Novel Fe-S structure allows the development of more efficient catalysts
Iron-sulfur (Fe-S) complexes are central to the activity of a whole array of natural enzymes and synthetic catalysts, such as enzymes that bind nitrogen oxide, and catalysts that remove sulfur from oil. But the discovery of a natural Fe-S complex with a unique structure and novel activity could lead to the development of much more efficient catalysts, report a chemist and biochemist from Brookhaven National Laboratory, New York, US.
The most common type of Fe-S complex found in proteins consists of two iron atoms and two sulfur atoms, where each iron atom binds to two amino acids, usually cysteines. However, researchers recently isolated a protein from the bacterium Desulfovibrio desulfuricans that possessed an Fe-S complex that seemed to differ from this standard. This novel complex reacts much more strongly with oxygen than do normal Fe-S complexes. Indeed, its vulnerability to oxidative destruction meant that a team of researchers led by Brookhaven biochemist Isabel Abreu was unable to determine its structural geometry using standard techniques, such as x-ray diffraction.
Abreu and her team suggested that this behaviour may be a result of one of the iron atoms only binding to a single cysteine, which would leave the complex more exposed than in the standard structure. To test this hypothesis, Abreu, together with Jos? Rodriguez, worked out the theoretical structure of the complex using density functional theory, which calculates structure based on electronic density.
They discovered that the most stable configuration for the complex did indeed involve one of the iron atoms binding to just one cysteine. The chemists also found that a protein containing an Fe-S complex with this structure should be much more chemically active than other enzymes and catalysts known to contain iron and sulfur.
’This particular unit should be four to five times more reactive than the catalysts currently used, which is very significant,’ says Rodriguez. ’The key is that you have an open side of the molecule to bind things and do chemistry.’
The chemists are now looking to develop synthetic versions of this enzyme. ’Even if we can’t use this exact enzyme, then maybe we could create other molecules or particles with this type of structure using synthetic methods,’ says Abreu.
J A Rodriguez and I A Abreu, J. Phys. Chem. B (DOI: 10.1021/jp0405355)