Title: The Catalytic Cycle of Hydrogenase and Wateroxidase Elucidated by Spectroscopic Studies
Speaker: Prof. Wolfgang Lubitz, Director, Max Planck Institute for Chemical Energy Conversion, Germany
Time: 10:00-11:30a.m., Oct. 24th, 2017
Venue: Room 214, Building No. 16, Wushan Campus

[Abstract]
In this contribution the present knowledge of structure, function and dynamics of the enzymes wateroxidase and hydrogenase are discussed.

The reversible heterolytic splitting of molecular hydrogen is catalyzed by hydrogenases carrying complex metal centers ([NiFe], [FeFe]) as active sites.[1] For the [NiFe] hydrogenases it is shown that all intermediates of the catalytic cycle can be trapped and spectroscopically characterized. DFT calculations relate the obtained parameters to the structure of the active site, yielding information about the intermediates and the catalytic cycle. The value of ultra-high resolution X-ray crystallography is demonstrated [2]. Furthermore the oxygen sensitivity and tolerance of hydrogenases is discussed. The O2 tolerance can significantly be increase by embedding the enzyme in a tailor-made polymer matrix [3]. For the [FeFe] hydrogenase inorganic model complexes mimicking the [2Fe] subcluster of the active site can be incorporated into the apoenzyme yielding fully active enzyme [4]. Prospects and limitations of this finding for hydrogenase research and biotechnological applications are demonstrated.

All organisms performing oxygenic photosynthesis are able to split water using a tetranuclear Mn cluster (Mn4OxCa) [5] located in photosystem (PS) II. The cluster cycles through 5 intermediate states (Si, i=0-4) during light-driven catalysis. Since all states are paramagnetic cw and pulse EPR, and related double resonance techniques (EDNMR, ENDOR), are the methods of choice to study these intermediates. Together with theoretical approaches a robust model for the geometry, dynamics and electronic structure of the Mn4OxCa cluster has been obtained with important implications for the catalytic mechanism [6]. Furthermore the binding of substrate water to the cluster was probed using 17O-labeled water. Recent EPR work on the state directly preceding the O-O bond formation gave insight into the mechanism of water oxidation, oxygen bond formation and O2 release [8].

1. W. Lubitz, H. Ogata, O. Rüdiger, E. Reijerse, Chem. Rev., 2014, 114, 4081.

2. H. Ogata, K. Nishikawa, W. Lubitz, Nature, 2015, 520, 571.

3. N. Plumeré, et al. Nat. Chem., 2014, 6, 822; A. A. Oughli et al. Angew. Chem.Int. Ed., 2015, 54, 12329.

4. J. Esselborn et al., Nat. Chem. Biol., 2013, 10, 607.

5. Y. Umena et al., Nature, 2011, 473, 55; M. Suga et al., Nature, 2015, 517, 99

6. V. Krewald et al., Chem. Sci., 2015, 6, 1676; V. Krewald et al. Inorg. Chem., 2016, 55, 488.

7. L. Rapatskiy et al., J. Am. Chem. Soc. 2012, 134, 16619

8. N. Cox et al., Science, 2014, 345, 804. M. Pérez-Navarro et al., Curr. Opin. Chem. Biol., 2016, 31, 113.

[Biography]

Wolfgang Lubitz studied Chemistry at the Freie Universität (FU) Berlin (1969 – 1974), where he also received his doctoral degree (1977), and his habilitation (1982). He worked as a research scientist at UC San Diego, USA (1983/84) and as Assistant and Associate Professor at the FU Berlin (1979 -1989).

In 1989 he became Professor in the Physics Department of the Universität Stuttgart, before he took over a Chair of Physical Chemistry at the Technische Universität (TU) Berlin in 1991. In 2000 he became a Scientific Member of the Max Planck Society and Director at the Max Planck Institute for Chemical Energy Conversion (formerly Max Planck Institute for Bioinorganic Chemistry) in Mülheim/Ruhr, Germany. Professor Lubitz is an Honorary Professor at the Universität Düsseldorf. His scientific work is focused on energy conversion processes in natural and artificial photosynthesis, the investigation of metalloproteins (hydrogenases, water oxidase) and the development and application of molecular spectroscopy, especially magnetic resonance methods.

His work has been published in over 400 scientific publications in prestigious journals such as Nature, Science, Nature Chemistry, Chemical Reviews, etc. (with total citation over 20000, H-index=74). He is Fellow of the Royal Society of Chemistry (UK). He has been honored with a number of awards, including the Gold Medal of the International EPR Society (2005), as Fellow of ISMAR (International Society of Magnetic Resonance) (2010) and as Foreign Member of the Academy of Sciences of the Republic of Tatarstan (2012). He has been President of the International EPR Society (2005–2008) and is currently Vice President of the Council for the Annual Nobel Laureate Meetings in Lindau. He is an editorial board member of several international journals, including the RSC journal Energy & Environmental Sciences.