Small But Useful Enzymes Could Initiate Emission-Free Plastic Production

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Max-Planck-Institut für Terrestrische Mikrobiologie

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As researchers from the Max Planck Institute for Terrestrial Microbiology in Marburg (Germany) now state, bacterial enzymes could make plastic production less emission-intensive ...

To meet the current demand for plastics and chemical raw materials, ethylene is currently being produced on a large scale from fossil fuels. According to Max Planck researchers, the conventional production of ethylene—the starting material or monomer used to produce the thermoplastic polyethylene (PE) through polymerization—releases a relatively large amount of greenhouse gases. However, a bacterial enzyme could potentially enable the production of ethylene without CO₂ emissions in the future. The Marburg experts have studied the structure and function of the enzyme. The results obtained provide the biochemical foundations for deriving a more sustainable biotechnological production of ethylene. At the same time, they could shed light on how early biochemical processes on Earth may have occurred. Finding an enzyme that can form ethylene without emitting emissions is rare—but it worked!

A Bacterium Amazes the Scientific Community

The scientific community reacted with great interest when the enzyme methylthioalkane reductase was discovered a few years ago in the bacterium Rhodospirillum rubrum. Using this enzyme, the bacterium actually produces ethylene under oxygen-free conditions without releasing carbon dioxide. However, the fact that the production occurs under oxygen-free conditions is also a challenge. Due to significant difficulties in purifying and handling the oxygen-sensitive metalloenzymes, methylthioalkane reductase has so far only been studied within cell cultures. There has been no direct evidence of its activity outside the cell. Therefore, many important questions remain unanswered before it can be used biotechnologically. It must be clarified how the catalytic mechanism functions and what properties influence it. But the researchers in Marburg are on the trail of these answers!

Very Special Enzymes: "Great Clusters of Biology"

Researchers, under the leadership of Dr. Johannes Rebelein in collaboration with RPTU Kaiserslautern, have now purified the enzyme and elucidated its structure, as reported. In doing so, they made an exciting discovery. The reaction is driven by large, complex iron-sulfur clusters, which were previously thought to occur only in nitrogenases—incidentally, the oldest enzymes on Earth. The enzyme is thus the first known non-nitrogenase enzyme to contain these metal clusters. Nitrogenases emerged billions of years ago and are the only known enzymes capable of making gaseous nitrogen from the atmosphere available for life by incorporating it into biomolecules (such as DNA and proteins) through nitrogen reduction, as explained by the Marburg researchers. This uniqueness can be attributed to their particularly large and complex iron-sulfur clusters. Due to their structural complexity and geochemical significance, the metal clusters of nitrogenases are considered part of the so-called "Great Clusters of Biology."