title: Stereochemical inversion of (S)-reticuline by a cytochrome P450 fusion in opium poppy.
abstract: The gateway to morphine biosynthesis in opium poppy (Papaver somniferum) is the stereochemical inversion of (S)-reticuline since the enzyme yielding the first committed intermediate salutaridine is specific for (R)-reticuline. A fusion between a cytochrome P450 (CYP) and an aldo-keto reductase (AKR) catalyzes the S-to-R epimerization of reticuline via 1,2-dehydroreticuline. The reticuline epimerase (REPI) fusion was detected in opium poppy and in Papaver bracteatum, which accumulates thebaine. In contrast, orthologs encoding independent CYP and AKR enzymes catalyzing the respective synthesis and reduction of 1,2-dehydroreticuline were isolated from Papaver rhoeas, which does not accumulate morphinan alkaloids. An ancestral relationship between these enzymes is supported by a conservation of introns in the gene fusions and independent orthologs. Suppression of REPI transcripts using virus-induced gene silencing in opium poppy reduced levels of (R)-reticuline and morphinan alkaloids and increased the overall abundance of (S)-reticuline and its O-methylated derivatives. Discovery of REPI completes the isolation of genes responsible for known steps of morphine biosynthesis.
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Farrow
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Jillian M
authors.initials: JM
authors.lastname: Hagel
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Guillaume A W
authors.initials: GA
authors.lastname: Beaudoin
authors.affiliation: Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Darcy C
authors.initials: DC
authors.lastname: Burns
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Peter J
authors.identifier: 000000027693290X
authors.initials: PJ
authors.lastname: Facchini
mesh_terms: D000449:Aldehyde Reductase / Q000235:genetics / Q000378:metabolism*; D000074408:Aldo-Keto Reductases; D000470:Alkaloids / Q000096:biosynthesis / Q000737:chemistry; D001483:Base Sequence; D044182:Benzylisoquinolines / Q000737:chemistry / Q000378:metabolism; D019177:Bromoviridae / Q000235:genetics / Q000378:metabolism; D002238:Carbohydrate Epimerases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005091:Exons; D018506:Gene Expression Regulation, Plant; D050939:Gene Fusion; D007438:Introns; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009019:Morphinans / Q000737:chemistry / Q000378:metabolism; D009020:Morphine / Q000096:biosynthesis* / Q000737:chemistry; D016366:Open Reading Frames; D009892:Opium / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010207:Papaver / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids; D044182:Benzylisoquinolines; D009019:Morphinans; D010940:Plant Proteins; D011994:Recombinant Proteins; D009020:Morphine; C009270:salutaridine; D009892:Opium; D003577:Cytochrome P-450 Enzyme System; D000074408:Aldo-Keto Reductases; D000449:Aldehyde Reductase; D002238:Carbohydrate Epimerases; D008025:Ligases; C003298:reticuline