A recent breakthrough by researchers at the Max Planck Institute for Terrestrial Microbiology has unveiled a bacterial enzyme capable of producing ethylene sustainably. The enzyme, called methylthio-alkane reductase, is derived from the bacterium Rhodospirillum rubrum and operates effectively in oxygen-free conditions. This development could significantly impact the renewable production of ethylene, a critical component for plastics, without the associated carbon dioxide emissions typically generated in fossil fuel processes.
The global demand for plastics relies heavily on large-scale ethylene production from fossil fuels, prompting the need for alternative, renewable methods. Traditional bacterial enzymes that can catalyze ethylene formation often require energy-rich substrates and produce carbon dioxide as a by-product. The discovery of methylthio-alkane reductase a few years ago sparked excitement in the scientific community due to its unique ability to generate ethylene without releasing carbon dioxide.
Despite its promise, challenges in purifying and handling this oxygen-sensitive metalloenzyme had limited research to cell cultures. Many questions regarding its biotechnological applications remained unanswered, including how the enzyme catalyzes the reaction and what properties influence its efficiency.
In a collaborative effort with RPTU Kaiserslautern, the team led by Johannes Rebelein successfully purified the enzyme and characterized its structure. Their findings revealed that the reaction is driven by complex iron-sulfur clusters, structures previously thought to exist only in nitrogenases, some of the oldest enzymes on Earth.
According to Ana Lago-Maciel, a doctoral student and the first author of the study, “The methylthio-alkane reductase is the first non-nitrogenase enzyme known to contain these metal clusters.” This discovery highlights the enzyme’s unique capabilities and suggests a broader evolutionary role for such clusters in biological processes.
Nitrogenases are renowned for their ability to convert atmospheric nitrogen into a usable form for life, incorporating it into vital biomolecules like DNA and proteins. The iron-sulfur clusters found in nitrogenases are classified among the “great clusters of biology” due to their structural complexity and geochemical significance. The research led by Rebelein provides a biochemical and structural basis for understanding a geochemically significant source of hydrocarbons.
The versatility of methylthio-alkane reductase is noteworthy; it can sustainably produce not only ethylene but also other hydrocarbons like ethane and methane. This diverse substrate spectrum differs significantly from that of nitrogenases, broadening the scope of understanding regarding how metal cluster reactivity is influenced by protein structures.
“Our study provides the in-depth structural knowledge we need to tame these reductases biotechnologically and adapt their product spectrum to our needs,” Rebelein stated. The results also offer insights into the evolutionary history of these essential metal clusters, suggesting that structurally similar enzymes may have been utilizing these clusters for reductive catalysis long before nitrogenases evolved.
This research marks a significant shift in our understanding of how such enzymes have played a role in Earth’s history and highlights the potential for developing sustainable methods for producing essential materials in a world increasingly focused on reducing carbon emissions.
