Biochemical and Structural Studies of the Carminomycin 4-O-Methyltransferase DnrK.

Structural and functional studies of the carminomycin 4-O-methyltransferase DnrK are described, with an emphasis on interrogating the acceptor substrate scope of DnrK. Specifically, the evaluation of 100 structurally and functionally diverse natural products and natural product mimetics revealed an array of pharmacophores as productive DnrK substrates. Representative newly identified DnrK substrates from this study included anthracyclines, angucyclines, anthraquinone-fused enediynes, flavonoids, pyranonaphthoquinones, and polyketides. The ligand-bound structure of DnrK bound to a non-native fluorescent hydroxycoumarin acceptor, 4-methylumbelliferone, along with corresponding DnrK kinetic parameters for 4-methylumbelliferone and native acceptor carminomycin are also reported for the first time. The demonstrated unique permissivity of DnrK highlights the potential for DnrK as a new tool in future biocatalytic and/or strain engineering applications. In addition, the comparative bioactivity assessment (cancer cell line cytotoxicity, 4E-BP1 phosphorylation, and axolotl embryo tail regeneration) of a select set of DnrK substrates/products highlights the ability of anthracycline 4-O-methylation to dictate diverse functional outcomes.

RF-3192C and other polyketides from the marine endophytic Aspergillus niger ASSB4: structure assignment and bioactivity investigation.

Chemical investigation of the methanolic extract of endophytic Aspergillus niger SB4, isolated from the marine alga Laurencia obtuse, afforded the pentacyclic polyketide, RF-3192C (1), the dimeric coumarin orlandin (2), fonsecin B (3), TMC-256A1 (4), cyclo-(Leu-Ala) (5), and cerebroside A (6).The chemical structure of RF-3192C (1) is assigned herein for the first time using 1D/2D NMR and HRESI-MS. Additionally, the revision of the NMR assignments of orlandin (2) was reported herein as well. Investigation of the antimicrobial activities of isolated compounds revealed the high activity of RF-3192C (1) against Pseudomonas aeruginosa and Bacillus subtilis, and moderate activity against yeast. Moreover, an in vitro cytotoxic activity against liver (HEPG2), cervical (HELA), lung (A549), prostate (PC3), and breast (MCF7) cancer cell lines of the isolated compounds was evaluated. The isolation and taxonomical characterization of the producing fungus was reported as well.

Diverse Combinatorial Biosynthesis Strategies for C-H Functionalization of Anthracyclinones.

Streptomyces spp. are "nature's antibiotic factories" that produce valuable bioactive metabolites, such as the cytotoxic anthracycline polyketides. While the anthracyclines have hundreds of natural and chemically synthesized analogues, much of the chemical diversity stems from enzymatic modifications to the saccharide chains and, to a lesser extent, from alterations to the core scaffold. Previous work has resulted in the generation of a BioBricks synthetic biology toolbox in Streptomyces coelicolor M1152ΔmatAB that could produce aklavinone, 9-epi-aklavinone, auramycinone, and nogalamycinone. In this work, we extended the platform to generate oxidatively modified analogues via two crucial strategies. (i) We swapped the ketoreductase and first-ring cyclase enzymes for the aromatase cyclase from the mithramycin biosynthetic pathway in our polyketide synthase (PKS) cassettes to generate 2-hydroxylated analogues. (ii) Next, we engineered several multioxygenase cassettes to catalyze 11-hydroxylation, 1-hydroxylation, 10-hydroxylation, 10-decarboxylation, and 4-hydroxyl regioisomerization. We also developed improved plasmid vectors and S. coelicolor M1152ΔmatAB expression hosts to produce anthracyclinones. This work sets the stage for the combinatorial biosynthesis of bespoke anthracyclines using recombinant Streptomyces spp. hosts.