An essential methionine residue involved in substrate binding by phosphofructokinases

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Phosphofructokinases (PFKs) are key regulatory enzymes in glycolysis.
• PFKs utilize either ATP or pyrophosphate (PPi) as substrates.
• Conserved residues are critical for enzyme function and substrate interaction.

Purpose of the Study:

• To investigate the role of a conserved methionine residue in PFK activity.
• To determine the effect of methionine substitution on fructose-6-phosphate binding and catalytic efficiency.
• To compare the function of ATP-PFK and PPi-PFK enzymes.

Main Methods:

• Sequence alignment of PPi-dependent and ATP-dependent PFKs.
• Analysis of crystal structure of Escherichia coli PFK.
• Site-directed mutagenesis of conserved methionine residues.
• Enzyme kinetics assays to measure affinity and velocity.

Main Results:

• Few fully conserved residues were identified between PPi-PFK and ATP-PFK families.
• A conserved methionine residue interacts with fructose-6-phosphate in E. coli PFK.
• Mutagenesis of methionine to leucine or isoleucine drastically reduced enzyme affinity or velocity.
• Methionine is essential for specific fructose-6-phosphate binding and transition state stabilization.

Conclusions:

• The conserved methionine residue plays a vital role in the catalytic mechanism of PFKs.
• This residue is critical for both substrate binding and stabilizing the transition state.
• Understanding this interaction provides insights into enzyme evolution and regulation.