Cluster: Integrale Konzepte der Katalyse (Teilbereich B 2)

Reversible cleavage of H2 into protons and electrons is a prevalent metabolic process in microorganisms, catalysed by two major classes of enzymes, the [NiFe]- and the [FeFe] hydrogenases. The project centres on the elucidation of the redox chemistry catalysed by oxygen-tolerant [NiFe] hydrogenases. Their active site is composed of an intricate complex of transition metals, forming a heterodinuclear Ni-Fe cofactor that is coupled to intramolecular electron and proton pathways. Crystal structures and advanced spectroscopic analyses, combined with molecular and biochemical tools have paved the way to a basic understanding of the reaction mechanism. It is generally accepted that the nickel-iron centre in the [NiFe] hydrogenases provides a free coordination site for binding hydrogen. In the oxidised state of [NiFe] hydrogenases, this site is usually occupied by oxygen which has to be reductively removed prior to catalysis. The nature of the vacant site, of which subtle modifications may exist, provides one of the keys to understanding the catalytic properties of hydrogenases and offers potential targets for optimising the catalyst by genetic engineering. This research field focuses on the three [NiFe] hydrogenases in the ß-proteobacterium Ralstonia eutropha, which utilise the hydrogen splitting reactions to perform different physiological functions, i.e. energy conservation, production of reducing equivalents and transcriptional regulation (hydrogen-sensing). Our major goal is to elucidate the molecular reaction mechanism of this group of [NiFe] hydrogenases in particular the background for their oxygen tolerance and carbon monoxide insensitivity. Both features are crucial for the application of a hydrogen activating catalyst.