Engineered biosynthesis of bacterial aromatic polyketides

Aromatic polyketides are a large group of complex and structurally diverse natural products with important pharmaceutical applications. Attributed to their rich and diverse chemical structures, biosynthetic engineering represents a powerful way for structural diversification and analog production. One of my research goals is to understand and engineer the molecular machinery nature employs during tetracycline synthesis. Tetracyclines are a family of bacterial aromatic polyketides with broad-spectrum antibiotic activities. Engineered biosynthesis of tetracycline analogs is an attractive option to accelerate the development of the next generation of tetracycline compounds exhibiting novel antibiotic and anticancer properties, as well as to overcome the current modes of antibiotic resistance. We sequenced the entire gene cluster of the oxytetracycline (oxy) polyketide synthase (PKS) from Streptomyces rimosus, and identified the minimal oxy PKS, the initiation module, the immediate tailoring enzymes, and the further downstream tailoring enzymes responsible for anhydrotetracycline biosynthesis in the heterologous host Streptomyces coelicolor. Many interesting biochemical features in tetracycline biosynthesis, including tetracyclic ring formation, amination, oxygenation and methylation were studied by combining in vivo and in vitro analyses. In addition, tetracycline intermediates, shunt products and analogs were generated and characterized, demonstrating our heterologous host/vector pair as a useful platform towards the engineered biosynthesis of new tetracycline analogs.;My second research goal is to reconstitute the biosynthesis of bacterial aromatic polyketides in the genetically superior host Escherichia coli. E. coli has been utilized as a dedicated biosynthetic microbial factory with high degrees of success for nearly all major classes of natural products. Nonetheless, attempts to synthesize the pharmaceutically important bacterial aromatic polyketides had previously been hindered due to the insolubility of key components of bacterial aromatic PKSs. By extracting and reassembling the minimal PKS from a non-reducing fungal megasynthase, we promoted the cross-talk between the bacterial and fungal PKSs, and synthesized complex bacterial aromatic polyketides in E. coli for the first time. This provides immense opportunities towards understanding and engineering of aromatic PKS enzymes in E. coli.