Structure of the deactive state of mammalian respiratory complex I

AbstractComplex I (NADH:ubiquinone oxidoreductase) is central to energy metabolism in mammalian mitochondria. It couples NADH oxidation by ubiquinone to proton transport across the energy-conserving inner membrane, catalyzing respiration and driving ATP synthesis. In the absence of substrates, ‘active’ complex I gradually enters a pronounced resting or ‘deactive’ state. The active-deactive transition occurs during ischemia and is crucial for controlling how respiration recovers upon reperfusion. Here, we set a highly-active preparation ofBos tauruscomplex I into the biochemically-defined deactive state, and used single-particle electron cryomicroscopy to determine its structure to 4.1 Å resolution. The deactive state arises when critical structural elements that form the ubiquinone-binding site become disordered, and we propose reactivation is induced when substrate binding templates their reordering. Our structure both rationalizes biochemical data on the deactive state, and offers new insights into its physiological and cellular roles.