C-N-Coupled Metabolites Yield Insights into Dynemicin A Biosynthesis.

The biosynthesis of the three structural subclasses of enediyne antitumor antibiotics remains largely unknown beyond a common C16 -hexaene precursor. For the anthraquinone-fused subtype, however, an unexpected iodoanthracene γ-thiolactone was established to be a mid-pathway intermediate to dynemicin A. Having deleted a putative flavin-dependent oxidoreductase from the dynemicin biosynthetic gene cluster, we can now report four metabolites that incorporate the iodoanthracene and reveal the formation of the C-N bond linking the anthraquinone and enediyne halves emblematic of this structural subclass. The coupling of an aryl iodide and an amine is familiar from organometallic chemistry, but has little or no precedent in natural product biosynthesis. These metabolites suggest further that enediyne formation occurs early in the overall biosynthesis, and that even earlier events might convert the C16 -hexaene to a common C15 intermediate that partitions to enediyne and anthraquinone building blocks for the heterodimerization.

Characterization of an Anthracene Intermediate in Dynemicin Biosynthesis.

Despite the identification of a ß-hydroxyhexaene produced by the enediyne polyketide synthases (PKSs), the post-PKS biosynthetic steps to the individual members of this antitumor and antibiotic family remain largely unknown. The massive biosynthetic gene clusters (BGCs) that direct the formation of each product caution that many steps could be required. It was recently demonstrated that the enediyne PKS in the dynemicin A BGC from Micromonospora chersina gives rise to both the anthraquinone and enediyne halves of the molecule. We now present the first evidence for a mid-pathway intermediate in dynemicin A biosynthesis, an iodoanthracene bearing a fused thiolactone, which was shown to be incorporated selectively into the final product. This unusual precursor reflects just how little is understood about these biosynthetic pathways, yet constrains the mechanisms that can act to achieve the key heterodimerization to the anthraquinone-containing subclass of enediynes.

A dual role for a polyketide synthase in dynemicin enediyne and anthraquinone biosynthesis.

Dynemicin A is a member of a subfamily of enediyne antitumour antibiotics characterized by a 10-membered carbocycle fused to an anthraquinone, both of polyketide origin. Sequencing of the dynemicin biosynthetic gene cluster in Micromonospora chersina previously identified an enediyne polyketide synthase (PKS), but no anthraquinone PKS, suggesting gene(s) for biosynthesis of the latter were distant from the core dynemicin cluster. To identify these gene(s), we sequenced and analysed the genome of M. chersina. Sequencing produced a short list of putative PKS candidates, yet CRISPR-Cas9 mutants of each locus retained dynemicin production. Subsequently, deletion of two cytochromes P450 in the dynemicin cluster suggested that the dynemicin enediyne PKS, DynE8, may biosynthesize the anthraquinone. Together with 18O-labelling studies, we now present evidence that DynE8 produces the core scaffolds of both the enediyne and anthraquinone, and provide a working model to account for their formation from the programmed octaketide of the enediyne PKS.

A new antibiotic kills pathogens without detectable resistance.

Antibiotic resistance is spreading faster than the introduction of new compounds into clinical practice, causing a public health crisis. Most antibiotics were produced by screening soil microorganisms, but this limited resource of cultivable bacteria was overmined by the 1960s. Synthetic approaches to produce antibiotics have been unable to replace this platform. Uncultured bacteria make up approximately 99% of all species in external environments, and are an untapped source of new antibiotics. We developed several methods to grow uncultured organisms by cultivation in situ or by using specific growth factors. Here we report a new antibiotic that we term teixobactin, discovered in a screen of uncultured bacteria. Teixobactin inhibits cell wall synthesis by binding to a highly conserved motif of lipid II (precursor of peptidoglycan) and lipid III (precursor of cell wall teichoic acid). We did not obtain any mutants of Staphylococcus aureus or Mycobacterium tuberculosis resistant to teixobactin. The properties of this compound suggest a path towards developing antibiotics that are likely to avoid development of resistance.