Unraveling tropane alkaloid biosynthesis in Erythroxylum coca

Abstract

Tropane alkaloids (TAs) are heterocyclic nitrogenous metabolites found across seven orders of angiosperms, including Malpighiales (Erythroxylaceae) and Solanales (Solanaceae). Despite cocaine being an infamous TA, the biosynthetic pathway has remained incomplete for decades. This work characterized a polyamine synthase along with amine oxidase-like enzymes in vitro, in yeast, and in planta, revealing that the first ring closure of TAs in E. coca occurs via bifunctional spermidine synthase/N-methyltransferases and both flavin- and copper-dependent amine oxidases. Identification of a SABATH family methyltransferase is responsible for the 2-carbomethoxy moiety characteristic of TAs from the Erythroxylaceae family. These results demonstrate that TA biosynthesis in Erythroxylaceae and Solanaceae is polyphyletic in origin, further revealing that independent recruitment of unique biosynthetic mechanisms and enzyme classes occurred at nearly every step in the evolution of this pathway.