S-layer

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As the S-layer (from the English. Surface layer - the surface layer), crystalline cell wall , S-layer (s) , or envelope proteins refers to membrane-like surface structures of many bacteria and almost all archaea on its cell wall are formed.

The designation "S-layer" (surface layer) was proposed in 1976 and generally accepted at the First International Workshop on Crystalline Bacterial Cell Surface Layers, in Vienna, Austria in 1984. At the workshop of the European Molecular Biology Organization on Crystalline Bacterial Cell Surface Layers in 1987 in Vienna, S-layers were defined as "Two-dimensional arrays of proteinaceous subunits forming surface layers on prokaryotic cells".

For a brief historical overview of the development of S-layer research, see the following publications

Structure of the S-Layer

Schematic illustration of the most common supramolecular architectures of the cell walls of prokaryotic microorganisms with S-layers. S-layers of archaea mostly consist of glycoproteins that have a “mushroom-like” morphology (a) whereby the stem-like, hydrophobic domain is anchored in the plasma membrane. The S-layer glycoproteins can also be anchored via covalently bound membrane proteins (b). Some archaea have a rigid wall component as an intermediate layer between the S-layer and the plasma membrane (c). In Gram-positive bacteria (d) the S-layer (glyco) proteins are mostly connected to the rigid peptidoglycan-containing cell wall layer via specific cell wall polymers. In the Gram-negative bacteria (e) the S-layer is bound to the lipopolysaccharide layer of the outer membrane. Occasionally organisms with more than one S-layer are observed. (Graphics adopted and translated from Reference Sleytr et al. 2014)

In contrast to the cell membrane , which is made up of lipids , the S-layer is usually made up of a single protein (or glycoprotein ) species. These protein monomers are able to self-organize to form layers with a symmetrically arranged lattice. Due to the regular arrangement of these layers, one also speaks of (two-dimensional) crystalline structures or organic crystals . As a rule, the S-layer proteins are non-covalently bound both to one another and to other cell wall components. Depending on the organism, very different S-layers were isolated; some species are even able to develop several different S-layers as required. In the S-layers identified so far, the monomers have a molar mass of 40 to 200  kDa . The layer thickness of the structures formed therefrom is 5 to 20 nm.

Function of the S-Layer

The S-Layer usually represents the outermost (or, as in the case of some archaea, the only) cell wall component and can fulfill different functions depending on the organism. It is assumed that in addition to its shape-forming function, in many cases of archaea the S-layer also serves to protect against harmful environmental influences (e.g. biomineralization ), but also against phages or, in the case of pathogenic germs, against phagocytosis . In addition, the S-Layer is a virulence factor of some bacterial strains, for example it causes Campylobacter spp . the in vivo variability (antigenic shift) and prevents the binding of C3b. In many cases, however, the purpose of this additional cell wall component is unknown; under laboratory conditions some species lose the ability to form S-layers. Recent data indicate that S-layers impart antifouling properties to cell surfaces.

self-organisation

S-layer monomers have the ability to assemble and recrystallize on the cell surface of growing and dividing cells in the form of coherent monomolecular (glyco) protein lattices. The decisive factor here is that the binding forces between the monomers are greater than between the monomers and the underlying cell wall (envelope) components. S layers thus represent the simplest protein membranes that have emerged in the course of evolution. S-layer monomers can be brought to recrystallization in the form of coherent monomolecular layers on a variety of solid supports (e.g. semiconductors, metals, polymers) as well as lipid films, liposomes and emulsomes as well as at other phase boundaries (e.g. water / air) become.

Application potential

Studies on the structure, chemistry, genetics, self-organization and function of S-layers have led to numerous applications in the fields of (nano) biotechnology, biomimetics, biomedicine and synthetic biology. Essential areas of application are derived from the fact that S-layer proteins can be fused with other functional proteins (e.g. enzymes, antibodies, antigens, ligands) and that these fusion proteins retain the ability to recrystallize in suspension, on surfaces and at phase interfaces. S-layers and S-layer fusion proteins can also be used as structural elements for the production of complex supramolecular structures.

Individual evidence

  1. ↑ UB Sleytr: Self-assembly of the hexagonally and tetragonally arranged subunits of bacterial surface layers and their reattachment to cell walls. In: J. Ultrastruct. Res. 55, 1976, pp. 360-367.
  2. ↑ UB Sleytr, P. Messner, D. Pum, M. Sára (Eds.): Crystalline Bacterial Cell Surface Layers . Springer, Berlin 1988, ISBN 3-540-19082-1 .
  3. ↑ a b c U. B. Sleytr, B. Schuster, EM Egelseer, D. Pum: S-layers: Principles and Applications. In: FEMS Microbiology Review. 38, 2014, pp. 823-864. doi: 10.1111 / 1574-6976.12063
  4. ↑ UB Sleytr: . Curiosity and Passion for Science and Art World Scientific Publishing Singapore 2016, ISBN 978-981-3141-81-0 . doi: 10.1142 / 10084
  5. ^ SV Albers, BH Meyer: The archaeal cell envelope. In: Nature Rev. Microbiology. 9, 2011, pp. 414-426.
  6. ^ H. König, H. Claus, A. Varma: Prokaryotic Cell Wall Compounds - Structure and Biochemistry. Springer, Berlin 2010, ISBN 978-3-642-05062-6 .
  7. ^ W. Baumeister, H. Engelhardt: Three-Dimensional Structure of Bacterial Surface Layers. In: JR Harris, RW Horne (eds.): Electron microscopy of proteins. Volume 6, Academic Press, London 1987, pp. 109-154.
  8. ↑ M. Rothbauer, S. Küpcü, D. Sticker, UB Sleytr, P. Ertl: Exploitation of S-layer Anisotropy: pH-dependent Nanolayer Orientation for Cellular Micropatterning. In: ACS Nano. 7, 2013, pp. 8020-8030. doi: 10.1021 / nn403198a
  9. ^ N. Ilk, EM Egelseer, UB Sleytr: S-layer fusion proteins - construction principles and applications. Curr. Opin. Biotech. 22, 2011, pp. 824-831.
  10. ↑ UB Sleytr, P. Messner, D. Pum, M. Sára: Crystalline bacterial cell surface layers (S layers): From supramolecular cell structure to biomimetics and nanotechnology. In: Angew. Chemistry Int. Ed. 38, 1999, pp. 1034-1054. doi : 10.1002 / (SICI) 1521-3773 (19990419) 38: 8 <1034 :: AID-ANIE1034> 3.0.CO; 2- #
  11. ↑ M. Mertig, R. Kirsch, W. Pompe, H. Engelhardt: Fabrication of highly oriented nanocluster arrays by biomolecular templating. In: Eur. Phys. JD D9, 1999, pp. 45-48.
  12. ↑ Reiner Wahl: Regular bacterial cell envelope proteins as a biomolecular template. Dissertation at the Technical University. Dresden 2003, urn : nbn: de: swb: 14-1055925295812-40846

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