P94: Identification of Novel Ginseng UDP-glycosyltransferases Acting on C3 Position of Protopanaxadiol to Produce Ginsenosides

Ginseng (Panax ginseng C.A. Meyer) is one of the most popular medicinal herbs and its pharmacological actions are attributed to various ginsenosides.  Ginsenosides are classified into two groups, protopanaxadiol (PPD) and protopanaxatriol (PPT), based on their hydroxylation patterns.  PPD and PPT are further modified by glycosylation into more than forty different ginsenosides.  PPD group ginsenosides are glycosylated at C3, C20 or both positions, while PPT group ginsenosides are glycosylated at C6, C20 or both positions.  However, glycosyltransferases of ginseng have not yet been identified.  To discover glycosyltransferases of ginseng, we cloned glycosyltransferase genes from the ginseng EST library and confirmed their enzymatic activity.  We found two glycosyltransferases named PgUGT74A1 and PgUGT94B1.  PgUGT74A1 converted PPD to ginsenoside Rh₂ by attaching a glucose at C3 position of PPD with an O-glycosidic linkage, while PgUGT94B1 converted ginsenoside Rh₂ to ginsenoside Rg₃ by adding a glucose to ginsenoside Rh₂ with a beta-(1->2)-glycosidic linkage.  Furthermore, PgUGT74A1 and PgUGT94B1 converted Compound K to ginsenoside F₂ and ginsenoside F₂ to ginsenoside Rd, respectively.  By using these two glycosyltransferases in the same reaction, we could convert either PPD directly to ginsenoside Rg₃ or Compound K directly to ginsenoside Rd. Our results indicate that our glycosyltransferases are very useful in producing various kinds of ginsenosides with specific pharmacological functions.