Cloning and catalytic analysis of Isatis indigotica chalcone isomerase in vitro / 中国中药杂志

Chalcone isomerase is a key rate-limiting enzyme in the biosynthesis of flavonoids in higher plants, which determines the production of flavonoids in plants. In this study, RNA was extracted from different parts of Isatis indigotica and reverse-transcribed into cDNA. Specific primers with enzyme restriction sites were designed, and a chalcone isomerase gene was cloned from I. indigotica, named IiCHI. IiCHI was 756 bp in length, containing a complete open reading frame and encoding 251 amino acids. Homology analysis showed that IiCHI was closely related to CHI protein of Arabidopsis thaliana and had typical active sites of chalcone isomerase. Phylogenetic tree analysis showed that IiCHI was classified into type Ⅰ CHI clade. Recombinant prokaryotic expression vector pET28a-IiCHI was constructed and purified to obtain IiCHI recombinant protein. In vitro enzymatic analysis showed that the IiCHI protein could convert naringenin chalcone into naringenin, but could not catalyze the production of liquiritigenin by isoliquiritigenin. The results of real-time quantitative polymerase chain reaction(qPCR) showed that the expression level of IiCHI in the aboveground parts was higher than that in the underground parts and the expression level was the highest in the flowers of the aboveground parts, followed by leaves and stems, and no expression was observed in the roots and rhizomes of the underground parts. This study has confirmed the function of chalcone isomerase in I. indigotica and provided references for the biosynthesis of flavonoid components.

The UGT74L2 of Andrographis paniculata catalyzes phloretin to produce trilobatin and its enzymatic study / 药学学报

The last essential enzyme in the biosynthetic pathway of trilobatin, phloretin-4'-O glycosyltransferase (P4'-OGT), catalyzes the conversion of trilobatin to phloretin in vitro. However, only a few P4'-OGTs have been found in plants. This study used Malus domestica phloretin-4'-O glycosyltransferase (MdPh-4'-OGT) as a query to identify and clone two UDP-glucuronosyltransferase (UGT) genes, designated UGT74L2 and UGT74L3, from the transcriptome of Andrographis paniculata. According to a phylogenetic tree analysis, UGT74L2 and UGT74L3 belonged to the UGT74 family, which has been linked to several activities in other species. The in vitro enzymatic reaction demonstrated that UGT74L2 could particularly catalyze the formation of trilobatin from phloretin, but UGT74L3 had no effects. By using Ni-NTA affinity chromatography to extract the soluble UGT74L2 recombinant protein, the enzymatic kinetics of the activity was investigated using phloretin as the substrate. The results showed that the optimal temperature and pH for UGT74L2 enzymatic reaction were 40 ℃ and 8.0 (Tris-HCl system), respectively. Three metal ions (Ca2+, Mn2+ and Co2+) showed inhibitory effect on the activity of UGT74L2, while Mg2+ could improve the activity of UGT74L2. Other tested metal ions have no significant effect on UGT74L2. The results of enzymatic kinetic parameters that the Km value was 29.84 μmol·L-1, the kcat was 0.02 s-1, and the kcat·Km-1 was 572.6 mol-1·s-1. By homology modeling, molecular docking and mutation experiments, we found that multiple amino acids residues around the substrate binding pocket play quite an important role during catalytic process, In summary, we identified a novel P4'-OGT gene from medicinal plant Andrographis paniculata and provided a new efficient catalyst to synthesize trilobatin. Meanwhile, this study provides a reference for mining new efficient glycosylation modules from plants.

Biopathway construction of plant natural products / 药学学报

Plant natural products (PNPs) are important sources of innovative drugs. They are mainly obtained by isolation or extraction from plants. Low content and with structural analogues in plants result in high production cost, which restricts the research and application of PNPs. While biopathway construction by synthetic biology provides an alternative for production of PNPs. By biosynthetic pathway analysis of PNPs and reconstructing the biopathway in microorganisms, we can produce PNPs in cell factories efficiently. Recently, several predominantly international reports about biosynthesis of PNPs and its synthetic biology production, triggered the researches of PNPs. Abundant traditional Chinese medicine resources and profound cultural heritage of Chinese medicine make biosynthesis pathway analysis of PNPs to be a research hotspot. And some of the studies have achieved significant progress. Here, recent progress in the biosynthesis of plant natural products and its synthetic biology was reviewed. In particular, the application of new methods and technologies in recent years were summarized and discussed. This will provide reference for the biopathway construction of plant natural products.