Lateral Diffusion of Lipids in Silane-, Dextran-, and S-Layer-Supported Mono- and Bilayers

Abstract

Supported lipid bilayers on planar silicon substrates have been formed using crystalline bacterial cell surface (S-layer) protein as support onto which DMPC (pure or mixture with 30 mol % cholesterol) or DPPC bilayers were deposited. Lateral diffusion of fluorescence lipid probes in these layers have been investigated with fluorescence recovery after photobleaching technique (FRAP). For comparison, hybrid lipid bilayers (lipid monolayer on alkylsilanes) and lipid bilayers on dextran composed of the same lipids as for S-layer-supported systems were studied. The mobility of lipids was highest in the S-layer-supported bilayers. No significant difference in mobility was observed for supports of the two S-layer proteins from Bacillus coagulans E38-66 or Bacillus sphaericus CCM2177. DMPC/cholesterol-layers revealed mostly a homogeneous structure, whereas in planar DPPC layers defects could be observed. In S-layer-supported DPPC bilayers, clear cracks could be seen below Tm whereas above Tm inhomogeneous round structures were formed. In another set of experiments the supported bilayers have been covered by S-layer proteins using three different techniques for protein recrystallization (trough, vertical, and horizontal). The recrystallization of S-layers was visualized in large scale by electron microscopy (EM) and more specific on the different substrates by atomic force microscopy (AFM). The S-layer cover induced an enhanced mobility of the probe in the lipid layer. Furthermore it was noticed that the S-layer lattice cover could prevent the formation of cracks and other inhomogenities in the bilayers.