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44399-G1
Regiospecific Synthesis of Polyketide Natural Products Using Polyketide Synthase

Sheryl Tsai, University of California, Irvine

Aromatic (Type II) Polyketide Synthase produces many medically important aromatic natural products, such as doxorubicin (anticancer) and tetracycline (antibiotic). Understanding the structures and functions of PKS is the key to rationally engineer PKS to biosynthesize new “unnatural” natural products that may be screened for novel pharmaceutical activities. How the aromatic PKS controls its reduction and cyclization patterns is not well understood. The support from ACS-PRF have resulted in the following progress:

1. Solved the crystal structures of ketoreductase (KR) that illuminate the stereo- and regio-specificity of polyketide reduction.

2. Solved the crystal structure of two aromatase/cyclase (ARO/CYCs), tcm ARO/CYC and whiE ARO/CYC, which catalyze highly specific aromatic ring formation.

3. Developed in vitro assay to determine the molecular basis of KR stereospecificity and ARO cyclization specificity.

4. Determined the enzyme mechanism of KR and ARO

5. Produced more than 50 mutants that change the specificities of KR and ARO to produce new “unnatural” natural products with different reduction and cyclization patterns.

6. Solved 21 mutant and substrate/inhibitor-bound cocrystal structures of KR and ARO/CYC that dissect the specificities of these two enzymes at an unprecedented molecular level.

7. Generated KS/CLF mutants and solved crystal structures to facilitate future directed biosynthesis of "unnatural" natural products

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