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Chembiochem. 2018 Jan 4;19(1):53-57. doi: 10.1002/cbic.201700594. Epub 2017 Dec 12.

Flavin-N5 Covalent Intermediate in a Nonredox Dehalogenation Reaction Catalyzed by an Atypical Flavoenzyme.

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Department of Biochemistry, Virginia Tech, 360 West Campus Drive, Blacksburg, Virginia, 24061, USA.
Department of Biochemistry, University of Missouri, Columbia, Missouri, 65211, USA.
Department of Chemistry, University of Missouri, Columbia, Missouri, 65211, USA.


The flavin-dependent enzyme 2-haloacrylate hydratase (2-HAH) catalyzes the conversion of 2-chloroacrylate, a major component in the manufacture of acrylic polymers, to pyruvate. The enzyme was expressed in Escherichia coli, purified, and characterized. 2-HAH was shown to be monomeric in solution and contained a non-covalent, yet tightly bound, flavin adenine dinucleotide (FAD). Although the catalyzed reaction was redox-neutral, 2-HAH was active only in the reduced state. A covalent flavin-substrate intermediate, consistent with the flavin-acrylate iminium ion, was trapped with cyanoborohydride and characterized by mass spectrometry. Small-angle X-ray scattering was consistent with 2-HAH belonging to the succinate dehydrogenase/fumarate reductase family of flavoproteins. These studies establish 2-HAH as a novel noncanonical flavoenzyme.


covalent adduct; dehalogenation; flavin; iminium adduct; non-redox reactions

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