Functional Dynamics of an Ancient Membrane-Bound Hydrogenase.

The membrane-bound hydrogenase (Mbh) is a redox-driven Na+/H+ transporter that employs the energy from hydrogen gas (H2) production to catalyze proton pumping and Na+/H+ exchange across cytoplasmic membranes of archaea. Despite a recently resolved structure of this ancient energy-transducing enzyme [Yu et al. Cell 2018, 173, 1636-1649], the molecular principles of its redox-driven ion-transport mechanism remain puzzling and of major interest for understanding bioenergetic principles of early cells. Here we use atomistic molecular dynamics (MD) simulations in combination with data clustering methods and quantum chemical calculations to probe principles underlying proton reduction as well as proton and sodium transport in Mbh from the hyperthermophilic archaeon Pyrococcus furiosus. We identify putative Na+ binding sites and proton pathways leading across the membrane and to the NiFe-active center as well as conformational changes that regulate ion uptake. We suggest that Na+ binding and protonation changes at a putative ion-binding site couple to proton transfer across the antiporter-like MbhH subunit by modulating the conformational state of a conserved ion pair at the subunit interface. Our findings illustrate conserved coupling principles within the complex I superfamily and provide functional insight into archaeal energy transduction mechanisms.