1n0h

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Revision as of 19:44, 20 November 2007

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spinqualitylabelsall models 1n0h, resolution 2.8Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of Yeast Acetohydroxyacid Synthase in Complex with a Sulfonylurea Herbicide, Chlorimuron Ethyl

Overview

Acetohydroxyacid synthase (AHAS) and acetolactate synthase (ALS) are, thiamine diphosphate (ThDP)-dependent enzymes that catalyze the, decarboxylation of pyruvate to give a cofactor-bound hydroxyethyl group, which is transferred to a second molecule of pyruvate to give, 2-acetolactate. AHAS is found in plants, fungi, and bacteria, is involved, in the biosynthesis of the branched-chain amino acids, and contains, non-catalytic FAD. ALS is found only in some bacteria, is a catabolic, enzyme required for the butanediol fermentation, and does not contain FAD., Here we report the 2.3-A crystal structure of Klebsiella pneumoniae ALS., The overall structure is similar to AHAS except for a groove that, accommodates FAD in AHAS, which is filled with amino acid side chains in, ALS. The ThDP cofactor has an unusual conformation that is unprecedented, among the 26 known three-dimensional structures of nine ThDP-dependent, enzymes, including AHAS. This conformation suggests a novel mechanism for, ALS. A second structure, at 2.0 A, is described in which the enzyme is, trapped halfway through the catalytic cycle so that it contains the, hydroxyethyl intermediate bound to ThDP. The cofactor has a tricyclic, structure that has not been observed previously in any ThDP-dependent, enzyme, although similar structures are well known for free thiamine. This, structure is consistent with our proposed mechanism and probably results, from an intramolecular proton transfer within a tricyclic carbanion that, is the true reaction intermediate. Modeling of the second molecule of, pyruvate into the active site of the enzyme with the bound intermediate is, consistent with the stereochemistry and specificity of ALS.

About this Structure

1N0H is a Single protein structure of sequence from Saccharomyces cerevisiae with K, MG, CIE, DTT, AYD, FAD and TPP as ligands. Active as Acetolactate synthase, with EC number 2.2.1.6 Full crystallographic information is available from OCA.

Reference

The crystal structures of Klebsiella pneumoniae acetolactate synthase with enzyme-bound cofactor and with an unusual intermediate., Pang SS, Duggleby RG, Schowen RL, Guddat LW, J Biol Chem. 2004 Jan 16;279(3):2242-53. Epub 2003 Oct 13. PMID:14557277

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