Intact lipid vesicles reversibly tethered to a bacterial S-layer protein lattice

The present paper reports on the generation and characterization of a biomimetic scaffolding composed of engineered S-layer proteins and a layer of intact lipid vesicles tethered onto this lattice. For this purpose a His-tag has been fused to a C-terminal truncated form of the S-layer protein SbpA from Lysinibacillus sphaericus CCM 2177 resulting in the recombinant derivative rSbpA/His. Due to the N-terminal interaction of SbpA with the corresponding heteropolysaccharide, which has previously been isolated from L. sphaericus CCM 2177, thiolated, and chemisorbed on gold, rSbpA/His could be self-assembled in the desired orientation presenting the His-tag. Combined SPR, QCM-D, and AFM measurements revealed a regular topography of the rSbpA/His lattice with a thickness of about 11 nm. The effective density of the rSbpA/His layer has been calculated as 1.10 g cm-3 with a volume fraction occupied by the S-layer protein of about 30%. Whereas on plain rSbpA no unspecific adsorption of vesicles could be observed, a layer of vesicles was tethered via the specific nickel–His-tag linkage on rSbpA/His. Thus, the C-terminal, outer surface of the S-layer protein constitutes a surface-repelling element for lipid vesicles. For the vesicular layer estimates of 0.0017 Pa s for the effective viscosity and 32 +/- 20 nm for the thickness, indicating a about 35% flattening of the vesicles on the surface, have been observed. The specific interaction of lipid vesicles and rSpbA/His has been shown to be reversible, allowing the regeneration of the protein surface.