Reversible unfolding of dimeric phosphofructokinase-2 from Escherichia coli reveals a dominant role of inter-subunit contacts for stability

Escherichia coli phosphofructokinase-2 (Pfk-2) is a homodimer whose subunits consist of a large domain and an additional β-sheet that provides the interfacial contacts between the subunits, creating a β-barrel flattened-like structure with the adjacent subunit’s β-sheet. To determine how the structural organization of Pfk-2 determines its stability, the reversible unfolding of the enzyme was characterized under equilibrium conditions by enzymatic activity, circular dichroism, fluorescence and hydrodynamic measurements. Pfk-2 undergoes a cooperative unfolding/dissociation process with the accumulation of an expanded and unstructured monomeric intermediate with a marginal stability and a large solvent accessibility with respect to the native dimer.