GM1 Softens POPC Membranes and Induces the Formation of Micron-Sized Domains

Abstract

The influence of the glycolipid GM1 on the physical properties of POPC membranes was studied systematically by using different methods applied to giant and large unilamellar vesicles. The charge per GM1 molecule in the membrane was estimated from electrophoretic mobility measurements. Optical microscopy and differential scanning calorimetry were employed to construct a partial phase diagram of the GM1/POPC system. At room temperature, phase separation in the membrane was detected for GM1 fractions at and above ∼5 mol %, whereby GM1-rich gel-like domains were observed by fluorescent microscopy. Fluctuation analysis, vesicle electrodeformation, and micropipette aspiration were used to assess the bending rigidity of the membrane as a function of GM1 content. In the fluid phase, GM1 was shown to strongly soften the bilayer. In the region of coexistence of fluid and gel-like domains, the micropipette aspiration technique allowed measurements of the bending rigidity of the fluid phase only, whereas electrodeformation and fluctuation analysis were affected by the presence of the gel-phase domains. The observation that GM1 decreased the bilayer bending rigidity is important for understanding the role of this ganglioside in the flexibility of neuronal membranes.

Highly Efficient Protein-free Membrane Fusion: A Giant Vesicle Study

“…Because the elliptical deformation as induced by the electric field is suppressed during fusion, we can assume that the generated spontaneous tension, which brings back the vesicle to a sphere, is higher than the electric-field tension. The latter can be roughly estimated from the vesicle shape (before the onset of fusion) and field amplitude (74) and in our experiments is on the order of 10 À2 mN/m. This implies that the lower limit of the spontaneous tension is of similar magnitude.…”

Membrane Nanotubes Increase the Robustness of Giant Vesicles

“…We prepared GUVs, composed of the phospholipid POPC, a few mol % of the glycolipid (or ganglioside) GM1, and 0.1 mol % of the fluorescently labeled lipid Texas-Red-DHPE (dihexadecanoylglycerophosphoethanolamine) by electroformation 28 as described in the Methods section. The same preparation method has been previously used in ref 29. However, in contrast to the latter study, we subsequently diluted the vesicle suspension ten-to eleven-fold with native buffer, which led to the formation of stable nanotubes inside the GUVs, reflecting the larger GM1 concentration within the inner bilayer leaflets.…”

“…At room temperature, the binary lipid mixture of POPC and GM1 undergoes phase separation when the mole fraction of GM1 exceeds about 5 mol %. 29 Here, we focused on lipid compositions with 2 and 4 mol % of GM1 for which we did not detect any intramembrane domains.…”

“…The bending rigidity κ of POPC membranes doped with GM1 has been previously measured in ref 29. In the latter study, the GUVs were prepared without the additional dilution step and thus without the GM1 desorption from the outer leaflet that acts to reduce the final GM1 concentration in the membranes.…”

Augmented interaction of multivalent arginine coated gold nanoclusters with lipid membranes and cells

“…This effect was also amplied when increasing the amount of negatively charged lipids present in the lipid bilayer including with GM1 as charged glycolipid 31 (Fig. 3A).…”