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Four new efrotomycins, A1-A4 (

Lobophorins (LOBs) belong to a large family of spirotetronate antibiotics with antibacterial and antitumor activities. In this study, we demonstrated the function of LobP1, a P450 monooxygenase encoded in the LOB biosynthetic gene cluster, by in vivo deletion and in vitro biochemical assays. The disruption of lobP1 led to the isolation of three new LOBs derivatives (3‒5) and three known ones (6‒8) without the hydroxyl group at C-32. LobP1 was shown to have relatively broad substrate scope. Determing the kinetic parameters of LobP1 towards different substrates revealed that LobP1 preferred substrate with a nitrosugar. The major product LOB E (6) from the ∆lobP1 mutant displayed better cytotoxic activities against several cancer cell lines than LOB B, the C-32 hydroxlated counterpart.

The installation of halogen atoms into aromatic and less activated polyketide substrates by halogenases is a powerful strategy to tune the bioactivity, bioavailability, and reactivity of compounds. In the biosynthetic pathway of totopotensamide A (

Tiacumicin B (also known as fidaxomicin or difimicin) is a marketed 18-membered macrolide antibiotic for the treatment of Clostridium difficile infections. Tiacumicin B is structurally characterized with two chlorine atoms substituted on the aromatic ring, which is installed by the halogenase TiaM. During the study on halide compatibility of TiaM, a facile and nonenzymatic iodination method of didechlorotiacumicin B was discovered, requiring NaI, acid and air for iodination at room temperature. This method was also amenable to other 9 aromatic substrates with electron-rich sites for iodination.

Fluostatins belong to the atypical angucyclinone aromatic polyketides featuring a distinctive tetracyclic benzo[a]fluorene skeleton. To understand the formation of the heavily oxidized A-ring in fluostatins, a flavin adenine dinucleotide-binding oxidoreductase-encoding gene flsP was inactivated, leading to the production of an unprecedented 1,4-oxazepine-linked seco-fluostatin heterodimer difluostatin I (7) and five new fluostatin-related derivatives, fluostatins T-X (8-12). Their structures were elucidated by mass spectrometry, nuclear magnetic resonance, X-ray diffraction analysis, and biosynthetic considerations. Difluostatin I (7) represents the first example with an A-ring-cleaved 3',4'-seco-fluostatin skeleton. The absolute configuration of fluostatin T (8) was determined by X-ray diffraction analysis. Fluostatin W (11) contains an uncommon isoxazolinone ring. These findings highlight the structural diversity of fluostatins.

Two new piericidins A5 (1) and G1 (2), a previously synthesized piericidin G2 (3), and two known piericidins A1 (4) and A2 (5) were isolated from the marine-derived Streptomyces sp. SCSIO 40063. The structures of 1-5 were elucidated by HRESIMS, 1 D, 2 D NMR data analyses and comparisons with the known compounds. Compound 2 showed moderate cytotoxicities against four human tumor cell lines SF-268, MCF-7, HepG2 and A549 with IC50 values between 10.0 and 12.7 μM.

Trichoderma harzianum is a widely used biocontrol agent in agriculture. Obtaining a full inventory of the small molecules that can be biosynthesized from the encoded biosynthetic gene clusters (BGCs) is therefore useful for understanding associated plant-microbe and microbe-microbe interactions. Here we heterologously reconstituted a polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) encoding gene cluster from T. harzianum t-22 in Aspergillus nidulans A1145. Six new tetronate natural products trihazone A-F (1-6) were isolated and elucidated by HRESIMS and 1D and 2D NMR data. Three of the products contain an exocyclic olefin, which is derived from the oxidative decarboxylation of an α-ketoglutarate-dependent dioxygenase ThnC as shown by biochemical assays.

A new cyclo-heptadepsipeptide xanthostatin B (1), together with isobutyryl hexapeptide (2), xanthostatin (3), TXS-1 (4) and TXS-2 (5), were isolated from the marine sponge derived Streptomyces sp. SCSIO 40064. The structures were elucidated by comprehensive spectroscopic data analyses and comparison with the literatures. The D-Val unit in 1 was assigned by Marfey's method. The absolute configuration of 4 was determined by X-ray crystallographic analysis. Compounds 1‒5 were evaluated for the inhibitory activities against four pharmaceutical targets and six antibacterial indicator strains. Compound 5 displayed α-glucosidase inhibitory activity with IC50 value of 18.67 ± 1.27 µM.

Epoxide hydrolases (EHs) have been characterized and engineered as biocatalysts that convert epoxides to valuable chiral vicinal diol precursors of drugs and bioactive compounds. Nonetheless, the regioselectivity control of the epoxide ring opening by EHs remains challenging. Alp1U is an α/β-fold EH that exhibits poor regioselectivity in the epoxide hydrolysis of fluostatin C (compound 1) and produces a pair of stereoisomers. Herein, we established the absolute configuration of the two stereoisomeric products and determined the crystal structure of Alp1U. A Trp-186/Trp-187/Tyr-247 oxirane oxygen hole was identified in Alp1U that replaced the canonical Tyr/Tyr pair in α/β-EHs. Mutation of residues in the atypical oxirane oxygen hole of Alp1U improved the regioselectivity for epoxide hydrolysis on 1. The single site Y247F mutation led to highly regioselective (98%) attack at C-3 of 1, whereas the double mutation W187F/Y247F resulted in regioselective (94%) nucleophilic attack at C-2. Furthermore, single-crystal X-ray structures of the two regioselective Alp1U variants in complex with 1 were determined. These findings allowed insights into the reaction details of Alp1U and provided a new approach for engineering regioselective epoxide hydrolases.

Angucyclinces belong to the class of aromatic polyketides and display a wide variety of structure diversity and pharmaceutical significance. Herein we report the isolation, structure elucidation, and bioactivity evaluation of structure-diversified angucyclinone derivatives and anthracene from the South China Sea-derived Micromonospora echinospora SCSIO 04089, including a thioether, gephysulfuromycin (1), two new benzo[b]phenanthridines, homophenanthroviridone (2) and homophenanthridonamide (3), a new benzo[b]fluorene, homostealthin D (4), a new naphtho[2,3-b]benzofuran, nenesfuran (5), a new naphthoquinone, WS-5995 D (6) and a new anthracene, nenesophanol (7), together with three known compounds (8-10). Their structures were elucidated by extensive spectroscopic analyses. The structures of 1-3 and 5-8 were confirmed by X-ray crystallographic analyses. Gephysulfuromycin (1) featured a rare single S-bridged 3,12a-epithiotetraphene skeleton. Homophenanthroviridone (2) was found to be cytotoxic to SF-268, MCF-7, and HepG2 cell lines with IC50 values of 5.4 ± 0.4, 6.8 ± 0.3, and 1.4 ± 0.1 μM, respectively. Compound 2 was also active against Gram-positive bacteria with MIC (minimal inhibition concentration) values ranging 2-4 μg mL-1.

Cyanogramide (1) from the marine actinomycete Actinoalloteichus cyanogriseus WH1-2216-6 features a unique spirooxindole skeleton and exhibits significant bioactivity to efficiently reverse drug resistance in tumor cells. The biosynthetic gene cluster of 1 in A. cyanogriseus WH1-2216-6 was identified and refactored by promoter engineering for heterologous expression in Streptomyces coelicolor YF11, thereby enabling the production of 1 and five new derivatives. Interesting, four of them, including 1, were identified as enantiomeric mixtures in different ratios. The functions of tailoring enzymes, including two methyltransferases (CyaEF), and three cytochrome P450 monooxygenases (CyaGHI) were confirmed by gene inactivation and feeding experiments, leading to the elucidation of a concise biosynthetic pathway for 1. Notably, CyaH was biochemically verified to catalyze the formation of the spirooxindole skeleton in 1 through an unusual carbocation-mediated semipinacol-type rearrangement reaction.

Overexpression of phosphopantetheinyl transferase (PPtase)-encoding genes sfp and svp in the marine-derived Verrucosispora sp. SCSIO 40062 led to the production of two new aminofuran monomers, proximicin F (1) and proximicin G (3) and a new dimer diproximicin A (2), along with two known compounds, proximicins B (4) and C (5). Their structures were unambiguously elucidated on the basis of detailed NMR spectroscopic analysis and high-resolution electrospray ionization mass spectrometry (HRESIMS) data. Proximicin B (4) showed moderate antibacterial activities against Staphylococcus aureus, methicillin-resistant S. aureus, and Bacillus subtilis.

Totopotensamide A (TPM A, 1) is a polyketide-peptide glycoside featuring a nonproteinogenic amino acid 4-chloro-6-methyl-5,7-dihydroxyphenylglycine (ClMeDPG). The biosynthetic gene cluster (BGC) of totopotensamides (tot) was previously activated by manipulating transcription regulators in marine-derived Streptomyces pactum SCSIO 02999. Herein, we report the heterologous expression of the tot BGC in Streptomyces lividans TK64, and the production improvement of TPM A via in-frame deletion of two negative regulators totR5 and totR3. The formation of ClMeDPG was proposed to require six enzymes, including four enzymes TotC1C2C3C4 for 3,5-dihydroxyphenylglycine (DPG) biosynthesis and two modifying enzymes TotH (halogenase) and TotM (methyltransferase). Heterologous expression of the four-gene cassette totC1C2C3C4 led to production of 3,5-dihydroxyphenylglyoxylate (DPGX). The aminotransferase TotC4 was biochemically characterized to convert DPGX to S-DPG. Inactivation of totH led to a mutant accumulated a deschloro derivative TPM H1, and the ΔtotHi/ΔtotMi double mutant afforded two deschloro-desmethyl products TPMs HM1 and HM2. A hydrolysis experiment demonstrated that the DPG moiety in TPM HM2 was S-DPG, consistent with that of the TotC4 enzymatic product. These results confirmed that TotH and TotM were responsible for ClMeDPG biosynthesis. Bioinformatics analysis indicated that both TotH and TotM might act on thiolation domain-tethered substrates. This study provided evidence for deciphering enzymes leading to ClMeDPG in TPM A, and unambiguously determined its absolute configuration as S.

The heterologous expression of the lobophorin biosynthetic gene cluster from marine-derived Streptomyces pactum SCSIO 02999 has led to the discovery of new analogues that carry d-kijanose (or its variants with a 3-amino or hydroxyl group) at C-9. The identification of intermediates resulting from the inactivation of lobG1 (encoding C-17 kijanosyltransferase) and lobG3 (encoding C-9 digitoxosyltransferase) demonstrates the substrate flexibility of LobG3 to also accept d-kijanose and its variants. Notably, two lobophorins with d-kijanose at C-9 show improved bioactivities.

Trichostatins are potent inhibitors of histone deacetylase (HDAC). In this work, a new trichostatin derivative isotrichostatin RK (1) and five known compounds trichostatin RK (2), JBIR-111 (3), 9179B (4), trichostatic acid (5) and trichostatin A (6) were isolated from marine-derived Streptomyces sp. SCSIO 40028. The biosynthetic gene cluster (tsnB) for trichostatins was identified from Streptomyces sp. SCSIO 40028 and validated by heterologous expression in Streptomyces lividans TK64. N-Methyltransferase TsnB8 was demonstrated to catalyze successive methyltransfer reactions by in vivo gene inactivation and in vitro enzyme assays.

Functions of the tailoring enzymes for the biosynthesis of tiacumicin B (1) have been previously determined. However, the reaction timing remains elusive. Herein, we report the in vitro biochemical characterization of two P450 enzymes TiaP1 and TiaP2. The investigation of their substrate scope and kinetic parameters clearly demonstrates that the TiaP2-catalyzed C-20 hydroxylation is the first tailoring step and the TiaP1-catalyzed C-18 hydroxylation is the last step in the biosynthesis of 1.

Berninamycins are a class of thiopeptide antibiotics with potent activity against Gram-positive bacteria. Heterologous expression of the berninamycin (ber) biosynthetic gene cluster from marine-derived Streptomyces sp. SCSIO 11878 in different terrestrial model Streptomyces hosts led to the production of berninamycins A (1) and B (2) in Streptomyces lividans SBT18 and Streptomyces coelicolor M1154, while two new linearized berninamycins J (3) and K (4) were obtained in Streptomyces albus J1074. Their structures were elucidated by detailed interpretation of NMR data and Marfey's method. Bioactivity assays showed that the linear thiopeptides 3 and 4 were less potent than 1 and 2 in antibacterial activity. This work indicates that undefined host-dependent enzymes might be responsible for generating the linear thiopeptides 3 and 4 in S. albus J1074.

Fluostatins belong to the atypical angucyclinone aromatic polyketides featuring a distinctive tetracyclic benzo[

Benzofluorene-containing atypical angucyclines are an important family of natural products with a broad spectrum of antibacterial and cytotoxic properties. Interestingly, symmetric and asymmetric dimers showed better activity than the monomer in this class of compounds. Herein, we reported the isolation of a new asymmetric dimer nenestatin B (2) from the deep sea actinomycete Micromonospora echinospora SCSIO 04089 and a monomer nenestatin C (3) from an NmrA family regulatory protein coding gene nes18 inactivated mutant. The structural elucidation of 3 indicated the essential role of Nes18 in the biosynthetic pathway of 2, specifically in dimerization via C–C bond formation.

Two new piericidins A5 (

Heterologous expression of the fluostatin biosynthetic gene cluster from the marine-derived Micromonospora rosaria SCSIO N160 in Streptomyces albus J1074 led to the isolation of a novel isoindolequinone albumycin (1) and a known isoquinolinequinone mansouramycin A (2). The structure of 1 was elucidated on the basis of detailed 1D and 2D NMR spectroscopic analysis. Mansouramycin A (2) is active against methicillin-resistant Staphylococcus aureus ATCC 43300, with a MIC of 8 μg ml-1, while albumycin (1) displayed negligible antibacterial activities. This study represents another example of activation of secondary metabolites that are non-relevant to the heterologously introduced biosynthetic gene cluster in a bacterial host.

Trichoderma harzianum is a widely used biocontrol agent in agriculture. Obtaining a full inventory of the small molecules that can be biosynthesized from the encoded biosynthetic gene clusters (BGCs) is therefore useful for understanding associated plant-microbe and microbe-microbe interactions. Here we heterologously reconstituted a polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) encoding gene cluster from T. harzianum t-22 in Aspergillus nidulans A1145. Six new tetronate natural products trihazone A-F (1-6) were isolated and elucidated by HRESIMS and 1D and 2D NMR data. Three of the products contain an exocyclic olefin, which is derived from the oxidative decarboxylation of an α-ketoglutarate-dependent dioxygenase ThnC as shown by biochemical assays.

A new cyclo-heptadepsipeptide xanthostatin B (

The mangrove forests are a complex ecosystem, and the microbial communities in mangrove sediments play a critical role in the biogeochemical cycles of mangrove ecosystems. Mangrove sediments-derived microbes (MSM), as a rich reservoir of natural product diversity, could be utilized in the exploration of new antibiotics or drugs. To understand the structural diversity and bioactivities of the metabolites of MSM, this review for the first time provides a comprehensive overview of 519 natural products isolated from MSM with their bioactivities, up to 2021. Most of the structural types of these compounds are alkaloids, lactones, xanthones, quinones, terpenoids, and steroids. Among them, 210 compounds are obtained from bacteria, most of which are from Streptomyces, while 309 compounds are from fungus, especially genus Aspergillus and Penicillium. The pharmacological mechanisms of some representative lead compounds are well studied, revealing that they have important medicinal potentials, such as piericidins with anti-renal cell cancer effects, azalomycins with anti-MRSA activities, and ophiobolins as antineoplastic agents. The biosynthetic pathways of representative natural products from MSM have also been summarized, especially ikarugamycin, piericidins, divergolides, and azalomycins. In addition, the total synthetic strategies of representative secondary metabolites from MSM are also reviewed, such as piericidin A and borrelidin. This review provides an important reference for the research status of natural products isolated from MSM and the lead compounds worthy of further development, and reveals that MSM have important medicinal values and are worthy of further development.

Amine compounds biosynthesis using ω-transaminases has received considerable attention in the pharmaceutical industry. However, the application of ω-transaminases was hampered by the fundamental challenge of severe by-product inhibition. Here, we report that ω-transaminase CrmG from Actinoalloteichus cyanogriseus WH1-2216-6 is insensitive to inhibition from by-product α-ketoglutarate or pyruvate. Combined with structural and QM/MM studies, we establish the detailed catalytic mechanism for CrmG. Our structural and biochemical studies reveal that the roof of the active site in PMP-bound CrmG is flexible, which will facilitate the PMP or by-product to dissociate from PMP-bound CrmG. Our results also show that amino acceptor caerulomycin M (CRM M), but not α-ketoglutarate or pyruvate, can form strong interactions with the roof of the active site in PMP-bound CrmG. Based on our results, we propose that the flexible roof of the active site in PMP-bound CrmG may facilitate CrmG to overcome inhibition from the by-product., Xu, Tang et al. show that ω-transaminase CrmG is insensitive to the inhibition from by-products α-ketoglutarate or pyruvate. They find that these by-products cannot interact strongly with the flexible roof of the active site in CrmG. This study provides insights into the rational design of transaminase to eliminate by-product inhibition.

Overexpression of phosphopantetheinyl transferase (PPtase)-encoding genes

Marine polyketide natural products have attracted immense attentions due to their complex structures, significant bioactivities, and great potentials in drug leads discovery. It is well-known that fascinating assembly lines with unique enzymatic modifications, which could occur before, during and after polyketide chain assembly, contribute to the vast structural diversity of marine polyketides. This article describes the biosynthetic origin of more than 80 marine natural products derived from polyketide synthases (PKSs), with a focus on highlighting the current knowledge of chemistry and enzymology that are embedded in the assembly line and post-PKS modifications to support their structure diversity and important biological activities.

Two polyketides neoenterocins A (1) and B (2), featuring a neighboring dicarbonyl motif and a furan-containing 5/6 ring system, were isolated from the enterocin producer Streptomyces sp. SCSIO 11863. Heterologous expression, gene disruptions, and isotope feeding experiments indicated that 1 and 2 were derived from the enterocin biosynthetic gene cluster. However, 2 was demonstrated as an artifact from enterocin via a unique skeleton rearrangement.

Microbes can enter into healthy plants as endophytes and confer beneficial functions. The entry of commensal microbes into plants involves penetrating plant defense. Most mechanisms about overcoming plant defense are focused on adapted pathogens, while the mechanism involved in beneficial endophyte evades plant defense to achieve harmonious commensalism is unclear. Here, we discover a mechanism that an endophyte bacterium Bacillus subtilis BSn5 reduce to stimulate the plant defensive response by producing lantibiotic subtilomycin to bind self-produced flagellin. Subtilomycin bind with flagellin and affect flg22-induced plant defense, by which means promotes the endophytic colonization in A. thaliana. Subtilomycin also promotes the BSn5 colonization in a distinct plant, Amorphophallus konjac, where the BSn5 was isolated. Our investigation shows more independent subtilomycin/-like producers are isolated from distinct plants. Our work unveils a common strategy that is used for bacterial endophytic colonization.

A nonribosomal peptide synthetase (NRPS) gene cluster (sfa) was identified in Streptomyces thioluteus to direct the biosynthesis of the diisonitrile antibiotic SF2768. Its biosynthetic pathway was reasonably proposed based on bioinformatics analysis, metabolic profiles of mutants, and the elucidation of the intermediate and shunt product structures. Bioinformatics-based alignment found a putative ATP-binding cassette (ABC) transporter related to iron import within the biosynthetic gene cluster, which implied that the product might be a siderophore. However, characterization of the metal-binding properties by high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), metal-ligand titration, thin-layer chromatography (TLC), and chrome azurol S (CAS) assays revealed that the final product SF2768 and its diisonitrile derivatives specifically bind copper, rather than iron, to form stable complexes. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that the intracellular cupric content of S. thioluteus significantly increased upon incubation with the copper-SF2768 complex, direct evidence for the copper acquisition function of SF2768. Further in vivo functional characterization of the transport elements for the copper-SF2768 complexes not only confirmed the chalkophore identity of the compound but also gave initial clues into the copper uptake mechanism of this nonmethanotrophic microorganism.

A 92 kb silent hybrid polyketide and nonribosomal peptide gene cluster in marine-derived Streptomyces pactum SCSIO 02999 was activated by genetically manipulating the regulatory genes, including the knockout of two negative regulators (totR5 and totR3) and overexpression of a positive regulator totR1, to direct the production of the known totopotensamides (TPMs) A (1) and B (3) and a novel sulfonate-containing analogue TPM C (2). Inactivation of totG led to accumulation of TPM B (3) lacking the glycosyl moiety, which indicated TotG as a dedicated glycosyltransferase in the biosynthesis of 1 and 2.

We formulate the fusion of RGB and depth modalities as a collaborative sparse representation leaning problem.RGB and depth features are joint reconstructed, and their respective advantages are utilized to significantly boost the recognition efficiency.A collaborative sparse representation leaning model is specially designed for RGBD action recognition, which automatic make fusion to find the optimal reconstruction coefficients, further boosting the performance. Multi-modalities action recognition becomes a hot research topic, and this paper proposes a collaborative sparse representation leaning model for RGB-D action recognition where RGB and depth information are adaptive fused. Specifically, dense trajectory feature is firstly extracted and Bag-of-Word (BoW) weight scheme is employed for RGB modality, and then for depth modality, the human pose representation model (HPM) and temporal modeling (TM) representation are utilized. Meanwhile, the collaborative reconstruction structure and corresponding objective functions for the multiple modalities are designed, and then the proposed model is collaboratively optimized which is used to discover the latent complementary information between RGB and depth data. Finally, the collaborative reconstruction error is employed as our classification scheme. Large scale experimental results on challenging and public DHA, M2I and Northwestern-UCLA action datasets show that the performances of our model on two modalities are much better than traditional sole modality, which can boost the performance of human action recognition by taking advance of complementary characteristics from both RGB and depth modalities.

Five new phenylspirodrimanes, stachybomycins A − E (1–5), together with four known compounds (6–9), were isolated from the marine-derived fungus Stachybotrys sp. SCSIO 40434. Their structures were elucidated by comprehensive spectroscopic analyses of NMR and HRESIMS. The absolute configuration of 1 was confirmed by single crystal X-ray diffraction analysis. Compounds 5 and 7 showed moderate antibacterial activities against Micrococcus luteus, Staphylococcus aureus and methicillin resistant Staphylococcus aureus with minimal inhibition concentration (MIC) values of 8, 16 and 16 μg mL−1, respectively.

Pyrazolofluostatins A–C (1–3), three new benzo[a]fluorenes with an unprecedented carbon skeleton, were obtained from the South China Sea-derived Micromonospora rosaria SCSIO N160. Their structures were elucidated by extensive spectroscopic analyses. The structure of pyrazolofluostatin A (1) was confirmed by X-ray crystallographic analysis. Notably, 1–3 possessed a benzo[cd]indeno[2,1-f]indazol skeleton with a pyrazole-fused 6/5/6/6/5 pentacyclic ring system. Pyrazolofluostatin A (1) showed moderate antioxidation activity (EC50 48.6 μM).

Flavoenzymes are ubiquitous in biological systems and catalyze a diverse range of chemical transformations. The flavoenzyme XiaK from the biosynthetic pathway of the indolosesquiterpene xiamycin A is demonstrated to mediate the in vivo biotransformation of xiamycin A into multiple products, including a chlorinated adduct as well as dimers characterized by C–N and N–N linkages that are hypothesized to form via radical-based mechanisms. Isolation and characterization of XiaK in vitro shows that it acts as a flavin-dependent N-hydroxylase that catalyzes the hydroxylation of xiamycin A at the carbazole nitrogen to form N-hydroxyxiamycin, a product which was overlooked in earlier in vivo experiments because its chemical and chromatographic properties are similar to those of oxiamycin. N-Hydroxyxiamycin is shown to be unstable under aerobic conditions, and characterization by electron paramagnetic resonance spectroscopy demonstrates formation of an N-hydroxycarbazole radical adduct. This radical species is proposed to serve as a key intermediate leading to the formation of the multiple xiamycin A adducts. This study suggests that non-enzyme catalyzed reactions may play a greater role in the biosynthesis of natural products than has been previously recognized.

Polycyclic tetramate macrolactams (PTMs) are a growing class of natural products and are derived from a hybrid polyketide synthase (PKS)/non-ribosomal peptide synthetase (NRPS) pathway. PTM biosynthetic gene clusters are conserved and widely distributed in bacteria, however, most of them remain silent. Herein we report the activation of a PTM gene cluster in marine-derived Streptomyces pactum SCSIO 02999 by promoter engineering and heterologous expression, leading to the discovery of six new PTMs, pactamides A-F (11-16), with potent cytotoxic activity upon several human cancer cell lines. In vivo gene disruption experiments and in vitro biochemical assays reveal a reductive cyclization cascade for polycycle formation, with reactions sequentially generating the 5, 5/5 and 5/5/6 carbocyclic ring systems, catalysed by the phytoene dehydrogenase PtmB2, the oxidoreductase PtmB1, and the alcohol dehydrogenase PtmC, respectively. Furthermore, PtmC was demonstrated as a bifunctional cyclase for catalyzing the formation of the inner five-membered ring in ikarugamycin. This study suggests the possibility of finding more bioactive PTMs by genome mining and discloses a general mechanism for the formation of 5/5/6-type carbocyclic rings in PTMs.

A new uridine derivative 11457 A (