A regiospecific rhamnosyltransferase from Epimedium pseudowushanense catalyzes the 3-O- rhamnosylation of prenylflavonols

摘要

Epimedium is used in traditional Chinese medicine and contains flavonol glycosides that exhibit multiple biological activities. These bioactive flavonol glycosides usually have a rhamnose moiety at the 3-OH position of prenylflavonols, such as icariin (9), baohuoside Ⅰ (1a) and baohuoside Ⅱ (2a). However, to date, no rhamnosyltransferase has been reported to catalyze the 3-O-rhamnosylation of prenylflavonols. In this article, a flavonol rhamnosyltransferase, EpPF3RT, was identified from E pseudowushanense B. L. Guo. The recombinant enzyme regiospecifically transfers a rhamnose moiety to 8-prenytkaempferol (1) and anhydroicaritin (2) at the 3-OH position to form baohuoside Ⅱ (1a) and baohuoside Ⅰ (2a) in vitro. In addition, a UDP-rhamnose synthase gene, EpRhS, from E pseudowushanense was functionally characterized and used to produce the UDP-rhamnose sugar donor. Furthermore, an engineered Escherichia coli strain containing EpPF3RT and EpRhS was established to produce baohuoside Ⅱ (1a) from whole cells. These studies indicate the significant potential of an enzymatic approach for the rhamnosylation of bioactive flavonoids in Epimedium plants and will provide a promising alternative for producing bioactive rhamnosylated flavonoids combined with other genes/enzymes by synthetic biology.