Artificial Membranes Using Langmuir-Blodgett Films

Model Lipid Membranes

Understanding the functional roles of lipids in biological membranes has continued to evolve since the introduction of the fluid mosaic model in 1972.  Far from being passive matrices that simply support membrane constituents, lipids now appear to provide active roles in organizing and modulating events at the cellular membrane.  One of the more intriguing and enigmatic roles that has emerged from these studies involves the formation of nanometric lipid domains termed lipid rafts.  These small, dynamic domains represent compositional heterogeneities in the membrane that are thought to be important in signaling and organizational processes. 

The formation of domains in complex mixtures, such as those found in biomembranes, is neither surprising nor unexpected.  Characterizing their physical, chemical, and biological properties, however, has proven problematic in natural membranes given the complexity of the system and often lack of clear controls.  Moreover, the small size and dynamic nature of lipid rafts makes them difficult to probe directly in intact membranes, which has led to some controversy in the literature.  These challenges have led to the widespread use of model membranes where specific interactions can be probed in highly controlled environments.  These studies have proven invaluable for understanding how putative raft components interact in various lipid environments and identifying key interactions that modify membrane structure.  For example, these studies have characterized the formation of domains in lipid membranes, elucidated the effect of cholesterol on membrane fluidity, and characterized the complex partitioning of lipid raft components.  For the latter, studies involving the ganglioside GM1, a putative raft component, illustrates the complexity that can be encountered even in simple membrane mixtures.