Blaž Babnik

Amphiphile-induced tubular budding of the bilayer membrane

Amphiphile-induced tubular budding of the erythrocyte membrane was studied using transmission electron microscopy. No chiral patterns of the intramembraneous particles were found, either on the cylindrical buds, or on the tubular nanoexovesicles. In agreement with these observations, the tubular budding may be explained by in-plane ordering of anisotropic membrane inclusions in the buds where the difference between the principal membrane curvatures is very large. In contrast to previously reported theories, no direct external mechanical force is needed to explain tubular budding of the bilayer membrane.

Shape transformation and burst of giant POPC unilamellar liposomes modulated by non-ionic detergent C12E8.

We studied spontaneous shape transformations and burst of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles with exogeneously added non-ionic detergent octaethylene-glycol dodecylether C(12)E(8). The addition of C(12)E(8) increased the speed of the vesicle shape transformation, so that we were able to study for the first time the complete sequence of POPC vesicle shapes starting from initial spherical vesicle with long thin tubular protrusion to final shape with invagination(s). The average mean curvature of the vesicle membrane continuously decreases during this process. The shape of the invaginations is usually spherical, however also non-spherical shapes of invaginations were observed. C(12)E(8) increases amplitudes of the fluctuations of the vesicle membrane. At higher concentrations in the membrane, C(12)E(8) induces the membrane leakage and burst of the vesicles.

On the role of membrane anisotropy in the beading transition of undulated tubular membrane structures

The Helfrich expression for the isotropic membrane bending energy was generalized for the case of anisotropic membranes by taking into account two intrinsic (spontaneous) curvatures, i.e., the intrinsic mean curvature Hm and the intrinsic curvature deviator Dm. Using this generalized expression for the membrane bending energy the shape equation for closed axisymmetric anisotropic membranes is solved numerically for the case of undulated tubular shapes. It is shown that the variation of one of the two intrinsic curvatures, Hm or Dm, may induce the first-order-like shape transitions between the undulated tubular membrane structures. The predicted discontinuous shape transitions were applied to explain the beading transitions without stretching, which were recently observed in nerve fibres.

Attachment of β2-glycoprotein I to negatively charged liposomes may prevent the release of daughter vesicles from the parent membrane

The temperature-induced budding of POPC–cardiolipin–cholesterol, POPC–POPS–cholesterol and POPC–POPG–cholesterol giant lipid vesicles in the presence of β2-glycoprotein I (β2-GPI) in the outer solution was studied experimentally and theoretically. The observed budding transition of vesicles was continuous which can be explained by taking into account the orientational ordering and direct interactions between oriented lipids. The attachment of positively charged β2-GPI to the negatively charged outer surface of POPC–cardiolipin–cholesterol, POPC–POPS–cholesterol and POPC–POPG–cholesterol giant vesicles caused coalescence of the spheroidal membrane bud with the parent vesicle before the bud could detach from the parent vesicle, i.e. vesiculate. Theoretically, the protein-mediated attraction between the membrane of a bud and the parent membrane was described as an interaction between two electric double layers. It was shown that the specific spatial distribution of charge within β2-GPI molecules attached to the negatively charged membrane surface may explain the observed attraction between like-charged membrane surfaces.

Shape and Size of Giant Unilamellar Phospholipid Vesicles Containing Cardiolipin

The effect of cardiolipin content on the shape and size of giant palmitoyloleylphosphatidylcholine/cardiolipin vesicles was studied. Unilamellar vesicles were prepared in sugar solution by the method of electroformation, from mixtures containing up to 50% weight ratio of cardiolipin. At room temperature the vesicles containing cardiolipin exhibited abrupt changes in the curvature of the vesicle contour indicating regions of phase separation. The deviations from the spherical shape were larger if vesicles were made from mixtures with a higher content of cardiolipin. Numerous vesicles with soft fluctuating walls were observed. The estimated size of the vesicles containing cardiolipin was found to be smaller than the size of pure palmitoyloleylphosphatidylcholine vesicles.

Stable Shapes of Thin Anisotropic Nano-strips

Abstract The elastic properties of a thin anisotropic nano‐strip are characterized by its intrinsic mean curvature and intrinsic curvature deviator. It is shown that minimization of the elastic energy of the strip including the deviatoric contribution may explain the stability of the observed helical and twisted shapes of inorganic nano‐strips (helix A and B).

Stability of giant phospholipid vesicles at different concentrations of C/sub 12/E/sub 8/

Membrane properties of giant POPC phospholipids vesicles have been studied in the past. It has been observed that addition of the C/sub 12/E/sub 8/ surfactant may increase the speed of membrane transformation, induce the formation of vesicle protrusions and reduce the lifespan of the POPC vesicles. In this paper we studied the influence of different concentrations of the C/sub 12/E/sub 8/ surfactant on the stability of the giant phospholipids vesicles and the speed of their disintegration. We have observed that at low concentrations of C/sub 12/E/sub 8/ the vesicles eventually adopt a stable shape with the daughter endovesicle and may remain in such state unchanged for at least two hours. At higher concentrations of C/sub 12/E/sub 8/ the vesicles gradually begin to shrink and disintegrate altogether within an hour after addition of the surfactant. We propose possible molecular mechanisms underlying the reported phenomena.