Density functional theory calculations on the active site of biotin synthase: mechanism of S transfer from the Fe2S2 cluster and the role of 1st and 2nd sphere residues

EPR-Derived Structure of a Paramagnetic Intermediate Generated by Biotin Synthase BioB

Biotin (vitamin B7) is an enzyme cofactor required by organisms from all branches of life but synthesized only in microbes and plants. In the final step of biotin biosynthesis, a radical S-adenosyl-l-methionine (SAM) enzyme, biotin synthase (BioB), converts the substrate dethiobiotin to biotin through the stepwise formation of two C-S bonds. Previous electron paramagnetic resonance (EPR) spectroscopic studies identified a semistable intermediate in the formation of the first C-S bond as 9-mercaptodethiobiotin linked to a paramagnetic [2Fe-2S] cluster through one of its bridging sulfides. Herein, we report orientation-selected pulse EPR spectroscopic results that reveal hyperfine interactions between the [2Fe-2S] cluster and a number of magnetic nuclei (e.g., 57Fe, 15N, 13C, and 2H) introduced in a site-specific manner via biosynthetic methods. Combining these results with quantum chemical modeling gives a structural model of the intermediate showing that C6, the target of the second hydrogen-atom abstraction, is now in close proximity to the nascent thioether sulfur and is ideally positioned for the second C-S bond forming event.

Effect of iron doping on protein molecular conductance

This study analyzes the role of Fe in electron transfer through non-heme iron-containing proteins.

Oxidative Cyclization in Natural Product Biosynthesis

Oxidative cyclizations are important transformations that occur widely during natural product biosynthesis. The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity, and biological activities. Some of the most dramatic structural alterations in natural product biosynthesis occur through oxidative cyclization. In this Review, we examine the different strategies used by nature to create new intra(inter)molecular bonds via redox chemistry. This Review will cover both oxidation- and reduction-enabled cyclization mechanisms, with an emphasis on the former. Radical cyclizations catalyzed by P450, nonheme iron, α-KG-dependent oxygenases, and radical SAM enzymes are discussed to illustrate the use of molecular oxygen and S-adenosylmethionine to forge new bonds at unactivated sites via one-electron manifolds. Nonradical cyclizations catalyzed by flavin-dependent monooxygenases and NAD(P)H-dependent reductases are covered to show the use of two-electron manifolds in initiating cyclization reactions. The oxidative installations of epoxides and halogens into acyclic scaffolds to drive subsequent cyclizations are separately discussed as examples of "disappearing" reactive handles. Last, oxidative rearrangement of rings systems, including contractions and expansions, will be covered.