Dirigent protein

Last updated

Dirigent proteins are members of a class of proteins which dictate the stereochemistry of a compound synthesized by other enzymes. [1] The first dirigent protein was discovered in Forsythia intermedia . This protein has been found to direct the stereoselective biosynthesis of (+)-pinoresinol from coniferyl alcohol monomers: [2]

Contents

(+)-Pinoresinol Biosynthesis.svg

Lignan biosynthesis is catalysed by oxidative enzymes. [3] In the test tube the reaction results in a heteregenous mixture of dimeric compounds. [4] When a dirigent protein is present during the reaction, one stereoisomer of one compound is highly enriched. Dirigent proteins appear to possess no oxidative radical forming activity of their own; in the absence of oxidative enzyme, no reaction will occur. [5]

Recently, a second, enantiocomplementary dirigent protein was identified in Arabidopsis thaliana , which directs enantioselective synthesis of (-)-pinoresinol. [6]

Activity

In lignan biosynthesis, oxidative enzymes perform proton coupled electron transfer to remove a hydrogen atom from monolignols, forming a radical intermediate. These intermediates then couple in a radical termination reaction to form one of a variety of dimers, known as lignans. [7] In vitro reactions of coniferyl alcohol (a common monolignol) in the presence of oxidative enzymes produce a wide variety of different dimers at varying concentrations. [8] When dirigent protein from "Forsythia intermedia" is present, production of (+)-pinoresinol is greatly enriched, and other products are far less abundant. Because this enrichment is so pronounced, the enzyme is hypothesized to produce (+)-pinoresinol exclusively, and to compete with the non-protein-mediated coupling reaction, which produces a heterologous mix of products. [9] This has been confirmed by analyzing the various mixtures produced with different concentrations of dirigent proteins present. The mechanism by which this stereoselectivity is achieved is not well understood at this time. However, since no reaction proceeds in the absence of oxidative enzymes, dirigent protein does not itself appear to catalyze the oxidation of coniferyl alcohol to form radicals.

In the presence of dirigent protein from Forsythia intermedia, production of (+)-pinoresinol is greatly enriched while production of other products of dimerization is inhibited. Activity of Dirigent protein.png
In the presence of dirigent protein from Forsythia intermedia, production of (+)-pinoresinol is greatly enriched while production of other products of dimerization is inhibited.

The activity of dirigent protein from Forsythia intermedia is specific to coniferyl alcohol. [10] When other monolignols, such as p-coumaryl alcohol and sinapyl alcohol, are reacted in vitro with oxidative enzymes in the presence of dirigent protein, they produce a heterologous mixture of products indistinguishable from identical experiments in the absence of dirigent protein.

Structure

Circular dichroism experiments have shown that the secondary structure of dirigent protein from Forsythia intermedia is composed primarily of β-pleated sheets and loop structures. The tertiary structure has not been solved, but the protein has been confirmed to be dimeric. Each dimer has a single binding site for coniferyl alcohol, for a total of two binding sites. [11] One coniferyl alcohol can bind to each site, so that the reaction geometry between the two is confined, increasing the production of (+)-pinoresinol and inhibiting the production of other products.

Biological importance

In the absence of dirigent protein, pinoresinol is a relatively minor product of lignas biosynthesis. When dirigent protein is present, it becomes the major product. The biological significance of (+)-pinoresinol in plants is not fully understood, but it has been found to be effective as a feeding deterrent against ants in caterpillars of the cabbage butterfly, which obtain the compound from their diet. [12] It may serve a similar defensive purpose in Forsythia intermedia. [13]

Related Research Articles

<span class="mw-page-title-main">Lignin</span> Structural phenolic polymer in plant cell walls

Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are polymers made by cross-linking phenolic precursors.

In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non-stereospecific creation of a new stereocenter or during a non-stereospecific transformation of a pre-existing one. The selectivity arises from differences in steric and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite: both products are at least possible and merely differ in amount. However, in favorable cases, the minor stereoisomer may not be detectable by the analytic methods used.

The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the Latin word for "wood". Lignans are precursors to phytoestrogens. They may play a role as antifeedants in the defense of seeds and plants against herbivores.

<span class="mw-page-title-main">Podophyllotoxin</span> Chemical compound

Podophyllotoxin (PPT) is the active ingredient in Podofilox, which is a medical cream that is used to treat genital warts and molluscum contagiosum. It is not recommended in HPV infections without external warts. It can be applied either by a healthcare provider or the person themselves.

Guaiacol is an organic compound with the formula C6H4(OH)(OCH3). It is a phenolic compound containing a methoxy functional group. Guaiacol appears as a viscous colorless oil, although aged or impure samples are often yellowish. It occurs widely in nature and is a common product of the pyrolysis of wood.

<span class="mw-page-title-main">Coniferyl alcohol</span> Chemical compound

Coniferyl alcohol is an organic compound with the formula HO(CH3O)C6H3CH=CHCH2OH. A colourless or white solid, it is one of the monolignols, produced via the phenylpropanoid biochemical pathway. When copolymerized with related aromatic compounds, coniferyl alcohol forms lignin or lignans. Coniferin is a glucoside of coniferyl alcohol. Coniferyl alcohol is an intermediate in biosynthesis of eugenol and of stilbenoids and coumarin. Gum benzoin contains significant amount of coniferyl alcohol and its esters. It is found in both gymnosperm and angiosperm plants. Sinapyl alcohol and paracoumaryl alcohol, the other two lignin monomers, are found in angiosperm plants and grasses.

<span class="mw-page-title-main">Phenylpropanoid</span>

The phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the amino acids phenylalanine and tyrosine. Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of coumaric acid, which is the central intermediate in phenylpropanoid biosynthesis. From 4-coumaroyl-CoA emanates the biosynthesis of myriad natural products including lignols, flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. The coumaroyl component is produced from cinnamic acid.

<span class="mw-page-title-main">Syringol</span> Chemical compound

Syringol is the organic compound with the formula HO(CH3O)2C6H3. The molecule is a phenol, with methoxy groups in the flanking (2 and 6) positions. It is the symmetrically dimethylated derivative of pyrogallol. It is a colorless solid, although typical samples are brown owing to air-oxidized impurities. Together with guaiacol, syringol and its derivatives are produced by the pyrolysis of lignin. Specifically, syringol is derived from the thermal decomposition of the sinapyl alcohol component. As such, syringol is an important component of wood smoke.

<span class="mw-page-title-main">Monolignol</span>

Monolignols, also called lignols, are the source materials for biosynthesis of both lignans and lignin and consist mainly of paracoumaryl alcohol (H), coniferyl alcohol (G) and sinapyl alcohol (S). These monolignols differ in their degree of methoxilation of the aromatic ring.

<span class="mw-page-title-main">Sinapyl alcohol</span> Chemical compound

Sinapyl alcohol is an organic compound structurally related to cinnamic acid. It is biosynthetized via the phenylpropanoid biochemical pathway, its immediate precursor being sinapaldehyde. This phytochemical is one of the monolignols, which are precursor to lignin or lignans. It is also a biosynthetic precursor to various stilbenoids and coumarins.

In enzymology, a dihydrokaempferol 4-reductase (EC 1.1.1.219) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Cinnamoyl-CoA reductase</span>

Cinnamoyl-CoA reductase (EC 1.2.1.44), systematically named cinnamaldehyde:NADP+ oxidoreductase (CoA-cinnamoylating) but commonly referred to by the acronym CCR, is an enzyme that catalyzes the reduction of a substituted cinnamoyl-CoA to its corresponding cinnamaldehyde, utilizing NADPH and H+ and releasing free CoA and NADP+ in the process. Common biologically relevant cinnamoyl-CoA substrates for CCR include p-coumaroyl-CoA and feruloyl-CoA, which are converted into p-coumaraldehyde and coniferaldehyde, respectively, though most CCRs show activity toward a variety of other substituted cinnamoyl-CoA's as well. Catalyzing the first committed step in monolignol biosynthesis, this enzyme plays a critical role in lignin formation, a process important in plants both for structural development and defense response.

<i>Forsythia suspensa</i> Species of flowering plant in the olive family Oleaceae

Forsythia suspensa, commonly known as weeping forsythia or golden-bell, is a species of flowering plant in the family Oleaceae, it is native to China.

<i>Forsythia <span style="font-style:normal;">×</span> intermedia</i> Hybrid flowering plant in the olive family Oleaceae

Forsythia × intermedia, or border forsythia, is an ornamental deciduous shrub of garden origin.

<span class="mw-page-title-main">Sinapaldehyde</span> Chemical compound

Sinapaldehyde is an organic compound with the formula HO(CH3O)2C6H2CH=CHCHO. It is a derivative of cinnamaldehyde, featuring one hydroxy group and two methoxy groups as substituents. It is an intermediate in the formation of sinapyl alcohol, a lignol that is a major precursor to lignin.

<span class="mw-page-title-main">Coniferyl aldehyde</span> Chemical compound

Coniferyl aldehyde is an organic compound with the formula HO(CH3O)C6H3CH=CHCHO. It is a derivative of cinnamaldehyde, featuring 4-hydroxy and 3-methoxy substituents. It is a major precursor to lignin.

<span class="mw-page-title-main">Pinoresinol</span> Chemical compound

Pinoresinol is a tetrahydrofuran lignan found in Styrax sp., Forsythia suspensa, and in Forsythia koreana. It is also found in the caterpillar of the cabbage butterfly, Pieris rapae where it serves as a defence against ants.

Eugenol synthase (EC 1.1.1.318, LtCES1, EGS1, EGS2) is an enzyme with systematic name eugenol:NADP+ oxidoreductase (coniferyl ester reducing). This enzyme catalyses the following chemical reaction: eugenol + a carboxylate + NADP+ a coniferyl ester + NADPH + H+

Secoisolariciresinol dehydrogenase (EC 1.1.1.331) is an enzyme with the systematic name (-)-secoisolariciresinol:NAD+ oxidoreductase. This enzyme catalyses the following chemical reaction:

<span class="mw-page-title-main">Silychristin</span> Natural chemical compound

Silychristin is a natural product and one of the constituents of silymarin, the standardized, active extract of the fruit of milk thistle, Silybum marianum. It is the second most abundant constituent in silymarin, after silybin. Silychristin is a flavonolignan, along with many other silymarin constituents, meaning it is composed up of a flavonoid and a lignan. It is estimated that up to 65–80% of silymarin extract is made up of flavonolignans, like silychristin, which give silymarin its well known potent antioxidant and hepatoprotective properties. Silychristin can exist as two stereoisomers, silychristin A and silychristin B. The marianum variety of S. marianum includes silychristin A as a major flavonolignan constituent, while the lesser known and studied albiflorum variety includes unique flavonolignans, including silyhermin, (–)-silandrin, and (+)-silymonin.

References

  1. ↑ Nicholson, Ralph L.; Wilfred Vermerris; Vermerris Wilfred (2006). Phenolic compound biochemistry . Berlin: Springer. pp.  107–108. ISBN   1-4020-5163-8.
  2. ↑ Davin LB, Wang HB, Crowell AL, et al. (1997). "Stereoselective bimolecular phenoxy radical coupling by an auxiliary (dirigent) protein without an active center". Science. 275 (5298): 362–6. doi:10.1126/science.275.5298.362. PMID   8994027. S2CID   41957412.
  3. ↑ Ward R.S. (1982). "The synthesis of lignans and neolignans". Chemical Society Reviews. 11 (2): 75–125. doi:10.1039/CS9821100075.
  4. ↑ Fournand D, Cathala B, Lapierre C (January 2003). "Initial steps of the peroxidase-catalyzed polymerization of coniferyl alcohol and/or sinapyl aldehyde: capillary zone electrophoresis study of pH effect". Phytochemistry. 62 (2): 139–46. doi:10.1016/S0031-9422(02)00573-3. PMID   12482448.
  5. ↑ Davin L.B.; Lewis N.G. (August 2005). "Dirigent phenoxy radical coupling: advances and challenges". Current Opinion in Biotechnology. 16 (4): 398–406. doi:10.1016/j.copbio.2005.06.010. PMID   16023845.
  6. ↑ Pickel B, Constantin M-A, Pfannsteil J, Conrad J, Beifuss U, Schaffer A (March 2007). "An Enantiocomplementary Dirigent Protein for the Enantioselective Laccase-Catalyzed Oxidative Coupling of Phenols". Angewandte Chemie. 53 (4): 273–284. doi: 10.1007/s10086-007-0892-x . S2CID   195313754.
  7. ↑ Sarkanen, Simo; Lewis, Norman (1998). Lignin and lignan biosynthesis. Columbus, OH: American Chemical Society. ISBN   0-8412-3566-X.
  8. ↑ Fournand D, Cathala B, Lapierre C (January 2003). "Initial steps of the peroxidase-catalyzed polymerization of coniferyl alcohol and/or sinapyl aldehyde: capillary zone electrophoresis study of pH effect". Phytochemistry. 62 (2): 139–46. doi:10.1016/S0031-9422(02)00573-3. PMID   12482448.
  9. ↑ Halls SC, Davin LB, Kramer DM, Lewis NG (2004). "Kinetic study of coniferyl alcohol radical binding to the (+)-pinoresinol forming dirigent protein". Biochemistry. 43 (9): 2587–95. doi:10.1021/bi035959o. PMID   14992596.
  10. ↑ Kim, M.K.; Jeon J.-H.; Fujita M.; Davin L.B.; Lewis N.G. (2002). "The western red cedar (Thuja plicata) 8-8′ DIRIGENT family displays diverse expression patterns and conserved monolignol coupling specificity". Plant Molecular Biology. 49 (2): 199–214. doi:10.1023/A:1014940930703. PMID   11999375. S2CID   8042373.
  11. ↑ Halls SC, Lewis NG (July 2002). "Secondary and quaternary structures of the (+)-pinoresinol-forming dirigent protein". Biochemistry. 41 (30): 9455–61. doi:10.1021/bi0259709. PMID   12135368.
  12. ↑ Schroeder FC, del Campo ML, Grant JB, et al. (October 2006). "Pinoresinol: A lignol of plant origin serving for defense in a caterpillar". Proc. Natl. Acad. Sci. U.S.A. 103 (42): 15497–501. doi: 10.1073/pnas.0605921103 . PMC   1622851 . PMID   17030818.
  13. ↑ Schmitt J, Peterson M (2002). "Pinoresinol and matairesinol accumulation in a Forsythia × intermedia cell suspension culture". Plant Cell, Tissue and Organ Culture. 68 (1): 91–98. doi:10.1023/A:1012909131741. S2CID   19282302.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.