Biosynthesis of the [FeFe] Hydrogenase H Cluster: A Central Role for the Radical SAM Enzyme HydG

Abstract

Hydrogenase enzymes catalyze the rapid and reversible interconversion of H2 with protons and electrons. The active site of the [FeFe] hydrogenase is the H cluster, which consists of a [4Fe–4S]H subcluster linked to an organometallic [2Fe]H subcluster. Understanding the biosynthesis and catalytic mechanism of this structurally unusual active site will aid in the development of synthetic and biological hydrogenase catalysts for applications in solar fuel generation. The [2Fe]H subcluster is synthesized and inserted by three maturase enzymes—HydE, HydF, and HydG—in a complex process that involves inorganic, organometallic, and organic radical chemistry. HydG is a member of the radical S-adenosyl-L-methionine (SAM) family of enzymes and is thought to play a prominent role in [2Fe]H subcluster biosynthesis by converting inorganic Fe2+, L-cysteine (Cys), and L-tyrosine (Tyr) into an organometallic [(Cys)Fe(CO)2(CN)]− intermediate that is eventually incorporated into the [2Fe]H subcluster. In this Forum Article, the mechanism of [2Fe]H subcluster biosynthesis is discussed with a focus on how this key [(Cys)Fe(CO)2(CN)]− species is formed. Particular attention is given to the initial metallocluster composition of HydG, the modes of substrate binding (Fe2+, Cys, Tyr, and SAM), the mechanism of SAM-mediated Tyr cleavage to CO and CN−, and the identification of the final organometallic products of the reaction.

Artificial Maturation of the Highly Active Heterodimeric [FeFe] Hydrogenase from Desulfovibrio desulfuricans ATCC 7757

“…There are three maturases: HydE, HydF, and HydG. HydE and HydG are radical S‐adenosylmethionine (SAM) enzymes that are involved in the synthesis of [2Fe] H on the putative scaffold protein HydF, which then delivers the cluster to the hydrogenase . It was possible to co‐express the maturases from other species in E. coli and produce active [FeFe] hydrogenases ,.…”

Enzymkaskadenreaktionen in der Biosynthese

“…[104] Bei der Umwandlung der inaktiven Apo-Formen mikrobieller [FeFe]-Hydrogenasen in die aktiven Formen, die sowohl Kohlenmonoxid als auch Cyanid als Liganden an den aktiven Zentren der Eisen-Schwefel-Cluster enthalten, wird die Aminosäure Ty rosin zu p-Cresol sowie zum Cyanid-Ion und Kohlenmonoxid-Molekülmit jeweils einem Kohlenstoff-Atom fragmentiert (Schema 40). [105] Dies ist eine faszinierende Kaskade mit Radikal-SAM-Enzymen. Es wird angenommen, dass etwa ein Drittel der mehr als 100 000 offenen Leserahmen, die als Radikal-SAM-Enzymei nP roteindatenbanken prognostiziert wurden, auch Vitamin B 12 Bisher sind noch keine Biosynthese-Analoga von ¾quivalenten der metallkoordinierten Alkenmetathese in der Enzymkatalyse bekannt.…”

Overview of the Maturation Machinery of the H-Cluster of [FeFe]-Hydrogenases with a Focus on HydF

“…HydG has long been recognized to provide the CO and CN − ligands of the [2Fe] H cluster. Recently, mostly through a combination of isotopic labeling and pulsed EPR experiments the role of HydG in the maturation pathway has been further expanded [ 41 , 44 , 45 , 46 , 47 ]: it has been shown to synthesize the synthon of the [2Fe] H cluster, a low-spin iron complex, Fe(CO) 2 (CN)Cys. The assembly of the synthon is a multi-step process involving both active sites of the enzyme.…”