1I2P: Crystal Structure Of Escherichia Coli Transaldolase B Mutant D17a

Citation:
Abstract
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.
PDB ID: 1I2PDownload
MMDB ID: 16094
PDB Deposition Date: 2001/2/12
Updated in MMDB: 2017/10
Experimental Method:
x-ray diffraction
Resolution: 2.05  Å
Source Organism:
Similar Structures:
Biological Unit for 1I2P: dimeric; determined by author
Molecular Components in 1I2P
Label Count Molecule
Proteins (2 molecules)
2
Transaldolase B(Gene symbol: talB)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB
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