(613h) Structure of Multi-Component, Gel-Phase Lipid Bilayers

The composition of lipid membranes has a strong impact on the membrane’s structure and transport properties. While fluid-phase phospholipid bilayers have been studied extensively, far less is known about how lipid composition and packing influence the behavior of dense, gel-phase bilayers. Molecular dynamics (MD) simulations of multi-component, gel-phase bilayers of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), free fatty acids (FFA), and alcohol (OH) molecules of varying chain lengths and composition are used to elucidate the role of lipid composition on gel-phase membranes. Specifically, binary and ternary systems are studied, and the effect of molecular substitution, chain length and DSPC fraction on the bilayer properties are examined. In agreement with previous work^1,2, large headgroups are found to increase the area-per-lipid, area-per-tail, and tilt angle, while longer chain lengths increase the bilayer height. Interdigitation is found to depend on the relative fraction of the protruding tails and tail length asymmetry between molecular groups. Both binary and ternary systems demonstrate placement of molecular groups at different depths within the bilayer as a result of the competing molecular interactions. The relative depths of molecules can subsequently affect further displacement within the bilayer due to steric repulsions, tail interactions, and electrostatic forces from multiple components. Alcohol molecules located at a depth between two molecular groups push the deeper group deeper into the bilayer due to steric repulsions overcoming any electrostatic attraction. Free fatty acid molecules located at a depth between two molecular groups attract the deeper group closer to the bilayer surface due to electrostatic attractions overcoming steric repulsions. Finally, depending on the length of tails, interdigitation can drive molecular groups deeper within the bilayer or closer to the surface. The balance between steric repulsions from head groups, van der Waals interactions from tails, and electrostatic interactions affects the structure of multi-component, gel-phase bilayers in complex, yet rational ways.

Works Cited:

[1] Hartkamp, R.; Moore, T. C.; Iacovella, C. R.; Thompson, M. A.; Bulsara, P. A.; Moore, D. J.; McCabe, C. Journal of Physical Chemistry B, 2016, 120, 12863-12871

[2] Hartkamp, R; Moore, T. C.; Iacovella, C. R.; Thompson, M.; Bulsara, P; Moore, D. J.; McCabe, C. Biophysical Journal, 2016, 111, 813-823