Lateral diffusion of lipids in silane-, dextran-, and S-layer-supported mono- and bilayers

Supported lipid bilayers on planar silicon substrates have been formed usin g crystalline bacterial cell surface (S-layer) protein as support onto whic h DMPC (pure or mixture with 30 mol % cholesterol) or DPPC bilayers were de posited. Lateral diffusion of fluorescence lipid probes in these layers hav e been investigated with fluorescence recovery after photobleaching techniq ue (FRAP). For comparison, hybrid lipid bilayers (lipid monolayer on alkyls ilanes) 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 Df the two S-layer proteins from Bacillus coagulans E 38-66 or Bacillus sphaericus CCM2177. DMPC/cholesterol-layers revealed most ly a homogeneous structure, whereas in planar DPPC layers defects could be observed. In S-layer-supported DPPC bilayers, clear cracks could be seen be low T-m whereas above T-m inhomogeneous round structures were formed. In an other set of experiments the supported bilayers have been covered by S-laye r proteins using three different techniques for protein recrystallization ( trough, vertical, and horizontal). The recrystallization of S-layers was vi sualized in large scale by electron microscopy (EM) and more specific on th e different substrates by atomic force microscopy (AFM). The S-layer cover induced an enhanced mobility of the probe in the lipid layer. Furthermore i t was noticed that the S-layer lattice cover could prevent the formation of cracks and other inhomogenities in the bilayers.