A Molecular Machine At Work

The greenhouse gas nitrous oxide (N₂O) is produced as a by-product of industrial processes and through the use of fertilizers in agriculture. It makes a steadily growing contribution to climate change and ozone depletion. It is so chemically inert that it remains in the atmosphere for a very long time. So far, only one enzyme is known in nature that can convert this gas into harmless nitrogen and water: N₂O reductase. However, this is a copper-containing metalloenzyme and as such is sensitive to the oxygen in the air we breathe. Dr. Christoph Müller and Dr. Lin Zhang from the research group of Prof. Dr. Oliver Einsle at the Institute of Biochemistry at the University of Freiburg, together with Prof. Dr. Juan Du and Prof. Dr. Wei Lü from the Van Andel Research Institute in Grand Rapids/USA, have now made significant progress in understanding this enzyme.

Components of a molecular machine isolated and characterized

With regard to biotechnological applications of N₂O reductase, it is crucial to understand and control the supply of copper ions during the assembly of the enzyme in the cell. The research teams have therefore isolated the components of a multipartite molecular machinery that accomplishes this assembly and characterized them using cryo-electron microscopy. They have presented their work in the current issue of the journal Nature.

Mechanical process: maturation of the metal centers of N₂O reductase

The maturation of the metal centers of N₂O reductase is a surprisingly mechanical process in which conformational changes of the membrane protein NosDFY (see figure) are triggered by the consumption of biochemical energy in the cell. This enables the complex to accept a single copper ion from a special transport protein, NosL, and then offer it to the still copper-free or only partially assembled N₂O reductase.

New function discovered

Using a variety of high-resolution structural models, the researchers were able to map and understand the individual steps of this complex process in great detail. They discovered a previously undescribed function of this important class of membrane proteins and took a major step towards harnessing the enzyme N₂O reductase for the reduction of atmospheric nitrous oxide.

Fact Sheet:

• Prof. Dr. Oliver Einsle is Professor of Biochemistry at the Faculty of Chemistry and Pharmacy at the University of Freiburg.
• He and his team study the structure and function, as well as the biogenesis of complex enzyme systems. The focus of their work is on the enzymatic activation of small molecules such as nitrogen, nitrous oxide or carbon monoxide, which are difficult to convert due to their chemical stability, but at the same time are of great ecological and economic importance.
• He is a member of several DFG projects at the University of Freiburg. In 2020, he was elected to the Leopoldina.
• Original publication:Müller, C., Zhang, L., Zipfel, S., Topitsch, A., Lutz, M., Eckert, J., Prasser, B., Chami, M., Lü, W., Du, J., Einsle, O. (2022): Molecular interplay of an assembly machinery for nitrous oxide reductase. Nature. DOI: 10.1038/s41586-022-05015-2.

Figure
Three states of the maturation apparatus of N₂O reductase: A complex of the proteins NosF (yellow), NosY (red) and NosD (green) changes its conformation by consuming biochemical energy and can thus take over a copper ion from the transport protein NosL (blue) and pass it on to the enzyme in the next step. Illustration: Group Einsle

Pressphoto for Download