Studies on the enzymatic synthesis of a new PPT-type ginsenoside via UDP-glycosyltransferase PgUGT74AE2 from Panax ginseng

UDP-glycosyltransferase PgUGT74AE2 from Panax ginseng can transfer a glucose moiety to the free C-3 hydroxyl of protopanaxadiol (PPD) to produce ginsenoside Rh2. However, no report demonstrates that PgUGT74AE2 can transfer a glucose moiety to the free C-3 hydroxyl of protopanaxatriol (PPT) to produce a PPT-type ginsenoside. In this study, the expression plasmid pET-32a-PgUGT74AE2 was constructed for expression of the recombinant protein and transferred into Escherichia coli Transetta (DE3) to generate the recombinant strain Transetta-PgUGT74AE2. The recombinant enzyme PgUGT74AE2 was expressed by induction of isopropyl-β-D-thiogalactoside (IPTG). An in vitro enzymatic reaction system was established with the recombinant enzyme PgUGT74AE2 and the substrate PPT. PgUGT74AE2 catalyzed the glycosylation of the free C-3 hydroxyl of PPT to produce 3-O-β-D-glucopyranosyl-dammar-24-ene-3β,6α,12β,20S-tetraol, a new PPT-type ginsenoside. This study provides an efficient approach for the biosynthesis of a new PPT-type ginsenoside through in vitro enzymatic reaction, which may pave a way to produce promising lead in drug discovery.