NASA Astrobiology Institute (NAI)

Iron-sulfur clusters are thought to be among the most ancient cofactors in living systems. The Fe-S enzyme thrust is focused on examining the structure, mechanism, and biosynthesis of the complex Fe-S enzymes nitrogenase and hydrogenase.

Structure, Function, and Biosynthesis of the Complex Iron-Sulfur Clusters at the Active Sites of Nitrogenases and Hydrogenases

(Peters, Broderick, & Szilagyi)

One of the key major thrusts of the ABRC is defining the relationship between structure and function of Fe-S enzymes. We are using a variety of approaches to characterize the physical and electronic structure of the complex Fe-S enzyme active sites of [FeFe]-hydrogenase and nitrogenases to elucidate the structural determinants of reactivity. In addition, we are examining how complex Fe-S clusters are assembled and matured in these systems. This analysis provides the inspiration for ABRC Fe-S mineral and synthetic/biomimetic catalysis teams to generate modified iron-sulfur mineral motifs with analogous features and assess the impact on reactivity. The results of this work are aimed at bridging our understanding of the relationship between abiotically and biotically derived iron-sulfur motifs and provide insights into the role of Fe-S mineral based catalysis in the origin of life. Combining experimental structure determination using X-ray diffraction methods with computational chemistry we have presented results suggesting that the composition of the ligand is dithiomethylether. The results provide the basis to revisit mechanistic schemes for reversible hydrogen oxidation at the H cluster and also to consider oxygen containing metabolites as precursors for the ligand for its biosynthesis. In other work, we report biochemical evidence that the accessory protein HydF functions as a scaffold in H cluster biosynthesis. This is the first function ascribed to an accessory enzyme in H cluster biosynthesis and the result provides the basis to systematically investigate the function of the remaining accessory proteins and to screen metabolic precursors of the unique nonprotein ligands. We have determined the three-dimensional structure of BchL, a component of protochlorophyllide reductase involved in bacteriochlorophyll biosynthesis. We have shown in this work that BchL is structurally very similar to the nitrogenase Fe proteins but have been able to identify structural differences that likely discriminate their respective functional roles.