Redox-Triggered Coupling Network Mediates Long-Range Energy Trans-duction in Respiratory Complex I

Complex I is a gigantic redox-driven proton pump that powers oxidative phosphorylation by a unique long-range (>200 [A]) proton-coupled electron transfer process. To elucidate the molecular principles underlying this intricate action-at-a-distance effect, we combine here multiscale quantum/classical (QM/MM) simulations with site-directed mutagenesis, proteoliposome experiments, and cryo-electron microscopy (cryo-EM). We find that quinol binding at a distinct site within a local membrane cavity, triggers a long-range protonation cascade over water-mediated proton wires along a conserved carboxylate pathway (E-channel). We identify a central mechanical switch point, comprising the conserved Tyr156H, the mutation of which impedes conformational changes along conserved loops, but not the proton transfer reaction itself. Using our integrative multi-disciplinary approach, we reveal central coupling sites along the redox-driven proton transport process mediating energy conversion in Complex I, and illustrate the power of theory-guided experiments.