Divergent camptothecin biosynthetic pathway in Ophiorrhiza pumila

Mengquan Yang,Guoyin Kai,Yuchen Liang,Can Wang,Jianbo Chen,Yining Liu,Youli Xiao,Xiaolong Hao,Qiang Wang

doi:10.1186/s12915-021-01051-y

Abstract

BackgroundThe anticancer drug camptothecin (CPT), first isolated from Camptotheca acuminata, was subsequently discovered in unrelated plants, including Ophiorrhiza pumila. Unlike known monoterpene indole alkaloids, CPT in C. acuminata is biosynthesized via the key intermediate strictosidinic acid, but how O. pumila synthesizes CPT has not been determined.ResultsIn this study, we used nontargeted metabolite profiling to show that 3α-(S)-strictosidine and 3-(S), 21-(S)-strictosidinic acid coexist in O. pumila. After identifying the enzymes OpLAMT, OpSLS, and OpSTR as participants in CPT biosynthesis, we compared these enzymes to their homologues from two other representative CPT-producing plants, C. acuminata and Nothapodytes nimmoniana, to elucidate their phylogenetic relationship. Finally, using labelled intermediates to resolve the CPT biosynthesis pathway in O. pumila, we showed that 3α-(S)-strictosidine, not 3-(S), 21-(S)-strictosidinic acid, is the exclusive intermediate in CPT biosynthesis.ConclusionsIn our study, we found that O. pumila, another representative CPT-producing plant, exhibits metabolite diversity in its central intermediates consisting of both 3-(S), 21-(S)-strictosidinic acid and 3α-(S)-strictosidine and utilizes 3α-(S)-strictosidine as the exclusive intermediate in the CPT biosynthetic pathway, which differs from C. acuminata. Our results show that enzymes likely to be involved in CPT biosynthesis in O. pumila, C. acuminata, and N. nimmoniana have evolved divergently. Overall, our new data regarding CPT biosynthesis in O. pumila suggest evolutionary divergence in CPT-producing plants. These results shed new light on CPT biosynthesis and pave the way towards its industrial production through enzymatic or metabolic engineering approaches.

Highlights

The anticancer drug camptothecin (CPT), first isolated from Camptotheca acuminata, was subsequently discovered in unrelated plants, including Ophiorrhiza pumila
Two parallel pathways of CPT biosynthesis were proposed by metabolite profiling of intermediates in O. pumila The distribution of the bioactive compound CPT varies across O. pumila tissues [23]
We annotated 15 metabolites in the CPT biosynthetic pathway based on accurate mass measurements of positive ions and fragments observed in mass spectrometry (MS) and MS/MS mass spectra (Fig. 2a and Additional file 1: Table S1) and confirmed them against the metabolite profiles detected in C. acuminata [15]

Summary

Introduction

The anticancer drug camptothecin (CPT), first isolated from Camptotheca acuminata, was subsequently discovered in unrelated plants, including Ophiorrhiza pumila. Unlike known monoterpene indole alkaloids, CPT in C. acuminata is biosynthesized via the key intermediate strictosidinic acid, but how O. pumila synthesizes CPT has not been determined. The alkaloid camptothecin (CPT) was first isolated in 1966 from the bark of the tree Camptotheca acuminata (“Xi-Shu” in Chinese, which translates to happy tree). C. acuminata, Nothapodytes nimmoniana, and Ophiorrhiza pumila are the three main representative CPT-producing plants (Fig. 1a). In 1994, the US Food and Drug Administration (FDA) approved the therapeutic use of two well-known antitumour CPT derivatives, irinotecan and topotecan, which inhibit the replication, growth, and reproduction of cancer cells by inhibiting DNA topoisomerase I [3]. The clinical applications of these two CPT-derived drugs to the treatment of cancer have greatly increased demand, raising issues about the sustainable production of CPT

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