Erythromycin biosynthesis. Highly efficient incorporation of polyketide chain elongation intermediates into 6-deoxyerythronolide B in an engineered Streptomyces host

Feeding of (2S,3R)-[2,3-13C2]-2-methyl-3-hydroxypentanoyl NAC thioester (1a) to the recombinant organism Streptomyces coelicolor CH999/pCK7 harboring the complete set of eryA genes from Saccharopolyspora erythraea encoding the 6-deoxyerythronolide B synthase (DEBS) resulted in the formation of 6-deoxyerythronolide B (2a) labeled with 13C at C-12 and C-13, as evidenced by the appearance of a pair of enhanced and coupled doublets in the 13C NMR spectrum. The level of 13C enrichment was 15-20 atom% 13C, as much as 100 times higher than the usually observed efficiency of incorporation of NAC thioesters into polyketide metabolites. Similar incorporation of (2S,3R)-[3-2H,3-13C]-2-methyl-3-hydroxypentanoyl NAC thioester (1b) gave 6-deoxyerythronolide B (2b) labeled with both 13C and deuterium at C-13. The intact incorporation of both precursors confirms the normal functioning of the recombinant DEBS proteins in the heterologous host.

Engineered biosynthesis of a complete macrolactone in a heterologous host

Macrocyclic polyketides have been subjects of great interest in synthetic and biosynthetic chemistry because of their structural complexity and medicinal activities. With expression of the entire 6-deoxyerythronolide B synthase (DEBS) (10,283 amino acids) in a heterologous host, substantial quantities of 6-deoxyerythronolide B (6dEB), the aglycone of the macrolide antibiotic erythromycin, and 8,8a-deoxyoleandolide, a 14-membered lactone ring identical to 6dEB except for a methyl group side chain in place of an ethyl unit, were synthesized in Streptomyces coelicolor. The biosynthetic strategy utilizes a genetic approach that facilitates rapid structural manipulation of DEBS or other modular polyketide synthases (PKSs), including those found in actinomycetes with poorly developed genetic methods. From a technological viewpoint, this approach should allow the rational design of biosynthetic products and may eventually lead to the generation of diverse polyketide libraries by means of combinatorial cloning of naturally occurring and mutant PKS modules.