Biosynthesis of the highly oxygenated tetracyclic core skeleton of Taxol

Taxol is a widely-applied anticancer drug that inhibits microtubule dynamics in actively replicating cells. Although a minimum 19-step biosynthetic pathway has been proposed and 16 enzymes likely involved have been characterized, stepwise biosynthetic reactions from the well-characterized di-oxygenated taxoids to Taxol tetracyclic core skeleton are yet to be elucidated. Here, we uncover the biosynthetic pathways for a few tri-oxygenated taxoids via confirming the critical reaction order of the second and third hydroxylation steps, unearth a taxoid 9 alpha-hydroxylase catalyzing the fourth hydroxylation, and identify CYP725A55 catalyzing the oxetane ester formation via a cascade oxidation-concerted acyl rearrangement mechanism. After identifying a acetyltransferase catalyzing the formation of C7-OAc, the pathway producing the highly-oxygenated 1 beta-dehydroxybaccatin VI with the Taxol tetracyclic core skeleton is elucidated and its complete biosynthesis from taxa-4(20),11(12)-diene-5 alpha-ol is achieved in an engineered yeast. These systematic studies lay the foundation for the complete elucidation of the biosynthetic pathway of Taxol. Despite intensive investigation, stepwise reactions from diol to Taxol tetracyclic core skeleton remain unclear. Here, authors fill this gap by identifying two P450s and confirming the reaction order.