The effect of introducing small cavities on the allosteric inhibition of phosphofructokinase from Bacillus stearothermophilus

• Ile → val introduces small cavities into PFK from Bacillus stearothermophilus.
• Small cavities influence allosteric behavior without appreciably affecting catalysis.
• Small cavities have a bigger effect on the allosteric coupling ΔH and TΔS than on ΔG.
• Small cavities can enhance or diminish the inhibition by PEP depending on location.

The allosteric coupling free energy between ligands fructose-6-phosphate (Fru-6-P) and phospho(enol)pyruvate (PEP) for phosphofructokinase-1 (PFK) from the moderate thermophile, Bacillus stearothermophilus (BsPFK), results from compensating enthalpy and entropy components. In BsPFK the positive coupling free energy that defines inhibition is opposite in sign from the negative enthalpy term and is therefore determined by the larger absolute value of the negative entropy term. Variants of BsPFK were made to determine the effect of adding small cavities to the structure on the allosteric function of the enzyme. The BsPFK Ile → Val (cavity containing) mutants have varied values for the coupling free energy between PEP and Fru-6-P, indicating that the modifications altered the effectiveness of PEP as an inhibitor. Notably, the mutation I153V had a substantial positive impact on the magnitude of inhibition by PEP. Van't Hoff analysis determined that this is the result of decreased entropy-enthalpy compensation with a larger change in the enthalpy term compared to the entropy term.