Lipids with bulky head groups generate large membrane curvatures by small compositional asymmetries

Area of Science:

• Biophysics
• Computational Biology
• Materials Science

Background:

• Glycolipids, such as GM1, possess bulky head groups that influence phospholipid bilayer structure.
• Previous observations showed that compositional asymmetry in lipid bilayers can lead to spontaneous tubulation of giant vesicles at the micrometer scale.

Purpose of the Study:

• To investigate the nanometer-scale behavior of mixed lipid-glycolipid membranes using molecular simulations.
• To quantify the relationship between lipid composition, membrane curvature, and spontaneous curvature in bilayers.

Main Methods:

• Coarse-grained molecular dynamics simulations were employed to model mixed phospholipid-glycolipid bilayers.
• Density and stress profiles were calculated to determine membrane properties.
• The spontaneous curvature was derived from the stress profiles and leaflet compositions.

Main Results:

• Symmetric and tensionless bilayers composed of phospholipids and glycolipids are stable across all compositions.
• Both area compressibility modulus and bending rigidity exhibit non-monotonic behavior with varying leaflet mole fraction.
• A linear relationship was established between compositional asymmetry and spontaneous curvature, with small asymmetries yielding large curvature values (e.g., 1/(63 nm) for Δϕ = 0.04).

Conclusions:

• Compositional asymmetry in lipid bilayers is a key driver of spontaneous curvature.
• The findings provide a quantitative link between molecular composition and macroscopic membrane shape.
• The significant spontaneous curvature values observed are expected to be crucial for understanding membrane dynamics in processes like vesicle budding and engulfment.