Isolation and Characterization of Reticuline N-Methyltransferase Involved in Biosynthesis of the Aporphine Alkaloid Magnoflorine in Opium Poppy
Bibliographic record
Abstract
Benzylisoquinoline alkaloids are a large group of plant-specialized metabolites displaying an array of biological and pharmacological properties associated with numerous structural scaffolds and diverse functional group modification. N-Methylation is one of the most common tailoring reactions, yielding tertiary and quaternary pathway intermediates and products. Two N-methyltransferases accepting (i) early 1-benzylisoquinoline intermediates possessing a secondary amine and leading to the key branch-point intermediate (S)-reticuline and (ii) downstream protoberberines containing a tertiary amine and forming quaternary intermediates destined for phthalideisoquinolines and antimicrobial benzo[c]phenanthridines were previously characterized. We report the isolation and characterization of a phylogenetically related yet functionally distinct N-methyltransferase (NMT) from opium poppy (Papaver somniferum) that primarily accepts 1-benzylisoquinoline and aporphine substrates possessing a tertiary amine. The preferred substrates were the R and S conformers of reticuline and the aporphine (S)-corytuberine, which are proposed intermediates in the biosynthesis of magnoflorine, a quaternary aporphine alkaloid common in plants. Suppression of the gene encoding reticuline N-methyltransferase (RNMT) using virus-induced gene silencing in opium poppy resulted in a significant decrease in magnoflorine accumulation and a concomitant increase in corytuberine levels in roots. RNMT transcript levels were also most abundant in roots, in contrast to the distribution of transcripts encoding other NMTs, which occur predominantly in aerial plant organs. The characterization of a third functionally unique NMT involved in benzylisoquinoline alkaloid metabolism will facilitate the establishment of structure-function relationships among a large group of related enzymes. Benzylisoquinoline alkaloids are a large group of plant-specialized metabolites displaying an array of biological and pharmacological properties associated with numerous structural scaffolds and diverse functional group modification. N-Methylation is one of the most common tailoring reactions, yielding tertiary and quaternary pathway intermediates and products. Two N-methyltransferases accepting (i) early 1-benzylisoquinoline intermediates possessing a secondary amine and leading to the key branch-point intermediate (S)-reticuline and (ii) downstream protoberberines containing a tertiary amine and forming quaternary intermediates destined for phthalideisoquinolines and antimicrobial benzo[c]phenanthridines were previously characterized. We report the isolation and characterization of a phylogenetically related yet functionally distinct N-methyltransferase (NMT) from opium poppy (Papaver somniferum) that primarily accepts 1-benzylisoquinoline and aporphine substrates possessing a tertiary amine. The preferred substrates were the R and S conformers of reticuline and the aporphine (S)-corytuberine, which are proposed intermediates in the biosynthesis of magnoflorine, a quaternary aporphine alkaloid common in plants. Suppression of the gene encoding reticuline N-methyltransferase (RNMT) using virus-induced gene silencing in opium poppy resulted in a significant decrease in magnoflorine accumulation and a concomitant increase in corytuberine levels in roots. RNMT transcript levels were also most abundant in roots, in contrast to the distribution of transcripts encoding other NMTs, which occur predominantly in aerial plant organs. The characterization of a third functionally unique NMT involved in benzylisoquinoline alkaloid metabolism will facilitate the establishment of structure-function relationships among a large group of related enzymes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".