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Open AccessArticle

Characterization of a Flavonoid 3’/5’/7-O-Methyltransferase from Citrus reticulata and Evaluation of the In Vitro Cytotoxicity of Its Methylated Products

by Xiaojuan Liu 1,2,3,†, Yue Wang 1,2,3,†, Yezhi Chen 1,2,3, Shuting Xu 1,2,3, Qin Gong 1,2,3, Chenning Zhao 1,2,3, Jinping Cao 1,2,3 and Chongde Sun 1,2,3,*
1
College of Agriculture & Biotechnology, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
2
Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
3
The State Agriculture Ministry Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Molecules 2020, 25(4), 858; https://doi.org/10.3390/molecules25040858 (registering DOI)
Received: 18 January 2020 / Revised: 9 February 2020 / Accepted: 12 February 2020 / Published: 15 February 2020
(This article belongs to the Section Natural Products Chemistry)
O-methylation of flavonoids is an important modification reaction that occurs in plants. O-methylation contributes to the structural diversity of flavonoids, which have several biological and pharmacological functions. In this study, an O-methyltransferase gene (CrOMT2) was isolated from the fruit peel of Citrus reticulata, which encoding a multifunctional O-methyltransferase and could effectively catalyze the methylation of 3’-, 5’-, and 7-OH of flavonoids with vicinal hydroxyl substitutions. Substrate preference assays indicated that this recombinant enzyme favored polymethoxylated flavones (PMF)-type substrates in vitro, thereby providing biochemical evidence for the potential role of the enzyme in plants. Additionally, the cytotoxicity of the methylated products from the enzymatic catalytic reaction was evaluated in vitro using human gastric cell lines SGC-7901 and BGC-823. The results showed that the in vitro cytotoxicity of the flavonoids with the unsaturated C2-C3 bond was increased after being methylated at position 3’. These combined results provide biochemical insight regarding CrOMT2 in vitro and indicate the in vitro cytotoxicity of the products methylated by its catalytic reaction. View Full-Text
Keywords: citrus; flavonoids; O-methyltransferase; bioactivity; cytotoxicity citrus; flavonoids; O-methyltransferase; bioactivity; cytotoxicity
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MDPI and ACS Style

Liu, X.; Wang, Y.; Chen, Y.; Xu, S.; Gong, Q.; Zhao, C.; Cao, J.; Sun, C. Characterization of a Flavonoid 3’/5’/7-O-Methyltransferase from Citrus reticulata and Evaluation of the In Vitro Cytotoxicity of Its Methylated Products. Molecules 2020, 25, 858.

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