title: Precursor-directed biosynthesis of 16-membered macrolides by the erythromycin polyketide synthase.
abstract: Streptomyces coelicolor CH999/pJRJ2 harbors a plasmid encoding DEBS(KS1 degrees ), a mutant form of 6-deoxyerythronolide B synthase that is blocked in the formation of 6-deoxyerythronolide B (1, 6-dEB) due to a mutation in the active site of the ketosynthase (KS1) domain that normally catalyzes the first polyketide chain elongation step of 6-dEB biosynthesis. Administration of (2E,4S,5R)-2,4-dimethyl-5-hydroxy-2-heptenoic acid, N-acetylcysteamine thioester (6) an unsaturated triketide analogue of the natural triketide chain elongation intermediate to cultures of S. coelicolor CH999/pJRJ2 results in formation of a 16-membered macrolactone, which is isolated in the hemiketal form 33. The formation of the octaketide 33 indicates that the triketide substrate has been processed by DEBS module 2 as if it were a diketide analogue. The substrate specificity of this novel reaction has been explored by the incubation of three additional analogues of the unsaturated triketide 6, compounds 18, 31, and 32, with S. coelicolor CH999/pJRJ2, resulting in the formation of the corresponding macrolactones 34, 35, and 36. By contrast, the unsaturated triketide 10, lacking a methyl group at C-2, did not give rise to any detectable macrolactone product when incubated with S. coelicolor CH999/pJRJ2.
authors.affiliation: Department of Chemistry, Box H, Brown University, Providence, Rhode Island 02912-9108, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kinoshita
authors.forename: P G
authors.initials: PG
authors.lastname: Williard
authors.forename: C
authors.initials: C
authors.lastname: Khosla
authors.forename: D E
authors.initials: DE
authors.lastname: Cane
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D018942:Macrolides; D008968:Molecular Conformation; D009097:Multienzyme Complexes / Q000502:physiology*; D013302:Streptomyces / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D009097:Multienzyme Complexes