Two Distinct Cyclodipeptide Synthases from a Marine Actinomycete Catalyze Biosynthesis of the Same Diketopiperazine Natural Product

Diketopiperazine natural products are structurally diverse and offer many biological activities. Cyclodipeptide synthases (CDPSs) were recently unveiled as a novel enzyme family that employs aminoacyl-tRNAs as substrates for 2,5-diketopiperazine assembly. Here, the Nocardiopsis sp. CMB-M0232 genome is predicted to encode two CDPSs, NozA and NcdA. Metabolite profiles from E. coli expressing these genes and assays with purified recombinant enzymes revealed that NozA and NcdA catalyze cyclo(l-Trp-l-Trp) (1) biosynthesis from tryptophanyl-tRNA and do not accept other aromatic aminoacyl-tRNA substrates. Fidelity is uncommon among characterized CDPSs, making NozA and NcdA important CDPS family additions. Further, 1 was previously supported as a biosynthetic precursor of the nocardioazines; the current study suggests that Nocardiopsis sp. may derive this precursor from both NozA and NcdA. This study offers a rare example of a single bacterium encoding multiple phylogenetically distinct enzymes that yield the same secondary metabolite and provides tools for chemoenzymatic syntheses of indole alkaloid diketopiperazines.