Shock discovery about methane producing enzyme

Researchers have made an unexpected discovery concerning methyl-coenzyme M reductase (MCR), the only enzyme known to produce methane.

Methane, a greenhouse gas with a global warming impact 30 times greater than carbon, is produced from both geological and biological sources, including from a group of microorganisms called methanogens. These microscopic organisms produce methane as the byproduct of their metabolism, creating gigatons of methane around the globe every year.

These methanogens, which have the MCR enzyme, are often used in the production of methane biogas. Increasingly, a range of research projects are showing the significant potential methane gas has as a renewable fuel and source of power in anything from buses to farming machinery.

Until now, it had been believed that a set of unique modifications present in MCR were essential to how the enzyme functions. The latest research, by a team from the Carl R. Woese Institute for Genomic Biology (IGB) at the University of Illinois at Urbana-Champaign, shows that these modifications were not in fact essential.

"This is a hugely important enzyme," said Professor of Molecular and Cellular Biology William Metcalf, co-author of the paper and leader of IGB's Mining Microbial Genomes (MMG) theme. "I would argue it's one of the most important enzymes on earth for the carbon cycle."

Unlike most enzymes, MCR has a series of modifications that change its amino acids. It is these modifications that were previously believed to be behind the production of methane.

Douglas Mitchell, a professor of chemistry at IGB, hypothesised that this was not the case, after studying a class of molecules which had one of the modifications present in MCR. He and his colleague turned to IGB Fellow Dipti Nayak, who had developed a genetic tool that could manipulate this type of organism, even in anaerobic environments.

Analysing MCR, the scientists were shocked to find that the modification was not essential to the enzyme’s function.

"When I started this project, I didn't quite know as much about the importance of these modifications," Nayak said. "As the project moved along . . . I realized the impact of the discovery we made, that this modification we thought was important and involved in making methane or breaking down methane, suddenly was not playing as important a role as people in the literature had been talking about for the last 10 or 15 years -- maybe even longer, actually."

The findings suggest there is a great deal more to be learnt about this enzyme, which plays such a crucial role in the creation of methane.

The study has been published in the journal eLife. 

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