APPLICATIONS OF S-LAYERS

The wealth of information existing on the general principle of S-layer s has revealed a broad application potential. The most relevant featur es exploited in applied S-layer research are: (i) pores passing throug h S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and i n the pores are aligned in well-defined positions and orientations and accessible for binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from many organisms are capable of rec rystallizing as closed monolayers onto solid supports at the air-water interface, on lipid monolayers or onto the surface of liposomes. Part icularly their repetitive physicochemical properties down to the subna nometer scale make S-layers unique structures for functionalization of surfaces and interfaces down to the ultimate resolution limit. The fo llowing review focuses on selected applications in biotechnology, diag nostics, Vaccine development, biomimetic membranes, supramolecular eng ineering and nanotechnology. Despite progress in the characterization of S-layers and the exploitation of S-layers for the applications desc ribed in this chapter, it is clear that the field lags behind others ( e.g. enzyme engineering) in applying recent advances in protein engine ering. Genetic modification and targeted chemical modification would a llow several possibilities including the manipulation of pore permeati on properties, the introduction of switches to open and close the pore s, and the covalent attachment to surfaces or other macromolecules thr ough defined sites on the S-layer protein. The application of protein engineering to S-layers will require the development of straightforwar d expression systems, the development of simple assays for assembly an d function that are suitable for the rapid screening of numerous mutan ts and the acquisition of structural information at atomic resolution. attention should be given to these areas in the coming years.