Characterization and use of crystalline bacterial cell surface layers

Crystalline bacterial cell surface layers (S-layers) are one of the most co mmon outermost cell envelope components of prokaryotic organisms (archaea a nd bacteria). S-layers are monomolecular arrays composed of a single protei n or glycoprotein species and represent the simplest biological membranes d eveloped during evolution. S-layers as the most abundant of prokaryotic cel lular proteins are appealing model systems for studying the structure, synt hesis, genetics, assembly and function of proteinaceous supramolecular stru ctures. The wealth of information existing on the general principle of S-la yers have revealed a broad application potential. The most relevant feature s exploited in applied S-layer research are: (i) pores passing through S-la yers show identical size and morphology and are in the range of ultrafiltra tion membranes: (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for chemi cal modifications and binding functional molecules in very precise fashion: (iii) isolated S-layer subunits from a variety of organisms are capable of recrystallizing as closed monolayers onto solid supports (e.g., metals, po lymers, silicon wafers) at the air-water interface, on lipid films or onto the surface of liposomes; (iv) functional domains can be incorporated in S- layer proteins by genetic engineering. Thus, Slayer technologies particular ly provide new approaches for biotechnology, biomimetics, molecular nanotec hnology, nanopatterning of surfaces and formation of ordered arrays of meta l clusters or nanoparticles as required for nanoelectronics. (C) 2001 Elsev ier Science Ltd. All rights reserved.