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

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.

Abbreviations: methenyl-H₄MPT⁺, methenyl-tetrahydromethanopterin, methylene-H₄MPT, methylene-tetrahydromethanopterin, FeGP, iron–guanylylpyridinol, EXAFS, extended X-ray absorption fine structure, ATR-IR, attenuated total reflection infrared, DTT, dithiothreitol, r.m.s., root-mean-square, GP, guanylylpyridinol

Keywords: Hydrogenase, Iron–guanylylpyridinol-cofactor, Methanogenic archaea, Iron complex, X-ray crystal structure, X-ray absorption spectroscopy