Towards the biosynthesis of modified natural products

Natural product-based pharmaceuticals, particularly polyketide or nonribosomal peptide-based antibiotics, have played essential roles in human health since their introduction. To prolong the age of antibiotics past a period of discovery void following the golden age of antibiotics discovery, scientists have turned to medicinal chemistry in order to develop successive generations of existing antibiotics. However, as the clinical pipeline continues to dwindle amidst ever rising threats of bacterial resistance to antibiotics, we are in dire need of new approaches to solving familiar problems. One promising way to facilitate the process by which next generation natural product-based drugs are made is to establish an efficient system for combinatorial biosynthesis. This thesis examines the challenge of combinatorial biosynthesis from multiple vantage points. A detailed structure-function analysis of an acyltransferase (AT) domain is used to gain insight into the substrate-protein interaction involved in polyketide biosynthesis. We have found the substrate carrier-AT domain interaction to be important in substrate recognition. Expanding the focus from a single catalytic domain, biochemical analysis of an entire siderophore polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) hybrid is presented. The characterization of the hybrid PKS/NRPS is an essential step towards engineering the system, and the possibility of utilizing this system for artificial evolution of PKS and NRPS domains is discussed. The research presented in this thesis represents significant progress towards using combinatorial biosynthesis for the production of modified natural products.