The oxidative ring cleavage in jadomycin biosynthesis: a multistep oxygenation cascade in a biosynthetic black box.

The antibiotic jadomycin B is derived from an angucycline intermediate that undergoes oxidative ring cleavage and the unique incorporation of l-isoleucine into its polyketide backbone. To elucidate the enzymes and substrates involved in this key oxygenation event, we have investigated a region of the jad gene cluster that is located immediately downstream of the previously identified oxygenase genes jadF and jadG and contains a third putative oxygenase gene, jadH, as well as a potential hydrolase gene, jadK. Inactivation of jadG and jadH, respectively, led to the accumulation of several shunt products and a novel potential pathway intermediate, named prejadomycin. Production of these angucyclines and the failure to generate a ring-cleavage product in various mutant strains illustrates the complex protein–protein interaction network within the oxygenase subcluster. Furthermore, these results demonstrate that both JadF and JadH display secondary dehydratase activities that contrary to their oxygenase activities, appear to be independent of the respective protein-complex binding partners. The polyketide glycoside antibiotic jadomycin B (2) and its aglycon jadomycin A (1) (Scheme 1) are produced by the soil bacterium Streptomyces venezuelae ISP5230 under stress conditions such as heat shock, phage infection, and particularly ethanol treatment. The jadomycin family possesses a unique nitrogen-containing pentacyclic benz[b]oxazolophenanthridine backbone that has been shown by precursor-directed biosynthesis with various amino acids as well as feeding experiments with C-labeled acetate to derive from the fusion of an l-amino acid, for exam-