# Progress on the Studies of the Key Enzymes of Ginsnoside Biosynthesis
## 8 UDP-Glycosyltransferase  
UDP-Glycosyltransferases (UGTs) catalyze the glycosylation reaction, which is the final step of ginsenoside biosynthesis. UGTs transfer glycosyl residues from activated sugars to the aglycones of ginsenosides, thus regulating properties of ginsenosides, such as bioactivity, solubility and stability. Glycoslation also determines the diversity of ginsenosides. UGTs exist in plants as a gene family with high specificity. UGTs are different by the different transferred glycosyl groups or different acceptors of glycosyl group. [PERSON] et al. [PERSON] et al. (2018) isolated a kind of UGT from _P. ginseng_ hairy root cultures whose molecular weight was 56.6 kD by SDS-PAGE. The enzymatic characteristics were also investigated in a preliminary study. [PERSON] et al. [PERSON] et al. (2018) purified a UGT from the suspension cells of _P. notoginseng_, which can convert Rd to Rb1. This work provides the basis for further molecular study on the ginsenoside biosynthesis and it is also useful for potential application to in vitro biotransformation from ginsenoside Rd to Rb1. [PERSON] et al. [PERSON] et al. (2018) identified 253 UGT genes from the transcriptomes of _P. ginseng_ root by 454 sequencing technology, and then selected six transcripts of UGTs that were most likely to be involved in ginsenoside biosynthesis. [PERSON] et al. [PERSON] et al. (2018) analyzed the transcriptome of _P. notoginseng_ root and proposed UGT gene Pn00082 to be likely involved in glycosylation of aglycones for ginsenoside biosynthesis from 242 UGT genes by phylogenetic analysis. These studies lay an important foundation for further screening of UGT genes involved in ginsenoside biosynthesis. In the past few years, significant advances have been made in the study of UGTs involved in ginsenoside biosynthesis. Several UGTs have been cloned and functionally identified from _Panax_ species. [PERSON] et al. [PERSON] et al. (2018) cloned and characterized UGTPg1 from _P. ginseng_, the first characterized UGT for glucagonylation of tetracycline triterpen substrates from plants which regiospecifically glycoslate C20-OH of DM and PPD. This was the key to the successful biosynthesis of CK in a one-pot reaction from simple sugars. This study provides not only a cost-effective CK-manufacturing method for its potential clinical applications, but also deepens our understanding of the biosynthetic pathways of ginsenosides within the _Panax_ plants. [PERSON] et al. [PERSON] et al. (2018) cloned and identified two UGTs from _P. ginseng_. UGTPg45 selectively transfers a glucose moiety to the C3-OH of PPD and its ginsenosides. UGTPg29 selectively transfers a glucose moiety to the C3 glucose of Rb2 to form a 1-2-glycosidic bond. Yeast cell factories were built to produce Rh2 and/or Rg3 from glucose based on the two UGTs and a yeast chassis to produce PPD. [PERSON] et al. (2018) sequenced and assembled the ginseng transcriptome and characterized two UGTs: PgUGT74 AE2 and PgUGT94Q2. PgUGT74 AE2 transfers a glucose moiety to the C3-OH of PPD and compound K to form Rh2 and F2, respectively, whereas PgUGT94Q2 transfers a glucose moiety to Rh2 and F2 to form Rg3 and Rd, respectively. Introduction of the two UGT genes into yeast together with DS and PPDS resulted in the production of Rg3. This result indicates that these two UGTs are key enzymes for the synthesis of ginseng, and provides a method for producing specific ginsenosides through yeast fermentation. [PERSON] et al. (2018) cloned and characterized UGT encoding genes catalyzing the glycosylation of PPT. Some key amino acid residues of the UGTs responsible for the activities and substrate regio-specificities were identified in the same study. The construction of yeast cell factories producing the bioactive ginsenosides F1 and Rh1 paves the way to manufacture these two high-value natural compounds through microbial fermentation in the future. The identity of UGTg45 and PgUGT74 AE2 was 95.4%, while the identity of UGTg29 and PgUGT94Q2 was 99.77%. [PERSON] et al.