July 31, 2018

Greenhouse gas as raw material for producing methionine
 

Professor Arne Skerra of the Technical University of Munich (TUM) has succeeded for the first time in using gaseous CO2 as a basic material for the production of methionine in a biotechnical reaction.

This newly developed enzymatic process could replace the current petrochemical production of methionine, which is used as an essential amino acid in animal feed.  The results have been published in the journal Nature Catalysis.

The industrial production of methionine from petrochemical source materials is done via a six-step chemical process that requires highly toxic hydrogen cyanide, among other substrates.
 

In 2013, Evonik Industries, one of the world's largest manufacturers of methionine, invited university researchers to propose new processes for making the substance safer to produce. Methional, which occurs in nature as a degradation product of methionine, is formed as a facile intermediate during the conventional process.

"Based on the idea that methionine in microorganisms is degraded by enzymes to methional with the release of CO2, we tried to reverse this process, because every chemical reaction is, in principle, reversible, while often only with the extensive use of energy and pressure."
 

Skerra participated in the call for proposals with this idea. In response, Evonik awarded the concept and supported the project.

Backed by postdoctoral researcher Lukas Eisoldt, Skerra began to determine the parameters for the manufacturing process and the production of the necessary biocatalysts (enzymes). The scientists conducted initial experiments and determined the CO2 pressure which would be needed to produce methionine from methional in a biocatalytic process.
 

Surprisingly, an unexpectedly high yield resulted even at a relatively low pressure - approximately corresponding to the one in a car tire of approximately two bars. Based upon the achievements after just one year, Evonik extended the funding; currently, the team, reinforced by Ph.D. student Julia Martin, are investigating the biochemical background of the reaction and optimising the enzymes involved using protein engineering.

After several years of work, it is not only possible to improve the reaction on a laboratory scale to a yield of 40%, but also to elucidate the theoretical background of the biochemical processes.

"Compared to the complex photosynthesis, in which nature also biocatalytically incorporates CO2 into biomolecules as a building block, our process is highly elegant and simple," Professor Skerra said. "Photosynthesis uses 14 enzymes and has a yield of only 20%, while our method requires just two enzymes."

The basic principle of this novel biocatalytic reaction can potentially serve as a model for the industrial production of other valuable amino acids or precursors for pharmaceuticals.
 

For now, Professor Skerra's team will refine the process, which has been patented, using protein engineering so that it will become suitable for large-scale application.

It could also be the first time that a biotechnological manufacturing process uses gaseous CO2 as an immediate chemical precursor. Previous attempts to recycle the greenhouse gas have failed due to the extremely high energy required.
 

-  Technical University of Munich