Stabilizing effect of an S-layer on liposomes towards thermal or mechanical stress

Abstract

Isolated subunits of the crystalline cell surface layer (S-layer) protein of Bacillus stearothermophilus PV72/p2 were recrystallized on positively charged unilamellar liposomes. Liposomes were composed of dipalmitoylphosphatidylcholine (DPPC), cholesterol and hexadecylamine (HDA) in a molar ratio of 10:5:4 and they were prepared by the dehydration-rehydration method followed by an extrusion procedure. The S-layer protein to DPPC ratio was 5.7 nmol/micromol which approximately corresponds to the theoretical value estimated by using the areas occupied by the S-layer lattice and the lipid membrane. Coating of the positively charged liposomes with S-layer protein resulted in inversion of the zeta-potential from +29.1 mV to -27.1 mV. Covalent crosslinking of the recrystallized S-layer protein was achieved with glutaraldehyde. Chemical analysis revealed that almost all amino groups (>95%) from HDA in the liposomal membrane were involved in the reaction. To study the influence of an S-layer lattice on the stability of the liposomes, the hydrophilic marker carboxyfluoresceine (CF) was encapsulated and its release was determined for plain and S-layer-coated liposomes in the course of mechanical and thermal challenges. In comparison to plain liposomes, S-layer-coated liposomes released only half the amount of enclosed CF upon exposure to shear forces or ultrasonication as mechanical stress factors. Furthermore, temperature shifts from 25 degrees C to 55 degrees C and vice versa induced considerably less CF release from S-layer-coated than from plain liposomes. A similar stabilizing effect of the S-layer lattice was observed after glutaraldehyde treatment of plain and S-layer-coated liposomes.

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

“…This is the orientation identical to the S-layer lattice on intact cells. Coating of the positively charged liposomes with the S-layer protein SbsB from G. stearothermophilus PV72/p2 resulted in inversion of the zeta-potential from an initially positive value to a negative one [114]. A similar behaviour was observed for liposomes coated with S-layer proteins from lactobacilli [227,228].…”

“…The SAMs carried methyl, hydroxyl, carboxylic acid or mannose, respectively, as terminating functional groups. It was confirmed that electrostatic interaction (carboxylic acid functional groups) induces a faster adsorption than hydrophobic (methyl groups) or hydrophilic (hydroxyl groups) interaction-as already shown for the reattachment on the bacterial cell [75,112] and at liposomes and polyelectrolyte nanocapsules [113][114][115][116].…”

“…Furthermore, S-layer lattices as the outermost envelope structure covering the spherical containers constitute biomimetic 'artificial cell envelopes' or 'artificial virus-like particles', both enabling stabilization of the nanocarriers and presenting addressor molecules in a well-defined orientation and special distribution (figure 4). Isolated S-layer subunits were recrystallized on positively charged, unilamellar liposomes comprising 1,2-dipalmitoylsn-glycero-3-phosphocholine (DPPC), cholesterol and hexadecylamine [22,114,115]. The S-layer attached to positively charged liposomes by their inner, negatively charged face.…”

S-layer-streptavidin fusion proteins as template for nanopatterned molecular arrays

“…The chargeable nanopatterned surface or interface also allows new approaches for diagnostics, affinity matrices, enzyme membranes, biocompatible surfaces, biological templating, and composite vaccines (5,27,28). Furthermore, the S-layer-coated liposomes mimic the cell envelope of archaea, and the lipid membrane is stabilized by the S-layer (18). In combination with the affinity to biotinylated binding partners, 5-layer-stabilized liposomes offer new prospects for liposome targeting, drugdelivery systems, and the design of biomimetic virus envelopes and vehicles for gene therapy.…”

S-Layer Proteins

“…Whole-cell preparations or partially purified cell products are currently used as attenuated vaccines against fish pathogens (57,143). Another broad application for S-layers is based on the ability of subunits to recrystallize into coherent lattices on functional lipid membranes (105,135), including liposomes (68,75,94). These S-layer-stabilized lipid membranes mimic the supramolecular structure of those archaeal envelopes which possess S-layers as exclusive wall components or virus envelopes.…”