Regiospecific hydroxylase and O-methyltransferase for the biosynthesis of anticancer alkaloids in Tabernaemontana elegans (toad tree)

Abstract

Monoterpenoid indole alkaloids (MIAs) are a structurally diverse class natural products with significant medicinal properties. Bis-MIAs, such as chemotherapeutic vinblastine and anti-autophagic conodurine, are synthesized through enzymatic coupling of monomeric MIAs, often requiring specific modifications to activate reactive centers. In this study, we report the identification and characterization of a regiospecific enzyme pair, coronaridine 11-hydroxylase (TeC11H) and 11-hydroxycoronaridine O-methyltransferase (TeHCOMT), from Tabernaemontana elegans (toad tree). The C11-methoxylation of coronaridine activates C10 and C12 on the indole for subsequent coupling with a vobasinyl monomer, representing a critical transformation in the biosynthesis of a series of 11-methoxycoronaridine derived bis-iboga-vobasinyl MIAs in T. elegans root with potent anticancer and anti-autophagy activities. Biochemical analysis and homology modeling of TeC11H and TeHCOMT, along with their Tabernanthe iboga (iboga) homologs for coronaridine C10-methoxylation, reveal key residues at their highly similar active sites responsible for distinct regioselectivity, demonstrating how coronaridine is oriented to favour C11 or C10 methoxylation. Our discovery sheds light on the coordinated specification of active sites in metabolically linked enzymes during evolutionary adaptation in different lineages. TeC11H and TeHCOMT represent a valuable tool for metabolic engineering, offering new opportunities to biosynthesize anticancer alkaloids and explore the therapeutic potential of novel bis-MIAs.