Cloning and regiospecificity studies of two flavonoid glucosyltransferases from Allium cepa

• Published in: Phytochemistry (Oxford) Vol. 64; no. 6; pp. 1069 - 1076
• Main Authors: Kramer, Catherine M., Prata, Rogerio T.N., Willits, Michael G., De Luca, Vincenzo, Steffens, John C., Graser, Gerson
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.11.2003; Elsevier
• Subjects: Alliaceae; Allium cepa; Amino Acid Sequence; amino acid sequences; binding sites; Biological and medical sciences; Cloning, Molecular; complementary DNA; DNA, Complementary - genetics; enzyme activity; Enzymes; Escherichia coli; Flavonoids; Flavonoids - chemistry; Flavonoids - metabolism; Fundamental and applied biological sciences. Psychology; glucosyltransferase; Glucosyltransferases; Glucosyltransferases - chemistry; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; Glycosylation; hexosyltransferases; Metabolism; molecular cloning; Molecular Sequence Data; nucleotide sequences; Onion; onions; Onions - enzymology; Plant physiology and development; plant proteins; Quercetin; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Regiospecificity; sequence analysis; Sequence Homology, Amino Acid; Stereoisomerism; Substrate Specificity; vegetable crops; Allium cepa; Flavonoids; Onion; Substrate specificity; Quercetin; Glucosyltransferases; Alliaceae; Regiospecificity; Monocotyledones; Quecetin; Enzyme; Transferases; Glycosyltransferases; Biosynthesis; Glucose; Flavonoid; Glucosyltransferases: Substrate specificity; Regiospecifieity; Liliaceae; Angiospermae; Spermatophyta; Recombinant protein
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(03)00507-7

Two UDP-glucose-dependent flavonoid glucosyltransferases (EC 2.4.1.-) isolated from the epidermal layer of yellow onion ( Allium cepa) were functionally expressed in Escherichia coli and their substrate specificity investigated. The two enzymes exhibited different substrate- and regio-specificity profiles. A. cepa UGT73G1 used a wide range of different flavonoid substrates including flavonoids not naturally occurring in onion. Regiospecificity was indicated for hydroxyl-groups of the C-3, C-7 and C-4′ positions of the flavan backbone structure to yield flavonoid mono- and diglucosides. In contrast, A. cepa UGT73J1 showed activity only with the flavonoid mono-glucoside isoquercitrin and the isoflavone aglycone genistein, with regiospecificity for the C-7 position. The regiospecificity for both enzymes included positions that are glucosylated in flavonoids of onion bulbs, indicating their involvement in flavonoid biosynthesis in A. cepa. Two UDP-glucose-dependent flavonoid glucosyltransferases isolated from the epidermal layer of yellow onion ( Allium cepa) were heterologously expressed for the first time and their substrate specificity investigated. The two enzymes exhibited significantly different substrate specificity, but regiospecificity of both was consistent with quercetin glucosides found in A. cepa.