1ec8
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(New page: 200px<br /><applet load="1ec8" size="450" color="white" frame="true" align="right" spinBox="true" caption="1ec8, resolution 1.9Å" /> '''E. COLI GLUCARATE DEH...)
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Revision as of 11:46, 20 November 2007
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E. COLI GLUCARATE DEHYDRATASE BOUND TO PRODUCT 2,3-DIHYDROXY-5-OXO-HEXANEDIOATE
Overview
D-Glucarate dehydratase (GlucD) from Escherichia coli catalyzes the, dehydration of both D-glucarate and L-idarate as well as their, interconversion via epimerization. GlucD is a member of the mandelate, racemase (MR) subgroup of the enolase superfamily, the members of which, catalyze reactions that are initiated by abstraction of the alpha-proton, of a carboxylate anion substrate. Alignment of the sequence of GlucD with, that of MR reveals a conserved Lys-X-Lys motif and a His-Asp dyad, homologous to the S- and R-specific bases in the active site of MR., Crystals of GlucD have been obtained into which the substrate D-glucarate, and two competitive inhibitors, 4-deoxy-D-glucarate and xylarohydroxamate, could be diffused; D-glucarate is converted to the dehydration product, 5-keto-4-deoxy-D-glucarate (KDG). The structures of these complexes have, been determined and reveal the identities of the ligands for the required, Mg(2+) (Asp(235), Glu(266), and Asn(289)) as well as confirm the expected, presence of Lys(207) and His(339), the catalytic bases that are properly, positioned to abstract the proton from C5 of L-idarate and D-glucarate, respectively. Surprisingly, the C6 carboxylate group of KDG is a bidentate, ligand to the Mg(2+), with the resulting geometry of the bound KDG, suggesting that stereochemical roles of Lys(207) and His(339) are reversed, from the predictions made on the basis of the established, structure-function relationships for the MR-catalyzed reaction. The, catalytic roles of these residues have been examined by characterization, of mutant enzymes, although we were unable to use these to demonstrate the, catalytic independence of Lys(207) and His(339) as was possible for the, homologous Lys(166) and His(297) in the MR-catalyzed reaction.
About this Structure
1EC8 is a Single protein structure of sequence from Escherichia coli with MG, GLR and IPA as ligands. Active as Glucarate dehydratase, with EC number 4.2.1.40 Full crystallographic information is available from OCA.
Reference
Evolution of enzymatic activities in the enolase superfamily: crystallographic and mutagenesis studies of the reaction catalyzed by D-glucarate dehydratase from Escherichia coli., Gulick AM, Hubbard BK, Gerlt JA, Rayment I, Biochemistry. 2000 Apr 25;39(16):4590-602. PMID:10769114
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