1qq6
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(New page: 200px<br /><applet load="1qq6" size="450" color="white" frame="true" align="right" spinBox="true" caption="1qq6, resolution 2.10Å" /> '''STRUCTURE OF L-2-HAL...)
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Revision as of 22:45, 20 November 2007
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STRUCTURE OF L-2-HALOACID DEHALOGENASE FROM XANTHOBACTER AUTOTROPHICUS WITH CHLOROACETIC ACID COVALENTLY BOUND
Overview
The L-2-haloacid dehalogenase from the 1,2-dichloroethane-degrading, bacterium Xanthobacter autotrophicus GJ10 catalyzes the hydrolytic, dehalogenation of small L-2-haloalkanoates to their corresponding, D-2-hydroxyalkanoates, with inversion of the configuration at the C(2), atom. The structure of the apoenzyme at pH 8 was refined at 1.5-A, resolution. By lowering the pH, the catalytic activity of the enzyme was, considerably reduced, allowing the crystal structure determination of the, complexes with L-2-monochloropropionate and monochloroacetate at 1.7 and, 2.1 A resolution, respectively. Both complexes showed unambiguous electron, density extending from the nucleophile Asp(8) to the C(2) atom of the, dechlorinated substrates corresponding to a covalent enzyme-ester reaction, intermediate. The halide ion that is cleaved off is found in line with the, Asp(8) Odelta1-C(2) bond in a halide-stabilizing cradle made up of, Arg(39), Asn(115), and Phe(175). In both complexes, the Asp(8) Odelta2, carbonyl oxygen atom interacts with Thr(12), Ser(171), and Asn(173), which, possibly constitute the oxyanion hole in the hydrolysis of the ester bond., The carboxyl moiety of the substrate is held in position by interactions, with Ser(114), Lys(147), and main chain NH groups. The, L-2-monochloropropionate CH(3) group is located in a small pocket formed, by side chain atoms of Lys(147), Asn(173), Phe(175), and Asp(176). The, size and position of the pocket explain the stereospecificity and the, limited substrate specificity of the enzyme. These crystallographic, results demonstrate that the reaction of the enzyme proceeds via the, formation of a covalent enzyme-ester intermediate at the nucleophile, Asp(8).
About this Structure
1QQ6 is a Single protein structure of sequence from Xanthobacter autotrophicus with CL as ligand. Active as (S)-2-haloacid dehalogenase, with EC number 3.8.1.2 Full crystallographic information is available from OCA.
Reference
Crystal structures of intermediates in the dehalogenation of haloalkanoates by L-2-haloacid dehalogenase., Ridder IS, Rozeboom HJ, Kalk KH, Dijkstra BW, J Biol Chem. 1999 Oct 22;274(43):30672-8. PMID:10521454
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