Science: Turning methane into fuel, the secrets of this amazing bacteria are being revealed

▎WuXi AppTec Content Team Editor We know that methane is a highly potent greenhouse gas and an important factor in exacerbating global warming
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But what you may not know is that out of sight of us, a class of methanotrophs, also known as methanotrophs, are helping us consume methane
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Each year, these bacteria "eat" 30 million tons of methane, converting it into methanol, which can be used as fuel
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For us, such a response was clearly intriguing
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If this skill of methanotrophs can be understood and harnessed, it could be possible to kill two birds with one stone, producing energy while reducing greenhouse gases
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Unfortunately, little is known in the scientific community about how this complex process happens
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Now, a new Science study has revealed important clues
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The research team from Northwestern University in the United States took a deep look at the enzymes that methanophilic bacteria use to convert methane and found the key structure that drives this process
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Building on this breakthrough, scientists in the future may be able to develop artificial catalysts to help convert methane into fuel
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"Methane is covalently strong, so it's very interesting to have enzymes that can do this [catalyze the methane reaction]," said Amy Rosenzweig, a professor of chemistry at Northwestern University and corresponding author of the paper.
The mechanism of action of the enzyme makes it impossible to design and optimize the enzyme for applications in biotechnology
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” The enzyme of interest in this study is called particulate methane monooxygenase (pMMO)
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Three years ago, Professor Rosenzweig's team revealed in a Science paper the site where this enzyme catalyzes the methane conversion reaction
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However, compared to the ultimate goal, such a breakthrough is far from enough
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▲The 2019 study revealed the site where the pMMO enzyme catalyzes the methane conversion reaction (Image source: Northwestern University) pMMO enzymes are extremely difficult to study because the protein is embedded in the cell membrane of bacteria
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Typically, when studying these methanotrophs, researchers use a detergent to detach the proteins from their cell membranes
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Although this process can separate the enzyme, the activity of the enzyme is also lost in the process
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So what the researchers got was like a heart that couldn't beat -- only the structure could be seen, but no way of knowing how it worked
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In this study, the research team took a completely new approach
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It's a strategy based on reverse thinking: If an isolated enzyme is put back into an artificial membrane similar to its original environment, will the enzyme regain its activity? So the research team used bacterial lipids to create a bilayer membrane that contains a layer of nanophospholipids called nanodiscs, which function to maintain structural stability and biological activity
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They then embedded the previously isolated pMMO enzyme into the artificial membrane
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The result was a success: the pMMO enzyme regained its activity, so the team was able to use high-resolution cryo-electron microscopy to observe the enzyme's active structure in the lipid environment
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In this way, the research team discovered a subunit region that had never been observed before and detected a completely new copper-binding site
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▲Under the cryo-electron microscope, the structure of the pMMO enzyme when it is active (Image source: Northwestern University, USA) Christopher Koo, the first author of the paper and a doctoral student in Rosenzweig's lab, said: "After creating the original environment of the enzyme with nanodisc, we recovered the enzyme activity
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Subsequently, we revealed at the atomic scale how the lipid bilayer recapitulates activity
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We see the complete arrangement of copper sites in the enzyme, where the methane oxidation reaction likely occurs
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"Based on the recent revolution in cryo-EM resolution, we can see structural details at the atomic level," said Professor Rosenzweig
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These findings revolutionized previous speculation about the enzyme's active site
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"▲ Cryo-electron microscopy revealed a previously undiscovered subunit structure (Image source: Reference [1]) On the basis of this research, a series of new questions are waiting to be further explored
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How does methane enter the active site of the enzyme? How does the produced methanol leave? How does the copper at the active site participate in the reaction? Next, the team plans to study the pMMO enzyme directly in the bacterial membrane using cryo-electron tomography
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If it goes well, the researchers will be able to accurately "Understanding how an enzyme is embedded in the cell membrane, how it works in its natural environment, and whether other surrounding proteins interact with it
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These findings will fill in the missing link for the artificial design of relevant enzymes for methane conversion
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Reference: [1] Christopher Koo et al.
, Recovery of particulate methane monooxygenase structure and activity in a lipid bilayer.
Science 2022) DOI: 10.
1126/science.
abm3282[2] Methane-eating bacteria convert greenhouse gas to fuel.
Retrieved Mar .
17, 2022 from https://