The three-dimensional structure of NiFeSe hydrogenase from Desulfovibrio vulgaris Hildenborough: a hydrogenase without a bridging ligand in the active site in its oxidised, "as-isolated" state

Hydrogen is a good energy vector, and its production from renewable sources is a requirement for its widespread use. [NiFeSe] hydrogenases, (Hases) are attractive candidates for the biological production of hydrogen because they are capable of high production rates even in the presence of moderate amounts of O-2, lessening the requirements for anaerobic conditions. The three-dimensional structure of the [NiFeSe] Hase from Desulfovibrio vulgaris Hildenborough has been determined in its oxidised "as-isolated" form at 2.04-angstrom resolution. Remarkably, this is the first structure of an oxidised Hase of the [NiFe] fan-Lily that does not contain an oxide bridging ligand at the active site. Instead, an extra sulfur atom is observed binding Ni and Se, leading to a SeCys conformation that shields the NiFe site from contact with oxygen. This structure provides several insights that may explain the fast activation and O-2 tolerance of these enzymes.