S-Layer Architectures: Extending the Morphogenetic Potential of S-Layer Protein Self Assembly.

摘要

Nature has developed a broad range of nanometer scale architectures based on the self-assembly of molecular building blocks. An outstanding example has been optimized by nature is Crystalline bacterial surface layers, termed S- layers. Based on the detailed knowledge about S-layer proteins, the fabrication of three-dimensional hollow S-layer protein cages was defined as the main objective of this project. S-layers are the most commonly observed cell surface structures in prokaryotic organisms (bacteria and archaea). S-layers are highly porous protein meshworks with unit cell sizes in the range of 3 to 30 nm and pore sizes of 2 to 8 nm. One of the most important properties for this project is their intrinsic tendency to reassemble into two-dimensional arrays in solution and at various interfaces. S-layer coated liposomes have paved the way towards spatially expanded architectures. The mechanical robustness of S-layer coated liposomes was obtained by subsequent deposition of a thin layer of biogenic silica. Hollow S-layer protein cages were finally obtained after dissolution of the supporting liposomes with detergents. Proof-of-principle was shown by using liposomes previously filled with fluorescent dyes as scaffolds for S-layer reassembly and silica deposition and studying disruption and release of the dyes by fluorimetry. TEM and Electron Energy loss Spectroscopy (EELS) confirmed that hollow S-layer protein cages had been obtained. In addition, 2-3 micron sized nanocapsules with calcium carbonate (CaCO3) as core material were used as spherical scaffolds, too. The particles could be downsized to a few hundred nanometers. The particles were fluorescently labeled, coated with S-layer protein and silicified. Dissolution of the core lead to stable silica supported S-layer architectures as demonstrated by fluorescence microscopy and SEM.