The Strongly Conserved Lysine 256 of Saccharomyces cerevisiae Phosphoenolpyruvate Carboxykinase Is Essential for Phosphoryl Transfer

• Published in: Biochemistry (Easton) 1998-05, Vol.37 (18), p.6295-6302
• Main Authors: Krautwurst, Hans, Bazaes, Sergio, González, Fernando D, Jabalquinto, Ana María, Frey, Perry A, Cardemil, Emilio
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Circular Dichroism; Crystallography, X-Ray; Kinetics; Lysine - analysis; Lysine - metabolism; Models, Molecular; Phosphoenolpyruvate Carboxykinase (ATP) - chemistry; Phosphoenolpyruvate Carboxykinase (ATP) - metabolism; Saccharomyces cerevisiae; Saccharomyces cerevisiae - enzymology
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi971515e

Lysine 256, a conserved amino acid of Saccharomyces cerevisiae phosphoenolpyruvate (PEP) carboxykinase located in the consensus kinase 1a sequence of the enzyme, was changed to alanine, arginine, or glutamine by site-directed mutagenesis. These substitutions did not result in gross changes in the protein structure, as indicated by circular dichroism, tryptophan fluorescence spectroscopy, and gel-exclusion chromatography. The three variant enzymes showed almost unaltered K m for MnADP but about a 20 000-fold decrease in V max for the PEP carboxylation reaction, as compared to wild-type PEP carboxykinase. The variant enzymes presented oxaloacetate decarboxylase activity at levels similar to those of the native protein; however, they lacked pyruvate kinase-like activity. The dissociation constant for the enzyme−MnATP complex was 1.3 ± 0.3 μM for wild-type S. cerevisiae PEP carboxykinase, and the corresponding values for the Lys256Arg, Lys256Gln, and Lys256Ala mutants were 2.0 ± 0.6 μM, 17 ± 2 μM, and 20 ± 6 μM, respectively. These results collectively show that a positively charged residue is required for proper binding of MnATP and that Lys256 plays an essential role in transition state stabilization during phosphoryl transfer for S. cerevisiae PEP carboxykinase.