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Pathway Description
Shikimate Pathway (Chorismate Biosynthesis)
Arabidopsis thaliana
Metabolic Pathway
The shikimate pathway is composed of seven enzymatic reactions in the chloroplast by which phosphoenolpyruvate (PEP) and D-erythrose 4-phosphate (E4P) are converted to chorismate, the common precursor of the aromatic amino acids phenylalanine, tyrosine, and tryptophan as well as other metabolites (e.g. folates). The pathway's absence in animals makes it an attractive target for new antimicrobial agents, anti-parasitic agents, and herbicides. PEP can enter this pathway either from plastidic glycolysis or cytosolic glycolysis. If it enters from the cytosol, then it is pumped into the chloroplast by PEP/phosphate translocator (PPT), an antiporter that exports phosphate into the cytosol simultaneously. Firstly, DAHP synthase, with the help of reduced thioredoxin (TRX) and a divalent cation (e.g. manganese) as cofactors, converts PEP, E4P, and water to 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) and phosphate. Secondly, 3-dehydroquinate synthase eliminates a phosphate from DAHP resulting in 3-dehydroquinate. This enzyme requires NAD+ and a divalent cation (e.g. cobalt) as cofactors. The next two reactions are catalyzed by the bifunctional enzyme 3-dehydroquinate dehydratase-shikimate dehydrogenase (DHQ-SDH). In the pathway's third reaction, the enzyme's DHQ domain dehydrates 3-dehydroquinate to 3-dehydroshikimate. In the fourth reaction, the enzyme's SDH domain uses NADPH to reversibly reduce 3-dehydroshikimate to shikimate, releasing NADP in the process. Fifthly, shikimate kinase, which requires a divalent cation (e.g. manganese) as a cofactor, catalyzes the ATP-dependent phosphorylation of shikimate to shikimate 3-phosphate. Sixthly, 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase converts shikimate-3-phosphate and PEP to EPSP, releasing a phosphate in the process. Seventhly, chorismate synthase (CS) catalyzes the 1,4-trans elimination of the phosphate group from EPSP to form chorismate. This enzyme requires reduced flavin mononucleotide (FMNH2) as a cofactor.
References
Shikimate Pathway (Chorismate Biosynthesis) References
Tzin V, Galili G: The Biosynthetic Pathways for Shikimate and Aromatic Amino Acids in Arabidopsis thaliana. Arabidopsis Book. 2010;8:e0132. doi: 10.1199/tab.0132. Epub 2010 May 17.
Pubmed: 22303258
Tzin V, Malitsky S, Ben Zvi MM, Bedair M, Sumner L, Aharoni A, Galili G: Expression of a bacterial feedback-insensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase of the shikimate pathway in Arabidopsis elucidates potential metabolic bottlenecks between primary and secondary metabolism. New Phytol. 2012 Apr;194(2):430-9. doi: 10.1111/j.1469-8137.2012.04052.x. Epub 2012 Feb 1.
Pubmed: 22296303
Maeda H, Dudareva N: The shikimate pathway and aromatic amino Acid biosynthesis in plants. Annu Rev Plant Biol. 2012;63:73-105. doi: 10.1146/annurev-arplant-042811-105439.
Pubmed: 22554242
Knappe S, Lottgert T, Schneider A, Voll L, Flugge UI, Fischer K: Characterization of two functional phosphoenolpyruvate/phosphate translocator (PPT) genes in Arabidopsis--AtPPT1 may be involved in the provision of signals for correct mesophyll development. Plant J. 2003 Nov;36(3):411-20.
Pubmed: 14617097
Entus R, Poling M, Herrmann KM: Redox regulation of Arabidopsis 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase. Plant Physiol. 2002 Aug;129(4):1866-71. doi: 10.1104/pp.002626.
Pubmed: 12177500
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