Plant and Cell Physiology Advance Access originally published online on June 27, 2009
Plant and Cell Physiology 2009 50(8):1401-1415; doi:10.1093/pcp/pcp088
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Rapid Paper |
Functional and Structural Characterization of a Flavonoid Glucoside 1,6-Glucosyltransferase from Catharanthus roseus
1Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, 467-8603 Japan
2Venture Business Laboratory, Nagoya University, Nagoya, 464-8603 Japan
*Corresponding author: E-mail, hajimem{at}phar.nagoya-cu.ac.jp; Fax, +81-52-836-3415.
| Abstract |
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Sugar–sugar glycosyltransferases play an important role in structural diversity of small molecule glycosides in higher plants. We isolated a cDNA clone encoding a sugar–sugar glucosyltransferase (CaUGT3) catalyzing 1,6-glucosylation of flavonol and flavone glucosides for the first time from Catharanthus roseus. CaUGT3 exhibited a unique glucosyl chain elongation activity forming not only gentiobioside but also gentiotrioside and gentiotetroside in a sequential manner. We investigated the functional properties of CaUGT3 using homology modeling and site-directed mutagenesis, and identified amino acids positioned in the acceptor-binding pocket as crucial for providing enough space to accommodate flavonoid glucosides instead of flavonoid aglycones. These results provide basic information for understanding and engineering the catalytic functions of sugar–sugar glycosyltransferases involved in biosynthesis of plant glycosides.
Keywords: Catharanthus roseus - Flavonoid glucoside 1,6-glucosyltransferase - Functional characterization - Homology modeling - Sugar–sugar glycosyltransferase
Abbreviations: DMSO, dimethylsulfoxide; ESI, electrospray ionization; HMBC, heteronuclear multiple bond connectivity; LC-MS, liquid chromatography–mass spectrometry; MJ, methyl jasmonate; MOE, molecular operating environment; NMR, nuclear magnetic resonance; ORF, open reading frame; PSPG, plant secondary product glycosyltransferase; RACE, rapid amplification of cDNA ends; UCGT, UDP-glucose: curcumin glucosyltransferase; UCGGT, UDP-glucose:curcumin glucoside glucosyltransferase; UGT, family 1 glycosyltransferase
3Present address: Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801 Japan.
(Received April 11, 2009; Accepted June 16, 2009)
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