Structure of the Deactive State of Mammalian Respiratory Complex I

Kutti R Vinothkumar,James N Blaza,Judy Hirst

doi:10.1016/j.str.2017.12.014

Abstract

SummaryComplex 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 of Bos taurus complex I into the biochemically defined deactive state, and used single-particle electron cryomicroscopy to determine its structure to 4.1 Å resolution. We show that 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 to the NADH-reduced enzyme templates their reordering. Our structure both rationalizes biochemical data on the deactive state and offers new insights into its physiological and cellular roles.

Highlights

Complex I (NADH:ubiquinone oxidoreductase), a crucial enzyme in oxidative phosphorylation, uses NADH oxidation and ubiquinone reduction to build the proton motive force across the inner mitochondrial membrane, catalyzing respiration and driving ATP synthesis (Hirst, 2013; Sazanov, 2015)
Mammalian complex I, one of the largest membrane-bound enzymes in the cell, contains 45 subunits with a combined mass of 1 MDa; the 14 fully conserved core subunits are required for catalysis, while the 31 supernumerary subunits may be required for enzyme assembly, stability, or regulation (Fiedorczuk et al, 2016; Hirst et al, 2003; Stroud et al, 2016; Vinothkumar et al, 2014; Walker, 1992; Zhu et al, 2016)
In the absence of substrates, complex I relaxes into a profound resting state, known as the deactive state, that can be reactivated by addition of NADH and ubiquinone (Babot et al, 2014a; Galkin and Moncada, 2017; Kotlyar and Vinogradov, 1990; Vinogradov, 1998)

Summary

Introduction

Complex I (NADH:ubiquinone oxidoreductase), a crucial enzyme in oxidative phosphorylation, uses NADH oxidation and ubiquinone reduction to build the proton motive force across the inner mitochondrial membrane, catalyzing respiration and driving ATP synthesis (Hirst, 2013; Sazanov, 2015). Because the respiratory chain cannot catalyze in the absence of O2 (lack of an electron acceptor prevents electron flux along the chain), ischemia promotes complex I deactivation (Galkin et al, 2009; Maklashina et al, 2002, 2004). Controlling complex I reactivation provides a rational strategy for combating ischemia-reperfusion injury (Burwell et al, 2009; Chouchani et al, 2013). Forming the deactive state may tend to increase ischemia-reperfusion injury because it is more susceptible to oxidative damage than the active state (Gorenkova et al, 2013), and strategies to target and protect the deactive state may prove effective

Methods

Findings

Discussion

Conclusion