1i2r
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(New page: 200px<br /><applet load="1i2r" size="450" color="white" frame="true" align="right" spinBox="true" caption="1i2r, resolution 2.10Å" /> '''CRYSTAL STRUCTURE OF...)
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Revision as of 14:53, 20 November 2007
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CRYSTAL STRUCTURE OF ESCHERICHIA COLI TRANSALDOLASE B MUTANT S176A
Overview
The roles of invariant residues at the active site of transaldolase B from, Escherichia coli have been probed by site-directed mutagenesis. The mutant, enzymes D17A, N35A, E96A, T156A, and S176A were purified from a, talB-deficient host and analyzed with respect to their 3D structure and, kinetic behavior. X-ray analysis showed that side chain replacement did, not induce unanticipated structural changes in the mutant enzymes. Three, mutations, N35A, E96A, and T156A resulted mainly in an effect on apparent, kcat, with little changes in apparent Km values for the substrates., Residues N35 and T156 are involved in the positioning of a catalytic water, molecule at the active site and the side chain of E96 participates in, concert with this water molecule in proton transfer during catalysis., Substitution of Ser176 by alanine resulted in a mutant enzyme with 2.5%, residual activity. The apparent Km value for the donor substrate, fructose, 6-phosphate, was increased nearly fivefold while the apparent Km value for, the acceptor substrate, erythrose 4-phosphate remained unchanged, consistent with a function for S176 in the binding of the C1 hydroxyl, group of the donor substrate. The mutant D17A showed a 300-fold decrease, in kcat, and a fivefold increase in the apparent Km value for the acceptor, substrate erythrose 4-phosphate, suggesting a role of this residue in, carbon-carbon bond cleavage and stabilization of the carbanion/enamine, intermediate.
About this Structure
1I2R is a Single protein structure of sequence from Escherichia coli. Active as Transaldolase, with EC number 2.2.1.2 Full crystallographic information is available from OCA.
Reference
Identification of catalytically important residues in the active site of Escherichia coli transaldolase., Schorken U, Thorell S, Schurmann M, Jia J, Sprenger GA, Schneider G, Eur J Biochem. 2001 Apr;268(8):2408-15. PMID:11298760
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