Functional and structural characterization of a flavonoid glucoside 1,6-glucosyltransferase from Catharanthus roseus.
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.
Masada
Sayaka
S
Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
Terasaka
Kazuyoshi
K
Oguchi
Yukie
Y
Okazaki
Seiji
S
Mizushima
Tunehiro
T
Mizukami
Hajime
H
D000595:Amino Acid Sequence; D030008:Catharanthus / Q000201:enzymology* / Q000235:genetics; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D005419:Flavonoids / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D006027:Glycosides / Q000096:biosynthesis; D006031:Glycosylation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011794:Quercetin / Q000378:metabolism; D013379:Substrate Specificity
D018076:DNA, Complementary; D018744:DNA, Plant; D005419:Flavonoids; D006027:Glycosides; D010940:Plant Proteins; D011794:Quercetin; D005964:Glucosyltransferases