(37f) Raft Registration Across Bilayers by Coarse-Grained Molecular Dynamics

Membrane lateral heterogeneity is accepted as a requirement for the function of biological membranes. The raft hypothesis embodies this concept, and lipid rafts are generally believed to be spatially co-localized across the membrane i.e. registration. Lateral order-disorder phase segregation has also been seen in polymer vesicles with registration of the domains at both sides of the leaflets. Registration mechanisms remain undetermined and several suggestions have been made: including chain interdigitation, cholesterol translocation in the case of lipids, interfacial energy, electrostatic coupling, van der Waals interactions and composition-curvature coupling.

We show that registration is spontaneous in coarse grained molecular dynamics simulations in a model completely devoid of charges and simply reparametrized from a previous polyethylene glycol (PEG) surfactant model. Electrostatic coupling is clearly not necessary and interfacial energy does not seem the only factor inducing the registration; instead, our results revealed that membrane curvature plays a key role. Distortions of the disordered phase play an important role in helping the ordered domains in opposite leaflet sense the proximity of each other.