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Mononuclear non-heme iron enzymes are a large class of enzymes catalyzing a wide-range of reactions. In this work, we report that a non-heme iron enzyme in Methyloversatilis thermotolerans , OvoA Mtht, has two different activities, as a thiol oxygenase and a sulfoxide synthase. When cysteine is presented as the only substrate, OvoA Mtht is a thiol oxygenase. In the presence of both histidine and cysteine as substrates, OvoA Mtht catalyzes the oxidative coupling between histidine and cysteine (a sulfoxide synthase). Additionally, we demonstrate that both substrates and the active site iron's secondary coordination shell residues exert exquisite control over the dual activities of OvoA Mtht (sulfoxide synthase vs. thiol oxygenase activities). OvoA Mtht is an excellent system for future detailed mechanistic investigation on how metal ligands and secondary coordination shell residues fine-tune the iron-center electronic properties to achieve different reactivities. 

Ergothioneine (ESH) and ovothiol A (OSHA) are two natural thiol‐histidine derivatives. ESH has been implicated as a longevity vitamin and OSHA inhibits the proliferation of hepatocarcinoma. The key biosynthetic step of ESH and OSHA in the aerobic pathways is the O₂‐dependent C−S bond formation catalyzed by non‐heme iron enzymes (e.g., OvoA in ovothiol biosynthesis), but due to the lack of identification of key reactive intermediate the mechanism of this novel reaction is unresolved. In this study, we report the identification and characterization of a kinetically competentS=1 iron(IV) intermediate supported by a four‐histidine ligand environment (three from the protein residues and one from the substrate) in enabling C−S bond formation in OvoA fromMethyloversatilis thermotoleran, which represents the first experimentally observed intermediate spin iron(IV) species in non‐heme iron enzymes. Results reported in this study thus set the stage to further dissect the mechanism of enzymatic oxidative C−S bond formation in the OSHA biosynthesis pathway. They also afford new opportunities to study the structure‐function relationship of high‐valent iron intermediates supported by a histidine rich ligand environment.

 

Ergothioneine (ESH) and ovothiol A (OSHA) are two natural thiol‐histidine derivatives. ESH has been implicated as a longevity vitamin and OSHA inhibits the proliferation of hepatocarcinoma. The key biosynthetic step of ESH and OSHA in the aerobic pathways is the O₂‐dependent C−S bond formation catalyzed by non‐heme iron enzymes (e.g., OvoA in ovothiol biosynthesis), but due to the lack of identification of key reactive intermediate the mechanism of this novel reaction is unresolved. In this study, we report the identification and characterization of a kinetically competentS=1 iron(IV) intermediate supported by a four‐histidine ligand environment (three from the protein residues and one from the substrate) in enabling C−S bond formation in OvoA fromMethyloversatilis thermotoleran, which represents the first experimentally observed intermediate spin iron(IV) species in non‐heme iron enzymes. Results reported in this study thus set the stage to further dissect the mechanism of enzymatic oxidative C−S bond formation in the OSHA biosynthesis pathway. They also afford new opportunities to study the structure‐function relationship of high‐valent iron intermediates supported by a histidine rich ligand environment.

 

Hydrogen bonds (H‐bonds) have been shown to modulate the chemical reactivities of iron centers in iron‐containing dioxygen‐activating enzymes and model complexes. However, few examples are available that investigate how systematic changes in intramolecular H‐bonds within the secondary coordination sphere influence specific properties of iron intermediates, such as iron‐oxido/hydroxido species. Here, we used⁵⁷Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the Fe‐O/OH vibrations in a series of Fe^III‐hydroxido and Fe^IV/III‐oxido complexes with varying H‐bonding networks but having similar trigonal bipyramidal primary coordination spheres. The data show that even subtle changes in the H‐bonds to the Fe‐O/OH units result in significant changes in their vibrational frequencies, thus demonstrating the utility of NRVS in studying the effect of the secondary coordination sphere to the reactivities of iron complexes.

 

Hydrogen bonds (H‐bonds) have been shown to modulate the chemical reactivities of iron centers in iron‐containing dioxygen‐activating enzymes and model complexes. However, few examples are available that investigate how systematic changes in intramolecular H‐bonds within the secondary coordination sphere influence specific properties of iron intermediates, such as iron‐oxido/hydroxido species. Here, we used⁵⁷Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the Fe‐O/OH vibrations in a series of Fe^III‐hydroxido and Fe^IV/III‐oxido complexes with varying H‐bonding networks but having similar trigonal bipyramidal primary coordination spheres. The data show that even subtle changes in the H‐bonds to the Fe‐O/OH units result in significant changes in their vibrational frequencies, thus demonstrating the utility of NRVS in studying the effect of the secondary coordination sphere to the reactivities of iron complexes.

 

Enhancing the redox properties of Fe^IIwith a bis(sulfonamido)amine pincer ligand leads to catalytic cyclic amination reactivity.