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Richard A. Dixon – One of the best experts on this subject based on the ideXlab platform.
unusual 4 hydroxybenzaldehyde synthase activity from tissue cultures of the vanilla orchid vanilla planifoliaPhytochemistry, 2002Co-Authors: Andrzej Podstolski, Daphna Havkinfrenkel, Jacek Malinowski, Jack W. Blount, Galina Kourteva, Richard A. DixonAbstract:
Abstract Tissue cultures of the vanilla orchid, Vanilla planifolia, produce the flavor compound vanillin (4-hydroxy-3-methoxybenzaldehyde) and vanillin precursors such as 4-hydroxybenzaldehyde. A constitutively expressed enzyme activity catalyzing chain shortening of a hydroxycinnamic Acid, believed to be the first reaction specific for formation of vanilla flavor compounds, was identified in these cultures. The enzyme converts 4-Coumaric Acid non-oxidatively to 4-hydroxybenzaldehyde in the presence of a thiol reagent but with no co-factor requirement. Several forms of this 4-hydroxybenzaldehyde synthase (4HBS) were resolved and partially purified by a combination of hydrophobic interaction, ion exchange and gel filtration chromatography. These forms appear to be interconvertible. The unusual properties of the 4HBS, and its appearance in different protein fractions, raise questions as to its physiological role in vanillin biosynthesis in vivo.
Monolignol biosynthesis in microsomal preparations from lignifying stems of alfalfa (Medicago sativa L.).Phytochemistry, 2002Co-Authors: Dianjing Guo, Fang Chen, Richard A. DixonAbstract:
Abstract Microsomal preparations from lignifying stems of alfalfa ( Medicago sativa L.) contained coniferaldehyde 5-hydroxylase activity and immunodetectable caffeic Acid 3- O -methyltransferase (COMT), and catalyzed the S-adenosyl l -methionine (SAM) dependent methylation of caffeic Acid, caffeyl aldehyde and caffeyl alcohol. When supplied with NADPH and SAM, the microsomes converted caffeyl aldehyde to coniferaldehyde, 5-hydroxyconiferaldehyde, and traces of sinapaldehyde. Coniferaldehyde was a better precursor of sinapaldehyde than was 5-hydroxyconiferaldehyde. The alfalfa microsomes could not metabolize 4-Coumaric Acid, 4-coumaraldehyde, 4-coumaroyl CoA, or ferulic Acid. No metabolism of monolignol precursors was observed in microsomal preparations from transgenic alfalfa down-regulated in COMT expression. In most microsomal preparations, the level of the metabolic conversions was independent of added recombinant COMT. Taken together, the data provide only limited support for the concept of metabolic channeling in the biosynthesis of S monolignols via coniferaldehyde.
Transgene-Mediated and Elicitor-Induced Perturbation of Metabolic Channeling at the Entry Point into the Phenylpropanoid PathwayThe Plant cell, 1999Co-Authors: Susanne Rasmussen, Richard A. DixonAbstract:
3 H–l-Phenylalanine is incorporated into a range of phenylpropanoid compounds when fed to tobacco cell cultures. A significant proportion of 3 H– trans -cinnamic Acid formed from 3 H–l-phenylalanine did not equilibrate with exogenous trans -cinnamic Acid and therefore may be rapidly channeled through the cinnamate 4-hydroxylase (C4H) reaction to 4-Coumaric Acid. Such compartmentalization of trans -cinnamic Acid was not observed after elicitation or in cell cultures constitutively expressing a bean phenylalanine ammonia–lyase ( PAL ) transgene. Channeling between PAL and C4H was confirmed in vitro in isolated microsomes from tobacco stems or cell suspension cultures. This channeling was strongly reduced in microsomes from stems or cell cultures of transgenic PAL -overexpressing plants or after elicitation of wild-type cell cultures. Protein gel blot analysis showed that tobacco PAL1 and bean PAL were localized in both soluble and microsomal fractions, whereas tobacco PAL2 was found only in the soluble fraction. We propose that metabolic channeling of trans -cinnamic Acid requires the close association of specific forms of PAL with C4H on microsomal membranes.
Sueharu Horinouchi – One of the best experts on this subject based on the ideXlab platform.
heterologous production of flavanones in escherichia coli potential for combinatorial biosynthesis of flavonoids in bacteriaJournal of Industrial Microbiology & Biotechnology, 2003Co-Authors: Masafumi Kaneko, Eui Il Hwang, Yasuo Ohnishi, Sueharu HorinouchiAbstract:
Chalcones, the central precursor of flavonoids, are synthesized exclusively in plants from tyrosine and phenylalanine via the sequential reaction of phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate:coenzyme A ligase (4CL) and chalcone synthase (CHS). Chalcones are converted into the corresponding flavanones by the action of chalcone isomerase (CHI), or non-enzymatically under alkaline conditions. PAL from the yeast Rhodotorula rubra, 4CL from an actinomycete Streptomyces coelicolor A3(2), and CHS from a licorice plant Glycyrrhiza echinata, assembled as artificial gene clusters in different organizations, were used for fermentation production of flavanones in Escherichia coli. Because the bacterial 4CL enzyme attaches CoA to both cinnamic Acid and 4-Coumaric Acid, the designed biosynthetic pathway bypassed the C4H step. E. coli carrying one of the designed gene clusters produced about 450 μg naringenin/l from tyrosine and 750 μg pinocembrin/l from phenylalanine. The successful production of plant-specific flavanones in bacteria demonstrates the usefulness of combinatorial biosynthesis approaches not only for the production of various compounds of plant and animal origin but also for the construction of libraries of “unnatural” natural compounds.
production of plant specific flavanones by escherichia coli containing an artificial gene clusterApplied and Environmental Microbiology, 2003Co-Authors: Eui Il Hwang, Masafumi Kaneko, Yasuo Ohnishi, Sueharu HorinouchiAbstract:
In plants, the phenylpropanoid pathway is responsible for the synthesis of a wide variety of secondary metabolic compounds, including lignins, salicylates, coumarins, hydroxycinnamic amides, pigments, and flavonoids. In addition to their roles in the structure and protection of the plant, phenylpropanoid compounds have an important effect on plant qualities, such as texture, flavor, color, and other characteristics (29). Recently, the flavonoid-derived plant natural products have drawn much attention because of their benefits to human health, such as antimicrobial, cancer chemopreventive, antioxidant, and antiasthmatic activities (6, 14). These phenylpropanoid and flavonoid biosynthetic enzymes are therefore attractive targets for metabolic engineering to provide enhancement or initiation of the production of economically desirable traits or compounds. The phenylpropanoid and flavonoid biosynthetic pathways and their regulation have been the subject of many studies (4, 5, 25, 29). Recent advances in the regulation of the pathways and the biochemistry of specific enzymes and enzyme complexes have opened up strategies for the enhancement of flavonoid compounds by modifying the pathways (4).
The phenylpropanoid pathway in plants converts phenylalanine into naringenin chalcone (Fig. (Fig.1).1). As the first step, phenylalanine is deaminated to yield cinnamic Acid by the action of phenylalanine ammonia lyase (PAL). Cinnamic Acid is hydroxylated by cinnamate-4-hydroxylase (C4H) to 4-Coumaric Acid, which is then activated to 4-coumaroyl-coenzyme A (CoA) by the action of 4-coumarate:CoA ligase (4CL). Chalcone synthase (CHS) catalyzes the stepwise condensation of three acetate units from malonyl-CoA with 4-coumaroyl-CoA to yield naringenin chalcone, the precursor for a large number of flavonoids (29). Naringenin chalcone is converted to naringenin by chalcone isomerase or nonenzymatically in vitro (5, 19, 24, 25). Because some of the PALs show tyrosine ammonia lyase activity, tyrosine is also used as the precursor (2, 15, 22, 26).
Flavanone biosynthetic pathway in plants. The dashed arrows represent the expected flavanone biosynthetic pathway in E. coli containing the artificial gene cluster including PAL, 4CL, and CHS. TAL, tyrosine ammonia-lyase; CHI, chalcone isomerase.
Production of flavanones or flavonoids by genetically engineered bacteria has not been reported before, although the heterologous expression of phenylpropanoid biosynthetic enzymes in bacteria has been reported (1, 8, 16, 30). One of the barriers for the production of these compounds is the difficulty in expression of active C4H, which would not be efficiently expressed due to its instability and the lack of its specific cytochrome P-450 reductase in bacteria (8, 20). We have recently discovered a 4CL in the gram-positive filamentous bacterium Streptomyces coelicolor A3(2) that can activate cinnamic Acid to cinnamoyl-CoA, as well as 4-Coumaric Acid to 4-coumaroyl-CoA (12). The use of the bacterial 4CL enzyme would bypass the C4H step for the production of pinocembrin chalcone from phenylalanine via the phenylpropanoid pathway (Fig. (Fig.1).1). On the basis of this idea, we constructed an artificial gene cluster containing PAL from a yeast, Rhodotorula rubra; 4CL from an actinomycete, S. coelicolor A3(2); and CHS from a licorice plant, Glycyrrhiza echinata, to produce a plant-specific flavanone, pinocembrin. As expected, the Escherichia coli cells containing the gene cluster produced pinocembrin. In addition, the E. coli cells produced naringenin, because the yeast PAL enzyme also used tyrosine as a substrate and yielded 4-Coumaric Acid, as is found for many PALs (2, 22, 26), and the 4CL enzyme used cinnamic Acid and 4-Coumaric Acid to yield the corresponding CoA thioester compounds. This paper describes successful production of plant-specific flavanones, pinocembrin and naringenin, in E. coli. Furthermore, we compared the yields of the flavanones by E. coli cells that contained the gene clusters in different organizations.
Production of plant-specific flavanones by Escherichia coli containing an artificial gene clusterApplied and Environmental Microbiology, 2003Co-Authors: Eui Il Hwang, Masafumi Kaneko, Yoshito Ohnishi, Sueharu HorinouchiAbstract:
In plants, chalcones are precursors for a large number of flavonoid-derived plant natural products and are converted to flavanones by chalcone isomerase or nonenzymatically. Chalcones are synthesized from tyrosine and phenylalanine via the phenylpropanoid pathway involving phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate:coenzyme A ligase (4CL), and chalcone synthase (CHS). For the purpose of production of flavanones in Escherichia coli, three sets of an artificial gene cluster which contained three genes of heterologous origins–PAL from the yeast Rhodotorula rubra, 4CL from the actinomycete Streptomyces coelicolor A3(2), and CHS from the licorice plant Glycyrrhiza echinata–were constructed. The constructions of the three sets were done as follows: (i) PAL, 4CL, and CHS were placed in that order under the control of the T7 promoter (P(T7)) and the ribosome-binding sequence (RBS) in the pET vector, where the initiation codons of 4CL and CHS were overlapped with the termination codons of the preceding genes; (ii) the three genes were transcribed by a single P(T7) in front of PAL, and each of the three contained the RBS at appropriate positions; and (iii) all three genes contained both P(T7) and the RBS. These pathways bypassed C4H, a cytochrome P-450 hydroxylase, because the bacterial 4CL enzyme ligated coenzyme A to both cinnamic Acid and 4-Coumaric Acid. E. coli cells containing the gene clusters produced two flavanones, pinocembrin from phenylalanine and naringenin from tyrosine, in addition to their precursors, cinnamic Acid and 4-Coumaric Acid. Of the three sets, the third gene cluster conferred on the host the highest ability to produce the flavanones. This is a new metabolic engineering technique for the production in bacteria of a variety of compounds of plant and animal origin.
Takayuki Oniki – One of the best experts on this subject based on the ideXlab platform.
3, 4-Dihydroxyphenylalanine is oxidized by phenoxyl radicals of hydroxycinnamic Acid esters in leaves ofVicia faba LJournal of Plant Research, 1998Co-Authors: Umeo Takahama, Takayuki OnikiAbstract:
Mechanisms of oxidation of 3,4-dihydroxyphenylalanine (dopa) in leaves of Vicia faba have not yet been elucidated in details. The author hypothesized its oxidation by radicals of hydroxycinnamic Acid esters that were generated by a peroxidase-dependent reaction in vacuoles. The results obtained in this study were followings. 1) Vacuolar peroxidase isolated from the leaves oxidized dopa more slowly than 4-Coumaric and caffeic Acid esters isolated from the leaves. 2) The hydroxycinnamic Acid esters enhanced peroxidase-dependent oxidation of dopa and dopa suppressed their oxidation. 3) Degree of the enhancement was roughly correlated with rates of the oxidation of hydroxycinnamic Acid esters. 4) The hydroxycinnamic Acid esters increased levels of dopa radical in the presence of peroxidase. 5) In protoplasts of mesophyll cells of V. faba , hydrogen peroxide-induced oxidation of dopa was faster than that of 4-Coumaric Acid and caffeic Acid esters. These results support the above hypothesis that dopa in vacuoles is oxidized by phenoxyl radicals of hydroxycinnamic Acid esters that are generated by vacuolar peroxidase.
enhancement of peroxidase dependent oxidation of sinapyl alcohol by an apoplastic component 4 coumaric Acid ester isolated from epicotyls of vigna angularis lPlant and Cell Physiology, 1997Co-Authors: Umeo Takahama, Takayuki OnikiAbstract:
A water-soluble component that enhanced the peroxidase-dependent (POX-dependent) oxidation of sinapyl alcohol was isolated from epicotyls of Vigna angularis. This compound was an ester of 4-Coumaric Acid and a hexose, and it was found in both the apoplast and the symplast. The ester was oxidized by a basic POX isozyme (Km, about 20 pM) and by an Acidic POX isozyme (Km, about 40 fiM) that had been partially purified from the apoplastic fraction of epicotyls of V. angularis. These POX isozymes oxidized sinapyl alcohol at only a very low rate, but a 15-fold enhancement was observed upon addition of the ester. The concentrations of the ester required for the half-maximal enhancement were similar to the Km values of the ester for its oxidation by the respective isozymes. The apoplastic concentration of the ester was higher than 130 fM, suggesting that this ester might act as a donor of electrons to the apoplastic POX isozymes in situ. Coniferyl alcohol also enhanced the POX-catalyzed oxidation of sinapyl alcohol. The concentrations of coniferyl alcohol required for halfmaximal enhancement of the oxidation of sinapyl alcohol were about 23 and 250 /JM when reactions were catalyzed by the basic and Acidic POXs, respectively. These values were similar to the Km values of coniferyl alcohol for its oxidation by the respective isozymes. These results suggest that 4-Coumaric Acid ester and coniferyl alcohol, if it is present in the apoplast, can enhance the POX-dependent oxidation of sinapyl alcohol in the apoplast of epicotyls of V. angularis.
a possible mechanism for the oxidation of sinapyl alcohol by peroxidase dependent reactions in the apoplast enhancement of the oxidation by hydroxycinnamic Acids and components of the apoplastPlant and Cell Physiology, 1996Co-Authors: Umeo Takahama, Takayuki Oniki, Hidetoshi ShimokawaAbstract:
Apoplastic peroxidase isoenzymes from stems of Nicotiana tabacum rapidly oxidized sinapic Acid and sinapyl alcohol, in addition to 4-Coumaric Acid, ferulic Acid and coniferyl alcohol. By contrast, the peroxidase isoenzymes from stems of Vigna angularis oxidized sinapic Acid and sinapyl alcohol quite slowly but rapidly oxidized compounds with a 4-hydroxyphenyl or a guaiacyl group. However, the oxidation of sinapyl alcohol was greatly enhanced by 4-Coumaric Acid, ferulic Acid and an ester of ferulic Acid. Intercellular washing fluid of V. angularis, which contained apoplastic components, also enhanced the oxidation of sinapyl alcohol. Based on these results, a possible mechanism for the oxidation of sinapyl alcohol is discussed on the assumption that the biosynthesis of lignin proceeds mainly via peroxidases which cannot oxidize sinapyl alcohol in V. angularis.