2-Succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylic-acid synthase

Classification

This enzyme belongs to a family of enzymes that transfer aldehyde or ketonic groups. To be specific, this enzyme belongs to the transketolase and transaldolase families. Common names for the enzyme are:

• MenD
• SEPHCHC synthase
• 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylic-acid synthase
• Systematic name: isochorismate:2-oxoglutarate 4-oxopentanoatetransferase

Reaction

In the biosynthesis of vitamin K, SEPHCHC is involved in the second step of the pathway. The type of reaction is decarboxylating, and to have maximum activity, this enzymes uses the cofactor Mg2+, a magnesium ion. In previous years, it was thought that this reaction led to SHCHC, the product MenH. After further research, we now know that this reaction is a new step in the pathway. The actual product of this enzyme can lose a pyruvate spontaneously.

Structure

The structures reveal a stable dimer-of-dimers association in agreement with gel filtration and analytical studies confirm the classification of MenD in the pyruvate oxidase family. The active site is highly basic with a hydrophobic patch. These features match with the chemical properties of the substrates.

Homologues

There are many similar structures to MenD. Though it is commonly found in E. Coli, but can be found in other organisms as well. Bacillus subtilis and Mycobacterium tuberculosis are two homologues. All of the organisms share something in common, being that catalyze decarboxylation reactions.

References

References

1. "Enzyme entry EC: 2.2.1.9".
2. (September 2010). "The Enzyme List Class 2".
3. "Enzyme 2.2.1.9".
4. (December 2008). "Specificity and reactivity in menaquinone biosynthesis: the structure of Escherichia coli MenD (2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase)". Journal of Molecular Biology.