1hxq
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(New page: 200px<br /><applet load="1hxq" size="450" color="white" frame="true" align="right" spinBox="true" caption="1hxq, resolution 1.86Å" /> '''THE STRUCTURE OF NUC...)
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Revision as of 14:46, 20 November 2007
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THE STRUCTURE OF NUCLEOTIDYLATED GALACTOSE-1-PHOSPHATE URIDYLYLTRANSFERASE FROM ESCHERICHIA COLI AT 1.86 ANGSTROMS RESOLUTION
Overview
Galactose-1-phosphate uridylyltransferase catalyzes the reaction of, UDP-glucose with galactose 1-phosphate to form UDP-galactose and glucose, 1-phosphate during normal cellular metabolism. The reaction proceeds, through a double displacement mechanism characterized by the formation of, a stable nucleotidylated histidine intermediate. This paper describes the, preparation of the uridylyl-enzyme complex on the crystalline enzyme from, Escherichia coli and its subsequent structure determination by X-ray, crystallography. The refined structure has an R-factor of 19.6% (data, between 65 and 1.86 A resolution) and reveals modest conformational, changes at the active site compared to the inactive UMP/UDP-enzyme complex, reported previously [Wedekind, J.E., Frey, P.A., & Rayment, I. (1995), Biochemistry 34, 11049-11061]. In particular, positions of the respective, UMP alpha-phosphoryl groups differ by approximately 4 A. Well-defined, electron density for the nucleotidylated imidazole supports the existence, of a covalent bond between N epsilon 2 of the nucleophile and the, alpha-phosphorus of UMP. A hydrogen bond that is conserved in both, complexes between His 166 N delta 1 and the carbonyl O of His 164 serves, to properly orient the nucleophile and electrostatically stabilize the, positively charged imidazolium that results from nucleotidylation., Hydrogen bonds from side-chain Gln 168 to the nonbridging phosphoryl, oxygens of the nucleotidyl intermediate appear crucial for the formation, and reaction of the uridylyl-enzyme complex as well. The significance of, the latter interaction is underscored by the fact that the predominant, cause of the metabolic disease galactosemia is the mutation of the, corresponding Gln (Gln 188 in humans) to Arg. A comparison to other, phosphohistidyl enzymes is described, as well as a revised model for the, mechanism of the uridylyltransferase.
About this Structure
1HXQ is a Single protein structure of sequence from Escherichia coli with ZN, FE and U5P as ligands. Active as UDP-glucose--hexose-1-phosphate uridylyltransferase, with EC number 2.7.7.12 Full crystallographic information is available from OCA.
Reference
The structure of nucleotidylated histidine-166 of galactose-1-phosphate uridylyltransferase provides insight into phosphoryl group transfer., Wedekind JE, Frey PA, Rayment I, Biochemistry. 1996 Sep 10;35(36):11560-9. PMID:8794735
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