Fungal P450 Deconstructs the 2,5-Diazabicyclo[2.2.2]octane Ring En Route to the Complete Biosynthesis of 21R-Citrinadin A

Prenylated indole alkaloids (PIAs)possess great structural diversityand show biological activities. Despite significant efforts in investigatingthe biosynthetic mechanism, the key step in the transformation of2,5-diazabicyclo[2.2.2]octane-containing PIAs into a distinct classof pentacyclic compounds remains unknown. Here, using a combinationof gene deletion, heterologous expression, and biochemical characterization,we show that a unique fungal P450 enzyme CtdY catalyzes the cleavageof the amide bond in the 2,5-diazabicyclo[2.2.2]octane system, followedby a decarboxylation step to form the 6/5/5/6/6 pentacyclic ring in21R-citrinadin A. We also demonstrate the functionof a subsequent cascade of stereospecific oxygenases to further modifythe 6/5/5/6/6 pentacyclic intermediate en route tothe complete 21R-citrinadin A biosynthesis. Our findingsreveal a key enzyme CtdY for the pathway divergence in the biosynthesisof PIAs and uncover the complex late-stage post-translational modificationsin 21R-citrinadin A biosynthesis.

Automated summary

Using gene deletion, heterologous expression, and biochemical characterization, researchers identified a unique fungal enzyme called CtdY that catalyzes the cleavage of the amide bond and formation of the 6/5/5/6/6 pentacyclic ring in the biosynthesis of PIAs. They also discovered a cascade of stereospecific oxygenases that further modify the pentacyclic intermediate in the production of 21R-citrinadin A. These findings provide insight into the key enzyme involved in the biosynthesis of PIAs and the complex post-translational modifications in the production of 21R-citrinadin A.