Cloning and regiospecificity studies of two flavonoid glucosyltransferases from Allium cepa.
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.
Syngenta Biotechnology Incorporated, 3054 Cornwallis Road, Research Triangle Park, NC 27709, USA.
Catherine M
CM
Kramer
Rogerio T N
RT
Prata
Michael G
MG
Willits
Vincenzo
V
De Luca
John C
JC
Steffens
Gerson
G
Graser
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism*; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006031:Glycosylation; D008969:Molecular Sequence Data; D019697:Onions / Q000201:enzymology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013237:Stereoisomerism; D013379:Substrate Specificity
D018076:DNA, Complementary; D005419:Flavonoids; D011994:Recombinant Proteins; D005964:Glucosyltransferases