1cd5
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(New page: 200px<br /><applet load="1cd5" size="450" color="white" frame="true" align="right" spinBox="true" caption="1cd5, resolution 2.3Å" /> '''GLUCOSAMINE-6-PHOSPHA...)
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Revision as of 10:14, 20 November 2007
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GLUCOSAMINE-6-PHOSPHATE DEAMINASE FROM E.COLI, T CONFORMER
Overview
BACKGROUND: The allosteric hexameric enzyme glucosamine-6-phosphate, deaminase from Escherichia coli catalyses the regulatory step of, N-acetylglucosamine catabolism, which consists of the isomerisation and, deamination of glucosamine 6-phosphate (GlcN6P) to form fructose, 6-phosphate (Fru6P) and ammonia. The reversibility of the catalysis and, its rapid-equilibrium random kinetic mechanism, among other properties, make this enzyme a good model for studying allosteric processes. RESULTS:, Here we present the structure of P6(3)22 crystals, obtained in sodium, acetate, of GlcN6P deaminase in its ligand-free T state. These crystals, are very sensitive to X-ray radiation and have a high (78%) solvent, content. The activesite lid (residues 162-185) is highly disordered in the, T conformer; this may contribute significantly to the free-energy change, of the whole allosteric transition. Comparison of the structure with the, crystallographic coordinates of the R conformer (Brookhaven Protein Data, Bank entry 1 dea) allows us to describe the geometrical changes associated, with the allosteric transition as the movement of two rigid entities, within each monomer. The active site, located in a deep cleft between, these two rigid entities, presents a more open geometry in the T conformer, than in the R conformer. CONCLUSIONS: The differences in active-site, geometry are related to alterations in the substrate-binding properties, associated with the allosteric transition. The rigid nature of the two, mobile structural units of each monomer seems to be essential in order to, explain the observed kinetics of the deaminase hexamer. The triggers for, both the homotropic and heterotropic allosteric transitions are discussed, and particular residues are assigned to these functions. A structural, basis for an entropic term in the allosteric transition is an interesting, new feature that emerges from this study.
About this Structure
1CD5 is a Single protein structure of sequence from Escherichia coli. Active as Glucosamine-6-phosphate deaminase, with EC number 3.5.99.6 Full crystallographic information is available from OCA.
Reference
The allosteric transition of glucosamine-6-phosphate deaminase: the structure of the T state at 2.3 A resolution., Horjales E, Altamirano MM, Calcagno ML, Garratt RC, Oliva G, Structure. 1999 May;7(5):527-37. PMID:10378272
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