Oxygen Sensor Protein Offers Solution for Enhancing Nitrogen Fixation in Plants

A small helper for big tasks: an oxygen sensor protein protects the enzymatic machinery of biological nitrogen fixation from serious damage. Its use in biotechnology could help to reduce the use of synthetic fertilizer in agriculture in the future. A research team led by biochemist Prof. Dr Oliver Einsle from the Faculty of Chemistry and Pharmacy and the Centre for Biological Signalling Studies (BIOSS) at the University of Freiburg has discovered exactly how the so-called Shethna protein II works. The scientists used the newly established cryo-electron microscopy in Freiburg. Their results have been published in the journal Nature.

Nitrogen Fertilizer is Ecologically Problematic

The element nitrogen is an essential component of all living organisms; in agriculture, it is often added as fertilizer to enable high yields over the long term. However, the production and application of these fertilizers is problematic in terms of energy and the environment. For years, attempts have therefore been made to transfer the natural nitrogen fixation in bacteria and archaea to crops. The enzyme nitrogenase is responsible for the binding of nitrogen. One of the most serious problems with the transfer to plants is that nitrogenase is extremely sensitive to atmospheric oxygen, which is produced by plants themselves during the process of photosynthesis.

Shethna Protein II Forms a Complex with the Enzyme Nitrogenase.

Philipp Franke, Simon Freiberger and Dr. Lin Zhang from the team led by Prof. Oliver Einsle has now been able to show how a small factor, the Shethna protein II, registers an increase in oxygen concentration. It then very quickly forms a complex with the two components of the enzyme nitrogenase, which protects them from oxidative damage. In this process, the activated Shethna protein II binds the much larger nitrogenase and its associated reductase, forming long filaments with both proteins in which oxygen cannot reach the active centres of the nitrogenase. As soon as the cells overcome this oxidative stress, the complex dissolves and the enzyme can resume its work.

Use in Plant Cells is Conceivable

Even if nitrogenase is produced directly in plant cells, it is likely that such short stress phases with increased oxygen concentrations will occur again and again. In the case of biotechnological use, the co-production of the small Shethna protein II could then help to protect the elaborately synthesised enzymes in their new environment and maintain their function in the plant cell.

The production of functioning nitrogenase in plants would initiate a paradigm shift in green biotechnology, and this small protein can make a decisive contribution to making this possible."

Prof. Dr Oliver Einsle, Faculty of Chemistry and Pharmacy and the Centre for Biological Signalling Studies (BIOSS), University of Freiburg