S-layer ultrafiltration membranes: A new support for stabilizing functionalized lipid membranes

We report on a simple method to generate bilayer membranes on a smooth laye r of crystalline bacterial cell surface (S-layer) protein lattices, deposit ed on a microfiltration membrane (MFM), the so-called S-layer ultrafiltrati on membrane (SUM). Folded bilayers, MFM-, and SUM-supported lipid membranes showed a specific capacitance of 0.6-0.7 muF/cm(2). The S-layer produced a stabilizing effect on the lipid membrane; folded and MFM-supported membran es ruptured at the application of a first and a second voltage ramp, respec tively, whereas the SUM-supported membranes could withstand multiple voltag e ramps. The lifetime of the lipid membranes increased significantly in the order MFM-supported membrane < folded membrane < SUM-supported membrane. B y contrast with MFM-supported lipid membranes, successful reconstitution of staphylococcal alpha -hemolysin (alpha HL) was observed in both folded and SUM-supported membranes. The unitary conductance of an alpha HL pore was s imilar when reconstituted in folded and in SUM-supported lipid membranes. A s an alternative to hybrid and tethered lipid membranes, SUM-supported lipi d bilayers provide a biomimetic environment for transmembrane proteins.