Stable supported lipid bilayers on zirconium phosphonate surfaces.

Supported lipid bilayers that can fully represent biological cell membranes are attractive biomimetic models for biophysical and biomedical applications. In this study, we develop a new approach to engineering stable supported lipid membranes and demonstrate their utility for the study of protein-membrane interactions. This system uses a zirconium phosphonate monolayer to modify a substrate and generate a reactive surface that tethers the lipid membrane via a highly covalent bond between surface zirconium ions and divalent phosphate groups in the lipid assembly, for example, from phosphatidic acid. An advantage of the approach is that the zirconium phosphonate modifier can be applied to nearly any surface, allowing the same methods to be used on glass, gold, silicon, or plastic supports. The lipid bilayers are formed by vesicle fusion, either directly on the zirconated surface to form symmetric bilayers or following deposition of a Langmuir-Blodgett lipid layer to generate asymmetric bilayers. The membrane formation was studied by surface plasmon resonance enhanced ellipsometry (SPREE) as the phosphatidic acid composition was varied. We found that 10% of phosphatidic acid generates supported lipid bilayers stable to dehydration. The two-dimensional fluidity of these systems was characterized by fluorescence recovery after photobleaching (FRAP) measurements. Uniform, mobile supported lipid bilayers with lipid diffusion coefficients of approximately 4 mum(2)/s were obtained. SPREE was also used to measure kinetic parameters of the binding of melittin, a bee venom peptide, to asymmetric lipid bilayers with different electrostatic properties. The results are comparable to those obtained by other research groups, confirming that the model membranes behave as expected. Overall, the results of this study prove that supported lipid bilayers on zirconium phosphonate inorganic surfaces make up an attractive biomimetic system that is highly stable, can be used with multiple substrates, and does not require any biomolecule synthetic modifications.