Glycosyltransferases (GTs) are bidirectional biocatalysts catalyzing the glycosylation of diverse molecules. However, the extensive applications of GTs in glycosides formation are limited due to their requirements of expensive nucleotide diphosphate (NDP)-sugars or NDP as the substrates. Here, in an effort to characterize flexible GTs for glycodiversification of natural products, we isolated a cDNA, designated as OcUGT1 from Ornithogalum caudatum, which encoded a flavonoid GT that was able to catalyze the trans-glycosylation reactions, allowing the formation of glycosides without the additions of NDP-sugars or NDP. In addition, OcUGT1 was observed to exhibit additional five types of functions, including classical sugar transfer reaction and three reversible reactions namely NDP-sugar synthesis, sugars exchange and aglycons exchange reactions, as well as enzymatic hydrolysis reaction, suggesting OcUGT1 displays both glycosyltransferase and glycosidase activities. Expression profiles revealed that the expression of OcUGT1 was development-dependent and affected by environmental factors. The unusual multifunctionality of OcUGT1 broadens the applicability of OcUGT1, thereby generating diverse carbohydrate-containing structures. Glycosylation is one of the most important modification reactions, in which sugar moieties are transferred to small molecular acceptors thereby leading to the formation of diverse glycosides with therapeutical potentials 1 . The enzyme-based glycosylations are mainly performed by two types of carbohydrate-active enzymes (CAZymes), glycosyltransferases (GTs, EC 2.4.x.y) and glycosidases (glycoside hydrolases; EC 3.2.x.y) 2 . Glycosidases are naturally hydrolytic enzymes that normally cleave glycosidic bonds 3 . However, glycosidase-assisted glycosylations are able to be achieved by trans-glycosylation reactions under certain controlled conditions 4 . The majority of glycosylation reactions in nature are performed in GT-catalyzed fashion, in which the carbohydrate moieties from activated NDP-sugars are transferred to acceptor molecules 5 . Also, GT-catalyzed glycosylations were accomplished by running the GT reactions in reverse 6 . New glycosides can be generated by reversible sugar or aglycon exchange reactions catalyzed by GTs with the addition of excess of NDP 6,7 . It is therefore obvious that GTs are generally perceived as bidirectional biocatalysts used in glycosylation of small molecules 1, 8, 9 . Yet, despite the validated potential of GTs in glycosides production, the extensive applications of GTs in industry remained limited due to the requirement of expensive NDP-sugars or NDP in GT-catalyzed forward or reversible reactions. Here, we report that a flavonoid GT, designated as OcUGT1, catalyzes the trans-glycosylation reactions, allowing the formation of glycosides without the additions of NDP-sugars or NDP. Specifically, in a screen of novel biocatalysts for flavonoid glycosylations from medicinal plant Ornithogalum caudatum, we found a multifunctional flavonoid GT OcUGT1 exhibiting at least six types of functions, including classical sugar transfer reaction and three reversible reactions namely NDP-sugar synthesis, sugars exchange and aglycons exchange reactions, as well as glycosidase specific hydrolysis and trans-glycosylation reactions. These evidences indicated that OcUGT1 shows
Output: Isolation and characterization of a multifunctional flavonoid glycosyltransferase from Ornithogalum caudatum with glycosidase activity OPEN