FaGT2: a multifunctional enzyme from strawberry (Fragaria × ananassa) fruits involved in the metabolism of natural and xenobiotic compounds

Fragaria × ananassa UDP-glucose:cinnamate glucosyltransferase (FaGT2) catalyzes the formation of cinnamic acid and p-coumaric acid glucose esters during strawberry fruit ripening. Here, the ripening and oxidative stress induced enzyme was further characterized by testing a range of structurally different substrates of natural and unnatural origin in vitro and comparing their kinetic parameters to elucidate its additional biological functions. The accepted substrates ranged from derivatives of cinnamic acid and benzoic acid to heterocyclic and aliphatic compounds resulting in the formation of O- and S-glucose esters, as well as O-glucosides. In planta assays confirmed the formation of glucose derivatives after injection of the substrates into strawberry fruits. Common chemical and structural features required for activity were the easy subtraction of a proton from the glucosylation site and the conjugation of the formed anion with π-electrons as best realized in the simplest substrate sorbic acid. In addition to cinnamic acid, the natural compounds anthranilic acid, trans-2-hexenoic acid, nicotinic acid and 2,5-dimethyl-4-hydroxy-3[2H]-furanone were glucosylated in vitro. But FaGT2 was also capable of efficiently converting xenobiotic substances like the herbicide 2,4,5-trichlorophenol and the herbicide analogue 3,5-dichloro-4-hydroxybenzoic acid. The results suggest that FaGT2 is involved in the detoxification of xenobiotics in accordance to its induction by oxidative stress.