Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L

• Published in: Proceedings of the National Academy of Sciences - PNAS 2016-08, Vol.113 (34), p.E5082-E5089
• Main Authors: Luo, Dan, Callari, Roberta, Hamberger, Britta, Wubshet, Sileshi Gizachew, Nielsen, Morten T., Andersen-Ranberg, Johan, Hallström, Björn M., Cozzi, Federico, Heider, Harald, Møller, Birger Lindberg, Staerk, Dan, Hamberger, Björn
• Format: Article
• Language: English
• Subjects: Alcohol Dehydrogenase - genetics; Alcohol Dehydrogenase - metabolism; Antineoplastic Agents, Phytogenic - biosynthesis; Antineoplastic Agents, Phytogenic - chemistry; BASIC BIOLOGICAL SCIENCES; Biological Sciences; Biosynthesis; Cloning, Molecular; Cyclization; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Diterpenes - chemistry; Diterpenes - metabolism; Enzymes; Euphorbia - chemistry; Euphorbia - genetics; Euphorbia - metabolism; Flowers & plants; Gene Expression; Gene Expression Profiling; Isoenzymes - genetics; Isoenzymes - metabolism; Nicotiana - genetics; Nicotiana - metabolism; nonconventional cyclization; Oxidation; Oxidation-Reduction; Phenylpropionates - chemistry; Phenylpropionates - metabolism; Plant Oils - chemistry; Plant Oils - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; PNAS Plus; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; regio-specific oxidation; Seeds; Seeds - chemistry; Seeds - genetics; Seeds - metabolism; terpenoid biosynthesis; Transcriptome; transcriptomic analysis
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1607504113

The seed oil of Euphorbia lathyris L. contains a series of macrocyclic diterpenoids known as Euphorbia factors. They are the current industrial source of ingenol mebutate, which is approved for the treatment of actinic keratosis, a precancerous skin condition. Here, we report an alcohol dehydrogenase-mediated cyclization step in the biosynthetic pathway of Euphorbia factors, illustrating the origin of the intramolecular carbon–carbon bonds present in lathyrane and ingenane diterpenoids. This unconventional cyclization describes the ring closure of the macrocyclic diterpene casbene. Through transcriptomic analysis of E. lathyris L. mature seeds and in planta functional characterization, we identified three enzymes involved in the cyclization route from casbene to jolkinol C, a lathyrane diterpene. These enzymes include two cytochromes P450 from the CYP71 clan and an alcohol dehydrogenase (ADH). CYP71D445 and CYP726A27 catalyze regio-specific 9-oxidation and 5-oxidation of casbene, respectively. When coupled with these P450-catalyzed monooxygenations, E. lathyris ADH1 catalyzes dehydrogenation of the hydroxyl groups, leading to the subsequent rearrangement and cyclization. The discovery of this nonconventional cyclization may provide the key link to complete elucidation of the biosynthetic pathways of ingenol mebutate and other bioactive macrocyclic diterpenoids.