Reconstitution of the lipid matrix of the outer membrane of gram-negative bacteria as asymmetric planar bilayer.
This paper is a report on the reconstitution of the lipid matrix of the outer membrane of Gram-negative bacteria as an asymmetric planar bilayer. This is the first time that a planar membrane is described, which consists on one side of a phospholipid (PL) mixture and on the other side of lipopolysaccharide (LPS). Therefore, strong emphasis is placed on a physical characterization of this membrane via its electrical properties. The membranes were prepared from spread monolayers or from vesicle-derived monolayers. Contrary to observations for symmetric phospholipid membranes, specific capacitances of (0.67 +/- 0.02) mu F.cm-2, breakdown voltages between 200 and 400 mV and specific conductances between 10(-8) and 2 x 10(-7) S.cm-2 were obtained independent of the preparation method. The LPS-containing membranes were stable up to 3 hr if they were formed and kept at temperatures above the hydrocarbon chain melting temperature of the LPS. For the specific capacitance, a dependence on the aperture radius was observed. This is explained by assuming a toroidal transition zone at the rim of the aperture. First results on the action of the pore-forming alpha-toxin from Staphylococcus aureus on bilayers of different composition demonstrate particular characteristics of this asymmetric bilayer system. The pore-formation rate is highest in symmetric phospholipid bilayers, considerably lower in asymmetric PL/LPS systems and fully inhibited in LPS/LPS systems.
Forschungsinstitut Borstel, Division of Biophysics, Federal Republic of Germany.
U
U
Seydel
G
G
Schröder
K
K
Brandenburg
D001427:Bacterial Toxins / Q000494:pharmacology; D002462:Cell Membrane / Q000032:analysis / Q000502:physiology*; D004553:Electric Conductivity; D006460:Hemolysin Proteins; D008051:Lipid Bilayers / Q000032:analysis; D008070:Lipopolysaccharides / Q000032:analysis; D008081:Liposomes; D008563:Membrane Lipids / Q000032:analysis; D008564:Membrane Potentials; D015394:Molecular Structure; D010743:Phospholipids / Q000032:analysis; D012475:Salmonella / Q000032:analysis*; D013211:Staphylococcus aureus
D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D008070:Lipopolysaccharides; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; C021091:staphylococcal alpha-toxin