Enzymatic dehydrogenation and flavin-mediated photocatalytic skeletal rearrangement of strictosamide, a key intermediate in camptothecin biosynthesis.

Camptothecin is a valuable monoterpene indole alkaloid (MIA) with antitumor activity, and strictosamide represents the first specialized intermediate in camptothecin biosynthesis. The proposed camptothecin biosynthetic pathway involves several oxidation-reduction reactions, while there have been no reports on the involvement of 2-oxoglutarate-dependent dioxygenases (2OGDs) in Ophiorrhiza pumila. In this study, the genome-wide identification of 2OGDs was performed in O. pumila, and a total of 140 2OGD genes were identified. Functional characterization revealed that five Op2OGDs catalyze the dehydrogenation of the C-3 and C-14 positions of strictosamide to produce dehydrostrictosamide. Unexpectedly, strictosamide was found to undergo a rapid flavin-mediated photocatalytic skeletal rearrangement to form pumiloside. According to the chromosomal localization of functional Op2OGD genes and camptothecin biosynthetic genes, we identified an MIA gene cluster on chromosome 5 of O. pumila, including two 2OGDs identified in this study and four previously characterized genes. These findings support that camptothecin biosynthesis in O. pumila proceeds through a biosynthetic network rather than a linear pathway. This study provides important insights into the elucidation of the camptothecin biosynthetic pathway.