Dual Catalytic Activity of a Cytochrome P450 Controls Bifurcation at a Metabolic Branch Point of Alkaloid Biosynthesis in Rauwolfia serpentina

Abstract

Plants create tremendous chemical diversity from a single biosynthetic intermediate. In plant‐derived ajmalan alkaloid pathways, the biosynthetic intermediate vomilenine can be transformed into the anti‐arrhythmic compound ajmaline, or alternatively, can isomerize to form perakine, an alkaloid with a structurally distinct scaffold. Here we report the discovery and characterization of vinorine hydroxylase, a cytochrome P450 enzyme that hydroxylates vinorine to form vomilenine, which was found to exist as a mixture of rapidly interconverting epimers. Surprisingly, this cytochrome P450 also catalyzes the non‐oxidative isomerization of the ajmaline precursor vomilenine to perakine. This unusual dual catalytic activity of vinorine hydroxylase thereby provides a control mechanism for the bifurcation of these alkaloid pathway branches. This discovery highlights the unusual catalytic functionality that has evolved in plant pathways.

Harnessing the Chemistry of the Indole Heterocycle to Drive Discoveries in Biology and Medicine

“…Indole alkaloids are produced by plants using a series of unique biosynthetic pathways, leading to an impressive diversity of complex natural products . Many indole alkaloids are endowed with significant biological activities important to human health and the treatment of disease (Scheme ) . The indole alkaloids vincristine ( 88 ) and vinblastine ( 70 ) were discovered in Catharanthus roseus (Madagascar periwinkle) and have had a remarkable impact on cancer therapies over the past several decades .…”

“…With the significant therapeutic value of indole alkaloids and derived natural products (e.g., quinine 100 , camptothecin 102 ; quinoline‐derived alkaloids from strictosidine; Scheme ), extensive investigations regarding the biosynthetic pathways of these alkaloids has been an area of intense interest . Many details regarding the enzymes and chemical transformations involved in the biosynthesis of monoterpene indole alkaloids have been elucidated; however, additional information is needed to fully elucidate these pathways.…”

“…Many details regarding the enzymes and chemical transformations involved in the biosynthesis of monoterpene indole alkaloids have been elucidated; however, additional information is needed to fully elucidate these pathways. O'Connor and co‐workers have made significant contributions towards our understanding of monoterpenoid indole alkaloid biosynthesis . Currently, efforts are aimed at employing synthetic biology strategies to produce therapeutically valuable indole alkaloids (e.g., vincristine, ibogaine) to support therapeutic applications in human medicine.…”

“…Monoterpene indole alkaloids are biosynthesized from tryptophan and isopentenyl diphosphate (IPP, 92 ; precursor to all terpenoids) . Tryptophan ( 91 ) is decarboxylated by the pyridoxal dependent enzyme tryptophan decarboxylase (TD, Scheme ) to form tryptamine ( 49 ), while IPP undergoes an extensive series of biosynthetic transformations to the aldehyde‐containing intermediate secologanin ( 93 ) .…”

“…quinoline-derived alkaloidsf rom strictosidine;S cheme 9), extensivei nvestigations regarding the biosynthetic pathways of these alkaloids has been an area of intensei nterest. [4,6,[69][70][71][72][73]99] Many detailsr egarding the enzymes andc hemical transformations involved in the biosynthesis of monoterpene indole alkaloids have been elucidated;h owever,a dditional information is neededt of ully elucidate these pathways. O'Connor and coworkers have made significant contributions towards our understanding of monoterpenoid indole alkaloid biosynthe-sis.…”