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Toxins 2017, 9(2), 58; doi:10.3390/toxins9020058

Synthesis of Mono- and Di-Glucosides of Zearalenone and α-/β-Zearalenol by Recombinant Barley Glucosyltransferase HvUGT14077

1
Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz Straße 24, 3430 Tulln, Austria
2
Department of Food Chemistry and Toxicology, University of Vienna, Währinger Straße 38, 1090 Vienna, Austria
3
Center for Analytical Chemistry and Christian Doppler Laboratory for Mycotoxin Metabolism, Department of Agrobiotechnology (IFA-Tulln), BOKU, Konrad Lorenz Straße 20, 3430 Tulln, Austria
4
Dipartimento di Scienze Agrarie, degli Alimenti e dell’Ambiente, Università degli Studi di Foggia, Via-Napoli 25, 71122 Foggia, Italy
5
Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163, 1060 Vienna, Austria
*
Author to whom correspondence should be addressed.
Academic Editor: Isabelle P. Oswald
Received: 12 December 2016 / Revised: 2 February 2017 / Accepted: 6 February 2017 / Published: 9 February 2017
(This article belongs to the Section Mycotoxins)
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Abstract

Zearalenone (ZEN) is an estrogenic mycotoxin occurring in Fusarium-infected cereals. Glucosylation is an important plant defense mechanism and generally reduces the acute toxicity of mycotoxins to humans and animals. Toxicological information about ZEN-glucosides is limited due to the unavailability of larger amounts required for animal studies. HvUGT14077, a recently-validated ZEN-conjugating barley UDP-glucosyltransferase was expressed in Escherichia coli, affinity purified, and characterized. HvUGT14077 possesses high affinity (Km = 3 µM) and catalytic efficiency (kcat/Km = 190 s−1·mM−1) with ZEN. It also efficiently glucosylates the phase-I ZEN-metabolites α-zearalenol and β-zearalenol, with kcat/Km of 40 and 74 s−1·mM−1, respectively. HvUGT14077 catalyzes O-glucosylation at C-14 and C-16 with preference of 14-glucoside synthesis. Furthermore, relatively slow consecutive formation of 14,16-di-glucosides was observed; their structures were tentatively identified by mass spectrometry and for ZEN-14,16-di-glucoside confirmed by nuclear magnetic resonance spectroscopy. Recombinant HvUGT14077 allowed efficient preparative synthesis of ZEN-glucosides, yielding about 90% ZEN-14-glucoside and 10% ZEN-16-glucoside. The yield of ZEN-16-glucoside could be increased to 85% by co-incubation with a β-glucosidase highly selective for ZEN-14-glucoside. Depletion of the co-substrate UDP-glucose was counteracted by a sucrose synthase based regeneration system. This strategy could also be of interest to increase the yield of minor glucosides synthesized by other glucosyltransferases. View Full-Text
Keywords: zearalenone-14-glucoside; zearalenone-16-glucoside; masked mycotoxin; glycosylation; sucrose synthase; secondary metabolite zearalenone-14-glucoside; zearalenone-16-glucoside; masked mycotoxin; glycosylation; sucrose synthase; secondary metabolite
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MDPI and ACS Style

Michlmayr, H.; Varga, E.; Lupi, F.; Malachová, A.; Hametner, C.; Berthiller, F.; Adam, G. Synthesis of Mono- and Di-Glucosides of Zearalenone and α-/β-Zearalenol by Recombinant Barley Glucosyltransferase HvUGT14077. Toxins 2017, 9, 58.

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