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.

• Authors: C Mader, S Küpcü, M Sára, U B Sleytr
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 1418 Issue 1 Pg. 106-16 (Apr 14 1999) ISSN: 0006-3002 [Print] Netherlands
• PMID: 10209215 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Bacterial Proteins
• Fluoresceins
• Liposomes
• Membrane Proteins
• SbsB protein, Bacillus stearothermophilus
• 6-carboxyfluorescein
• Glutaral

Topics

• Bacterial Proteins (chemistry)
• Crystallization
• Fluoresceins
• Geobacillus stearothermophilus (chemistry, genetics)
• Glutaral
• Liposomes (chemistry, ultrastructure)
• Membrane Proteins (chemistry)
• Stress, Mechanical
• Temperature
• Ultrasonics