Structural and functional roles of Cys-238 and Cys-295 in Escherichia coli phosphofructokinase-2

• Published in: Biochemical journal 2003-11, Vol.376 (Pt 1), p.277-283
• Main Authors: Baez, Mauricio, Rodríguez, Patricio H, Babul, Jorge, Guixé, Victoria
• Format: Article
• Language: English
• Subjects: Allosteric Regulation; Amino Acid Sequence; Cysteine - chemistry; Cysteine - physiology; Dimerization; Eosine Yellowish-(YS) - analogs & derivatives; Eosine Yellowish-(YS) - chemistry; Escherichia coli; Escherichia coli - enzymology; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; Kinetics; Maleimides - chemistry; Molecular Sequence Data; Phosphofructokinase-2 - chemistry; Phosphofructokinase-2 - metabolism; Protein Structure, Quaternary; Solvents - chemistry; Sulfhydryl Reagents - chemistry
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/BJ20030795

Modification of Escherichia coli phosphofructokinase-2 (Pfk-2) with pyrene maleimide (PM) results in a rapid inactivation of the enzyme. The loss of enzyme activity correlates with the incorporation of 2 mol of PM/mol of subunit and the concomitant dissociation of the dimeric enzyme. The two modified residues were identified as Cys-238 and Cys-295. In the presence of the negative allosteric effector, MgATP, Cys-238 was the only modified cysteine residue. Kinetic characterization of the Cys-238-labelled Pfk-2 indicates that the enzyme is fully active, with the kinetic constants ( K(m), kcat) being almost identical to the ones obtained for the native enzyme. The modified enzyme is a monomer in the absence of ligands and, like the native enzyme, behaves as a tetramer in the presence of the nucleotide. However, in the presence of fructose-6-phosphate (fru-6-P) and ATP(-4), the enzyme behaves as a dimer, suggesting that the monomers undergo re-association in the presence of the substrates and that the active species is a dimer. Modification of Pfk-2 with eosin-5-maleimide (EM) results in the labelling of Cys-295. This modified enzyme is inactive and is not able to bind to the allosteric effector, remaining as a dimer in its presence. Nonetheless, Cys-295-labelled Pfk-2 is able to bind to the substrate fru-6-P in an hyperbolic fashion with a K(d) value that is 6-fold higher than the one determined for the native enzyme. These are the first residues to be implicated in the activity and/or structure of the Pfk-2.