Molecular cloning and characterization of a flavonoid glucosyltransferase from Byungkyool (Citrus platymamma hort. ex Tanaka)

Uridine diphosphate glucosyltransferase (UGT) attaches glucoside to proteins, various flavonoids, and phenolic compounds. The modification of flavonoid affects its water solubility, stability, and bioavailability of flavonoids. In this study, citrus genomic sequence database was searched for UGTs of citrus, and a UDP-glucosyltransferase (bGT173) was isolated from Byungkyool (Citrus platymamma hort. ex Tanaka). The cloned cDNA gene was 1365 bp in length and encoded 456 amino acids. Phylogenetic analysis suggested that bGT173 was a member of the flavonoid 3-O-glucosyltransferase group. mRNA expression of bGT173 was higher in leaves compared to flowers, stems, and fruits. The recombinant protein of bGT173 was expressed in Escherichia coli, and tested for its activity on seven flavonoids (apigenin, eriodictyol, hesperetin, kaempferol, luteolin, naringenin, and quercetin). Both kaempferol and quercetin were good substrates for bGT173, demonstrating that bGT173 preferentially glucosylated the 3-hydroxyl group of flavonols. Furthermore, quercetin 3-O-glucoside produced in E. coli showed the same anti-migration activity on pancreatic cancer cells similar to the standard chemical, suggesting that bGT173 is a good candidate for bioconversion of quercetin to quercetin 3-O-glucoside.