Structural Investigation of a Dimeric Variant of Pyruvate Kinase Muscle Isoform 2.

Pyruvate kinase muscle isoform 2 (PKM2) catalyzes the terminal step in glycolysis, transferring a phosphoryl group from phosphoenolpyruvate to ADP, to produce pyruvate and ATP. PKM2 activity is allosterically regulated by fructose 1,6-bisphosphate (FBP), an upstream glycolytic intermediate. FBP stabilizes the tetrameric form of the enzyme. In its absence, the PKM2 tetramers dissociate, yielding a dimer-monomer mixture having lower enzymatic activity. The S437Y variant of PKM2 is incapable of binding FBP. Consistent with that defect, we find that S437Y exists in a monomer-dimer equilibrium in solution, with a K of ∼20 μM. Interestingly, however, the protein crystallizes as a tetramer, providing insight into the structural basis for impaired FBP binding of S437Y.