title: The membrane-permeabilizing effect of avenacin A-1 involves the reorganization of bilayer cholesterol.
abstract: Avenacin A-1 is a member of a group of naturally occurring compounds called saponins. It is found in oat plants, where it protects against fungal pathogens. A combined electrical and optical chamber was used to determine the interaction of avenacin A-1 with Montal-Mueller planar lipid bilayers. This system allowed simultaneous measurement of the effect of avenacin A-1 on the fluorescence and lateral diffusion of a fluorescent lipid probe and permeability of the planar lipid bilayer. As expected, cholesterol was required for avenacin A-1-induced bilayer permeabilization. The planar lipid bilayers were also challenged with monodeglucosyl, bis-deglucosyl, and aglycone derivatives of avenacin A-1. The results show that the permeabilizing activity of the native avenacin A-1 was completely abolished after one, two, or all three sugar residues are hydrolyzed (monodeglucosyl, bis-deglucosyl, and aglycone derivatives, respectively). Fluorescence recovery after photobleaching (FRAP) measurements on cholesterol-containing planar lipid bilayers revealed that avenacin A-1 caused a small but significant reduction in the lateral diffusion of the phospholipid probe N-(7-nitrobenzoyl-2-oxa-1,3-diazol-4-yl)-1, 2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (NBD-PE). Similarly, with the sterol probe (22-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3beta-ol (NBD-Chol), avenacin A-1, but not its derivatives, caused a more pronounced reduction in the lateral diffusion than that observed with the phospholipid probe. The data indicate that an intact sugar moiety of avenacin A-1 is required to reorganize membrane cholesterol into pores.
authors.affiliation: Food Biophysics Department, Norwich Research Park, Colney, Norwich NR4 7UA, England.
authors.forename: C N
authors.initials: CN
authors.lastname: Armah
authors.forename: A R
authors.initials: AR
authors.lastname: Mackie
authors.forename: C
authors.initials: C
authors.lastname: Roy
authors.forename: K
authors.initials: K
authors.lastname: Price
authors.forename: A E
authors.initials: AE
authors.lastname: Osbourn
authors.forename: P
authors.initials: P
authors.lastname: Bowyer
authors.forename: S
authors.initials: S
authors.lastname: Ladha
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives; D055592:Biophysical Phenomena; D001703:Biophysics; D002240:Carbohydrate Sequence; D002784:Cholesterol / Q000031:analogs & derivatives / Q000737:chemistry*; D004058:Diffusion; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010539:Permeability; D010714:Phosphatidylethanolamines; D012503:Saponins / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010714:Phosphatidylethanolamines; D012503:Saponins; C042077:N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine; C035784:N(1)-cholesterylcarbamoyl-N(8)-(4-nitrobenzo-2-oxa-1,3-diazole)-3,6-dioxaoctyl-1,8-diamine; C091460:avenacin A 1; D002784:Cholesterol; D009327:4-Chloro-7-nitrobenzofurazan