Nano-Structuring and Molecular Domain Organizations in Lipid-Protein Membranous Interfaces

Cell membranes, lung surfactants and other liquid crystalline systems have become an interesting area for structural studies, due to recent evidence suggesting that such supra-molecular assemblies have micronano scale organizations or domains. Such domains play a critical role in functioning of membrane proteins, as well as phase segregation and liquid ordering of soft-materials in two dimensions. These domains can be imaged dynamically from an air-water interface of Langmuir films of 17-25 Å thickness using a number of correlated physico-chemical methods. We have employed a series of correlated imaging techniques such as fluorescence, atomic force microscopy (AFM), time of flight-secondary ion mass (TOF-SIMS) and Raman-confocal spectroscopy to image micro and nano-scale organizations of specific components in lipid-rafts, bacterial and lung surfactant membranes. Using fluorescence, AFM and Raman the phase transition process and their respective domains in liquid-crystalline, gel and fluidordered states in monolayer films and bilayer liposomes could be dynamically observed. The lipid confirmations, tilt, specific lipid compositions of domains in some of these systems could also be imaged. Some recent evidence indicates that structural disorganization and anisotropy of domain structures detected using these imaging methods in membrane dysfunction, may allow for a better understanding of the molecular basis of some disease forms.