Insights into the generation of structural diversity in a tRNA-dependent pathway for highly modified bioactive cyclic dipeptides.

The nocazines are a newly defined family of antibacterial and cytotoxic cyclic dipeptides produced by different actinobacterial species. Here, we identify a nocazine biosynthetic gene cluster in Nocardiopsis dassonvillei and describe the elucidation of the biosynthetic pathway leading to the nocazine family members nocazine E and XR334. Diketopiperazine (DKP) formation is carried out by a tRNA-dependent cyclodipeptide synthase (CDPS) showing an unknown product profile, while tailoring of the DKP-scaffold is achieved through the combined and combinatorial action of a cyclodipeptide oxidase and two distinct SAM-dependent O-/N-methyltransferases. Our results help to illuminate the biosynthetic logic resulting in the structural diversity of the nocazine family and set the stage for exploring the biological function of modified cyclic dipeptides as possible mediators of host-pathogen and host-parasite interactions.