Biosynthesis of Diverse Type II Polyketide Core Structures in Streptomyces coelicolor M1152

Investigating the initial steps of auricin biosynthesis using synthetic biology

Streptomyces lavendulae subsp. lavendulae CCM 3239 (formerly Streptomyces aureofaciens CCM 3239) contains a type II polyketide synthase (PKS) biosynthetic gene cluster (BGC) aur1 whose genes were highly similar to angucycline BGCs. However, its product auricin is structurally different from all known angucyclines. It contains a spiroketal pyranonaphthoquinone aglycone similar to griseusins and is modified with D-forosamine. Here, we describe the characterization of the initial steps in auricin biosynthesis using a synthetic-biology-based approach. We have created a plasmid system based on the strong kasOp* promoter, RBS and phage PhiBT1-based integration vector, where each gene in the artificial operon can be easily replaced by another gene using unique restriction sites surrounding each gene in the operon. The system was validated with the initial landomycin biosynthetic genes lanABCFDLE, leading to the production of rabelomycin after its integration into Streptomyces coelicolor M1146. However, the aur1DEFCGHA homologous genes from the auricin aur1 BGC failed to produce rabelomycin in this system. The cause of this failure was inactive aur1DE genes encoding ketosynthases α and β (KSα, KSβ). Their replacement with homologous aur2AB genes from the adjacent aur2 BGC resulted in rabelomycin production that was even higher after the insertion of two genes from the aur1 BGC, aur1L encoding 4-phosphopantetheinyl transferase (PPTase) and aur1M encoding malonyl-CoA:ACP transacylase (MCAT), suggesting that Aur1L PPTase is essential for the activation of the acyl carrier protein Aur1F. These results suggest an interesting communication of two BGCs, aur1 and aur2, in the biosynthesis of the initial structure of auricin aglycone.

Investigation of the Molecular Landscape of Bacterial Aromatic Polyketides by Global Analysis of Type II Polyketide Synthases

Aromatic polyketides biosynthesized by microorganisms are a prominent class of natural products widely used in clinical treatments. Although genome mining approaches have accelerated the discovery of these molecules, the molecular diversity, abundance, and distribution of bacterial aromatic polyketides at a global scale remain elusive. Here, we provide a global atlas of bacterial aromatic polyketides based on large-scale analysis of type II polyketide synthases. We first established the chain length factor protein as a marker that can predict both chemical class and molecular uniqueness of the biosynthetic product, and analyzed the abundance, taxonomic distribution, estimated structural diversity, and the total number of aromatic polyketides in bacteria. We further show the identification of oryzanaphthopyrans with an unprecedented angular naphthopyran scaffold from a rare actinobacterium by genome mining guided by the global atlas. These results serve as a compass for exploiting the entire type II polyketide synthase-derived aromatic polyketides in bacteria.

Himalaquinones A-G, Angucyclinone-Derived Metabolites Produced by the Himalayan Isolate Streptomyces sp. PU-MM59

Himalaquinones A-G, seven new anthraquinone-derived metabolites, were obtained from the Himalayan-based Streptomyces sp. PU-MM59. The chemical structures of the new compounds were identified based on cumulative analyses of HRESIMS and NMR spectra. Himalaquinones A-F were determined to be unique anthraquinones that contained unusual C-4a 3-methylbut-3-enoic acid aromatic substitutions, while himalaquinone G was identified as a new 5,6-dihydrodiol-bearing angucyclinone. Comparative bioactivity assessment (antimicrobial, cancer cell line cytotoxicity, impact on 4E-BP1 phosphorylation, and effect on axolotl embryo tail regeneration) revealed cytotoxic landomycin and saquayamycin analogues to inhibit 4E-BP1p and inhibit regeneration. In contrast, himalaquinone G, while also cytotoxic and a regeneration inhibitor, did not affect 4E-BP1p status at the doses tested. As such, this work implicates a unique mechanism for himalaquinone G and possibly other 5,6-dihydrodiol-bearing angucyclinones.