Researchers from the Forschungszentrum Rossendorf (FZR) in Dresden, Germany have, for the first time, exactly characterized the bonding between metals and the surface protein layer (S-layer) of Bacillus sphaericus. This paves the way for the genetic engineering of the protein to enable the construction of materials with new optic, magnetic, catalytic, and other novel physical properties.
Bacillus sphaericus, discovered in 1997, is able to survive in the extreme environment of a uranium mining waste pile. The S-layer of the bacterium exhibits a high metal-binding capacity that likely provides a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nanosized heavy metal cluster arrays.
The S-layer of B. sphaericus is very regularly structured with pores of identical size on the nanometer scale. On this grid-like matrix, a team of FZR biologists applied a metallic salt of palladium ions to investigate the metal-protein interactions and their impact on the secondary structure using a variety of methodologies.
Within the pores of the S-layer, the metallic salt is transformed into the noble metal palladium by the use of hydrogen. The result are nanoclusters of metallic palladium, each comprising of 50 to 80 atoms, which are regularly arranged on the surface layer.
This combined metal-protein layer shows new physical and chemical effects. Because the metal stabilizes the protein and vice versa, the S-layer stays stable to higher temperatures or even in an acidic environment. In relation to their size the nanoclusters possess many atoms on the surface where other substances can bind.
Palladium is often used as a catalyst in the chemical and automotive industries. Nano-catalysts made from palladium offer the prospect of accelerating chemical reactions even at low temperatures, and several laboratories are already producing and testing this new technology.
By decoding the mechanism through which the bacteria bonds noble metals on its protective surface layer, the FZR team is targeting the production of innovative nano-catalysts out of noble metals such as gold or modelling the size of the metallic nanoclusters. This could lead to more efficient nano-catalysts or to completely new fields of application.
The results are published in the Biophysical Journal.
“Secondary Structure and Pd(II) Coordination in S-Layer Proteins from Bacillus sphaericus Studied by Infrared and X-Ray Absorption Spectroscopy”; Karim Fahmy, Mohamed Merroun, Katrin Pollmann, Johannes Raff, Olesya Savchuk, Christoph Hennig and Sonja Selenska-Pobell; Biophysical Journal 91:996-1007 (2006)