chemistry / Q000378:metabolism; D006460:Hemolysin Proteins; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D021962:Membrane Microdomains / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D013109:Sphingomyelins / Q000737:chemistry / Q000378:metabolism; D013211:Staphylococcus aureus; D013552:Swine
D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D005452:Fluoresceins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010455:Peptides; D010713:Phosphatidylcholines; D013109:Sphingomyelins; C024098:6-carboxyfluorescein; C025994:delta hemolysin protein, Staphylococcus aureus; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine