2020 journal article

Epoxidation Catalyzed by the Nonheme Iron(II)- and 2-Oxoglutarate-Dependent Oxygenase, AsqJ: Mechanistic Elucidation of Oxygen Atom Transfer by a Ferryl Intermediate

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142(13), 6268–6284.

By: J. Li*, H. Liao*, Y. Tang*, J. Huang n, L. Cha n, T. Lin*, J. Lee*, I. Kurnikov* ...

co-author countries: Taiwan, Province of China 🇹🇼 United States of America 🇺🇸
MeSH headings : Aspergillus nidulans / chemistry; Aspergillus nidulans / enzymology; Aspergillus nidulans / metabolism; Crystallography, X-Ray; Epoxy Compounds / chemistry; Epoxy Compounds / metabolism; Fungal Proteins / chemistry; Fungal Proteins / metabolism; Iron / chemistry; Iron / metabolism; Ketoglutaric Acids / metabolism; Models, Molecular; Oxygen / chemistry; Oxygen / metabolism; Oxygenases / chemistry; Oxygenases / metabolism
Source: Web Of Science
Added: May 26, 2020

Mechanisms of enzymatic epoxidation via oxygen atom transfer (OAT) to an olefin moiety is mainly derived from the studies on thiolate-heme containing epoxidases, such as cytochrome P450 epoxidases. The molecular basis of epoxidation catalyzed by nonheme-iron enzymes is much less explored. Herein, we present a detailed study on epoxidation catalyzed by the nonheme iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenase, AsqJ. The native substrate and analogues with different para substituents ranging from electron-donating groups (e.g., methoxy) to electron-withdrawing groups (e.g., trifluoromethyl) were used to probe the mechanism. The results derived from transient-state enzyme kinetics, Mössbauer spectroscopy, reaction product analysis, X-ray crystallography, density functional theory calculations, and molecular dynamic simulations collectively revealed the following mechanistic insights: (1) The rapid O2 addition to the AsqJ Fe(II) center occurs with the iron-bound 2OG adopting an online-binding mode in which the C1 carboxylate group of 2OG is trans to the proximal histidine (His134) of the 2-His-1-carboxylate facial triad, instead of assuming the offline-binding mode with the C1 carboxylate group trans to the distal histidine (His211); (2) The decay rate constant of the ferryl intermediate is not strongly affected by the nature of the para substituents of the substrate during the OAT step, a reactivity behavior that is drastically different from nonheme Fe(IV)-oxo synthetic model complexes; (3) The OAT step most likely proceeds through a stepwise process with the initial formation of a C(benzylic)–O bond to generate an Fe-alkoxide species, which is observed in the AsqJ crystal structure. The subsequent C3–O bond formation completes the epoxide installation.