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 T m whereas above T m 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.

Crystalline Bacterial Cell Surface Layers (S Layers): From Supramolecular Cell Structure to Biomimetics and Nanotechnology

“…[195±198] The recrystallization of S layer proteins into coherent monolayer or phospholipid films depends on 1) the nature of the lipid headgroup, 2) the phase state of the lipid film, and 3) the ionic content and pH value of the subphase. [198±201] To obtain more information about the interaction between the S layer protein lattice and lipid membranes and to study how the interaction points influence fluidity in a lipid layer, different biophysical methods including X-ray reflectivity and grazing incidence diffraction, [202] fluorescence recovery after photobleaching, [203] atomic force microscopy, [199] sound velocity and density measurements, [204] and microcalorimetric studies [205] have been performed. As the interaction of the lipid head groups in such composite membranes with the repetitive domains of the associated S layer lattice ( Figure 11) can significantly modulate the characteristics of the lipid film (particularly its fluidity and local order on the nanometer scale), the terminology ªsemifluid membranesº has been used to describe membranes supported by S layers.…”

Self-catalyzed growth of S layers via an amorphous-to-crystalline transition limited by folding kinetics

“…Because SbpA readily forms 2D crystals in vitro in the presence of Ca 2þ , it has been utilized in a broad range of applications both in suspensions and on natural or synthetic surfaces (16-18). In particular, lipid layers carrying zwitterionic groups such as phosphocholine or phosphoethylamine have been adopted to support SbpA crystals on a matrix similar to a natural biological membrane (16,19,20). At least one previous investigation attempted to follow S-layer SbpA growth by AFM, but Si wafers were used as substrates and neither the process of nucleation nor the molecular-scale details of the growth process were observed (15).…”

Biomimetic interfaces based on S-layer proteins, lipid membranes and functional biomolecules

“…S-layer proteins have been recrystallized on glass and modified silicon surfaces before generating a tetraether lipid monolayer (figure 3e) or a BLM (figure 3f ) by the Langmuir-Blodgett (vertical transfer of a lipid monolayer)/ Langmuir-Schaefer (horizontal transfer of a lipid monolayer) (LB/LS) technique [215,216].…”

“…This calculation is based on the lattice constants of SbpA having a square unit cell with a spacing of 13.1 nm [97,116] and an area per lipid molecule of 0.65 nm 2 [246]. These nanopatterned lipid membranes are also referred to as 'semifluid lipid membranes' [95] because of their widely retained fluid behaviour [209,215]. Most important, although peptide side groups of the S-layer protein interpenetrate the phospholipid head group regions almost to their entire depth, no impact on the hydrophobic lipid alkyl chains has been observed [106][107][108]196,207].…”

“…SsLMs prepared by the LB/LS technique without the need for an aperture have been compared with a silane-and dextran-supported phospholipid bilayer [215]. Most probably owing to the repetitive local interaction of the S-layer lattice with the lipid head groups, the nanopatterned fluidity of lipids was highest in SsLMs compared with the other supported bilayers, as determined by the fluorescence recovery after photobleaching technique.…”