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Biosynthesis of Calystegines

Calystegia sepium

Calystegia sepium

Calystegines are polyhydroxyl nortropane alkaloids.  They occur in Solanaceae, that produce medicinal tropane alkaloids,  such as atropine (racemic hyoscyamine) in  Atropa belladonna, Hyoscyamus niger and Datura stramonium. Calystegines are also found in potato tubers (Solanum tuberosum) and in wire weed (Calystegia sepium,  Convolvulaceae). Biosynthetic steps of calystegine formation are  elucidated by metabolite analysis, application of precursors, and  isolation of enzymes and genes involved.

Calystegines are formed by the tropane alkaloid biosynthetic pathway (see picture). Putrescine N-methyltransferase  (PMT) and tropinone reductases (TR) take part in calystegine formation.  cDNA sequences from potato with high similarity to PMT- and TR-coding sequences from Hyoscyamus niger and Datura stramonium produce active and specific enzymes when expressed in E. coli. Thus tropane alkaloid biosynthesis takes place in potato, in other Solanum species  and also in Convolvulaceae like wire weed.

Tropane alkaloid biosynthesis

Tropane alkaloid biosynthesis

Tropane alkaloid biosynthesis

Regulation and evolution of tropane alkaloid biosynthesis are investigated using putrescine N-methyltransferase  and tropinone reductase as examples. During evolution, tropinone  reductases may have evolved stepwise from short-chain  dehydrogenases of primary metabolism. The current questions are directed  towards the function of the ancestor enzymes and towards the  developmental steps necessary for specialised tropinone reductase  evolution. Methods are comparison of DNA and protein sequences, protein  expression and substrate and product specificity analysis. Immuno-histochemical localisation of both tropinone reductases in Solanum tuberosum is intended to broaden the understanding of the regulation of calystegine formation. Putrescine N-methyltransferase  cDNA was cloned from various calystegines forming plants. PMT, judging  from sequence similarity, evolved from spermidine synthase and amino  acid exchanges required and effectual for change of function are  retrieved. Research for the evolution of tropane alkaloid enzymes is  part of the DFG priority programme EvoMe.

Co-operations:

  • Faculté de Pharmacie, Université de Picardie Jules Vernes, Amiens, France - Prof. Dr. Marc A. Filiniaux and Dr. Francois Mesnard

  • Leipniz-Institute for Plant Biochemistry Halle - Dr. Bettina  Hause, Prof. Dr. Dieter Strack, Prof. Dr. Ludger Wessjohann, Dr.  Wolfgang Brandt
  • Institute of Biochemistry and Biotechnology, Martin-Luther-University - Prof. Dr. Milton Stubbs and Dr. Christoph Parthier

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