Off-loading Dieckmann cyclase, NcmC, that installs the tetramate head group in nocamycin, a hybrid polyketide/nonribosomalpeptide natural product. A conserved thioesterase-like scaffold has been adapted to perform a new chemical reaction: heterocyclization. The catalytic triad for the cyclization reaction consists of Cys89, Asp116, and His254 in 9pseu-NcmC. Dieckmann cyclase (TrdC, SlgL, LipX2, KirHI,and FacH) last step which generate actinomycete-derived tetramic acid and pyridone natural products in the biosynthetic pathways for Tirandamycin, Streptolydigin, alpha-Lipomycin, Kirromycin, and Factumycin
While several bioactive natural products that contain tetramate or pyridone heterocycles have been described, information on the enzymology underpinning these functionalities has been limited. Here we biochemically characterize an off-loading Dieckmann cyclase, NcmC, that installs the tetramate headgroup in nocamycin, a hybrid polyketide/nonribosomal peptide natural product. Crystal structures of the enzyme (1.6 A) and its covalent complex with the epoxide cerulenin (1.6 A) guide additional structure-based mutagenesis and product-profile analyses. Our results offer mechanistic insights into how the conserved thioesterase-like scaffold has been adapted to perform a new chemical reaction, namely, heterocyclization. Additional bioinformatics combined with docking and modeling identifies likely candidates for heterocycle formation in underexplored gene clusters and uncovers a modular basis of substrate recognition by the two subdomains of these Dieckmann cyclases.
Title: Discovery of a new family of Dieckmann cyclases essential to tetramic acid and pyridone-based natural products biosynthesis Gui C, Li Q, Mo X, Qin X, Ma J, Ju J Ref: Org Lett, 17:628, 2015 : PubMed
Bioinformatic analyses indicate that TrdC, SlgL, LipX2, KirHI, and FacHI belong to a group of highly homologous proteins involved in biosynthesis of actinomycete-derived tirandamycin B, streptolydigin, alpha-lipomycin, kirromycin, and factumycin, respectively. However, assignment of their biosynthetic roles has remained elusive. Gene inactivation and complementation, in vitro biochemical assays with synthetic analogues, point mutations, and phylogenetic tree analyses reveal that these proteins represent a new family of Dieckmann cyclases that drive tetramic acid and pyridone scaffold biosynthesis.
