The membrane-permeabilizing effect of avenacin A-1 involves the reorganization of bilayer cholesterol.
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.
Armah
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CN
Food Biophysics Department, Norwich Research Park, Colney, Norwich NR4 7UA, England.
Mackie
A R
AR
Roy
C
C
Price
K
K
Osbourn
A E
AE
Bowyer
P
P
Ladha
S
S
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*
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