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My research focuses on the use and production of sustainable and clean biofuels, such as molecular hydrogen and biomethane. Based on studying fundamental mechanisms of biocatalysts by biochemical and spectroscopic techniques, my research aims at understanding the assembly, electron transfer and substrate conversion of synthetic enzymes and H2 driven cascades.
Fundamental aspects of biocatalysis
The NAD+ reducing hydrogenase from Ralstonia eutropha (SH) catalyzes the reversible oxidation of H2 in connection with the reduction of NAD+ in the presence of O2. The remarkable O2 tolerance was previously related to an unusual [NiFe] active site with four instead of two cyanide ligands. We rejected this hypothesis by using in situ EPR and infrared spectroscopy on SH containing cells (Horch, Lauterbach et al. 2010). Indeed, we showed that the [NiFe] center of the SH reacted with O2 and that the O2tolerance of the SH is based on a continuous reactivation of the oxidized [NiFe] active site. Electrons generated through H2 oxidation serve as “health insurance” and are reused for O2 reduction and formation of hydrogen peroxide and non-toxic water (Lauterbach and Lenz 2013). Recent studies indicate that the SH detoxifies O2catalytically by means of an NADH-dependent oxidase reaction involving the intermediary formation of stable cysteine sulfonates (Horch, Lauterbach et al. 2015).
The function-structural relationship of the SH involved cofactors was largely unknown. In cooperation with Stephen Cramer (UC Davis, USA) we investigated the various metal cofactors present in this kind of enzyme by using 57Fe specific nuclear resonance vibrational and 61Ni Mössbauer spectroscopy. The approach explored the complex vibrational signature of ferredoxins, the SH and the electronic properties of Ni reconstituted rubredoxin (i.a. Lauterbach et al. 2016, Gee et al. 2016).
Molecular hydrogen (H2) is a carbon-free, clean and renewable alternative fuel and reductant in a world where sustainable energy carriers have become increasingly important. Due to the O2 tolerance, the SH is a promising enzyme for H2-driven biotechnological approaches (Lauterbach, Lenz, Vincent 2013; Preissler et al. 2018). In cooperation with other groups, we demonstrated the H2-driven NADH regeneration in various coupled enzymatic reactions (i.a. Patent about cofactor regeneration system; in cooperation with Prof. Dr. Kylie Vincent (Oxford university); Lonsdale, Lauterbach et al.2015).
In a current DFG funded project in cooperation with Dr. Bettina Nestl (Universität Stuttgart), we are currently working on H2-driven N-heterocycle production. Nitrogen containing heterocycles are important building blocks for the production of agrochemicals and pharmaceuticals. 2- and 3-substituted piperidines are generated in a three-step enzymatic cascade using imine reductase, an engineered flavoprotein oxidase variant and SH. Excellent conversion up to 97% was obtained in the H2-driven transformation of the diamine substrate 1,5-diaminopentane to the corresponding piperidine product.
Light-driven H2 production
Hydrogenases can also be utilized for H2 production. H2 has a high-energy content and its oxidation with O2 leaves only water as a by-product making it attractive for future H2-based transport system and industry. The coupling of an O2-tolerant hydrogenase with photosystem would make light-driven H2 production possible. In a DFG funded project in cooperation with Prof Dr. Andreas Schmid/ Prof. Dr. Bruno Bühler, UFZ Leipzig, we modify the SH by rational engineering to enable the enzyme for H2production.