4-coumaroyl-coenzyme-a and naringenin-chalcone

Flavonoids are a diverse group of phenolic secondary metabolites that occur naturally in plants and therefore form an integral component of the human diet. Many of the compounds belonging to this group are potent antioxidants in vitro and epidemiological studies suggest a direct correlation between high flavonoid intake and decreased risk of cardiovascular disease, cancer and other age-related diseases. Enhancing flavonoid biosynthesis in chosen crops may provide new raw materials that have the potential to be used in foods designed for specific benefits to human health. Using genetic modification, it was possible to generate several tomato lines with significantly altered flavonoid content and to probe the role and importance of several key enzymatic steps in the tomato flavonoid biosynthetic pathway. Most notably an up to 78-fold increase in total fruit flavonols was achieved through ectopic expression of a single biosynthetic enzyme, chalcone isomerase. In addition, chalcone synthase and flavonol synthase transgenes were found to act synergistically to up-regulate flavonol biosynthesis significantly in tomato flesh tissues.

Topics: Acyl Coenzyme A; Acyltransferases; Antioxidants; Chalcone; Chalcones; Flavonoids; Flavonols; Fruit; Gene Expression Regulation, Enzymologic; Humans; Intramolecular Lyases; Kaempferols; Malonyl Coenzyme A; Molecular Structure; Oxidoreductases; Plant Epidermis; Plant Proteins; Plants, Genetically Modified; Quercetin; Solanum lycopersicum

Quinolone alkaloids, found abundantly in the roots of bael (Aegle marmelos), possess various biological activities and have recently gained attention as potential lead molecules for novel drug designing. Here, we report the characterization of a novel Type III polyketide synthase, quinolone synthase (QNS), from A. marmelos that is involved in the biosynthesis of quinolone alkaloid. Using homology-based structural modeling, we identify two crucial amino acid residues (Ser-132 and Ala-133) at the putative QNS active site. Substitution of Ser-132 to Thr and Ala-133 to Ser apparently constricted the active site cavity resulting in production of naringenin chalcone from p-coumaroyl-CoA. Measurement of steady-state kinetic parameters demonstrates that the catalytic efficiency of QNS was severalfold higher for larger acyl-coenzymeA substrates as compared with smaller precursors. Our mutagenic studies suggest that this protein might have evolved from an evolutionarily related member of chalcone synthase superfamily by mere substitution of two active site residues. The identification and characterization of QNS offers a promising target for gene manipulation studies toward the production of novel alkaloid scaffolds.

Topics: Acyl Coenzyme A; Aegle; Alkaloids; Amino Acid Sequence; Amino Acid Substitution; Base Sequence; Biocatalysis; Catalytic Domain; Chalcones; Cloning, Molecular; Kinetics; Mass Spectrometry; Models, Molecular; Molecular Sequence Data; Mutation; Phylogeny; Plant Proteins; Polyketide Synthases; Protein Binding; Protein Structure, Tertiary; Quinolones; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Substrate Specificity