Functional characterization, structural basis, and regio-selectivity control of a promiscuous flavonoid 7,4'-di- O -glycosyltransferase from Ziziphus jujuba var. spinosa .

A highly efficient and promiscuous 7,4'-di- O -glycosyltransferase ZjOGT3 was discovered from the medicinal plant Ziziphus jujuba var. spinosa . ZjOGT3 could sequentially catalyse 4'- and 7- O -glycosylation of flavones to produce 7,4'-di- O -glycosides with obvious regio-selectivity. For 7,4'-dihydroxyl flavanones and 3- O -glycosylated 7,4'-dihydroxyl flavones, ZjOGT3 selectively catalyses 7- O -glycosylation. The crystal structure of ZjOGT3 was solved. Structural analysis, DFT calculations, MD simulations, and site-directed mutagenesis reveal that the regio-selectivity is mainly controlled by the enzyme microenvironment for 7,4'-dihydroxyl flavones and 3- O -glycosylated 7,4'-dihydroxyl flavones. For 7,4'-dihydroxyl flavanones, the selectivity is mainly controlled by intrinsic reactivity. ZjOGT3 is the first plant flavonoid 7,4'-di- O -glycosyltransferase with a crystal structure. This work could help understand the catalytic mechanisms of multi-site glycosyltransferases and provides an efficient approach to synthesise O -glycosides with medicinal potential.