title: Mechanism of thioesterase-catalyzed chain release in the biosynthesis of the polyether antibiotic nanchangmycin.
abstract: The polyketide backbone of the polyether ionophore antibiotic nanchangmycin (1) is assembled by a modular polyketide synthase in Streptomyces nanchangensis NS3226. The ACP-bound polyketide is thought to undergo a cascade of oxidative cyclizations to generate the characteristic polyether. Deletion of the glycosyl transferase gene nanG5 resulted in accumulation of the corresponding nanchangmycin aglycone (6). The discrete thioesterase NanE exhibited a nearly 17-fold preference for hydrolysis of 4, the N-acetylcysteamine (SNAC) thioester of nanchangmycin, over 7, the corresponding SNAC derivative of the aglycone, consistent with NanE-catalyzed hydrolysis of ACP-bound nanchangmycin being the final step in the biosynthetic pathway. Site-directed mutagenesis established that Ser96, His261, and Asp120, the proposed components of the NanE catalytic triad, were all essential for thioesterase activity, while Trp97 was shown to influence the preference for polyether over polyketide substrates.
authors.affiliation: Laboratory of Microbial Metabolism and School of Life Science and Biotechnology, Shanghai Jiaotong University, Shanghai, China.
authors.forename: Tiangang
authors.initials: T
authors.lastname: Liu
authors.forename: Xin
authors.initials: X
authors.lastname: Lin
authors.forename: Xiufen
authors.initials: X
authors.lastname: Zhou
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
authors.forename: David E
authors.initials: DE
authors.lastname: Cane
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000378:metabolism; D002384:Catalysis; D004950:Esterases / Q000737:chemistry / Q000378:metabolism*; D004987:Ethers / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017386:Sequence Homology, Amino Acid; D013141:Spiro Compounds / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000900:Anti-Bacterial Agents; D004987:Ethers; D013141:Spiro Compounds; C452419:nanchangmycin; D004950:Esterases