title: Lipid domain depletion at small localized bends imposed by a step geometry.
abstract: Natural processes in biological cells rely on molecules to be in the right place at the right time to maintain the dynamics of living processes. When lipids in bilayer membranes move and mix, they experience kinetic and thermodynamic barriers that affect the time scales of their locations and associations with each other. One of these barriers is that of the membrane shape. Using spin coating as a deposition technique, we formed multilamellar supported lipid bilayers on topologically patterned substrates with defined step rise heights of 13 and 27 nm measured by atomic force microscopy. Each step rise imposed two ridges on the lipid bilayers, and the ridge angles were measured by atomic force microscopy. The lipid composition of this system was 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and cholesterol (4:4:2), doped with a fluorescent lipid, which displays liquid-ordered-liquid-disordered (Lo-Ld) phase coexistence upon cooling to 25 °C. The DPPC-rich Lo domains in the upper bilayers were established to have boundaries and positions that responded to local forces. We found that these Lo domains were depleted at the location of each step rise. We employed an equation for local bending at a ridge and demonstrate that Lo domain densities at each rise correspond to these energies. Remarkably, an energy barrier greater than 1k(B)T is erected at a small deflection (1.3°) from planar geometry at the ridge, resulting in depletion of the majority of the optically visible Lo domains from the step rise. This work provides a means to design substrates that, in conjunction with supported lipid bilayers, provide defined localized topological energy barriers that can be used in biomembrane engineering. It also provides a method for easily analyzing the energetics of cusp-like shapes in cellular membrane structures.
authors.affiliation: Biophysics Graduate Group, and ‡Department of Chemical Engineering and Materials Science, University of California , Davis, California 95616, United States.
authors.forename: Matthew I
authors.initials: MI
authors.lastname: Hoopes
authors.forename: Roland
authors.initials: R
authors.lastname: Faller
authors.forename: Marjorie L
authors.initials: ML
authors.lastname: Longo
mesh_terms: D000327:Adsorption; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D008055:Lipids