CO and CN- syntheses by [FeFe]-hydrogenase maturase HydG are catalytically differentiated events.

The synthesis and assembly of the active site [FeFe] unit of [FeFe]-hydrogenases require at least three maturases. The radical S-adenosyl-l-methionine HydG， the best characterized of these proteins， is responsible for the synthesis of the hydrogenase CO and CN(-) ligands from tyrosine-derived dehydroglycine (DHG). We speculated that CN(-) and the CO precursor (-):CO2H may be generated through an elimination reaction. We tested this hypothesis with both wild type and HydG variants defective in second iron-sulfur cluster coordination by measuring the in vitro production of CO， CN(-)， and (-):CO2H-derived formate. We indeed observed formate production under these conditions. We conclude that HydG is a multifunctional enzyme that produces DHG， CN(-)， and CO at three well-differentiated catalytic sites. We also speculate that homocysteine， cysteine， or a related ligand could be involved in Fe(CO)x(CN)y transfer to the HydF carrier/scaffold.