View source for Biology:2-Succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylic-acid synthase

{{Short description|Enzyme}}
{{Infobox enzyme
| Name       = 2-Succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylic-acid synthase
| EC_number  = 2.2.1.9
| CAS_number = 122007-88-9
| GO_code    =
| image      = MenDpicture2.png
| width      = 
| caption    = This image shows the two chains that come together to make up this enzyme 
}}
In [[Biology:Enzymology|enzymology]], '''SEPHCHC synthase'''  ([[Biology:Enzyme Commission number|EC]] {{EC number|2.2.1.9}}), encoded by menD gene in ''E. coli'', is an enzyme that catalyzes the second step of menaquinone (vitamin K2) biosynthesis. The two substrates of this enzyme are 2-oxoglutarate and isochorismate. The products of this enzyme are 5-enolpyruvoyl-6-hydroxy-2-succinyl-cyclohex-3-ene-1-carboxylate and CO<sub>2</sub>. It belongs to the transferase family.

== Classification ==
This enzyme belongs to a family of enzymes that transfer [[Chemistry:Aldehyde|aldehyde]] or ketonic groups. To be specific, this enzyme belongs to the [[Biology:Transketolase|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.<ref>{{Cite web|url = http://enzyme.expasy.org/cgi-bin/enzyme/enzyme-search-ec|title = Enzyme entry EC: 2.2.1.9|date = |accessdate = |website = ExPASy|publisher = |last = |first = }}</ref> The type of reaction is decarboxylating, and to have maximum activity, this enzymes uses the cofactor Mg2+, a magnesium ion.<ref>{{Cite web |url = http://www.enzyme-database.org/downloads/ec2.pdf|title = The Enzyme List Class 2 |date = September 2010 |accessdate = 25 August 2016}}</ref> In previous years, it was thought that this reaction led to SHCHC, the product [[Biology:2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate synthase|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.<ref>{{Cite web|url = http://www.genome.jp/dbget-bin/www_bget?ec:2.2.1.9|title = Enzyme 2.2.1.9|date = |accessdate = |website = KEGG|publisher = |last = |first = }}</ref>

[[File:MenD.png|thumb|610x610px|Step 2 in the biosynthesis of menaquinone]]

== 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.<ref name="pmid18983854">{{PDB|2jla}}; {{cite journal | vauthors = Dawson A, Fyfe PK, Hunter WN | title = Specificity and reactivity in menaquinone biosynthesis: the structure of Escherichia coli MenD (2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase) | journal = Journal of Molecular Biology | volume = 384 | issue = 5 | pages = 1353–68 | date = December 2008 | pmid = 18983854 | pmc = 3656419 | doi = 10.1016/j.jmb.2008.10.048 }}</ref>

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

== References ==
{{reflist}}

{{Aldehyde-ketone transferases}}
{{Enzymes}}

[[Category:Bacterial enzymes]]
[[Category:EC 2.2.1]]

{{Sourceattribution|2-Succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylic-acid synthase}}