Behavior of supported phospholipid bilayers both by themselves and after introduction of relevant materials including polymers and proteins

Lipid bilayer morphology of the ordered gel state and disordered liquid state, in addition to the phase transition behavior between them have been examined using AFM and ellipsometry.  For example, we showed that supported bilayers, unlike lipid vesicles in solution, exhibit two gel-to-fluid phase transitions because the two lipid leaflets are decoupled as shown in the Figure.  The origin of this decoupling is the strong interaction of the lower bilayer leaflet with the support.  This finding has important implications to the use of supported lipid bilayers as model systems for processes occurring at cell and organelle membranes. 

Presently, we are examining the interaction of different proteins and polymers with mixed lipid bilayer films as a function of temperature, pressure, and applied field.  The incorporation of different proteins and lipid species in bilayer films is investigated to develop an understanding of the basis for non-equilibrium behavior such as rafting and budding.  In these processes, proteins and other cell membrane constituents change the physical properties of the bilayer and give rise to spatial localization not seen in the fluid phase alone. 

Figure: MAC-mode AFM images from DMPC bilayer on mica at indicated temperatures(a-h) (5 ´5 µm); (c) reveals the transition within one downwards scanning image (i) shows the relationship between protrusion percentage coverage and temperature.