Biosynthesis and assembly of hydrogenase [NiFe]-cofactor: recent advances and perspectives.

The large subunit of all [NiFe]-hydrogenases in bacteria and archaea has a heterobimetallic NiFe(CN)2CO cofactor coordinated by four cysteine residues. The iron ion has two cyanides and a carbon monoxide as diatomic ligands. Six ancillary Hyp (ABCDEF) proteins are necessary for anaerobic synthesis of this cofactor, while under oxic conditions at least one further protein, HypX, is required for CO synthesis. The Fe(CN)2CO moiety of the cofactor is synthesized on a separate HypCD scaffold complex. Nickel is inserted into the apo-large subunit only after Fe(CN)2CO has been introduced. Recent biochemical and structural studies have significantly advanced our understanding of cofactor biosynthesis for these important metalloenzymes. Despite these gains in mechanistic insight, many questions still remain, the most pressing of which is the origin of the CO ligand in anaerobic microorganisms. This minireview provides an overview of the current status of this research field and highlights recent advances and unresolved issues.