Investigating the formation of patterns in lipid bilayers with the coexistence of liquid phases

The cell membrane is a complex system composed of assorted phospholipids and cholesterol. Model membranes prepared in vitro using controlled and precise methods show that lipid mixtures mimicking the composition of the plasma membrane outer leaflet can form a coexistence of liquid phases, namely liquid-disordered (Ld) and liquid ordered (Lo) phases. These phases have distinct properties, such as the Lo phase being more ordered, stiff, and thicker. We can effectively model this system by examining the competition of interactions between the line tension and the repulsive interactions that arise from the Lo phase. Line tension is an interfacial tension originating from the contact of Ld and Lo phases in the domain boundary. Depending on the lipid composition and, consequently, the lipid interaction of the system, domains can coalesce, forming large domains. Changes in lipid composition and reduced domain line tension may break domains apart, resulting in smaller domains. Further decreases in line tension drive the formation of modulated phases. Here we prepare Giant Unilamellar Vesicles (GUVs) with different lipid compositions, and we tune the line tension by varying the fraction of a hybrid lipid that acts as a weak line active. We investigate and compare the correlation function of different patterns from confocal microscopy images of these GUVs. We calculate the correlation function from the images, and we compare the correlation length for different morphologies. This analysis has been optimized to help us uncover how effectively lineactant molecules can alter domain morphologies. Interestingly, the Ld/Lo interface can act as a defect, rendering the bilayer more vulnerable to viral infiltration. Lineactant such as Vitamine E decreases the hydrophobic mismatch of the interface, decreasing susceptibility to virus infection.