Bacterial and archaeal S-layer proteins: structure-function relationships and their biotechnological applications

Crystalline cell surface layers (S-layers) composed of planar assemblies of protein or glycoprotein subunits are one of the most commonly observed cell envelope structures of bacteria and archaea. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at liquid-surface interfaces, including lipid films, on liposomes and on solid supports. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattices are aligned in well-defined positions and orientations. These characteristic features of S-layers have led to various applications in biotechnology, vaccine development, diagnostics, biomimetics and molecular nanotechnology.