CeNS Colloquium

Prof. Oliver Einsle
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg

The biogeochemical nitrogen cycle includes some of the most challenging catalyses known in biology. These include in particular the essential conversions of elementary dinitrogen (N₂). Due to its extraordinary stability, this molecule forms a sink for more than 99% of all nitrogen available in the biosphere. It is generated from nitrous oxide (N₂O) by the copper-containing metalloenzyme nitrous oxide reductase, and the only reaction known to cleave its stable triple bond is that of nitrogenase. Intricate metal clusters are found at the active sites of both proteins, and in spite of extensive biochemical data published over several decades, the details of how these enzymes activate and reduce their inert substrates remain to be elucidated. The substrates of nitrous oxide reductase and nitrogenase are critical pollutants such as the greenhouse gas N₂O and carbon monoxide (CO), and the reduction of N₂ to bioavailable ammonium is the biological equivalent of the industrial Haber-Bosch process that currently produces nitrogen fertilizer for crops that feed 40% of the human population.

We have studied nitrous oxide reductase and nitrogenase using EPR and UV/vis spectroscopy, biochemical assays and X-ray crystallography. Based on most recent data we now understand the architecture of the unique and highly oxygen-sensitive metal clusters in atomic detail and we have found the first hints towards the binding and activation mode during catalysis.

1) Spatzal, T., Aksoyoglu, M., Zhang, L., Andrade, S.L.A., Schleicher, E., Weber, S., Rees, D.C. & Einsle, O. (2011) Evidence for interstitial carbon in nitrogenase FeMo cofactor. Science, in press.
2) Pomowski, A., Zumft, W.G., Kroneck, P.M.H. & Einsle, O. (2011) N₂O binding at a [4Cu:2S] copper-sulphur cluster in nitrous oxide reductase. Nature, 477, 234-237
3) Einsle, O., Tezcan, F. A., Andrade, S. L., Schmid, B., Yoshida, M., Howard, J. B. & Rees, D. C. (2002). Nitrogenase MoFe protein at 1.16 Å resolution: A central ligand in the FeMo cofactor. Science, 297, 1696-1700.