New aminocoumarin antibiotics from genetically engineered Streptomyces strains

The aminocoumarin antibiotics novobiocin, clorobiocin and coumermycin A, are produced by different Streptomyces strains and are potent inhibitors of DNA gyrase. The biosynthetic gene clusters of all three antibiotics have been cloned and sequenced, and the function of most genes contained therein has been elucidated. In the last years. a number of "unnatural" aminocoumarins could be generated using the genetic information for the biosynthesis of these antibiotics. The investigated enzymes of aminocoumarin biosynthesis have less-than-perfect substrate specificity, facilitating the production of new antibiotics by various methods. Several new aminocoumarins could be produced by targeted genetic manipulation in the natural producers, but also in heterologous host Streptomyces coelicolor after expression of the respective gene cluster. Mutasynthesis experiments, i.e. generation of a cloQ-defective mutant of the clorobiocin producer and feeding of 13 different structural analogs of 3-dimethylallyl-4-hydroxybenzoic acid to this mutant, allowed the isolation of 32 new aminocoumarins. These compounds contained, instead of the genuine 3-dimethylallyl-4-hydroxybenzoyl moiety, the externally added analogs as the acyl components in their structures. Production of new aminocoumarins was also achieved by chemoenzymatic synthesis in vitro. Several biosynthetic enzymes have been heterologously expressed, purified and used for chemoenzymatic synthesis. The structures of the new aminocoumarins were elucidated by NMR and mass spectroscopy. Their inhibitory activity on gyrase in vitro as well as their antibacterial activity was determined. These results give further insight into the structure-activity relationships of aminocoumarins.