Insights into stereoselective ring formation in canonical strigolactone: Identification of a dirigent domaincontaining enzyme catalyzing orobanchol synthesis

• 成果类型: Article
• 署名作者: Homma, Masato; Wakabayashi, Takatoshi; Moriwaki, Yoshitaka; Shiotani, Nanami; Shigeta, Takumi; Isobe, Kazuki; Okazawa, Atsushi; Ohta, Daisaku; Terada, Tohru; Shimizu, Kentaro; Mizutani, Masaharu; Takikawa, Hirosato; Sugimoto, Yukihiro
• 署名单位: Kobe University; University of Tokyo; University of Tokyo; University of Tokyo; Osaka Metropolitan University; Osaka Metropolitan University; Institute of Science Tokyo; Tokyo Medical & Dental University (TMDU)
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-14907
• DOI: 10.1073/pnas.2313683121
• 发表日期: 2024-06-25
• 关键词: evolutionary conservation; proteins; biosynthesis; carlactone; inhibition; witchweed; max1

摘要

Strigolactones (SLs) are plant apocarotenoids with diverse roles and structures. Canonical SLs, widespread and characterized by structural variations in their tricyclic lactone (ABC- ring), are classified into two types based on C- ring configurations. The steric C- ring configuration emerges during the BC- ring closure, downstream of the biosynthetic intermediate, carlactonoic acid (CLA). Most plants produce either type of canonical SLs stereoselectively, e.g., tomato (Solanum lycopersicum) yields orobanchol with an alpha- oriented C- ring. The mechanisms driving SL structural diversification are partially understood, with limited insight into functional implications. Furthermore, the exact molecular mechanism for the stereoselective BC- ring closure reaction is yet to be known. We identified an enzyme, the stereoselective BC- ring- forming factor (SRF), from the dirigent protein (DIR) family, specifically the DIR- f subfamily, whose biochemical function had not been characterized, making it a key enzyme in stereoselective canonical SL biosynthesis with the alpha- oriented C- ring. We first confirm the precise catalytic function of the tomato cytochrome P450 SlCYP722C, previously shown to be involved convert CLA to 18- oxocarlactonoic acid. We then show that SRF catalyzes the stereoselective BC- ring closure reaction of 18- oxocarlactonoic acid, forming orobanchol. Our methodology combines experimental and computational techniques, including SRF structure prediction and conducting molecular dynamics simulations, suggesting a catalytic mechanism based on the conrotatory 4 pi- electrocyclic reaction for the stereoselective BC- ring formation in orobanchol. This study sheds light on the molecular basis of how plants produce SLs with specific stereochemistry in a controlled manner.