Bioinspired hybrid nanomaterials based on self-assembling proteins

Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (Fig. 1a) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements. On other cells, S-layers may act for example as immobilization matrix for exoenzymes, as molecular sieve or as ion and molecule trap.
These properties and their ability to self-assemble in suspension, on surfaces and at interfaces qualify S-layers as interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and novel bio-inorganic hybrid materials with multiple functions can be produced.
Currently three materials are in the focus: metal filters, catalysts and sensors (Fig. 1b). Biocomposites made of microsieves and S-layers are under development to selectively recover strategic metals from aqueous solutions. S-layer proteins with immobilized and regularly arranged metals or metal oxides are useful for diverse catalytic applications. Furthermore, S-layer coatings combining highly specific receptors like aptamers and stable fluorescence dyes are very promising for the construction of new biosensors for organics or pharmaceuticals.
Basis for those materials and their industrial application is an effective production of S-layer proteins. The latter is possible by the extraction of the S-layers from growing cells or by heterologous expression of the proteins. In bacteria or yeasts expressed S-layers can be genetically engineered with molecular modifications to further combine the outstanding S layer protein characteristics with additional expedient features. Native as well as engineered S-layer proteins have an application potential going far beyond above mentioned applications ranging from the chemical industry, water and environmental technologies to medicine.