In this lecture, I will describe how a team of researchers from the Institute of Chemistry and the Institute of Statistical Science have recently teamed up together at Academia Sinica to obtain the cryo-EM structure at 2.5 Å of a methane oxidizer from a methanotrophic bacteria. This methane oxidizer, typically referred to as particulate methane monooxygenase (pMMO), converts methane into methanol selectively and efficiently under ambient conditions. Our high resolution cryo-EM structure of pMMO from Methylococcus capsulatus (Bath) offers the first glimpse of the catalytic machinery capable of performing this challenging chemistry, an important milestone in the field.
Methane is one of the major greenhouse gases. Although smaller amounts of methane gas are produced on planet Earth compared with carbon dioxide, methane is 33 times more detrimental molecule for molecule toward global warming and climate change. Presently, methane accounts for ca. 20 % of the global warming problem. The methane in the Earth’s atmosphere is almost entirely produced by biology involving methanogens that inhabit natural ecosystems, such as ocean sediments, wetlands, and animal digestion, along with a small contribution from thermogenic sources including volcanism, oil and gas production. Fortunately, the emission of methane produced from ecological systems is controlled by other microbes that metabolize methane as their sole source of carbon and energy. These methanotrophs convert substantial amounts of the methane produced by the methanogenic bacteria into methanol by the oxygen in air. Over the past several decades, scientists have purified and studied in depth the proteins responsible for this chemistry. Methane oxidation is extremely difficult to perform in the laboratory, but scientists have discovered the chemical principles governing how these enzymes work. Based on this fundamental knowledge, a catalyst has been recently developed capable of efficient and selective conversion of methane into methanol at room temperature. This catalyst has already been applied to liquefy natural gas into its product oxygenates with success. The outcomes are sufficiently promising that we have begun to consider scaling up the catalyst and integrating the technology platform with other technologies that we are also developing to enhance catalytic performance for the capture and collection of seeping natural gas from stationary sources as well as methane emissions from various human activities.