The biological oxidation of methane to carbon dioxide proceeds sequentially--through methanol, formaldehyde, and formic acid. Carrying out these reactions under mild conditions demands exquisite control, which generally translates into precisely structured metal centers and diffusion-restricted intermediates. Myronova et al. have isolated an enzyme complex containing the membrane-bound (or particulate) form of methane monooxygenase (pMMO) and methanol dehydrogenase (MDH), and they map its structure using cryoelectron microscopy. They are able to fit three copies of the previously solved crystal structure of pMMO, an enzyme with mononuclear and binuclear copper centers, into the body of a 500-kD assembly; likewise, three copies of the crystal structure of MDH can be fitted into the cap, which is connected to the body via three arms. This supramolecular organization may facilitate the controlled transfer of electrons, which appears to be a common theme among membrane-bound enzymes catalyzing redox chemistry. -- GJC
Biochemistry 45, 10.1021/bi061294p (2006).
