Lipid domain depletion at small localized bends imposed by a step geometry

Area of Science:

• Biophysics
• Materials Science
• Cell Biology

Background:

• Biological processes depend on precise molecular organization within cell membranes.
• Lipid diffusion in membranes is influenced by kinetic and thermodynamic barriers, including membrane shape.
• Understanding these barriers is crucial for biomembrane engineering.

Purpose of the Study:

• To investigate how membrane topology, specifically step rises, affects lipid domain organization.
• To quantify the energy barriers associated with membrane curvature.
• To explore the potential for designing substrates that control lipid bilayer behavior.

Main Methods:

• Fabrication of supported lipid bilayers on patterned substrates with defined step heights (13 and 27 nm) using spin coating.
• Characterization of substrate topography and lipid bilayer ridge angles using atomic force microscopy.
• Observation of liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence in a lipid mixture (DOPC:DPPC:Cholesterol) doped with a fluorescent lipid.
• Analysis of Lo domain depletion at step rises and correlation with local bending energy.

Main Results:

• Supported lipid bilayers formed on patterned substrates exhibited distinct ridges at step rises.
• Liquid-ordered (Lo) domains were significantly depleted at the membrane step rises.
• Calculated bending energies at the ridges correlated with observed Lo domain densities.
• An energy barrier exceeding 1k(B)T was identified at small deflections (1.3°) from planar geometry, causing Lo domain depletion.

Conclusions:

• Membrane topology, specifically ridges, creates significant energy barriers that spatially control lipid domain organization.
• These topological energy barriers can be engineered using patterned substrates to direct lipid bilayer behavior.
• The findings offer insights into the energetics of cellular membrane structures and provide tools for biomembrane engineering.