Enolpyruvylshikimate-3-Phosphate Synthase

Baerson, S.R., D.J. Rodriguez, M. Tran, Y. Feng, N.A. Biest, and G.M. Dill (2002). Glyphosate-resistant goosegrass Identification of a mutation in the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase. Plant Physiol., 129 1265-1275. 

Klee, H.J., Muskopf, Y.M., and Gasser, C.S. 1987. Cloning of an arabidopsis-thaliana gene encoding 5-enolpyruvylshikimate-3-phosphate synthase sequence-analysis and manipulation to obtain glyphosate-tolerant plants. Mol. Gen. Genet., 210, 437-442. 

For example, glyphosate inhibits the enzyme, EPSP (5-enolpyruvylshikimate 3-phosphate) synthase, that catalyzes a step in the synthesis of the aromatic amino acids. Similarly, both the imidazolinones and sulfonylureas inhibit acetolactate synthase (ALS), the enzyme that catalyzes the first step in the formation of branched-chain amino acids (11). Triazine herbicides act by binding to a specific protein in the thylakoid membranes of the chloroplasts, preventing the flow of electrons and inhibiting photosynthesis (12). 

Figure 3. Schematic outline of various intermediates and products including enzymes of the phenolic pathway in plants. Enzymes 1, 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase 2, 5-dehydroquinate synthase 3, shikimate dehydrogenase 4, shikimate kinase 5, 5-enolpyruvylshikimate-3-phosphate synthase 6, chorismate synthase 7, chorismate mutase 8, prephenate dehydrogenase 9, tyrosine aminotransferase 10, prephenate dehydratase 11, phenylalanine aminotransferase 12, anthranilate synthase 13, tryptophan synthase 14, phenylalanine ammonia-lyase 15, tyrosine ammonia-lyase and 16, polyphenol oxidase.

Figure 14. Conversion of shikimate-3-phosphate to 5-enolpyruvylshikimate-3-phosphate blocked by glyphosate inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (%1).

EPSPS a single copy of the gene coding for glyphosate tolerance CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4 EPSPS) bom Agrobacterium sp. strain CP4. 

The conversion of shikimate-3-phosphate (7) to 5-enolp-yruvylshikimate (EPSP) (8) by 5-enolpyruvylshikimate-3-phosphate synthase represents a rare type of reaction in which the enolpyruvate fragment of phosphoenolpyruvate (2) is transferred to a molecule of (— )-shikimate-3-phos-phate (7) (Figure 7.1). The herbicide glyphosate (10) blocks the enzyme that catalyzed this reaction (Fig. 7.3). In 1984, sales of this herbicide totalled 480 million (Amrhein, 1986 Floss, 1986). 

Fig. 7.3. Stereochemical course of the 5-enolpyruvylshikimate 3-phosphate synthase reaction (adapted with permission from Asano et al., 1985, copyright 1985, American Chemical Society).

KOWAL, H.G. FLOSS. 1985. Steric course of the reactions catalyzed by 5-enolpyruvylshikimate-3-phosphate synthase, chorismate mutase and anthranilate synthase. J. Amer. Chem. Soc. 107, 4314-4320. 

Fig. 6. Mechanism proposed for the reaction catalyzed by 5-enolpyruvylshikimate 3-phosphate synthase (see Reference 66).

Glyphosate inhibition of 5-enolpyruvylshikimate 3-phosphate synthase from suspension-cultured cells of Nicotiana silvestris. Plant Physiol. 75 829-845. 

Steinriicken, H.C. and Amrhein, N. (1984) 5-Enolpyruvylshikimate-3-phosphate Synthase of Klebsiella pneumoniae. 2. Inhibition by Glyphosate [N-(phosphono-methyOglycine], Eur. J. Biochem., 143, 351-357. 

Alberg, D.G. and Bartlett, P.A. (1989) Potent Inhibition of 5-Enolpyruvylshikimate-3-phosphate Synthase by a Reaction Intermediate Analog, J. Am. Chem. Soc., Ill, 2337-2338. 

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