Induced Order and Chain Interdigitation in DPPC/DOPC Asymmetrical Lipid Membranes

Asymmetrical lipid bilayers closely resemble real cell membranes, and their structural and dynamic properties differ significantly from traditional symmetrical membranes. We investigated asymmetrical lipid bilayers consisting of dioleoylphosphatidylcholine (DOPC)/ dipalmitoylphosphatidylcholine (DPPC) at 300 K using Atomistic Molecular Dynamics simulation. The bilayers exhibit acyl chain interdigitation near the bilayer midplane, with DOPC chains penetrating the DPPC leaflet. In addition, the DOPC chains exhibit an increase in order parameter, indicating that the DPPC leaflet induces a higher order in the opposite leaflet. To further explore the effects of induced order, lateral pressure (up to 25 atm) was applied to the DOPC bilayers to reduce their area per lipid by approximately 10% before constructing the asymmetric bilayer. Asymmetric bilayers with uncompressed DPPC and previously compressed DOPC leaflets display reduced interdigitation while maintaining elevated order. Our results highlight some unique features of asymmetrical bilayers that do not appear in symmetrical bilayers, including induced order by the opposite leaflet, induced chain interdigitation, and changes in lipid concentration and composition within individual leaflets.