Cryo-transmission electron microscopy of a superstructure of fluid dioleoylphosphatidylcholine (DOPC) membranes

The membrane-destabilizing effect of the peptide melittin on phosphatidylcholine membranes is modulated by the presence of cholesterol. This investigation shows that inclusion of 40 mol % cholesterol in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine or 1,2-dioleoyl-sn-glycero-3-phosphocholine liposomes reduces melittin's affinity for the membrane. It is significant that the presence of cholesterol does not increase the amount of membrane-associated melittin needed to cause maximum leakage from, or major structural rearrangements of, the liposomes. Furthermore, comparison of microscopy and leakage data suggests that melittin-induced leakage occurs via different mechanisms in the cholesterol-free and cholesterol-supplemented systems. In the absence of cholesterol, leakage of carboxyfluorescein takes place from intact liposomes in a manner compatible with the presence of small melittin-induced pores. In the presence of cholesterol, on the other hand, adsorption of the peptide causes complete membrane disruption and the formation of long-lived open-bilayer structures. Moreover, in the case of cholesterol-supplemented systems, melittin induces pronounced liposome aggregation. Cryotransmission electron microscopy was used, together with ellipsometry, circular dichroism, turbidity, and leakage measurements, to investigate the effects of melittin on phosphatidylcholine membranes in the absence and presence of cholesterol. The melittin partitioning behavior in the membrane systems was estimated by means of steady-state fluorescence spectroscopy measurements.

Section: Liposome Preparationmentioning

confidence: 86%

Melittin-Lipid Bilayer Interactions and the Role of Cholesterol

Wessman

Strömstedt

Malmsten

et al. 2008

“…Therefore, it is not possible, without knowing the nature of the saddle-like actors, to compare the experimentally observed lattice spacings with the calculated ones. This suggests however, because experiments on different systems have reported lattice spacing ranging from 4 nm (Klösgen and Helfrich, 1997) to 75 nm (Meyer et al, 1990), that the possible saddle-like defects involved might have different origins.…”

Section: Possible Relationship With the Experimentally Observed Egg-cartons Superstructures Of Membranesmentioning

confidence: 99%

“…Another reason for postulating the existence of such superstructures is some evidence of anomalous membrane roughness suggested by studies of membrane adhesion (Servuss and Helfrich, 1989). Recent experiments using cryo-transmission electron microscopy on dilute vesicle dispersions have also shown the formation of disordered superstructures in fluid dioleoyl-phosphatidylcholine membranes (Klösgen and Helfrich, 1997).…”

Section: Possible Relationship With the Experimentally Observed Egg-cartons Superstructures Of Membranesmentioning

confidence: 99%

The Many-Body Problem for Anisotropic Membrane Inclusions and the Self-Assembly of “Saddle” Defects into an “Egg Carton”

Dommersnes

Fournier

2002

We calculate the many-body, nonpairwise interaction between N rigid, anisotropic membrane inclusions by modeling them as point-like constraints on the membrane's curvature tensor and by minimizing the membrane's curvature energy. Because multipolar distortions of higher-order decay on very short distances, our calculation gives the correct elastic interaction energy for inclusions separated by distances of the order of several times their size. As an application, we show by thermally equilibrating the many-body elastic energy using a Monte Carlo algorithm, that inclusions shaped as "saddles" attract each other and build an "egg-carton" structure. The latter is reminiscent of some patterns observed in membranes obtained from biological extracts, the origin of which is still mysterious.

“…The associated decrease of the surface area of the vesicle was interpreted in both cases as a loss of lipids from the vesicle membrane. Sandre, using fluorescence microscopy, observed some small fluorescent particles close to de-swelling vesicles that he interpreted in terms of a concentrated lipid superstructure (bicontinuous cubic phase; Kummrow and Helfrich, 1996;Klösgen and Helfrich, 1997), formed by the collapse of the excess of membrane. These lipid wells might be involved in the behavior observed in this work, the transition being possibly associated with the strong applied osmotic pressure, since neither significant budding nor daughter vesicles were observed using phase contrast microscopy.…”

Section: Osmotic Pressurementioning

confidence: 99%

Giant Lipid Vesicles Filled with a Gel: Shape Instability Induced by Osmotic Shrinkage

Viallat¹,

Dalous²,

Abkarian³

2004

We report the properties of giant lipid vesicles enclosing an agarose gel. In this system, the lipid bilayer retains some basic properties of biological membranes and the internal fluid exhibits viscoelastic properties, thus permitting us to address the question of the deformation of a cell membrane in relation to the mechanical properties of its cytoskeleton. The agarose gel (concentration c0gel = 0.07%, 0.18%, 0.36%, and 1% w/w), likely not anchored to the membrane, confers to the internal volume elastic moduli in the range of 10-10(4) Pa. Shapes and kinetics of de-swelling of gel-filled and aqueous solution-filled vesicles are compared upon either a progressive or a fast osmotic shrinkage. Both systems exhibit similar kinetics. Shapes of solution-filled vesicles are well described using the area difference elasticity model, whereas gel-filled vesicles present original patterns: facets, bumps, spikes (c0gel < 0.36%), or wrinkles (c0gel > or = 0.36%). These shapes partially vanish upon re-swelling, and some of them are reminiscent of echinocytic shapes of erythrocytes. Their characteristic size (microns) decreases upon increasing c0gel. A possible origin of these patterns, relying on the formation of a dense impermeable gel layer at the vesicle surface and associated with a transition toward a collapsed gel phase, is advanced.