Modification of a catalytically important residue of indoleglycerol-phosphate synthase from Escherichia coli.
The active-site residues of indoleglycerol-phosphate synthase from Escherichia coli were tentatively localized by comparing crystallographic data with the amino acid identities among the known indoleglycerol-phosphate synthase sequences. To test the validity of the resulting model of catalysis one of the residues in the presumptive active site, Lys 55, was changed to serine using oligonucleotide-directed mutagenesis. The specificity constant kcat/Km of the mutant is 3 x 10(4)-times lower than that of the wild-type enzyme, due to a 60-fold decrease in kcat and a 450-fold increase in Km. This finding shows that Lys 55 is important for both catalysis and substrate binding.
Eberhard
M
M
Biozentrum der Universität, Abteilung Biophysikalische Chemie, Basel, Switzerland.
Kirschner
K
K
D000595:Amino Acid Sequence; D001665:Binding Sites; D002262:Carboxy-Lyases / Q000378:metabolism*; D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology*; D007209:Indole-3-Glycerol-Phosphate Synthase / Q000235:genetics / Q000378:metabolism*; D008239:Lysine; D009154:Mutation; D012694:Serine; D013329:Structure-Activity Relationship
D012694:Serine; D002262:Carboxy-Lyases; D007209:Indole-3-Glycerol-Phosphate Synthase; D008239:Lysine