Bacterial proteins help turn harmful methane into sustainable biofuel

The findings could support the creation of environmentally-friendly fuel

 
 
Csp1 protein (green) forms a 4-helix bundle with the 13 Cu(I) ions (orange) packed in the centre channel. The size of the protein is approximately 10,000 smaller than a fine human hair. Courtesy of Neil Paterson.
 

A group of UK scientists has discovered a protein inside methanotrophic bacteria (methanotrophs) that allows them to safely store copper ions to aid the consumption of the harmful greenhouse gas methane. These organisms use a  copper-enzyme to transform methane into methanol, providing carbon and energy for the bacteria. By exploiting this process, it may be possible to develop new and more economical means of both mitigating release of this gas into the atmosphere and simultaneously producing effective biofuels.

The group of scientists, from Newcastle University, used Diamond beamlines I24 (microfocus MX crystallography) and I02 (MX crystallography). The beam on I24 is extremely finely focussed at just 1/30th the width of a human hair and both beamlines are also highly automated, allowing users to quickly study large numbers of samples with a tuneable X-ray energy. On I24 and I02, the group were able to study these proteins and how they bind copper ions at the atomic level.
 
The study reports the discovery of a protein, called Csp1, found in methanotrophs that allows them to store up large quantities of copper for methane oxidation. Each copy of this small protein binds 13 copper ions tightly enough to prevent poisoning of the cell, yet allows them to be removed, as required, for methane oxidation. The group propose that it is these stores of copper that ensure the bacteria possess sufficient copper to oxidise the methane, transforming it into methanol. Recognising this element of the oxidation process in atomic detail is a real step forwards in determining how to exploit methanotrophs on an industrial scale.
 

There are already available non-biological methods of oxidising methane and turning it into methanol; however current methods are too costly to be workable. But if scientists can learn how to capitalise on the natural systems by which bacteria carry out this process, then it may be possible to transform this greenhouse gas into a viable biofuel.

Lead author Chris Dennison, Professor of Biological Chemistry at Newcastle University explains: “Methane is such a useful and plentiful commodity but we need more cost effective methods to unlock its potential. Using bacteria could be the best option so a better knowledge of how these bacteria operate is required. As copper is so important for the oxidation of methane, all potential applications based on this reactivity requires knowing how methanotrophs acquire and store copper. The discovery of the Csps adds a new dimension to our understanding of this complex process.”
 
Co-author Colin Murrell, Professor in Environmental Microbiology at the University of East Anglia, adds: “We have known that copper is a vital element for biological methane oxidation for over thirty years and this new information will really help us to formulate new strategies for exploiting these bacteria both in the laboratory and in the environment.”
 
To address the 21st century’s environmental challenges, we need tools to perform research and a (well-funded) vibrant academic and industrial base engaged in bringing the best science to Diamond. Dr Neil Paterson, a post-doctoral research associate on I24 and co-author on the paper, highlights the significance of synchrotron light to supporting this research: “In this case, Diamond’s tuneable X-ray energy allowed us to use the intrinsic copper ions within the protein to solve the crystal structure by X-ray diffraction and also define their oxidation state through X-ray fluorescence spectroscopy.”
 
Whilst this work is still in its early stages, the discovery of the Csp1 protein is an important step forward in learning how to unlock the potential of bacteria to transform methane into biofuel. Methane availability is rising as the extraction of natural gas booms, and more of it is escaping into the atmosphere, and these finding constitute a small but significant step forwards in finding a way to make the world a cleaner, greener place.
 
Conversion of methane to methanol in methanotrophic bacteria is performed by pMMO, which requires copper. Courtesy of Neil Paterson.
Conversion of methane to methanol in methanotrophic bacteria is performed by pMMO, which requires copper. Courtesy of Neil Paterson.