Combinatorial Biosynthesis of Polyketide Compounds Guided By Structural Enzymology.

DIACOVICH L., MITCHEL D., MELGAR M., PHAM H., TANG Y., KHOSLA C., GRAMAJO H., TSAI S.

Proctor Academy Andover, NH, USA.

Conferencia; Bioorganic Chemistry, Gordon Research Conferences.; 2004

Gordon Research Conferences

Polyketide natural products include many cholesterol-lowering, anticancer and antibiotic pharmaceuticals. They are made by enzymes of the polyketide pathway. Three enzyme clusters are involved: acyl-CoA carboxylase (ACCase), polyketide synthase (PKS) and deoxy-sugar enzymes. Libraries of “unnatural” polyketides have been generated by in vivo domain swapping or precursor feeding of these enzyme complexes. The combinatorial biosynthesis of polyketide products result in a great diversity of products via a controlled variation of extender units, chain length and chain modifications. To understand the molecular principles underlying the biosynthesis of polyketides, X-ray crystal structures of the polyketide pathway enzymes were solved. The structurally-derived hypotheses were tested via mutational analysis. By the elucidation of structural and mechanistic features that govern the biosynthesis of polyketides, the bioengineering of these enzymes to generate “unnatural” natural products for novel drug discovery has become possible. Two examples are presented to demonstrate the feasibility of structure-guided combinatorial biosynthesis: the extender unit biosynthesis (beta subunit of ACCase) and the chain length control (KS/CLF). The structures of both enzymes, coupled with sequence comparison, help to explain their substrate specificity and versatility, and provide the first clue about the tertiary structure of the multi-enzyme PKS assembly, where a flexible “robotic arm” is involved in intermediate transportation.