New kind of interaction discovered in hydrogen-producing enzymes

Most efficient hydrogen producers

The so called class of [FeFe]-hydrogenases, which are for example found in green algae, are nature's most efficient hydrogen producers. They can both produce and split hydrogen. The actual chemical reaction takes place at the active site buried deep inside the enzyme. "The electrons and protons required for the reaction must therefore find an efficient way to get there," explains Dr. Oliver Lampret from the Photobiotechnology Research Group in Bochum, one of the authors of the paper. Electron transport takes place via an electric wire, so to speak, consisting of several iron-sulphur clusters. The protons are transported to the active centre via a proton transfer pathway consisting of five amino acids and one water molecule.

"Although it was known that there was a proton-coupled electron transfer mechanism, researchers had so far assumed that the coupling only takes place at the active centre itself," says Professor Thomas Happe, Head of the Photobiotechnology Research Group.

Protein engineering makes coupling visible

The team manipulated the hydrogenases in such a way that the proton transfer was significantly slower, but hydrogen could still be converted. Using dynamic electrochemistry, they showed that hydrogen conversion decreased significantly and more importantly, significant overpotentials were needed to catalyse the production or splitting of hydrogen. By manipulating the proton transfer pathway, the researchers had indirectly reduced the rate of electron transfer.

"As the two transfer routes are spatially separated, we assume that a cooperative long-range coupling of both processes is necessary for efficient catalysis," concludes Oliver Lampret. The findings should help to develop more efficient miniaturised hydrogenase catalysts in the future.