LARGE-SCALE RECONSTITUTION OF CRYSTALLINE BACTERIAL SURFACE-LAYER PROTEINS AT THE AIR-WATER-INTERFACE AND ON LIPID FILMS

Isolated subunits from the crystalline cell surface (S layer) proteins of Bacillus sphaericus CCM2177 could be recrystallized into large coherent double layers at the air-water interface and as monolayers on dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine (DPPE) monolayer films spread on a Langmuir-Blodgett (LB) trough. The recrystallized S layer proteins and the S layer/DPPE layers could be chemically cross-linked from the subphase with glutaraldehyde. This cross-linking step enhanced the stability of the recrystallized S layer protein films and the composite S layer/DPPE layers considerably for subsequent handling procedures. By transferring a second phospholipid film onto the S layer/DPPE layers it was possible to mimic the structural principle of those archaeobacterial cell envelopes which are exclusively composed of a plasma membrane and a closely associated S layer. The high stability of S layer supported lipid membranes and the possibility for producing this composite structure on a large scale by standard LB techniques open new ways for exploiting structural and functional principles of membrane associated and integrated molecules.