MMOD-induced structural changes of hydroxylase in soluble methane monooxygenase

Abstract

SummarySoluble methane monooxygenase in methanotrophs converts methane to methanol under ambient conditions1-3. The maximum catalytic activity of hydroxylase (MMOH) is achieved via interplay of its regulatory protein (MMOB) and reductase4-6. An additional auxiliary protein, MMOD, is believed to function as an inhibitor of the catalytic activity of MMOH; however, the mechanism of its action remains unknown7,8. Herein, we report the crystal structure of MMOH–MMOD complex fromMethylosinus sporiumstrain 5 (2.6 Å), which illustrates that two molecules of MMOD associate symmetrically with the canyon region of MMOH in a manner similar to MMOB, indicating that MMOD competes with MMOB for MMOH recognition. Further, MMOD binding disrupts the geometry of the di-iron centre and opens the substrate access channel. Notably, the electron density of 1,6-hexanediol at the substrate access channel mimics products of sMMO in hydrocarbon oxidation. The crystal structure of MMOH–MMOD unravels the inhibitory mechanism by which MMOD suppresses the MMOH catalytic activity, and reveals how hydrocarbon substrates/products access to the di-iron centre.