Khosla 9417419 Our research focuses on understanding the relationships between structure and function of natural and designed biosynthetic enzymes. Polyketide synthases (PKSs) are examples of these enzymes. They catalyze the biosynthesis of polyketides (a structurally diverse family of bioactive natural products) via repeated condensations between carboxylic acid derivatives. After each condensation, the added -keto group is suitably reduced. It is the controlled variation in chain length, choice of chain- binding units, extent of each reductive cycle, and regiospecificity in cyclization that leads to the variation among naturally occurring polyketides. Our work seeks (i) to understand how PKS structure controls catalysis, specificity, and subunit assembly, and (ii) to develop biosynthetic rules for the rational design of novel polyketides. Towards this end, we have recently generated and characterized several novel polyketides by using genetic engineering. On one hand, this knowledge leads to new insights of molecule reconstruction and opens the possibility of expanding nature's repertoire of polyketide compounds. The present research extends studies on a group of PKSs involved in aromatic polyketide biosynthesis, which exhibit four principal catalytic degrees of freedom. The structural determinants of these degrees of freedom will be defined. %%% Molecular biology owes much of its appeal and technological power to the elucidation of mechanisms for DNA, RNA, and protein biosynthesis. In particular, these biosynthetic mechanism have in common the use of "template" molecules that determine the structure of the product molecule. However, it is well-known that DNA, RNA, and proteins are not the only biomolecules synthesized by iterative mechanisms. An examination of the molecular diversity of a number of natural products leads one to speculate that the equivalent of a genetic code must also exist for these molecules. However, the apparent absence of "t emplates" has frustrated attempts determine how compound structural specificity is achieved along these biosynthetic pathways. Our work uses the complementary tools of genetics and chemistry to unravel the structural and mechanistic basis for molecular diversity in one family of natural products: the polyketides. The research directions proposed here seek to (i) understand how PKS structure controls catalysis, specificity, and subunit assembly, and (ii) develop biosynthetic rules for the rational design of novel polyketides. This project is funded jointly by the Metabolic Biochemistry Program (Division of Molecular and Cellular Biosciences) and the Organic Synthesis Section of the Organic and Macromolecular Chemistry Program (Division of Chemistry). ***
