The crystal structure of C176A mutated [Fe]‐hydrogenase suggests an acyl‐iron ligation in the active site iron complex

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Abstract
[Fe]‐hydrogenase is one of three types of enzymes known to activate H2. Crystal structure analysis recently revealed that its active site iron is ligated square‐pyramidally by Cys176‐sulfur, two CO, an “unknown” ligand and the sp2‐hybridized nitrogen of a unique iron–guanylylpyridinol‐cofactor. We report here on the structure of the C176A mutated enzyme crystallized in the presence of dithiothreitol (DTT). It suggests an iron center octahedrally coordinated by one DTT‐sulfur and one DTT‐oxygen, two CO, the 2‐pyridinol's nitrogen and the 2‐pyridinol's 6‐formylmethyl group in an acyl‐iron ligation. This result led to a re‐interpretation of the iron ligation in the wild‐type.