Characterization and protein engineering of glycosyltransferases for the biosynthesis of diverse hepatoprotective cycloartane-type saponins in Astragalus membranaceus.

Although plant secondary metabolites are important source of new drugs, obtaining these compounds is challenging due to their high structural diversity and low abundance. The roots of Astragalus membranaceus are a popular herbal medicine worldwide. It contains a series of cycloartane-type saponins (astragalosides) as hepatoprotective and antivirus components. However, astragalosides exhibit complex sugar substitution patterns which hindered their purification and bioactivity investigation. In this work, glycosyltransferases (GT) from A. membranaceus were studied to synthesize structurally diverse astragalosides. Three new GTs, AmGT1/5 and AmGT9, were characterized as 3-O-glycosyltransferase and 25-O-glycosyltransferase of cycloastragenol respectively. AmGT1G146V/I variants were obtained as specific 3-O-xylosyltransferases by sequence alignment, molecular modelling and site-directed mutagenesis. A combinatorial synthesis system was established using AmGT1/5/9, AmGT1G146V/S and the reported AmGT8 and AmGT8A394F . The system allowed the synthesis of 13 astragalosides in Astragalus root with conversion rates from 22.6% to 98.7%, covering most of the sugar-substitution patterns for astragalosides. In addition, AmGT1 exhibited remarkable sugar donor promiscuity to use 10 different donors, and was used to synthesize three novel astragalosides and ginsenosides. Glycosylation remarkably improved the hepatoprotective and SARS-CoV-2 inhibition activities for triterpenoids. This is one of the first attempts to produce a series of herbal constituents via combinatorial synthesis. The results provided new biocatalytic tools for saponin biosynthesis.

Drought Stress Stimulates the Terpenoid Backbone and Triterpenoid Biosynthesis Pathway to Promote the Synthesis of Saikosaponin in Bupleurum chinense DC. Roots.

Bupleurum chinense is an important medicinal plant in China; however, little is known regarding how this plant transcribes and synthesizes saikosaponins under drought stress. Herein, we investigated how drought stress stimulates the transcriptional changes of B. chinense to synthesize saikosaponins. Short-term drought stress induced the accumulation of saikosaponins, especially from the first re-watering stage (RD_1 stage) to the second re-watering stage (RD_2 stage). Saikosaponin-a and saikosaponin-d increased by 84.60% and 75.13%, respectively, from the RD_1 stage to the RD_2 stage. Drought stress also stimulated a rapid increase in the levels of the hormones abscisic acid, salicylic acid, and jasmonic acid. We screened 49 Unigenes regarding the terpenoid backbone and triterpenoid biosynthesis, of which 33 differential genes were significantly up-regulated during drought stress. Moreover, one P450 and two UGTs are possibly involved in the synthesis of saikosaponins, while some transcription factors may be involved in regulating the expression of key enzyme genes. Our study provides a reference for the cultivation of B. chinense and a practical means to ensure the quality (safety and effectiveness) of B. chinense for medicinal use, as well as insights into the modernization of the China Agriculture Research System.

Distribution, Biotransformation, Pharmacological Effects, Metabolic Mechanism and Safety Evaluation of Platycodin D: A Comprehensive Review.

Platycodonis Radix (Jiegeng), the dried root of Platycodon grandiflorum, is a traditional herb used as both medicine and food. Its clinical application for the treatment of cough, phlegm, sore throat, pulmonary and respiratory diseases has been thousands of years in China. Platycodin D is the main active ingredient in Platycodonis Radix, which belongs to the family of pentacyclic triterpenoid saponins because it contains an oleanolane type aglycone linked with double sugar chains. Modern pharmacology has demonstrated that Platycodin D displays various biological activities, such as analgesics, expectoration and cough suppression, promoting weight loss, anti-tumor and immune regulation, suggesting that Platycodin D has the potential to be a drug candidate and an interesting target as a natural product for clinical research. In this review, the distribution and biotransformation, pharmacological effects, metabolic mechanism and safety evaluation of Platycodin D are summarized to lay the foundation for further studies.

SARS-CoV-2 main protease inhibition by compounds isolated from Luffa cylindrica using molecular docking.

In this study, chemical investigation of methanol extract of the air-dried fruits of Luffa cylindrica led to the identification of a new δ-valerolactone (1), along with sixteen known compounds (2-17). Their chemical structures including the absolute configuration were elucidated by extensive spectroscopic analysis and electronic circular dichroism analysis, as well as by comparison with those reported in the literature. For the first time in literature, we have examined the binding potential of the isolated compounds to highly conserved protein, Mpro of SARS-CoV-2 using the molecular docking technique. We found that the isolated saponins (14-17) bind to the substrate-binding pocket of SARS-CoV-2 Mpro with docking energy scores of -7.13, -7.29, -7.47, and -7.54 kcal.mol-1, respectively, along with binding abilities equivalent to an already claimed N3 protease inhibitor (-7.51 kcal.mol-1).

Discovery and structural optimization of 3-O-ß-chacotriosyl oleanane-type triterpenoids as potent entry inhibitors of SARS-CoV-2 virus infections.

Currently, SARS-CoV-2 virus is an emerging pathogen that has posed a serious threat to public health worldwide. However, no agents have been approved to treat SARS-CoV-2 infections to date, underscoring the great need for effective and practical therapies for SARS-CoV-2 outbreaks. We reported that a focused screen of OA saponins identified 3-O-ß-chacotriosyl OA benzyl ester 2 as a novel small molecule inhibitor of SARS-CoV-2 virus entry, via binding to SARS-CoV-2 glycoprotein (S). We performed structure-activity relationship profiling of 2 and discovered C-17-COOH of OA was an important modification site that improved both inhibitor potency toward SARS-CoV-2 and selectivity index. Then optimization from hit to lead resulted in a potent fusion inhibitor 12f displaying strong inhibition against infectious SARS-CoV-2 with an IC50 value of 0.97 µM in vitro. Mechanism studies confirmed that inhibition of SARS-CoV-2 viral entry of 12f was mediated by the direct interaction with SARS-CoV-2 S2 subunit to block membrane fusion. These 3-O-ß-chacotriosyl OA amide saponins are suitable for further optimization as SARS-CoV-2 entry inhibitors with the potential to be developed as therapeutic agents for the treatment of SARS-CoV-2 virus infections.

Computational assessment of saikosaponins as adjuvant treatment for COVID-19: molecular docking, dynamics, and network pharmacology analysis.

Saikosaponins are major biologically active triterpenoids, usually as glucosides, isolated from Traditional Chinese Medicines (TCM) such as Bupleurum spp., Heteromorpha spp., and Scrophularia scorodonia with their antiviral and immunomodulatory potential. This investigation presents molecular docking, molecular dynamics simulation, and free energy calculation studies of saikosaponins as adjuvant therapy in the treatment for COVID19. Molecular docking studies for 23 saikosaponins on the crystal structures of the extracellular domains of human lnterleukin-6 receptor (IL6), human Janus Kinase-3 (JAK3), and dehydrogenase domain of Cylindrospermum stagnale NADPH-oxidase 5 (NOX5) were performed, and selected protein-ligand complexes were subjected to 100 ns molecular dynamics simulations. The molecular dynamics trajectories were subjected to free energy calculation by the MM-GBSA method. Molecular docking and molecular dynamics simulation studies revealed that IL6 in complex with Saikosaponin_U and Saikosaponin_V, JAK3 in complex with Saikosaponin_B4 and Saikosaponin_I, and NOX5 in complex with Saikosaponin_BK1 and Saikosaponin_C have good docking and molecular dynamics profiles. However, the Janus Kinase-3 is the best interacting partner for the saikosaponin compounds. The network pharmacology analysis suggests saikosaponins interact with the proteins CAT Gene CAT (Catalase) and Checkpoint kinase 1 (CHEK1); both of these enzymes play a major role in cell homeostasis and DNA damage during infection, suggesting a possible improvement in immune response toward COVID-19.