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Mechanistic Insights into Ring Cleavage of Hydroquinone by PnpCD from Quantum Mechanical/Molecular Mechanical Calculations

Abstract

PnpCD is a mononuclear non-heme iron(II) dioxygenases containing an unusual 2His-1Glu-1Asn metal binding motif. To get insights into the catalytic mechanism of ring opening of hydroquinone by PnpCD, the hybrid quantum mechanics/molecular mechanics calculations have been performed by using two models with different protonation state of substrate (nonionized and ionized forms of the Fe-bound hydroxyl group of hydroquinone). In both cases, the structure of the reactive Fe-O2 species reveals a trigonal bipyramidal complex, in which Asn258 is no longer coordinated to the iron center. The catalytic process mainly involves the attack of superoxo radical, O-O bond cleavage, three-membered ring closure and opening, attack of the Fe-bound oxyl radical, and ring-opening of seven-membered ring. The transition state for the peroxo O-O bond cleavage was found to be rate-determining transition state. The second-sphere Glu248 serves as a proton acceptor to deprotonate the unbound substrate hydroxyl group, and hence facilitating the electron transfer between substrate and dioxygen. The first-sphere Glu262 can act as an acid-base catalyst to lower the rate-limiting barrier, thus providing a useful clue for improving the catalytic efficiency.

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Publication details

The article was received on 10 May 2019, accepted on 13 Aug 2019 and first published on 13 Aug 2019


Article type: Paper
DOI: 10.1039/C9OB01084J
Org. Biomol. Chem., 2019, Accepted Manuscript

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    Mechanistic Insights into Ring Cleavage of Hydroquinone by PnpCD from Quantum Mechanical/Molecular Mechanical Calculations

    S. Li, J. Lu and W. Lai, Org. Biomol. Chem., 2019, Accepted Manuscript , DOI: 10.1039/C9OB01084J

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