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uni'wissen 02-2012 ENG

This reliable source of nitrogen is why legumi- nous plants are particularly rich in protein and thrive even in poor soil with low nitrogen content. After studying this symbiosis in the laboratory, the Freiburg biochemist aims to extend it to other plants in agricultural practice, enabling them to take up bacteria with the enzyme nitrogenase in their roots and provide themselves with suffi- cient N2. This would make industrial fertilizer su- perfluous. “We are creating chemical systems that fulfill important metabolic tasks and bringing them to organisms that otherwise would not have this ability,” explains Einsle. He stresses that the potential for this method is not limited to the edi- ble parts of crop plants. Switching Individual Components On and Off As an initial step, Einsle and his team ana- lyzed the enzyme in detail in order to understand the foundations of the function of nitrogenase. In the process, they explained the precise structure of its complex metal center, in which the chemi- cal activation of N2 takes place. Einsle reported these findings in two articles published in the re- nowned journal Science. The second step will in- volve determining which processes each of the individual components of the metal center are re- sponsible for. Then the researchers will reassem- ble the enzyme in a model bacterium step by step and switch the individual components on and off as a test: Only in this way can Einsle find out which parts of the system engage with each other during the cleavage of N2 and how they do so. “In the end we will have to optimize the stabil- ity of the system,” explains the biochemist, be- cause the oxygen sensitivity of the bacteria and their enzyme nitrogenase is a big problem. Legu- “We place the bacteria under evolutionary pressure and tell them what to do for us” In his project “N-ABLE,” funded by the Euro- pean Research Council and the German Re- search Foundation, Einsle and his team will be reconstructing the complex and highly oxygen- sensitive enzyme systems in model organisms in the coming years. This has never been achieved before, neither in biological nor in chemical re- search: “We first need to reach a complete un- derstanding of the basic properties and functions of the enzymes, even if this is a time-consuming endeavor.” Einsle is concentrating his efforts on a solution suggested by nature: Leguminous plants – such as peas, beans, or soybeans – as- sociate with a particular type of soil bacteria, rhi- zobia. The plant forms a special organ on its root for these bacteria. The organ protects the micro- organisms from oxygen (O2), which is harmful for them, and provides them with the nutrients they need to go about the laborious process of nitro- gen fixation. Rhizobia possess the enzyme nitro- genase and capture N2 from the atmosphere. The researchers analyzed the enzyme nitrogenase in order to understand its function. They found out that its metal center, at which the chemical acti- vation of nitrogen takes place, is composed of iron atoms (gray), sulfur atoms (yellow), a molyb- denum atom (brown), and a carbon atom (black). Solution from nature: The roots of leguminous plants, such as peas, beans, or soybeans, possess special bacteria that fix nitrogen from the atmosphere. These plants thus grow well even in poor soil.18