A Cytochrome P450 Enzyme Catalyses Oxetane Ring Formation in Paclitaxel Biosynthesis.

Oxetane synthase (TmCYP1), a novel cytochrome P450 enzyme from Taxus × media cell cultures, has been functionally characterized to efficiently catalyse the formation of the oxetane ring in tetracyclic taxoids. Transient expression of TmCYP1 in Nicotiana benthamiana using 2α,5α,7ß,9α,10ß,13α-hexaacetoxytaxa-4(20),11(12)-diene (1) as a substrate led to the production of a major oxetane derivative, 1ß-dehydroxybaccatin IV (1a), and a minor 4ß,20-epoxide derivative, baccatin I (1b). However, feeding the substrate decinnamoyltaxinine J (2), a 5-deacetylated derivative of 1, yielded only 5α-deacetylbaccatin I (2b), a 4ß,20-epoxide. A possible reaction mechanism was proposed on the basis of substrate-feeding, 2H and 18O isotope labelling experiments, and density functional theory calculations. This reaction could be an intramolecular oxidation-acetoxyl rearrangement and the construction of the oxetane ring may occur through a concerted process; however, the 4ß,20-epoxide might be a shunt product. In this process, the C5-O-acetyl group in substrate is crucial for the oxetane ring formation but not for the 4(20)-epoxy ring formation by TmCYP1. These findings provide a better understanding of the enzymatic formation of the oxetane ring in paclitaxel biosynthesis.

Unravelling and reconstructing the biosynthetic pathway of bergenin.

Bergenin, a rare C-glycoside of 4-O-methyl gallic acid with pharmacological properties of antitussive and expectorant, is widely used in clinics to treat chronic tracheitis in China. However, its low abundance in nature and structural specificity hampers the accessibility through traditional crop-based manufacturing or chemical synthesis. In the present work, we elucidate the biosynthetic pathway of bergenin in Ardisia japonica by identifying the highly regio- and/or stereoselective 2-C-glycosyltransferases and 4-O-methyltransferases. Then, in Escherichia coli, we reconstruct the de novo biosynthetic pathway of 4-O-methyl gallic acid 2-C-ß-D-glycoside, which is the direct precursor of bergenin and is conveniently esterified into bergenin by in situ acid treatment. Moreover, further metabolic engineering improves the production of bergenin to 1.41 g L-1 in a 3-L bioreactor. Our work provides a foundation for sustainable supply of bergenin and alleviates its resource shortage via a synthetic biology approach.

Targeted Discovery of Glycosylated Natural Products by Tailoring Enzyme-Guided Genome Mining and MS-Based Metabolome Analysis.

Glycosides make up a biomedically important class of secondary metabolites. Most naturally occurring glycosides were isolated from plants and bacteria; however, the chemical diversity of glycosylated natural products in fungi remains largely unexplored. Herein, we present a paradigm to specifically discover diverse and bioactive glycosylated natural products from fungi by combining tailoring enzyme-guided genome mining with mass spectrometry (MS)-based metabolome analysis. Through in vivo genes deletion and heterologous expression, the first fungal C-glycosyltransferase AuCGT involved in the biosynthesis of stromemycin was identified from Aspergillus ustus. Subsequent homology-based genome mining for fungal glycosyltransferases by using AuCGT as a probe revealed a variety of biosynthetic gene clusters (BGCs) containing its homologues in diverse fungi, of which the glycoside-producing capability was corroborated by high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. Consequently, 28 fungal aromatic polyketide C/O-glycosides, including 20 new compounds, were efficiently discovered and isolated from the three selected fungi. Moreover, several novel fungal C/O-glycosyltransferases, especially three novel α-pyrone C-glycosyltransferases, were functionally characterized and verified in the biosynthesis of these glycosides. In addition, a proof of principle for combinatorial biosynthesis was applied to design the production of unnatural glycosides in Aspergillus nidulans. Notably, the newly discovered glycosides exhibited significant antiviral, antibacterial, and antidiabetic activities. Our work demonstrates the promise of tailoring enzyme-guided genome-mining approach for the targeted discovery of fungal glycosides and promotes the exploration of a broader chemical space for natural products with a target structural motif in microbial genomes.

Exploring the catalytic diversity of two short-chain dehydrogenases/reductases from Stachybotrys chartarum.

Short-chain dehydrogenase/reductases (SDRs) belong to the NAD(P)(H)-dependent oxidoreductase superfamily, which have various functions of catalyzing oxidation/reduction reactions and have been generally used as powerful biocatalysts in the production of pharmaceuticals. In this study, ScSDR1 and ScSDR2, two new SDRs have been identified and characterized from Stachybotrys chartarum 3.5365. Substrate scope investigation revealed that both of the enzymes possessed the ability to oxidize ß-OH to ketone specifically, and exhibited substrate promiscuity and high stereo-selectivity for efficiently catalyzing the structurally different prochiral ketones to chiral alcohols. These findings not only suggest that ScSDR1 and ScSDR2 might be potent synthetic tools in drug research and development, but also provide good examples for further engineered enzymes with higher efficiency and stereo-selectivity.

3D Honeycomb Fe/MXene Derived from Prussian Blue Microcubes with a Tunable Structure for Efficient Low-Frequency and Flexible Electromagnetic Absorbers.

The unique layered structure and high conductivity of MXene materials make them highly promising for microwave absorption. However, the finite loss mechanism and severe agglomeration present challenging obstacles for ideal microwave absorbers, which could be effectively improved by constructing a three-dimensional (3D) porous structure. This study reports a 3D honeycomb MXene using a straightforward template method. The 3D MXene framework offers ample cavities to anchor the Prussian blue microcubes and their derivatives including Fe microboxes and Fe clusters by a simple annealing process. Based on the superiority of the 3D honeycomb architecture and magnetic-dielectric synergistic effects, the Fe/MXene absorbers demonstrate outstanding microwave absorption capabilities with the optimum reflection loss value of -40.3 dB at 2.00 mm in the low-frequency range from 4.2 to 5.6 GHz. The absorber also manifests superior radar wave attenuation by finite element analysis and exhibits great potential to be a flexible and thermal insulation material in a wide range of temperatures. This work proposes a useful reference for the design of 3D MXene-based porous architectures, and the synergistic magnetic-dielectric strategy further expands the potential of MXene-based absorbers, enabling them to be used as flexible and highly efficient microwave absorbers.

Functional Characterization and Cyclization Mechanism of a Diterpene Synthase Catalyzing the Skeleton Formation of Cephalotane-Type Diterpenoids.

CsCTS, a new diterpene synthase from Cephalotaxus sinensis responsible for forming cephalotene, the core skeleton of cephalotane-type diterpenoids with a highly rigid 6/6/5/7 tetracyclic ring system, was functionally characterized. The stepwise cyclization mechanism is proposed mainly based on structural investigation of its derailment products, and further demonstrated through isotopic labeling experiments and density functional theory calculations. Homology modeling and molecular dynamics simulation combined with site-directed mutagenesis revealed the critical amino acid residues for the unique carbocation-driven cascade cyclization mechanism of CsCTS. Altogether, this study reports the discovery of the diterpene synthase that catalyzes the first committed step of cephalotane-type diterpenoid biosynthesis and delineates its cyclization mechanism, laying the foundation to decipher and artificially construct the complete biosynthetic pathway of this type diterpenoids.

Structural diversification of bioactive bibenzyls through modular co-culture leading to the discovery of a novel neuroprotective agent.

Bibenzyls, a kind of important plant polyphenols, have attracted growing attention for their broad and remarkable pharmacological activities. However, due to the low abundance in nature, uncontrollable and environmentally unfriendly chemical synthesis processes, these compounds are not readily accessible. Herein, one high-yield bibenzyl backbone-producing Escherichia coli strain was constructed by using a highly active and substrate-promiscuous bibenzyl synthase identified from Dendrobium officinale in combination with starter and extender biosynthetic enzymes. Three types of efficiently post-modifying modular strains were engineered by employing methyltransferases, prenyltransferase, and glycosyltransferase with high activity and substrate tolerance together with their corresponding donor biosynthetic modules. Structurally different bibenzyl derivatives were tandemly and/or divergently synthesized by co-culture engineering in various combination modes. Especially, a prenylated bibenzyl derivative (12) was found to be an antioxidant that exhibited potent neuroprotective activity in the cellular and rat models of ischemia stroke. RNA-seq, quantitative RT-PCR, and Western-blot analysis demonstrated that 12 could up-regulate the expression level of an apoptosis-inducing factor, mitochondria associated 3 (Aifm3), suggesting that Aifm3 might be a new target in ischemic stroke therapy. This study provides a flexible plug-and-play strategy for the easy-to-implement synthesis of structurally diverse bibenzyls through a modular co-culture engineering pipeline for drug discovery.

Functional characterization of a cycloartenol synthase and four glycosyltransferases in the biosynthesis of cycloastragenol-type astragalosides from Astragalus membranaceus.

Astragalosides are the main active constituents of traditional Chinese medicine Huang-Qi, of which cycloastragenol-type glycosides are the most typical and major bioactive compounds. This kind of compounds exhibit various biological functions including cardiovascular protective, neuroprotective, etc. Owing to the limitations of natural sources and the difficulties encountered in chemical synthesis, re-engineering of biosynthetic machinery will offer an alternative and promising approach to producing astragalosides. However, the biosynthetic pathway for astragalosides remains elusive due to their complex structures and numerous reaction types and steps. Herein, guided by transcriptome and phylogenetic analyses, a cycloartenol synthase and four glycosyltransferases catalyzing the committed steps in the biosynthesis of such bioactive astragalosides were functionally characterized from Astragalus membranaceus. AmCAS1, the first reported cycloartenol synthase from Astragalus genus, is capable of catalyzing the formation of cycloartenol; AmUGT15, AmUGT14, AmUGT13, and AmUGT7 are four glycosyltransferases biochemically characterized to catalyze 3-O-xylosylation, 3-O-glucosylation, 25-O-glucosylation/O-xylosylation and 2'-O-glucosylation of cycloastragenol glycosides, respectively. These findings not only clarified the crucial enzymes for the biosynthesis and the molecular basis for the structural diversity of astragalosides in Astragalus plants, also paved the way for further completely deciphering the biosynthetic pathway and constructing an artificial pathway for their efficient production.

Enzymatic synthesis of anhydroicaritin, baohuoside and icariin.

Anhydroicaritin (1a), baohuoside (1b) and icariin (1c) were recognized as major pharmacologically active ingredients of Epimedium plants. Their primary means of acquisition were chemical isolation from plants. However, it suffers from low yield, environmental pollution and shortage of plants. Herein, to remedy these problems, biosynthesis was explored to obtain the three active ingredients. Fortunately, with SfFPT as 8-prenyltransferase, EpPF3RT and Ep7GT as glycosyltransferases, kaempferide (1) was transferred to 1a, 1b and 1c enzymatically. Thus, we report the details of this method. This approach represents a promising environmental friendly alternative for the production of these compounds from an abundant analogue.

Electromagnetic absorption enhancing mechanisms by modified biochar derived from Enteromorpha prolifera: a combined experimental and simulation study.

Although the rapid advances of wireless technologies and electronic devices largely improve the quality of life, electromagnetic (EM) pollution increases the risk of exposure to EM radiation. Developing high-efficiency absorbers with a rational structure and wideband characteristics is of great significance to eliminate radiation pollution. Herein, Enteromorpha prolifera derived biochar which would provide a suitable surface and multiple polarizations has been prepared as the supporter to anchor nanoparticles. In addition, theoretical simulation results further confirm that radar wave scattering could be largely inhibited after coating with absorbing materials. As a result, the hybrid absorbers achieve remarkable EM absorption properties attributed to the synergistic magnetic-dielectric loss. Elaborate compositional and structural characterization studies indicate that the absorber has a large specific area and numerous polarization centers, which would make full use of waste biomass as light weight and broadband high-performance EM absorption materials.

Dengratiols E-G, three bioactive pairs of enantiomeric bibenzyl dimers from Dendrobium gratiosissimum.

Three pairs of enantiomeric bibenzyl dimers, (±)-dengratiols E-G [(±)-1-3], were obtained through various chromatographic techniques including chiral HPLC, from the ethanol extract of Dendrobium gratiosissimum. Their structures were elucidated to be R-(+)-1 and S-(-)-1, R-(+)-2 and S-(-)-2, and αR, α'R-(-)-3 and αS, α'S-(+)-3 on the basis of the extensive spectroscopic data and ECD analyses, respectively. The isolated enantiomerically pure along with their racemic forms showed moderate cytotoxicity against human HCT116, U87-MG, HepG2, BGC823, and PC9 cancer cell lines (IC50 9.25-48.01 µM). Enantiomers (+)-1 and (-)-1, and their racemate (±)-1 showed antiviral effects against HIV-1 with IC50 values of 12.26, 6.01, and 4.47 µM, respectively. Enantiomers (+)-2, and (-)-2 and their racemic form showed significant protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values of 5.07, 3.11, and 4.37 µM, respectively.

Two new 5/6/6 polyketide-amino acid hybrids from a genetic mutant of Periconia sp. F-31.

Peridecalins C and D (1 and 2), one decalin and one oxygen-decalin containing polyketide-amino acid hybrids with 5/6/6 ring system, was isolated from a genetic mutant of Periconia sp. F-31. Their structures were elucidated through extensive spectroscopic data analysis, including 1 D/2D NMR and HR-MS spectra. Biosynthetically, two proposed Diels-Alder reactions are supposed to be involved in the skeleton construction of 1 and 2.

Sesquiterpenes from the endophytic fungus Periconia sp. F-31.

One new eremophilane sesquiterpene periconianone L (1), together with four known guaiane-type sesquiterpenes 4,10,11-trihydroxyguaiane (2), (-)-guai-1(10)-ene-4α,11-diolhydroxymecuration (3), guaidiol A (4), and epi-guaidiol A (5) were isolated from the endophytic fungus Periconia sp. F-31. The structure of the new compound was established by spectroscopic methods, including UV, IR, HRESIMS, and extensive NMR techniques. Compound 3 was isolated as natural product for the first time.

Dengratiols A-D, four new bibenzyl derivatives from Dendrobium gratiossimum.

Dengratiol A (1), an unprecedented bibenzyl derivative bearing a tropolone unit together with three pairs of bibenzyl enantiomers (±)-dengratiols B-D [(±)-2-(±)-4], were isolated from Dendrobium gratiossimum Rchb.f. The resolution of enantiomers was performed with chiral HPLC. Their structures were characterized by extensive spectroscopic data analysis and calculated electronic circular dichroism (ECD). A hypothetical biosynthetic pathway for 1 is proposed. Biological assay revealed that (-)-2 showed moderate antiviral effect against IAV with IC50 value of 6.3 µM, and (±)-2 displayed cytotoxic activities against five human tumor cell lines with IC50 values ranging from 15.5 to 42.5 µM.

Morusalisins A-F, six new Diels-Alder type adducts, as potential PTP1B inhibitors from cell cultures of Morus alba.

Six new Diels-Alder type adducts, morusalisins A-F (1-6), were isolated from Morus alba cell cultures. The structures of 1-6 were determined by extensive spectroscopic data analysis, including HRESIMS, NMR, and ECD experiments. Furthermore, compounds 1-6 exhibited potent protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values ranging from 1.14 to 2.24 µM, making them promising as bioactive compounds for anti-diabetic drug discovery.

Biosynthesis of polyketides by two type III polyketide synthases from Aloe barbadensis.

Various bioactive polyketides have been found in Aloe barbadensis. However, the polyketide synthases (PKSs), which participate in biosynthesis of polyketides in A. barbadensis remain unknown. In this study, two type III PKSs (AbPKS1 and AbPKS2) were identified from A. barbadensis. AbPKS1 and AbPKS2 were able to utilize malonyl-CoA to yield heptaketides (TW93a and aloesone) and octaketides (SEK4 and SEK4b), respectively. AbPKS1 also exhibited catalytic promiscuity in recognizing CoA thioesters of aromatics to produce unusual polyketides. What Is more, a whole cell biocatalysis system with the capability of producing 26.4 mg/L of SEK4/SEK4b and 2.1 mg/L of aloesone was successfully established.

Bistachybotrysin K, one new phenylspirodrimane dimer from Stachybotrys chartarum with potent cytotoxic activity.

Bistachybotrysin K (1), one new phenylspirodrimane dimer with a central 6/7 oxygen heterocycle core, was isolated from the fungus Stachybotrys chartarum CGMCC 3.5365. Its structure was elucidated by extensive spectroscopic data and single-crystal X-ray diffraction. Compound 1 showed significant cytotoxicity against human tumor cell lines HCT116, NCI-H460, BGC823, Daoy, and HepG2 with IC50 values in the range of 1.1-4.7 µM.

Morusalones A-D, Diels-Alder Adducts with 6/7/6/6/6/6 Hexacyclic Ring Systems as Potential PTP1B Inhibitors from Cell Cultures of Morus alba.

Morusalones A-D (1-4), a new class of Diels-Alder adducts featuring unprecedented 6/7/6/6/6/6 hexacyclic core skeletons with a unique bridged cycloheptenone ring, were isolated from Morus alba cell cultures. The biosyntheses for 1-4 were proposed through an unusual Diels-Alder cycloaddition with quinostilbenes as dienophiles and prenyl 2-phenylbenzofuran as a diene to yield the typical methylhexene unit and a rare intramolecular nucleophilic addition to form the cycloheptenone ring. Compounds 1-4 exhibited protein tyrosine phosphatase 1B inhibitory activity.

Ep7GT, a glycosyltransferase with sugar donor flexibility from Epimedium pseudowushanense, catalyzes the 7-O-glycosylation of baohuoside.

Icariin (1a), a 7-O-glycosylated flavonoid glycoside, is recognized as the major pharmacologically active ingredient of Epimedium plants, which have been used in traditional Chinese medicine for thousands of years. However, no glycosyltransferase (GT) responsible for the 7-O-glycosylation of flavonoids has been identified from Epimedium plants to date. Herein, a GT, Ep7GT, was identified from E. pseudowushanense B. L. Guo, which can regiospecifically transfer a glucose moiety to baohuoside (1) at 7-OH to form icariin (1a). Ep7GT showed a rare broad donor substrate spectrum, including UDP-glucose, UDP-xylose, UDP-N-acetylglucosamine, UDP-rhamnose, UDP-galactose, UDP-glucuronic acid and TDP-glucose. Moreover, two new derivatives of icariin (1a), 7-O-ß-d-[2-(acetylamino)-2-deoxy-glucopyranosyl]-baohuoside (1b) and 7-O-ß-d-xylosyl-baohuoside (1c), were biosynthesized by using Ep7GT in vitro. Engineered Escherichia coli harbouring Ep7GT was constructed, and 10.1 µg mL-1 icariin (1a) was yielded by whole-cell biotransformation with baohuoside (1) as the substrate. The present work not only characterizes the GT responsible for the 7-O-glycosylation in the biosynthesis of icariin in Epimedium plants, but also indicates the significant potential of an enzymatic approach for the production of glycosylated baohuoside derivatives with different sugar moieties. What's more, these findings also provide a promising alternative for producing natural/unnatural bioactive flavonoid glycosides by metabolic engineering.

Enzymatic Synthesis of Bioactive O-Glucuronides Using Plant Glucuronosyltransferases.

Many O-glucuronides exhibiting various pharmacological activities have been found in nature and in drug metabolism. The glucuronidation of bioactive natural products or drugs to generate glucuronides with better activity and druggability is important in drug discovery and research. In this study, by using two uridine diphosphate (UDP)-dependent glucuronosyltransferases (GATs, UGT88D4 and UGT88D7) from plants, we developed two glucuronidation approaches, pure enzyme catalysis in vitro and recombinant whole-cell catalysis in vivo, to efficiently synthesize bioactive O-glucuronides by the glucuronidation of natural products. In total, 14 O-glucuronides with different structures, including flavonoids, anthraquinones, coumarins, and lignans, were obtained, 7 of which were new compounds. Furthermore, one of the biosynthesized O-glucuronides, kaempferol-7- O-ß-d-glucuronide (3a), potently inhibited protein tyrosine phosphatase (PTP) 1B with an IC50 value of 8.02 × 10-6 M. Some of the biosynthesized O-glucuronides also exhibited significant antioxidant activities.