Comparative investigation into formycin A and pyrazofurin A biosynthesis reveals branch pathways for the construction ofC-nucleoside scaffolds

ABSTRACT Formycin A (FOR-A) and pyrazofurin A (PRF-A) are purine-related C -nucleoside antibiotics, in which ribose and a pyrazole-derived base are linked by a C -glycosidic bond, however, the logic underlying the biosynthesis of these molecules has remained largely unexplored. Here, we report the discovery of the pathways for FOR-A and PRF-A biosynthesis from diverse actinobacteria, and demonstrate that their biosynthesis is initiated by a lysine N 6 -monooxygenase. Moreover, we show that the forT and prfE (individually related to FOR-A and PRF-A biosynthesis) mutants are correspondingly capable of accumulating the unexpected pyrazole-related intermediates, compound 11 and 9a . We also decipher the enzymatic basis of ForT/PrfE for the C -glycosidic bond formation in FOR-A/PRF-A biosynthesis. To our knowledge, ForT/PrfE represents the first example of β-RFA-P (β-ribofuranosyl-aminobenzene 5’-phosphate) synthase-like enzymes governing C -nucleoside scaffold construction in natural product biosynthesis. These data establish a foundation for combinatorial biosynthesis of related purine nucleoside antibiotics, and also open the way for target-directed genome mining of PRF-A/FOR-A related antibiotics. IMPORTANCE Formycin A (FOR-A) and pyrazofurin A (PRF-A) are well known for their unusual chemical structures and remarkable biological activities. Actually, deciphering FOR-A/PRF-A biosynthesis will not only expand biochemical repertoire for novel enzymatic reactions, but also permit the target-oriented genome mining of FOR-A/PRF-A related C -nucleoside antibiotics.