Changes in the allosteric site of human liver pyruvate kinase upon activator binding include the breakage of an intersubunit cation-π bond.

Human liver pyruvate kinase (hLPYK) converts phosphoenolpyruvate to pyruvate in the final step of glycolysis. hLPYK is allosterically activated by fructose-1，6-bisphosphate (Fru-1，6-BP). The allosteric site， as defined by previous structural studies， is located in domain C between the phosphate-binding loop (residues 444-449) and the allosteric loop (residues 527-533). In this study， the X-ray crystal structures of four hLPYK variants were solved to make structural correlations with existing functional data. The variants are D499N， W527H， Δ529/S531G (called GGG here) and S531E. The results revealed a conformational toggle between the open and closed positions of the allosteric loop. In the absence of Fru-1，6-BP the open position is stabilized， in part， by a cation-π bond between Trp527 and Arg538' (from an adjacent monomer). In the S531E variant glutamate binds in place of the 6'-phosphate of Fru-1，6-BP in the allosteric site， leading to partial allosteric activation. Finally， the structure of the D499N mutant does not provide structural evidence for the previously observed allosteric activation of the D499N variant.