Role of Enzymes in the Biosynthesis of Hydrogenase H cluster

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Hydrogenases are a potential source of environmentally benign bioenergy, using complex cofactors to catalyze the reversible reduction of protons to form hydrogen. The most active subclass, the [FeFe]-hydrogenases, is dependent on a metallocofactor, the H cluster, that consists of a two iron subcluster ([2Fe]H) bridging to a classical cubane cluster ([4Fe-4S]H). The ligands coordinating to the diiron subcluster include an azadithiolate, three carbon monoxides, and two cyanides. To assemble this complex cofactor, three maturase enzymes, HydG, HydE and HydF are required. The biosynthesis of the diatomic ligands proceeds by an unusual fragmentation mechanism, and structural studies in combination with spectroscopic analysis have started to provide insights into the HydG mediated assembly of a [2Fe]H subcluster precursor. An organometallic intermediate CysFe(CO)2CN, is proposed as the product of HydG. It functions as a synthon for subsequent H-cluster assembly. Studies will focus on understanding the chemical mechanisms of H cluster assembly. Structural studies will concentrate on understanding substrate binding to the active site of HydG. Spectroscopic and biochemical studies will focus on characterising the organometallic intermediate generated by HydG and elucidating the subsequent steps required for hydrogenase activation