Cloning, sequencing and analysis of the enterocin biosynthesis gene cluster from the marine isolate 'Streptomyces maritimus': evidence for the derailment of an aromatic polyketide synthase

Background: Polycyclic aromatic polyketides, such as the tetracyclines and anthracyclines, are synthesized by bacterial aromatic polyketide synthases (PKSs). Such PKSs contain a single set of iteratively used individual prote ins for the construction of a highly labile poly-P-carbonyl intermediate th at is cyclized by associated enzymes to the core aromatic polyketide. A uni que polyketide biosynthetic pathway recently identified in the marine strai n 'Streptomyces maritimus' deviates from the normal aromatic PKS model in t he generation of a diverse series of chiral, non-aromatic polyketides. Results: A 21.3 kb gene cluster encoding the biosynthesis of the enterocin and wailupemycin family of polyketides from 'S. maritimus' has been cloned and sequenced. The biosynthesis of these structurally diverse polyketides i s encoded on a 20 open reading frames gene set containing a centrally locat ed aromatic PKS. The architecture of this novel type II gene set differs fr om all other aromatic PKS clusters by the absence of cyclase and aromatase encoding genes and the presence of genes encoding the biosynthesis and atta chment of the unique benzoyl-CoA starter unit. In addition to the previousl y reported heterologous expression of the gene set, in vitro and in vivo ex pression studies with the cytochrome P-450 EncR and the ketoreductase EncD, respectively, support the involvement of the cloned genes in enterocin bio synthesis. Conclusions: The enterocin biosynthesis gene cluster represents the most ve rsatile type II PKS system investigated to date. A large series of divergen t metabolites are naturally generated from the single biochemical pathway, which has several metabolic options for creating structural diversity. The absence of cyclase and aromatase gene products and the involvement of an ox ygenase-catalyzed Favorskii-like rearrangement provide insight into the obs erved spontaneity of this pathway. This system provides the foundation for engineering hybrid expression sets in the generation of structurally novel compounds for use in drug discovery.