Membrane mechanical properties of synthetic asymmetric phospholipid vesicles

Abstract

Synthetic lipid vesicles have served as important model systems to study cellular membrane biology. Research has shown that the mechanical properties of bilayer membranes significantly affects their biological behavior. The properties of a lipid bilayer are governed by lipid acyl chain length, headgroup type, and the presence of membrane proteins. However, few studies have explored how membrane architecture, in particular trans-bilayer lipid asymmetry, influences membrane mechanical properties. In this study, we investigated the effects of lipid bilayer architecture (i.e. asymmetry) on the mechanical properties of biological membranes. This was achieved using a customized micropipette aspiration system and a novel microfluidic technique previously developed by our team for building asymmetric phospholipid vesicles with tailored bilayer architecture. We found that the bending modulus and area expansion modulus of the synthetic asymmetric bilayers were up to 50% larger than the values acquired for symmetric bilayers. This was caused by the dissimilar lipid distribution in each leaflet of the bilayer for the asymmetric membrane. To the best of our knowledge, this is the first report on the impact of trans-bilayer asymmetry on the area expansion modulus of synthetic bilayer membranes. Since the mechanical properties of bilayer membranes play an important role in numerous cellular processes, these results have significant implications for membrane biology studies.

Mechanical characterization of vesicles and cells: A review

“…Upon a sustained suction, the membrane slips and deforms inside the tube. Studies have reported distinct bending and (membrane surface) area expansion regimes over extended periods of time . In the bending regime (Fig.…”

“…), the lipid bilayer behaves like an incompressible material conserving the total membrane area. On the other hand, in the area expansion regime with higher tensions, the membrane is strained due to the direct expansion of the surface area per lipid molecule .…”

“…Schematic of tension–strain measurement of a giant unilamellar vesicle: (top) the bending regime and (bottom) area expansion regime. Reproduced from with permission from the Royal Society of Chemistry, copyright 2016.…”

Optimization of the Inverted Emulsion Method for High‐Yield Production of Biomimetic Giant Unilamellar Vesicles

“…Any protocol, which uses an oil phase to form lipid membranes should have the membrane inspected. This could be one of the major reasons for lack of widespread acceptance and usage of this method, even though a couple of studies have shown no significant changes in the membrane mechanics of GUVs prepared from inverted emulsions . In addition to this, the method must be optimized for compatibility with a range of salt concentrations and pH values, as well as having charged/uncharged macromolecules inside or outside the GUVs to make them as biomimetic as possible.…”

Mechanical properties of plasma membrane vesicles correlate with lipid order and viscosity and depend on cell density

“…This is partly because bilayer bending rigidity cannot be considered as a simple superposition of the bending rigidities of the composing monolayers (74). Previous studies have indicated large stiffening effects associated with membrane phospholipid asymmetry (75,76), but these effects could be compensated by fast-flipping membrane components such as cholesterol (77), which is abundant in GPMVs. Because we cannot yet control the extent of GPMV lipid asymmetry this questions is not directly addressed here.…”