The respiratory Complex I is the first enzyme of the respiratory chain and a crucial enzyme for energy transduction in the cell. Complex I takes up electrons from NADH and transfers them to a quinone molecule. These redox reactions occurring in the hydrophilic domain are coupled to the pumping of four protons across the inner mitochondrial membrane, contributing to the generation of a proton motive force that powers the synthesis of ATP. Despite its fundamental role and its association to several mitochondrial disease, the molecular mechanism of Complex I is still highly debated. To study the key principles of the long-range proton pumping, we have dissected here the antiporter-like subunits of the membrane domain of Complex I to study their proton conduction by combining time-resolved spectroscopy, site-directed mutagenesis, and multiscale molecular simulations. We identified key gating residues that modulate the proton conduction in proteoliposomes. Our combined findings provide new insights into the elusive long-range energy transduction mechanism of Complex I and to molecular principles underlying ion transport across biological membranes.
Sofia Badolato (Sun,) studied this question.