Biosynthesis of an Anti-Addiction Agent from the Iboga Plant

Farrow, Scott C.; Kamileen, Mohamed O.; Caputi, Lorenzo; Bussey, K.; Mundy, Julia E. A.; McAtee, Rory C.; Stephenson, Corey R. J.; O’Connor, Sarah E.

doi:10.1021/jacs.9b05999

Cited by 46 publications

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“…2 . Cloning of DPAS and CorS from Tabernanthe iboga was reported in Farrow et al 6 . CS, TS and CorS mutants were generated by overlap extension PCR.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, we identified a reductase (DPAS) and cyclase (CorS) pair (from the plant Tabernanthe iboga ) that react with precondylocarpine acetate to form the iboga alkaloid (–)-coronaridine ( 6 ), which is similar in structure to (+)-catharanthine, but has the opposite configuration as well as a reduced oxidation state ( Fig. 1 ) 6 . These three cyclases have high amino acid identity ( Supplementary Fig.…”

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confidence: 99%

“…Angryline ( 3c ) was incubated with CS or TS to yield (+)-catharanthine ( 4 ) or (–)-tabersonine ( 5 ), respectively ( Supplementary Figs. 7-8 ) and with CorS and DPAS ( T. iboga ) to yield (–)-coronaridine ( 6 ) 6 . The isolation of angryline suggests that desacetoxylation of dihydroprecondylocarpine acetate ( 2 ) to form dehydrosecodine ( 3a ) occurs either in solution, through a Grob-type fragmentation 9 , or in the active site of DPAS, and that the sole function of CS, TS and CorS is to catalyse cyclization.…”

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confidence: 99%

“…CorS reacts with angryline to form an unstable product that is reduced by DPAS to form (–)-coronaridine ( 6 ) 6 . We hypothesize that CorS converts angryline ( 3c ) to (–)-coronaridine iminium ( 9 ) through an aza-Diels-Alder reaction or a stepwise mechanism 14 ( Supplementary Fig.…”

mentioning

confidence: 99%

“…15d ), although this proposed iminium is too unstable to isolate. Furthermore, while (+)-catharanthine ( 4 ) and (–)-tabersonine ( 5 ) appear to form directly from dehydrosecodine enamine ( 3b ), reaction in D 2 O suggests that the formation of (–)-coronaridine ( 6 ) requires tautomerization of the dihydropyridine moiety of 3b to form 3d and 3e 6 ( Supplementary Fig. 15d ).…”

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confidence: 99%

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Structural basis of cycloaddition in biosynthesis of iboga and aspidosperma alkaloids

et al. 2020

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Cycloaddition reactions generate chemical complexity in a single step. Here we report the crystal structures of three homologous plant-derived cyclases involved in the biosynthesis of iboga and aspidosperma alkaloids. These enzymes act on the same substrate, named angryline, to generate three distinct scaffolds. Mutational analysis reveals how these highly similar enzymes control regio- and stereo-selectivity.

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“…2 . Cloning of DPAS and CorS from Tabernanthe iboga was reported in Farrow et al 6 . CS, TS and CorS mutants were generated by overlap extension PCR.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Structural basis of cycloaddition in biosynthesis of iboga and aspidosperma alkaloids

et al. 2020

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Expansion of the Catalytic Repertoire of Alcohol Dehydrogenases in Plant Metabolism**

et al. 2022

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Medium‐chain alcohol dehydrogenases (ADHs) comprise a highly conserved enzyme family that catalyse the reversible reduction of aldehydes. However, recent discoveries in plant natural product biosynthesis suggest that the catalytic repertoire of ADHs has been expanded. Here we report the crystal structure of dihydroprecondylocarpine acetate synthase (DPAS), an ADH that catalyses the non‐canonical 1,4‐reduction of an α,β‐unsaturated iminium moiety. Comparison with structures of plant‐derived ADHs suggest the 1,4‐iminium reduction does not require a proton relay or the presence of a catalytic zinc ion in contrast to canonical 1,2‐aldehyde reducing ADHs that require the catalytic zinc and a proton relay. Furthermore, ADHs that catalysed 1,2‐iminium reduction required the presence of the catalytic zinc and the loss of the proton relay. This suggests how the ADH active site can be modified to perform atypical carbonyl reductions, providing insight into how chemical reactions are diversified in plant metabolism.

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Expansion of the Catalytic Repertoire of Alcohol Dehydrogenases in Plant Metabolism**

et al. 2022

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Medium-chain alcohol dehydrogenases (ADHs) comprise a highly conserved enzyme family that catalyse the reversible reduction of aldehydes. However, recent discoveries in plant natural product biosynthesis suggest that the catalytic repertoire of ADHs has been expanded. Here we report the crystal structure of dihydroprecondylocarpine acetate synthase (DPAS), an ADH that catalyses the non-canonical 1,4reduction of an α,β-unsaturated iminium moiety. Comparison with structures of plant-derived ADHs suggest the 1,4-iminium reduction does not require a proton relay or the presence of a catalytic zinc ion in contrast to canonical 1,2-aldehyde reducing ADHs that require the catalytic zinc and a proton relay. Furthermore, ADHs that catalysed 1,2-iminium reduction required the presence of the catalytic zinc and the loss of the proton relay. This suggests how the ADH active site can be modified to perform atypical carbonyl reductions, providing insight into how chemical reactions are diversified in plant metabolism.Alcohol dehydrogenases (ADHs EC 1.1.1.1) are NAD-(P)H-dependent medium-chain oxidoreductases found in all kingdoms of life. These enzymes typically catalyse the reversible reduction of aldehydes or ketones to the corresponding alcohol (Figure 1A). [1][2][3][4] The structural motifs of ADHs are highly conserved in all known eukaryotic examples; most notably, a zinc ion involved in catalysis, a second zinc ion involved in maintaining protein structure, and the Rossmann peptide-fold involved in cofactor binding (Figures S1). ADHs have been shown to catalyse many complex biochemical transformations in plant natural product biosynthesis, suggesting that their catalytic repertoire has been expanded. For example, we recently reported the discovery of dihydroprecondylocarpine acetate synthase (DPAS), an ADH involved in vinblastine biosynthesis in the plant Catharanthus roseus [5] and in ibogaine biosynthesis in the phylogenetically related species Tabernanthe iboga. [6] Since the product of DPAS is unstable and either immediately decomposes or rearranges in the presence of a downstream cyclase enzyme, the reaction remained unsubstantiated (Figure 1B). However, the cyclised products suggest that DPAS catalyses the 1,4-reduction of an α,β-unsaturated iminium which is an hitherto unprecedented reaction for an ADH. Here, we use isotopic labelling to definitively establish that DPAS catalyses this unusual 1,4-reduction. We report four crystal structures of apo-and substratebound DPAS from two phylogenetically related species. These structures reveal, surprisingly, the loss of the catalytic zinc ion from the DPAS active site, indicating that zinc is not strictly required for reduction by ADHs. We also report the structure of the ADH geissoschizine synthase (GS) that catalyses an atypical 1,2-iminium reduction. Comparison of the active site of DPAS and GS with other highly similar ADHs that catalyse either 1,2-aldehyde reduction or 1,2reduction of an iminium moiety suggests that changes in the proton relay system are also implic...

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Biosynthesis of an Anti-Addiction Agent from the Iboga Plant

Cited by 46 publications

References 17 publications

Structural basis of cycloaddition in biosynthesis of iboga and aspidosperma alkaloids

Structural basis of cycloaddition in biosynthesis of iboga and aspidosperma alkaloids

Expansion of the Catalytic Repertoire of Alcohol Dehydrogenases in Plant Metabolism**

Expansion of the Catalytic Repertoire of Alcohol Dehydrogenases in Plant Metabolism**

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