title: Temperature and composition dependence of the interaction of delta-lysin with ternary mixtures of sphingomyelin/cholesterol/POPC.
abstract: The kinetics of carboxyfluorescein efflux induced by the amphipathic peptide delta-lysin from vesicles of porcine brain sphingomyelin (BSM), 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and cholesterol (Chol) were investigated as a function of temperature and composition. Sphingomyelin (SM)/Chol mixtures form a liquid-ordered (L(o)) phase whereas POPC exists in the liquid-disordered (L(d)) phase at ambient temperature. delta-Lysin binds strongly to L(d) and poorly to L(o) phase. In BSM/Chol/POPC vesicles the rate of carboxyfluorescein efflux induced by delta-lysin increases as the POPC content decreases. This is explained by the increase of delta-lysin concentration in L(d) domains, which enhances membrane perturbation by the peptide. Phase separations in the micrometer scale have been observed by fluorescence microscopy in SM/Chol/POPC mixtures for some SM, though not for BSM. Thus, delta-lysin must detect heterogeneities (domains) in BSM/Chol/POPC on a much smaller scale. Advantage was taken of the inverse variation of the efflux rate with the L(d) content of BSM/Chol/POPC vesicles to estimate the L(d) fraction in those mixtures. These results were combined with differential scanning calorimetry to obtain the BSM/Chol/POPC phase diagram as a function of temperature.
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina-Wilmington, Wilmington, NC, USA.
authors.forename: Antje
authors.initials: A
authors.lastname: Pokorny
authors.forename: Lindsay E
authors.initials: LE
authors.lastname: Yandek
authors.forename: Adekunle I
authors.initials: AI
authors.lastname: Elegbede
authors.forename: Anne
authors.initials: A
authors.lastname: Hinderliter
authors.forename: Paulo F F
authors.initials: PF
authors.lastname: Almeida
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000737:chemistry* / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006460:Hemolysin Proteins; D006801:Humans; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry; D010539:Permeability; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D013109:Sphingomyelins / Q000737:chemistry* / Q000378:metabolism; D013552:Swine; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D013109:Sphingomyelins; C024098:6-carboxyfluorescein; C025994:delta hemolysin protein, Staphylococcus aureus; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine