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Plant Cell Physiol. 2009 Aug;50(8):1401-15. doi: 10.1093/pcp/pcp088. Epub 2009 Jun 27.

Functional and structural characterization of a flavonoid glucoside 1,6-glucosyltransferase from Catharanthus roseus.

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Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.


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.

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