Biosynthesis of Guanitoxin Enables Global Environmental Detection in Freshwater Cyanobacteria.

Harmful cyanobacterial blooms (cyanoHABs) cause recurrent toxic events in global watersheds. Although public health agencies monitor the causal toxins of most cyanoHABs and scientists in the field continue developing precise detection and prediction tools, the potent anticholinesterase neurotoxin, guanitoxin, is not presently environmentally monitored. This is largely due to its incompatibility with widely employed analytical methods and instability in the environment, despite guanitoxin being among the most lethal cyanotoxins.

Nonlinear Biosynthetic Assembly of Alpiniamide by a Hybrid /-AT PKS-NRPS.

Alpiniamide A is a linear polyketide produced by endophytic bacteria. Despite its relatively simple chemical structure suggestive of a linear assembly line biosynthetic construction involving a hybrid polyketide synthase-nonribosomal peptide synthetase enzymatic protein machine, we report an unexpected nonlinear synthesis of this bacterial natural product. Using a combination of genomics, heterologous expression, mutagenesis, isotope-labeling, and chain terminator experiments, we propose that alpiniamide A is assembled in two halves and then ligated into the mature molecule.

Biosynthesis of l-4-Chlorokynurenine, an Antidepressant Prodrug and a Non-Proteinogenic Amino Acid Found in Lipopeptide Antibiotics.

l-4-Chlorokynurenine (l-4-Cl-Kyn) is a neuropharmaceutical drug candidate that is in development for the treatment of major depressive disorder. Recently, this amino acid was naturally found as a residue in the lipopeptide antibiotic taromycin. Herein, we report the unprecedented conversion of l-tryptophan into l-4-Cl-Kyn catalyzed by four enzymes in the taromycin biosynthetic pathway from the marine bacterium Saccharomonospora sp.

Refactoring the Cryptic Streptophenazine Biosynthetic Gene Cluster Unites Phenazine, Polyketide, and Nonribosomal Peptide Biochemistry.

The disconnect between the genomic prediction of secondary metabolite biosynthetic potential and the observed laboratory production profile of microorganisms is well documented. While heterologous expression of biosynthetic gene clusters (BGCs) is often seen as a potential solution to bridge this gap, it is not immune to many challenges including impaired regulation, the inability to recruit essential building blocks, and transcriptional and/or translational silence of the biosynthetic genes. Here we report the discovery, cloning, refactoring, and heterologous expression of a cryptic hybrid phenazine-type BGC (spz) from the marine actinomycete Streptomyces sp.

Biosynthesis of the neurotoxin domoic acid in a bloom-forming diatom.

Oceanic harmful algal blooms of diatoms produce the potent mammalian neurotoxin domoic acid (DA). Despite decades of research, the molecular basis for its biosynthesis is not known. By using growth conditions known to induce DA production in , we implemented transcriptome sequencing in order to identify DA biosynthesis genes that colocalize in a genomic four-gene cluster.

Isolation and structure elucidation of lipopeptide antibiotic taromycin B from the activated taromycin biosynthetic gene cluster.

In the ongoing effort to unlock the chemical potential of marine bacteria, genetic engineering of biosynthetic gene clusters (BGCs) is increasingly used to awake or improve expression of biosynthetic genes that may lead to discovery of novel bioactive natural products. Previously, we reported the successful capture, engineering and heterologous expression of an orphan BGC from the marine actinomycete Saccharomonospora sp. CNQ-490, which resulted in the isolation of the novel lipopeptide antibiotic taromycin A.

Enzymology of Pyran Ring A Formation in Salinomycin Biosynthesis.

Tetrahydropyran rings are a common feature of complex polyketide natural products, but much remains to be learned about the enzymology of their formation. The enzyme SalBIII from the salinomycin biosynthetic pathway resembles other polyether epoxide hydrolases/cyclases of the MonB family, but SalBIII plays no role in the conventional cascade of ring opening/closing. Mutation in the gene gave a metabolite in which ring A is not formed.

Enzymology of Pyran Ring A Formation in Salinomycin Biosynthesis.

Tetrahydropyran rings are a common feature of complex polyketide natural products, but much remains to be learned about the enzymology of their formation. The enzyme SalBIII from the salinomycin biosynthetic pathway resembles other polyether epoxide hydrolases/cyclases of the MonB family, but SalBIII plays no role in the conventional cascade of ring opening/closing. Mutation in the salBIII gene gave a metabolite in which ring A is not formed.

Site-specific modification of the anticancer and antituberculosis polyether salinomycin by biosynthetic engineering.

The complex bis-spiroacetal polyether ionophore salinomycin has been identified as a uniquely selective agent against cancer stem cells and is also strikingly effective in an animal model of latent tuberculosis. The basis for these important activities is unknown. We show here that deletion of the salE gene abolishes salinomycin production and yields two new analogues, in both of which the C18C19 cis double bond is replaced by a hydroxy group stereospecifically located at C19, but which differ from each other in the configuration of the bis-spiroacetal.