Waste CO₂ as an Industrial Ingredient

At the Technical University of Munich (TUM), Professor Arne Skerra succeeded for the first time in a biotechnical reaction in using gaseous CO2 as a raw material for the production of a chemical mass-produced product. It is methionine, which is used as an essential amino acid, especially in the animal fattening. The newly developed enzymatic process could replace the previous petrochemical production.

Today's industrial production of methionine takes place in a 6-stage chemical process from petrochemical raw materials, which among other things highly toxic hydrocyanic acid is needed. In 2013, Evonik Industries, one of the world's largest manufacturers of methionine, invited Higher Education researchers to propose new processes to make the substance safer. In the course of the process used so far, the technically unproblematic intermediate methional, which occurs in nature as a degradation product of methionine, is produced.

"Based on the idea that methionine in microorganisms is degraded by enzymes releasing CO2 to methional, we tried to reverse this process," explains Professor Arne Skerra, holder of the Chair of Biological Chemistry at TUM. "Because every chemical reaction is in principle reversible, but often only with high use of energy and pressure." With this concept, Skerra participated in the tender. Evonik awarded the idea and supported the project. 

Together with postdoctoral researcher Lukas Eisoldt, Skerra began to determine the framework conditions for the manufacturing process and the necessary biocatalysts ( enzymes). The scientists made initial experiments and tested what CO2 pressure would be needed to produce methionine from methional in a biocatalytic process.

Surprisingly, an unexpectedly high yield was achieved even at relatively low pressure - roughly equivalent to the pressure in a car tire of about two bars. Due to the successes already achieved after one year, Evonik extended the promotion, and now the team examined, reinforced by the doctoral student Julia Martin , the biochemical background of the reaction and optimized with the help of protein engineering the enzymes involved.

MORE EFFICIENT THAN PHOTOSYNTHESIS

After several years of work, it was not only possible to improve the reaction on a laboratory scale to a yield of 40 percent, but also to elucidate the theoretical background of biochemical processes. "In comparison to complex photosynthesis, in which nature also biocatalytically incorporates CO2 as a building block into biomolecules, our process is highly elegant and simple," reports Arne Skerra. "Photosynthesis uses 14 enzymes and has a yield of only 20 percent, while our method requires only two enzymes."

In the future, the basic pattern of this novel biocatalytic reaction can serve as a model for the industrial production of other valuable amino acids or precursors for pharmaceuticals. The team of Professor Skerra will now refine the now patented process by protein engineering so that it is suitable for large-scale application.

This could be the first time a biotechnological manufacturing process using gaseous CO2 as a direct chemical raw material. Up to now, attempts to recycle the climate-damaging greenhouse gas failed due to the extremely high energy required to do so.

This article has been republished from materials provided by the Technical University of Munich. Note: material may have been edited for length and content. For further information, please contact the cited source.

Reference
Martin, J., Eisoldt, L. & Skerra, A .: Fixation of gaseous CO2 by reversing a decarboxylase for the biocatalytic synthesis of the essential amino acid L-methionine, Nature Catalysis 1, 555-561, 07/2018. DOI 10.1038 / s41929-018-0107-4.