![]() The Huc catalytic subunits form an octameric 833 kDa complex around a membrane-associated stalk, which transports and reduces menaquinone 94 Å from the membrane. Huc uses narrow hydrophobic gas channels to selectively bind atmospheric H 2 at the expense of O 2, and 3 clusters modulate the properties of the enzyme so that atmospheric H 2 oxidation is energetically feasible. ![]() Huc is a highly efficient oxygen-insensitive enzyme that couples oxidation of atmospheric H 2 to the hydrogenation of the respiratory electron carrier menaquinone. Here we determined the cryo-electron microscopy structure of the Mycobacterium smegmatis hydrogenase Huc and investigated its mechanism. However, it remains unresolved how these enzymes overcome the extraordinary catalytic challenge of oxidizing picomolar levels of H 2 amid ambient levels of the catalytic poison O 2 and how the derived electrons are transferred to the respiratory chain 1. Atmospheric H 2 oxidation is attributed to uncharacterized members of the hydrogenase superfamily 4, 5. This globally significant process regulates the composition of the atmosphere, enhances soil biodiversity and drives primary production in extreme environments 2, 3. Diverse aerobic bacteria use atmospheric H 2 as an energy source for growth and survival 1. ![]()
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