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MetaCyc Pathway: aloesone biosynthesis I
Inferred from experimentAuthor statement

Enzyme View:

Pathway diagram: aloesone biosynthesis I

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Superclasses: BiosynthesisSecondary Metabolites BiosynthesisPolyketides Biosynthesis

Some taxa known to possess this pathway include : Aloe arborescens, Rheum palmatum

Expected Taxonomic Range: Magnoliophyta

General Background

Polyketide (exclusive of fatty acids) represent a large group of natural products, i.e. secondary metabolites that are widespread in fungi, bacteria and plants [Birch68] [Schroder99] [Wink03]. Polyketides are often involved as intermediates in the formation of a vast variety of secondary metabolites with mixed biosynthetic origin. Polyketide such as chalcone and 6'-deoxychalcone are precursors in the biosynthesis of thousands of biologically important compounds functioning as pigments, anti-pathogens (phytoalexins), UV protectants, signals for the interaction with microorganisms and mediators of fertility [Schroder99a] [Schroder97a].

The entry enzymes of the biosynthesis of polyketides in plants are the polyketide synthases producing the general backbone of compounds who give rise to a large array of natural products representing an amazing degree of structural diversity. The chalcone synthase (CHS) and stilbene synthase (STS) are the most well-known plant polyketide synthases, however there exists a growing superfamily of related proteins referred to as CHS/STS-type proteins [Schroder99]. Depending on the specific polyketide synthase involved very diverse compound classes evolve such as chalcones ( flavonoid biosynthesis), stilbenes [Schroder99a], stilbenecarboxylates [Eckermann03], benzalacetone [BorejszaWysocki96], pyrone [Eckermann98], C-methylated chalcone [Shen00] and acridone alkaloids [Baumert94] [Junghanns95].

The formation of polyketides resembles the biosynthesis of fatty acids but is different in various aspects. In contrast to fatty acid synthases (FAS) plant polyketide synthases (PKS) are relatively small homodimeric enzymes, which do not use the acyl carrier protein (ACP) as activating agent but utilize acyl-CoA esters directly as substrates [Shen00] [Birch68]. Although the synthesis of chalcone usually does not involve modifications by other proteins the chalcone derivatives reduced at a specific position in the synthesized aromatic ring are frequently found in plants increasing the structural variability of derivatives [Schroder97a].

About This Pathway

The polyketide synthase (PKS) involved in the biosynthesis of aloesone represents a novel type of PKSs catalyzing six successive condensations steps with malonyl-CoA and acetyl-CoA as the starter unit. The product is an aromatic heptaketide, aloesone. The aloesone synthase (EC 2.3.1.-) isolated from rhubarb ( Rheum palmatum) belongs to the CHS superfamily (PKS type III). The aloesone synthase is a plant-specific, unique enzyme taking up a central function in the biosynthesis of chromones [Abe04].

Created 13-Sep-2005 by Foerster H, TAIR


Abe04: Abe I, Utsumi Y, Oguro S, Noguchi H (2004). "The first plant type III polyketide synthase that catalyzes formation of aromatic heptaketide." FEBS Lett 562(1-3);171-6. PMID: 15044020

Baumert94: Baumert A, Maier W, Groger D, Deutzmann R (1994). "Purification and properties of acridone synthase from cell suspension cultures of Ruta graveolens L." Z Naturforsch [C] 49(1-2);26-32. PMID: 8148006

Birch68: Birch AJ (1968). "Polyketide metabolism." Annual Review of Plant Physiology 19, 321-332.

BorejszaWysocki96: Borejsza-Wysocki W, Hrazdina G (1996). "Aromatic Polyketide Synthases (Purification, Characterization, and Antibody Development to Benzalacetone Synthase from Raspberry Fruits)." Plant Physiol 110(3);791-799. PMID: 12226219

Eckermann03: Eckermann C, Schroder G, Eckermann S, Strack D, Schmidt J, Schneider B, Schroder J (2003). "Stilbenecarboxylate biosynthesis: a new function in the family of chalcone synthase-related proteins." Phytochemistry 62(3);271-86. PMID: 12620338

Eckermann98: Eckermann S, Schroder G, Schmidt J, Strack D, Edrada RA, Helariutta Y, Elomaa P, Kotilainen M, Kilpelaeinen I, Proksch P, Teeri TH, Schroder J (1998). "New pathway to polyketides in plants." Nature 396 (26), 387-390.

Junghanns95: Junghanns KT, Kneusel RE, Baumert A, Maier W, Groger D, Matern U (1995). "Molecular cloning and heterologous expression of acridone synthase from elicited Ruta graveolens L. cell suspension cultures." Plant Mol Biol 27(4);681-92. PMID: 7727746

Schroder97a: Schroder J (1997). "A family of plant-specific polyketide synthases: facts and predictions." Trends in plant science 2(10), 373-378.

Schroder99: Schroder J (1999). "The chalcone/stilbene synthase-type family of condensing enzymes." In: Comprehensive natural products chemistry Vol. 1: Sankawa, U. (editor), Polyketides and other secondary metabolites including fatty acids and their derivatives. Amsterdam, New York: Elsevier, 773-82323.

Schroder99a: Schroder J (1999). "Probing plant polyketide biosynthesis." Nat Struct Biol 6(8);714-6. PMID: 10426943

Shen00: Shen B (2000). "Biosynthesis of Aromatic Polyketides." Topics in Current Chemistry 209, 1-51.

Wink03: Wink M (2003). "Evolution of secondary metabolites from an ecological and molecular phylogenetic perspective." Phytochemistry 64(1);3-19. PMID: 12946402

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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