Stabilizing effect of an S-layer on liposomes towards thermal or mechanical stress.
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.
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Zentrum für Ultrastrukturforschung und Ludwig Boltzmann-Institut für Molekulare Nanotechnologie, Universität für Bodenkultur Wien, Gregor-Mendelstr. 33, A-1180, Vienna, Austria.
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D001426:Bacterial Proteins / Q000737:chemistry*; D003460:Crystallization; D005452:Fluoresceins; D001411:Geobacillus stearothermophilus / Q000737:chemistry* / Q000235:genetics; D005976:Glutaral; D008081:Liposomes / Q000737:chemistry* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000737:chemistry*; D013314:Stress, Mechanical; D013696:Temperature; D014465:Ultrasonics
D001426:Bacterial Proteins; D005452:Fluoresceins; D008081:Liposomes; D008565:Membrane Proteins; C104635:SbsB protein, Bacillus stearothermophilus; C024098:6-carboxyfluorescein; D005976:Glutaral