Membrane nanotechnology based on lipid films, S-layer proteins and secondary cell wall polymers: A biomimetic approach

Living cells build, especially due to an universal molecular construction kit, self-assembly structures in the nanometre scale which perform complex functions in a controllable way. The proposed project applies a construction principle, which is found in nature at the cell envelopes of archaea, to investigate its capability to generate highly specific amperometric sensors. Membrane proteins and membrane-active peptides constitute thereby nanotechnological elements which are in analogy to detectors in electrical engineering. The main problem at the generation of these biosensors is that membrane proteins have to be reconstituted in lipid membranes to retain their native conformation and thus, its functionality. In addition, lipid membranes have to constitute a barrier for ions and small charged molecules to allow low-noise measurements for a long period of time. The suggested solution to this problem is the application of crystalline bacterial cell surface layers (S-layers) which are built up by identical protein subunits. If assembled on solid or porous supports, the nanometre-thick S-layers separate lipid membranes from the inorganic surfaces and stabilize the fragile lipid membranes. Membranes composed of polymerizable lipids can be patterned by UV-light. Polymerized lipids build up a tight isolating layer whereas patches composed of not-irradiated monomeric lipids can be extracted and filling it up with phospho- or tetraether lipids to generate fluid membranes. Further on, an enhanced stability of the layered architectures can be achieved by the use of this construction kit. Solid supports can be covered by the "secondary cell wall polymer" (SCWP) and thus, lectin-like bonds between SCWP and S-layer lattice can be introduced. On the other hand, biotinylated molecules like lipids or membrane proteins can be anchored on streptavidin S-layer fusion proteins. The proposed concept using S-layer (fusion) proteins, SCWP, biotinylated lipids and proteins, phospho- and tetraether lipids, and patterned polymerizable lipids is new and might have considerable impact on the development of solid-supported biomimetic membranes. The latter shall provide application potential in the development of membrane-based biosensors (lipid chips) and in pharmaceutical high throughput screening.

Living cells build, especially due to a universal molecular construction kit, self-assembly structures in the nanometre scale which perform complex functions in a controllable way. The proposed project applies a construction principle, which is found in nature at the cell envelopes of archaea, to investigate its capability to generate highly specific sensors. Membrane proteins and membrane-active peptides constitute thereby nanotechnological elements which are in analogy to detectors in electrical engineering. The main problem at the generation of these biosensors is that membrane proteins have to be reconstituted in lipid membranes to retain their native conformation and thus, its functionality. Lipid membranes, however, should constitute tight structures with a high long-term stability but should at the same time provide a high degree of mobility for lipid molecules within the supported membrane. The suggested solution to this problem is the application of crystalline bacterial cell surface layers (S-layers) which are built up by identical protein subunits. If assembled on solid or porous supports, the nanometre-thick S- layers separate lipid membranes from the inorganic surfaces and stabilize the fragile lipid membranes. As demonstrated by the obtained results an enhanced stability of the layered architectures can be achieved by the use of this construction kit. Solid supports can also be covered by the "secondary cell wall polymer" (SCWP) and thus, lectin-like bonds between SCWP and S-layer lattice can be introduced. On the other hand, molecules like biotinylated linker lipids can be anchored on streptavidin S-layer fusion proteins. Furthermore, a second S-layer cover may be recrystallized on the top acting as molecular sieve to further enhance the long-term stability of the composite membrane. The proposed concept using S-layer (fusion) proteins, SCWP, linker lipids, and phospholipids is new and revealed a considerable impact on the development of solid-supported biomimetic membranes. The latter shall provide application potential in the development of membrane-based biosensors (lipid chips) and in pharmaceutical high throughput screening.