The biosynthetic gene cluster for the microtubule-stabilizing agents epothilones A and B from Sorangium cellulosum So ce90

Background: Epothilones are produced by the myxobacterium Sorangium cellulo sum So ce90, and, like paclitaxel (Taxol(R)), they inhibit microtubule depo lymerisation and arrest the cell cycle at the G2-M phase. They are effectiv e against P-glycoprotein-expressing multiple-drug-resistant tumor cell line s and are more water soluble than paclitaxel, The total synthesis of epothi lones has been achieved, but has not provided an economically viable altern ative to fermentation. We set out to clone, sequence and analyze the gene c luster responsible for the biosynthesis of the epothilones in S. cellulosum So ce90. Results: A cluster of 22 open reading frames spanning 68,750 base pairs of the S. cellulosum So ce90 genome has been sequenced and found to encode nin e modules of a polyketide synthase (PKS), one module of a nonribosomal pept ide synthetase (NRPS), a cytochrome P450, and two putative antibiotic trans port proteins. Disruptions in the genes encoding the PKS abolished epothilo ne production. The first PKS module and the NRPS module are proposed to cc- operate in forming the thiazole heterocycle of epothilone from an acetate a nd a cysteine by condensation, cyclodehydration and subsequent dehydrogenat ion. The remaining eight PKS modules are responsible for the elaboration of the rest of the epothilone carbon skeleton. Conclusions: The overall architecture of the gene cluster responsible for e pothilone biosynthesis has been determined. The availability of the cluster should facilitate the generation of designer epothilones by combinatorial biosynthesis approaches, and the heterologous expression of epothilones in surrogate microbial hosts.