Ordered Protein Layers

FIG. 8 Electron micrographs of freeze-etched preparations of whole cells from (a, b) Bacillus sphaericus CCM 2120 exhibiting a square S-layer lattice or from (c, d) Thermoanaerobacter ther-mohydrosulfuricus Llll-69 carrying a hexagonally ordered S-layer lattice, (a, c) Native S-layer lattices (b, d) S-layer lattices after covalent binding of ferritin to carbodiknide-activated carboxylic acid groups of the S-layer protein. Bars, 100 nm. 

Fig. 14 A schematic illustration of an orientated immobilization strategy via crystallized S-layer proteins a side view of the crystalline ordered S-layer proteins fused with the recognition center streptavidin for biotinylated biomolecules probes b front view of the orientated and crystalline ordered S-layer proteins...

The present knowledge about molecular organization in lyotropic liquid crystalline phases is summarized. Particular attention is given to biologicaly relevant structures in lipid-water systems and to lipid-protein interactions. "New findings are presented on stable phases (gel type) that have ordered lipid layers and high water content. Furthermore, electrical properties of various lipid structures are discussed. A simple model of l/l noise in nerve membranes is presented as an example of interaction between structural and electrical properties of lipids and lipidr-protein complexes. 

It is well known that well-ordered (3-chitin (a polysaccharide) associated with a less ordered protein in the (3-sheet conformation is the main component of nacreous organic matrix in shell. The amino acid sequence of such proteins is very similar to those of silk fibroins. Indeed, the amino acid sequence of a major protein from the nacreous shell layer of the pearl oyster resembles that of spidroin (Sudo et al., 1997 Weiner and Traub, 1980). The question of whether silk-like proteins play an important role in shell formation is raised. When Falini et al. (1996) did the experiment with the proteins from the shell, they assembled a substrate in vitro that contained (3-chitin and natural silk fibroin and concluded that the silk fibroin may influence ion diffusion or the accessibility to the chi tin surface or both. Furthermore, cryo-TEM study of the structure of the Atrina shell nacreous organic matrix without dehydration... 

Interactions between proteins and polysaccharides give rise to various textures in food. Protein-stabilized emulsions can be made more stable by the addition of a polysaccharide. A complex of whey protein isolate and carboxymethylcellulose was found to possess superior emulsifying properties compared to those of the protein alone (Girard et al., 2002). The structure of emulsion interfaces formed by complexes of proteins and carbohydrates can be manipulated by the conditions of the preparation. The sequence of the addition of the biopolymers can alter the interfacial composition of emulsions. The ability to alter interfacial structure of emulsions is a lever which can be used to tailor the delivery of food components and nutrients (Dickinson, 2008). Polysaccharides can be used to control protein adsorption at an air-water interface (Ganzevles et al., 2006). The interface of simultaneously adsorbed films (from mixtures of proteins and polysaccharides) and sequentially adsorbed films (where the protein layer is adsorbed prior to addition of the polysaccharide) are different. The presence of the polysaccharide at the start of the adsorption process hinders the formation of a dense primary interfacial layer (Ganzelves et al., 2008). These observations demonstrate how the order of addition of components can influence interfacial structure. This has implications for foaming and emulsifying applications. 

Ideally we would like to use different color tags in order to locate both proteins in a mixture. This requires optical microscopy below the diffraction limit and the use of near-field microscopy. SNOM can be used to visualize the displacement of tagged proteins by surfactants (Gunning et al., 2001) but, at present, the resolution achievable is only about 50 ran. This is not sufficient, at present, to visualize individual proteins in a mixture using different colored tags. Advances in SNOMs should lead to improved resolution and the imaging of mixed protein layers should become possible in the future. 

Fig. 12 Illustration of the difference between the small-load approximation and the perturbation analysis for a film in liquid. Experimental data obtained with an adsorbed protein layer in buffer. Dashed line fit with third-order perturbation analysis. Fit parameters df = 14 nm, = 13 300 GPa , and P =- 1 gold electrodes as in Fig. 11. The viscosity of the buffer was 0.96 cP. Solid line simulation with the small-load approximation and the same model parameters as the input to the dashed line. There is a systematic differeuce. (Experimeutal data kiudly provided by 1. Reviakiue)...

The interaction of protein with water is also an important consideration because the electrical conductivity of the adsorbed protein layer depends on the mechanism of charge transfer. The conduction in proteins with low water content is electronic, whereas at higher water contents it is protonic and/or due to small inorganic ions (35, 36). Water is considered (37) to exist in two structural forms clusters (ordered) formed by hydrogen bonds, and free unbounded water (monomeric). Any factors, such as temperature, that favor monomeric water tend to increase the protein s catalytic activity, and factors favoring cluster formation tend to decrease catalytic activity. In addition, increased catalytic activity is probably related to increased binding properties to foreign surfaces. 

These findings led us to a strategy for optimized protein binding even at well-ordered monolayers by using binary mixtures of biotin -and OH -terminated self-assembly systems. Figure 3 shows the surface-plasmon optical results of the thickness determinations for co-adsorbed SAM s and of their streptavidin binding. The striking result is the maximum protein layer thickness at ca 5-10 mole% biotinylated thiol indi-... 

S-layers represent a fascinating model of self-assembhng a supramolecular structure. In vivo, the S-layer monomers after secretion are transported to the cell surface where they crystallize into a regularly ordered protein lattice that covers the whole cell surface. 

---