Researchers have made a major breakthrough in understanding the enzyme catalysing the production of almost all methane of biological origin. A researcher says that the study, which found a surprising evolutionary link to another important enzyme, may help to alleviate methane emissions from cattle.
In groundbreaking research, scientists have discovered how methyl-coenzyme M reductase (MCR) is activated. MCR is a specialised enzyme that causes microorganisms to produce methane.
The discovery is useful because MCR catalyses the production of almost all methane. It has a key role in nature’s methane cycle and has been an enigma for years.
Interest in understanding this important biological process has been great, because methane is a potent greenhouse gas that contributes significantly to global warming.
The research shows not only how MCR is activated but also that the same molecular mechanisms operate in the nitrogenase enzyme that makes nitrogen in the atmosphere available to living organisms.
The researchers thus linked two of life’s most important processes and found a common evolutionary background.
“This suggests that these two biological systems – the production of methane and nitrogen – share a common molecular family tree. They have very different functions today but can be traced back to the same evolutionary origin. Our study establishes an overlooked evolutionary link between two fundamental biological processes: the production of methane and nitrogen fixation from the atmosphere,” explains a researcher behind the study, Jan Michael Schuller, Group Leader, Center for Synthetic Microbiology (SYNMIKRO), University of Marburg, Germany.
The research has been published in Nature.
Methane is produced in wetlands and by cattle
The production of methane is almost as old as life on Earth. Methane-producing archaea microorganisms have existed for billions of years and still produce up to 1 billion tonnes of methane annually.
Methane-producing microorganisms are present throughout nature – including in wetlands and in the stomachs of cows, sheep and other ruminants. They create enormous amounts of methane and release it into the atmosphere.
Methane can also function as an important and renewable energy source, since it is abundant, and there is therefore considerable interest in understanding what methane-producing archaea do and how they do it.
The key to how archaea produce methane is MCR, which requires coenzyme F430 in the active site to function. F430 only functions if it contains nickel in a highly reduced form, but reducing nickel in this way is extremely difficult. No one knew how nature does it until the researchers figured this out by understanding how MCR achieves this.
“Reducing nickel to its most reduced form is extremely difficult, and how nature achieves this has been an enigma until this study, which provides the answer for the first time,” says Jan Michael Schuller.
Linking methane production to nitrogen fixing
Through various complex methods, the researchers determined how nickel is reduced in F430 and thereby MCR and thus how MCR catalyses the production of methane.
The process requires energy in the form of ATP, the energy molecule of all cells, plus three complexes of iron and sulfur: iron-sulfur-carbon clusters. These act as small metal clusters that transfer electrons – with shapes, structure and topologies only known from nitrogenases.
The discovery linking the origins of MCR and nitrogenases in a common evolutionary history had been completely overlooked until now.
In fact, the study shows that MCR probably used iron-sulfur-carbon clusters before nitrogenases arose.
This indicates that iron-sulfur-carbon clusters evolved in methane-producing archaea and not in nitrogen-fixing bacteria – as previously presumed.
“Our discovery has major implications for understanding the origins of life on Earth. We can now show that all nitrogen-fixing enzymes evolved after the methane-producing enzymes evolved. This tells us that nitrogen fixation evolved from a side reaction of methane production,” notes Jan Michael Schuller.
Potential for fighting climate change
According to Jan Michael Schuller, the discovery is important for several reasons.
It provides evolutionary insight, and links two of life’s most important processes in one common origin.
This could shed completely new light on how life developed on Earth.
The discovery could also be relevant today, especially in attempting to slow climate change.
Jan Michael Schuller envisions that the new knowledge can assist in thinking of ways to slow MCR, such as in the stomachs of cows, so that the cows do not produce as much climate-damaging methane, which would reduce the pressure on the global climate.
“The way these clusters bind to their enzymes is unique. This means that we can target MCR very precisely without harming other biological systems. Developing substances that inhibit MCR in, for example, the stomachs of cows could provide a new and precise method for reducing methane emissions – without harming the animals. This makes the discovery not only relevant for basic research but also for combatting climate change,” he concludes.
