• Methane-eating bacteria convert greenhou

    From ScienceDaily@1:317/3 to All on Thursday, March 17, 2022 22:30:46
    Methane-eating bacteria convert greenhouse gas to fuel
    State-of-the-art method reveals never-before-seen atomic structures controlling the process

    Date:
    March 17, 2022
    Source:
    Northwestern University
    Summary:
    Methanotrophic bacteria consume 30 million metric tons of methane
    per year and have captivated researchers for their natural ability
    to convert the potent greenhouse gas into usable fuel. Yet we know
    very little about how the complex reaction occurs, limiting our
    ability to use the double benefit to our advantage.



    FULL STORY ========================================================================== Methanotrophic bacteria consume 30 million metric tons of methane per
    year and have captivated researchers for their natural ability to convert
    the potent greenhouse gas into usable fuel. Yet we know very little about
    how the complex reaction occurs, limiting our ability to use the double
    benefit to our advantage.


    ==========================================================================
    By studying the enzyme the bacteria use to catalyze the reaction, a team
    at Northwestern University now has discovered key structures that may
    drive the process.

    Their findings, to be published Friday (March 18) in the journal Science, ultimately could lead to the development of human-made biological
    catalysts that convert methane gas into methanol.

    "Methane has a very strong bond, so it's pretty remarkable there's an
    enzyme that can do this," said Northwestern's Amy Rosenzweig, senior
    author of the paper. "If we don't understand exactly how the enzyme
    performs this difficult chemistry, we're not going to be able to engineer
    and optimize it for biotechnological applications." Rosenzweig is the
    Weinberg Family Distinguished Professor of Life Sciences in Northwestern's Weinberg College of Arts and Sciences, where she holds appointments in
    both molecular biosciences and chemistry.

    The enzyme, called particulate methane monooxygenase (pMMO), is a
    particularly difficult protein to study because it's embedded in the
    cell membrane of the bacteria.



    ========================================================================== Typically, when researchers study these methanotrophic bacteria, they use
    a harsh process in which the proteins are ripped out of the cell membranes using a detergent solution. While this procedure effectively isolates the enzyme, it also kills all enzyme activity and limits how much information researchers can gather -- like monitoring a heart without the heartbeat.

    In this study, the team used a new technique entirely. Christopher Koo,
    the first author and a Ph.D. candidate in Rosenzweig's lab, wondered if
    by putting the enzyme back into a membrane that resembles its native environment, they could learn something new. Koo used lipids from
    the bacteria to form a membrane within a protective particle called a
    nanodisc, and then embedded the enzyme into that membrane.

    "By recreating the enzyme's native environment within the nanodisc,
    we were able to restore activity to the enzyme," Koo said. "Then, we
    were able to use structural techniques to determine at the atomic level
    how the lipid bilayer restored activity. In doing so, we discovered the
    full arrangement of the copper site in the enzyme where methane oxidation likely occurs." The researchers used cryo-electron microscopy (cryo-EM),
    a technique well- suited to membrane proteins because the lipid membrane environment is undisturbed throughout the experiment. This allowed them
    to visualize the atomic structure of the active enzyme at high resolution
    for the first time.

    "As a consequence of the recent 'resolution revolution' in cryo-EM, we
    were able to see the structure in atomic detail," Rosenzweig said. "What
    we saw completely changed the way we were thinking about the active site
    of this enzyme." Rosenzweig said that the cryo-EM structures provide a
    new starting point to answer the questions that continue to pile on. How
    does methane travel to the enzyme active site? Or methanol travel out
    of the enzyme? How does the copper in the active site do the chemical
    reaction? Next, the team plans to study the enzyme directly within the bacterial cell using a forefront imaging technique called cryo-electron tomography (cryo-ET).

    If successful, the researchers will be able to see exactly how the enzyme
    is arranged in the cell membrane, determine how it operates in its truly
    native environment and learn whether other proteins around the enzyme
    interact with it. These discoveries would provide a key missing link
    to engineers.

    "If you want to optimize the enzyme to plug it into biomanufacturing
    pathways or to consume pollutants other than methane, then we need to
    know what it looks like in its native environment and where the methane
    binds," Rosenzweig said.

    "You could use bacteria with an engineered enzyme to harvest methane from fracking sites or to clean up oil spills." The study was supported by
    the National Institutes of Health (grant numbers R35GM118035, T32GM008382, T32GM105538 and R01GM135651).


    ========================================================================== Story Source: Materials provided by Northwestern_University. Original
    written by Win Reynolds. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Christopher W. Koo, Frank J. Tucci, Yuan He, Amy
    C. Rosenzweig. Recovery
    of particulate methane monooxygenase structure and activity
    in a lipid bilayer. Science, 2022; 375 (6586): 1287 DOI:
    10.1126/science.abm3282 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220317143713.htm

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