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The non‐heme iron ergothioneine synthase (EgtB) is a sulfoxide synthase that catalyzes oxidative C−S bond formation in the synthesis of ergothioneine, which plays roles against oxidative stress in cells. Despite extensive experimental and computational studies of the catalytic mechanisms of EgtB, the root causes for the selective C−S bond formation remain elusive. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we show herein that a coordination switch of the sulfoxide intermediate is involved in the catalysis of the non‐heme iron EgtB. This coordination switch from the S to the O atom is driven by the S/π electrostatic interactions, which efficiently promotes the observed stereoselective C−S bond formation while bypassing cysteine dioxygenation. The present mechanism is in agreement with all available experimental data, including regioselectivity, stereoselectivity and KIE results. This match underscores the critical role of coordination switching in the catalysis of non‐heme enzymes. [ABSTRACT FROM AUTHOR]

The 2‐oxoglutarate (2OG)‐dependent non‐heme enzyme FtmOx1 catalyzes the endoperoxide biosynthesis of verruculogen. Although several mechanistic studies have been carried out, the catalytic mechanism of FtmOx1 is not well determined owing to the lack of a reliable complex structure of FtmOx1 with fumitremorgin B. Herein we provide the X‐ray crystal structure of the ternary complex FtmOx1⋅2OG⋅fumitremorgin B at a resolution of 1.22 Å. Our structures show that the binding of fumitremorgin B induces significant compression of the active pocket and that Y68 is in close proximity to C26 of the substrate. Further MD simulation and QM/MM calculations support a CarC‐like mechanism, in which Y68 acts as the H atom donor for quenching the C26‐centered substrate radical. Our results are consistent with all available experimental data and highlight the importance of accurate complex structures in the mechanistic study of enzymatic catalysis. [ABSTRACT FROM AUTHOR]