Pore Formation in a Binary Giant Vesicle Induced by Cone-Shaped Lipids

Abstract

We have investigated shape deformations of binary giant unilamellar vesicles (GUVs) composed of cone- and cylinder-shaped lipids. By coupling the spontaneous curvature of lipids with the phase separation, we demonstrated pore opening and closing in GUVs. When the temperature was set below the chain melting transition temperature of the cylinder-shaped lipid, the GUVs burst and then formed a single large pore, where the cone shape lipids form a cap at the edge of the bilayer to stabilize the pore. The pore closed when we increased the temperature above the transition temperature. The pore showed three types of shapes depending on the cone-shaped lipid concentration: simple circular, rolled-rim, and wrinkled-rim pores. These pore shape changes indicate that the distribution of the cone- and cylinder-shaped lipids is asymmetric between the inner and outer leaflets in the bilayer. We have proposed a theoretical model for a two-component membrane with an edge of bilayer where lipids can transfer between two leaflets. Using this model, we have reproduced numerically the observed shape deformations at the rim of pore.

Induction of Highly Curved Structures in Relation to Membrane Permeabilization and Budding by the Triterpenoid Saponins, α- and δ-Hederin

“…The induction of spontaneous curvature induced by ␣-hederin is supported by the following: (i) nonbilayer structures with a higher rate of Brownian tumbling or lateral diffusion around the vesicle observed by 31 P NMR (64,65) in accordance with the reduction of the chemical shift anisotropy; (ii) the new structures of different sizes evidenced by dynamic light scattering; (iii) the decrease of GP ex and DPH fluorescence anisotropy values observed at 37°C (42, 63); (iv) the formation of macroscopic pores (16), and (v) budding (66).…”

“…The rim of the pore rolled itself up through the external side of the membrane (Fig. 10, A-C), resulting in the rolled rim shape as described by Sakuma et al (16). When the complete vesicle had been "rolled up," the resulting form often resembled an angulated torus (Fig.…”

“…This would lead to the formation of pores, small buds, and/or micelles, which is in accordance with our results. The critical role of a three-dimensional molecular shape and the ability to induce curvature have also been proposed to explain membrane permeabilization induced by the following: (i) dioscin (71); (ii) glycoalkaloids (10); (iii) coneshaped amphiphiles (57), and (iv) cone-shaped lipids (16).…”

“…Appearance of Membrane Deformations, Micrometric Pore Formation, and Budding-To ascertain the critical role of the sugars branched on the genin, we aimed to visualize the earliest alterations induced by ␣-hederin, ␦-hederin, and hederagenin and their ability to promote shape deformations on GUVs containing cholesterol (16). An initial image was captured immediately after the addition of GUVs to the solution containing the compound.…”

“…1) with cholesterol and to identify their membrane permeabilizing ability. To understand the molecular mechanism involved and to establish a model explaining their ability to induce membrane permeabilization, we used complementary information afforded by lipid models of mem-branes (large unilamellar vesicles (LUV), 2 multilamellar vesicles (MLV), and giant unilamellar vesicles (GUV)) (13)(14)(15)(16).The biological relevance of our study and the importance of membrane cholesterol for cytotoxicity were ascertained by monitoring the effect of ␣-hederin on a human monocytic cell line depleted or not for cholesterol.…”