WS9326A, a novel tachykinin antagonist isolated from Streptomyces violaceusniger no. 9326. I. Taxonomy, fermentation, isolation, physico-chemical properties and biological activities

A Versatile Thioesterase Involved in Dimerization during Cinnamoyl Lipid Biosynthesis

The cinnamoyl lipid compound youssoufene A1 (1), featuring a unique dearomatic carbon-bridged dimeric skeleton, exhibits increased inhibition against multidrug resistant Enterococcus faecalis as compared to monomeric youssoufenes. However, the formation process of this intriguing dearomatization/dimerization remains unknown. In this study, an unusual "gene-within-gene" thioesterase (TE) gene ysfF was functionally characterized. The gene was found to naturally encodes two proteins, an entire YsfF with α/β-hydrolase and 4-hydroxybenzoyl-CoA thioesterase (4-HBT)-like enzyme domains, and a nested YsfFHBT (4-HBT-like enzyme). Using an intracellular tagged carrier-protein tracking (ITCT) strategy, in vitro reconstitution and in vivo experiments, we found that: i) both domains of YsfF displayed thioesterase activities; ii) YsfF/YsfFHBT could accomplish the 6π-electrocyclic ring closure for benzene ring formation; and iii) YsfF and cyclase YsfX together were responsible for the ACP-tethered dearomatization/dimerization process, possibly through an unprecedented Michael-type addition reaction. Moreover, site-directed mutagenesis experiments demonstrated that N301, E483 and H566 of YsfF are critical residues for both the 6π-electrocyclization and dimerization processes. This study enhances our understanding of the multifunctionality of the TE protein family.

Genome Mining of Cinnamoyl-Containing Nonribosomal Peptide Gene Clusters Directs the Production of Malacinnamycin

Cinnamoyl-containing nonribosomal peptides (CCNPs) constitute a unique family of actinobacterial secondary metabolites that display a broad spectrum of biological activities. Here, we present a genome mining approach targeting cyclase and is isomerase to discover new CCNPs, which led to the identification of 207 putative CCNP gene clusters from public bacterial genome databases. After strain prioritization, a novel class of CCNP-type glycopeptides named malacinnamycin was identified. A plausible biosynthetic pathway for malacinnamycin was deduced by bioinformatics analysis.

Structural diversity, biosynthesis, and biological functions of lipopeptides from Streptomyces

Covering: up to 2022Streptomyces are ubiquitous in terrestrial and marine environments, where they display a fascinating metabolic diversity. As a result, these bacteria are a prolific source of active natural products. One important class of these natural products is the nonribosomal lipopeptides, which have diverse biological activities and play important roles in the lifestyle of Streptomyces. The importance of this class is highlighted by the use of related antibiotics in the clinic, such as daptomycin (tradename Cubicin). By virtue of recent advances spanning chemistry and biology, significant progress has been made in biosynthetic studies on the lipopeptide antibiotics produced by Streptomyces. This review will serve as a comprehensive guide for researchers working in this multidisciplinary field, providing a summary of recent progress regarding the investigation of lipopeptides from Streptomyces. In particular, we highlight the structures, properties, biosynthetic mechanisms, chemical and chemoenzymatic synthesis, and biological functions of lipopeptides. In addition, the application of genome mining techniques to Streptomyces that have led to the discovery of many novel lipopeptides is discussed, further demonstrating the potential of lipopeptides from Streptomyces for future development in modern medicine.

Anulamycins A-F, Cinnamoyl-Containing Peptides from a Lake Sediment Derived Streptomyces

Bioinformatics analysis of a whole genome sequence coupled with HPLC-DAD analysis revealed that Streptomyces sp. Hu103 has the capacity to produce skyllamycin analogues. A subsequent chemical investigation of this strain yielded four new cinnamoyl-containing cyclopeptides, anulamycins A-D (1-4), two new cinnamoyl-containing linear peptides, anulamycins E and F (5 and 6), and two known cyclopeptides, skyllamycins A (7) and B (8). Their structures including absolute configurations were elucidated by detailed analysis of NMR and HRESIMS/MS spectroscopic data and the advanced Marfey's method. Compounds 1-4 exhibited antibacterial activity comparable to those of skyllamycins A and B.

Production of chain-extended cinnamoyl compounds by overexpressing two adjacent cluster-situated LuxR regulators in Streptomyces globisporus C-1027

Natural products from microorganisms are important sources for drug discovery. With the development of high-throughput sequencing technology and bioinformatics, a large amount of uncharacterized biosynthetic gene clusters (BGCs) in microorganisms have been found, which show the potential for novel natural product production. Nine BGCs containing PKS and/or NRPS in Streptomyces globisporus C-1027 were transcriptionally low/silent under the experimental fermentation conditions, and the products of these clusters are unknown. Thus, we tried to activate these BGCs to explore cryptic products of this strain. We constructed the cluster-situated regulator overexpressing strains which contained regulator gene(s) under the control of the constitutive promoter ermE*p in S. globisporus C-1027. Overexpression of regulators in cluster 26 resulted in significant transcriptional upregulation of biosynthetic genes. With the separation and identification of products from the overexpressing strain OELuxR1R2, three ortho-methyl phenyl alkenoic acids (compounds 1-3) were obtained. Gene disruption showed that compounds 1 and 2 were completely abolished in the mutant GlaEKO, but were hardly affected by deletion of the genes orf3 or echA in cluster 26. The type II PKS biosynthetic pathway of chain-extended cinnamoyl compounds was deduced by bioinformatics analysis. This study showed that overexpression of the two adjacent cluster-situated LuxR regulator(s) is an effective strategy to connect the orphan BGC to its products.

Marinoquinolones and Marinobactoic Acid: Antimicrobial and Cytotoxic ortho-Dialkylbenzene-Class Metabolites Produced by a Marine Obligate Gammaproteobacterium of the Genus Marinobacterium

Chemical investigation of the culture extract of a marine obligate proteobacterium, Marinobacterium sp. C17-8, isolated from scleractinian coral Euphyllia sp., led to the discovery of three new o-dialkylbenzene-class metabolites, designated marinoquinolones A (1) and B (2) and marinobactoic acid (3). Spectroscopic analysis using MS and NMR revealed the structures of 1 and 2 to be 4-quinolones with an o-dialkylbenzene-containing side chain at C3 and 3 to be a fatty acid bearing an o-dialkylbenzene substructure. The 4-quinolone form of 1 and 2 was unequivocally determined by comparison of the ¹H, ¹³C, and ¹⁵N chemical shifts of 1 with those predicted for 2-methyl-4-quinolone A and its tautomer 2-methyl-4-quinolinol B by quantum chemical calculation. Compound 1 was proven to be racemic by X-ray crystallographic analysis and chiral-phase HPLC analysis of its chemical degradation product. Compounds 1-3 exhibited antimicrobial activity against bacteria and filamentous fungi at MIC of 6.3-50 μg/mL. In addition, all compounds showed cytotoxicity against P388 murine leukemia cells at micromolar ranges.

Epoxinnamide: An Epoxy Cinnamoyl-Containing Nonribosomal Peptide from an Intertidal Mudflat-Derived Streptomyces sp

Cinnamoyl-containing nonribosomal peptides (CCNPs) form a unique family of actinobacterial secondary metabolites and display various biological activities. A new CCNP named epoxinnamide (1) was discovered from intertidal mudflat-derived Streptomyces sp. OID44. The structure of 1 was determined by the analysis of one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) data along with a mass spectrum. The absolute configuration of 1 was assigned by the combination of advanced Marfey’s method, ³J_HH and rotating-frame overhauser effect spectroscopy (ROESY) analysis, DP4 calculation, and genomic analysis. The putative biosynthetic pathway of epoxinnamide (1) was identified through the whole-genome sequencing of Streptomyces sp. OID44. In particular, the thioesterase domain in the nonribosomal peptide synthetase (NRPS) biosynthetic gene cluster was proposed as a bifunctional enzyme, which catalyzes both epimerization and macrocyclization. Epoxinnamide (1) induced quinone reductase (QR) activity in murine Hepa-1c1c7 cells by 1.6-fold at 5 μM. It also exhibited effective antiangiogenesis activity in human umbilical vein endothelial cells (IC₅₀ = 13.4 μM).

Nyuzenamide C, an Antiangiogenic Epoxy Cinnamic Acid-Containing Bicyclic Peptide from a Riverine Streptomyces sp

A new nonribosomal peptide, nyuzenamide C (1), was discovered from riverine sediment-derived Streptomyces sp. DM14. Comprehensive analysis of the spectroscopic data of nyuzenamide C (1) revealed that 1 has a bicyclic backbone composed of six common amino acid residues (Asn, Leu, Pro, Gly, Val, and Thr) and four nonproteinogenic amino acid units, including hydroxyglycine, β-hydroxyphenylalanine, p-hydroxyphenylglycine, and 3,β-dihydroxytyrosine, along with 1,2-epoxypropyl cinnamic acid. The absolute configuration of 1 was proposed by J-based configuration analysis, the advanced Marfey's method, quantum mechanics-based DP4 calculations, and bioinformatic analysis of its nonribosomal peptide synthetase biosynthetic gene cluster. Nyuzenamide C (1) displayed antiangiogenic activity in human umbilical vein endothelial cells and induced quinone reductase in murine Hepa-1c1c7 cells.

Aminoacyl chain translocation catalysed by a type II thioesterase domain in an unusual non-ribosomal peptide synthetase

Non-Ribosomal Peptide Synthetases (NRPSs) assemble a diverse range of natural products with important applications in both medicine and agriculture. They consist of several multienzyme subunits that must interact with each other in a highly controlled manner to facilitate efficient chain transfer, thus ensuring biosynthetic fidelity. Several mechanisms for chain transfer are known for NRPSs, promoting structural diversity. Herein, we report the first biochemically characterized example of a type II thioesterase (TE_II) domain capable of catalysing aminoacyl chain transfer between thiolation (T) domains on two separate NRPS subunits responsible for installation of a dehydrobutyrine moiety. Biochemical dissection of this process reveals the central role of the TE_II-catalysed chain translocation event and expands the enzymatic scope of TE_II domains beyond canonical (amino)acyl chain hydrolysis. The apparent co-evolution of the TE_II domain with the NRPS subunits highlights a unique feature of this enzymatic cassette, which will undoubtedly find utility in biosynthetic engineering efforts.

Non-Ribosomal Peptide Synthetases (NRPSs) are responsible for the construction of many types of natural products. Here the authors characterize a key type II thioesterase domain that sheds light on the chain translocation processes of legonmycin NRPSs.

Genome mining methods to discover bioactive natural products

Covering: 2016 to 2021With genetic information available for hundreds of thousands of organisms in publicly accessible databases, scientists have an unprecedented opportunity to meticulously survey the diversity and inner workings of life. The natural product research community has harnessed this breadth of sequence information to mine microbes, plants, and animals for biosynthetic enzymes capable of producing bioactive compounds. Several orthogonal genome mining strategies have been developed in recent years to target specific chemical features or biological properties of bioactive molecules using biosynthetic, resistance, or transporter proteins. These "biosynthetic hooks" allow researchers to query for biosynthetic gene clusters with a high probability of encoding previously undiscovered, bioactive compounds. This review highlights recent case studies that feature orthogonal approaches that exploit genomic information to specifically discover bioactive natural products and their gene clusters.

Role of Two Exceptional trans Adenylation Domains and MbtH-like Proteins in the Biosynthesis of the Nonribosomal Peptide WS9324A from Streptomyces calvus ATCC 13382

Nonribosomal peptide synthetases (NRPS) are organized in a modular arrangement. Usually, the modular order corresponds to the assembly of the amino acids in the respective peptide, following the collinearity rule. The WS9326A biosynthetic gene cluster from Streptomyces calvus shows deviations from this rule. Most interesting is the presence of two trans adenylation domains that are located downstream of the modular NRPS arrangement. Adenylation domains are responsible for the activation of their respective amino acids. In this study, we confirmed the involvement of the trans adenylation domains in WS9326A biosynthesis by performing gene knockout experiments and by observing the selective adenylation of their predicted amino acid substrates in vitro. We conclude that the trans adenylation domains are essential for WS9326A biosynthesis. Moreover, both adenylation domains are observed to have MbtH‐like protein dependency. Overall, we conclude that the trans adenylation domains are essential for WS9326A biosynthesis.

Reclassification of Streptomyces castelarensis and Streptomyces sporoclivatus as later heterotypic synonyms of Streptomyces antimycoticus

We investigated the taxonomic relationship between Streptomyces antimycoticus, Streptomyces castelarensis, Streptomyces sporoclivatus, and Streptomyces violaceusniger. Digital DNA-DNA hybridisation using whole genome sequences and multilocus sequence analysis indicated that S. antimycoticus, S. castelarensis, and S. sporoclivatus belong to the same genomospecies. Previously reported phenotypic data also supported this synonymy. Therefore, S. castelarensis and S. sporoclivatus should be reclassified as later heterotypic synonyms of S. antimycoticus. The type strain of S. antimycoticus is NBRC 12839^T (=ATCC 23880^T=CBS 660.68^T=RIA 1198^T=CGMCC 4.1591^T=DSM 40284^T=JCM 4228^T=JCM 4621^T=KCTC 9694^T=NRRL 2421^T=NRRL ISP-5284^T=VKM Ac-1824^T). This study also revealed that genome sequence-published S. violaceusniger NRRL F-8817 should be reclassified into S. antimycoticus.

Identification of novel cytochrome P450 monooxygenases from actinomycetes capable of intermolecular oxidative C-C coupling reactions

The cross-coupling reaction is one of the most important chemical reactions in the modern organic chemistry. Biocatalysts capable of catalyzing C-C coupling reactions are desired in the chemical industry for sustainable development. Cytochrome P450 monooxygenases (P450s) have received considerable attention as biocatalysts capable of catalyzing such reactions. Here, we focused on actinomycete P450s, which have high homology with CYP158A2, involved in the oxidative C-C coupling reaction for flaviolin dimerization in Streptomyces coelicolor A3(2). The screening of a chemical library composed of 426 aromatic compounds identified several combinations of P450s and their potential substrates. The type-I difference spectrum indicated that the identified substrates bind to the active sites of a P450, named StVI from Streptomyces violaceusniger. A redshift of the absorption maximum of the reaction products, together with LC-MS analysis suggested the presence of extended conjugate systems in the products through direct C-C coupling between two aromatic rings. The results demonstrated that actinomycete P450s have great potential to be utilized as biocatalysts for oxidative C-C coupling reactions and to facilitate the synthesis of diverse coupling products.

Rational Design of Hybrid Natural Products by Utilizing the Promiscuity of an Amide Synthetase

WS9326A and annimycin are produced by Streptomyces asterosporus DSM 41452. WS9326A is a nonribosomal peptide synthetase-(NRPS-) derived depsipeptide containing a cinnamoyl moiety, while annimycin is a linear polyketide bearing a 2-amino-3-hydroxycyclopent-2-enone (C₅N) group. Both gene clusters have been sequenced and annotated. In this study, we show that the amide synthetase Ann1, responsible for attaching the C₅N unit during annimycin biosynthesis, has the ability to catalyze fortuitous side reactions to polyenoic acids in addition to its main reaction. Novel compounds were generated by feeding experiments and in vitro studies. We also rationally designed a hybrid natural product consisting of the cinnamoyl moiety of WS9326A and the C₅N moiety of annimycin by creating a mutant of S. asterosporus that retains genes encoding biosynthesis of the C₅N unit of annimycin and the cinnamoyl group of WS9326A. The promiscuity of Ann1 also proved useful for trapping compounds that arise from acyl-ACP intermediates, which occur in the biosynthesis of the cinnamoyl moiety of WS9326A, by hydrolysis. In this pathway, we postulate that sas27 and sas28 genes are involved in the biosynthesis of the cinnamoyl moiety in WS9326A.

Targeted Rediscovery and Biosynthesis of the Farnesyl-Transferase Inhibitor Pepticinnamin E

The natural product pepticinnamin E potently inhibits protein farnesyl transferases and has potential applications in treating cancer and malaria. Pepticinnamin E contains a rare N-terminal cinnamoyl moiety as well as several nonproteinogenic amino acids, including the unusual 2-chloro-3-hydroxy-4-methoxy-N-methyl-L-phenylalanine. The biosynthesis of pepticinnamin E has remained uncharacterized because its original producing strain is no longer available. Here we identified a gene cluster (pcm) for this natural product in a new producer, Actinobacteria bacterium OK006, by means of a targeted rediscovery strategy. We demonstrated that the pcm cluster is responsible for the biosynthesis of pepticinnamin E, a nonribosomal peptide/polyketide hybrid. We also characterized a key O-methyltransferase that modifies 3,4-dihydroxy-l-phenylalanine. Our work has identified the gene cluster for pepticinnamins for the first time and sets the stage for elucidating the unique chemistry required for biosynthesis.

Discovery and Biosynthesis of Atrovimycin, an Antitubercular and Antifungal Cyclodepsipeptide Featuring Vicinal-dihydroxylated Cinnamic Acyl Chain

Atrovimycin (1), a cyclodepsipeptide containing a unique vicinal-hydroxylated cinnamic acyl chain, was isolated and elucidated from Streptomyces atrovirens LQ13. The biosynthetic pathway of 1 was achieved, revealing cytochrome P450 (Avm43) and epoxide hydrolase (Avm29) enzymes constructing the vicinal-dihydroxy substitution, as well as a tailoring P450 (Avm28) enzyme catalyzing β-hydroxylation of the l-Phe moiety. Atrovimycin shows in vitro antifungal activity and antitubercular activity against Mycobacterium tuberculosis H37Rv both in vitro (with MIC of 2.5 μg/mL) and in vivo.

Genome mining and biosynthesis of kitacinnamycins as a STING activator

Genome mining targeting unique type II PKS and NRPS led to the identification of a novel class of glycopeptides named kitacinnamycins.

Cinnamoyl-containing nonribosomal peptides (CCNPs) are a small group of secondary metabolites with potent biological activities produced by actinobacteria. Two remarkable features in the biosynthesis of CCNPs include the nonribosomal peptide synthases (NRPSs) for assembly of the depsipeptide backbone and the type II polyketide synthases (PKSs) for N-terminal cinnamoyl moiety construction. Here, we present a genome mining approach targeting both NRPS and type II PKS for discovery of new CCNPs, which led to the identification of 51 putative CCNP gene clusters from public bacterial genome databases. After strain prioritization, a novel class of CCNP-type glycopeptides named kitacinnamycins, one of which showing potent activation ability towards the stimulator of interferon genes (STING) protein, was identified. Bioinformatic, genetic and biochemical analysis revealed the use of the NRPS assembly line to form the macrocyclic peptide backbone, followed by a P450 monooxygenase to generate terminal oxidized groups. A glycosyltransferase with relatively broad substrate specificity transfers sugars to the newly generated OH/COOH group. The protein crystallographic study further provided structural insights into this glycosylation. Our results not only demonstrated the feasibility of genome mining and strain prioritization for the discovery of new bioactive natural products but also disclosed the biosynthetic pathway for kitacinnamycins.

Genome mining reveals the origin of a bald phenotype and a cryptic nucleocidin gene cluster in Streptomyces asterosporus DSM 41452

Streptomyces asterosporus DSM 41452 is a producer of the polyketide annimycin and the non-ribosomal depsipeptide WS9326A. This strain is also notable for exhibiting a bald phenotype that is devoid of spores and aerial mycelium when grown on solid media. Based on the similarity of the 16S rRNA sequence to Streptomyces calvus, the only known producer of the fluorometabolite nucleocidin, the genome of S. asterosporus DSM 41452 was sequenced and analyzed. Twenty-nine natural product gene clusters were detected in the genome, including a gene cluster predicted to encode the fluorometabolite nucleocidin. Through genome analysis and gene complementation experiments, we demonstrate that the bald phenotype arises from a transposon gene inserted within the promoter sequence for the pleiotropic regulator adpA. Complementation of S. asterosporus DSM 41452 with a functional adpA sequence restored morphological differentiation and promoted the production of nucleocidin.

Atmospheric Precipitations, Hailstone and Rainwater, as a Novel Source of Streptomyces Producing Bioactive Natural Products

A cultivation-dependent approach revealed that highly diverse populations of Streptomyces were present in atmospheric precipitations from a hailstorm event sampled in February 2016 in the Cantabrian Sea coast, North of Spain. A total of 29 bioactive Streptomyces strains isolated from small samples of hailstone and rainwater, collected from this hailstorm event, were studied here. Taxonomic identification by 16S rRNA sequencing revealed more than 20 different Streptomyces species, with their closest homologs displaying mainly oceanic but also terrestrial origins. Backward trajectory analysis revealed that the air-mass sources of the hailstorm event, with North Western winds, were originated in the Arctic Ocean (West Greenland and North Iceland) and Canada (Labrador), depending on the altitude. After traveling across the North Atlantic Ocean during 4 days the air mass reached Europe and precipitated as hailstone and rain water at the sampling place in Spain. The finding of Streptomyces species able to survive and disperse through the atmosphere increases our knowledge of the biogeography of genus Streptomyces on Earth, and reinforces our previous dispersion model, suggesting a generalized feature for the genus which could have been essential in his evolution. This unique atmospheric-derived Streptomyces collection was screened for production of bioactive secondary metabolites. Analyses of isolates ethyl acetate extracts by LC-UV-MS and further database comparison revealed an extraordinary diversity of bioactive natural products. One hundred molecules were identified, mostly displaying contrasted antibiotic and antitumor/cytotoxic activities, but also antiparasitic, antiviral, anti-inflammatory, neuroprotector, and insecticide properties. More interestingly, 38 molecules not identified in natural products databases might represent new natural products. Our results revealed for the first time an extraordinary diversity of Streptomyces species in the atmosphere able to produce an extraordinary repertoire of bioactive molecules, thus providing a very promising source for the discovery of novel pharmaceutical natural products.

New WS9326A Derivatives and One New Annimycin Derivative with Antimalarial Activity are Produced by Streptomyces asterosporus DSM 41452 and Its Mutant

In this study, we report that Streptomyces asterosporus DSM 41452 is a producer of new molecules related to the nonribosomal cyclodepsipeptide WS9326A and the polyketide annimycin. S. asterosporus DSM 41452 is shown to produce six cyclodepsipeptides and peptides, WS9326A to G. Notably, the compounds WS9326F and WS9326G have not been described before. The genome of S. asterosporus DSM 41452 was sequenced, and a putative WS9326A gene cluster was identified. Gene-deletion experiments confirmed that this cluster was responsible for the biosynthesis of WS9326A to G. Additionally, a gene-deletion experiment demonstrated that sas16 encoding a cytochrome P450 monooxygenase was involved in the synthesis of the novel (E)-2,3-dehydrotyrosine residue found in WS9326A and its derivatives. An insertion mutation within the putative annimycin gene cluster led to the production of a new annimycin derivative, annimycin B, which exhibited modest inhibitory activity against Plasmodium falciparum.

Quorum Quenching Strategy Targeting Gram-Positive Pathogenic Bacteria

Quorum sensing (QS) is a cell density-dependent regulatory system that orchestrates the group behavior of unicellular organisms by synchronizing the expression of certain gene(s) within the clonal community of same species. Bacterial pathogens often employ QS system to establish efficiently an infection. A large part of low GC Gram-positive bacteria belonging to phylum Firmicutes use thiolactone/lactone peptides as communication signals so-called autoinducing peptides (AIPs) to coordinate QS circuit. In particular, QS of staphylococci, enterococci, and clostridia have been intensively studied in terms of alternative target of anti-pathogenic chemotherapy independent of bactericidal antibiotics. Thus far, a number of quorum quenching (QQ) agents that targeting the QS circuit of these Gram-positive pathogens have been developed by random screening of natural compounds or rationale design of AIP antagonists. This review summarizes those QQ agents and previews their potential as post-antibiotic drugs.

Application of 3D NMR for Structure Determination of Peptide Natural Products

Despite the advances in NMR, structure determination is often slow and constitutes a bottleneck in natural products discovery. Removal of this bottleneck would greatly improve the throughput for antibiotic discovery as well as other therapeutic areas. Overall, faster structure methods for structure determination will serve the natural products community in a broad manner. This report describes the first application of 3D NMR for elucidation of two microbially produced peptide natural products with novel structures. The methods are cost-effective and greatly improve the confidence in a proposed structure.

Cyclodepsipeptides produced by actinomycetes inhibit cyclic-peptide-mediated quorum sensing in Gram-positive bacteria

Cyclic peptides are commonly used as quorum-sensing autoinducers in Gram-positive Firmicutes bacteria. Well-studied examples of such molecules are thiolactone and lactone, used to regulate the expression of a series of virulence genes in the agr system of Staphylococcus aureus and the fsr system of Enterococcus faecalis, respectively. Three cyclodepsipeptides WS9326A, WS9326B and cochinmicin II/III were identified as a result of screening actinomycetes culture extracts for activity against the agr/fsr system. These molecules are already known as receptor antagonists, the first two for tachykinin and the last one for endothelin. WS9326A also inhibited the transcription of pfoA regulated by the VirSR two-component system in Clostridium perfringens. Receptor-binding assays using a fluorescence-labeled autoinducer (FITC-GBAP) showed that WS9326A and WS9326B act as receptor antagonists in this system. In addition, an ex vivo assay showed that WS9326B substantially attenuated the toxicity of S. aureus for human corneal epithelial cells. These results suggest that these three natural cyclodepsipeptides have therapeutic potential for targeting the cyclic peptide-mediated quorum sensing of Gram-positive pathogens.

New WS9326A congeners from Streptomyces sp. 9078 inhibiting Brugia malayi asparaginyl-tRNA synthetase

Lymphatic filariasis is caused by the Brugia malayi parasite. Three new congeners of the depsipeptide WS9326A (1), WS9326C (2), WS9326D (3), and WS9326E (4), were isolated from Streptomyces sp. 9078 by using a B. malayi asparaginyl-tRNA synthetase (BmAsnRS) inhibition assay. WS9326D specifically inhibits the BmAsnRS, kills the adult B. malayi parasite, and does not exhibit significant general cytotoxicity to human hepatic cells, representing a new lead scaffold for antifilarial drug discovery.

Biosynthetic gene cluster of the non-ribosomally synthesized cyclodepsipeptide skyllamycin: deciphering unprecedented ways of unusual hydroxylation reactions

The cyclic depsipeptide skyllamycin A is a potent inhibitor of the platelet-derived growth factor (PDGF) signaling pathway by inhibiting binding of homodimeric PDGF BB to the PDGF β-receptor. Its structure contains a cinnamoyl side chain and shows a high amount of β-hydroxylated amino acids as well as an unusual α-hydroxyglycine moiety as a rare structural modification. The skyllamycin biosynthetic gene cluster was cloned and sequenced from Streptomyces sp. Acta 2897. Its analysis revealed the presence of open reading frames encoding proteins for fatty acid precursor biosynthesis, non-ribosomal peptide synthetases, regulators, and transporters along with other modifying enzymes. Specific in-frame mutagenesis of these tailoring enzymes resulted in the production of novel skyllamycin derivatives revealing that β-hydroxy groups in skyllamycin A are introduced by a promiscuous cytochrome P450 monooxygenase, whereas a two-component flavin-dependent monooxygenase is involved in α-hydroxylation.

Novel polyene carboxylic acids from Streptomyces

Reinvestigation of the production of the unusual polyene carboxylic acid serpentene (1a) from Streptomycessp. Tü 3851 revealed the presence of additional polyene carboxylic acids. The methyl esters of the new all-trans serpentene (2) and four new dicarboxylic acids (3-6) were isolated after methylation of the isolated polyene fraction. The dicarboxylic acids might result from omega- and beta-oxidation of the parent compounds 1 and 2.

Novel screen methodologies for identification of new microbial metabolites with pharmacological activity

Micro-organisms continue to provide an important source of chemical diversity for the discovery of compounds with new biological activities. Microbial metabolites discovered recently using assays to detect compounds with potential pharmacological utility are surveyed and found to represent an extensive range of structural types produced by a wide variety of organisms. Assays used for screening samples produced by microbial processes must be robust, sensitive and specific and able to operate above a background of potential interferences from a number of sources. Discovery assays currently in use fall into three main categories cell-based, receptor-ligand interaction and enzyme inhibition assays. Trends in the use of these assays and new developments in assay technology applicable to the screening of microbial samples are examined with particular reference to the high throughput screening environment. For microbial screening to be a competitive route to new drug leads, the disciplines involved must be engineered into a seamlessly integrated process to deliver novel compounds with the required biological properties rapidly.

Protection against bradykinin-induced bronchoconstriction in asthmatic patients by neurokinin receptor antagonist

Axon reflex mechanisms may be involved in the pathogenesis of asthma, but there has been no direct evidence that endogenous tachykinins cause bronchoconstriction in asthmatic subjects. We have studied the effect of a tachykinin receptor antagonist (FK-224) on bronchoconstriction induced by inhalation of bradykinin in asthmatic patients. In a double-blind, placebo-controlled, crossover trial, ten subjects with stable asthma were given FK-224 (4 mg) or placebo by inhalation 20 min before challenge with bradykinin (0-1250 micrograms/ml, five breaths of each concentration) given with 5 min intervals. Bradykinin caused dose-dependent bronchoconstriction in all subjects. FK-224 significantly opposed the bronchoconstrictor effect; the geometric mean of the cumulative concentration required to elicit a 35% fall in specific airway conductance was 5.3 micrograms/ml after placebo and 40 micrograms/ml after FK-224 (p < 0.001). Inhalation of bradykinin caused coughing in three subjects, which was inhibited by FK-224 in all three. Antagonism of the tachykinin receptor by FK-224 greatly inhibited both bronchoconstriction and coughing induced by bradykinin in asthmatic patients, suggesting that tachykinin release from the airway sensory nerves is involved in responses to bradykinin. Tachykinin receptor antagonists may be useful in the treatment of asthma.