Cryo-EM structures define ubiquinone-10 binding to mitochondrial complex I and conformational transitions accompanying Q-site occupancy

Mitochondrial complex I is a central metabolic enzyme that uses the reducing potential of NADH to reduce ubiquinone-10 (Q(10)) and drive four protons across the inner mitochondrial membrane, powering oxidative phosphorylation. Although many complex I structures are now available, the mechanisms of Q(10) reduction and energy transduction remain controversial. Here, we reconstitute mammalian complex I into phospholipid nanodiscs with exogenous Q(10). Using cryo-EM, we reveal a Q(10) molecule occupying the full length of the Q-binding site in the 'active' (ready-to-go) resting state together with a matching substrate-free structure, and apply molecular dynamics simulations to propose how the charge states of key residues influence the Q(10) binding pose. By comparing ligand-bound and ligand-free forms of the 'deactive' resting state (that require reactivating to catalyse), we begin to define how substrate binding restructures the deactive Q-binding site, providing insights into its physiological and mechanistic relevance. Using cryo-EM, Chung et al. investigate conformational states of mammalian respiratory complex I to reveal an ubiquinone-10 molecule occupying the full length of the Q-binding channel. Molecular dynamics simulations suggest how the charge states of key residues influence the substrate binding pose.

Automated summary

In this study, the authors reconstitute mammalian complex I and use cryo-EM and molecular dynamics simulations to investigate the binding and structural changes of Q(10) in the complex. The findings provide insights into the mechanism of Q(10) reduction and substrate binding in complex I.