Line Active Hybrid Lipids Promote the Formation of Nanoscale Domains in Model Membranes

A ternary mixture model is proposed to describe the phase behavior of model membranes composed of saturated, unsaturated and line active hybrid lipids. In particular, the formation and the stability of nanoscale domains, motivated by the presence of lipid rafts in cells, are studied. The asymmetric hybrid lipid (with one saturated and one unsaturated chain) can reduce the packing incompatibility between domains of saturated and unsaturated lipids by residing at their boundary. The model predicts the nanostructure and phase behavior by taking into account the dependence of the interactions of the hybrid lipids on their orientations in a simple manner. In the single phase, mixed regime, the theory predicts correlation lengths and correlation times that are, respectively, shorter and longer when hybrid lipids are added. Nanoscale fluctuation domains similar to lipid rafts are more probable and have longer lifetimes than in two-component, saturated/unsaturated mixtures. In the phase separated (coexistence) regime, zero line tension between domains rich in saturated/unsaturated lipids is predicted to occur at physiologically relevant temperatures and large hybrid fractions. Under these conditions, the membrane can spontaneously form more interfaces and promote the formation of stable nanoscale domains.

 

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