Zincophorin - biosynthesis in Streptomyces griseus and antibiotic properties

Initiating polyketide biosynthesis by on-line methyl esterification

Aurantinins (ARTs) are antibacterial polyketides featuring a unique 6/7/8/5-fused tetracyclic ring system and a triene side chain with a carboxyl terminus. Here we identify the art gene cluster and dissect ART’s C-methyl incorporation patterns to study its biosynthesis. During this process, an apparently redundant methyltransferase Art28 was characterized as a malonyl-acyl carrier protein O-methyltransferase, which represents an unusual on-line methyl esterification initiation strategy for polyketide biosynthesis. The methyl ester bond introduced by Art28 is kept until the last step of ART biosynthesis, in which it is hydrolyzed by Art9 to convert inactive ART 9B to active ART B. The cryptic reactions catalyzed by Art28 and Art9 represent a protecting group biosynthetic logic to render the ART carboxyl terminus inert to unwanted side reactions and to protect producing organisms from toxic ART intermediates. Further analyses revealed a wide distribution of this initiation strategy for polyketide biosynthesis in various bacteria.

Aurantinins are polyketides with unusual connectivities and broad antibacterial activity. Here the authors show the biosynthesis of aurantinins, which proceeds via an on-line methyl esterification at the terminus that enables the iterative chain elongations prior to condensation and cyclization.

Zinc(II)-The Overlooked Éminence Grise of Chloroquine's Fight against COVID-19?

Zn(II) is an inhibitor of SARS-CoV-2's RNA-dependent RNA polymerase, and chloroquine and hydroxychloroquine are Zn(II) ionophores-this statement gives a curious mind a lot to think about. We show results of the first clinical trials on chloroquine (CQ) and hydroxychloroquine (HCQ) in the treatment of COVID-19, as well as earlier reports on the anticoronaviral properties of these two compounds and of Zn(II) itself. Other FDA-approved Zn(II) ionophores are given a decent amount of attention and are thought of as possible COVID-19 therapeutics.

Taxonomic Characterization and Secondary Metabolite Analysis of NEAU-wh3-1: An Embleya Strain with Antitumor and Antibacterial Activity

Cancer is a serious threat to human health. With the increasing resistance to known drugs, it is still urgent to find new drugs or pro-drugs with anti-tumor effects. Natural products produced by microorganisms have played an important role in the history of drug discovery, particularly in the anticancer and anti-infective areas. The plant rhizosphere ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science, especially Streptomyces. We screened Streptomyces-like strains from the rhizosphere soil of wheat (Triticum aestivum L.) in Hebei province, China, and thirty-nine strains were obtained. Among them, the extracts of 14 isolates inhibited the growth of colon tumor cell line HCT-116. Strain NEAU-wh-3-1 exhibited better inhibitory activity, and its active ingredients were further studied. Then, 16S rRNA gene sequence similarity studies showed that strain NEAU-wh3-1 with high sequence similarities to Embleya scabrispora DSM 41855T (99.65%), Embleya hyalina MB891-A1T (99.45%), and Streptomyces lasii 5H-CA11T (98.62%). Moreover, multilocus sequence analysis based on the five other house-keeping genes (atpD, gyrB, rpoB, recA, and trpB) and polyphasic taxonomic approach comprising chemotaxonomic, phylogenetic, morphological, and physiological characterization indicated that the isolate should be assigned to the genus Embleya and was different from its closely related strains, therefore, it is proposed that strain NEAU-wh3-1 may be classified as representatives of a novel species of the genus Embleya. Furthermore, active substances in the fermentation broth of strain NEAU-wh-3-1 were isolated by bioassay-guided analysis and identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. Consequently, one new Zincophorin analogue together with seven known compounds was detected. The new compound showed highest antitumor activity against three human cell lines with the 50% inhibition (IC50) values of 8.8-11.6 μg/mL and good antibacterial activity against four pathogenic bacteria, the other known compounds also exhibit certain biological activity.

Discovery and Characterization of Diazenylaryl Sulfonic Acids as Inhibitors of Viral and Bacterial Neuraminidases

Viral neuraminidases are an established drug target to combat influenza. Severe complications observed in influenza patients are primarily caused by secondary infections with e.g., Streptococcus pneumoniae. These bacteria engage in a lethal synergism with influenza A viruses (IAVs) and also express neuraminidases. Therefore, inhibitors with dual activity on viral and bacterial neuraminidases are expected to be advantageous for the treatment of influenza infections. Here we report on the discovery and characterization of diazenylaryl sulfonic acids as dual inhibitors of viral and Streptococcus pneumoniae neuraminidase. The initial hit came from a virtual screening campaign for inhibitors of viral neuraminidases. For the most active compound, 7-[2-[4-[2-[4-[2-(2-hydroxy-3,6-disulfo-1-naphthalenyl)diazenyl]-2-methylphenyl]diazenyl]-2-methylphenyl]diazenyl]-1,3-naphthalenedisulfonic acid (NSC65847; 1), the Ki-values measured in a fluorescence-based assay were lower than 1.5 μM for both viral and pneumococcal neuraminidases. The compound also inhibited N1 virus variants containing neuraminidase inhibitor resistance-conferring substitutions. Via enzyme kinetics and nonlinear regression modeling, 1 was suggested to impair the viral neuraminidases and pneumococcal neuraminidase with a mixed-type inhibition mode. Given its antiviral and antipneumococcal activity, 1 was identified as a starting point for the development of novel, dual-acting anti-infectives.