Recrystallization of Bacterial S‐Layers on Flat Polyelectrolyte Surfaces and Hollow Polyelectrolyte Capsules

Abstract

Polyelectrolyte multilayer (PE) deposition and S-layer technology have been combined to make novel robust biomimetic surfaces and membranes. Isolated subunits of the bacterial cell surface layer from Bacillus sphaericus CCM2177 SbpA was self-assembled on PE multilayer supports, with the composition of the multilayer playing a crucial role in determining the structure of the resulting supported protein layers. Flat substrates were studied using atomic force microscopy and neutron reflectometry; protein on suitable PE combinations showed a crystalline structure with lattice constants equal to those found in vivo on bacterial surfaces. The mechanical stability of the S-layer is higher when recrystallized on PEs than directly on silicon supports. The recrystallization process was subsequently used to coat colloidal particles, permitting the determination of zeta potentials before and after coating. Hollow capsules could also be coated in the same way, as proven by various techniques. Our results suggest that electrostatic interactions via divalent cations are important for the assembly process. The results also demonstrate that the versatility of the PE multilayer membranes can be successfully combined with the well-defined surface chemistry and structure of 2D protein crystals.

Chemical and thermal denaturation of crystalline bacterial S‐layer proteins: An atomic force microscopy study

“…S-layers are currently used in biotechnology due to the ability of their subunits to reassemble into monomolecular arrays at the air water-interface (Pum and Sleytr, 1995), and on lipid films (Gufler et al, 2004), liposomes (Mader et al, 2000), solid supports (Gyorvary et al, 2003), and hollow polelectrolyte capsules (Toca-Herrera et al, 2004). They also have been used to make fusion proteins with functional biomolecules (Moll et al, 2002;Völlenkle et al 2004).…”

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

“…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].…”

From Native to Non‐Native Two‐Dimensional Protein Lattices through Underlying Hydrophilic/Hydrophobic Nanoprotrusions

“…Figure 5 a shows forcedistance curves for S-layers formed on SAMs with m = + +6 and m = À6 in water; the difference between the curves reveals that the surface properties are different. The interactions between the AFM tip and the S-layer when m = À6 in water greatly resemble those observed on S-layers deposited on hydrophilic supports, such as silicon wafers, [10] polyelectrolytes, [11] or lipid layers. [14] On the other hand, the long- range repulsion observed when m = + +6 is mainly of electrostatic nature, since it is screened out when electrolyte is added (100 mm NaCl, Figure 5 b).…”

“…m varying from -6 to + 6), while the lattice constants increase from 13 nm (typical values found in bacteria) [7] to 15.5 nm. Furthermore, the S-layer thickness changes from 14-15 nm (a bilayer) [10,11] down to 8 nm (a monolayer), [12,13] as indicated in Table 1. Not only the outcome but also the process is different.…”

“…[7] The S-layers act as selective, protective barriers that mediate cell development. [8] The chemical nanotuner is a set of selfassembled monolayers (SAMs) of dialkyldisulfide derivatives with the formula CH 3 (CH 2 ) 11+m SS(CH 2 ) 11 OH, in which m is the chain-length difference in methylene units between the methyl-and the hydroxy-terminated branches. [9] The resulting surface is composed of OH-and CH 3 -terminated thiolates in a stand-up conformation with a defined chemical functionality ratio of 50 %.…”