Chain Termination Steps in Nonribosomal Peptide Synthetase Assembly Lines: Directed Acyl-S-Enzyme Breakdown in Antibiotic and Siderophore Biosynthesis

The multidomain enzymes that biosynthesize important natural peptide products such as cyclosporin and vancomycin carry the growing biopolymer chains covalently attached as thioesters. For the mature chain to be released from the enzyme, this thioester must be cleaved, a task that falls to specialized enzymatic domains that can hydrolyze these thioesters, reduce them, or macrocyclize the substrate to form a new amide bond (schematically shown for the tyrocidine thioesterase). This Minireview examines these terminating domains and their mechanisms. NAC=N-acetylcysteaminyl.