Structural highlights
Function
MEND_ECOLI Catalyzes the thiamine diphosphate-dependent decarboxylation of 2-oxoglutarate and the subsequent addition of the resulting succinic semialdehyde-thiamine pyrophosphate anion to isochorismate to yield 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylate (SEPHCHC).[1] [2]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
The thiamine diphosphate (ThDP) and metal-ion-dependent enzyme 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase, or MenD, catalyze the Stetter-like conjugate addition of alpha-ketoglutarate with isochorismate to release 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate and carbon dioxide. This reaction represents the first committed step for biosynthesis of menaquinone, or vitamin K2, a key cofactor for electron transport in bacteria and a metabolite for posttranslational modification of proteins in mammals. The medium-resolution structure of MenD from Escherichia coli (EcMenD) in complex with its cofactor and Mn2+ has been determined in two related hexagonal crystal forms. The subunit displays the typical three-domain structure observed for ThDP-dependent enzymes in which two of the domains bind and force the cofactor into a configuration that supports formation of a reactive ylide. The structures reveal a stable dimer-of-dimers association in agreement with gel filtration and analytical ultracentrifugation studies and confirm the classification of MenD in the pyruvate oxidase family of ThDP-dependent enzymes. The active site, created by contributions from a pair of subunits, is highly basic with a pronounced hydrophobic patch. These features, formed by highly conserved amino acids, match well to the chemical properties of the substrates. A model of the covalent intermediate formed after reaction with the first substrate alpha-ketoglutarate and with the second substrate isochorismate positioned to accept nucleophilic attack has been prepared. This, in addition to structural and sequence comparisons with putative MenD orthologues, provides insight into the specificity and reactivity of MenD and allows a two-stage reaction mechanism to be proposed.
Specificity and reactivity in menaquinone biosynthesis: the structure of Escherichia coli MenD (2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase).,Dawson A, Fyfe PK, Hunter WN J Mol Biol. 2008 Dec 31;384(5):1353-68. Epub 2008 Nov 1. PMID:18983854[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Palaniappan C, Sharma V, Hudspeth ME, Meganathan R. Menaquinone (vitamin K2) biosynthesis: evidence that the Escherichia coli menD gene encodes both 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylic acid synthase and alpha-ketoglutarate decarboxylase activities. J Bacteriol. 1992 Dec;174(24):8111-8. PMID:1459959
- ↑ Jiang M, Cao Y, Guo ZF, Chen M, Chen X, Guo Z. Menaquinone biosynthesis in Escherichia coli: identification of 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylate as a novel intermediate and re-evaluation of MenD activity. Biochemistry. 2007 Sep 25;46(38):10979-89. Epub 2007 Aug 31. PMID:17760421 doi:http://dx.doi.org/10.1021/bi700810x
- ↑ Dawson A, Fyfe PK, Hunter WN. Specificity and reactivity in menaquinone biosynthesis: the structure of Escherichia coli MenD (2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase). J Mol Biol. 2008 Dec 31;384(5):1353-68. Epub 2008 Nov 1. PMID:18983854 doi:10.1016/j.jmb.2008.10.048
