S-layer protein

Surface layer proteins (S-layers) represent a unique self-assembling system. Their remarkable property of self-assembUng and their repetitive physicochemical properties, down to the nanometer scale, are promising for various applications. 

Messner, P., 1996. Chemical composition and bios3Tithesis of S-layers. In Sleytr, U.B., Messner, P., Pum, D., Sara, M. (Eds.), Crystalline Bacterial Cell Surface Layer Proteins (S-layers). Academic Press, Landes Company, Austin, TX, pp. 35—76. 

Chapter 3, Self-assembly of nanobiomaterials, prepared by Varga et al., offers a recent review regarding the surface-layer proteins (S-layers) that represent a unique self-assembling system. Their remarkable property of self-assembling and their repetitive physicochemical properties down to the nanometer scale led to various applications in the fields of bio- and nanotechnology. Chapter 3 focuses on the basic principles and self-assembly properties of the S-layer protein of Sporosarcina ureae. 

Leokband D et al 1993 Measurements of oonformational ohanges during adhesion of lipid and protein (polylysine and S-layer) surfaoes Biotech. Bloeng. 42 167-77... 

Molecular Nanotechnology and Nanobiotechnology with Two-Dimensional Protein Crystals (S-Layers)... 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

FIG. 1 Freeze-etching image of a bacterial cell of (a) Desulfotomaculum nigrificans (bar, 100 nm). Atomic force micrographs of the S-layer proteins of (b) Bacillus sphaericus CCM 2177 and (c) Bacillus stearothermophilus PV72/p2 recrystallized in monolayers on silicon wafers. Bars, 50 nm. The insets in (b) and (c) show the corresponding computer-image reconstructions. 

FIG. 3 Three-dimensional model of the protein mass distribution of the S-layer of Bacillus stearothermophilus NRS 2004/3a [(a) outer, (b) inner face]. The square S-layer is about 8 nm thick and exhibits a center-to-center spacing of the morphological units of 13.5 nm. The protein meshwork composed of a single protein species shows one square-shaped, two elongated, and four small pores per morphological unit. (Modified from Ref. 7.)... 

In most S-layer proteins, about 20% of the amino acids are organized as a-helices and about 40% occur as P-sheets. 

Posttranslational modifications of S-layer proteins include cleavage of N- or C-terminal fragments, glycosylation, and phosphorylation of amino acid residues. 

TABLE 2 Survey of S-Layer Proteins Whose Amino Acid Sequences Are Known... 

Most important for many applications of S-layer lattices in molecular nanotechnology, biotechnology, and biomimetics was the observation that S-layer proteins are capable of reassembling into large coherent monolayers on solid supports (e.g., silicon wafers, polymers, metals) at the air/water interface and on Langmuir lipid films (Fig. 6) (see Sections V and VIII). 

The influence of attaching different nucleophiles to the EDC-activaed carboxylic acid groups from the S-layer protein on the adsorption of selected test proteins was evaluated via relative flux losses (1 — Rf, given X 100 in %) of SUMs after filtration of the respective protein solution (BSA, OVA, CA, MYO). 

To conclude, a strong correlation was found to exist between the net charge of the proteins in solution, the net charge of the SUM surface, and the extent of protein adsorption, which was expressed in terms of flux losses measured after filtration of the different protein solutions. Moreover, in the case of charge-neutral SUMs, flux losses increased with the hydrophobicity of the nucleophiles bound to the S-layer lattice. All proteins caused higher flux losses on SUMs modified with HDA than on those modified with GME or... 

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