Effect of anionic lipids on mammalian plasma cell membrane properties

The effect of lipid composition on models of the inner leaflet of mammalian cell membranes has been investigated. Grazing incidence X-ray diffraction and X-ray and neutron reflectivity have been used to characterize lipid packing and solvation, while electrochemical and infrared spectroscopic methods have been
employed to probe phase behavior in an applied electric field. Introducing a small quantity of the anionic lipid dimyristoylphosphatidylserine (DMPS) into bilayers of zwitterionic dimyristoylphosphatidylethanolamine (DMPE) results in a significant change to bilayer response to an applied field: the tilt of the hydrocarbon
chains increases before returning to the original tilt angle on detachment of the bilayer. Equimolar mixtures, with slightly closer chain packing, exhibit a similar but weaker response. The latter also tend to incorporate more solvent during this electrochemical phase transition, at similar levels to pure DMPS. Reflectivity
measurements reveal greater solvation of lipid layers for DMPS >30 mol%, matching the greater propensity for DMPS-rich bilayers to incorporate water. Taken together, the data indicate that the range 10-35 mol% DMPS provides optimum bilayer properties (in flexibility and function as a barrier), which may explain why the DMPS content of cell membranes tends to be found within this range.