Molecular Basis of the Unusual Seven-Membered Methylenedioxy Bridge Formation Catalyzed by Fe(II)/α-KG-Dependent Oxygenase CTB9
Xuanzhong Liu, Zhenbo Yuan, Hao Su, Xiaodong Hou, Zhiwei Deng, Huibin Xu, Baodang Guo, Dejing Yin, Xiang Sheng, Yijian Rao
Abstract
Methylenedioxy bridges (MDBs) are architecturally important motifs in natural products and bioactive molecules. Cercosporin, a typical perylenequinone pigment, contains an unusual seven-membered MDB, which has versatile biological and photocatalytic activities. Although cercosporin has been isolated, characterized, and studied for several decades, its biosynthetic pathway, especially the formation of the seven-membered MDB, has remained unclear. Here, we show that the formation of the seven-membered MDB is catalyzed by Fe(II)/α-ketoglutaric acid (α-KG)-dependent dioxygenase CTB9 in cercosporin biosynthesis. Moreover, crystal structures of CTB9 in complex with an α-KG analogue NOG (CTB9·Cu·NOG) and its substrate pre-cercosporin with NOG (CTB9·Cu·NOG·pre-cercosporin) were determined. These structures, together with site-directed mutagenesis studies and quantum mechanics calculations, help define the mechanism of the unique seven-membered MDB in cercosporin biosynthesis. In summary, these results provide molecular insights into other biosynthetic pathways of natural products containing MDBs.