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 ...
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.
Related Citations:
Crystallization and Preliminary X-ray Analysis of Recombinant Transaldolase B from Escherichia coli Jia, J., Lindqvist, Y., Schneider, G., Schoerken, U., Sahm, H., Sprenger, G.A. (1996) Acta Crystallogr D Biol Crystallogr 52: 192
Crystal Structure of Transaldolase B from Escherichia coli Suggests a Circular Permutation of the Alpha/beta Barrel Within the Class I Aldolase Family Jia, J., Huang, W., Schoerken, U., Sahm, H., Sprenger, G.A., Lindqvist, Y., Schneider, G. (1996) Structure 4: 715
Crystal Structure of the Reduced Schiff-base Intermediate Complex of Transaldolase B from Escherichia coli: Mechanistic Implications for Class I Aldolases Jia, J., Schoerken, U., Lindqvist, Y., Sprenger, G.A., Schneider, G. (1997) Protein Sci 6: 119
The Three-dimensional Structure of Human Transaldolase Thorell, S., Gergely Jr., P., Banki, K., Perl, A., Schneider, G. (2000) FEBS Lett 475: 205
Organizational Affiliation:
Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, Germany.
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