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Biosynthesis and biotechnology of plant natural products

  • Plants form an amazing diversity of natural products. The majority of the biologically active compounds originate from secondary metabolism. Elucidation of biosynthetic pathways and their regulation provides the basis for metabolic engineering and synthetic biology approaches. Goals are to modify medicinal plants and derived cell cultures for improved patterns of therapeutically valuable compounds and to establish plant biosynthetic pathways in engineered microorganisms. Our work focuses on the biosynthesis of polyketide derivatives. more...

1. Benzophenone and xanthone metabolism

  • Benzophenone derivatives possess anti-tumoral, anti-bacterial and HIV-inhibitory properties. Their carbon skeleton is formed from a CoA-linked benzoic acid and three molecules of malonyl-CoA. This reaction is catalyzed by benzophenone synthase, a type III polyketide synthase. The benzophenone synthase cDNA was cloned and the enzyme was functionally expressed. Amino acids lining the active site cavity were altered by site-directed mutagenesis. A single amino acid substitution converted benzophenone synthase into phenylpyrone synthase, a new type III PKS variant. Homology modeling suggested that the point mutation may open a new pocket in the active site cavity. more...

2. Hyperforin biosynthesis in St. John's wort

  • Extracts from Hypericum perforatum (St. John’s wort) are widely used for the treatment of mild to moderate depression. An important active constituent is hyperforin. It inhibits non-selectively the reuptake of neurotransmitters into the axoplasm. The target structure is TRPC6. Hyperforin is structurally and functionally a novel antidepressant. In addition, the compound exhibits anti-bacterial activity against gram-positive bacteria and anti-inflammatory properties. These activities explain the traditional use of St. John’s wort extracts for the local treatment of infected wounds and skin irritations. more...

3. Biphenyl and dibenzofuran formation in apple

  • Biphenyls and dibenzofurans are the phytoalexins of the Malinae, a subtribe of the Rosaceae. The Malinae include a number of economically important fruit trees, such as apple and pear, and the medicinally used whitethorn. The accumulation of biphenyls and dibenzofurans is an active pathogen defense strategy, which is restricted to the Malinae. Its contribution to the defence against fire blight and scab is studied. The key enzyme of the biosynthesis is biphenyl synthase (BIS), which was first detected in elicitor-treated cell cultures of Sorbus aucuparia. In the apple genome sequence, the BIS gene family consists of at least nine members, which are differentially regulated. more...

5. Benzoic acids as precursors

  • Besides involvement in benzophenone and biphenyl biosyntheses, benzoic acids are precursors of a variety of natural products, such as taxol, cocaine and reserpine. In addition, salicylic acid and its methyl ester are important signal molecules in systemic acquired resistance, i.e. enhanced resistance to secondary infection. Benzoic acids are biogenetically related to aromatic aldehydes and alcohols, e.g. vanillin and saligenin. Oxidative decarboxylation leads to simple phenols such as hydroquinone. more...

4. Evolution of polyketide synthases and CoA ligases

  • In a phylogenetic tree of type III polyketide synthases (PKS), the amino acid sequences from angiosperms diverge into two clusters. One group consists of chalcone synthases (CHS). CHS is ubiquitously distributed in higher plants. The second cluster is formed by PKSs which functionally differ from CHS, such as benzophenone synthase (BPS) and biphenyl synthase (BIS). The two clusters appear to originate from the duplication of a common ancestral gene prior to the speciation of the angiosperms. One gene after the duplication event retained the CHS function which is indispensable for plants (UV protection, flower pigmentation etc.). more...
 

  aktualisiert am 29.12.2011
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