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.
Kramer
Catherine M
CM
Syngenta Biotechnology Incorporated, 3054 Cornwallis Road, Research Triangle Park, NC 27709, USA.
Prata
Rogerio T N
RT
Willits
Michael G
MG
De Luca
Vincenzo
V
Steffens
John C
JC
Graser
Gerson
G
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