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Northwestern team identifies site in enzyme responsible for methane-methanol conversion

Methanotrophic bacteria remove methane from the environment and convert it into methanol. An interdisciplinary team at Northwestern University has found that the enzyme responsible for the methane-methanol conversion catalyzes this reaction at a site that contains just one copper ion. The study is published in the journal Science.

Bacteria that oxidize methane to methanol are central to mitigating emissions of methane, a potent greenhouse gas. The nature of the copper active site in the primary metabolic enzyme of these bacteria, particulate methane monooxygenase (pMMO), has been controversial owing to seemingly contradictory biochemical, spectroscopic, and crystallographic results. We present biochemical and electron paramagnetic resonance spectroscopic characterization most consistent with two monocopper sites within pMMO: one in the soluble PmoB subunit at the previously assigned active site (CuB) and one ~2 nanometers away in the membrane-bound PmoC subunit (CuC). On the basis of these results, we propose that a monocopper site is able to catalyze methane oxidation in pMMO.

—Ross et al.

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The primary metabolic enzyme in methanotrophic bacteria, particulate methane monooxygenase (pMMO), catalyzes the methane-to-methanol conversion at a site with one copper ion. Credit: Northwestern University

This finding could lead to newly designed, human-made catalysts that can convert methane—a highly potent greenhouse gas—to readily usable methanol with the same effortless mechanism.

The identity and structure of the metal ions responsible for catalysis have remained elusive for decades. Our study provides a major leap forward in understanding how bacteria methane-to-methanol conversion.

—,Amy C. Rosenzweig, co-senior author

By identifying the type of copper center involved, we have laid the foundation for determining how nature carries out one of its most challenging reactions.

—Brian M. Hoffman, co-senior author

Current industrial processes to catalyze a methane-to-methanol reaction require tremendous pressure and extreme temperatures, reaching higher than 1,300 degrees Celsius. Methanotrophs, however, perform the reaction at room temperature and “for free.”

While copper sites are known to catalyze methane-to-methanol conversion in human-made materials, methane-to-methanol catalysis at a monocopper site under ambient conditions is unprecedented. If we can develop a complete understanding of how they perform this conversion at such mild conditions, we can optimize our own catalysts.

—Matthew O. Ross, first author

The study was supported by the National Institutes of Health (award numbers GM118035, GM111097 and 5T32GM008382) and the National Science Foundation (award number 1534743).

Resources

  • Matthew O. Ross, Fraser MacMillan, Jingzhou Wang, Alex Nisthal, Thomas J. Lawton, Barry D. Olafson, Stephen L. Mayo, Amy C. Rosenzweig, Brian M. Hoffman (2019) “ Particulate methane monooxygenase contains only mononuclear copper centers” Science Vol. 364, Issue 6440, pp. 566-570 doi: 10.1126/science.aav2572

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