TY - JOUR

T1 - Post-Cyclization Skeletal Rearrangements in Plant Triterpenoid Biosynthesis by a Pair of Branchpoint Isomerases

AU - Chuang, Ling

AU - Liu, Shenyu

AU - Franke, Jakob

N1 - Funding Information: The authors thank Prof. Dr. David Nelson (Department of Molecular Science, University of Tennessee, Memphis, USA) and the P450 nomenclature committee for naming AaCYP88A154, Yvonne Leye and Miriam Fent for excellent horticultural support, Katja Körner for excellent technical support, and Johanna Wolf and Yue Sun for assistance with the transient expression screening. The authors thank Prof. Dr. Christian Hertweck (Leibniz Institute for Natural Product Research and Infection Biology, HKI, Jena, Germany) and Prof. Dr. Sarah O’Connor (Max Planck Institute for Chemical Ecology, Jena, Germany) for helpful discussions. The authors gratefully acknowledge financial support by the Fonds der Chemischen Industrie, the Emmy Noether program of the Deutsche Forschungsgemeinschaft (FR 3720/3-1), and the SMART BIOTECS alliance between the Technische Universität Braunschweig and the Leibniz Universität Hannover, supported by the Ministry of Science and Culture (MWK) of Lower Saxony. The authors also thank the DFG for the provision of NMR equipment (INST 187/686-1). In addition, this work was supported by the LUH compute cluster, which is funded by the Leibniz Universität Hannover, the Lower Saxony Ministry of Science and Culture (MWK), and the German Research Association (DFG).

PY - 2023/3/8

Y1 - 2023/3/8

N2 - Triterpenoids possess potent biological activities, but their polycyclic skeletons are challenging to synthesize. The skeletal diversity of triterpenoids in plants is generated by oxidosqualene cyclases based on epoxide-triggered cationic rearrangement cascades. Normally, triterpenoid skeletons then remain unaltered during subsequent tailoring steps. In contrast, the highly modified triterpenoids found in Sapindales plants imply the existence of post-cyclization skeletal rearrangement enzymes that have not yet been found. We report here a biosynthetic pathway in Sapindales plants for the modification of already cyclized tirucallane triterpenoids, controlling the pathway bifurcation between different plant triterpenoid classes. Using a combination of bioinformatics, heterologous expression in plants and chemical analyses, we identified a cytochrome P450 monooxygenase and two isomerases which harness the epoxidation-rearrangement biosynthetic logic of triterpene cyclizations for modifying the tirucallane scaffold. The two isomerases share the same epoxide substrate made by the cytochrome P450 monooxygenase CYP88A154, but generate two different rearrangement products, one containing a cyclopropane ring. Our findings reveal a process for skeletal rearrangements of triterpenoids in nature that expands their scaffold diversity after the initial cyclization. In addition, the enzymes described here are crucial for the biotechnological production of limonoid, quassinoid, apoprotolimonoid, and glabretane triterpenoids.

AB - Triterpenoids possess potent biological activities, but their polycyclic skeletons are challenging to synthesize. The skeletal diversity of triterpenoids in plants is generated by oxidosqualene cyclases based on epoxide-triggered cationic rearrangement cascades. Normally, triterpenoid skeletons then remain unaltered during subsequent tailoring steps. In contrast, the highly modified triterpenoids found in Sapindales plants imply the existence of post-cyclization skeletal rearrangement enzymes that have not yet been found. We report here a biosynthetic pathway in Sapindales plants for the modification of already cyclized tirucallane triterpenoids, controlling the pathway bifurcation between different plant triterpenoid classes. Using a combination of bioinformatics, heterologous expression in plants and chemical analyses, we identified a cytochrome P450 monooxygenase and two isomerases which harness the epoxidation-rearrangement biosynthetic logic of triterpene cyclizations for modifying the tirucallane scaffold. The two isomerases share the same epoxide substrate made by the cytochrome P450 monooxygenase CYP88A154, but generate two different rearrangement products, one containing a cyclopropane ring. Our findings reveal a process for skeletal rearrangements of triterpenoids in nature that expands their scaffold diversity after the initial cyclization. In addition, the enzymes described here are crucial for the biotechnological production of limonoid, quassinoid, apoprotolimonoid, and glabretane triterpenoids.

UR - http://www.scopus.com/inward/record.url?scp=85148944854&partnerID=8YFLogxK

U2 - 10.1021/jacs.2c10838

DO - 10.1021/jacs.2c10838

M3 - Article

C2 - 36821810

AN - SCOPUS:85148944854

VL - 145

SP - 5083

EP - 5091

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 9

ER -