Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Ziegler, J.; Voigtländer, S.; Schmidt, J.; Kramell, R.; Miersch, O.; Ammer, C.; Gesell, A.; Kutchan, T. M.;Comparative transcript and alkaloid profiling in Papaver species identifies a short chain dehydrogenase/reductase involved in morphine biosynthesisPlant J.48177-192(2006)DOI: 10.1111/j.1365-313X.2006.02860.x
Plants of the order Ranunculales, especially members of the species Papaver , accumulate a large variety of benzylisoquinoline alkaloids with about 2500 structures, but only the opium poppy (Papaver somniferum ) and Papaver setigerum are able to produce the analgesic and narcotic morphine and the antitussive codeine. In this study, we investigated the molecular basis for this exceptional biosynthetic capability by comparison of alkaloid profiles with gene expression profiles between 16 different Papaver species. Out of 2000 expressed sequence tags obtained from P. somniferum , 69 show increased expression in morphinan alkaloid‐containing species. One of these cDNAs, exhibiting an expression pattern very similar to previously isolated cDNAs coding for enzymes in benzylisoquinoline biosynthesis, showed the highest amino acid identity to reductases in menthol biosynthesis. After overexpression, the protein encoded by this cDNA reduced the keto group of salutaridine yielding salutaridinol, an intermediate in morphine biosynthesis. The stereoisomer 7‐epi ‐salutaridinol was not formed. Based on its similarities to a previously purified protein from P. somniferum with respect to the high substrate specificity, molecular mass and kinetic data, the recombinant protein was identified as salutaridine reductase (SalR; EC 1.1.1.248). Unlike codeinone reductase, an enzyme acting later in the pathway that catalyses the reduction of a keto group and which belongs to the family of the aldo‐keto reductases, the cDNA identified in this study as SalR belongs to the family of short chain dehydrogenases/reductases and is related to reductases in monoterpene metabolism.
Publikation
Ounaroon, A.; Decker, G.; Schmidt, J.; Lottspeich, F.; Kutchan, T. M.;(R,S)-Reticuline 7-O-methyltransferase and (R,S)-norcoclaurine 6-O-methyltransferase of Papaver somniferum-cDNA cloning and characterization of methyl transfer enzymes of alkaloid biosynthesis in opium poppyPlant J.36808-819(2003)DOI: 10.1046/j.1365-313X.2003.01928.x
S‐Adenosyl‐l ‐methionine:(R,S )‐reticuline 7‐O‐methyltransferase converts reticuline to laudanine in tetrahydrobenzylisoquinoline biosynthesis in the opium poppy Papaver somniferum . This enzyme activity has not yet been detected in plants. A proteomic analysis of P. somniferum latex identified a gel spot that contained a protein(s) whose partial amino acid sequences were homologous to those of plant O‐methyltransferases. cDNA was amplified from P. somniferum RNA by reverse transcription PCR using primers based on these internal amino acid sequences. Recombinant protein was then expressed in Spodoptera frugiperda Sf9 cells in a baculovirus expression vector. Steady‐state kinetic measurements with one heterologously expressed enzyme and mass spectrometric analysis of the enzymatic products suggested that this unusual enzyme is capable of carrying through sequential O‐methylations on the isoquinoline and on the benzyl moiety of several substrates. The tetrahydrobenzylisoquinolines (R )‐reticuline (4.2 sec−1 mm −1), (S )‐reticuline (4.5 sec−1 mm −1), (R )‐protosinomenine (1.7 sec−1 mm −1), and (R,S )‐isoorientaline (1.4 sec−1 mm −1) as well as guaiacol (5.9 sec−1 mm −1) and isovanillic acid (1.2 sec−1 mm −1) are O‐methylated by the enzyme with the ratio k cat/K m shown in parentheses. A P. somniferum cDNA encoding (R,S )‐norcoclaurine 6‐O‐methyltransferase was similarly isolated and characterized. This enzyme was less permissive, methylating only (R,S )‐norcoclaurine (7.4 sec−1 mm −1), (R )‐norprotosinomenine (4.1 sec−1 mm −1), (S )‐norprotosinomenine (4.0 sec−1 mm −1) and (R,S )‐isoorientaline (1.0 sec−1 mm −1). A phylogenetic comparison of the amino acid sequences of these O‐methyltransferases to those from 28 other plant species suggests that these enzymes group more closely to isoquinoline biosynthetic O‐methyltransferases from Coptis japonica than to those from Thalictrum tuberosum that can O‐methylate both alkaloid and phenylpropanoid substrates.
Publikation
Unterlinner, B.; Lenz, R.; Kutchan, T. M.;Molecular cloning and functional expression of codeinone reductase: the penultimate enzyme in morphine biosynthesis in the opium poppy Papaver somniferumPlant J.18465-475(1999)DOI: 10.1046/j.1365-313X.1999.00470.x
The narcotic analgesic morphine is the major alkaloid of the opium poppy Papaver somniferum . Its biosynthetic precursor codeine is currently the most widely used and effective antitussive agent. Along the morphine biosynthetic pathway in opium poppy, codeinone reductase catalyzes the NADPH‐dependent reduction of codeinone to codeine. In this study, we have isolated and characterized four cDNAs encoding codeinone reductase isoforms and have functionally expressed them in Escherichia coli . Heterologously expressed codeinone reductase‐calmodulin‐binding peptide fusion protein was purified from E. coli using calmodulin affinity column chromatography in a yield of 10 mg enzyme l ‐1 . These four isoforms demonstrated very similar physical properties and substrate specificity. As least six alleles appear to be present in the poppy genome. A comparison of the translations of the nucleotide sequences indicate that the codeinone reductase isoforms are 53% identical to 6′‐deoxychalcone synthase from soybean suggesting an evolutionary although not a functional link between enzymes of phenylpropanoid and alkaloid biosynthesis. By sequence comparison, both codeinone reductase and 6′‐deoxy‐ chalcone synthase belong to the aldo/keto reductase family, a group of structurally and functionally related NADPH‐dependent oxidoreductases, and thereby possibly arise from primary metabolism.
Publikation
Frick, S.; Kutchan, T. M.;Molecular cloning and functional expression of O-methyltransferases common to isoquinoline alkaloid and phenylpropanoid biosynthesisPlant J.17329-339(1999)DOI: 10.1046/j.1365-313X.1999.00379.x
In cell suspension cultures of the meadow rue Thalictrum tuberosum , biosynthesis of the anti‐microbial alkaloid berberine can be induced by addition of methyl jasmonate to the culture medium. The activities of the four methyltransferases involved in the formation of berberine from L‐tyrosine are increased in response to elicitor addition. Partial clones generated by RT–PCR with methyltransferase‐specific primers were used as hybridization probes to isolate four cDNAs encoding O ‐methyltransferases from a cDNA library prepared from poly(A)+ RNA isolated from methyl jasmonate‐induced cell suspension cultures of T. tuberosum . RNA gel blot hybridization indicated that the transcripts for the methyltransferases accumulated in response to addition of methyl jasmonate to the cell culture medium. The cDNAs were functionally expressed in Spodoptera frugiperda Sf9 cells and were shown to have varying and broad substrate specificities. A difference of a single amino acid residue between two of the enzymes was sufficient to alter the substrate specificity. The four cDNAs were expressed either as four homodimers or as six heterodimers by co‐infection with all possible combinations of the four recombinant baculoviruses. These 10 isoforms thus produced displayed distinct substrate specificities and in some cases co‐infection with two different recombinant baculoviruses led to the O ‐methylation of new substrates. The substrates that were O ‐methylated varied in structural complexity from simple catechols to phenylpropanoids, tetrahydrobenzylisoquinoline, protoberberine and tetrahydrophenethylisoquinoline alkaloids, suggesting that some biosynthetic enzymes may be common to both phenylpropanoid and alkaloid anabolism.